diff --git a/tools/buildman/kconfiglib.py b/tools/buildman/kconfiglib.py
index d68af05..3908985 100644
--- a/tools/buildman/kconfiglib.py
+++ b/tools/buildman/kconfiglib.py
@@ -1,3544 +1,7030 @@
+# Copyright (c) 2011-2019, Ulf Magnusson
 # SPDX-License-Identifier: ISC
-#
-# Author: Ulf Magnusson
-#   https://github.com/ulfalizer/Kconfiglib
-
-# This is Kconfiglib, a Python library for scripting, debugging, and extracting
-# information from Kconfig-based configuration systems. To view the
-# documentation, run
-#
-#  $ pydoc kconfiglib
-#
-# or, if you prefer HTML,
-#
-#  $ pydoc -w kconfiglib
-#
-# The examples/ subdirectory contains examples, to be run with e.g.
-#
-#  $ make scriptconfig SCRIPT=Kconfiglib/examples/print_tree.py
-#
-# Look in testsuite.py for the test suite.
 
 """
-Kconfiglib is a Python library for scripting and extracting information from
-Kconfig-based configuration systems. Features include the following:
+Overview
+========
 
- - Symbol values and properties can be looked up and values assigned
-   programmatically.
- - .config files can be read and written.
- - Expressions can be evaluated in the context of a Kconfig configuration.
- - Relations between symbols can be quickly determined, such as finding all
-   symbols that reference a particular symbol.
- - Highly compatible with the scripts/kconfig/*conf utilities. The test suite
-   automatically compares outputs between Kconfiglib and the C implementation
-   for a large number of cases.
+Kconfiglib is a Python 2/3 library for scripting and extracting information
+from Kconfig (https://www.kernel.org/doc/Documentation/kbuild/kconfig-language.txt)
+configuration systems.
 
-For the Linux kernel, scripts are run using
+See the homepage at https://github.com/ulfalizer/Kconfiglib for a longer
+overview.
 
- $ make scriptconfig [ARCH=<arch>] SCRIPT=<path to script> [SCRIPT_ARG=<arg>]
+Since Kconfiglib 12.0.0, the library version is available in
+kconfiglib.VERSION, which is a (<major>, <minor>, <patch>) tuple, e.g.
+(12, 0, 0).
 
-Using the 'scriptconfig' target ensures that required environment variables
-(SRCARCH, ARCH, srctree, KERNELVERSION, etc.) are set up correctly.
 
-Scripts receive the name of the Kconfig file to load in sys.argv[1]. As of
-Linux 4.1.0-rc5, this is always "Kconfig" from the kernel top-level directory.
-If an argument is provided with SCRIPT_ARG, it appears as sys.argv[2].
+Using Kconfiglib on the Linux kernel with the Makefile targets
+==============================================================
 
-To get an interactive Python prompt with Kconfiglib preloaded and a Config
-object 'c' created, run
+For the Linux kernel, a handy interface is provided by the
+scripts/kconfig/Makefile patch, which can be applied with either 'git am' or
+the 'patch' utility:
 
- $ make iscriptconfig [ARCH=<arch>]
+  $ wget -qO- https://raw.githubusercontent.com/ulfalizer/Kconfiglib/master/makefile.patch | git am
+  $ wget -qO- https://raw.githubusercontent.com/ulfalizer/Kconfiglib/master/makefile.patch | patch -p1
 
-Kconfiglib supports both Python 2 and Python 3. For (i)scriptconfig, the Python
-interpreter to use can be passed in PYTHONCMD, which defaults to 'python'. PyPy
-works well too, and might give a nice speedup for long-running jobs.
+Warning: Not passing -p1 to patch will cause the wrong file to be patched.
 
-The examples/ directory contains short example scripts, which can be run with
-e.g.
+Please tell me if the patch does not apply. It should be trivial to apply
+manually, as it's just a block of text that needs to be inserted near the other
+*conf: targets in scripts/kconfig/Makefile.
 
- $ make scriptconfig SCRIPT=Kconfiglib/examples/print_tree.py
+Look further down for a motivation for the Makefile patch and for instructions
+on how you can use Kconfiglib without it.
 
-or
+If you do not wish to install Kconfiglib via pip, the Makefile patch is set up
+so that you can also just clone Kconfiglib into the kernel root:
 
- $ make scriptconfig SCRIPT=Kconfiglib/examples/help_grep.py SCRIPT_ARG=kernel
+  $ git clone git://github.com/ulfalizer/Kconfiglib.git
+  $ git am Kconfiglib/makefile.patch  (or 'patch -p1 < Kconfiglib/makefile.patch')
 
-testsuite.py contains the test suite. See the top of the script for how to run
-it.
+Warning: The directory name Kconfiglib/ is significant in this case, because
+it's added to PYTHONPATH by the new targets in makefile.patch.
 
-Credits: Written by Ulf "Ulfalizer" Magnusson
+The targets added by the Makefile patch are described in the following
+sections.
 
-Send bug reports, suggestions and other feedback to ulfalizer a.t Google's
-email service. Don't wrestle with internal APIs. Tell me what you need and I
-might add it in a safe way as a client API instead."""
-
-import os
-import platform
-import re
-import sys
-
-# File layout:
-#
-# Public classes
-# Public functions
-# Internal classes
-# Internal functions
-# Internal global constants
 
-# Line length: 79 columns
+make kmenuconfig
+----------------
 
-#
-# Public classes
-#
+This target runs the curses menuconfig interface with Python 3. As of
+Kconfiglib 12.2.0, both Python 2 and Python 3 are supported (previously, only
+Python 3 was supported, so this was a backport).
 
-class Config(object):
 
-    """Represents a Kconfig configuration, e.g. for i386 or ARM. This is the
-    set of symbols and other items appearing in the configuration together with
-    their values. Creating any number of Config objects -- including for
-    different architectures -- is safe; Kconfiglib has no global state."""
+make guiconfig
+--------------
 
-    #
-    # Public interface
-    #
+This target runs the Tkinter menuconfig interface. Both Python 2 and Python 3
+are supported. To change the Python interpreter used, pass
+PYTHONCMD=<executable> to 'make'. The default is 'python'.
 
-    def __init__(self, filename="Kconfig", base_dir=None, print_warnings=True,
-                 print_undef_assign=False):
-        """Creates a new Config object, representing a Kconfig configuration.
-        Raises Kconfig_Syntax_Error on syntax errors.
 
-        filename (default: "Kconfig"): The base Kconfig file of the
-           configuration. For the Linux kernel, you'll probably want "Kconfig"
-           from the top-level directory, as environment variables will make
-           sure the right Kconfig is included from there
-           (arch/<architecture>/Kconfig). If you are using Kconfiglib via 'make
-           scriptconfig', the filename of the base base Kconfig file will be in
-           sys.argv[1].
+make [ARCH=<arch>] iscriptconfig
+--------------------------------
 
-        base_dir (default: None): The base directory relative to which 'source'
-           statements within Kconfig files will work. For the Linux kernel this
-           should be the top-level directory of the kernel tree. $-references
-           to existing environment variables will be expanded.
+This target gives an interactive Python prompt where a Kconfig instance has
+been preloaded and is available in 'kconf'. To change the Python interpreter
+used, pass PYTHONCMD=<executable> to 'make'. The default is 'python'.
 
-           If None (the default), the environment variable 'srctree' will be
-           used if set, and the current directory otherwise. 'srctree' is set
-           by the Linux makefiles to the top-level kernel directory. A default
-           of "." would not work with an alternative build directory.
+To get a feel for the API, try evaluating and printing the symbols in
+kconf.defined_syms, and explore the MenuNode menu tree starting at
+kconf.top_node by following 'next' and 'list' pointers.
 
-        print_warnings (default: True): Set to True if warnings related to this
-           configuration should be printed to stderr. This can be changed later
-           with Config.set_print_warnings(). It is provided as a constructor
-           argument since warnings might be generated during parsing.
+The item contained in a menu node is found in MenuNode.item (note that this can
+be one of the constants kconfiglib.MENU and kconfiglib.COMMENT), and all
+symbols and choices have a 'nodes' attribute containing their menu nodes
+(usually only one). Printing a menu node will print its item, in Kconfig
+format.
 
-        print_undef_assign (default: False): Set to True if informational
-           messages related to assignments to undefined symbols should be
-           printed to stderr for this configuration. Can be changed later with
-           Config.set_print_undef_assign()."""
+If you want to look up a symbol by name, use the kconf.syms dictionary.
 
-        # The set of all symbols, indexed by name (a string)
-        self.syms = {}
-        # Python 2/3 compatibility hack. This is the only one needed.
-        self.syms_iter = self.syms.values if sys.version_info[0] >= 3 else \
-                         self.syms.itervalues
 
-        # The set of all defined symbols in the configuration in the order they
-        # appear in the Kconfig files. This excludes the special symbols n, m,
-        # and y as well as symbols that are referenced but never defined.
-        self.kconfig_syms = []
+make scriptconfig SCRIPT=<script> [SCRIPT_ARG=<arg>]
+----------------------------------------------------
 
-        # The set of all named choices (yes, choices can have names), indexed
-        # by name (a string)
-        self.named_choices = {}
+This target runs the Python script given by the SCRIPT parameter on the
+configuration. sys.argv[1] holds the name of the top-level Kconfig file
+(currently always "Kconfig" in practice), and sys.argv[2] holds the SCRIPT_ARG
+argument, if given.
 
-        # Lists containing all choices, menus and comments in the configuration
-        self.choices = []
-        self.menus = []
-        self.comments = []
+See the examples/ subdirectory for example scripts.
 
-        def register_special_symbol(type_, name, val):
-            sym = Symbol()
-            sym.is_special_ = True
-            sym.is_defined_ = True
-            sym.config = self
-            sym.name = name
-            sym.type = type_
-            sym.cached_val = val
-            self.syms[name] = sym
-            return sym
 
-        # The special symbols n, m and y, used as shorthand for "n", "m" and
-        # "y"
-        self.n = register_special_symbol(TRISTATE, "n", "n")
-        self.m = register_special_symbol(TRISTATE, "m", "m")
-        self.y = register_special_symbol(TRISTATE, "y", "y")
-        # DEFCONFIG_LIST uses this
-        register_special_symbol(STRING, "UNAME_RELEASE", platform.uname()[2])
+make dumpvarsconfig
+-------------------
 
-        # The symbol with "option defconfig_list" set, containing a list of
-        # default .config files
-        self.defconfig_sym = None
+This target prints a list of all environment variables referenced from the
+Kconfig files, together with their values. See the
+Kconfiglib/examples/dumpvars.py script.
 
-        # See Symbol.get_(src)arch()
-        self.arch = os.environ.get("ARCH")
-        self.srcarch = os.environ.get("SRCARCH")
+Only environment variables that are referenced via the Kconfig preprocessor
+$(FOO) syntax are included. The preprocessor was added in Linux 4.18.
 
-        # If you set CONFIG_ in the environment, Kconfig will prefix all symbols
-        # with its value when saving the configuration, instead of using the default, "CONFIG_".
-        self.config_prefix = os.environ.get("CONFIG_")
-        if self.config_prefix is None:
-            self.config_prefix = "CONFIG_"
 
-        # See Config.__init__(). We need this for get_defconfig_filename().
-        self.srctree = os.environ.get("srctree")
-        if self.srctree is None:
-            self.srctree = "."
+Using Kconfiglib without the Makefile targets
+=============================================
 
-        self.filename = filename
-        self.base_dir = self.srctree if base_dir is None else \
-                        os.path.expandvars(base_dir)
+The make targets are only needed to pick up environment variables exported from
+the Kbuild makefiles and referenced inside Kconfig files, via e.g.
+'source "arch/$(SRCARCH)/Kconfig" and commands run via '$(shell,...)'.
 
-        # The 'mainmenu' text
-        self.mainmenu_text = None
+These variables are referenced as of writing (Linux 4.18), together with sample
+values:
 
-        # The filename of the most recently loaded .config file
-        self.config_filename = None
-        # The textual header of the most recently loaded .config, uncommented
-        self.config_header = None
+  srctree          (.)
+  ARCH             (x86)
+  SRCARCH          (x86)
+  KERNELVERSION    (4.18.0)
+  CC               (gcc)
+  HOSTCC           (gcc)
+  HOSTCXX          (g++)
+  CC_VERSION_TEXT  (gcc (Ubuntu 7.3.0-16ubuntu3) 7.3.0)
 
-        self.print_warnings = print_warnings
-        self.print_undef_assign = print_undef_assign
-        self._warnings = []
+Older kernels only reference ARCH, SRCARCH, and KERNELVERSION.
 
-        # For parsing routines that stop when finding a line belonging to a
-        # different construct, these holds that line and the tokenized version
-        # of that line. The purpose is to avoid having to re-tokenize the line,
-        # which is inefficient and causes problems when recording references to
-        # symbols.
-        self.end_line = None
-        self.end_line_tokens = None
+If your kernel is recent enough (4.18+), you can get a list of referenced
+environment variables via 'make dumpvarsconfig' (see above). Note that this
+command is added by the Makefile patch.
 
-        # See the comment in _parse_expr().
-        self._cur_item = None
-        self._line = None
-        self._filename = None
-        self._linenr = None
-        self._transform_m = None
+To run Kconfiglib without the Makefile patch, set the environment variables
+manually:
 
-        # Parse the Kconfig files
-        self.top_block = []
-        self._parse_file(filename, None, None, None, self.top_block)
+  $ srctree=. ARCH=x86 SRCARCH=x86 KERNELVERSION=`make kernelversion` ... python(3)
+  >>> import kconfiglib
+  >>> kconf = kconfiglib.Kconfig()  # filename defaults to "Kconfig"
 
-        # Build Symbol.dep for all symbols
-        self._build_dep()
+Search the top-level Makefile for "Additional ARCH settings" to see other
+possibilities for ARCH and SRCARCH.
 
-    def get_arch(self):
-        """Returns the value the environment variable ARCH had at the time the
-        Config instance was created, or None if ARCH was not set. For the
-        kernel, this corresponds to the architecture being built for, with
-        values such as "i386" or "mips"."""
-        return self.arch
 
-    def get_srcarch(self):
-        """Returns the value the environment variable SRCARCH had at the time
-        the Config instance was created, or None if SRCARCH was not set. For
-        the kernel, this corresponds to the particular arch/ subdirectory
-        containing architecture-specific code."""
-        return self.srcarch
+Intro to symbol values
+======================
 
-    def get_srctree(self):
-        """Returns the value the environment variable srctree had at the time
-        the Config instance was created, or None if srctree was not defined.
-        This variable points to the source directory and is used when building
-        in a separate directory."""
-        return self.srctree
+Kconfiglib has the same assignment semantics as the C implementation.
 
-    def get_base_dir(self):
-        """Returns the base directory relative to which 'source' statements
-        will work, passed as an argument to Config.__init__()."""
-        return self.base_dir
+Any symbol can be assigned a value by the user (via Kconfig.load_config() or
+Symbol.set_value()), but this user value is only respected if the symbol is
+visible, which corresponds to it (currently) being visible in the menuconfig
+interface.
 
-    def get_kconfig_filename(self):
-        """Returns the name of the (base) kconfig file this configuration was
-        loaded from."""
-        return self.filename
+For symbols with prompts, the visibility of the symbol is determined by the
+condition on the prompt. Symbols without prompts are never visible, so setting
+a user value on them is pointless. A warning will be printed by default if
+Symbol.set_value() is called on a promptless symbol. Assignments to promptless
+symbols are normal within a .config file, so no similar warning will be printed
+by load_config().
 
-    def get_config_filename(self):
-        """Returns the filename of the most recently loaded configuration file,
-        or None if no configuration has been loaded."""
-        return self.config_filename
+Dependencies from parents and 'if'/'depends on' are propagated to properties,
+including prompts, so these two configurations are logically equivalent:
 
-    def get_config_header(self):
-        """Returns the (uncommented) textual header of the .config file most
-        recently loaded with load_config(). Returns None if no .config file has
-        been loaded or if the most recently loaded .config file has no header.
-        The header consists of all lines up to but not including the first line
-        that either
+(1)
 
-        1. Does not start with "#"
-        2. Has the form "# CONFIG_FOO is not set."
-        """
-        return self.config_header
+  menu "menu"
+      depends on A
 
-    def get_mainmenu_text(self):
-        """Returns the text of the 'mainmenu' statement (with $-references to
-        symbols replaced by symbol values), or None if the configuration has no
-        'mainmenu' statement."""
-        return None if self.mainmenu_text is None else \
-          self._expand_sym_refs(self.mainmenu_text)
+  if B
 
-    def get_defconfig_filename(self):
-        """Returns the name of the defconfig file, which is the first existing
-        file in the list given in a symbol having 'option defconfig_list' set.
-        $-references to symbols will be expanded ("$FOO bar" -> "foo bar" if
-        FOO has the value "foo"). Returns None in case of no defconfig file.
-        Setting 'option defconfig_list' on multiple symbols currently results
-        in undefined behavior.
+  config FOO
+      tristate "foo" if D
+      default y
+      depends on C
 
-        If the environment variable 'srctree' was set when the Config was
-        created, get_defconfig_filename() will first look relative to that
-        directory before looking in the current directory; see
-        Config.__init__().
+  endif
 
-        WARNING: A wart here is that scripts/kconfig/Makefile sometimes uses
-        the --defconfig=<defconfig> option when calling the C implementation of
-        e.g. 'make defconfig'. This option overrides the 'option
-        defconfig_list' symbol, meaning the result from
-        get_defconfig_filename() might not match what 'make defconfig' would
-        use. That probably ought to be worked around somehow, so that this
-        function always gives the "expected" result."""
-        if self.defconfig_sym is None:
-            return None
-        for filename, cond_expr in self.defconfig_sym.def_exprs:
-            if self._eval_expr(cond_expr) == "y":
-                filename = self._expand_sym_refs(filename)
-                # We first look in $srctree. os.path.join() won't work here as
-                # an absolute path in filename would override $srctree.
-                srctree_filename = os.path.normpath(self.srctree + "/" +
-                                                    filename)
-                if os.path.exists(srctree_filename):
-                    return srctree_filename
-                if os.path.exists(filename):
-                    return filename
-        return None
+  endmenu
 
-    def get_symbol(self, name):
-        """Returns the symbol with name 'name', or None if no such symbol
-        appears in the configuration. An alternative shorthand is conf[name],
-        where conf is a Config instance, though that will instead raise
-        KeyError if the symbol does not exist."""
-        return self.syms.get(name)
+(2)
 
-    def __getitem__(self, name):
-        """Returns the symbol with name 'name'. Raises KeyError if the symbol
-        does not appear in the configuration."""
-        return self.syms[name]
+  menu "menu"
+      depends on A
 
-    def get_symbols(self, all_symbols=True):
-        """Returns a list of symbols from the configuration. An alternative for
-        iterating over all defined symbols (in the order of definition) is
+  config FOO
+      tristate "foo" if A && B && C && D
+      default y if A && B && C
 
-        for sym in config:
-            ...
+  endmenu
 
-        which relies on Config implementing __iter__() and is equivalent to
+In this example, A && B && C && D (the prompt condition) needs to be non-n for
+FOO to be visible (assignable). If its value is m, the symbol can only be
+assigned the value m: The visibility sets an upper bound on the value that can
+be assigned by the user, and any higher user value will be truncated down.
 
-        for sym in config.get_symbols(False):
-            ...
+'default' properties are independent of the visibility, though a 'default' will
+often get the same condition as the prompt due to dependency propagation.
+'default' properties are used if the symbol is not visible or has no user
+value.
 
-        all_symbols (default: True): If True, all symbols -- including special
-           and undefined symbols -- will be included in the result, in an
-           undefined order. If False, only symbols actually defined and not
-           merely referred to in the configuration will be included in the
-           result, and will appear in the order that they are defined within
-           the Kconfig configuration files."""
-        return list(self.syms.values()) if all_symbols else self.kconfig_syms
+Symbols with no user value (or that have a user value but are not visible) and
+no (active) 'default' default to n for bool/tristate symbols, and to the empty
+string for other symbol types.
 
-    def __iter__(self):
-        """Convenience function for iterating over the set of all defined
-        symbols in the configuration, used like
+'select' works similarly to symbol visibility, but sets a lower bound on the
+value of the symbol. The lower bound is determined by the value of the
+select*ing* symbol. 'select' does not respect visibility, so non-visible
+symbols can be forced to a particular (minimum) value by a select as well.
 
-        for sym in conf:
-            ...
+For non-bool/tristate symbols, it only matters whether the visibility is n or
+non-n: m visibility acts the same as y visibility.
 
-        The iteration happens in the order of definition within the Kconfig
-        configuration files. Symbols only referred to but not defined will not
-        be included, nor will the special symbols n, m, and y. If you want to
-        include such symbols as well, see config.get_symbols()."""
-        return iter(self.kconfig_syms)
+Conditions on 'default' and 'select' work in mostly intuitive ways. If the
+condition is n, the 'default' or 'select' is disabled. If it is m, the
+'default' or 'select' value (the value of the selecting symbol) is truncated
+down to m.
 
-    def get_choices(self):
-        """Returns a list containing all choice statements in the
-        configuration, in the order they appear in the Kconfig files."""
-        return self.choices
+When writing a configuration with Kconfig.write_config(), only symbols that are
+visible, have an (active) default, or are selected will get written out (note
+that this includes all symbols that would accept user values). Kconfiglib
+matches the .config format produced by the C implementations down to the
+character. This eases testing.
 
-    def get_menus(self):
-        """Returns a list containing all menus in the configuration, in the
-        order they appear in the Kconfig files."""
-        return self.menus
+For a visible bool/tristate symbol FOO with value n, this line is written to
+.config:
 
-    def get_comments(self):
-        """Returns a list containing all comments in the configuration, in the
-        order they appear in the Kconfig files."""
-        return self.comments
+    # CONFIG_FOO is not set
 
-    def get_top_level_items(self):
-        """Returns a list containing the items (symbols, menus, choices, and
-        comments) at the top level of the configuration -- that is, all items
-        that do not appear within a menu or choice. The items appear in the
-        same order as within the configuration."""
-        return self.top_block
+The point is to remember the user n selection (which might differ from the
+default value the symbol would get), while at the same sticking to the rule
+that undefined corresponds to n (.config uses Makefile format, making the line
+above a comment). When the .config file is read back in, this line will be
+treated the same as the following assignment:
 
-    def load_config(self, filename, replace=True):
-        """Loads symbol values from a file in the familiar .config format.
-        Equivalent to calling Symbol.set_user_value() to set each of the
-        values.
+    CONFIG_FOO=n
 
-        "# CONFIG_FOO is not set" within a .config file is treated specially
-        and sets the user value of FOO to 'n'. The C implementation works the
-        same way.
+In Kconfiglib, the set of (currently) assignable values for a bool/tristate
+symbol appear in Symbol.assignable. For other symbol types, just check if
+sym.visibility is non-0 (non-n) to see whether the user value will have an
+effect.
 
-        filename: The .config file to load. $-references to existing
-          environment variables will be expanded. For scripts to work even when
-          an alternative build directory is used with the Linux kernel, you
-          need to refer to the top-level kernel directory with "$srctree".
 
-        replace (default: True): True if the configuration should replace the
-           old configuration; False if it should add to it.
+Intro to the menu tree
+======================
 
-        Returns a list or warnings (hopefully empty)
-        """
+The menu structure, as seen in e.g. menuconfig, is represented by a tree of
+MenuNode objects. The top node of the configuration corresponds to an implicit
+top-level menu, the title of which is shown at the top in the standard
+menuconfig interface. (The title is also available in Kconfig.mainmenu_text in
+Kconfiglib.)
 
-        self._warnings = []
-        # Regular expressions for parsing .config files
-        _set_re_match = re.compile(r"{}(\w+)=(.*)".format(self.config_prefix)).match
-        _unset_re_match = re.compile(r"# {}(\w+) is not set".format(self.config_prefix)).match
+The top node is found in Kconfig.top_node. From there, you can visit child menu
+nodes by following the 'list' pointer, and any following menu nodes by
+following the 'next' pointer. Usually, a non-None 'list' pointer indicates a
+menu or Choice, but menu nodes for symbols can sometimes have a non-None 'list'
+pointer too due to submenus created implicitly from dependencies.
 
-        # Put this first so that a missing file doesn't screw up our state
-        filename = os.path.expandvars(filename)
-        line_feeder = _FileFeed(filename)
+MenuNode.item is either a Symbol or a Choice object, or one of the constants
+MENU and COMMENT. The prompt of the menu node can be found in MenuNode.prompt,
+which also holds the title for menus and comments. For Symbol and Choice,
+MenuNode.help holds the help text (if any, otherwise None).
 
-        self.config_filename = filename
+Most symbols will only have a single menu node. A symbol defined in multiple
+locations will have one menu node for each location. The list of menu nodes for
+a Symbol or Choice can be found in the Symbol/Choice.nodes attribute.
 
-        #
-        # Read header
-        #
+Note that prompts and help texts for symbols and choices are stored in their
+menu node(s) rather than in the Symbol or Choice objects themselves. This makes
+it possible to define a symbol in multiple locations with a different prompt or
+help text in each location. To get the help text or prompt for a symbol with a
+single menu node, do sym.nodes[0].help and sym.nodes[0].prompt, respectively.
+The prompt is a (text, condition) tuple, where condition determines the
+visibility (see 'Intro to expressions' below).
 
-        def is_header_line(line):
-            return line is not None and line.startswith("#") and \
-                   not _unset_re_match(line)
+This organization mirrors the C implementation. MenuNode is called
+'struct menu' there, but I thought "menu" was a confusing name.
 
-        self.config_header = None
+It is possible to give a Choice a name and define it in multiple locations,
+hence why Choice.nodes is also a list.
 
-        line = line_feeder.peek_next()
-        if is_header_line(line):
-            self.config_header = ""
-            while is_header_line(line_feeder.peek_next()):
-                self.config_header += line_feeder.get_next()[1:]
-            # Remove trailing newline
-            if self.config_header.endswith("\n"):
-                self.config_header = self.config_header[:-1]
+As a convenience, the properties added at a particular definition location are
+available on the MenuNode itself, in e.g. MenuNode.defaults. This is helpful
+when generating documentation, so that symbols/choices defined in multiple
+locations can be shown with the correct properties at each location.
 
-        #
-        # Read assignments. Hotspot for some workloads.
-        #
 
-        def warn_override(filename, linenr, name, old_user_val, new_user_val):
-            self._warn('overriding the value of {0}. '
-                       'Old value: "{1}", new value: "{2}".'
-                       .format(name, old_user_val, new_user_val),
-                       filename, linenr)
+Intro to expressions
+====================
 
-        # Invalidate everything to keep things simple. It might be possible to
-        # improve performance for the case where multiple configurations are
-        # loaded by only invalidating a symbol (and its dependent symbols) if
-        # the new user value differs from the old. One complication would be
-        # that symbols not mentioned in the .config must lose their user value
-        # when replace = True, which is the usual case.
-        if replace:
-            self.unset_user_values()
-        else:
-            self._invalidate_all()
+Expressions can be evaluated with the expr_value() function and printed with
+the expr_str() function (these are used internally as well). Evaluating an
+expression always yields a tristate value, where n, m, and y are represented as
+0, 1, and 2, respectively.
 
-        while 1:
-            line = line_feeder.get_next()
-            if line is None:
-                return self._warnings
+The following table should help you figure out how expressions are represented.
+A, B, C, ... are symbols (Symbol instances), NOT is the kconfiglib.NOT
+constant, etc.
 
-            line = line.rstrip()
+Expression            Representation
+----------            --------------
+A                     A
+"A"                   A (constant symbol)
+!A                    (NOT, A)
+A && B                (AND, A, B)
+A && B && C           (AND, A, (AND, B, C))
+A || B                (OR, A, B)
+A || (B && C && D)    (OR, A, (AND, B, (AND, C, D)))
+A = B                 (EQUAL, A, B)
+A != "foo"            (UNEQUAL, A, foo (constant symbol))
+A && B = C && D       (AND, A, (AND, (EQUAL, B, C), D))
+n                     Kconfig.n (constant symbol)
+m                     Kconfig.m (constant symbol)
+y                     Kconfig.y (constant symbol)
+"y"                   Kconfig.y (constant symbol)
 
-            set_match = _set_re_match(line)
-            if set_match:
-                name, val = set_match.groups()
+Strings like "foo" in 'default "foo"' or 'depends on SYM = "foo"' are
+represented as constant symbols, so the only values that appear in expressions
+are symbols***. This mirrors the C implementation.
 
-                if val.startswith('"'):
-                    if len(val) < 2 or val[-1] != '"':
-                        _parse_error(line, "malformed string literal",
-                                     line_feeder.filename, line_feeder.linenr)
-                    # Strip quotes and remove escapings. The unescaping
-                    # procedure should be safe since " can only appear as \"
-                    # inside the string.
-                    val = val[1:-1].replace('\\"', '"').replace("\\\\", "\\")
+***For choice symbols, the parent Choice will appear in expressions as well,
+but it's usually invisible as the value interfaces of Symbol and Choice are
+identical. This mirrors the C implementation and makes different choice modes
+"just work".
 
-                if name in self.syms:
-                    sym = self.syms[name]
-                    if sym.user_val is not None:
-                        warn_override(line_feeder.filename, line_feeder.linenr,
-                                      name, sym.user_val, val)
+Manual evaluation examples:
 
-                    if sym.is_choice_sym:
-                        user_mode = sym.parent.user_mode
-                        if user_mode is not None and user_mode != val:
-                            self._warn("assignment to {0} changes mode of "
-                                       'containing choice from "{1}" to "{2}".'
-                                       .format(name, val, user_mode),
-                                       line_feeder.filename,
-                                       line_feeder.linenr)
+  - The value of A && B is min(A.tri_value, B.tri_value)
 
-                    sym._set_user_value_no_invalidate(val, True)
-                else:
-                    if self.print_undef_assign:
-                        _stderr_msg('note: attempt to assign the value "{0}" '
-                                    "to the undefined symbol {1}."
-                                    .format(val, name),
-                                    line_feeder.filename, line_feeder.linenr)
-            else:
-                unset_match = _unset_re_match(line)
-                if unset_match:
-                    name = unset_match.group(1)
-                    if name in self.syms:
-                        sym = self.syms[name]
-                        if sym.user_val is not None:
-                            warn_override(line_feeder.filename,
-                                          line_feeder.linenr,
-                                          name, sym.user_val, "n")
+  - The value of A || B is max(A.tri_value, B.tri_value)
 
-                        sym._set_user_value_no_invalidate("n", True)
+  - The value of !A is 2 - A.tri_value
 
-    def write_config(self, filename, header=None):
-        """Writes out symbol values in the familiar .config format.
+  - The value of A = B is 2 (y) if A.str_value == B.str_value, and 0 (n)
+    otherwise. Note that str_value is used here instead of tri_value.
 
-        Kconfiglib makes sure the format matches what the C implementation
-        would generate, down to whitespace. This eases testing.
+    For constant (as well as undefined) symbols, str_value matches the name of
+    the symbol. This mirrors the C implementation and explains why
+    'depends on SYM = "foo"' above works as expected.
 
-        filename: The filename under which to save the configuration.
+n/m/y are automatically converted to the corresponding constant symbols
+"n"/"m"/"y" (Kconfig.n/m/y) during parsing.
 
-        header (default: None): A textual header that will appear at the
-           beginning of the file, with each line commented out automatically.
-           None means no header."""
+Kconfig.const_syms is a dictionary like Kconfig.syms but for constant symbols.
 
-        for sym in self.syms_iter():
-            sym.already_written = False
+If a condition is missing (e.g., <cond> when the 'if <cond>' is removed from
+'default A if <cond>'), it is actually Kconfig.y. The standard __str__()
+functions just avoid printing 'if y' conditions to give cleaner output.
 
-        with open(filename, "w") as f:
-            # Write header
-            if header is not None:
-                f.write(_comment(header) + "\n")
 
-            # Build and write configuration
-            conf_strings = []
-            _make_block_conf(self.top_block, conf_strings.append)
-            f.write("\n".join(conf_strings) + "\n")
+Kconfig extensions
+==================
 
-    def eval(self, s):
-        """Returns the value of the expression 's' -- where 's' is represented
-        as a string -- in the context of the configuration. Raises
-        Kconfig_Syntax_Error if syntax errors are detected in 's'.
+Kconfiglib includes a couple of Kconfig extensions:
 
-        For example, if FOO and BAR are tristate symbols at least one of which
-        has the value "y", then config.eval("y && (FOO || BAR)") => "y"
+'source' with relative path
+---------------------------
 
-        This function always yields a tristate value. To get the value of
-        non-bool, non-tristate symbols, use Symbol.get_value().
+The 'rsource' statement sources Kconfig files with a path relative to directory
+of the Kconfig file containing the 'rsource' statement, instead of relative to
+the project root.
 
-        The result of this function is consistent with how evaluation works for
-        conditional expressions in the configuration as well as in the C
-        implementation. "m" and m are rewritten as '"m" && MODULES' and 'm &&
-        MODULES', respectively, and a result of "m" will get promoted to "y" if
-        we're running without modules.
+Consider following directory tree:
 
-        Syntax checking is somewhat lax, partly to be compatible with lax
-        parsing in the C implementation."""
-        return self._eval_expr(self._parse_expr(self._tokenize(s, True), # Feed
-                                                None, # Current symbol/choice
-                                                s))   # line
+  Project
+  +--Kconfig
+  |
+  +--src
+     +--Kconfig
+     |
+     +--SubSystem1
+        +--Kconfig
+        |
+        +--ModuleA
+           +--Kconfig
 
-    def unset_user_values(self):
-        """Resets the values of all symbols, as if Config.load_config() or
-        Symbol.set_user_value() had never been called."""
-        for sym in self.syms_iter():
-            sym._unset_user_value_no_recursive_invalidate()
+In this example, assume that src/SubSystem1/Kconfig wants to source
+src/SubSystem1/ModuleA/Kconfig.
 
-    def set_print_warnings(self, print_warnings):
-        """Determines whether warnings related to this configuration (for
-        things like attempting to assign illegal values to symbols with
-        Symbol.set_user_value()) should be printed to stderr.
+With 'source', this statement would be used:
 
-        print_warnings: True if warnings should be printed."""
-        self.print_warnings = print_warnings
+  source "src/SubSystem1/ModuleA/Kconfig"
 
-    def set_print_undef_assign(self, print_undef_assign):
-        """Determines whether informational messages related to assignments to
-        undefined symbols should be printed to stderr for this configuration.
+With 'rsource', this turns into
 
-        print_undef_assign: If True, such messages will be printed."""
-        self.print_undef_assign = print_undef_assign
+  rsource "ModuleA/Kconfig"
 
-    def __str__(self):
-        """Returns a string containing various information about the Config."""
-        return _lines("Configuration",
-                      "File                                   : " +
-                        self.filename,
-                      "Base directory                         : " +
-                        self.base_dir,
-                      "Value of $ARCH at creation time        : " +
-                        ("(not set)" if self.arch is None else self.arch),
-                      "Value of $SRCARCH at creation time     : " +
-                        ("(not set)" if self.srcarch is None else
-                                        self.srcarch),
-                      "Source tree (derived from $srctree;",
-                      "defaults to '.' if $srctree isn't set) : " +
-                        self.srctree,
-                      "Most recently loaded .config           : " +
-                        ("(no .config loaded)"
-                          if self.config_filename is None else
-                             self.config_filename),
-                      "Print warnings                         : " +
-                        BOOL_STR[self.print_warnings],
-                      "Print assignments to undefined symbols : " +
-                        BOOL_STR[self.print_undef_assign])
+If an absolute path is given to 'rsource', it acts the same as 'source'.
 
-    #
-    # Private methods
-    #
+'rsource' can be used to create "position-independent" Kconfig trees that can
+be moved around freely.
 
-    #
-    # Kconfig parsing
-    #
 
-    def _parse_file(self, filename, parent, deps, visible_if_deps, block):
-        """Parses the Kconfig file 'filename'. Appends the Items in the file
-        (and any file it sources) to the list passed in the 'block' parameter.
-        See _parse_block() for the meaning of the parameters."""
-        self._parse_block(_FileFeed(filename), None, parent, deps,
-                          visible_if_deps, block)
+Globbing 'source'
+-----------------
 
-    def _parse_block(self, line_feeder, end_marker, parent, deps,
-                     visible_if_deps, block):
-        """Parses a block, which is the contents of either a file or an if,
-        menu, or choice statement. Appends the Items to the list passed in the
-        'block' parameter.
+'source' and 'rsource' accept glob patterns, sourcing all matching Kconfig
+files. They require at least one matching file, raising a KconfigError
+otherwise.
 
-        line_feeder: A _FileFeed instance feeding lines from a file. The
-          Kconfig language is line-based in practice.
+For example, the following statement might source sub1/foofoofoo and
+sub2/foobarfoo:
 
-        end_marker: The token that ends the block, e.g. T_ENDIF ("endif") for
-           ifs. None for files.
+  source "sub[12]/foo*foo"
 
-        parent: The enclosing menu or choice, or None if we're at the top
-           level.
+The glob patterns accepted are the same as for the standard glob.glob()
+function.
 
-        deps: Dependencies from enclosing menus, choices and ifs.
+Two additional statements are provided for cases where it's acceptable for a
+pattern to match no files: 'osource' and 'orsource' (the o is for "optional").
 
-        visible_if_deps (default: None): 'visible if' dependencies from
-           enclosing menus.
+For example, the following statements will be no-ops if neither "foo" nor any
+files matching "bar*" exist:
 
-        block: The list to add items to."""
+  osource "foo"
+  osource "bar*"
 
-        while 1:
-            # Do we already have a tokenized line that we determined wasn't
-            # part of whatever we were parsing earlier? See comment in
-            # Config.__init__().
-            if self.end_line is not None:
-                line = self.end_line
-                tokens = self.end_line_tokens
-                tokens.unget_all()
+'orsource' does a relative optional source.
 
-                self.end_line = None
-                self.end_line_tokens = None
-            else:
-                line = line_feeder.get_next()
-                if line is None:
-                    if end_marker is not None:
-                        raise Kconfig_Syntax_Error("Unexpected end of file {0}"
-                                                 .format(line_feeder.filename))
-                    return
+'source' and 'osource' are analogous to 'include' and '-include' in Make.
 
-                tokens = self._tokenize(line, False, line_feeder.filename,
-                                        line_feeder.linenr)
 
-            t0 = tokens.get_next()
-            if t0 is None:
-                continue
+Generalized def_* keywords
+--------------------------
 
-            # Cases are ordered roughly by frequency, which speeds things up a
-            # bit
+def_int, def_hex, and def_string are available in addition to def_bool and
+def_tristate, allowing int, hex, and string symbols to be given a type and a
+default at the same time.
 
-            if t0 == T_CONFIG or t0 == T_MENUCONFIG:
-                # The tokenizer will automatically allocate a new Symbol object
-                # for any new names it encounters, so we don't need to worry
-                # about that here.
-                sym = tokens.get_next()
 
-                # Symbols defined in multiple places get the parent of their
-                # first definition. However, for symbols whose parents are
-                # choice statements, the choice statement takes precedence.
-                if not sym.is_defined_ or isinstance(parent, Choice):
-                    sym.parent = parent
-                sym.is_defined_ = True
+Extra optional warnings
+-----------------------
 
-                self._parse_properties(line_feeder, sym, deps, visible_if_deps)
+Some optional warnings can be controlled via environment variables:
 
-                self.kconfig_syms.append(sym)
-                block.append(sym)
+  - KCONFIG_WARN_UNDEF: If set to 'y', warnings will be generated for all
+    references to undefined symbols within Kconfig files. The only gotcha is
+    that all hex literals must be prefixed with "0x" or "0X", to make it
+    possible to distinguish them from symbol references.
 
-            elif t0 == T_SOURCE:
-                kconfig_file = tokens.get_next()
-                exp_kconfig_file = self._expand_sym_refs(kconfig_file)
-                f = os.path.join(self.base_dir, exp_kconfig_file)
-                if not os.path.exists(f):
-                    raise IOError('{0}:{1}: sourced file "{2}" (expands to '
-                                  '"{3}") not found. Perhaps base_dir '
-                                  '(argument to Config.__init__(), currently '
-                                  '"{4}") is set to the wrong value.'
-                                  .format(line_feeder.filename,
-                                          line_feeder.linenr,
-                                          kconfig_file, exp_kconfig_file,
-                                          self.base_dir))
-                # Add items to the same block
-                self._parse_file(f, parent, deps, visible_if_deps, block)
+    Some projects (e.g. the Linux kernel) use multiple Kconfig trees with many
+    shared Kconfig files, leading to some safe undefined symbol references.
+    KCONFIG_WARN_UNDEF is useful in projects that only have a single Kconfig
+    tree though.
 
-            elif t0 == end_marker:
-                # We have reached the end of the block
-                return
+    KCONFIG_STRICT is an older alias for this environment variable, supported
+    for backwards compatibility.
 
-            elif t0 == T_IF:
-                # If statements are treated as syntactic sugar for adding
-                # dependencies to enclosed items and do not have an explicit
-                # object representation.
+  - KCONFIG_WARN_UNDEF_ASSIGN: If set to 'y', warnings will be generated for
+    all assignments to undefined symbols within .config files. By default, no
+    such warnings are generated.
 
-                dep_expr = self._parse_expr(tokens, None, line,
-                                            line_feeder.filename,
-                                            line_feeder.linenr)
-                # Add items to the same block
-                self._parse_block(line_feeder, T_ENDIF, parent,
-                                  _make_and(dep_expr, deps),
-                                  visible_if_deps, block)
+    This warning can also be enabled/disabled via the Kconfig.warn_assign_undef
+    variable.
 
-            elif t0 == T_COMMENT:
-                comment = Comment()
-                comment.config = self
-                comment.parent = parent
-                comment.filename = line_feeder.filename
-                comment.linenr = line_feeder.linenr
-                comment.text = tokens.get_next()
 
-                self._parse_properties(line_feeder, comment, deps,
-                                       visible_if_deps)
+Preprocessor user functions defined in Python
+---------------------------------------------
 
-                self.comments.append(comment)
-                block.append(comment)
+Preprocessor functions can be defined in Python, which makes it simple to
+integrate information from existing Python tools into Kconfig (e.g. to have
+Kconfig symbols depend on hardware information stored in some other format).
 
-            elif t0 == T_MENU:
-                menu = Menu()
-                menu.config = self
-                menu.parent = parent
-                menu.filename = line_feeder.filename
-                menu.linenr = line_feeder.linenr
-                menu.title = tokens.get_next()
+Putting a Python module named kconfigfunctions(.py) anywhere in sys.path will
+cause it to be imported by Kconfiglib (in Kconfig.__init__()). Note that
+sys.path can be customized via PYTHONPATH, and includes the directory of the
+module being run by default, as well as installation directories.
 
-                self._parse_properties(line_feeder, menu, deps,
-                                       visible_if_deps)
+If the KCONFIG_FUNCTIONS environment variable is set, it gives a different
+module name to use instead of 'kconfigfunctions'.
 
-                # This needs to go before _parse_block() so that we get the
-                # proper menu ordering in the case of nested functions
-                self.menus.append(menu)
-                # Parse contents and put Items in menu.block
-                self._parse_block(line_feeder, T_ENDMENU, menu, menu.dep_expr,
-                                  _make_and(visible_if_deps,
-                                            menu.visible_if_expr),
-                                  menu.block)
+The imported module is expected to define a global dictionary named 'functions'
+that maps function names to Python functions, as follows:
 
-                block.append(menu)
+  def my_fn(kconf, name, arg_1, arg_2, ...):
+      # kconf:
+      #   Kconfig instance
+      #
+      # name:
+      #   Name of the user-defined function ("my-fn"). Think argv[0].
+      #
+      # arg_1, arg_2, ...:
+      #   Arguments passed to the function from Kconfig (strings)
+      #
+      # Returns a string to be substituted as the result of calling the
+      # function
+      ...
 
-            elif t0 == T_CHOICE:
-                name = tokens.get_next()
-                if name is None:
-                    choice = Choice()
-                    self.choices.append(choice)
-                else:
-                    # Named choice
-                    choice = self.named_choices.get(name)
-                    if choice is None:
-                        choice = Choice()
-                        choice.name = name
-                        self.named_choices[name] = choice
-                        self.choices.append(choice)
+  def my_other_fn(kconf, name, arg_1, arg_2, ...):
+      ...
 
-                choice.config = self
-                choice.parent = parent
+  functions = {
+      "my-fn":       (my_fn,       <min.args>, <max.args>/None),
+      "my-other-fn": (my_other_fn, <min.args>, <max.args>/None),
+      ...
+  }
 
-                choice.def_locations.append((line_feeder.filename,
-                                             line_feeder.linenr))
+  ...
 
-                self._parse_properties(line_feeder, choice, deps,
-                                       visible_if_deps)
+<min.args> and <max.args> are the minimum and maximum number of arguments
+expected by the function (excluding the implicit 'name' argument). If
+<max.args> is None, there is no upper limit to the number of arguments. Passing
+an invalid number of arguments will generate a KconfigError exception.
 
-                # Parse contents and put Items in choice.block
-                self._parse_block(line_feeder, T_ENDCHOICE, choice, deps,
-                                  visible_if_deps, choice.block)
+Functions can access the current parsing location as kconf.filename/linenr.
+Accessing other fields of the Kconfig object is not safe. See the warning
+below.
 
-                choice._determine_actual_symbols()
+Keep in mind that for a variable defined like 'foo = $(fn)', 'fn' will be
+called only when 'foo' is expanded. If 'fn' uses the parsing location and the
+intent is to use the location of the assignment, you want 'foo := $(fn)'
+instead, which calls the function immediately.
 
-                # If no type is specified for the choice, its type is that of
-                # the first choice item with a specified type
-                if choice.type == UNKNOWN:
-                    for item in choice.actual_symbols:
-                        if item.type != UNKNOWN:
-                            choice.type = item.type
-                            break
+Once defined, user functions can be called from Kconfig in the same way as
+other preprocessor functions:
 
-                # Each choice item of UNKNOWN type gets the type of the choice
-                for item in choice.actual_symbols:
-                    if item.type == UNKNOWN:
-                        item.type = choice.type
+    config FOO
+        ...
+        depends on $(my-fn,arg1,arg2)
 
-                block.append(choice)
+If my_fn() returns "n", this will result in
 
-            elif t0 == T_MAINMENU:
-                text = tokens.get_next()
-                if self.mainmenu_text is not None:
-                    self._warn("overriding 'mainmenu' text. "
-                               'Old value: "{0}", new value: "{1}".'
-                               .format(self.mainmenu_text, text),
-                               line_feeder.filename, line_feeder.linenr)
-                self.mainmenu_text = text
+    config FOO
+        ...
+        depends on n
 
-            else:
-                _parse_error(line, "unrecognized construct",
-                             line_feeder.filename, line_feeder.linenr)
+Warning
+*******
 
-    def _parse_properties(self, line_feeder, stmt, deps, visible_if_deps):
-        """Parsing of properties for symbols, menus, choices, and comments.
-        Takes care of propagating dependencies from enclosing menus and ifs."""
+User-defined preprocessor functions are called as they're encountered at parse
+time, before all Kconfig files have been processed, and before the menu tree
+has been finalized. There are no guarantees that accessing Kconfig symbols or
+the menu tree via the 'kconf' parameter will work, and it could potentially
+lead to a crash.
 
-        def parse_val_and_cond(tokens, line, filename, linenr):
-            """Parses '<expr1> if <expr2>' constructs, where the 'if' part is
-            optional. Returns a tuple containing the parsed expressions, with
-            None as the second element if the 'if' part is missing."""
-            return (self._parse_expr(tokens, stmt, line, filename, linenr,
-                                     False),
-                    self._parse_expr(tokens, stmt, line, filename, linenr)
-                    if tokens.check(T_IF) else None)
+Preferably, user-defined functions should be stateless.
 
-        # In case the symbol is defined in multiple locations, we need to
-        # remember what prompts, defaults, selects, and implies are new for
-        # this definition, as "depends on" should only apply to the local
-        # definition.
-        new_prompt = None
-        new_def_exprs = []
-        new_selects = []
-        new_implies = []
 
-        # Dependencies from 'depends on' statements
-        depends_on_expr = None
+Feedback
+========
 
-        while 1:
-            line = line_feeder.get_next()
-            if line is None:
-                break
+Send bug reports, suggestions, and questions to ulfalizer a.t Google's email
+service, or open a ticket on the GitHub page.
+"""
+import errno
+import importlib
+import os
+import re
+import sys
 
-            filename = line_feeder.filename
-            linenr = line_feeder.linenr
+# Get rid of some attribute lookups. These are obvious in context.
+from glob import iglob
+from os.path import dirname, exists, expandvars, islink, join, realpath
 
-            tokens = self._tokenize(line, False, filename, linenr)
 
-            t0 = tokens.get_next()
-            if t0 is None:
-                continue
+VERSION = (12, 14, 0)
 
-            # Cases are ordered roughly by frequency, which speeds things up a
-            # bit
 
-            if t0 == T_DEPENDS:
-                if not tokens.check(T_ON):
-                    _parse_error(line, 'expected "on" after "depends"',
-                                 filename, linenr)
+# File layout:
+#
+# Public classes
+# Public functions
+# Internal functions
+# Global constants
 
-                parsed_deps = self._parse_expr(tokens, stmt, line, filename,
-                                               linenr)
+# Line length: 79 columns
 
-                if isinstance(stmt, (Menu, Comment)):
-                    stmt.orig_deps = _make_and(stmt.orig_deps, parsed_deps)
-                else:
-                    depends_on_expr = _make_and(depends_on_expr, parsed_deps)
 
-            elif t0 == T_HELP:
-                # Find first non-blank (not all-space) line and get its
-                # indentation
-                line = line_feeder.next_nonblank()
-                if line is None:
-                    stmt.help = ""
-                    break
-                indent = _indentation(line)
-                if indent == 0:
-                    # If the first non-empty lines has zero indent, there is no
-                    # help text
-                    stmt.help = ""
-                    line_feeder.unget()
-                    break
+#
+# Public classes
+#
 
-                # The help text goes on till the first non-empty line with less
-                # indent
-                help_lines = [_deindent(line, indent)]
-                while 1:
-                    line = line_feeder.get_next()
-                    if line is None or \
-                       (not line.isspace() and _indentation(line) < indent):
-                        stmt.help = "".join(help_lines)
-                        break
-                    help_lines.append(_deindent(line, indent))
 
-                if line is None:
-                    break
+class Kconfig(object):
+    """
+    Represents a Kconfig configuration, e.g. for x86 or ARM. This is the set of
+    symbols, choices, and menu nodes appearing in the configuration. Creating
+    any number of Kconfig objects (including for different architectures) is
+    safe. Kconfiglib doesn't keep any global state.
 
-                line_feeder.unget()
+    The following attributes are available. They should be treated as
+    read-only, and some are implemented through @property magic.
 
-            elif t0 == T_SELECT:
-                target = tokens.get_next()
+    syms:
+      A dictionary with all symbols in the configuration, indexed by name. Also
+      includes all symbols that are referenced in expressions but never
+      defined, except for constant (quoted) symbols.
 
-                stmt.referenced_syms.add(target)
-                stmt.selected_syms.add(target)
+      Undefined symbols can be recognized by Symbol.nodes being empty -- see
+      the 'Intro to the menu tree' section in the module docstring.
 
-                new_selects.append(
-                    (target,
-                     self._parse_expr(tokens, stmt, line, filename, linenr)
-                     if tokens.check(T_IF) else None))
+    const_syms:
+      A dictionary like 'syms' for constant (quoted) symbols
 
-            elif t0 == T_IMPLY:
-                target = tokens.get_next()
+    named_choices:
+      A dictionary like 'syms' for named choices (choice FOO)
 
-                stmt.referenced_syms.add(target)
-                stmt.implied_syms.add(target)
+    defined_syms:
+      A list with all defined symbols, in the same order as they appear in the
+      Kconfig files. Symbols defined in multiple locations appear multiple
+      times.
 
-                new_implies.append(
-                    (target,
-                     self._parse_expr(tokens, stmt, line, filename, linenr)
-                     if tokens.check(T_IF) else None))
+      Note: You probably want to use 'unique_defined_syms' instead. This
+      attribute is mostly maintained for backwards compatibility.
 
-            elif t0 in (T_BOOL, T_TRISTATE, T_INT, T_HEX, T_STRING):
-                stmt.type = TOKEN_TO_TYPE[t0]
-                if tokens.peek_next() is not None:
-                    new_prompt = parse_val_and_cond(tokens, line, filename,
-                                                    linenr)
+    unique_defined_syms:
+      A list like 'defined_syms', but with duplicates removed. Just the first
+      instance is kept for symbols defined in multiple locations. Kconfig order
+      is preserved otherwise.
 
-            elif t0 == T_DEFAULT:
-                new_def_exprs.append(parse_val_and_cond(tokens, line, filename,
-                                                        linenr))
+      Using this attribute instead of 'defined_syms' can save work, and
+      automatically gives reasonable behavior when writing configuration output
+      (symbols defined in multiple locations only generate output once, while
+      still preserving Kconfig order for readability).
 
-            elif t0 == T_DEF_BOOL:
-                stmt.type = BOOL
-                if tokens.peek_next() is not None:
-                    new_def_exprs.append(parse_val_and_cond(tokens, line,
-                                                            filename, linenr))
+    choices:
+      A list with all choices, in the same order as they appear in the Kconfig
+      files.
 
-            elif t0 == T_PROMPT:
-                # 'prompt' properties override each other within a single
-                # definition of a symbol, but additional prompts can be added
-                # by defining the symbol multiple times; hence 'new_prompt'
-                # instead of 'prompt'.
-                new_prompt = parse_val_and_cond(tokens, line, filename, linenr)
+      Note: You probably want to use 'unique_choices' instead. This attribute
+      is mostly maintained for backwards compatibility.
 
-            elif t0 == T_RANGE:
-                low = tokens.get_next()
-                high = tokens.get_next()
-                stmt.referenced_syms.add(low)
-                stmt.referenced_syms.add(high)
+    unique_choices:
+      Analogous to 'unique_defined_syms', for choices. Named choices can have
+      multiple definition locations.
 
-                stmt.ranges.append(
-                    (low, high,
-                     self._parse_expr(tokens, stmt, line, filename, linenr)
-                     if tokens.check(T_IF) else None))
+    menus:
+      A list with all menus, in the same order as they appear in the Kconfig
+      files
 
-            elif t0 == T_DEF_TRISTATE:
-                stmt.type = TRISTATE
-                if tokens.peek_next() is not None:
-                    new_def_exprs.append(parse_val_and_cond(tokens, line,
-                                                            filename, linenr))
+    comments:
+      A list with all comments, in the same order as they appear in the Kconfig
+      files
 
-            elif t0 == T_OPTION:
-                if tokens.check(T_ENV) and tokens.check(T_EQUAL):
-                    env_var = tokens.get_next()
+    kconfig_filenames:
+      A list with the filenames of all Kconfig files included in the
+      configuration, relative to $srctree (or relative to the current directory
+      if $srctree isn't set), except absolute paths (e.g.
+      'source "/foo/Kconfig"') are kept as-is.
 
-                    stmt.is_special_ = True
-                    stmt.is_from_env = True
+      The files are listed in the order they are source'd, starting with the
+      top-level Kconfig file. If a file is source'd multiple times, it will
+      appear multiple times. Use set() to get unique filenames.
 
-                    if env_var not in os.environ:
-                        self._warn("The symbol {0} references the "
-                                   "non-existent environment variable {1} and "
-                                   "will get the empty string as its value. "
-                                   "If you're using Kconfiglib via "
-                                   "'make (i)scriptconfig', it should have "
-                                   "set up the environment correctly for you. "
-                                   "If you still got this message, that "
-                                   "might be an error, and you should email "
-                                   "ulfalizer a.t Google's email service."""
-                                   .format(stmt.name, env_var),
-                                   filename, linenr)
+      Note that Kconfig.sync_deps() already indirectly catches any file
+      modifications that change configuration output.
 
-                        stmt.cached_val = ""
-                    else:
-                        stmt.cached_val = os.environ[env_var]
+    env_vars:
+      A set() with the names of all environment variables referenced in the
+      Kconfig files.
 
-                elif tokens.check(T_DEFCONFIG_LIST):
-                    self.defconfig_sym = stmt
+      Only environment variables referenced with the preprocessor $(FOO) syntax
+      will be registered. The older $FOO syntax is only supported for backwards
+      compatibility.
 
-                elif tokens.check(T_MODULES):
-                    # To reduce warning spam, only warn if 'option modules' is
-                    # set on some symbol that isn't MODULES, which should be
-                    # safe. I haven't run into any projects that make use
-                    # modules besides the kernel yet, and there it's likely to
-                    # keep being called "MODULES".
-                    if stmt.name != "MODULES":
-                        self._warn("the 'modules' option is not supported. "
-                                   "Let me know if this is a problem for you; "
-                                   "it shouldn't be that hard to implement. "
-                                   "(Note that modules are still supported -- "
-                                   "Kconfiglib just assumes the symbol name "
-                                   "MODULES, like older versions of the C "
-                                   "implementation did when 'option modules' "
-                                   "wasn't used.)",
-                                   filename, linenr)
+      Also note that $(FOO) won't be registered unless the environment variable
+      $FOO is actually set. If it isn't, $(FOO) is an expansion of an unset
+      preprocessor variable (which gives the empty string).
 
-                elif tokens.check(T_ALLNOCONFIG_Y):
-                    if not isinstance(stmt, Symbol):
-                        _parse_error(line,
-                                     "the 'allnoconfig_y' option is only "
-                                     "valid for symbols",
-                                     filename, linenr)
-                    stmt.allnoconfig_y = True
+      Another gotcha is that environment variables referenced in the values of
+      recursively expanded preprocessor variables (those defined with =) will
+      only be registered if the variable is actually used (expanded) somewhere.
 
-                else:
-                    _parse_error(line, "unrecognized option", filename, linenr)
+      The note from the 'kconfig_filenames' documentation applies here too.
 
-            elif t0 == T_VISIBLE:
-                if not tokens.check(T_IF):
-                    _parse_error(line, 'expected "if" after "visible"',
-                                 filename, linenr)
-                if not isinstance(stmt, Menu):
-                    _parse_error(line,
-                                 "'visible if' is only valid for menus",
-                                 filename, linenr)
+    n/m/y:
+      The predefined constant symbols n/m/y. Also available in const_syms.
 
-                parsed_deps = self._parse_expr(tokens, stmt, line, filename,
-                                               linenr)
-                stmt.visible_if_expr = _make_and(stmt.visible_if_expr,
-                                                 parsed_deps)
+    modules:
+      The Symbol instance for the modules symbol. Currently hardcoded to
+      MODULES, which is backwards compatible. Kconfiglib will warn if
+      'option modules' is set on some other symbol. Tell me if you need proper
+      'option modules' support.
 
-            elif t0 == T_OPTIONAL:
-                if not isinstance(stmt, Choice):
-                    _parse_error(line,
-                                 '"optional" is only valid for choices',
-                                 filename,
-                                 linenr)
-                stmt.optional = True
+      'modules' is never None. If the MODULES symbol is not explicitly defined,
+      its tri_value will be 0 (n), as expected.
 
-            else:
-                # See comment in Config.__init__()
-                self.end_line = line
-                self.end_line_tokens = tokens
-                break
+      A simple way to enable modules is to do 'kconf.modules.set_value(2)'
+      (provided the MODULES symbol is defined and visible). Modules are
+      disabled by default in the kernel Kconfig files as of writing, though
+      nearly all defconfig files enable them (with 'CONFIG_MODULES=y').
 
-        # Done parsing properties. Now propagate 'depends on' and enclosing
-        # menu/if dependencies to expressions.
+    defconfig_list:
+      The Symbol instance for the 'option defconfig_list' symbol, or None if no
+      defconfig_list symbol exists. The defconfig filename derived from this
+      symbol can be found in Kconfig.defconfig_filename.
 
-        # The set of symbols referenced directly by the statement plus all
-        # symbols referenced by enclosing menus and ifs
-        stmt.all_referenced_syms = stmt.referenced_syms | _get_expr_syms(deps)
+    defconfig_filename:
+      The filename given by the defconfig_list symbol. This is taken from the
+      first 'default' with a satisfied condition where the specified file
+      exists (can be opened for reading). If a defconfig file foo/defconfig is
+      not found and $srctree was set when the Kconfig was created,
+      $srctree/foo/defconfig is looked up as well.
 
-        # Save original dependencies from enclosing menus and ifs
-        stmt.deps_from_containing = deps
+      'defconfig_filename' is None if either no defconfig_list symbol exists,
+      or if the defconfig_list symbol has no 'default' with a satisfied
+      condition that specifies a file that exists.
 
-        if isinstance(stmt, (Menu, Comment)):
-            stmt.dep_expr = _make_and(stmt.orig_deps, deps)
-        else:
-            # Symbol or Choice
+      Gotcha: scripts/kconfig/Makefile might pass --defconfig=<defconfig> to
+      scripts/kconfig/conf when running e.g. 'make defconfig'. This option
+      overrides the defconfig_list symbol, meaning defconfig_filename might not
+      always match what 'make defconfig' would use.
 
-            # See comment for 'menu_dep'
-            stmt.menu_dep = _make_and(deps, depends_on_expr)
+    top_node:
+      The menu node (see the MenuNode class) of the implicit top-level menu.
+      Acts as the root of the menu tree.
 
-            # Propagate dependencies to prompts
+    mainmenu_text:
+      The prompt (title) of the top menu (top_node). Defaults to "Main menu".
+      Can be changed with the 'mainmenu' statement (see kconfig-language.txt).
 
-            if new_prompt is not None:
-                prompt, cond_expr = new_prompt
-                # Propagate 'visible if' dependencies from menus and local
-                # 'depends on' dependencies
-                cond_expr = _make_and(_make_and(cond_expr, visible_if_deps),
-                                      depends_on_expr)
-                # Save original
-                stmt.orig_prompts.append((prompt, cond_expr))
-                # Finalize with dependencies from enclosing menus and ifs
-                stmt.prompts.append((prompt, _make_and(cond_expr, deps)))
+    variables:
+      A dictionary with all preprocessor variables, indexed by name. See the
+      Variable class.
 
-            # Propagate dependencies to defaults
+    warn:
+      Set this variable to True/False to enable/disable warnings. See
+      Kconfig.__init__().
 
-            # Propagate 'depends on' dependencies
-            new_def_exprs = [(val_expr, _make_and(cond_expr, depends_on_expr))
-                             for val_expr, cond_expr in new_def_exprs]
-            # Save original
-            stmt.orig_def_exprs.extend(new_def_exprs)
-            # Finalize with dependencies from enclosing menus and ifs
-            stmt.def_exprs.extend([(val_expr, _make_and(cond_expr, deps))
-                                   for val_expr, cond_expr in new_def_exprs])
+      When 'warn' is False, the values of the other warning-related variables
+      are ignored.
 
-            # Propagate dependencies to selects and implies
+      This variable as well as the other warn* variables can be read to check
+      the current warning settings.
 
-            # Only symbols can select and imply
-            if isinstance(stmt, Symbol):
-                # Propagate 'depends on' dependencies
-                new_selects = [(target, _make_and(cond_expr, depends_on_expr))
-                               for target, cond_expr in new_selects]
-                new_implies = [(target, _make_and(cond_expr, depends_on_expr))
-                               for target, cond_expr in new_implies]
-                # Save original
-                stmt.orig_selects.extend(new_selects)
-                stmt.orig_implies.extend(new_implies)
-                # Finalize with dependencies from enclosing menus and ifs
-                for target, cond in new_selects:
-                    target.rev_dep = \
-                        _make_or(target.rev_dep,
-                                 _make_and(stmt, _make_and(cond, deps)))
-                for target, cond in new_implies:
-                    target.weak_rev_dep = \
-                        _make_or(target.weak_rev_dep,
-                                 _make_and(stmt, _make_and(cond, deps)))
+    warn_to_stderr:
+      Set this variable to True/False to enable/disable warnings on stderr. See
+      Kconfig.__init__().
 
-    def _parse_expr(self, feed, cur_item, line, filename=None, linenr=None,
-                    transform_m=True):
-        """Parses an expression from the tokens in 'feed' using a simple
-        top-down approach. The result has the form
-        '(<operator>, [<parsed operands>])', where <operator> is e.g.
-        kconfiglib.AND. If there is only one operand (i.e., no && or ||), then
-        the operand is returned directly. This also goes for subexpressions.
+    warn_assign_undef:
+      Set this variable to True to generate warnings for assignments to
+      undefined symbols in configuration files.
 
-        feed: _Feed instance containing the tokens for the expression.
+      This variable is False by default unless the KCONFIG_WARN_UNDEF_ASSIGN
+      environment variable was set to 'y' when the Kconfig instance was
+      created.
 
-        cur_item: The item (Symbol, Choice, Menu, or Comment) currently being
-           parsed, or None if we're not parsing an item. Used for recording
-           references to symbols.
+    warn_assign_override:
+      Set this variable to True to generate warnings for multiple assignments
+      to the same symbol in configuration files, where the assignments set
+      different values (e.g. CONFIG_FOO=m followed by CONFIG_FOO=y, where the
+      last value would get used).
 
-        line: The line containing the expression being parsed.
+      This variable is True by default. Disabling it might be useful when
+      merging configurations.
 
-        filename (default: None): The file containing the expression.
+    warn_assign_redun:
+      Like warn_assign_override, but for multiple assignments setting a symbol
+      to the same value.
 
-        linenr (default: None): The line number containing the expression.
+      This variable is True by default. Disabling it might be useful when
+      merging configurations.
 
-        transform_m (default: False): Determines if 'm' should be rewritten to
-           'm && MODULES' -- see parse_val_and_cond().
+    warnings:
+      A list of strings containing all warnings that have been generated, for
+      cases where more flexibility is needed.
 
-        Expression grammar, in decreasing order of precedence:
+      See the 'warn_to_stderr' parameter to Kconfig.__init__() and the
+      Kconfig.warn_to_stderr variable as well. Note that warnings still get
+      added to Kconfig.warnings when 'warn_to_stderr' is True.
 
-        <expr> -> <symbol>
-                  <symbol> '=' <symbol>
-                  <symbol> '!=' <symbol>
-                  '(' <expr> ')'
-                  '!' <expr>
-                  <expr> '&&' <expr>
-                  <expr> '||' <expr>"""
+      Just as for warnings printed to stderr, only warnings that are enabled
+      will get added to Kconfig.warnings. See the various Kconfig.warn*
+      variables.
 
-        # Use instance variables to avoid having to pass these as arguments
-        # through the top-down parser in _parse_expr_rec(), which is tedious
-        # and obfuscates the code. A profiler run shows no noticeable
-        # performance difference.
-        self._cur_item = cur_item
-        self._transform_m = transform_m
-        self._line = line
-        self._filename = filename
-        self._linenr = linenr
+    missing_syms:
+      A list with (name, value) tuples for all assignments to undefined symbols
+      within the most recently loaded .config file(s). 'name' is the symbol
+      name without the 'CONFIG_' prefix. 'value' is a string that gives the
+      right-hand side of the assignment verbatim.
 
-        return self._parse_expr_rec(feed)
+      See Kconfig.load_config() as well.
 
-    def _parse_expr_rec(self, feed):
-        or_term = self._parse_or_term(feed)
-        if not feed.check(T_OR):
-            # Common case -- no need for an OR node since it's just a single
-            # operand
-            return or_term
-        or_terms = [or_term, self._parse_or_term(feed)]
-        while feed.check(T_OR):
-            or_terms.append(self._parse_or_term(feed))
-        return (OR, or_terms)
+    srctree:
+      The value of the $srctree environment variable when the configuration was
+      loaded, or the empty string if $srctree wasn't set. This gives nice
+      behavior with os.path.join(), which treats "" as the current directory,
+      without adding "./".
 
-    def _parse_or_term(self, feed):
-        and_term = self._parse_factor(feed)
-        if not feed.check(T_AND):
-            # Common case -- no need for an AND node since it's just a single
-            # operand
-            return and_term
-        and_terms = [and_term, self._parse_factor(feed)]
-        while feed.check(T_AND):
-            and_terms.append(self._parse_factor(feed))
-        return (AND, and_terms)
+      Kconfig files are looked up relative to $srctree (unless absolute paths
+      are used), and .config files are looked up relative to $srctree if they
+      are not found in the current directory. This is used to support
+      out-of-tree builds. The C tools use this environment variable in the same
+      way.
 
-    def _parse_factor(self, feed):
-        token = feed.get_next()
+      Changing $srctree after creating the Kconfig instance has no effect. Only
+      the value when the configuration is loaded matters. This avoids surprises
+      if multiple configurations are loaded with different values for $srctree.
 
-        if isinstance(token, (Symbol, str)):
-            if self._cur_item is not None and isinstance(token, Symbol):
-                self._cur_item.referenced_syms.add(token)
+    config_prefix:
+      The value of the $CONFIG_ environment variable when the configuration was
+      loaded. This is the prefix used (and expected) on symbol names in .config
+      files and C headers. Defaults to "CONFIG_". Used in the same way in the C
+      tools.
 
-            next_token = feed.peek_next()
-            # For conditional expressions ('depends on <expr>',
-            # '... if <expr>', # etc.), "m" and m are rewritten to
-            # "m" && MODULES.
-            if next_token != T_EQUAL and next_token != T_UNEQUAL:
-                if self._transform_m and (token is self.m or token == "m"):
-                    return (AND, ["m", self._sym_lookup("MODULES")])
-                return token
+      Like for srctree, only the value of $CONFIG_ when the configuration is
+      loaded matters.
 
-            relation = EQUAL if (feed.get_next() == T_EQUAL) else UNEQUAL
-            token_2 = feed.get_next()
-            if self._cur_item is not None and isinstance(token_2, Symbol):
-                self._cur_item.referenced_syms.add(token_2)
-            return (relation, token, token_2)
+    filename/linenr:
+      The current parsing location, for use in Python preprocessor functions.
+      See the module docstring.
+    """
+    __slots__ = (
+        "_encoding",
+        "_functions",
+        "_set_match",
+        "_srctree_prefix",
+        "_unset_match",
+        "_warn_assign_no_prompt",
+        "choices",
+        "comments",
+        "config_prefix",
+        "const_syms",
+        "defconfig_list",
+        "defined_syms",
+        "env_vars",
+        "kconfig_filenames",
+        "m",
+        "menus",
+        "missing_syms",
+        "modules",
+        "n",
+        "named_choices",
+        "srctree",
+        "syms",
+        "top_node",
+        "unique_choices",
+        "unique_defined_syms",
+        "variables",
+        "warn",
+        "warn_assign_override",
+        "warn_assign_redun",
+        "warn_assign_undef",
+        "warn_to_stderr",
+        "warnings",
+        "y",
 
-        if token == T_NOT:
-            return (NOT, self._parse_factor(feed))
+        # Parsing-related
+        "_parsing_kconfigs",
+        "_readline",
+        "filename",
+        "linenr",
+        "_include_path",
+        "_filestack",
+        "_line",
+        "_tokens",
+        "_tokens_i",
+        "_reuse_tokens",
+    )
 
-        if token == T_OPEN_PAREN:
-            expr_parse = self._parse_expr_rec(feed)
-            if not feed.check(T_CLOSE_PAREN):
-                _parse_error(self._line, "missing end parenthesis",
-                             self._filename, self._linenr)
-            return expr_parse
+    #
+    # Public interface
+    #
 
-        _parse_error(self._line, "malformed expression", self._filename,
-                     self._linenr)
+    def __init__(self, filename="Kconfig", warn=True, warn_to_stderr=True,
+                 encoding="utf-8"):
+        """
+        Creates a new Kconfig object by parsing Kconfig files.
+        Note that Kconfig files are not the same as .config files (which store
+        configuration symbol values).
 
-    def _tokenize(self, s, for_eval, filename=None, linenr=None):
-        """Returns a _Feed instance containing tokens derived from the string
-        's'. Registers any new symbols encountered (via _sym_lookup()).
+        See the module docstring for some environment variables that influence
+        default warning settings (KCONFIG_WARN_UNDEF and
+        KCONFIG_WARN_UNDEF_ASSIGN).
 
-        (I experimented with a pure regular expression implementation, but it
-        came out slower, less readable, and wouldn't have been as flexible.)
+        Raises KconfigError on syntax/semantic errors, and OSError or (possibly
+        a subclass of) IOError on IO errors ('errno', 'strerror', and
+        'filename' are available). Note that IOError is an alias for OSError on
+        Python 3, so it's enough to catch OSError there. If you need Python 2/3
+        compatibility, it's easiest to catch EnvironmentError, which is a
+        common base class of OSError/IOError on Python 2 and an alias for
+        OSError on Python 3.
 
-        for_eval: True when parsing an expression for a call to Config.eval(),
-           in which case we should not treat the first token specially nor
-           register new symbols."""
+        filename (default: "Kconfig"):
+          The Kconfig file to load. For the Linux kernel, you'll want "Kconfig"
+          from the top-level directory, as environment variables will make sure
+          the right Kconfig is included from there (arch/$SRCARCH/Kconfig as of
+          writing).
 
-        s = s.strip()
-        if s == "" or s[0] == "#":
-            return _Feed([])
+          If $srctree is set, 'filename' will be looked up relative to it.
+          $srctree is also used to look up source'd files within Kconfig files.
+          See the class documentation.
 
-        if for_eval:
-            previous = None # The previous token seen
-            tokens = []
-            i = 0 # The current index in the string being tokenized
+          If you are using Kconfiglib via 'make scriptconfig', the filename of
+          the base base Kconfig file will be in sys.argv[1]. It's currently
+          always "Kconfig" in practice.
 
-        else:
-            # The initial word on a line is parsed specially. Let
-            # command_chars = [A-Za-z0-9_]. Then
-            #  - leading non-command_chars characters are ignored, and
-            #  - the first token consists the following one or more
-            #    command_chars characters.
-            # This is why things like "----help--" are accepted.
-            initial_token_match = _initial_token_re_match(s)
-            if initial_token_match is None:
-                return _Feed([])
-            keyword = _get_keyword(initial_token_match.group(1))
-            if keyword == T_HELP:
-                # Avoid junk after "help", e.g. "---", being registered as a
-                # symbol
-                return _Feed([T_HELP])
-            if keyword is None:
-                # We expect a keyword as the first token
-                _tokenization_error(s, filename, linenr)
+        warn (default: True):
+          True if warnings related to this configuration should be generated.
+          This can be changed later by setting Kconfig.warn to True/False. It
+          is provided as a constructor argument since warnings might be
+          generated during parsing.
 
-            previous = keyword
-            tokens = [keyword]
-            # The current index in the string being tokenized
-            i = initial_token_match.end()
+          See the other Kconfig.warn_* variables as well, which enable or
+          suppress certain warnings when warnings are enabled.
 
-        # _tokenize() is a hotspot during parsing, and this speeds things up a
-        # bit
-        strlen = len(s)
-        append = tokens.append
+          All generated warnings are added to the Kconfig.warnings list. See
+          the class documentation.
 
-        # Main tokenization loop. (Handles tokens past the first one.)
-        while i < strlen:
-            # Test for an identifier/keyword preceded by whitespace first; this
-            # is the most common case.
-            id_keyword_match = _id_keyword_re_match(s, i)
-            if id_keyword_match:
-                # We have an identifier or keyword. The above also stripped any
-                # whitespace for us.
-                name = id_keyword_match.group(1)
-                # Jump past it
-                i = id_keyword_match.end()
+        warn_to_stderr (default: True):
+          True if warnings should be printed to stderr in addition to being
+          added to Kconfig.warnings.
 
-                keyword = _get_keyword(name)
-                if keyword is not None:
-                    # It's a keyword
-                    append(keyword)
-                elif previous in STRING_LEX:
-                    # What would ordinarily be considered an identifier is
-                    # treated as a string after certain tokens
-                    append(name)
-                else:
-                    # It's a symbol name. _sym_lookup() will take care of
-                    # allocating a new Symbol instance if it's the first time
-                    # we see it.
-                    sym = self._sym_lookup(name, for_eval)
+          This can be changed later by setting Kconfig.warn_to_stderr to
+          True/False.
 
-                    if previous == T_CONFIG or previous == T_MENUCONFIG:
-                        # If the previous token is T_(MENU)CONFIG
-                        # ("(menu)config"), we're tokenizing the first line of
-                        # a symbol definition, and should remember this as a
-                        # location where the symbol is defined
-                        sym.def_locations.append((filename, linenr))
-                    else:
-                        # Otherwise, it's a reference to the symbol
-                        sym.ref_locations.append((filename, linenr))
+        encoding (default: "utf-8"):
+          The encoding to use when reading and writing files, and when decoding
+          output from commands run via $(shell). If None, the encoding
+          specified in the current locale will be used.
 
-                    append(sym)
+          The "utf-8" default avoids exceptions on systems that are configured
+          to use the C locale, which implies an ASCII encoding.
 
-            else:
-                # Not an identifier/keyword
+          This parameter has no effect on Python 2, due to implementation
+          issues (regular strings turning into Unicode strings, which are
+          distinct in Python 2). Python 2 doesn't decode regular strings
+          anyway.
 
-                while i < strlen and s[i].isspace():
-                    i += 1
-                if i == strlen:
-                    break
-                c = s[i]
-                i += 1
+          Related PEP: https://www.python.org/dev/peps/pep-0538/
+        """
+        self._encoding = encoding
 
-                # String literal (constant symbol)
-                if c == '"' or c == "'":
-                    if "\\" in s:
-                        # Slow path: This could probably be sped up, but it's a
-                        # very unusual case anyway.
-                        quote = c
-                        val = ""
-                        while 1:
-                            if i >= len(s):
-                                _tokenization_error(s, filename, linenr)
-                            c = s[i]
-                            if c == quote:
-                                break
-                            if c == "\\":
-                                if i + 1 >= len(s):
-                                    _tokenization_error(s, filename, linenr)
-                                val += s[i + 1]
-                                i += 2
-                            else:
-                                val += c
-                                i += 1
-                        i += 1
-                        append(val)
-                    else:
-                        # Fast path: If the string contains no backslashes
-                        # (almost always) we can simply look for the matching
-                        # quote.
-                        end = s.find(c, i)
-                        if end == -1:
-                            _tokenization_error(s, filename, linenr)
-                        append(s[i:end])
-                        i = end + 1
+        self.srctree = os.getenv("srctree", "")
+        # A prefix we can reliably strip from glob() results to get a filename
+        # relative to $srctree. relpath() can cause issues for symlinks,
+        # because it assumes symlink/../foo is the same as foo/.
+        self._srctree_prefix = realpath(self.srctree) + os.sep
 
-                elif c == "&":
-                    # Invalid characters are ignored
-                    if i >= len(s) or s[i] != "&": continue
-                    append(T_AND)
-                    i += 1
+        self.warn = warn
+        self.warn_to_stderr = warn_to_stderr
+        self.warn_assign_undef = os.getenv("KCONFIG_WARN_UNDEF_ASSIGN") == "y"
+        self.warn_assign_override = True
+        self.warn_assign_redun = True
+        self._warn_assign_no_prompt = True
 
-                elif c == "|":
-                    # Invalid characters are ignored
-                    if i >= len(s) or s[i] != "|": continue
-                    append(T_OR)
-                    i += 1
+        self.warnings = []
 
-                elif c == "!":
-                    if i < len(s) and s[i] == "=":
-                        append(T_UNEQUAL)
-                        i += 1
-                    else:
-                        append(T_NOT)
+        self.config_prefix = os.getenv("CONFIG_", "CONFIG_")
+        # Regular expressions for parsing .config files
+        self._set_match = _re_match(self.config_prefix + r"([^=]+)=(.*)")
+        self._unset_match = _re_match(r"# {}([^ ]+) is not set".format(
+            self.config_prefix))
 
-                elif c == "=": append(T_EQUAL)
-                elif c == "(": append(T_OPEN_PAREN)
-                elif c == ")": append(T_CLOSE_PAREN)
-                elif c == "#": break # Comment
+        self.syms = {}
+        self.const_syms = {}
+        self.defined_syms = []
+        self.missing_syms = []
+        self.named_choices = {}
+        self.choices = []
+        self.menus = []
+        self.comments = []
 
-                else: continue # Invalid characters are ignored
+        for nmy in "n", "m", "y":
+            sym = Symbol()
+            sym.kconfig = self
+            sym.name = nmy
+            sym.is_constant = True
+            sym.orig_type = TRISTATE
+            sym._cached_tri_val = STR_TO_TRI[nmy]
 
-            previous = tokens[-1]
+            self.const_syms[nmy] = sym
 
-        return _Feed(tokens)
+        self.n = self.const_syms["n"]
+        self.m = self.const_syms["m"]
+        self.y = self.const_syms["y"]
 
-    def _sym_lookup(self, name, for_eval=False):
-        """Fetches the symbol 'name' from the symbol table, creating and
-        registering it if it does not exist. If 'for_eval' is True, the symbol
-        won't be added to the symbol table if it does not exist -- this is for
-        Config.eval()."""
-        if name in self.syms:
-            return self.syms[name]
+        # Make n/m/y well-formed symbols
+        for nmy in "n", "m", "y":
+            sym = self.const_syms[nmy]
+            sym.rev_dep = sym.weak_rev_dep = sym.direct_dep = self.n
 
-        new_sym = Symbol()
-        new_sym.config = self
-        new_sym.name = name
-        if for_eval:
-            self._warn("no symbol {0} in configuration".format(name))
-        else:
-            self.syms[name] = new_sym
-        return new_sym
+        # Maps preprocessor variables names to Variable instances
+        self.variables = {}
 
-    #
-    # Expression evaluation
-    #
+        # Predefined preprocessor functions, with min/max number of arguments
+        self._functions = {
+            "info":       (_info_fn,       1, 1),
+            "error-if":   (_error_if_fn,   2, 2),
+            "filename":   (_filename_fn,   0, 0),
+            "lineno":     (_lineno_fn,     0, 0),
+            "shell":      (_shell_fn,      1, 1),
+            "warning-if": (_warning_if_fn, 2, 2),
+        }
 
-    def _eval_expr(self, expr):
-        """Evaluates an expression to "n", "m", or "y"."""
+        # Add any user-defined preprocessor functions
+        try:
+            self._functions.update(
+                importlib.import_module(
+                    os.getenv("KCONFIG_FUNCTIONS", "kconfigfunctions")
+                ).functions)
+        except ImportError:
+            pass
 
-        # Handles e.g. an "x if y" condition where the "if y" part is missing.
-        if expr is None:
-            return "y"
+        # This determines whether previously unseen symbols are registered.
+        # They shouldn't be if we parse expressions after parsing, as part of
+        # Kconfig.eval_string().
+        self._parsing_kconfigs = True
 
-        res = self._eval_expr_rec(expr)
-        if res == "m":
-            # Promote "m" to "y" if we're running without modules.
-            #
-            # Internally, "m" is often rewritten to "m" && MODULES by both the
-            # C implementation and Kconfiglib, which takes care of cases where
-            # "m" should be demoted to "n" instead.
-            modules_sym = self.syms.get("MODULES")
-            if modules_sym is None or modules_sym.get_value() != "y":
-                return "y"
-        return res
+        self.modules = self._lookup_sym("MODULES")
+        self.defconfig_list = None
 
-    def _eval_expr_rec(self, expr):
-        if isinstance(expr, Symbol):
-            # Non-bool/tristate symbols are always "n" in a tristate sense,
-            # regardless of their value
-            if expr.type != BOOL and expr.type != TRISTATE:
-                return "n"
-            return expr.get_value()
+        self.top_node = MenuNode()
+        self.top_node.kconfig = self
+        self.top_node.item = MENU
+        self.top_node.is_menuconfig = True
+        self.top_node.visibility = self.y
+        self.top_node.prompt = ("Main menu", self.y)
+        self.top_node.parent = None
+        self.top_node.dep = self.y
+        self.top_node.filename = filename
+        self.top_node.linenr = 1
+        self.top_node.include_path = ()
 
-        if isinstance(expr, str):
-            return expr if (expr == "y" or expr == "m") else "n"
+        # Parse the Kconfig files
 
-        # Ordered by frequency
+        # Not used internally. Provided as a convenience.
+        self.kconfig_filenames = [filename]
+        self.env_vars = set()
 
-        if expr[0] == AND:
-            res = "y"
-            for subexpr in expr[1]:
-                ev = self._eval_expr_rec(subexpr)
-                # Return immediately upon discovering an "n" term
-                if ev == "n":
-                    return "n"
-                if ev == "m":
-                    res = "m"
-            # 'res' is either "m" or "y" here; we already handled the
-            # short-circuiting "n" case in the loop.
-            return res
+        # Keeps track of the location in the parent Kconfig files. Kconfig
+        # files usually source other Kconfig files. See _enter_file().
+        self._filestack = []
+        self._include_path = ()
 
-        if expr[0] == NOT:
-            ev = self._eval_expr_rec(expr[1])
-            if ev == "y":
-                return "n"
-            return "y" if (ev == "n") else "m"
+        # The current parsing location
+        self.filename = filename
+        self.linenr = 0
 
-        if expr[0] == OR:
-            res = "n"
-            for subexpr in expr[1]:
-                ev = self._eval_expr_rec(subexpr)
-                # Return immediately upon discovering a "y" term
-                if ev == "y":
-                    return "y"
-                if ev == "m":
-                    res = "m"
-            # 'res' is either "n" or "m" here; we already handled the
-            # short-circuiting "y" case in the loop.
-            return res
+        # Used to avoid retokenizing lines when we discover that they're not
+        # part of the construct currently being parsed. This is kinda like an
+        # unget operation.
+        self._reuse_tokens = False
 
-        if expr[0] == EQUAL:
-            return "y" if (_str_val(expr[1]) == _str_val(expr[2])) else "n"
+        # Open the top-level Kconfig file. Store the readline() method directly
+        # as a small optimization.
+        self._readline = self._open(join(self.srctree, filename), "r").readline
 
-        if expr[0] == UNEQUAL:
-            return "y" if (_str_val(expr[1]) != _str_val(expr[2])) else "n"
+        try:
+            # Parse the Kconfig files
+            self._parse_block(None, self.top_node, self.top_node)
+            self.top_node.list = self.top_node.next
+            self.top_node.next = None
+        except UnicodeDecodeError as e:
+            _decoding_error(e, self.filename)
 
-        _internal_error("Internal error while evaluating expression: "
-                        "unknown operation {0}.".format(expr[0]))
+        # Close the top-level Kconfig file. __self__ fetches the 'file' object
+        # for the method.
+        self._readline.__self__.close()
 
-    def _eval_min(self, e1, e2):
-        """Returns the minimum value of the two expressions. Equates None with
-        'y'."""
-        e1_eval = self._eval_expr(e1)
-        e2_eval = self._eval_expr(e2)
-        return e1_eval if tri_less(e1_eval, e2_eval) else e2_eval
+        self._parsing_kconfigs = False
 
-    def _eval_max(self, e1, e2):
-        """Returns the maximum value of the two expressions. Equates None with
-        'y'."""
-        e1_eval = self._eval_expr(e1)
-        e2_eval = self._eval_expr(e2)
-        return e1_eval if tri_greater(e1_eval, e2_eval) else e2_eval
+        # Do various menu tree post-processing
+        self._finalize_node(self.top_node, self.y)
 
-    #
-    # Dependency tracking (for caching and invalidation)
-    #
+        self.unique_defined_syms = _ordered_unique(self.defined_syms)
+        self.unique_choices = _ordered_unique(self.choices)
 
-    def _build_dep(self):
-        """Populates the Symbol.dep sets, linking the symbol to the symbols
-        that immediately depend on it in the sense that changing the value of
-        the symbol might affect the values of those other symbols. This is used
-        for caching/invalidation purposes. The calculated sets might be larger
-        than necessary as we don't do any complicated analysis of the
-        expressions."""
+        # Do sanity checks. Some of these depend on everything being finalized.
+        self._check_sym_sanity()
+        self._check_choice_sanity()
 
-        # Adds 'sym' as a directly dependent symbol to all symbols that appear
-        # in the expression 'e'
-        def add_expr_deps(e, sym):
-            for s in _get_expr_syms(e):
-                s.dep.add(sym)
+        # KCONFIG_STRICT is an older alias for KCONFIG_WARN_UNDEF, supported
+        # for backwards compatibility
+        if os.getenv("KCONFIG_WARN_UNDEF") == "y" or \
+           os.getenv("KCONFIG_STRICT") == "y":
 
-        # The directly dependent symbols of a symbol are:
-        #  - Any symbols whose prompts, default values, rev_dep (select
-        #    condition), weak_rev_dep (imply condition) or ranges depend on the
-        #    symbol
-        #  - Any symbols that belong to the same choice statement as the symbol
-        #    (these won't be included in 'dep' as that makes the dependency
-        #    graph unwieldy, but Symbol._get_dependent() will include them)
-        #  - Any symbols in a choice statement that depends on the symbol
-        for sym in self.syms_iter():
-            for _, e in sym.prompts:
-                add_expr_deps(e, sym)
+            self._check_undef_syms()
 
-            for v, e in sym.def_exprs:
-                add_expr_deps(v, sym)
-                add_expr_deps(e, sym)
+        # Build Symbol._dependents for all symbols and choices
+        self._build_dep()
 
-            add_expr_deps(sym.rev_dep, sym)
-            add_expr_deps(sym.weak_rev_dep, sym)
+        # Check for dependency loops
+        check_dep_loop_sym = _check_dep_loop_sym  # Micro-optimization
+        for sym in self.unique_defined_syms:
+            check_dep_loop_sym(sym, False)
 
-            for l, u, e in sym.ranges:
-                add_expr_deps(l, sym)
-                add_expr_deps(u, sym)
-                add_expr_deps(e, sym)
+        # Add extra dependencies from choices to choice symbols that get
+        # awkward during dependency loop detection
+        self._add_choice_deps()
 
-            if sym.is_choice_sym:
-                choice = sym.parent
-                for _, e in choice.prompts:
-                    add_expr_deps(e, sym)
-                for _, e in choice.def_exprs:
-                    add_expr_deps(e, sym)
+    @property
+    def mainmenu_text(self):
+        """
+        See the class documentation.
+        """
+        return self.top_node.prompt[0]
 
-    def _eq_to_sym(self, eq):
-        """_expr_depends_on() helper. For (in)equalities of the form sym = y/m
-        or sym != n, returns sym. For other (in)equalities, returns None."""
-        relation, left, right = eq
+    @property
+    def defconfig_filename(self):
+        """
+        See the class documentation.
+        """
+        if self.defconfig_list:
+            for filename, cond in self.defconfig_list.defaults:
+                if expr_value(cond):
+                    try:
+                        with self._open_config(filename.str_value) as f:
+                            return f.name
+                    except EnvironmentError:
+                        continue
 
-        def transform_y_m_n(item):
-            if item is self.y: return "y"
-            if item is self.m: return "m"
-            if item is self.n: return "n"
-            return item
+        return None
 
-        left = transform_y_m_n(left)
-        right = transform_y_m_n(right)
+    def load_config(self, filename=None, replace=True, verbose=None):
+        """
+        Loads symbol values from a file in the .config format. Equivalent to
+        calling Symbol.set_value() to set each of the values.
 
-        # Make sure the symbol (if any) appears to the left
-        if not isinstance(left, Symbol):
-            left, right = right, left
-        if not isinstance(left, Symbol):
-            return None
-        if (relation == EQUAL and (right == "y" or right == "m")) or \
-           (relation == UNEQUAL and right == "n"):
-            return left
-        return None
+        "# CONFIG_FOO is not set" within a .config file sets the user value of
+        FOO to n. The C tools work the same way.
 
-    def _expr_depends_on(self, expr, sym):
-        """Reimplementation of expr_depends_symbol() from mconf.c. Used to
-        determine if a submenu should be implicitly created, which influences
-        what items inside choice statements are considered choice items."""
-        if expr is None:
-            return False
+        For each symbol, the Symbol.user_value attribute holds the value the
+        symbol was assigned in the .config file (if any). The user value might
+        differ from Symbol.str/tri_value if there are unsatisfied dependencies.
 
-        def rec(expr):
-            if isinstance(expr, str):
-                return False
-            if isinstance(expr, Symbol):
-                return expr is sym
+        Calling this function also updates the Kconfig.missing_syms attribute
+        with a list of all assignments to undefined symbols within the
+        configuration file. Kconfig.missing_syms is cleared if 'replace' is
+        True, and appended to otherwise. See the documentation for
+        Kconfig.missing_syms as well.
 
-            if expr[0] in (EQUAL, UNEQUAL):
-                return self._eq_to_sym(expr) is sym
-            if expr[0] == AND:
-                for and_expr in expr[1]:
-                    if rec(and_expr):
-                        return True
-            return False
+        See the Kconfig.__init__() docstring for raised exceptions
+        (OSError/IOError). KconfigError is never raised here.
 
-        return rec(expr)
+        filename (default: None):
+          Path to load configuration from (a string). Respects $srctree if set
+          (see the class documentation).
 
-    def _invalidate_all(self):
-        for sym in self.syms_iter():
-            sym._invalidate()
+          If 'filename' is None (the default), the configuration file to load
+          (if any) is calculated automatically, giving the behavior you'd
+          usually want:
 
-    #
-    # Printing and misc.
-    #
+            1. If the KCONFIG_CONFIG environment variable is set, it gives the
+               path to the configuration file to load. Otherwise, ".config" is
+               used. See standard_config_filename().
 
-    def _expand_sym_refs(self, s):
-        """Expands $-references to symbols in 's' to symbol values, or to the
-        empty string for undefined symbols."""
+            2. If the path from (1.) doesn't exist, the configuration file
+               given by kconf.defconfig_filename is loaded instead, which is
+               derived from the 'option defconfig_list' symbol.
 
-        while 1:
-            sym_ref_match = _sym_ref_re_search(s)
-            if sym_ref_match is None:
-                return s
+            3. If (1.) and (2.) fail to find a configuration file to load, no
+               configuration file is loaded, and symbols retain their current
+               values (e.g., their default values). This is not an error.
 
-            sym_name = sym_ref_match.group(0)[1:]
-            sym = self.syms.get(sym_name)
-            expansion = "" if sym is None else sym.get_value()
+           See the return value as well.
 
-            s = s[:sym_ref_match.start()] + \
-                expansion + \
-                s[sym_ref_match.end():]
+        replace (default: True):
+          If True, all existing user values will be cleared before loading the
+          .config. Pass False to merge configurations.
 
-    def _expr_val_str(self, expr, no_value_str="(none)",
-                      get_val_instead_of_eval=False):
-        """Printing helper. Returns a string with 'expr' and its value.
+        verbose (default: None):
+          Limited backwards compatibility to prevent crashes. A warning is
+          printed if anything but None is passed.
 
-        no_value_str: String to return when 'expr' is missing (None).
+          Prior to Kconfiglib 12.0.0, this option enabled printing of messages
+          to stdout when 'filename' was None. A message is (always) returned
+          now instead, which is more flexible.
 
-        get_val_instead_of_eval: Assume 'expr' is a symbol or string (constant
-          symbol) and get its value directly instead of evaluating it to a
-          tristate value."""
+          Will probably be removed in some future version.
 
-        if expr is None:
-            return no_value_str
+        Returns a string with a message saying which file got loaded (or
+        possibly that no file got loaded, when 'filename' is None). This is
+        meant to reduce boilerplate in tools, which can do e.g.
+        print(kconf.load_config()). The returned message distinguishes between
+        loading (replace == True) and merging (replace == False).
+        """
+        if verbose is not None:
+            _warn_verbose_deprecated("load_config")
 
-        if get_val_instead_of_eval:
-            if isinstance(expr, str):
-                return _expr_to_str(expr)
-            val = expr.get_value()
-        else:
-            val = self._eval_expr(expr)
+        msg = None
+        if filename is None:
+            filename = standard_config_filename()
+            if not exists(filename) and \
+               not exists(join(self.srctree, filename)):
+                defconfig = self.defconfig_filename
+                if defconfig is None:
+                    return "Using default symbol values (no '{}')" \
+                           .format(filename)
 
-        return "{0} (value: {1})".format(_expr_to_str(expr), _expr_to_str(val))
+                msg = " default configuration '{}' (no '{}')" \
+                      .format(defconfig, filename)
+                filename = defconfig
 
-    def _get_sym_or_choice_str(self, sc):
-        """Symbols and choices have many properties in common, so we factor out
-        common __str__() stuff here. "sc" is short for "symbol or choice"."""
+        if not msg:
+            msg = " configuration '{}'".format(filename)
 
-        # As we deal a lot with string representations here, use some
-        # convenient shorthand:
-        s = _expr_to_str
+        # Disable the warning about assigning to symbols without prompts. This
+        # is normal and expected within a .config file.
+        self._warn_assign_no_prompt = False
 
-        #
-        # Common symbol/choice properties
-        #
+        # This stub only exists to make sure _warn_assign_no_prompt gets
+        # reenabled
+        try:
+            self._load_config(filename, replace)
+        except UnicodeDecodeError as e:
+            _decoding_error(e, filename)
+        finally:
+            self._warn_assign_no_prompt = True
 
-        user_val_str = "(no user value)" if sc.user_val is None else \
-                       s(sc.user_val)
+        return ("Loaded" if replace else "Merged") + msg
 
-        # Build prompts string
-        if not sc.prompts:
-            prompts_str = " (no prompts)"
-        else:
-            prompts_str_rows = []
-            for prompt, cond_expr in sc.orig_prompts:
-                prompts_str_rows.append(
-                    ' "{0}"'.format(prompt) if cond_expr is None else
-                    ' "{0}" if {1}'.format(prompt,
-                                           self._expr_val_str(cond_expr)))
-            prompts_str = "\n".join(prompts_str_rows)
+    def _load_config(self, filename, replace):
+        with self._open_config(filename) as f:
+            if replace:
+                self.missing_syms = []
 
-        # Build locations string
-        locations_str = "(no locations)" if not sc.def_locations else \
-                        " ".join(["{0}:{1}".format(filename, linenr) for
-                                  filename, linenr in sc.def_locations])
+                # If we're replacing the configuration, keep track of which
+                # symbols and choices got set so that we can unset the rest
+                # later. This avoids invalidating everything and is faster.
+                # Another benefit is that invalidation must be rock solid for
+                # it to work, making it a good test.
 
-        # Build additional-dependencies-from-menus-and-ifs string
-        additional_deps_str = " " + \
-          self._expr_val_str(sc.deps_from_containing,
-                             "(no additional dependencies)")
+                for sym in self.unique_defined_syms:
+                    sym._was_set = False
 
-        #
-        # Symbol-specific stuff
-        #
+                for choice in self.unique_choices:
+                    choice._was_set = False
 
-        if isinstance(sc, Symbol):
-            # Build ranges string
-            if isinstance(sc, Symbol):
-                if not sc.ranges:
-                    ranges_str = " (no ranges)"
-                else:
-                    ranges_str_rows = []
-                    for l, u, cond_expr in sc.ranges:
-                        ranges_str_rows.append(
-                            " [{0}, {1}]".format(s(l), s(u))
-                            if cond_expr is None else
-                            " [{0}, {1}] if {2}"
-                            .format(s(l), s(u), self._expr_val_str(cond_expr)))
-                    ranges_str = "\n".join(ranges_str_rows)
+            # Small optimizations
+            set_match = self._set_match
+            unset_match = self._unset_match
+            get_sym = self.syms.get
 
-            # Build default values string
-            if not sc.def_exprs:
-                defaults_str = " (no default values)"
-            else:
-                defaults_str_rows = []
-                for val_expr, cond_expr in sc.orig_def_exprs:
-                    row_str = " " + self._expr_val_str(val_expr, "(none)",
-                                                       sc.type == STRING)
-                    defaults_str_rows.append(row_str)
-                    defaults_str_rows.append("  Condition: " +
-                                               self._expr_val_str(cond_expr))
-                defaults_str = "\n".join(defaults_str_rows)
+            for linenr, line in enumerate(f, 1):
+                # The C tools ignore trailing whitespace
+                line = line.rstrip()
 
-            # Build selects string
-            if not sc.orig_selects:
-                selects_str = " (no selects)"
-            else:
-                selects_str_rows = []
-                for target, cond_expr in sc.orig_selects:
-                    selects_str_rows.append(
-                        " {0}".format(target.name) if cond_expr is None else
-                        " {0} if {1}".format(target.name,
-                                             self._expr_val_str(cond_expr)))
-                selects_str = "\n".join(selects_str_rows)
+                match = set_match(line)
+                if match:
+                    name, val = match.groups()
+                    sym = get_sym(name)
+                    if not sym or not sym.nodes:
+                        self._undef_assign(name, val, filename, linenr)
+                        continue
 
-            # Build implies string
-            if not sc.orig_implies:
-                implies_str = " (no implies)"
-            else:
-                implies_str_rows = []
-                for target, cond_expr in sc.orig_implies:
-                    implies_str_rows.append(
-                        " {0}".format(target.name) if cond_expr is None else
-                        " {0} if {1}".format(target.name,
-                                             self._expr_val_str(cond_expr)))
-                implies_str = "\n".join(implies_str_rows)
+                    if sym.orig_type in _BOOL_TRISTATE:
+                        # The C implementation only checks the first character
+                        # to the right of '=', for whatever reason
+                        if not (sym.orig_type is BOOL
+                                and val.startswith(("y", "n")) or
+                                sym.orig_type is TRISTATE
+                                and val.startswith(("y", "m", "n"))):
+                            self._warn("'{}' is not a valid value for the {} "
+                                       "symbol {}. Assignment ignored."
+                                       .format(val, TYPE_TO_STR[sym.orig_type],
+                                               _name_and_loc(sym)),
+                                       filename, linenr)
+                            continue
 
-            res = _lines("Symbol " +
-                           ("(no name)" if sc.name is None else sc.name),
-                         "Type           : " + TYPENAME[sc.type],
-                         "Value          : " + s(sc.get_value()),
-                         "User value     : " + user_val_str,
-                         "Visibility     : " + s(_get_visibility(sc)),
-                         "Is choice item : " + BOOL_STR[sc.is_choice_sym],
-                         "Is defined     : " + BOOL_STR[sc.is_defined_],
-                         "Is from env.   : " + BOOL_STR[sc.is_from_env],
-                         "Is special     : " + BOOL_STR[sc.is_special_] + "\n")
-            if sc.ranges:
-                res += _lines("Ranges:", ranges_str + "\n")
-            res += _lines("Prompts:",
-                          prompts_str,
-                          "Default values:",
-                          defaults_str,
-                          "Selects:",
-                          selects_str,
-                          "Implies:",
-                          implies_str,
-                          "Reverse (select-related) dependencies:",
-                          " (no reverse dependencies)"
-                          if sc.rev_dep == "n"
-                          else " " + self._expr_val_str(sc.rev_dep),
-                          "Weak reverse (imply-related) dependencies:",
-                          " (no weak reverse dependencies)"
-                          if sc.weak_rev_dep == "n"
-                          else " " + self._expr_val_str(sc.weak_rev_dep),
-                          "Additional dependencies from enclosing menus "
-                            "and ifs:",
-                          additional_deps_str,
-                          "Locations: " + locations_str)
+                        val = val[0]
 
-            return res
+                        if sym.choice and val != "n":
+                            # During .config loading, we infer the mode of the
+                            # choice from the kind of values that are assigned
+                            # to the choice symbols
 
-        #
-        # Choice-specific stuff
-        #
+                            prev_mode = sym.choice.user_value
+                            if prev_mode is not None and \
+                               TRI_TO_STR[prev_mode] != val:
 
-        # Build selected symbol string
-        sel = sc.get_selection()
-        sel_str = "(no selection)" if sel is None else sel.name
+                                self._warn("both m and y assigned to symbols "
+                                           "within the same choice",
+                                           filename, linenr)
 
-        # Build default values string
-        if not sc.def_exprs:
-            defaults_str = " (no default values)"
-        else:
-            defaults_str_rows = []
-            for sym, cond_expr in sc.orig_def_exprs:
-                defaults_str_rows.append(
-                    " {0}".format(sym.name) if cond_expr is None else
-                    " {0} if {1}".format(sym.name,
-                                         self._expr_val_str(cond_expr)))
-            defaults_str = "\n".join(defaults_str_rows)
+                            # Set the choice's mode
+                            sym.choice.set_value(val)
 
-        # Build contained symbols string
-        names = [sym.name for sym in sc.actual_symbols]
-        syms_string = " ".join(names) if names else "(empty)"
+                    elif sym.orig_type is STRING:
+                        match = _conf_string_match(val)
+                        if not match:
+                            self._warn("malformed string literal in "
+                                       "assignment to {}. Assignment ignored."
+                                       .format(_name_and_loc(sym)),
+                                       filename, linenr)
+                            continue
 
-        return _lines("Choice",
-                      "Name (for named choices): " +
-                        ("(no name)" if sc.name is None else sc.name),
-                      "Type            : " + TYPENAME[sc.type],
-                      "Selected symbol : " + sel_str,
-                      "User value      : " + user_val_str,
-                      "Mode            : " + s(sc.get_mode()),
-                      "Visibility      : " + s(_get_visibility(sc)),
-                      "Optional        : " + BOOL_STR[sc.optional],
-                      "Prompts:",
-                      prompts_str,
-                      "Defaults:",
-                      defaults_str,
-                      "Choice symbols:",
-                      " " + syms_string,
-                      "Additional dependencies from enclosing menus and "
-                        "ifs:",
-                      additional_deps_str,
-                      "Locations: " + locations_str)
+                        val = unescape(match.group(1))
 
-    def _warn(self, msg, filename=None, linenr=None):
-        """For printing warnings to stderr."""
-        msg = _build_msg("warning: " + msg, filename, linenr)
-        if self.print_warnings:
-            sys.stderr.write(msg + "\n")
-        self._warnings.append(msg)
+                else:
+                    match = unset_match(line)
+                    if not match:
+                        # Print a warning for lines that match neither
+                        # set_match() nor unset_match() and that are not blank
+                        # lines or comments. 'line' has already been
+                        # rstrip()'d, so blank lines show up as "" here.
+                        if line and not line.lstrip().startswith("#"):
+                            self._warn("ignoring malformed line '{}'"
+                                       .format(line),
+                                       filename, linenr)
 
-class Item(object):
+                        continue
 
-    """Base class for symbols and other Kconfig constructs. Subclasses are
-    Symbol, Choice, Menu, and Comment."""
+                    name = match.group(1)
+                    sym = get_sym(name)
+                    if not sym or not sym.nodes:
+                        self._undef_assign(name, "n", filename, linenr)
+                        continue
 
-    def is_symbol(self):
-        """Returns True if the item is a symbol. Short for
-        isinstance(item, kconfiglib.Symbol)."""
-        return isinstance(self, Symbol)
+                    if sym.orig_type not in _BOOL_TRISTATE:
+                        continue
 
-    def is_choice(self):
-        """Returns True if the item is a choice. Short for
-        isinstance(item, kconfiglib.Choice)."""
-        return isinstance(self, Choice)
+                    val = "n"
 
-    def is_menu(self):
-        """Returns True if the item is a menu. Short for
-        isinstance(item, kconfiglib.Menu)."""
-        return isinstance(self, Menu)
+                # Done parsing the assignment. Set the value.
 
-    def is_comment(self):
-        """Returns True if the item is a comment. Short for
-        isinstance(item, kconfiglib.Comment)."""
-        return isinstance(self, Comment)
+                if sym._was_set:
+                    self._assigned_twice(sym, val, filename, linenr)
 
-class Symbol(Item):
+                sym.set_value(val)
 
-    """Represents a configuration symbol - e.g. FOO for
+        if replace:
+            # If we're replacing the configuration, unset the symbols that
+            # didn't get set
 
-    config FOO
-        ..."""
+            for sym in self.unique_defined_syms:
+                if not sym._was_set:
+                    sym.unset_value()
 
-    #
-    # Public interface
-    #
+            for choice in self.unique_choices:
+                if not choice._was_set:
+                    choice.unset_value()
 
-    def get_config(self):
-        """Returns the Config instance this symbol is from."""
-        return self.config
+    def _undef_assign(self, name, val, filename, linenr):
+        # Called for assignments to undefined symbols during .config loading
 
-    def get_name(self):
-        """Returns the name of the symbol."""
-        return self.name
+        self.missing_syms.append((name, val))
+        if self.warn_assign_undef:
+            self._warn(
+                "attempt to assign the value '{}' to the undefined symbol {}"
+                .format(val, name), filename, linenr)
 
-    def get_type(self):
-        """Returns the type of the symbol: one of UNKNOWN, BOOL, TRISTATE,
-        STRING, HEX, or INT. These are defined at the top level of the module,
-        so you'd do something like
+    def _assigned_twice(self, sym, new_val, filename, linenr):
+        # Called when a symbol is assigned more than once in a .config file
 
-        if sym.get_type() == kconfiglib.STRING:
-            ..."""
-        return self.type
+        # Use strings for bool/tristate user values in the warning
+        if sym.orig_type in _BOOL_TRISTATE:
+            user_val = TRI_TO_STR[sym.user_value]
+        else:
+            user_val = sym.user_value
 
-    def get_prompts(self):
-        """Returns a list of prompts defined for the symbol, in the order they
-        appear in the configuration files. Returns the empty list for symbols
-        with no prompt.
+        msg = '{} set more than once. Old value "{}", new value "{}".'.format(
+            _name_and_loc(sym), user_val, new_val)
 
-        This list will have a single entry for the vast majority of symbols
-        having prompts, but having multiple prompts for a single symbol is
-        possible through having multiple 'config' entries for it."""
-        return [prompt for prompt, _ in self.orig_prompts]
+        if user_val == new_val:
+            if self.warn_assign_redun:
+                self._warn(msg, filename, linenr)
+        elif self.warn_assign_override:
+            self._warn(msg, filename, linenr)
 
-    def get_help(self):
-        """Returns the help text of the symbol, or None if the symbol has no
-        help text."""
-        return self.help
+    def write_autoconf(self, filename,
+                       header="/* Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib) */\n"):
+        r"""
+        Writes out symbol values as a C header file, matching the format used
+        by include/generated/autoconf.h in the kernel.
 
-    def get_parent(self):
-        """Returns the menu or choice statement that contains the symbol, or
-        None if the symbol is at the top level. Note that if statements are
-        treated as syntactic and do not have an explicit class
-        representation."""
-        return self.parent
+        The ordering of the #defines matches the one generated by
+        write_config(). The order in the C implementation depends on the hash
+        table implementation as of writing, and so won't match.
 
-    def get_def_locations(self):
-        """Returns a list of (filename, linenr) tuples, where filename (string)
-        and linenr (int) represent a location where the symbol is defined. For
-        the vast majority of symbols this list will only contain one element.
-        For the following Kconfig, FOO would get two entries: the lines marked
-        with *.
+        If 'filename' exists and its contents is identical to what would get
+        written out, it is left untouched. This avoids updating file metadata
+        like the modification time and possibly triggering redundant work in
+        build tools.
 
-        config FOO *
-            bool "foo prompt 1"
+        filename:
+          Self-explanatory.
 
-        config FOO *
-            bool "foo prompt 2"
+        header (default: "/* Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib) */\n"):
+          Text that will be inserted verbatim at the beginning of the file. You
+          would usually want it enclosed in '/* */' to make it a C comment,
+          and include a final terminating newline.
         """
-        return self.def_locations
-
-    def get_ref_locations(self):
-        """Returns a list of (filename, linenr) tuples, where filename (string)
-        and linenr (int) represent a location where the symbol is referenced in
-        the configuration. For example, the lines marked by * would be included
-        for FOO below:
+        self._write_if_changed(filename, self._autoconf_contents(header))
 
-        config A
-            bool
-            default BAR || FOO *
+    def _autoconf_contents(self, header):
+        # write_autoconf() helper. Returns the contents to write as a string,
+        # with 'header' at the beginning.
 
-        config B
-            tristate
-            depends on FOO *
-            default m if FOO *
+        # "".join()ed later
+        chunks = [header]
+        add = chunks.append
 
-        if FOO *
-            config A
-                bool "A"
-        endif
+        for sym in self.unique_defined_syms:
+            # _write_to_conf is determined when the value is calculated. This
+            # is a hidden function call due to property magic.
+            #
+            # Note: In client code, you can check if sym.config_string is empty
+            # instead, to avoid accessing the internal _write_to_conf variable
+            # (though it's likely to keep working).
+            val = sym.str_value
+            if not sym._write_to_conf:
+                continue
 
-        config FOO (definition not included)
-            bool
-        """
-        return self.ref_locations
+            if sym.orig_type in _BOOL_TRISTATE:
+                if val == "y":
+                    add("#define {}{} 1\n"
+                        .format(self.config_prefix, sym.name))
+                elif val == "m":
+                    add("#define {}{}_MODULE 1\n"
+                        .format(self.config_prefix, sym.name))
 
-    def get_value(self):
-        """Calculate and return the value of the symbol. See also
-        Symbol.set_user_value()."""
+            elif sym.orig_type is STRING:
+                add('#define {}{} "{}"\n'
+                    .format(self.config_prefix, sym.name, escape(val)))
 
-        if self.cached_val is not None:
-            return self.cached_val
+            else:  # sym.orig_type in _INT_HEX:
+                if sym.orig_type is HEX and \
+                   not val.startswith(("0x", "0X")):
+                    val = "0x" + val
 
-        # As a quirk of Kconfig, undefined symbols get their name as their
-        # value. This is why things like "FOO = bar" work for seeing if FOO has
-        # the value "bar".
-        if self.type == UNKNOWN:
-            self.cached_val = self.name
-            return self.name
+                add("#define {}{} {}\n"
+                    .format(self.config_prefix, sym.name, val))
 
-        new_val = DEFAULT_VALUE[self.type]
-        vis = _get_visibility(self)
+        return "".join(chunks)
 
-        # This is easiest to calculate together with the value
-        self.write_to_conf = False
+    def write_config(self, filename=None,
+                     header="# Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib)\n",
+                     save_old=True, verbose=None):
+        r"""
+        Writes out symbol values in the .config format. The format matches the
+        C implementation, including ordering.
 
-        if self.type == BOOL or self.type == TRISTATE:
-            # The visibility and mode (modules-only or single-selection) of
-            # choice items will be taken into account in _get_visibility()
-            if self.is_choice_sym:
-                if vis != "n":
-                    choice = self.parent
-                    mode = choice.get_mode()
+        Symbols appear in the same order in generated .config files as they do
+        in the Kconfig files. For symbols defined in multiple locations, a
+        single assignment is written out corresponding to the first location
+        where the symbol is defined.
 
-                    self.write_to_conf = (mode != "n")
+        See the 'Intro to symbol values' section in the module docstring to
+        understand which symbols get written out.
 
-                    if mode == "y":
-                        new_val = "y" if choice.get_selection() is self \
-                                  else "n"
-                    elif mode == "m":
-                        if self.user_val == "m" or self.user_val == "y":
-                            new_val = "m"
+        If 'filename' exists and its contents is identical to what would get
+        written out, it is left untouched. This avoids updating file metadata
+        like the modification time and possibly triggering redundant work in
+        build tools.
 
-            else:
-                # If the symbol is visible and has a user value, use that.
-                # Otherwise, look at defaults and weak reverse dependencies
-                # (implies).
-                use_defaults_and_weak_rev_deps = True
+        See the Kconfig.__init__() docstring for raised exceptions
+        (OSError/IOError). KconfigError is never raised here.
 
-                if vis != "n":
-                    self.write_to_conf = True
-                    if self.user_val is not None:
-                        new_val = self.config._eval_min(self.user_val, vis)
-                        use_defaults_and_weak_rev_deps = False
+        filename (default: None):
+          Filename to save configuration to (a string).
 
-                if use_defaults_and_weak_rev_deps:
-                    for val_expr, cond_expr in self.def_exprs:
-                        cond_eval = self.config._eval_expr(cond_expr)
-                        if cond_eval != "n":
-                            self.write_to_conf = True
-                            new_val = self.config._eval_min(val_expr,
-                                                            cond_eval)
-                            break
+          If None (the default), the filename in the environment variable
+          KCONFIG_CONFIG is used if set, and ".config" otherwise. See
+          standard_config_filename().
 
-                    weak_rev_dep_val = \
-                        self.config._eval_expr(self.weak_rev_dep)
-                    if weak_rev_dep_val != "n":
-                        self.write_to_conf = True
-                        new_val = self.config._eval_max(new_val,
-                                                        weak_rev_dep_val)
+        header (default: "# Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib)\n"):
+          Text that will be inserted verbatim at the beginning of the file. You
+          would usually want each line to start with '#' to make it a comment,
+          and include a final terminating newline.
 
-                # Reverse (select-related) dependencies take precedence
-                rev_dep_val = self.config._eval_expr(self.rev_dep)
-                if rev_dep_val != "n":
-                    self.write_to_conf = True
-                    new_val = self.config._eval_max(new_val, rev_dep_val)
+        save_old (default: True):
+          If True and <filename> already exists, a copy of it will be saved to
+          <filename>.old in the same directory before the new configuration is
+          written.
 
-            # We need to promote "m" to "y" in two circumstances:
-            #  1) If our type is boolean
-            #  2) If our weak_rev_dep (from IMPLY) is "y"
-            if new_val == "m" and \
-               (self.type == BOOL or
-                self.config._eval_expr(self.weak_rev_dep) == "y"):
-                new_val = "y"
+          Errors are silently ignored if <filename>.old cannot be written (e.g.
+          due to being a directory, or <filename> being something like
+          /dev/null).
 
-        elif self.type == INT or self.type == HEX:
-            has_active_range = False
-            low = None
-            high = None
-            use_defaults = True
+        verbose (default: None):
+          Limited backwards compatibility to prevent crashes. A warning is
+          printed if anything but None is passed.
 
-            base = 16 if self.type == HEX else 10
+          Prior to Kconfiglib 12.0.0, this option enabled printing of messages
+          to stdout when 'filename' was None. A message is (always) returned
+          now instead, which is more flexible.
 
-            for l, h, cond_expr in self.ranges:
-                if self.config._eval_expr(cond_expr) != "n":
-                    has_active_range = True
+          Will probably be removed in some future version.
 
-                    low_str = _str_val(l)
-                    high_str = _str_val(h)
-                    low = int(low_str, base) if \
-                      _is_base_n(low_str, base) else 0
-                    high = int(high_str, base) if \
-                      _is_base_n(high_str, base) else 0
+        Returns a string with a message saying which file got saved. This is
+        meant to reduce boilerplate in tools, which can do e.g.
+        print(kconf.write_config()).
+        """
+        if verbose is not None:
+            _warn_verbose_deprecated("write_config")
 
-                    break
+        if filename is None:
+            filename = standard_config_filename()
 
-            if vis != "n":
-                self.write_to_conf = True
+        contents = self._config_contents(header)
+        if self._contents_eq(filename, contents):
+            return "No change to '{}'".format(filename)
 
-                if self.user_val is not None and \
-                   _is_base_n(self.user_val, base) and \
-                   (not has_active_range or
-                    low <= int(self.user_val, base) <= high):
+        if save_old:
+            _save_old(filename)
 
-                    # If the user value is OK, it is stored in exactly the same
-                    # form as specified in the assignment (with or without
-                    # "0x", etc).
+        with self._open(filename, "w") as f:
+            f.write(contents)
 
-                    use_defaults = False
-                    new_val = self.user_val
+        return "Configuration saved to '{}'".format(filename)
 
-            if use_defaults:
-                for val_expr, cond_expr in self.def_exprs:
-                    if self.config._eval_expr(cond_expr) != "n":
-                        self.write_to_conf = True
+    def _config_contents(self, header):
+        # write_config() helper. Returns the contents to write as a string,
+        # with 'header' at the beginning.
+        #
+        # More memory friendly would be to 'yield' the strings and
+        # "".join(_config_contents()), but it was a bit slower on my system.
 
-                        # If the default value is OK, it is stored in exactly
-                        # the same form as specified. Otherwise, it is clamped
-                        # to the range, and the output has "0x" as appropriate
-                        # for the type.
+        # node_iter() was used here before commit 3aea9f7 ("Add '# end of
+        # <menu>' after menus in .config"). Those comments get tricky to
+        # implement with it.
 
-                        new_val = _str_val(val_expr)
+        for sym in self.unique_defined_syms:
+            sym._visited = False
 
-                        if _is_base_n(new_val, base):
-                            new_val_num = int(new_val, base)
-                            if has_active_range:
-                                clamped_val = None
+        # Did we just print an '# end of ...' comment?
+        after_end_comment = False
 
-                                if new_val_num < low:
-                                    clamped_val = low
-                                elif new_val_num > high:
-                                    clamped_val = high
+        # "".join()ed later
+        chunks = [header]
+        add = chunks.append
 
-                                if clamped_val is not None:
-                                    new_val = (hex(clamped_val) if \
-                                      self.type == HEX else str(clamped_val))
+        node = self.top_node
+        while 1:
+            # Jump to the next node with an iterative tree walk
+            if node.list:
+                node = node.list
+            elif node.next:
+                node = node.next
+            else:
+                while node.parent:
+                    node = node.parent
 
-                            break
-                else: # For the for loop
-                    # If no user value or default kicks in but the hex/int has
-                    # an active range, then the low end of the range is used,
-                    # provided it's > 0, with "0x" prepended as appropriate.
-                    if has_active_range and low > 0:
-                        new_val = (hex(low) if self.type == HEX else str(low))
+                    # Add a comment when leaving visible menus
+                    if node.item is MENU and expr_value(node.dep) and \
+                       expr_value(node.visibility) and \
+                       node is not self.top_node:
+                        add("# end of {}\n".format(node.prompt[0]))
+                        after_end_comment = True
 
-        elif self.type == STRING:
-            use_defaults = True
+                    if node.next:
+                        node = node.next
+                        break
+                else:
+                    # No more nodes
+                    return "".join(chunks)
 
-            if vis != "n":
-                self.write_to_conf = True
-                if self.user_val is not None:
-                    new_val = self.user_val
-                    use_defaults = False
+            # Generate configuration output for the node
 
-            if use_defaults:
-                for val_expr, cond_expr in self.def_exprs:
-                    if self.config._eval_expr(cond_expr) != "n":
-                        self.write_to_conf = True
-                        new_val = _str_val(val_expr)
-                        break
+            item = node.item
 
-        self.cached_val = new_val
-        return new_val
+            if item.__class__ is Symbol:
+                if item._visited:
+                    continue
+                item._visited = True
 
-    def get_user_value(self):
-        """Returns the value assigned to the symbol in a .config or via
-        Symbol.set_user_value() (provided the value was valid for the type of
-        the symbol). Returns None in case of no user value."""
-        return self.user_val
+                conf_string = item.config_string
+                if not conf_string:
+                    continue
 
-    def get_upper_bound(self):
-        """For string/hex/int symbols and for bool and tristate symbols that
-        cannot be modified (see is_modifiable()), returns None.
+                if after_end_comment:
+                    # Add a blank line before the first symbol printed after an
+                    # '# end of ...' comment
+                    after_end_comment = False
+                    add("\n")
+                add(conf_string)
 
-        Otherwise, returns the highest value the symbol can be set to with
-        Symbol.set_user_value() (that will not be truncated): one of "m" or
-        "y", arranged from lowest to highest. This corresponds to the highest
-        value the symbol could be given in e.g. the 'make menuconfig'
-        interface.
+            elif expr_value(node.dep) and \
+                 ((item is MENU and expr_value(node.visibility)) or
+                  item is COMMENT):
 
-        See also the tri_less*() and tri_greater*() functions, which could come
-        in handy."""
-        if self.type != BOOL and self.type != TRISTATE:
-            return None
-        rev_dep = self.config._eval_expr(self.rev_dep)
-        # A bool selected to "m" gets promoted to "y", pinning it
-        if rev_dep == "m" and self.type == BOOL:
-            return None
-        vis = _get_visibility(self)
-        if TRI_TO_INT[vis] > TRI_TO_INT[rev_dep]:
-            return vis
-        return None
+                add("\n#\n# {}\n#\n".format(node.prompt[0]))
+                after_end_comment = False
 
-    def get_lower_bound(self):
-        """For string/hex/int symbols and for bool and tristate symbols that
-        cannot be modified (see is_modifiable()), returns None.
+    def write_min_config(self, filename,
+                         header="# Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib)\n"):
+        """
+        Writes out a "minimal" configuration file, omitting symbols whose value
+        matches their default value. The format matches the one produced by
+        'make savedefconfig'.
 
-        Otherwise, returns the lowest value the symbol can be set to with
-        Symbol.set_user_value() (that will not be truncated): one of "n" or
-        "m", arranged from lowest to highest. This corresponds to the lowest
-        value the symbol could be given in e.g. the 'make menuconfig'
-        interface.
+        The resulting configuration file is incomplete, but a complete
+        configuration can be derived from it by loading it. Minimal
+        configuration files can serve as a more manageable configuration format
+        compared to a "full" .config file, especially when configurations files
+        are merged or edited by hand.
 
-        See also the tri_less*() and tri_greater*() functions, which could come
-        in handy."""
-        if self.type != BOOL and self.type != TRISTATE:
-            return None
-        rev_dep = self.config._eval_expr(self.rev_dep)
-        # A bool selected to "m" gets promoted to "y", pinning it
-        if rev_dep == "m" and self.type == BOOL:
-            return None
-        if TRI_TO_INT[_get_visibility(self)] > TRI_TO_INT[rev_dep]:
-            return rev_dep
-        return None
+        See the Kconfig.__init__() docstring for raised exceptions
+        (OSError/IOError). KconfigError is never raised here.
 
-    def get_assignable_values(self):
-        """For string/hex/int symbols and for bool and tristate symbols that
-        cannot be modified (see is_modifiable()), returns the empty list.
+        filename:
+          Self-explanatory.
 
-        Otherwise, returns a list containing the user values that can be
-        assigned to the symbol (that won't be truncated). Usage example:
+        header (default: "# Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib)\n"):
+          Text that will be inserted verbatim at the beginning of the file. You
+          would usually want each line to start with '#' to make it a comment,
+          and include a final terminating newline.
 
-        if "m" in sym.get_assignable_values():
-            sym.set_user_value("m")
+        Returns a string with a message saying which file got saved. This is
+        meant to reduce boilerplate in tools, which can do e.g.
+        print(kconf.write_min_config()).
+        """
+        contents = self._min_config_contents(header)
+        if self._contents_eq(filename, contents):
+            return "No change to '{}'".format(filename)
 
-        This is basically a more convenient interface to
-        get_lower/upper_bound() when wanting to test if a particular tristate
-        value can be assigned."""
-        if self.type != BOOL and self.type != TRISTATE:
-            return []
-        rev_dep = self.config._eval_expr(self.rev_dep)
-        # A bool selected to "m" gets promoted to "y", pinning it
-        if rev_dep == "m" and self.type == BOOL:
-            return []
-        res = ["n", "m", "y"][TRI_TO_INT[rev_dep] :
-                              TRI_TO_INT[_get_visibility(self)] + 1]
-        return res if len(res) > 1 else []
+        with self._open(filename, "w") as f:
+            f.write(contents)
 
-    def get_visibility(self):
-        """Returns the visibility of the symbol: one of "n", "m" or "y". For
-        bool and tristate symbols, this is an upper bound on the value users
-        can set for the symbol. For other types of symbols, a visibility of "n"
-        means the user value will be ignored. A visibility of "n" corresponds
-        to not being visible in the 'make *config' interfaces.
+        return "Minimal configuration saved to '{}'".format(filename)
 
-        Example (assuming we're running with modules enabled -- i.e., MODULES
-        set to 'y'):
+    def _min_config_contents(self, header):
+        # write_min_config() helper. Returns the contents to write as a string,
+        # with 'header' at the beginning.
 
-        # Assume this has been assigned 'n'
-        config N_SYM
-            tristate "N_SYM"
+        chunks = [header]
+        add = chunks.append
 
-        # Assume this has been assigned 'm'
-        config M_SYM
-            tristate "M_SYM"
+        for sym in self.unique_defined_syms:
+            # Skip symbols that cannot be changed. Only check
+            # non-choice symbols, as selects don't affect choice
+            # symbols.
+            if not sym.choice and \
+               sym.visibility <= expr_value(sym.rev_dep):
+                continue
 
-        # Has visibility 'n'
-        config A
-            tristate "A"
-            depends on N_SYM
+            # Skip symbols whose value matches their default
+            if sym.str_value == sym._str_default():
+                continue
 
-        # Has visibility 'm'
-        config B
-            tristate "B"
-            depends on M_SYM
+            # Skip symbols that would be selected by default in a
+            # choice, unless the choice is optional or the symbol type
+            # isn't bool (it might be possible to set the choice mode
+            # to n or the symbol to m in those cases).
+            if sym.choice and \
+               not sym.choice.is_optional and \
+               sym.choice._selection_from_defaults() is sym and \
+               sym.orig_type is BOOL and \
+               sym.tri_value == 2:
+                continue
 
-        # Has visibility 'y'
-        config C
-            tristate "C"
+            add(sym.config_string)
 
-        # Has no prompt, and hence visibility 'n'
-        config D
-            tristate
+        return "".join(chunks)
 
-        Having visibility be tri-valued ensures that e.g. a symbol cannot be
-        set to "y" by the user if it depends on a symbol with value "m", which
-        wouldn't be safe.
+    def sync_deps(self, path):
+        """
+        Creates or updates a directory structure that can be used to avoid
+        doing a full rebuild whenever the configuration is changed, mirroring
+        include/config/ in the kernel.
 
-        You should probably look at get_lower/upper_bound(),
-        get_assignable_values() and is_modifiable() before using this."""
-        return _get_visibility(self)
+        This function is intended to be called during each build, before
+        compiling source files that depend on configuration symbols.
 
-    def get_referenced_symbols(self, refs_from_enclosing=False):
-        """Returns the set() of all symbols referenced by this symbol. For
-        example, the symbol defined by
+        See the Kconfig.__init__() docstring for raised exceptions
+        (OSError/IOError). KconfigError is never raised here.
 
-        config FOO
-            bool
-            prompt "foo" if A && B
-            default C if D
-            depends on E
-            select F if G
+        path:
+          Path to directory
 
-        references the symbols A through G.
+        sync_deps(path) does the following:
 
-        refs_from_enclosing (default: False): If True, the symbols referenced
-           by enclosing menus and ifs will be included in the result."""
-        return self.all_referenced_syms if refs_from_enclosing else \
-               self.referenced_syms
+          1. If the directory <path> does not exist, it is created.
 
-    def get_selected_symbols(self):
-        """Returns the set() of all symbols X for which this symbol has a
-        'select X' or 'select X if Y' (regardless of whether Y is satisfied or
-        not). This is a subset of the symbols returned by
-        get_referenced_symbols()."""
-        return self.selected_syms
+          2. If <path>/auto.conf exists, old symbol values are loaded from it,
+             which are then compared against the current symbol values. If a
+             symbol has changed value (would generate different output in
+             autoconf.h compared to before), the change is signaled by
+             touch'ing a file corresponding to the symbol.
 
-    def get_implied_symbols(self):
-        """Returns the set() of all symbols X for which this symbol has an
-        'imply X' or 'imply X if Y' (regardless of whether Y is satisfied or
-        not). This is a subset of the symbols returned by
-        get_referenced_symbols()."""
-        return self.implied_syms
+             The first time sync_deps() is run on a directory, <path>/auto.conf
+             won't exist, and no old symbol values will be available. This
+             logically has the same effect as updating the entire
+             configuration.
 
-    def set_user_value(self, v):
-        """Sets the user value of the symbol.
+             The path to a symbol's file is calculated from the symbol's name
+             by replacing all '_' with '/' and appending '.h'. For example, the
+             symbol FOO_BAR_BAZ gets the file <path>/foo/bar/baz.h, and FOO
+             gets the file <path>/foo.h.
 
-        Equal in effect to assigning the value to the symbol within a .config
-        file. Use get_lower/upper_bound() or get_assignable_values() to find
-        the range of currently assignable values for bool and tristate symbols;
-        setting values outside this range will cause the user value to differ
-        from the result of Symbol.get_value() (be truncated). Values that are
-        invalid for the type (such as a_bool.set_user_value("foo")) are
-        ignored, and a warning is emitted if an attempt is made to assign such
-        a value.
+             This scheme matches the C tools. The point is to avoid having a
+             single directory with a huge number of files, which the underlying
+             filesystem might not handle well.
 
-        For any type of symbol, is_modifiable() can be used to check if a user
-        value will currently have any effect on the symbol, as determined by
-        its visibility and range of assignable values. Any value that is valid
-        for the type (bool, tristate, etc.) will end up being reflected in
-        get_user_value() though, and might have an effect later if conditions
-        change. To get rid of the user value, use unset_user_value().
+          3. A new auto.conf with the current symbol values is written, to keep
+             track of them for the next build.
 
-        Any symbols dependent on the symbol are (recursively) invalidated, so
-        things will just work with regards to dependencies.
+             If auto.conf exists and its contents is identical to what would
+             get written out, it is left untouched. This avoids updating file
+             metadata like the modification time and possibly triggering
+             redundant work in build tools.
 
-        v: The user value to give to the symbol."""
-        self._set_user_value_no_invalidate(v, False)
 
-        # There might be something more efficient you could do here, but play
-        # it safe.
-        if self.name == "MODULES":
-            self.config._invalidate_all()
-            return
+        The last piece of the puzzle is knowing what symbols each source file
+        depends on. Knowing that, dependencies can be added from source files
+        to the files corresponding to the symbols they depends on. The source
+        file will then get recompiled (only) when the symbol value changes
+        (provided sync_deps() is run first during each build).
 
-        self._invalidate()
-        self._invalidate_dependent()
+        The tool in the kernel that extracts symbol dependencies from source
+        files is scripts/basic/fixdep.c. Missing symbol files also correspond
+        to "not changed", which fixdep deals with by using the $(wildcard) Make
+        function when adding symbol prerequisites to source files.
 
-    def unset_user_value(self):
-        """Resets the user value of the symbol, as if the symbol had never
-        gotten a user value via Config.load_config() or
-        Symbol.set_user_value()."""
-        self._unset_user_value_no_recursive_invalidate()
-        self._invalidate_dependent()
+        In case you need a different scheme for your project, the sync_deps()
+        implementation can be used as a template.
+        """
+        if not exists(path):
+            os.mkdir(path, 0o755)
 
-    def is_modifiable(self):
-        """Returns True if the value of the symbol could be modified by calling
-        Symbol.set_user_value().
+        # Load old values from auto.conf, if any
+        self._load_old_vals(path)
 
-        For bools and tristates, this corresponds to the symbol being visible
-        in the 'make menuconfig' interface and not already being pinned to a
-        specific value (e.g. because it is selected by another symbol).
+        for sym in self.unique_defined_syms:
+            # _write_to_conf is determined when the value is calculated. This
+            # is a hidden function call due to property magic.
+            #
+            # Note: In client code, you can check if sym.config_string is empty
+            # instead, to avoid accessing the internal _write_to_conf variable
+            # (though it's likely to keep working).
+            val = sym.str_value
 
-        For strings and numbers, this corresponds to just being visible. (See
-        Symbol.get_visibility().)"""
-        if self.is_special_:
-            return False
-        if self.type == BOOL or self.type == TRISTATE:
-            rev_dep = self.config._eval_expr(self.rev_dep)
-            # A bool selected to "m" gets promoted to "y", pinning it
-            if rev_dep == "m" and self.type == BOOL:
-                return False
-            return TRI_TO_INT[_get_visibility(self)] > TRI_TO_INT[rev_dep]
-        return _get_visibility(self) != "n"
+            # n tristate values do not get written to auto.conf and autoconf.h,
+            # making a missing symbol logically equivalent to n
 
-    def is_defined(self):
-        """Returns False if the symbol is referred to in the Kconfig but never
-        actually defined."""
-        return self.is_defined_
+            if sym._write_to_conf:
+                if sym._old_val is None and \
+                   sym.orig_type in _BOOL_TRISTATE and \
+                   val == "n":
+                    # No old value (the symbol was missing or n), new value n.
+                    # No change.
+                    continue
 
-    def is_special(self):
-        """Returns True if the symbol is one of the special symbols n, m, y, or
-        UNAME_RELEASE, or gets its value from the environment."""
-        return self.is_special_
+                if val == sym._old_val:
+                    # New value matches old. No change.
+                    continue
 
-    def is_from_environment(self):
-        """Returns True if the symbol gets its value from the environment."""
-        return self.is_from_env
+            elif sym._old_val is None:
+                # The symbol wouldn't appear in autoconf.h (because
+                # _write_to_conf is false), and it wouldn't have appeared in
+                # autoconf.h previously either (because it didn't appear in
+                # auto.conf). No change.
+                continue
 
-    def has_ranges(self):
-        """Returns True if the symbol is of type INT or HEX and has ranges that
-        limit what values it can take on."""
-        return bool(self.ranges)
+            # 'sym' has a new value. Flag it.
+            _touch_dep_file(path, sym.name)
 
-    def is_choice_symbol(self):
-        """Returns True if the symbol is in a choice statement and is an actual
-        choice symbol (see Choice.get_symbols())."""
-        return self.is_choice_sym
+        # Remember the current values as the "new old" values.
+        #
+        # This call could go anywhere after the call to _load_old_vals(), but
+        # putting it last means _sync_deps() can be safely rerun if it fails
+        # before this point.
+        self._write_old_vals(path)
 
-    def is_choice_selection(self):
-        """Returns True if the symbol is contained in a choice statement and is
-        the selected item. Equivalent to
+    def _load_old_vals(self, path):
+        # Loads old symbol values from auto.conf into a dedicated
+        # Symbol._old_val field. Mirrors load_config().
+        #
+        # The extra field could be avoided with some trickery involving dumping
+        # symbol values and restoring them later, but this is simpler and
+        # faster. The C tools also use a dedicated field for this purpose.
 
-        sym.is_choice_symbol() and sym.get_parent().get_selection() is sym"""
-        return self.is_choice_sym and self.parent.get_selection() is self
+        for sym in self.unique_defined_syms:
+            sym._old_val = None
 
-    def is_allnoconfig_y(self):
-        """Returns True if the symbol has the 'allnoconfig_y' option set."""
-        return self.allnoconfig_y
+        try:
+            auto_conf = self._open(join(path, "auto.conf"), "r")
+        except EnvironmentError as e:
+            if e.errno == errno.ENOENT:
+                # No old values
+                return
+            raise
 
-    def __str__(self):
-        """Returns a string containing various information about the symbol."""
-        return self.config._get_sym_or_choice_str(self)
+        with auto_conf as f:
+            for line in f:
+                match = self._set_match(line)
+                if not match:
+                    # We only expect CONFIG_FOO=... (and possibly a header
+                    # comment) in auto.conf
+                    continue
 
-    #
-    # Private methods
-    #
+                name, val = match.groups()
+                if name in self.syms:
+                    sym = self.syms[name]
 
-    def __init__(self):
-        """Symbol constructor -- not intended to be called directly by
-        Kconfiglib clients."""
+                    if sym.orig_type is STRING:
+                        match = _conf_string_match(val)
+                        if not match:
+                            continue
+                        val = unescape(match.group(1))
 
-        self.name = None
-        self.type = UNKNOWN
-        self.prompts = []
-        self.def_exprs = [] # 'default' properties
-        self.ranges = [] # 'range' properties (for int and hex)
-        self.help = None # Help text
-        self.rev_dep = "n" # Reverse (select-related) dependencies
-        self.weak_rev_dep = "n" # Weak reverse (imply-related) dependencies
-        self.config = None
-        self.parent = None
+                    self.syms[name]._old_val = val
+                else:
+                    # Flag that the symbol no longer exists, in
+                    # case something still depends on it
+                    _touch_dep_file(path, name)
 
-        self.user_val = None # Value set by user
+    def _write_old_vals(self, path):
+        # Helper for writing auto.conf. Basically just a simplified
+        # write_config() that doesn't write any comments (including
+        # '# CONFIG_FOO is not set' comments). The format matches the C
+        # implementation, though the ordering is arbitrary there (depends on
+        # the hash table implementation).
+        #
+        # A separate helper function is neater than complicating write_config()
+        # by passing a flag to it, plus we only need to look at symbols here.
 
-        # The prompt, default value, select, and imply conditions without any
-        # dependencies from menus and ifs propagated to them
-        self.orig_prompts = []
-        self.orig_def_exprs = []
-        self.orig_selects = []
-        self.orig_implies = []
+        self._write_if_changed(
+            os.path.join(path, "auto.conf"),
+            self._old_vals_contents())
 
-        # Dependencies inherited from containing menus and ifs
-        self.deps_from_containing = None
-        # The set of symbols referenced by this symbol (see
-        # get_referenced_symbols())
-        self.referenced_syms = set()
-        # The set of symbols selected by this symbol (see
-        # get_selected_symbols())
-        self.selected_syms = set()
-        # The set of symbols implied by this symbol (see get_implied_symbols())
-        self.implied_syms = set()
-        # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and ifs
-        self.all_referenced_syms = set()
+    def _old_vals_contents(self):
+        # _write_old_vals() helper. Returns the contents to write as a string.
 
-        # This records only dependencies from enclosing ifs and menus together
-        # with local 'depends on' dependencies. Needed when determining actual
-        # choice items (hrrrr...). See Choice._determine_actual_symbols().
-        self.menu_dep = None
+        # Temporary list instead of generator makes this a bit faster
+        return "".join([
+            sym.config_string for sym in self.unique_defined_syms
+                if not (sym.orig_type in _BOOL_TRISTATE and not sym.tri_value)
+        ])
 
-        # See Symbol.get_ref/def_locations().
-        self.def_locations = []
-        self.ref_locations = []
+    def node_iter(self, unique_syms=False):
+        """
+        Returns a generator for iterating through all MenuNode's in the Kconfig
+        tree. The iteration is done in Kconfig definition order (each node is
+        visited before its children, and the children of a node are visited
+        before the next node).
 
-        # Populated in Config._build_dep() after parsing. Links the symbol to
-        # the symbols that immediately depend on it (in a caching/invalidation
-        # sense). The total set of dependent symbols for the symbol (the
-        # transitive closure) is calculated on an as-needed basis in
-        # _get_dependent().
-        self.dep = set()
+        The Kconfig.top_node menu node is skipped. It contains an implicit menu
+        that holds the top-level items.
 
-        # Cached values
+        As an example, the following code will produce a list equal to
+        Kconfig.defined_syms:
 
-        # Caches the calculated value
-        self.cached_val = None
-        # Caches the visibility, which acts as an upper bound on the value
-        self.cached_visibility = None
-        # Caches the total list of dependent symbols. Calculated in
-        # _get_dependent().
-        self.cached_deps = None
+          defined_syms = [node.item for node in kconf.node_iter()
+                          if isinstance(node.item, Symbol)]
 
-        # Flags
+        unique_syms (default: False):
+          If True, only the first MenuNode will be included for symbols defined
+          in multiple locations.
 
-        # Does the symbol have an entry in the Kconfig file? The trailing
-        # underscore avoids a collision with is_defined().
-        self.is_defined_ = False
-        # Should the symbol get an entry in .config?
-        self.write_to_conf = False
-        # Set to true when _make_conf() is called on a symbol, so that symbols
-        # defined in multiple locations only get one .config entry. We need to
-        # reset it prior to writing out a new .config.
-        self.already_written = False
-        # This is set to True for "actual" choice symbols; see
-        # Choice._determine_actual_symbols().
-        self.is_choice_sym = False
-        # Does the symbol get its value in some special way, e.g. from the
-        # environment or by being one of the special symbols n, m, and y? If
-        # so, the value is stored in self.cached_val, which is never
-        # invalidated. The trailing underscore avoids a collision with
-        # is_special().
-        self.is_special_ = False
-        # Does the symbol get its value from the environment?
-        self.is_from_env = False
-        # Does the symbol have the 'allnoconfig_y' option set?
-        self.allnoconfig_y = False
+          Using kconf.node_iter(True) in the example above would give a list
+          equal to unique_defined_syms.
+        """
+        if unique_syms:
+            for sym in self.unique_defined_syms:
+                sym._visited = False
+
+        node = self.top_node
+        while 1:
+            # Jump to the next node with an iterative tree walk
+            if node.list:
+                node = node.list
+            elif node.next:
+                node = node.next
+            else:
+                while node.parent:
+                    node = node.parent
+                    if node.next:
+                        node = node.next
+                        break
+                else:
+                    # No more nodes
+                    return
+
+            if unique_syms and node.item.__class__ is Symbol:
+                if node.item._visited:
+                    continue
+                node.item._visited = True
+
+            yield node
+
+    def eval_string(self, s):
+        """
+        Returns the tristate value of the expression 's', represented as 0, 1,
+        and 2 for n, m, and y, respectively. Raises KconfigError on syntax
+        errors. Warns if undefined symbols are referenced.
+
+        As an example, if FOO and BAR are tristate symbols at least one of
+        which has the value y, then eval_string("y && (FOO || BAR)") returns
+        2 (y).
+
+        To get the string value of non-bool/tristate symbols, use
+        Symbol.str_value. eval_string() always returns a tristate value, and
+        all non-bool/tristate symbols have the tristate value 0 (n).
+
+        The expression parsing is consistent with how parsing works for
+        conditional ('if ...') expressions in the configuration, and matches
+        the C implementation. m is rewritten to 'm && MODULES', so
+        eval_string("m") will return 0 (n) unless modules are enabled.
+        """
+        # The parser is optimized to be fast when parsing Kconfig files (where
+        # an expression can never appear at the beginning of a line). We have
+        # to monkey-patch things a bit here to reuse it.
+
+        self.filename = None
+
+        self._tokens = self._tokenize("if " + s)
+        # Strip "if " to avoid giving confusing error messages
+        self._line = s
+        self._tokens_i = 1  # Skip the 'if' token
+
+        return expr_value(self._expect_expr_and_eol())
+
+    def unset_values(self):
+        """
+        Removes any user values from all symbols, as if Kconfig.load_config()
+        or Symbol.set_value() had never been called.
+        """
+        self._warn_assign_no_prompt = False
+        try:
+            # set_value() already rejects undefined symbols, and they don't
+            # need to be invalidated (because their value never changes), so we
+            # can just iterate over defined symbols
+            for sym in self.unique_defined_syms:
+                sym.unset_value()
+
+            for choice in self.unique_choices:
+                choice.unset_value()
+        finally:
+            self._warn_assign_no_prompt = True
+
+    def enable_warnings(self):
+        """
+        Do 'Kconfig.warn = True' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn = True
+
+    def disable_warnings(self):
+        """
+        Do 'Kconfig.warn = False' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn = False
+
+    def enable_stderr_warnings(self):
+        """
+        Do 'Kconfig.warn_to_stderr = True' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn_to_stderr = True
+
+    def disable_stderr_warnings(self):
+        """
+        Do 'Kconfig.warn_to_stderr = False' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn_to_stderr = False
+
+    def enable_undef_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_undef = True' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn_assign_undef = True
+
+    def disable_undef_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_undef = False' instead. Maintained for
+        backwards compatibility.
+        """
+        self.warn_assign_undef = False
+
+    def enable_override_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_override = True' instead. Maintained for
+        backwards compatibility.
+        """
+        self.warn_assign_override = True
+
+    def disable_override_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_override = False' instead. Maintained for
+        backwards compatibility.
+        """
+        self.warn_assign_override = False
+
+    def enable_redun_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_redun = True' instead. Maintained for backwards
+        compatibility.
+        """
+        self.warn_assign_redun = True
+
+    def disable_redun_warnings(self):
+        """
+        Do 'Kconfig.warn_assign_redun = False' instead. Maintained for
+        backwards compatibility.
+        """
+        self.warn_assign_redun = False
+
+    def __repr__(self):
+        """
+        Returns a string with information about the Kconfig object when it is
+        evaluated on e.g. the interactive Python prompt.
+        """
+        def status(flag):
+            return "enabled" if flag else "disabled"
+
+        return "<{}>".format(", ".join((
+            "configuration with {} symbols".format(len(self.syms)),
+            'main menu prompt "{}"'.format(self.mainmenu_text),
+            "srctree is current directory" if not self.srctree else
+                'srctree "{}"'.format(self.srctree),
+            'config symbol prefix "{}"'.format(self.config_prefix),
+            "warnings " + status(self.warn),
+            "printing of warnings to stderr " + status(self.warn_to_stderr),
+            "undef. symbol assignment warnings " +
+                status(self.warn_assign_undef),
+            "overriding symbol assignment warnings " +
+                status(self.warn_assign_override),
+            "redundant symbol assignment warnings " +
+                status(self.warn_assign_redun)
+        )))
+
+    #
+    # Private methods
+    #
+
+
+    #
+    # File reading
+    #
+
+    def _open_config(self, filename):
+        # Opens a .config file. First tries to open 'filename', then
+        # '$srctree/filename' if $srctree was set when the configuration was
+        # loaded.
+
+        try:
+            return self._open(filename, "r")
+        except EnvironmentError as e:
+            # This will try opening the same file twice if $srctree is unset,
+            # but it's not a big deal
+            try:
+                return self._open(join(self.srctree, filename), "r")
+            except EnvironmentError as e2:
+                # This is needed for Python 3, because e2 is deleted after
+                # the try block:
+                #
+                # https://docs.python.org/3/reference/compound_stmts.html#the-try-statement
+                e = e2
+
+            raise _KconfigIOError(
+                e, "Could not open '{}' ({}: {}). Check that the $srctree "
+                   "environment variable ({}) is set correctly."
+                   .format(filename, errno.errorcode[e.errno], e.strerror,
+                           "set to '{}'".format(self.srctree) if self.srctree
+                               else "unset or blank"))
+
+    def _enter_file(self, filename):
+        # Jumps to the beginning of a sourced Kconfig file, saving the previous
+        # position and file object.
+        #
+        # filename:
+        #   Absolute path to file
+
+        # Path relative to $srctree, stored in e.g. self.filename (which makes
+        # it indirectly show up in MenuNode.filename). Equals 'filename' for
+        # absolute paths passed to 'source'.
+        if filename.startswith(self._srctree_prefix):
+            # Relative path (or a redundant absolute path to within $srctree,
+            # but it's probably fine to reduce those too)
+            rel_filename = filename[len(self._srctree_prefix):]
+        else:
+            # Absolute path
+            rel_filename = filename
+
+        self.kconfig_filenames.append(rel_filename)
+
+        # The parent Kconfig files are represented as a list of
+        # (<include path>, <Python 'file' object for Kconfig file>) tuples.
+        #
+        # <include path> is immutable and holds a *tuple* of
+        # (<filename>, <linenr>) tuples, giving the locations of the 'source'
+        # statements in the parent Kconfig files. The current include path is
+        # also available in Kconfig._include_path.
+        #
+        # The point of this redundant setup is to allow Kconfig._include_path
+        # to be assigned directly to MenuNode.include_path without having to
+        # copy it, sharing it wherever possible.
+
+        # Save include path and 'file' object (via its 'readline' function)
+        # before entering the file
+        self._filestack.append((self._include_path, self._readline))
+
+        # _include_path is a tuple, so this rebinds the variable instead of
+        # doing in-place modification
+        self._include_path += ((self.filename, self.linenr),)
+
+        # Check for recursive 'source'
+        for name, _ in self._include_path:
+            if name == rel_filename:
+                raise KconfigError(
+                    "\n{}:{}: recursive 'source' of '{}' detected. Check that "
+                    "environment variables are set correctly.\n"
+                    "Include path:\n{}"
+                    .format(self.filename, self.linenr, rel_filename,
+                            "\n".join("{}:{}".format(name, linenr)
+                                      for name, linenr in self._include_path)))
+
+        try:
+            self._readline = self._open(filename, "r").readline
+        except EnvironmentError as e:
+            # We already know that the file exists
+            raise _KconfigIOError(
+                e, "{}:{}: Could not open '{}' (in '{}') ({}: {})"
+                   .format(self.filename, self.linenr, filename,
+                           self._line.strip(),
+                           errno.errorcode[e.errno], e.strerror))
+
+        self.filename = rel_filename
+        self.linenr = 0
+
+    def _leave_file(self):
+        # Returns from a Kconfig file to the file that sourced it. See
+        # _enter_file().
+
+        # Restore location from parent Kconfig file
+        self.filename, self.linenr = self._include_path[-1]
+        # Restore include path and 'file' object
+        self._readline.__self__.close()  # __self__ fetches the 'file' object
+        self._include_path, self._readline = self._filestack.pop()
+
+    def _next_line(self):
+        # Fetches and tokenizes the next line from the current Kconfig file.
+        # Returns False at EOF and True otherwise.
+
+        # We might already have tokens from parsing a line and discovering that
+        # it's part of a different construct
+        if self._reuse_tokens:
+            self._reuse_tokens = False
+            # self._tokens_i is known to be 1 here, because _parse_properties()
+            # leaves it like that when it can't recognize a line (or parses
+            # a help text)
+            return True
+
+        # readline() returns '' over and over at EOF, which we rely on for help
+        # texts at the end of files (see _line_after_help())
+        line = self._readline()
+        if not line:
+            return False
+        self.linenr += 1
+
+        # Handle line joining
+        while line.endswith("\\\n"):
+            line = line[:-2] + self._readline()
+            self.linenr += 1
+
+        self._tokens = self._tokenize(line)
+        # Initialize to 1 instead of 0 to factor out code from _parse_block()
+        # and _parse_properties(). They immediately fetch self._tokens[0].
+        self._tokens_i = 1
+
+        return True
+
+    def _line_after_help(self, line):
+        # Tokenizes a line after a help text. This case is special in that the
+        # line has already been fetched (to discover that it isn't part of the
+        # help text).
+        #
+        # An earlier version used a _saved_line variable instead that was
+        # checked in _next_line(). This special-casing gets rid of it and makes
+        # _reuse_tokens alone sufficient to handle unget.
+
+        # Handle line joining
+        while line.endswith("\\\n"):
+            line = line[:-2] + self._readline()
+            self.linenr += 1
+
+        self._tokens = self._tokenize(line)
+        self._reuse_tokens = True
+
+    def _write_if_changed(self, filename, contents):
+        # Writes 'contents' into 'filename', but only if it differs from the
+        # current contents of the file.
+        #
+        # Another variant would be write a temporary file on the same
+        # filesystem, compare the files, and rename() the temporary file if it
+        # differs, but it breaks stuff like write_config("/dev/null"), which is
+        # used out there to force evaluation-related warnings to be generated.
+        # This simple version is pretty failsafe and portable.
+
+        if not self._contents_eq(filename, contents):
+            with self._open(filename, "w") as f:
+                f.write(contents)
+
+    def _contents_eq(self, filename, contents):
+        # Returns True if the contents of 'filename' is 'contents' (a string),
+        # and False otherwise (including if 'filename' can't be opened/read)
+
+        try:
+            with self._open(filename, "r") as f:
+                # Robust re. things like encoding and line endings (mmap()
+                # trickery isn't)
+                return f.read(len(contents) + 1) == contents
+        except EnvironmentError:
+            # If the error here would prevent writing the file as well, we'll
+            # notice it later
+            return False
+
+    #
+    # Tokenization
+    #
+
+    def _lookup_sym(self, name):
+        # Fetches the symbol 'name' from the symbol table, creating and
+        # registering it if it does not exist. If '_parsing_kconfigs' is False,
+        # it means we're in eval_string(), and new symbols won't be registered.
+
+        if name in self.syms:
+            return self.syms[name]
+
+        sym = Symbol()
+        sym.kconfig = self
+        sym.name = name
+        sym.is_constant = False
+        sym.rev_dep = sym.weak_rev_dep = sym.direct_dep = self.n
+
+        if self._parsing_kconfigs:
+            self.syms[name] = sym
+        else:
+            self._warn("no symbol {} in configuration".format(name))
+
+        return sym
+
+    def _lookup_const_sym(self, name):
+        # Like _lookup_sym(), for constant (quoted) symbols
+
+        if name in self.const_syms:
+            return self.const_syms[name]
+
+        sym = Symbol()
+        sym.kconfig = self
+        sym.name = name
+        sym.is_constant = True
+        sym.rev_dep = sym.weak_rev_dep = sym.direct_dep = self.n
+
+        if self._parsing_kconfigs:
+            self.const_syms[name] = sym
+
+        return sym
+
+    def _tokenize(self, s):
+        # Parses 's', returning a None-terminated list of tokens. Registers any
+        # new symbols encountered with _lookup(_const)_sym().
+        #
+        # Tries to be reasonably speedy by processing chunks of text via
+        # regexes and string operations where possible. This is the biggest
+        # hotspot during parsing.
+        #
+        # It might be possible to rewrite this to 'yield' tokens instead,
+        # working across multiple lines. Lookback and compatibility with old
+        # janky versions of the C tools complicate things though.
+
+        self._line = s  # Used for error reporting
+
+        # Initial token on the line
+        match = _command_match(s)
+        if not match:
+            if s.isspace() or s.lstrip().startswith("#"):
+                return (None,)
+            self._parse_error("unknown token at start of line")
+
+        # Tricky implementation detail: While parsing a token, 'token' refers
+        # to the previous token. See _STRING_LEX for why this is needed.
+        token = _get_keyword(match.group(1))
+        if not token:
+            # Backwards compatibility with old versions of the C tools, which
+            # (accidentally) accepted stuff like "--help--" and "-help---".
+            # This was fixed in the C tools by commit c2264564 ("kconfig: warn
+            # of unhandled characters in Kconfig commands"), committed in July
+            # 2015, but it seems people still run Kconfiglib on older kernels.
+            if s.strip(" \t\n-") == "help":
+                return (_T_HELP, None)
+
+            # If the first token is not a keyword (and not a weird help token),
+            # we have a preprocessor variable assignment (or a bare macro on a
+            # line)
+            self._parse_assignment(s)
+            return (None,)
+
+        tokens = [token]
+        # The current index in the string being tokenized
+        i = match.end()
+
+        # Main tokenization loop (for tokens past the first one)
+        while i < len(s):
+            # Test for an identifier/keyword first. This is the most common
+            # case.
+            match = _id_keyword_match(s, i)
+            if match:
+                # We have an identifier or keyword
+
+                # Check what it is. lookup_sym() will take care of allocating
+                # new symbols for us the first time we see them. Note that
+                # 'token' still refers to the previous token.
+
+                name = match.group(1)
+                keyword = _get_keyword(name)
+                if keyword:
+                    # It's a keyword
+                    token = keyword
+                    # Jump past it
+                    i = match.end()
+
+                elif token not in _STRING_LEX:
+                    # It's a non-const symbol, except we translate n, m, and y
+                    # into the corresponding constant symbols, like the C
+                    # implementation
+
+                    if "$" in name:
+                        # Macro expansion within symbol name
+                        name, s, i = self._expand_name(s, i)
+                    else:
+                        i = match.end()
+
+                    token = self.const_syms[name] if name in STR_TO_TRI else \
+                        self._lookup_sym(name)
+
+                else:
+                    # It's a case of missing quotes. For example, the
+                    # following is accepted:
+                    #
+                    #   menu unquoted_title
+                    #
+                    #   config A
+                    #       tristate unquoted_prompt
+                    #
+                    #   endmenu
+                    #
+                    # Named choices ('choice FOO') also end up here.
+
+                    if token is not _T_CHOICE:
+                        self._warn("style: quotes recommended around '{}' in '{}'"
+                                   .format(name, self._line.strip()),
+                                   self.filename, self.linenr)
+
+                    token = name
+                    i = match.end()
+
+            else:
+                # Neither a keyword nor a non-const symbol
+
+                # We always strip whitespace after tokens, so it is safe to
+                # assume that s[i] is the start of a token here.
+                c = s[i]
+
+                if c in "\"'":
+                    if "$" not in s and "\\" not in s:
+                        # Fast path for lines without $ and \. Find the
+                        # matching quote.
+                        end_i = s.find(c, i + 1) + 1
+                        if not end_i:
+                            self._parse_error("unterminated string")
+                        val = s[i + 1:end_i - 1]
+                        i = end_i
+                    else:
+                        # Slow path
+                        s, end_i = self._expand_str(s, i)
+
+                        # os.path.expandvars() and the $UNAME_RELEASE replace()
+                        # is a backwards compatibility hack, which should be
+                        # reasonably safe as expandvars() leaves references to
+                        # undefined env. vars. as is.
+                        #
+                        # The preprocessor functionality changed how
+                        # environment variables are referenced, to $(FOO).
+                        val = expandvars(s[i + 1:end_i - 1]
+                                         .replace("$UNAME_RELEASE",
+                                                  _UNAME_RELEASE))
+
+                        i = end_i
+
+                    # This is the only place where we don't survive with a
+                    # single token of lookback: 'option env="FOO"' does not
+                    # refer to a constant symbol named "FOO".
+                    token = \
+                        val if token in _STRING_LEX or tokens[0] is _T_OPTION \
+                        else self._lookup_const_sym(val)
+
+                elif s.startswith("&&", i):
+                    token = _T_AND
+                    i += 2
+
+                elif s.startswith("||", i):
+                    token = _T_OR
+                    i += 2
+
+                elif c == "=":
+                    token = _T_EQUAL
+                    i += 1
+
+                elif s.startswith("!=", i):
+                    token = _T_UNEQUAL
+                    i += 2
+
+                elif c == "!":
+                    token = _T_NOT
+                    i += 1
+
+                elif c == "(":
+                    token = _T_OPEN_PAREN
+                    i += 1
+
+                elif c == ")":
+                    token = _T_CLOSE_PAREN
+                    i += 1
+
+                elif c == "#":
+                    break
+
+
+                # Very rare
+
+                elif s.startswith("<=", i):
+                    token = _T_LESS_EQUAL
+                    i += 2
+
+                elif c == "<":
+                    token = _T_LESS
+                    i += 1
+
+                elif s.startswith(">=", i):
+                    token = _T_GREATER_EQUAL
+                    i += 2
+
+                elif c == ">":
+                    token = _T_GREATER
+                    i += 1
+
+
+                else:
+                    self._parse_error("unknown tokens in line")
+
+
+                # Skip trailing whitespace
+                while i < len(s) and s[i].isspace():
+                    i += 1
+
+
+            # Add the token
+            tokens.append(token)
+
+        # None-terminating the token list makes token fetching simpler/faster
+        tokens.append(None)
+
+        return tokens
+
+    # Helpers for syntax checking and token fetching. See the
+    # 'Intro to expressions' section for what a constant symbol is.
+    #
+    # More of these could be added, but the single-use cases are inlined as an
+    # optimization.
+
+    def _expect_sym(self):
+        token = self._tokens[self._tokens_i]
+        self._tokens_i += 1
+
+        if token.__class__ is not Symbol:
+            self._parse_error("expected symbol")
+
+        return token
+
+    def _expect_nonconst_sym(self):
+        # Used for 'select' and 'imply' only. We know the token indices.
+
+        token = self._tokens[1]
+        self._tokens_i = 2
+
+        if token.__class__ is not Symbol or token.is_constant:
+            self._parse_error("expected nonconstant symbol")
+
+        return token
+
+    def _expect_str_and_eol(self):
+        token = self._tokens[self._tokens_i]
+        self._tokens_i += 1
+
+        if token.__class__ is not str:
+            self._parse_error("expected string")
+
+        if self._tokens[self._tokens_i] is not None:
+            self._trailing_tokens_error()
+
+        return token
+
+    def _expect_expr_and_eol(self):
+        expr = self._parse_expr(True)
+
+        if self._tokens[self._tokens_i] is not None:
+            self._trailing_tokens_error()
+
+        return expr
+
+    def _check_token(self, token):
+        # If the next token is 'token', removes it and returns True
+
+        if self._tokens[self._tokens_i] is token:
+            self._tokens_i += 1
+            return True
+        return False
+
+    #
+    # Preprocessor logic
+    #
+
+    def _parse_assignment(self, s):
+        # Parses a preprocessor variable assignment, registering the variable
+        # if it doesn't already exist. Also takes care of bare macros on lines
+        # (which are allowed, and can be useful for their side effects).
+
+        # Expand any macros in the left-hand side of the assignment (the
+        # variable name)
+        s = s.lstrip()
+        i = 0
+        while 1:
+            i = _assignment_lhs_fragment_match(s, i).end()
+            if s.startswith("$(", i):
+                s, i = self._expand_macro(s, i, ())
+            else:
+                break
+
+        if s.isspace():
+            # We also accept a bare macro on a line (e.g.
+            # $(warning-if,$(foo),ops)), provided it expands to a blank string
+            return
+
+        # Assigned variable
+        name = s[:i]
+
+
+        # Extract assignment operator (=, :=, or +=) and value
+        rhs_match = _assignment_rhs_match(s, i)
+        if not rhs_match:
+            self._parse_error("syntax error")
+
+        op, val = rhs_match.groups()
+
+
+        if name in self.variables:
+            # Already seen variable
+            var = self.variables[name]
+        else:
+            # New variable
+            var = Variable()
+            var.kconfig = self
+            var.name = name
+            var._n_expansions = 0
+            self.variables[name] = var
+
+            # += acts like = on undefined variables (defines a recursive
+            # variable)
+            if op == "+=":
+                op = "="
+
+        if op == "=":
+            var.is_recursive = True
+            var.value = val
+        elif op == ":=":
+            var.is_recursive = False
+            var.value = self._expand_whole(val, ())
+        else:  # op == "+="
+            # += does immediate expansion if the variable was last set
+            # with :=
+            var.value += " " + (val if var.is_recursive else
+                                self._expand_whole(val, ()))
+
+    def _expand_whole(self, s, args):
+        # Expands preprocessor macros in all of 's'. Used whenever we don't
+        # have to worry about delimiters. See _expand_macro() re. the 'args'
+        # parameter.
+        #
+        # Returns the expanded string.
+
+        i = 0
+        while 1:
+            i = s.find("$(", i)
+            if i == -1:
+                break
+            s, i = self._expand_macro(s, i, args)
+        return s
+
+    def _expand_name(self, s, i):
+        # Expands a symbol name starting at index 'i' in 's'.
+        #
+        # Returns the expanded name, the expanded 's' (including the part
+        # before the name), and the index of the first character in the next
+        # token after the name.
+
+        s, end_i = self._expand_name_iter(s, i)
+        name = s[i:end_i]
+        # isspace() is False for empty strings
+        if not name.strip():
+            # Avoid creating a Kconfig symbol with a blank name. It's almost
+            # guaranteed to be an error.
+            self._parse_error("macro expanded to blank string")
+
+        # Skip trailing whitespace
+        while end_i < len(s) and s[end_i].isspace():
+            end_i += 1
+
+        return name, s, end_i
+
+    def _expand_name_iter(self, s, i):
+        # Expands a symbol name starting at index 'i' in 's'.
+        #
+        # Returns the expanded 's' (including the part before the name) and the
+        # index of the first character after the expanded name in 's'.
+
+        while 1:
+            match = _name_special_search(s, i)
+
+            if match.group() == "$(":
+                s, i = self._expand_macro(s, match.start(), ())
+            else:
+                return (s, match.start())
+
+    def _expand_str(self, s, i):
+        # Expands a quoted string starting at index 'i' in 's'. Handles both
+        # backslash escapes and macro expansion.
+        #
+        # Returns the expanded 's' (including the part before the string) and
+        # the index of the first character after the expanded string in 's'.
+
+        quote = s[i]
+        i += 1  # Skip over initial "/'
+        while 1:
+            match = _string_special_search(s, i)
+            if not match:
+                self._parse_error("unterminated string")
+
+
+            if match.group() == quote:
+                # Found the end of the string
+                return (s, match.end())
+
+            elif match.group() == "\\":
+                # Replace '\x' with 'x'. 'i' ends up pointing to the character
+                # after 'x', which allows macros to be canceled with '\$(foo)'.
+                i = match.end()
+                s = s[:match.start()] + s[i:]
+
+            elif match.group() == "$(":
+                # A macro call within the string
+                s, i = self._expand_macro(s, match.start(), ())
+
+            else:
+                # A ' quote within " quotes or vice versa
+                i += 1
+
+    def _expand_macro(self, s, i, args):
+        # Expands a macro starting at index 'i' in 's'. If this macro resulted
+        # from the expansion of another macro, 'args' holds the arguments
+        # passed to that macro.
+        #
+        # Returns the expanded 's' (including the part before the macro) and
+        # the index of the first character after the expanded macro in 's'.
+
+        start = i
+        i += 2  # Skip over "$("
+
+        # Start of current macro argument
+        arg_start = i
+
+        # Arguments of this macro call
+        new_args = []
+
+        while 1:
+            match = _macro_special_search(s, i)
+            if not match:
+                self._parse_error("missing end parenthesis in macro expansion")
+
+
+            if match.group() == ")":
+                # Found the end of the macro
+
+                new_args.append(s[arg_start:match.start()])
+
+                prefix = s[:start]
+
+                # $(1) is replaced by the first argument to the function, etc.,
+                # provided at least that many arguments were passed
+
+                try:
+                    # Does the macro look like an integer, with a corresponding
+                    # argument? If so, expand it to the value of the argument.
+                    prefix += args[int(new_args[0])]
+                except (ValueError, IndexError):
+                    # Regular variables are just functions without arguments,
+                    # and also go through the function value path
+                    prefix += self._fn_val(new_args)
+
+                return (prefix + s[match.end():],
+                        len(prefix))
+
+            elif match.group() == ",":
+                # Found the end of a macro argument
+                new_args.append(s[arg_start:match.start()])
+                arg_start = i = match.end()
+
+            else:  # match.group() == "$("
+                # A nested macro call within the macro
+                s, i = self._expand_macro(s, match.start(), args)
+
+    def _fn_val(self, args):
+        # Returns the result of calling the function args[0] with the arguments
+        # args[1..len(args)-1]. Plain variables are treated as functions
+        # without arguments.
+
+        fn = args[0]
+
+        if fn in self.variables:
+            var = self.variables[fn]
+
+            if len(args) == 1:
+                # Plain variable
+                if var._n_expansions:
+                    self._parse_error("Preprocessor variable {} recursively "
+                                      "references itself".format(var.name))
+            elif var._n_expansions > 100:
+                # Allow functions to call themselves, but guess that functions
+                # that are overly recursive are stuck
+                self._parse_error("Preprocessor function {} seems stuck "
+                                  "in infinite recursion".format(var.name))
+
+            var._n_expansions += 1
+            res = self._expand_whole(self.variables[fn].value, args)
+            var._n_expansions -= 1
+            return res
+
+        if fn in self._functions:
+            # Built-in or user-defined function
+
+            py_fn, min_arg, max_arg = self._functions[fn]
+
+            if len(args) - 1 < min_arg or \
+               (max_arg is not None and len(args) - 1 > max_arg):
+
+                if min_arg == max_arg:
+                    expected_args = min_arg
+                elif max_arg is None:
+                    expected_args = "{} or more".format(min_arg)
+                else:
+                    expected_args = "{}-{}".format(min_arg, max_arg)
+
+                raise KconfigError("{}:{}: bad number of arguments in call "
+                                   "to {}, expected {}, got {}"
+                                   .format(self.filename, self.linenr, fn,
+                                           expected_args, len(args) - 1))
+
+            return py_fn(self, *args)
+
+        # Environment variables are tried last
+        if fn in os.environ:
+            self.env_vars.add(fn)
+            return os.environ[fn]
+
+        return ""
+
+    #
+    # Parsing
+    #
+
+    def _make_and(self, e1, e2):
+        # Constructs an AND (&&) expression. Performs trivial simplification.
+
+        if e1 is self.y:
+            return e2
+
+        if e2 is self.y:
+            return e1
+
+        if e1 is self.n or e2 is self.n:
+            return self.n
+
+        return (AND, e1, e2)
+
+    def _make_or(self, e1, e2):
+        # Constructs an OR (||) expression. Performs trivial simplification.
+
+        if e1 is self.n:
+            return e2
+
+        if e2 is self.n:
+            return e1
+
+        if e1 is self.y or e2 is self.y:
+            return self.y
+
+        return (OR, e1, e2)
+
+    def _parse_block(self, end_token, parent, prev):
+        # Parses a block, which is the contents of either a file or an if,
+        # menu, or choice statement.
+        #
+        # end_token:
+        #   The token that ends the block, e.g. _T_ENDIF ("endif") for ifs.
+        #   None for files.
+        #
+        # parent:
+        #   The parent menu node, corresponding to a menu, Choice, or 'if'.
+        #   'if's are flattened after parsing.
+        #
+        # prev:
+        #   The previous menu node. New nodes will be added after this one (by
+        #   modifying their 'next' pointer).
+        #
+        #   'prev' is reused to parse a list of child menu nodes (for a menu or
+        #   Choice): After parsing the children, the 'next' pointer is assigned
+        #   to the 'list' pointer to "tilt up" the children above the node.
+        #
+        # Returns the final menu node in the block (or 'prev' if the block is
+        # empty). This allows chaining.
+
+        while self._next_line():
+            t0 = self._tokens[0]
+
+            if t0 is _T_CONFIG or t0 is _T_MENUCONFIG:
+                # The tokenizer allocates Symbol objects for us
+                sym = self._tokens[1]
+
+                if sym.__class__ is not Symbol or sym.is_constant:
+                    self._parse_error("missing or bad symbol name")
+
+                if self._tokens[2] is not None:
+                    self._trailing_tokens_error()
+
+                self.defined_syms.append(sym)
+
+                node = MenuNode()
+                node.kconfig = self
+                node.item = sym
+                node.is_menuconfig = (t0 is _T_MENUCONFIG)
+                node.prompt = node.help = node.list = None
+                node.parent = parent
+                node.filename = self.filename
+                node.linenr = self.linenr
+                node.include_path = self._include_path
+
+                sym.nodes.append(node)
+
+                self._parse_properties(node)
+
+                if node.is_menuconfig and not node.prompt:
+                    self._warn("the menuconfig symbol {} has no prompt"
+                               .format(_name_and_loc(sym)))
+
+                # Equivalent to
+                #
+                #   prev.next = node
+                #   prev = node
+                #
+                # due to tricky Python semantics. The order matters.
+                prev.next = prev = node
+
+            elif t0 is None:
+                # Blank line
+                continue
+
+            elif t0 in _SOURCE_TOKENS:
+                pattern = self._expect_str_and_eol()
+
+                if t0 in _REL_SOURCE_TOKENS:
+                    # Relative source
+                    pattern = join(dirname(self.filename), pattern)
+
+                # - glob() doesn't support globbing relative to a directory, so
+                #   we need to prepend $srctree to 'pattern'. Use join()
+                #   instead of '+' so that an absolute path in 'pattern' is
+                #   preserved.
+                #
+                # - Sort the glob results to ensure a consistent ordering of
+                #   Kconfig symbols, which indirectly ensures a consistent
+                #   ordering in e.g. .config files
+                filenames = sorted(iglob(join(self._srctree_prefix, pattern)))
+
+                if not filenames and t0 in _OBL_SOURCE_TOKENS:
+                    raise KconfigError(
+                        "{}:{}: '{}' not found (in '{}'). Check that "
+                        "environment variables are set correctly (e.g. "
+                        "$srctree, which is {}). Also note that unset "
+                        "environment variables expand to the empty string."
+                        .format(self.filename, self.linenr, pattern,
+                                self._line.strip(),
+                                "set to '{}'".format(self.srctree)
+                                    if self.srctree else "unset or blank"))
+
+                for filename in filenames:
+                    self._enter_file(filename)
+                    prev = self._parse_block(None, parent, prev)
+                    self._leave_file()
+
+            elif t0 is end_token:
+                # Reached the end of the block. Terminate the final node and
+                # return it.
+
+                if self._tokens[1] is not None:
+                    self._trailing_tokens_error()
+
+                prev.next = None
+                return prev
+
+            elif t0 is _T_IF:
+                node = MenuNode()
+                node.item = node.prompt = None
+                node.parent = parent
+                node.dep = self._expect_expr_and_eol()
+
+                self._parse_block(_T_ENDIF, node, node)
+                node.list = node.next
+
+                prev.next = prev = node
+
+            elif t0 is _T_MENU:
+                node = MenuNode()
+                node.kconfig = self
+                node.item = t0  # _T_MENU == MENU
+                node.is_menuconfig = True
+                node.prompt = (self._expect_str_and_eol(), self.y)
+                node.visibility = self.y
+                node.parent = parent
+                node.filename = self.filename
+                node.linenr = self.linenr
+                node.include_path = self._include_path
+
+                self.menus.append(node)
+
+                self._parse_properties(node)
+                self._parse_block(_T_ENDMENU, node, node)
+                node.list = node.next
+
+                prev.next = prev = node
+
+            elif t0 is _T_COMMENT:
+                node = MenuNode()
+                node.kconfig = self
+                node.item = t0  # _T_COMMENT == COMMENT
+                node.is_menuconfig = False
+                node.prompt = (self._expect_str_and_eol(), self.y)
+                node.list = None
+                node.parent = parent
+                node.filename = self.filename
+                node.linenr = self.linenr
+                node.include_path = self._include_path
+
+                self.comments.append(node)
+
+                self._parse_properties(node)
+
+                prev.next = prev = node
+
+            elif t0 is _T_CHOICE:
+                if self._tokens[1] is None:
+                    choice = Choice()
+                    choice.direct_dep = self.n
+                else:
+                    # Named choice
+                    name = self._expect_str_and_eol()
+                    choice = self.named_choices.get(name)
+                    if not choice:
+                        choice = Choice()
+                        choice.name = name
+                        choice.direct_dep = self.n
+                        self.named_choices[name] = choice
+
+                self.choices.append(choice)
+
+                node = MenuNode()
+                node.kconfig = choice.kconfig = self
+                node.item = choice
+                node.is_menuconfig = True
+                node.prompt = node.help = None
+                node.parent = parent
+                node.filename = self.filename
+                node.linenr = self.linenr
+                node.include_path = self._include_path
+
+                choice.nodes.append(node)
+
+                self._parse_properties(node)
+                self._parse_block(_T_ENDCHOICE, node, node)
+                node.list = node.next
+
+                prev.next = prev = node
+
+            elif t0 is _T_MAINMENU:
+                self.top_node.prompt = (self._expect_str_and_eol(), self.y)
+
+            else:
+                # A valid endchoice/endif/endmenu is caught by the 'end_token'
+                # check above
+                self._parse_error(
+                    "no corresponding 'choice'" if t0 is _T_ENDCHOICE else
+                    "no corresponding 'if'"     if t0 is _T_ENDIF else
+                    "no corresponding 'menu'"   if t0 is _T_ENDMENU else
+                    "unrecognized construct")
+
+        # End of file reached. Terminate the final node and return it.
+
+        if end_token:
+            raise KconfigError(
+                "expected '{}' at end of '{}'"
+                .format("endchoice" if end_token is _T_ENDCHOICE else
+                        "endif"     if end_token is _T_ENDIF else
+                        "endmenu",
+                        self.filename))
+
+        prev.next = None
+        return prev
+
+    def _parse_cond(self):
+        # Parses an optional 'if <expr>' construct and returns the parsed
+        # <expr>, or self.y if the next token is not _T_IF
+
+        expr = self._parse_expr(True) if self._check_token(_T_IF) else self.y
+
+        if self._tokens[self._tokens_i] is not None:
+            self._trailing_tokens_error()
+
+        return expr
+
+    def _parse_properties(self, node):
+        # Parses and adds properties to the MenuNode 'node' (type, 'prompt',
+        # 'default's, etc.) Properties are later copied up to symbols and
+        # choices in a separate pass after parsing, in e.g.
+        # _add_props_to_sym().
+        #
+        # An older version of this code added properties directly to symbols
+        # and choices instead of to their menu nodes (and handled dependency
+        # propagation simultaneously), but that loses information on where a
+        # property is added when a symbol or choice is defined in multiple
+        # locations. Some Kconfig configuration systems rely heavily on such
+        # symbols, and better docs can be generated by keeping track of where
+        # properties are added.
+        #
+        # node:
+        #   The menu node we're parsing properties on
+
+        # Dependencies from 'depends on'. Will get propagated to the properties
+        # below.
+        node.dep = self.y
+
+        while self._next_line():
+            t0 = self._tokens[0]
+
+            if t0 in _TYPE_TOKENS:
+                # Relies on '_T_BOOL is BOOL', etc., to save a conversion
+                self._set_type(node, t0)
+                if self._tokens[1] is not None:
+                    self._parse_prompt(node)
+
+            elif t0 is _T_DEPENDS:
+                if not self._check_token(_T_ON):
+                    self._parse_error("expected 'on' after 'depends'")
+
+                node.dep = self._make_and(node.dep,
+                                          self._expect_expr_and_eol())
+
+            elif t0 is _T_HELP:
+                self._parse_help(node)
+
+            elif t0 is _T_SELECT:
+                if node.item.__class__ is not Symbol:
+                    self._parse_error("only symbols can select")
+
+                node.selects.append((self._expect_nonconst_sym(),
+                                     self._parse_cond()))
+
+            elif t0 is None:
+                # Blank line
+                continue
+
+            elif t0 is _T_DEFAULT:
+                node.defaults.append((self._parse_expr(False),
+                                      self._parse_cond()))
+
+            elif t0 in _DEF_TOKEN_TO_TYPE:
+                self._set_type(node, _DEF_TOKEN_TO_TYPE[t0])
+                node.defaults.append((self._parse_expr(False),
+                                      self._parse_cond()))
+
+            elif t0 is _T_PROMPT:
+                self._parse_prompt(node)
+
+            elif t0 is _T_RANGE:
+                node.ranges.append((self._expect_sym(), self._expect_sym(),
+                                    self._parse_cond()))
+
+            elif t0 is _T_IMPLY:
+                if node.item.__class__ is not Symbol:
+                    self._parse_error("only symbols can imply")
+
+                node.implies.append((self._expect_nonconst_sym(),
+                                     self._parse_cond()))
+
+            elif t0 is _T_VISIBLE:
+                if not self._check_token(_T_IF):
+                    self._parse_error("expected 'if' after 'visible'")
+
+                node.visibility = self._make_and(node.visibility,
+                                                 self._expect_expr_and_eol())
+
+            elif t0 is _T_OPTION:
+                if self._check_token(_T_ENV):
+                    if not self._check_token(_T_EQUAL):
+                        self._parse_error("expected '=' after 'env'")
+
+                    env_var = self._expect_str_and_eol()
+                    node.item.env_var = env_var
+
+                    if env_var in os.environ:
+                        node.defaults.append(
+                            (self._lookup_const_sym(os.environ[env_var]),
+                             self.y))
+                    else:
+                        self._warn("{1} has 'option env=\"{0}\"', "
+                                   "but the environment variable {0} is not "
+                                   "set".format(node.item.name, env_var),
+                                   self.filename, self.linenr)
+
+                    if env_var != node.item.name:
+                        self._warn("Kconfiglib expands environment variables "
+                                   "in strings directly, meaning you do not "
+                                   "need 'option env=...' \"bounce\" symbols. "
+                                   "For compatibility with the C tools, "
+                                   "rename {} to {} (so that the symbol name "
+                                   "matches the environment variable name)."
+                                   .format(node.item.name, env_var),
+                                   self.filename, self.linenr)
+
+                elif self._check_token(_T_DEFCONFIG_LIST):
+                    if not self.defconfig_list:
+                        self.defconfig_list = node.item
+                    else:
+                        self._warn("'option defconfig_list' set on multiple "
+                                   "symbols ({0} and {1}). Only {0} will be "
+                                   "used.".format(self.defconfig_list.name,
+                                                  node.item.name),
+                                   self.filename, self.linenr)
+
+                elif self._check_token(_T_MODULES):
+                    # To reduce warning spam, only warn if 'option modules' is
+                    # set on some symbol that isn't MODULES, which should be
+                    # safe. I haven't run into any projects that make use
+                    # modules besides the kernel yet, and there it's likely to
+                    # keep being called "MODULES".
+                    if node.item is not self.modules:
+                        self._warn("the 'modules' option is not supported. "
+                                   "Let me know if this is a problem for you, "
+                                   "as it wouldn't be that hard to implement. "
+                                   "Note that modules are supported -- "
+                                   "Kconfiglib just assumes the symbol name "
+                                   "MODULES, like older versions of the C "
+                                   "implementation did when 'option modules' "
+                                   "wasn't used.",
+                                   self.filename, self.linenr)
+
+                elif self._check_token(_T_ALLNOCONFIG_Y):
+                    if node.item.__class__ is not Symbol:
+                        self._parse_error("the 'allnoconfig_y' option is only "
+                                          "valid for symbols")
+
+                    node.item.is_allnoconfig_y = True
+
+                else:
+                    self._parse_error("unrecognized option")
+
+            elif t0 is _T_OPTIONAL:
+                if node.item.__class__ is not Choice:
+                    self._parse_error('"optional" is only valid for choices')
+
+                node.item.is_optional = True
+
+            else:
+                # Reuse the tokens for the non-property line later
+                self._reuse_tokens = True
+                return
+
+    def _set_type(self, node, new_type):
+        # UNKNOWN is falsy
+        if node.item.orig_type and node.item.orig_type is not new_type:
+            self._warn("{} defined with multiple types, {} will be used"
+                       .format(_name_and_loc(node.item),
+                               TYPE_TO_STR[new_type]))
+
+        node.item.orig_type = new_type
+
+    def _parse_prompt(self, node):
+        # 'prompt' properties override each other within a single definition of
+        # a symbol, but additional prompts can be added by defining the symbol
+        # multiple times
+
+        if node.prompt:
+            self._warn(_name_and_loc(node.item) +
+                       " defined with multiple prompts in single location")
+
+        prompt = self._tokens[1]
+        self._tokens_i = 2
+
+        if prompt.__class__ is not str:
+            self._parse_error("expected prompt string")
+
+        if prompt != prompt.strip():
+            self._warn(_name_and_loc(node.item) +
+                       " has leading or trailing whitespace in its prompt")
+
+            # This avoid issues for e.g. reStructuredText documentation, where
+            # '*prompt *' is invalid
+            prompt = prompt.strip()
+
+        node.prompt = (prompt, self._parse_cond())
+
+    def _parse_help(self, node):
+        if node.help is not None:
+            self._warn(_name_and_loc(node.item) + " defined with more than "
+                       "one help text -- only the last one will be used")
+
+        # Micro-optimization. This code is pretty hot.
+        readline = self._readline
+
+        # Find first non-blank (not all-space) line and get its
+        # indentation
+
+        while 1:
+            line = readline()
+            self.linenr += 1
+            if not line:
+                self._empty_help(node, line)
+                return
+            if not line.isspace():
+                break
+
+        len_ = len  # Micro-optimization
+
+        # Use a separate 'expline' variable here and below to avoid stomping on
+        # any tabs people might've put deliberately into the first line after
+        # the help text
+        expline = line.expandtabs()
+        indent = len_(expline) - len_(expline.lstrip())
+        if not indent:
+            self._empty_help(node, line)
+            return
+
+        # The help text goes on till the first non-blank line with less indent
+        # than the first line
+
+        # Add the first line
+        lines = [expline[indent:]]
+        add_line = lines.append  # Micro-optimization
+
+        while 1:
+            line = readline()
+            if line.isspace():
+                # No need to preserve the exact whitespace in these
+                add_line("\n")
+            elif not line:
+                # End of file
+                break
+            else:
+                expline = line.expandtabs()
+                if len_(expline) - len_(expline.lstrip()) < indent:
+                    break
+                add_line(expline[indent:])
+
+        self.linenr += len_(lines)
+        node.help = "".join(lines).rstrip()
+        if line:
+            self._line_after_help(line)
+
+    def _empty_help(self, node, line):
+        self._warn(_name_and_loc(node.item) +
+                   " has 'help' but empty help text")
+        node.help = ""
+        if line:
+            self._line_after_help(line)
+
+    def _parse_expr(self, transform_m):
+        # Parses an expression from the tokens in Kconfig._tokens using a
+        # simple top-down approach. See the module docstring for the expression
+        # format.
+        #
+        # transform_m:
+        #   True if m should be rewritten to m && MODULES. See the
+        #   Kconfig.eval_string() documentation.
+
+        # Grammar:
+        #
+        #   expr:     and_expr ['||' expr]
+        #   and_expr: factor ['&&' and_expr]
+        #   factor:   <symbol> ['='/'!='/'<'/... <symbol>]
+        #             '!' factor
+        #             '(' expr ')'
+        #
+        # It helps to think of the 'expr: and_expr' case as a single-operand OR
+        # (no ||), and of the 'and_expr: factor' case as a single-operand AND
+        # (no &&). Parsing code is always a bit tricky.
+
+        # Mind dump: parse_factor() and two nested loops for OR and AND would
+        # work as well. The straightforward implementation there gives a
+        # (op, (op, (op, A, B), C), D) parse for A op B op C op D. Representing
+        # expressions as (op, [list of operands]) instead goes nicely with that
+        # version, but is wasteful for short expressions and complicates
+        # expression evaluation and other code that works on expressions (more
+        # complicated code likely offsets any performance gain from less
+        # recursion too). If we also try to optimize the list representation by
+        # merging lists when possible (e.g. when ANDing two AND expressions),
+        # we end up allocating a ton of lists instead of reusing expressions,
+        # which is bad.
+
+        and_expr = self._parse_and_expr(transform_m)
+
+        # Return 'and_expr' directly if we have a "single-operand" OR.
+        # Otherwise, parse the expression on the right and make an OR node.
+        # This turns A || B || C || D into (OR, A, (OR, B, (OR, C, D))).
+        return and_expr if not self._check_token(_T_OR) else \
+            (OR, and_expr, self._parse_expr(transform_m))
+
+    def _parse_and_expr(self, transform_m):
+        factor = self._parse_factor(transform_m)
+
+        # Return 'factor' directly if we have a "single-operand" AND.
+        # Otherwise, parse the right operand and make an AND node. This turns
+        # A && B && C && D into (AND, A, (AND, B, (AND, C, D))).
+        return factor if not self._check_token(_T_AND) else \
+            (AND, factor, self._parse_and_expr(transform_m))
+
+    def _parse_factor(self, transform_m):
+        token = self._tokens[self._tokens_i]
+        self._tokens_i += 1
+
+        if token.__class__ is Symbol:
+            # Plain symbol or relation
+
+            if self._tokens[self._tokens_i] not in _RELATIONS:
+                # Plain symbol
+
+                # For conditional expressions ('depends on <expr>',
+                # '... if <expr>', etc.), m is rewritten to m && MODULES.
+                if transform_m and token is self.m:
+                    return (AND, self.m, self.modules)
+
+                return token
+
+            # Relation
+            #
+            # _T_EQUAL, _T_UNEQUAL, etc., deliberately have the same values as
+            # EQUAL, UNEQUAL, etc., so we can just use the token directly
+            self._tokens_i += 1
+            return (self._tokens[self._tokens_i - 1], token,
+                    self._expect_sym())
+
+        if token is _T_NOT:
+            # token == _T_NOT == NOT
+            return (token, self._parse_factor(transform_m))
+
+        if token is _T_OPEN_PAREN:
+            expr_parse = self._parse_expr(transform_m)
+            if self._check_token(_T_CLOSE_PAREN):
+                return expr_parse
+
+        self._parse_error("malformed expression")
+
+    #
+    # Caching and invalidation
+    #
+
+    def _build_dep(self):
+        # Populates the Symbol/Choice._dependents sets, which contain all other
+        # items (symbols and choices) that immediately depend on the item in
+        # the sense that changing the value of the item might affect the value
+        # of the dependent items. This is used for caching/invalidation.
+        #
+        # The calculated sets might be larger than necessary as we don't do any
+        # complex analysis of the expressions.
+
+        make_depend_on = _make_depend_on  # Micro-optimization
+
+        # Only calculate _dependents for defined symbols. Constant and
+        # undefined symbols could theoretically be selected/implied, but it
+        # wouldn't change their value, so it's not a true dependency.
+        for sym in self.unique_defined_syms:
+            # Symbols depend on the following:
+
+            # The prompt conditions
+            for node in sym.nodes:
+                if node.prompt:
+                    make_depend_on(sym, node.prompt[1])
+
+            # The default values and their conditions
+            for value, cond in sym.defaults:
+                make_depend_on(sym, value)
+                make_depend_on(sym, cond)
+
+            # The reverse and weak reverse dependencies
+            make_depend_on(sym, sym.rev_dep)
+            make_depend_on(sym, sym.weak_rev_dep)
+
+            # The ranges along with their conditions
+            for low, high, cond in sym.ranges:
+                make_depend_on(sym, low)
+                make_depend_on(sym, high)
+                make_depend_on(sym, cond)
+
+            # The direct dependencies. This is usually redundant, as the direct
+            # dependencies get propagated to properties, but it's needed to get
+            # invalidation solid for 'imply', which only checks the direct
+            # dependencies (even if there are no properties to propagate it
+            # to).
+            make_depend_on(sym, sym.direct_dep)
+
+            # In addition to the above, choice symbols depend on the choice
+            # they're in, but that's handled automatically since the Choice is
+            # propagated to the conditions of the properties before
+            # _build_dep() runs.
+
+        for choice in self.unique_choices:
+            # Choices depend on the following:
+
+            # The prompt conditions
+            for node in choice.nodes:
+                if node.prompt:
+                    make_depend_on(choice, node.prompt[1])
+
+            # The default symbol conditions
+            for _, cond in choice.defaults:
+                make_depend_on(choice, cond)
+
+    def _add_choice_deps(self):
+        # Choices also depend on the choice symbols themselves, because the
+        # y-mode selection of the choice might change if a choice symbol's
+        # visibility changes.
+        #
+        # We add these dependencies separately after dependency loop detection.
+        # The invalidation algorithm can handle the resulting
+        # <choice symbol> <-> <choice> dependency loops, but they make loop
+        # detection awkward.
+
+        for choice in self.unique_choices:
+            for sym in choice.syms:
+                sym._dependents.add(choice)
+
+    def _invalidate_all(self):
+        # Undefined symbols never change value and don't need to be
+        # invalidated, so we can just iterate over defined symbols.
+        # Invalidating constant symbols would break things horribly.
+        for sym in self.unique_defined_syms:
+            sym._invalidate()
+
+        for choice in self.unique_choices:
+            choice._invalidate()
+
+    #
+    # Post-parsing menu tree processing, including dependency propagation and
+    # implicit submenu creation
+    #
+
+    def _finalize_node(self, node, visible_if):
+        # Finalizes a menu node and its children:
+        #
+        #  - Copies properties from menu nodes up to their contained
+        #    symbols/choices
+        #
+        #  - Propagates dependencies from parent to child nodes
+        #
+        #  - Creates implicit menus (see kconfig-language.txt)
+        #
+        #  - Removes 'if' nodes
+        #
+        #  - Sets 'choice' types and registers choice symbols
+        #
+        # menu_finalize() in the C implementation is similar.
+        #
+        # node:
+        #   The menu node to finalize. This node and its children will have
+        #   been finalized when the function returns, and any implicit menus
+        #   will have been created.
+        #
+        # visible_if:
+        #   Dependencies from 'visible if' on parent menus. These are added to
+        #   the prompts of symbols and choices.
+
+        if node.item.__class__ is Symbol:
+            # Copy defaults, ranges, selects, and implies to the Symbol
+            self._add_props_to_sym(node)
+
+            # Find any items that should go in an implicit menu rooted at the
+            # symbol
+            cur = node
+            while cur.next and _auto_menu_dep(node, cur.next):
+                # This makes implicit submenu creation work recursively, with
+                # implicit menus inside implicit menus
+                self._finalize_node(cur.next, visible_if)
+                cur = cur.next
+                cur.parent = node
+
+            if cur is not node:
+                # Found symbols that should go in an implicit submenu. Tilt
+                # them up above us.
+                node.list = node.next
+                node.next = cur.next
+                cur.next = None
+
+        elif node.list:
+            # The menu node is a choice, menu, or if. Finalize each child node.
+
+            if node.item is MENU:
+                visible_if = self._make_and(visible_if, node.visibility)
+
+            # Propagate the menu node's dependencies to each child menu node.
+            #
+            # This needs to go before the recursive _finalize_node() call so
+            # that implicit submenu creation can look ahead at dependencies.
+            self._propagate_deps(node, visible_if)
+
+            # Finalize the children
+            cur = node.list
+            while cur:
+                self._finalize_node(cur, visible_if)
+                cur = cur.next
+
+        if node.list:
+            # node's children have been individually finalized. Do final steps
+            # to finalize this "level" in the menu tree.
+            _flatten(node.list)
+            _remove_ifs(node)
+
+        # Empty choices (node.list None) are possible, so this needs to go
+        # outside
+        if node.item.__class__ is Choice:
+            # Add the node's non-node-specific properties to the choice, like
+            # _add_props_to_sym() does
+            choice = node.item
+            choice.direct_dep = self._make_or(choice.direct_dep, node.dep)
+            choice.defaults += node.defaults
+
+            _finalize_choice(node)
+
+    def _propagate_deps(self, node, visible_if):
+        # Propagates 'node's dependencies to its child menu nodes
+
+        # If the parent node holds a Choice, we use the Choice itself as the
+        # parent dependency. This makes sense as the value (mode) of the choice
+        # limits the visibility of the contained choice symbols. The C
+        # implementation works the same way.
+        #
+        # Due to the similar interface, Choice works as a drop-in replacement
+        # for Symbol here.
+        basedep = node.item if node.item.__class__ is Choice else node.dep
+
+        cur = node.list
+        while cur:
+            dep = cur.dep = self._make_and(cur.dep, basedep)
+
+            if cur.item.__class__ in _SYMBOL_CHOICE:
+                # Propagate 'visible if' and dependencies to the prompt
+                if cur.prompt:
+                    cur.prompt = (cur.prompt[0],
+                                  self._make_and(
+                                      cur.prompt[1],
+                                      self._make_and(visible_if, dep)))
+
+                # Propagate dependencies to defaults
+                if cur.defaults:
+                    cur.defaults = [(default, self._make_and(cond, dep))
+                                    for default, cond in cur.defaults]
+
+                # Propagate dependencies to ranges
+                if cur.ranges:
+                    cur.ranges = [(low, high, self._make_and(cond, dep))
+                                  for low, high, cond in cur.ranges]
+
+                # Propagate dependencies to selects
+                if cur.selects:
+                    cur.selects = [(target, self._make_and(cond, dep))
+                                   for target, cond in cur.selects]
+
+                # Propagate dependencies to implies
+                if cur.implies:
+                    cur.implies = [(target, self._make_and(cond, dep))
+                                   for target, cond in cur.implies]
+
+            elif cur.prompt:  # Not a symbol/choice
+                # Propagate dependencies to the prompt. 'visible if' is only
+                # propagated to symbols/choices.
+                cur.prompt = (cur.prompt[0],
+                              self._make_and(cur.prompt[1], dep))
+
+            cur = cur.next
+
+    def _add_props_to_sym(self, node):
+        # Copies properties from the menu node 'node' up to its contained
+        # symbol, and adds (weak) reverse dependencies to selected/implied
+        # symbols.
+        #
+        # This can't be rolled into _propagate_deps(), because that function
+        # traverses the menu tree roughly breadth-first, meaning properties on
+        # symbols defined in multiple locations could end up in the wrong
+        # order.
+
+        sym = node.item
+
+        # See the Symbol class docstring
+        sym.direct_dep = self._make_or(sym.direct_dep, node.dep)
+
+        sym.defaults += node.defaults
+        sym.ranges += node.ranges
+        sym.selects += node.selects
+        sym.implies += node.implies
+
+        # Modify the reverse dependencies of the selected symbol
+        for target, cond in node.selects:
+            target.rev_dep = self._make_or(
+                target.rev_dep,
+                self._make_and(sym, cond))
+
+        # Modify the weak reverse dependencies of the implied
+        # symbol
+        for target, cond in node.implies:
+            target.weak_rev_dep = self._make_or(
+                target.weak_rev_dep,
+                self._make_and(sym, cond))
+
+    #
+    # Misc.
+    #
+
+    def _check_sym_sanity(self):
+        # Checks various symbol properties that are handiest to check after
+        # parsing. Only generates errors and warnings.
+
+        def num_ok(sym, type_):
+            # Returns True if the (possibly constant) symbol 'sym' is valid as a value
+            # for a symbol of type type_ (INT or HEX)
+
+            # 'not sym.nodes' implies a constant or undefined symbol, e.g. a plain
+            # "123"
+            if not sym.nodes:
+                return _is_base_n(sym.name, _TYPE_TO_BASE[type_])
+
+            return sym.orig_type is type_
+
+        for sym in self.unique_defined_syms:
+            if sym.orig_type in _BOOL_TRISTATE:
+                # A helper function could be factored out here, but keep it
+                # speedy/straightforward
+
+                for target_sym, _ in sym.selects:
+                    if target_sym.orig_type not in _BOOL_TRISTATE_UNKNOWN:
+                        self._warn("{} selects the {} symbol {}, which is not "
+                                   "bool or tristate"
+                                   .format(_name_and_loc(sym),
+                                           TYPE_TO_STR[target_sym.orig_type],
+                                           _name_and_loc(target_sym)))
+
+                for target_sym, _ in sym.implies:
+                    if target_sym.orig_type not in _BOOL_TRISTATE_UNKNOWN:
+                        self._warn("{} implies the {} symbol {}, which is not "
+                                   "bool or tristate"
+                                   .format(_name_and_loc(sym),
+                                           TYPE_TO_STR[target_sym.orig_type],
+                                           _name_and_loc(target_sym)))
+
+            elif sym.orig_type:  # STRING/INT/HEX
+                for default, _ in sym.defaults:
+                    if default.__class__ is not Symbol:
+                        raise KconfigError(
+                            "the {} symbol {} has a malformed default {} -- expected "
+                            "a single symbol"
+                            .format(TYPE_TO_STR[sym.orig_type], _name_and_loc(sym),
+                                    expr_str(default)))
+
+                    if sym.orig_type is STRING:
+                        if not default.is_constant and not default.nodes and \
+                           not default.name.isupper():
+                            # 'default foo' on a string symbol could be either a symbol
+                            # reference or someone leaving out the quotes. Guess that
+                            # the quotes were left out if 'foo' isn't all-uppercase
+                            # (and no symbol named 'foo' exists).
+                            self._warn("style: quotes recommended around "
+                                       "default value for string symbol "
+                                       + _name_and_loc(sym))
+
+                    elif not num_ok(default, sym.orig_type):  # INT/HEX
+                        self._warn("the {0} symbol {1} has a non-{0} default {2}"
+                                   .format(TYPE_TO_STR[sym.orig_type],
+                                           _name_and_loc(sym),
+                                           _name_and_loc(default)))
+
+                if sym.selects or sym.implies:
+                    self._warn("the {} symbol {} has selects or implies"
+                               .format(TYPE_TO_STR[sym.orig_type],
+                                       _name_and_loc(sym)))
+
+            else:  # UNKNOWN
+                self._warn("{} defined without a type"
+                           .format(_name_and_loc(sym)))
+
+
+            if sym.ranges:
+                if sym.orig_type not in _INT_HEX:
+                    self._warn(
+                        "the {} symbol {} has ranges, but is not int or hex"
+                        .format(TYPE_TO_STR[sym.orig_type],
+                                _name_and_loc(sym)))
+                else:
+                    for low, high, _ in sym.ranges:
+                        if not num_ok(low, sym.orig_type) or \
+                           not num_ok(high, sym.orig_type):
+
+                            self._warn("the {0} symbol {1} has a non-{0} "
+                                       "range [{2}, {3}]"
+                                       .format(TYPE_TO_STR[sym.orig_type],
+                                               _name_and_loc(sym),
+                                               _name_and_loc(low),
+                                               _name_and_loc(high)))
+
+    def _check_choice_sanity(self):
+        # Checks various choice properties that are handiest to check after
+        # parsing. Only generates errors and warnings.
+
+        def warn_select_imply(sym, expr, expr_type):
+            msg = "the choice symbol {} is {} by the following symbols, but " \
+                  "select/imply has no effect on choice symbols" \
+                  .format(_name_and_loc(sym), expr_type)
+
+            # si = select/imply
+            for si in split_expr(expr, OR):
+                msg += "\n - " + _name_and_loc(split_expr(si, AND)[0])
+
+            self._warn(msg)
+
+        for choice in self.unique_choices:
+            if choice.orig_type not in _BOOL_TRISTATE:
+                self._warn("{} defined with type {}"
+                           .format(_name_and_loc(choice),
+                                   TYPE_TO_STR[choice.orig_type]))
+
+            for node in choice.nodes:
+                if node.prompt:
+                    break
+            else:
+                self._warn(_name_and_loc(choice) + " defined without a prompt")
+
+            for default, _ in choice.defaults:
+                if default.__class__ is not Symbol:
+                    raise KconfigError(
+                        "{} has a malformed default {}"
+                        .format(_name_and_loc(choice), expr_str(default)))
+
+                if default.choice is not choice:
+                    self._warn("the default selection {} of {} is not "
+                               "contained in the choice"
+                               .format(_name_and_loc(default),
+                                       _name_and_loc(choice)))
+
+            for sym in choice.syms:
+                if sym.defaults:
+                    self._warn("default on the choice symbol {} will have "
+                               "no effect, as defaults do not affect choice "
+                               "symbols".format(_name_and_loc(sym)))
+
+                if sym.rev_dep is not sym.kconfig.n:
+                    warn_select_imply(sym, sym.rev_dep, "selected")
+
+                if sym.weak_rev_dep is not sym.kconfig.n:
+                    warn_select_imply(sym, sym.weak_rev_dep, "implied")
+
+                for node in sym.nodes:
+                    if node.parent.item is choice:
+                        if not node.prompt:
+                            self._warn("the choice symbol {} has no prompt"
+                                       .format(_name_and_loc(sym)))
+
+                    elif node.prompt:
+                        self._warn("the choice symbol {} is defined with a "
+                                   "prompt outside the choice"
+                                   .format(_name_and_loc(sym)))
+
+    def _parse_error(self, msg):
+        raise KconfigError("{}couldn't parse '{}': {}".format(
+            "" if self.filename is None else
+                "{}:{}: ".format(self.filename, self.linenr),
+            self._line.strip(), msg))
+
+    def _trailing_tokens_error(self):
+        self._parse_error("extra tokens at end of line")
+
+    def _open(self, filename, mode):
+        # open() wrapper:
+        #
+        # - Enable universal newlines mode on Python 2 to ease
+        #   interoperability between Linux and Windows. It's already the
+        #   default on Python 3.
+        #
+        #   The "U" flag would currently work for both Python 2 and 3, but it's
+        #   deprecated on Python 3, so play it future-safe.
+        #
+        #   io.open() defaults to universal newlines on Python 2 (and is an
+        #   alias for open() on Python 3), but it returns 'unicode' strings and
+        #   slows things down:
+        #
+        #     Parsing x86 Kconfigs on Python 2
+        #
+        #     with open(..., "rU"):
+        #
+        #       real  0m0.930s
+        #       user  0m0.905s
+        #       sys   0m0.025s
+        #
+        #     with io.open():
+        #
+        #       real  0m1.069s
+        #       user  0m1.040s
+        #       sys   0m0.029s
+        #
+        #   There's no appreciable performance difference between "r" and
+        #   "rU" for parsing performance on Python 2.
+        #
+        # - For Python 3, force the encoding. Forcing the encoding on Python 2
+        #   turns strings into Unicode strings, which gets messy. Python 2
+        #   doesn't decode regular strings anyway.
+        return open(filename, "rU" if mode == "r" else mode) if _IS_PY2 else \
+               open(filename, mode, encoding=self._encoding)
+
+    def _check_undef_syms(self):
+        # Prints warnings for all references to undefined symbols within the
+        # Kconfig files
+
+        def is_num(s):
+            # Returns True if the string 's' looks like a number.
+            #
+            # Internally, all operands in Kconfig are symbols, only undefined symbols
+            # (which numbers usually are) get their name as their value.
+            #
+            # Only hex numbers that start with 0x/0X are classified as numbers.
+            # Otherwise, symbols whose names happen to contain only the letters A-F
+            # would trigger false positives.
+
+            try:
+                int(s)
+            except ValueError:
+                if not s.startswith(("0x", "0X")):
+                    return False
+
+                try:
+                    int(s, 16)
+                except ValueError:
+                    return False
+
+            return True
+
+        for sym in (self.syms.viewvalues if _IS_PY2 else self.syms.values)():
+            # - sym.nodes empty means the symbol is undefined (has no
+            #   definition locations)
+            #
+            # - Due to Kconfig internals, numbers show up as undefined Kconfig
+            #   symbols, but shouldn't be flagged
+            #
+            # - The MODULES symbol always exists
+            if not sym.nodes and not is_num(sym.name) and \
+               sym.name != "MODULES":
+
+                msg = "undefined symbol {}:".format(sym.name)
+                for node in self.node_iter():
+                    if sym in node.referenced:
+                        msg += "\n\n- Referenced at {}:{}:\n\n{}" \
+                               .format(node.filename, node.linenr, node)
+                self._warn(msg)
+
+    def _warn(self, msg, filename=None, linenr=None):
+        # For printing general warnings
+
+        if not self.warn:
+            return
+
+        msg = "warning: " + msg
+        if filename is not None:
+            msg = "{}:{}: {}".format(filename, linenr, msg)
+
+        self.warnings.append(msg)
+        if self.warn_to_stderr:
+            sys.stderr.write(msg + "\n")
+
+
+class Symbol(object):
+    """
+    Represents a configuration symbol:
+
+      (menu)config FOO
+          ...
+
+    The following attributes are available. They should be viewed as read-only,
+    and some are implemented through @property magic (but are still efficient
+    to access due to internal caching).
+
+    Note: Prompts, help texts, and locations are stored in the Symbol's
+    MenuNode(s) rather than in the Symbol itself. Check the MenuNode class and
+    the Symbol.nodes attribute. This organization matches the C tools.
+
+    name:
+      The name of the symbol, e.g. "FOO" for 'config FOO'.
+
+    type:
+      The type of the symbol. One of BOOL, TRISTATE, STRING, INT, HEX, UNKNOWN.
+      UNKNOWN is for undefined symbols, (non-special) constant symbols, and
+      symbols defined without a type.
+
+      When running without modules (MODULES having the value n), TRISTATE
+      symbols magically change type to BOOL. This also happens for symbols
+      within choices in "y" mode. This matches the C tools, and makes sense for
+      menuconfig-like functionality.
+
+    orig_type:
+      The type as given in the Kconfig file, without any magic applied. Used
+      when printing the symbol.
+
+    str_value:
+      The value of the symbol as a string. Gives the value for string/int/hex
+      symbols. For bool/tristate symbols, gives "n", "m", or "y".
+
+      This is the symbol value that's used in relational expressions
+      (A = B, A != B, etc.)
+
+      Gotcha: For int/hex symbols, the exact format of the value must often be
+      preserved (e.g., when writing a .config file), hence why you can't get it
+      directly as an int. Do int(int_sym.str_value) or
+      int(hex_sym.str_value, 16) to get the integer value.
+
+    tri_value:
+      The tristate value of the symbol as an integer. One of 0, 1, 2,
+      representing n, m, y. Always 0 (n) for non-bool/tristate symbols.
+
+      This is the symbol value that's used outside of relation expressions
+      (A, !A, A && B, A || B).
+
+    assignable:
+      A tuple containing the tristate user values that can currently be
+      assigned to the symbol (that would be respected), ordered from lowest (0,
+      representing n) to highest (2, representing y). This corresponds to the
+      selections available in the menuconfig interface. The set of assignable
+      values is calculated from the symbol's visibility and selects/implies.
+
+      Returns the empty set for non-bool/tristate symbols and for symbols with
+      visibility n. The other possible values are (0, 2), (0, 1, 2), (1, 2),
+      (1,), and (2,). A (1,) or (2,) result means the symbol is visible but
+      "locked" to m or y through a select, perhaps in combination with the
+      visibility. menuconfig represents this as -M- and -*-, respectively.
+
+      For string/hex/int symbols, check if Symbol.visibility is non-0 (non-n)
+      instead to determine if the value can be changed.
+
+      Some handy 'assignable' idioms:
+
+        # Is 'sym' an assignable (visible) bool/tristate symbol?
+        if sym.assignable:
+            # What's the highest value it can be assigned? [-1] in Python
+            # gives the last element.
+            sym_high = sym.assignable[-1]
+
+            # The lowest?
+            sym_low = sym.assignable[0]
+
+            # Can the symbol be set to at least m?
+            if sym.assignable[-1] >= 1:
+                ...
+
+        # Can the symbol be set to m?
+        if 1 in sym.assignable:
+            ...
+
+    visibility:
+      The visibility of the symbol. One of 0, 1, 2, representing n, m, y. See
+      the module documentation for an overview of symbol values and visibility.
+
+    user_value:
+      The user value of the symbol. None if no user value has been assigned
+      (via Kconfig.load_config() or Symbol.set_value()).
+
+      Holds 0, 1, or 2 for bool/tristate symbols, and a string for the other
+      symbol types.
+
+      WARNING: Do not assign directly to this. It will break things. Use
+      Symbol.set_value().
+
+    config_string:
+      The .config assignment string that would get written out for the symbol
+      by Kconfig.write_config(). Returns the empty string if no .config
+      assignment would get written out.
+
+      In general, visible symbols, symbols with (active) defaults, and selected
+      symbols get written out. This includes all non-n-valued bool/tristate
+      symbols, and all visible string/int/hex symbols.
+
+      Symbols with the (no longer needed) 'option env=...' option generate no
+      configuration output, and neither does the special
+      'option defconfig_list' symbol.
+
+      Tip: This field is useful when generating custom configuration output,
+      even for non-.config-like formats. To write just the symbols that would
+      get written out to .config files, do this:
+
+        if sym.config_string:
+            *Write symbol, e.g. by looking sym.str_value*
+
+      This is a superset of the symbols written out by write_autoconf().
+      That function skips all n-valued symbols.
+
+      There usually won't be any great harm in just writing all symbols either,
+      though you might get some special symbols and possibly some "redundant"
+      n-valued symbol entries in there.
+
+    nodes:
+      A list of MenuNodes for this symbol. Will contain a single MenuNode for
+      most symbols. Undefined and constant symbols have an empty nodes list.
+      Symbols defined in multiple locations get one node for each location.
+
+    choice:
+      Holds the parent Choice for choice symbols, and None for non-choice
+      symbols. Doubles as a flag for whether a symbol is a choice symbol.
+
+    defaults:
+      List of (default, cond) tuples for the symbol's 'default' properties. For
+      example, 'default A && B if C || D' is represented as
+      ((AND, A, B), (OR, C, D)). If no condition was given, 'cond' is
+      self.kconfig.y.
+
+      Note that 'depends on' and parent dependencies are propagated to
+      'default' conditions.
+
+    selects:
+      List of (symbol, cond) tuples for the symbol's 'select' properties. For
+      example, 'select A if B && C' is represented as (A, (AND, B, C)). If no
+      condition was given, 'cond' is self.kconfig.y.
+
+      Note that 'depends on' and parent dependencies are propagated to 'select'
+      conditions.
+
+    implies:
+      Like 'selects', for imply.
+
+    ranges:
+      List of (low, high, cond) tuples for the symbol's 'range' properties. For
+      example, 'range 1 2 if A' is represented as (1, 2, A). If there is no
+      condition, 'cond' is self.kconfig.y.
+
+      Note that 'depends on' and parent dependencies are propagated to 'range'
+      conditions.
+
+      Gotcha: 1 and 2 above will be represented as (undefined) Symbols rather
+      than plain integers. Undefined symbols get their name as their string
+      value, so this works out. The C tools work the same way.
+
+    orig_defaults:
+    orig_selects:
+    orig_implies:
+    orig_ranges:
+      See the corresponding attributes on the MenuNode class.
+
+    rev_dep:
+      Reverse dependency expression from other symbols selecting this symbol.
+      Multiple selections get ORed together. A condition on a select is ANDed
+      with the selecting symbol.
+
+      For example, if A has 'select FOO' and B has 'select FOO if C', then
+      FOO's rev_dep will be (OR, A, (AND, B, C)).
+
+    weak_rev_dep:
+      Like rev_dep, for imply.
+
+    direct_dep:
+      The direct ('depends on') dependencies for the symbol, or self.kconfig.y
+      if there are no direct dependencies.
+
+      This attribute includes any dependencies from surrounding menus and ifs.
+      Those get propagated to the direct dependencies, and the resulting direct
+      dependencies in turn get propagated to the conditions of all properties.
+
+      If the symbol is defined in multiple locations, the dependencies from the
+      different locations get ORed together.
+
+    referenced:
+      A set() with all symbols and choices referenced in the properties and
+      property conditions of the symbol.
+
+      Also includes dependencies from surrounding menus and ifs, because those
+      get propagated to the symbol (see the 'Intro to symbol values' section in
+      the module docstring).
+
+      Choices appear in the dependencies of choice symbols.
+
+      For the following definitions, only B and not C appears in A's
+      'referenced'. To get transitive references, you'll have to recursively
+      expand 'references' until no new items appear.
+
+        config A
+                bool
+                depends on B
+
+        config B
+                bool
+                depends on C
+
+        config C
+                bool
+
+      See the Symbol.direct_dep attribute if you're only interested in the
+      direct dependencies of the symbol (its 'depends on'). You can extract the
+      symbols in it with the global expr_items() function.
+
+    env_var:
+      If the Symbol has an 'option env="FOO"' option, this contains the name
+      ("FOO") of the environment variable. None for symbols without no
+      'option env'.
+
+      'option env="FOO"' acts like a 'default' property whose value is the
+      value of $FOO.
+
+      Symbols with 'option env' are never written out to .config files, even if
+      they are visible. env_var corresponds to a flag called SYMBOL_AUTO in the
+      C implementation.
+
+    is_allnoconfig_y:
+      True if the symbol has 'option allnoconfig_y' set on it. This has no
+      effect internally (except when printing symbols), but can be checked by
+      scripts.
+
+    is_constant:
+      True if the symbol is a constant (quoted) symbol.
+
+    kconfig:
+      The Kconfig instance this symbol is from.
+    """
+    __slots__ = (
+        "_cached_assignable",
+        "_cached_str_val",
+        "_cached_tri_val",
+        "_cached_vis",
+        "_dependents",
+        "_old_val",
+        "_visited",
+        "_was_set",
+        "_write_to_conf",
+        "choice",
+        "defaults",
+        "direct_dep",
+        "env_var",
+        "implies",
+        "is_allnoconfig_y",
+        "is_constant",
+        "kconfig",
+        "name",
+        "nodes",
+        "orig_type",
+        "ranges",
+        "rev_dep",
+        "selects",
+        "user_value",
+        "weak_rev_dep",
+    )
+
+    #
+    # Public interface
+    #
+
+    @property
+    def type(self):
+        """
+        See the class documentation.
+        """
+        if self.orig_type is TRISTATE and \
+           (self.choice and self.choice.tri_value == 2 or
+            not self.kconfig.modules.tri_value):
+
+            return BOOL
+
+        return self.orig_type
+
+    @property
+    def str_value(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_str_val is not None:
+            return self._cached_str_val
+
+        if self.orig_type in _BOOL_TRISTATE:
+            # Also calculates the visibility, so invalidation safe
+            self._cached_str_val = TRI_TO_STR[self.tri_value]
+            return self._cached_str_val
+
+        # As a quirk of Kconfig, undefined symbols get their name as their
+        # string value. This is why things like "FOO = bar" work for seeing if
+        # FOO has the value "bar".
+        if not self.orig_type:  # UNKNOWN
+            self._cached_str_val = self.name
+            return self.name
+
+        val = ""
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        vis = self.visibility
+
+        self._write_to_conf = (vis != 0)
+
+        if self.orig_type in _INT_HEX:
+            # The C implementation checks the user value against the range in a
+            # separate code path (post-processing after loading a .config).
+            # Checking all values here instead makes more sense for us. It
+            # requires that we check for a range first.
+
+            base = _TYPE_TO_BASE[self.orig_type]
+
+            # Check if a range is in effect
+            for low_expr, high_expr, cond in self.ranges:
+                if expr_value(cond):
+                    has_active_range = True
+
+                    # The zeros are from the C implementation running strtoll()
+                    # on empty strings
+                    low = int(low_expr.str_value, base) if \
+                      _is_base_n(low_expr.str_value, base) else 0
+                    high = int(high_expr.str_value, base) if \
+                      _is_base_n(high_expr.str_value, base) else 0
+
+                    break
+            else:
+                has_active_range = False
+
+            # Defaults are used if the symbol is invisible, lacks a user value,
+            # or has an out-of-range user value
+            use_defaults = True
+
+            if vis and self.user_value:
+                user_val = int(self.user_value, base)
+                if has_active_range and not low <= user_val <= high:
+                    num2str = str if base == 10 else hex
+                    self.kconfig._warn(
+                        "user value {} on the {} symbol {} ignored due to "
+                        "being outside the active range ([{}, {}]) -- falling "
+                        "back on defaults"
+                        .format(num2str(user_val), TYPE_TO_STR[self.orig_type],
+                                _name_and_loc(self),
+                                num2str(low), num2str(high)))
+                else:
+                    # If the user value is well-formed and satisfies range
+                    # contraints, it is stored in exactly the same form as
+                    # specified in the assignment (with or without "0x", etc.)
+                    val = self.user_value
+                    use_defaults = False
+
+            if use_defaults:
+                # No user value or invalid user value. Look at defaults.
+
+                # Used to implement the warning below
+                has_default = False
+
+                for sym, cond in self.defaults:
+                    if expr_value(cond):
+                        has_default = self._write_to_conf = True
+
+                        val = sym.str_value
+
+                        if _is_base_n(val, base):
+                            val_num = int(val, base)
+                        else:
+                            val_num = 0  # strtoll() on empty string
+
+                        break
+                else:
+                    val_num = 0  # strtoll() on empty string
+
+                # This clamping procedure runs even if there's no default
+                if has_active_range:
+                    clamp = None
+                    if val_num < low:
+                        clamp = low
+                    elif val_num > high:
+                        clamp = high
+
+                    if clamp is not None:
+                        # The value is rewritten to a standard form if it is
+                        # clamped
+                        val = str(clamp) \
+                              if self.orig_type is INT else \
+                              hex(clamp)
+
+                        if has_default:
+                            num2str = str if base == 10 else hex
+                            self.kconfig._warn(
+                                "default value {} on {} clamped to {} due to "
+                                "being outside the active range ([{}, {}])"
+                                .format(val_num, _name_and_loc(self),
+                                        num2str(clamp), num2str(low),
+                                        num2str(high)))
+
+        elif self.orig_type is STRING:
+            if vis and self.user_value is not None:
+                # If the symbol is visible and has a user value, use that
+                val = self.user_value
+            else:
+                # Otherwise, look at defaults
+                for sym, cond in self.defaults:
+                    if expr_value(cond):
+                        val = sym.str_value
+                        self._write_to_conf = True
+                        break
+
+        # env_var corresponds to SYMBOL_AUTO in the C implementation, and is
+        # also set on the defconfig_list symbol there. Test for the
+        # defconfig_list symbol explicitly instead here, to avoid a nonsensical
+        # env_var setting and the defconfig_list symbol being printed
+        # incorrectly. This code is pretty cold anyway.
+        if self.env_var is not None or self is self.kconfig.defconfig_list:
+            self._write_to_conf = False
+
+        self._cached_str_val = val
+        return val
+
+    @property
+    def tri_value(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_tri_val is not None:
+            return self._cached_tri_val
+
+        if self.orig_type not in _BOOL_TRISTATE:
+            if self.orig_type:  # != UNKNOWN
+                # Would take some work to give the location here
+                self.kconfig._warn(
+                    "The {} symbol {} is being evaluated in a logical context "
+                    "somewhere. It will always evaluate to n."
+                    .format(TYPE_TO_STR[self.orig_type], _name_and_loc(self)))
+
+            self._cached_tri_val = 0
+            return 0
+
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        vis = self.visibility
+        self._write_to_conf = (vis != 0)
+
+        val = 0
+
+        if not self.choice:
+            # Non-choice symbol
+
+            if vis and self.user_value is not None:
+                # If the symbol is visible and has a user value, use that
+                val = min(self.user_value, vis)
+
+            else:
+                # Otherwise, look at defaults and weak reverse dependencies
+                # (implies)
+
+                for default, cond in self.defaults:
+                    dep_val = expr_value(cond)
+                    if dep_val:
+                        val = min(expr_value(default), dep_val)
+                        if val:
+                            self._write_to_conf = True
+                        break
+
+                # Weak reverse dependencies are only considered if our
+                # direct dependencies are met
+                dep_val = expr_value(self.weak_rev_dep)
+                if dep_val and expr_value(self.direct_dep):
+                    val = max(dep_val, val)
+                    self._write_to_conf = True
+
+            # Reverse (select-related) dependencies take precedence
+            dep_val = expr_value(self.rev_dep)
+            if dep_val:
+                if expr_value(self.direct_dep) < dep_val:
+                    self._warn_select_unsatisfied_deps()
+
+                val = max(dep_val, val)
+                self._write_to_conf = True
+
+            # m is promoted to y for (1) bool symbols and (2) symbols with a
+            # weak_rev_dep (from imply) of y
+            if val == 1 and \
+               (self.type is BOOL or expr_value(self.weak_rev_dep) == 2):
+                val = 2
+
+        elif vis == 2:
+            # Visible choice symbol in y-mode choice. The choice mode limits
+            # the visibility of choice symbols, so it's sufficient to just
+            # check the visibility of the choice symbols themselves.
+            val = 2 if self.choice.selection is self else 0
+
+        elif vis and self.user_value:
+            # Visible choice symbol in m-mode choice, with set non-0 user value
+            val = 1
+
+        self._cached_tri_val = val
+        return val
+
+    @property
+    def assignable(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_assignable is None:
+            self._cached_assignable = self._assignable()
+        return self._cached_assignable
+
+    @property
+    def visibility(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_vis is None:
+            self._cached_vis = _visibility(self)
+        return self._cached_vis
+
+    @property
+    def config_string(self):
+        """
+        See the class documentation.
+        """
+        # _write_to_conf is determined when the value is calculated. This is a
+        # hidden function call due to property magic.
+        val = self.str_value
+        if not self._write_to_conf:
+            return ""
+
+        if self.orig_type in _BOOL_TRISTATE:
+            return "{}{}={}\n" \
+                   .format(self.kconfig.config_prefix, self.name, val) \
+                   if val != "n" else \
+                   "# {}{} is not set\n" \
+                   .format(self.kconfig.config_prefix, self.name)
+
+        if self.orig_type in _INT_HEX:
+            return "{}{}={}\n" \
+                   .format(self.kconfig.config_prefix, self.name, val)
+
+        # sym.orig_type is STRING
+        return '{}{}="{}"\n' \
+               .format(self.kconfig.config_prefix, self.name, escape(val))
+
+    def set_value(self, value):
+        """
+        Sets the user value of the symbol.
+
+        Equal in effect to assigning the value to the symbol within a .config
+        file. For bool and tristate symbols, use the 'assignable' attribute to
+        check which values can currently be assigned. Setting values outside
+        'assignable' will cause Symbol.user_value to differ from
+        Symbol.str/tri_value (be truncated down or up).
+
+        Setting a choice symbol to 2 (y) sets Choice.user_selection to the
+        choice symbol in addition to setting Symbol.user_value.
+        Choice.user_selection is considered when the choice is in y mode (the
+        "normal" mode).
+
+        Other symbols that depend (possibly indirectly) on this symbol are
+        automatically recalculated to reflect the assigned value.
+
+        value:
+          The user value to give to the symbol. For bool and tristate symbols,
+          n/m/y can be specified either as 0/1/2 (the usual format for tristate
+          values in Kconfiglib) or as one of the strings "n"/"m"/"y". For other
+          symbol types, pass a string.
+
+          Note that the value for an int/hex symbol is passed as a string, e.g.
+          "123" or "0x0123". The format of this string is preserved in the
+          output.
+
+          Values that are invalid for the type (such as "foo" or 1 (m) for a
+          BOOL or "0x123" for an INT) are ignored and won't be stored in
+          Symbol.user_value. Kconfiglib will print a warning by default for
+          invalid assignments, and set_value() will return False.
+
+        Returns True if the value is valid for the type of the symbol, and
+        False otherwise. This only looks at the form of the value. For BOOL and
+        TRISTATE symbols, check the Symbol.assignable attribute to see what
+        values are currently in range and would actually be reflected in the
+        value of the symbol. For other symbol types, check whether the
+        visibility is non-n.
+        """
+        if self.orig_type in _BOOL_TRISTATE and value in STR_TO_TRI:
+            value = STR_TO_TRI[value]
+
+        # If the new user value matches the old, nothing changes, and we can
+        # avoid invalidating cached values.
+        #
+        # This optimization is skipped for choice symbols: Setting a choice
+        # symbol's user value to y might change the state of the choice, so it
+        # wouldn't be safe (symbol user values always match the values set in a
+        # .config file or via set_value(), and are never implicitly updated).
+        if value == self.user_value and not self.choice:
+            self._was_set = True
+            return True
+
+        # Check if the value is valid for our type
+        if not (self.orig_type is BOOL     and value in (2, 0)     or
+                self.orig_type is TRISTATE and value in TRI_TO_STR or
+                value.__class__ is str and
+                (self.orig_type is STRING                        or
+                 self.orig_type is INT and _is_base_n(value, 10) or
+                 self.orig_type is HEX and _is_base_n(value, 16)
+                                       and int(value, 16) >= 0)):
+
+            # Display tristate values as n, m, y in the warning
+            self.kconfig._warn(
+                "the value {} is invalid for {}, which has type {} -- "
+                "assignment ignored"
+                .format(TRI_TO_STR[value] if value in TRI_TO_STR else
+                            "'{}'".format(value),
+                        _name_and_loc(self), TYPE_TO_STR[self.orig_type]))
+
+            return False
+
+        self.user_value = value
+        self._was_set = True
+
+        if self.choice and value == 2:
+            # Setting a choice symbol to y makes it the user selection of the
+            # choice. Like for symbol user values, the user selection is not
+            # guaranteed to match the actual selection of the choice, as
+            # dependencies come into play.
+            self.choice.user_selection = self
+            self.choice._was_set = True
+            self.choice._rec_invalidate()
+        else:
+            self._rec_invalidate_if_has_prompt()
+
+        return True
+
+    def unset_value(self):
+        """
+        Removes any user value from the symbol, as if the symbol had never
+        gotten a user value via Kconfig.load_config() or Symbol.set_value().
+        """
+        if self.user_value is not None:
+            self.user_value = None
+            self._rec_invalidate_if_has_prompt()
+
+    @property
+    def referenced(self):
+        """
+        See the class documentation.
+        """
+        return {item for node in self.nodes for item in node.referenced}
+
+    @property
+    def orig_defaults(self):
+        """
+        See the class documentation.
+        """
+        return [d for node in self.nodes for d in node.orig_defaults]
+
+    @property
+    def orig_selects(self):
+        """
+        See the class documentation.
+        """
+        return [s for node in self.nodes for s in node.orig_selects]
+
+    @property
+    def orig_implies(self):
+        """
+        See the class documentation.
+        """
+        return [i for node in self.nodes for i in node.orig_implies]
+
+    @property
+    def orig_ranges(self):
+        """
+        See the class documentation.
+        """
+        return [r for node in self.nodes for r in node.orig_ranges]
+
+    def __repr__(self):
+        """
+        Returns a string with information about the symbol (including its name,
+        value, visibility, and location(s)) when it is evaluated on e.g. the
+        interactive Python prompt.
+        """
+        fields = ["symbol " + self.name, TYPE_TO_STR[self.type]]
+        add = fields.append
+
+        for node in self.nodes:
+            if node.prompt:
+                add('"{}"'.format(node.prompt[0]))
+
+        # Only add quotes for non-bool/tristate symbols
+        add("value " + (self.str_value if self.orig_type in _BOOL_TRISTATE
+                        else '"{}"'.format(self.str_value)))
+
+        if not self.is_constant:
+            # These aren't helpful to show for constant symbols
+
+            if self.user_value is not None:
+                # Only add quotes for non-bool/tristate symbols
+                add("user value " + (TRI_TO_STR[self.user_value]
+                                     if self.orig_type in _BOOL_TRISTATE
+                                     else '"{}"'.format(self.user_value)))
+
+            add("visibility " + TRI_TO_STR[self.visibility])
+
+            if self.choice:
+                add("choice symbol")
+
+            if self.is_allnoconfig_y:
+                add("allnoconfig_y")
+
+            if self is self.kconfig.defconfig_list:
+                add("is the defconfig_list symbol")
+
+            if self.env_var is not None:
+                add("from environment variable " + self.env_var)
+
+            if self is self.kconfig.modules:
+                add("is the modules symbol")
+
+            add("direct deps " + TRI_TO_STR[expr_value(self.direct_dep)])
+
+        if self.nodes:
+            for node in self.nodes:
+                add("{}:{}".format(node.filename, node.linenr))
+        else:
+            add("constant" if self.is_constant else "undefined")
+
+        return "<{}>".format(", ".join(fields))
+
+    def __str__(self):
+        """
+        Returns a string representation of the symbol when it is printed.
+        Matches the Kconfig format, with any parent dependencies propagated to
+        the 'depends on' condition.
+
+        The string is constructed by joining the strings returned by
+        MenuNode.__str__() for each of the symbol's menu nodes, so symbols
+        defined in multiple locations will return a string with all
+        definitions.
+
+        The returned string does not end in a newline. An empty string is
+        returned for undefined and constant symbols.
+        """
+        return self.custom_str(standard_sc_expr_str)
+
+    def custom_str(self, sc_expr_str_fn):
+        """
+        Works like Symbol.__str__(), but allows a custom format to be used for
+        all symbol/choice references. See expr_str().
+        """
+        return "\n\n".join(node.custom_str(sc_expr_str_fn)
+                           for node in self.nodes)
+
+    #
+    # Private methods
+    #
+
+    def __init__(self):
+        """
+        Symbol constructor -- not intended to be called directly by Kconfiglib
+        clients.
+        """
+        # These attributes are always set on the instance from outside and
+        # don't need defaults:
+        #   kconfig
+        #   direct_dep
+        #   is_constant
+        #   name
+        #   rev_dep
+        #   weak_rev_dep
+
+        # - UNKNOWN == 0
+        # - _visited is used during tree iteration and dep. loop detection
+        self.orig_type = self._visited = 0
+
+        self.nodes = []
+
+        self.defaults = []
+        self.selects = []
+        self.implies = []
+        self.ranges = []
+
+        self.user_value = \
+        self.choice = \
+        self.env_var = \
+        self._cached_str_val = self._cached_tri_val = self._cached_vis = \
+        self._cached_assignable = None
+
+        # _write_to_conf is calculated along with the value. If True, the
+        # Symbol gets a .config entry.
+
+        self.is_allnoconfig_y = \
+        self._was_set = \
+        self._write_to_conf = False
+
+        # See Kconfig._build_dep()
+        self._dependents = set()
+
+    def _assignable(self):
+        # Worker function for the 'assignable' attribute
+
+        if self.orig_type not in _BOOL_TRISTATE:
+            return ()
+
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        vis = self.visibility
+        if not vis:
+            return ()
+
+        rev_dep_val = expr_value(self.rev_dep)
+
+        if vis == 2:
+            if self.choice:
+                return (2,)
+
+            if not rev_dep_val:
+                if self.type is BOOL or expr_value(self.weak_rev_dep) == 2:
+                    return (0, 2)
+                return (0, 1, 2)
+
+            if rev_dep_val == 2:
+                return (2,)
+
+            # rev_dep_val == 1
+
+            if self.type is BOOL or expr_value(self.weak_rev_dep) == 2:
+                return (2,)
+            return (1, 2)
+
+        # vis == 1
+
+        # Must be a tristate here, because bool m visibility gets promoted to y
+
+        if not rev_dep_val:
+            return (0, 1) if expr_value(self.weak_rev_dep) != 2 else (0, 2)
+
+        if rev_dep_val == 2:
+            return (2,)
+
+        # vis == rev_dep_val == 1
+
+        return (1,)
 
     def _invalidate(self):
-        if self.is_special_:
-            return
+        # Marks the symbol as needing to be recalculated
+
+        self._cached_str_val = self._cached_tri_val = self._cached_vis = \
+        self._cached_assignable = None
+
+    def _rec_invalidate(self):
+        # Invalidates the symbol and all items that (possibly) depend on it
+
+        if self is self.kconfig.modules:
+            # Invalidating MODULES has wide-ranging effects
+            self.kconfig._invalidate_all()
+        else:
+            self._invalidate()
+
+            for item in self._dependents:
+                # _cached_vis doubles as a flag that tells us whether 'item'
+                # has cached values, because it's calculated as a side effect
+                # of calculating all other (non-constant) cached values.
+                #
+                # If item._cached_vis is None, it means there can't be cached
+                # values on other items that depend on 'item', because if there
+                # were, some value on 'item' would have been calculated and
+                # item._cached_vis set as a side effect. It's therefore safe to
+                # stop the invalidation at symbols with _cached_vis None.
+                #
+                # This approach massively speeds up scripts that set a lot of
+                # values, vs simply invalidating all possibly dependent symbols
+                # (even when you already have a list of all the dependent
+                # symbols, because some symbols get huge dependency trees).
+                #
+                # This gracefully handles dependency loops too, which is nice
+                # for choices, where the choice depends on the choice symbols
+                # and vice versa.
+                if item._cached_vis is not None:
+                    item._rec_invalidate()
+
+    def _rec_invalidate_if_has_prompt(self):
+        # Invalidates the symbol and its dependent symbols, but only if the
+        # symbol has a prompt. User values never have an effect on promptless
+        # symbols, so we skip invalidation for them as an optimization.
+        #
+        # This also prevents constant (quoted) symbols from being invalidated
+        # if set_value() is called on them, which would make them lose their
+        # value and break things.
+        #
+        # Prints a warning if the symbol has no prompt. In some contexts (e.g.
+        # when loading a .config files) assignments to promptless symbols are
+        # normal and expected, so the warning can be disabled.
+
+        for node in self.nodes:
+            if node.prompt:
+                self._rec_invalidate()
+                return
+
+        if self.kconfig._warn_assign_no_prompt:
+            self.kconfig._warn(_name_and_loc(self) + " has no prompt, meaning "
+                               "user values have no effect on it")
+
+    def _str_default(self):
+        # write_min_config() helper function. Returns the value the symbol
+        # would get from defaults if it didn't have a user value. Uses exactly
+        # the same algorithm as the C implementation (though a bit cleaned up),
+        # for compatibility.
+
+        if self.orig_type in _BOOL_TRISTATE:
+            val = 0
+
+            # Defaults, selects, and implies do not affect choice symbols
+            if not self.choice:
+                for default, cond in self.defaults:
+                    cond_val = expr_value(cond)
+                    if cond_val:
+                        val = min(expr_value(default), cond_val)
+                        break
+
+                val = max(expr_value(self.rev_dep),
+                          expr_value(self.weak_rev_dep),
+                          val)
+
+                # Transpose mod to yes if type is bool (possibly due to modules
+                # being disabled)
+                if val == 1 and self.type is BOOL:
+                    val = 2
+
+            return TRI_TO_STR[val]
+
+        if self.orig_type:  # STRING/INT/HEX
+            for default, cond in self.defaults:
+                if expr_value(cond):
+                    return default.str_value
+
+        return ""
+
+    def _warn_select_unsatisfied_deps(self):
+        # Helper for printing an informative warning when a symbol with
+        # unsatisfied direct dependencies (dependencies from 'depends on', ifs,
+        # and menus) is selected by some other symbol. Also warn if a symbol
+        # whose direct dependencies evaluate to m is selected to y.
+
+        msg = "{} has direct dependencies {} with value {}, but is " \
+              "currently being {}-selected by the following symbols:" \
+              .format(_name_and_loc(self), expr_str(self.direct_dep),
+                      TRI_TO_STR[expr_value(self.direct_dep)],
+                      TRI_TO_STR[expr_value(self.rev_dep)])
+
+        # The reverse dependencies from each select are ORed together
+        for select in split_expr(self.rev_dep, OR):
+            if expr_value(select) <= expr_value(self.direct_dep):
+                # Only include selects that exceed the direct dependencies
+                continue
+
+            # - 'select A if B' turns into A && B
+            # - 'select A' just turns into A
+            #
+            # In both cases, we can split on AND and pick the first operand
+            selecting_sym = split_expr(select, AND)[0]
+
+            msg += "\n - {}, with value {}, direct dependencies {} " \
+                   "(value: {})" \
+                   .format(_name_and_loc(selecting_sym),
+                           selecting_sym.str_value,
+                           expr_str(selecting_sym.direct_dep),
+                           TRI_TO_STR[expr_value(selecting_sym.direct_dep)])
+
+            if select.__class__ is tuple:
+                msg += ", and select condition {} (value: {})" \
+                       .format(expr_str(select[2]),
+                               TRI_TO_STR[expr_value(select[2])])
+
+        self.kconfig._warn(msg)
+
+
+class Choice(object):
+    """
+    Represents a choice statement:
+
+      choice
+          ...
+      endchoice
+
+    The following attributes are available on Choice instances. They should be
+    treated as read-only, and some are implemented through @property magic (but
+    are still efficient to access due to internal caching).
+
+    Note: Prompts, help texts, and locations are stored in the Choice's
+    MenuNode(s) rather than in the Choice itself. Check the MenuNode class and
+    the Choice.nodes attribute. This organization matches the C tools.
+
+    name:
+      The name of the choice, e.g. "FOO" for 'choice FOO', or None if the
+      Choice has no name.
+
+    type:
+      The type of the choice. One of BOOL, TRISTATE, UNKNOWN. UNKNOWN is for
+      choices defined without a type where none of the contained symbols have a
+      type either (otherwise the choice inherits the type of the first symbol
+      defined with a type).
+
+      When running without modules (CONFIG_MODULES=n), TRISTATE choices
+      magically change type to BOOL. This matches the C tools, and makes sense
+      for menuconfig-like functionality.
+
+    orig_type:
+      The type as given in the Kconfig file, without any magic applied. Used
+      when printing the choice.
+
+    tri_value:
+      The tristate value (mode) of the choice. A choice can be in one of three
+      modes:
+
+        0 (n) - The choice is disabled and no symbols can be selected. For
+                visible choices, this mode is only possible for choices with
+                the 'optional' flag set (see kconfig-language.txt).
+
+        1 (m) - Any number of choice symbols can be set to m, the rest will
+                be n.
+
+        2 (y) - One symbol will be y, the rest n.
+
+      Only tristate choices can be in m mode. The visibility of the choice is
+      an upper bound on the mode, and the mode in turn is an upper bound on the
+      visibility of the choice symbols.
+
+      To change the mode, use Choice.set_value().
+
+      Implementation note:
+        The C tools internally represent choices as a type of symbol, with
+        special-casing in many code paths. This is why there is a lot of
+        similarity to Symbol. The value (mode) of a choice is really just a
+        normal symbol value, and an implicit reverse dependency forces its
+        lower bound to m for visible non-optional choices (the reverse
+        dependency is 'm && <visibility>').
+
+        Symbols within choices get the choice propagated as a dependency to
+        their properties. This turns the mode of the choice into an upper bound
+        on e.g. the visibility of choice symbols, and explains the gotcha
+        related to printing choice symbols mentioned in the module docstring.
+
+        Kconfiglib uses a separate Choice class only because it makes the code
+        and interface less confusing (especially in a user-facing interface).
+        Corresponding attributes have the same name in the Symbol and Choice
+        classes, for consistency and compatibility.
+
+    assignable:
+      See the symbol class documentation. Gives the assignable values (modes).
+
+    visibility:
+      See the Symbol class documentation. Acts on the value (mode).
+
+    selection:
+      The Symbol instance of the currently selected symbol. None if the Choice
+      is not in y mode or has no selected symbol (due to unsatisfied
+      dependencies on choice symbols).
+
+      WARNING: Do not assign directly to this. It will break things. Call
+      sym.set_value(2) on the choice symbol you want to select instead.
+
+    user_value:
+      The value (mode) selected by the user through Choice.set_value(). Either
+      0, 1, or 2, or None if the user hasn't selected a mode. See
+      Symbol.user_value.
+
+      WARNING: Do not assign directly to this. It will break things. Use
+      Choice.set_value() instead.
+
+    user_selection:
+      The symbol selected by the user (by setting it to y). Ignored if the
+      choice is not in y mode, but still remembered so that the choice "snaps
+      back" to the user selection if the mode is changed back to y. This might
+      differ from 'selection' due to unsatisfied dependencies.
+
+      WARNING: Do not assign directly to this. It will break things. Call
+      sym.set_value(2) on the choice symbol to be selected instead.
+
+    syms:
+      List of symbols contained in the choice.
+
+      Obscure gotcha: If a symbol depends on the previous symbol within a
+      choice so that an implicit menu is created, it won't be a choice symbol,
+      and won't be included in 'syms'.
+
+    nodes:
+      A list of MenuNodes for this choice. In practice, the list will probably
+      always contain a single MenuNode, but it is possible to give a choice a
+      name and define it in multiple locations.
+
+    defaults:
+      List of (symbol, cond) tuples for the choice's 'defaults' properties. For
+      example, 'default A if B && C' is represented as (A, (AND, B, C)). If
+      there is no condition, 'cond' is self.kconfig.y.
+
+      Note that 'depends on' and parent dependencies are propagated to
+      'default' conditions.
+
+    orig_defaults:
+      See the corresponding attribute on the MenuNode class.
+
+    direct_dep:
+      See Symbol.direct_dep.
+
+    referenced:
+      A set() with all symbols referenced in the properties and property
+      conditions of the choice.
+
+      Also includes dependencies from surrounding menus and ifs, because those
+      get propagated to the choice (see the 'Intro to symbol values' section in
+      the module docstring).
+
+    is_optional:
+      True if the choice has the 'optional' flag set on it and can be in
+      n mode.
+
+    kconfig:
+      The Kconfig instance this choice is from.
+    """
+    __slots__ = (
+        "_cached_assignable",
+        "_cached_selection",
+        "_cached_vis",
+        "_dependents",
+        "_visited",
+        "_was_set",
+        "defaults",
+        "direct_dep",
+        "is_constant",
+        "is_optional",
+        "kconfig",
+        "name",
+        "nodes",
+        "orig_type",
+        "syms",
+        "user_selection",
+        "user_value",
+    )
+
+    #
+    # Public interface
+    #
+
+    @property
+    def type(self):
+        """
+        Returns the type of the choice. See Symbol.type.
+        """
+        if self.orig_type is TRISTATE and not self.kconfig.modules.tri_value:
+            return BOOL
+        return self.orig_type
+
+    @property
+    def str_value(self):
+        """
+        See the class documentation.
+        """
+        return TRI_TO_STR[self.tri_value]
+
+    @property
+    def tri_value(self):
+        """
+        See the class documentation.
+        """
+        # This emulates a reverse dependency of 'm && visibility' for
+        # non-optional choices, which is how the C implementation does it
+
+        val = 0 if self.is_optional else 1
+
+        if self.user_value is not None:
+            val = max(val, self.user_value)
+
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        val = min(val, self.visibility)
+
+        # Promote m to y for boolean choices
+        return 2 if val == 1 and self.type is BOOL else val
+
+    @property
+    def assignable(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_assignable is None:
+            self._cached_assignable = self._assignable()
+        return self._cached_assignable
+
+    @property
+    def visibility(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_vis is None:
+            self._cached_vis = _visibility(self)
+        return self._cached_vis
+
+    @property
+    def selection(self):
+        """
+        See the class documentation.
+        """
+        if self._cached_selection is _NO_CACHED_SELECTION:
+            self._cached_selection = self._selection()
+        return self._cached_selection
+
+    def set_value(self, value):
+        """
+        Sets the user value (mode) of the choice. Like for Symbol.set_value(),
+        the visibility might truncate the value. Choices without the 'optional'
+        attribute (is_optional) can never be in n mode, but 0/"n" is still
+        accepted since it's not a malformed value (though it will have no
+        effect).
+
+        Returns True if the value is valid for the type of the choice, and
+        False otherwise. This only looks at the form of the value. Check the
+        Choice.assignable attribute to see what values are currently in range
+        and would actually be reflected in the mode of the choice.
+        """
+        if value in STR_TO_TRI:
+            value = STR_TO_TRI[value]
+
+        if value == self.user_value:
+            # We know the value must be valid if it was successfully set
+            # previously
+            self._was_set = True
+            return True
+
+        if not (self.orig_type is BOOL     and value in (2, 0) or
+                self.orig_type is TRISTATE and value in TRI_TO_STR):
+
+            # Display tristate values as n, m, y in the warning
+            self.kconfig._warn(
+                "the value {} is invalid for {}, which has type {} -- "
+                "assignment ignored"
+                .format(TRI_TO_STR[value] if value in TRI_TO_STR else
+                            "'{}'".format(value),
+                        _name_and_loc(self), TYPE_TO_STR[self.orig_type]))
+
+            return False
+
+        self.user_value = value
+        self._was_set = True
+        self._rec_invalidate()
+
+        return True
+
+    def unset_value(self):
+        """
+        Resets the user value (mode) and user selection of the Choice, as if
+        the user had never touched the mode or any of the choice symbols.
+        """
+        if self.user_value is not None or self.user_selection:
+            self.user_value = self.user_selection = None
+            self._rec_invalidate()
+
+    @property
+    def referenced(self):
+        """
+        See the class documentation.
+        """
+        return {item for node in self.nodes for item in node.referenced}
+
+    @property
+    def orig_defaults(self):
+        """
+        See the class documentation.
+        """
+        return [d for node in self.nodes for d in node.orig_defaults]
+
+    def __repr__(self):
+        """
+        Returns a string with information about the choice when it is evaluated
+        on e.g. the interactive Python prompt.
+        """
+        fields = ["choice " + self.name if self.name else "choice",
+                  TYPE_TO_STR[self.type]]
+        add = fields.append
+
+        for node in self.nodes:
+            if node.prompt:
+                add('"{}"'.format(node.prompt[0]))
+
+        add("mode " + self.str_value)
+
+        if self.user_value is not None:
+            add('user mode {}'.format(TRI_TO_STR[self.user_value]))
+
+        if self.selection:
+            add("{} selected".format(self.selection.name))
+
+        if self.user_selection:
+            user_sel_str = "{} selected by user" \
+                           .format(self.user_selection.name)
+
+            if self.selection is not self.user_selection:
+                user_sel_str += " (overridden)"
+
+            add(user_sel_str)
+
+        add("visibility " + TRI_TO_STR[self.visibility])
+
+        if self.is_optional:
+            add("optional")
+
+        for node in self.nodes:
+            add("{}:{}".format(node.filename, node.linenr))
+
+        return "<{}>".format(", ".join(fields))
+
+    def __str__(self):
+        """
+        Returns a string representation of the choice when it is printed.
+        Matches the Kconfig format (though without the contained choice
+        symbols), with any parent dependencies propagated to the 'depends on'
+        condition.
+
+        The returned string does not end in a newline.
+
+        See Symbol.__str__() as well.
+        """
+        return self.custom_str(standard_sc_expr_str)
+
+    def custom_str(self, sc_expr_str_fn):
+        """
+        Works like Choice.__str__(), but allows a custom format to be used for
+        all symbol/choice references. See expr_str().
+        """
+        return "\n\n".join(node.custom_str(sc_expr_str_fn)
+                           for node in self.nodes)
+
+    #
+    # Private methods
+    #
+
+    def __init__(self):
+        """
+        Choice constructor -- not intended to be called directly by Kconfiglib
+        clients.
+        """
+        # These attributes are always set on the instance from outside and
+        # don't need defaults:
+        #   direct_dep
+        #   kconfig
+
+        # - UNKNOWN == 0
+        # - _visited is used during dep. loop detection
+        self.orig_type = self._visited = 0
+
+        self.nodes = []
+
+        self.syms = []
+        self.defaults = []
+
+        self.name = \
+        self.user_value = self.user_selection = \
+        self._cached_vis = self._cached_assignable = None
+
+        self._cached_selection = _NO_CACHED_SELECTION
+
+        # is_constant is checked by _make_depend_on(). Just set it to avoid
+        # having to special-case choices.
+        self.is_constant = self.is_optional = False
+
+        # See Kconfig._build_dep()
+        self._dependents = set()
+
+    def _assignable(self):
+        # Worker function for the 'assignable' attribute
+
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        vis = self.visibility
+
+        if not vis:
+            return ()
+
+        if vis == 2:
+            if not self.is_optional:
+                return (2,) if self.type is BOOL else (1, 2)
+            return (0, 2) if self.type is BOOL else (0, 1, 2)
+
+        # vis == 1
+
+        return (0, 1) if self.is_optional else (1,)
+
+    def _selection(self):
+        # Worker function for the 'selection' attribute
+
+        # Warning: See Symbol._rec_invalidate(), and note that this is a hidden
+        # function call (property magic)
+        if self.tri_value != 2:
+            # Not in y mode, so no selection
+            return None
+
+        # Use the user selection if it's visible
+        if self.user_selection and self.user_selection.visibility:
+            return self.user_selection
+
+        # Otherwise, check if we have a default
+        return self._selection_from_defaults()
+
+    def _selection_from_defaults(self):
+        # Check if we have a default
+        for sym, cond in self.defaults:
+            # The default symbol must be visible too
+            if expr_value(cond) and sym.visibility:
+                return sym
+
+        # Otherwise, pick the first visible symbol, if any
+        for sym in self.syms:
+            if sym.visibility:
+                return sym
+
+        # Couldn't find a selection
+        return None
+
+    def _invalidate(self):
+        self._cached_vis = self._cached_assignable = None
+        self._cached_selection = _NO_CACHED_SELECTION
+
+    def _rec_invalidate(self):
+        # See Symbol._rec_invalidate()
+
+        self._invalidate()
+
+        for item in self._dependents:
+            if item._cached_vis is not None:
+                item._rec_invalidate()
+
+
+class MenuNode(object):
+    """
+    Represents a menu node in the configuration. This corresponds to an entry
+    in e.g. the 'make menuconfig' interface, though non-visible choices, menus,
+    and comments also get menu nodes. If a symbol or choice is defined in
+    multiple locations, it gets one menu node for each location.
+
+    The top-level menu node, corresponding to the implicit top-level menu, is
+    available in Kconfig.top_node.
+
+    The menu nodes for a Symbol or Choice can be found in the
+    Symbol/Choice.nodes attribute. Menus and comments are represented as plain
+    menu nodes, with their text stored in the prompt attribute (prompt[0]).
+    This mirrors the C implementation.
+
+    The following attributes are available on MenuNode instances. They should
+    be viewed as read-only.
+
+    item:
+      Either a Symbol, a Choice, or one of the constants MENU and COMMENT.
+      Menus and comments are represented as plain menu nodes. Ifs are collapsed
+      (matching the C implementation) and do not appear in the final menu tree.
+
+    next:
+      The following menu node. None if there is no following node.
+
+    list:
+      The first child menu node. None if there are no children.
+
+      Choices and menus naturally have children, but Symbols can also have
+      children because of menus created automatically from dependencies (see
+      kconfig-language.txt).
+
+    parent:
+      The parent menu node. None if there is no parent.
+
+    prompt:
+      A (string, cond) tuple with the prompt for the menu node and its
+      conditional expression (which is self.kconfig.y if there is no
+      condition). None if there is no prompt.
+
+      For symbols and choices, the prompt is stored in the MenuNode rather than
+      the Symbol or Choice instance. For menus and comments, the prompt holds
+      the text.
+
+    defaults:
+      The 'default' properties for this particular menu node. See
+      symbol.defaults.
+
+      When evaluating defaults, you should use Symbol/Choice.defaults instead,
+      as it include properties from all menu nodes (a symbol/choice can have
+      multiple definition locations/menu nodes). MenuNode.defaults is meant for
+      documentation generation.
+
+    selects:
+      Like MenuNode.defaults, for selects.
+
+    implies:
+      Like MenuNode.defaults, for implies.
+
+    ranges:
+      Like MenuNode.defaults, for ranges.
+
+    orig_prompt:
+    orig_defaults:
+    orig_selects:
+    orig_implies:
+    orig_ranges:
+      These work the like the corresponding attributes without orig_*, but omit
+      any dependencies propagated from 'depends on' and surrounding 'if's (the
+      direct dependencies, stored in MenuNode.dep).
+
+      One use for this is generating less cluttered documentation, by only
+      showing the direct dependencies in one place.
+
+    help:
+      The help text for the menu node for Symbols and Choices. None if there is
+      no help text. Always stored in the node rather than the Symbol or Choice.
+      It is possible to have a separate help text at each location if a symbol
+      is defined in multiple locations.
+
+      Trailing whitespace (including a final newline) is stripped from the help
+      text. This was not the case before Kconfiglib 10.21.0, where the format
+      was undocumented.
+
+    dep:
+      The direct ('depends on') dependencies for the menu node, or
+      self.kconfig.y if there are no direct dependencies.
+
+      This attribute includes any dependencies from surrounding menus and ifs.
+      Those get propagated to the direct dependencies, and the resulting direct
+      dependencies in turn get propagated to the conditions of all properties.
+
+      If a symbol or choice is defined in multiple locations, only the
+      properties defined at a particular location get the corresponding
+      MenuNode.dep dependencies propagated to them.
+
+    visibility:
+      The 'visible if' dependencies for the menu node (which must represent a
+      menu), or self.kconfig.y if there are no 'visible if' dependencies.
+      'visible if' dependencies are recursively propagated to the prompts of
+      symbols and choices within the menu.
+
+    referenced:
+      A set() with all symbols and choices referenced in the properties and
+      property conditions of the menu node.
+
+      Also includes dependencies inherited from surrounding menus and ifs.
+      Choices appear in the dependencies of choice symbols.
+
+    is_menuconfig:
+      Set to True if the children of the menu node should be displayed in a
+      separate menu. This is the case for the following items:
+
+        - Menus (node.item == MENU)
+
+        - Choices
+
+        - Symbols defined with the 'menuconfig' keyword. The children come from
+          implicitly created submenus, and should be displayed in a separate
+          menu rather than being indented.
+
+      'is_menuconfig' is just a hint on how to display the menu node. It's
+      ignored internally by Kconfiglib, except when printing symbols.
+
+    filename/linenr:
+      The location where the menu node appears. The filename is relative to
+      $srctree (or to the current directory if $srctree isn't set), except
+      absolute paths are used for paths outside $srctree.
+
+    include_path:
+      A tuple of (filename, linenr) tuples, giving the locations of the
+      'source' statements via which the Kconfig file containing this menu node
+      was included. The first element is the location of the 'source' statement
+      in the top-level Kconfig file passed to Kconfig.__init__(), etc.
+
+      Note that the Kconfig file of the menu node itself isn't included. Check
+      'filename' and 'linenr' for that.
+
+    kconfig:
+      The Kconfig instance the menu node is from.
+    """
+    __slots__ = (
+        "dep",
+        "filename",
+        "help",
+        "include_path",
+        "is_menuconfig",
+        "item",
+        "kconfig",
+        "linenr",
+        "list",
+        "next",
+        "parent",
+        "prompt",
+        "visibility",
+
+        # Properties
+        "defaults",
+        "selects",
+        "implies",
+        "ranges",
+    )
+
+    def __init__(self):
+        # Properties defined on this particular menu node. A local 'depends on'
+        # only applies to these, in case a symbol is defined in multiple
+        # locations.
+        self.defaults = []
+        self.selects = []
+        self.implies = []
+        self.ranges = []
+
+    @property
+    def orig_prompt(self):
+        """
+        See the class documentation.
+        """
+        if not self.prompt:
+            return None
+        return (self.prompt[0], self._strip_dep(self.prompt[1]))
+
+    @property
+    def orig_defaults(self):
+        """
+        See the class documentation.
+        """
+        return [(default, self._strip_dep(cond))
+                for default, cond in self.defaults]
 
-        if self.is_choice_sym:
-            self.parent._invalidate()
+    @property
+    def orig_selects(self):
+        """
+        See the class documentation.
+        """
+        return [(select, self._strip_dep(cond))
+                for select, cond in self.selects]
 
-        self.cached_val = None
-        self.cached_visibility = None
+    @property
+    def orig_implies(self):
+        """
+        See the class documentation.
+        """
+        return [(imply, self._strip_dep(cond))
+                for imply, cond in self.implies]
 
-    def _invalidate_dependent(self):
-        for sym in self._get_dependent():
-            sym._invalidate()
+    @property
+    def orig_ranges(self):
+        """
+        See the class documentation.
+        """
+        return [(low, high, self._strip_dep(cond))
+                for low, high, cond in self.ranges]
 
-    def _set_user_value_no_invalidate(self, v, suppress_load_warnings):
-        """Like set_user_value(), but does not invalidate any symbols.
+    @property
+    def referenced(self):
+        """
+        See the class documentation.
+        """
+        # self.dep is included to catch dependencies from a lone 'depends on'
+        # when there are no properties to propagate it to
+        res = expr_items(self.dep)
 
-        suppress_load_warnings: some warnings are annoying when loading a
-           .config that can be helpful when manually invoking set_user_value().
-           This flag is set to True to suppress such warnings.
+        if self.prompt:
+            res |= expr_items(self.prompt[1])
 
-           Perhaps this could be made optional for load_config() instead."""
+        if self.item is MENU:
+            res |= expr_items(self.visibility)
 
-        if self.is_special_:
-            if self.is_from_env:
-                self.config._warn('attempt to assign the value "{0}" to the '
-                                  'symbol {1}, which gets its value from the '
-                                  'environment. Assignment ignored.'
-                                  .format(v, self.name))
-            else:
-                self.config._warn('attempt to assign the value "{0}" to the '
-                                  'special symbol {1}. Assignment ignored.'
-                                  .format(v, self.name))
-            return
+        for value, cond in self.defaults:
+            res |= expr_items(value)
+            res |= expr_items(cond)
 
-        if not self.is_defined_:
-            filename, linenr = self.ref_locations[0]
-            if self.config.print_undef_assign:
-                _stderr_msg('note: attempt to assign the value "{0}" to {1}, '
-                            "which is referenced at {2}:{3} but never "
-                            "defined. Assignment ignored."
-                            .format(v, self.name, filename, linenr))
-            return
+        for value, cond in self.selects:
+            res.add(value)
+            res |= expr_items(cond)
 
-        # Check if the value is valid for our type
-        if not ((self.type == BOOL     and (v == "y" or v == "n")   ) or
-                (self.type == TRISTATE and (v == "y" or v == "m" or
-                                            v == "n")               ) or
-                (self.type == STRING                                ) or
-                (self.type == INT      and _is_base_n(v, 10)        ) or
-                (self.type == HEX      and _is_base_n(v, 16)        )):
-            self.config._warn('the value "{0}" is invalid for {1}, which has '
-                              "type {2}. Assignment ignored."
-                              .format(v, self.name, TYPENAME[self.type]))
-            return
+        for value, cond in self.implies:
+            res.add(value)
+            res |= expr_items(cond)
 
-        if not self.prompts and not suppress_load_warnings:
-            self.config._warn('assigning "{0}" to the symbol {1} which '
-                              'lacks prompts and thus has visibility "n". '
-                              'The assignment will have no effect.'
-                              .format(v, self.name))
+        for low, high, cond in self.ranges:
+            res.add(low)
+            res.add(high)
+            res |= expr_items(cond)
 
-        self.user_val = v
+        return res
 
-        if self.is_choice_sym and (self.type == BOOL or self.type == TRISTATE):
-            choice = self.parent
-            if v == "y":
-                choice.user_val = self
-                choice.user_mode = "y"
-            elif v == "m":
-                choice.user_val = None
-                choice.user_mode = "m"
+    def __repr__(self):
+        """
+        Returns a string with information about the menu node when it is
+        evaluated on e.g. the interactive Python prompt.
+        """
+        fields = []
+        add = fields.append
 
-    def _unset_user_value_no_recursive_invalidate(self):
-        self._invalidate()
-        self.user_val = None
+        if self.item.__class__ is Symbol:
+            add("menu node for symbol " + self.item.name)
 
-        if self.is_choice_sym:
-            self.parent._unset_user_value()
+        elif self.item.__class__ is Choice:
+            s = "menu node for choice"
+            if self.item.name is not None:
+                s += " " + self.item.name
+            add(s)
 
-    def _make_conf(self, append_fn):
-        if self.already_written:
-            return
+        elif self.item is MENU:
+            add("menu node for menu")
 
-        self.already_written = True
+        else:  # self.item is COMMENT
+            add("menu node for comment")
 
-        # Note: write_to_conf is determined in get_value()
-        val = self.get_value()
-        if not self.write_to_conf:
-            return
+        if self.prompt:
+            add('prompt "{}" (visibility {})'.format(
+                self.prompt[0], TRI_TO_STR[expr_value(self.prompt[1])]))
+
+        if self.item.__class__ is Symbol and self.is_menuconfig:
+            add("is menuconfig")
+
+        add("deps " + TRI_TO_STR[expr_value(self.dep)])
+
+        if self.item is MENU:
+            add("'visible if' deps " + TRI_TO_STR[expr_value(self.visibility)])
+
+        if self.item.__class__ in _SYMBOL_CHOICE and self.help is not None:
+            add("has help")
+
+        if self.list:
+            add("has child")
+
+        if self.next:
+            add("has next")
+
+        add("{}:{}".format(self.filename, self.linenr))
+
+        return "<{}>".format(", ".join(fields))
+
+    def __str__(self):
+        """
+        Returns a string representation of the menu node. Matches the Kconfig
+        format, with any parent dependencies propagated to the 'depends on'
+        condition.
+
+        The output could (almost) be fed back into a Kconfig parser to redefine
+        the object associated with the menu node. See the module documentation
+        for a gotcha related to choice symbols.
+
+        For symbols and choices with multiple menu nodes (multiple definition
+        locations), properties that aren't associated with a particular menu
+        node are shown on all menu nodes ('option env=...', 'optional' for
+        choices, etc.).
+
+        The returned string does not end in a newline.
+        """
+        return self.custom_str(standard_sc_expr_str)
+
+    def custom_str(self, sc_expr_str_fn):
+        """
+        Works like MenuNode.__str__(), but allows a custom format to be used
+        for all symbol/choice references. See expr_str().
+        """
+        return self._menu_comment_node_str(sc_expr_str_fn) \
+               if self.item in _MENU_COMMENT else \
+               self._sym_choice_node_str(sc_expr_str_fn)
 
-        if self.type == BOOL or self.type == TRISTATE:
-            append_fn("{0}{1}={2}".format(self.config.config_prefix, self.name, val)
-                      if val == "y" or val == "m" else
-                      "# {0}{1} is not set".format(self.config.config_prefix, self.name))
+    def _menu_comment_node_str(self, sc_expr_str_fn):
+        s = '{} "{}"'.format("menu" if self.item is MENU else "comment",
+                             self.prompt[0])
 
-        elif self.type == INT or self.type == HEX:
-            append_fn("{0}{1}={2}".format(self.config.config_prefix, self.name, val))
+        if self.dep is not self.kconfig.y:
+            s += "\n\tdepends on {}".format(expr_str(self.dep, sc_expr_str_fn))
 
-        elif self.type == STRING:
-            # Escape \ and "
-            append_fn('{0}{1}="{2}"'
-                      .format(self.config.config_prefix, self.name,
-                              val.replace("\\", "\\\\").replace('"', '\\"')))
+        if self.item is MENU and self.visibility is not self.kconfig.y:
+            s += "\n\tvisible if {}".format(expr_str(self.visibility,
+                                                     sc_expr_str_fn))
 
+        return s
+
+    def _sym_choice_node_str(self, sc_expr_str_fn):
+        def indent_add(s):
+            lines.append("\t" + s)
+
+        def indent_add_cond(s, cond):
+            if cond is not self.kconfig.y:
+                s += " if " + expr_str(cond, sc_expr_str_fn)
+            indent_add(s)
+
+        sc = self.item
+
+        if sc.__class__ is Symbol:
+            lines = [("menuconfig " if self.is_menuconfig else "config ")
+                     + sc.name]
         else:
-            _internal_error("Internal error while creating .config: unknown "
-                            'type "{0}".'.format(self.type))
+            lines = ["choice " + sc.name if sc.name else "choice"]
 
-    def _get_dependent(self):
-        """Returns the set of symbols that should be invalidated if the value
-        of the symbol changes, because they might be affected by the change.
-        Note that this is an internal API -- it's probably of limited
-        usefulness to clients."""
-        if self.cached_deps is not None:
-            return self.cached_deps
+        if sc.orig_type and not self.prompt:  # sc.orig_type != UNKNOWN
+            # If there's a prompt, we'll use the '<type> "prompt"' shorthand
+            # instead
+            indent_add(TYPE_TO_STR[sc.orig_type])
 
-        res = set(self.dep)
-        for s in self.dep:
-            res |= s._get_dependent()
+        if self.prompt:
+            if sc.orig_type:
+                prefix = TYPE_TO_STR[sc.orig_type]
+            else:
+                # Symbol defined without a type (which generates a warning)
+                prefix = "prompt"
 
-        if self.is_choice_sym:
-            # Choice symbols also depend (recursively) on their siblings. The
-            # siblings are not included in 'dep' to avoid dependency loops.
-            for sibling in self.parent.actual_symbols:
-                if sibling is not self:
-                    res.add(sibling)
-                    res |= sibling.dep
-                    for s in sibling.dep:
-                        res |= s._get_dependent()
+            indent_add_cond(prefix + ' "{}"'.format(escape(self.prompt[0])),
+                            self.orig_prompt[1])
 
-        self.cached_deps = res
-        return res
+        if sc.__class__ is Symbol:
+            if sc.is_allnoconfig_y:
+                indent_add("option allnoconfig_y")
 
-    def _has_auto_menu_dep_on(self, on):
-        """See Choice._determine_actual_symbols()."""
-        if not isinstance(self.parent, Choice):
-            _internal_error("Attempt to determine auto menu dependency for "
-                            "symbol ouside of choice.")
+            if sc is sc.kconfig.defconfig_list:
+                indent_add("option defconfig_list")
 
-        if not self.prompts:
-            # If we have no prompt, use the menu dependencies instead (what was
-            # specified with 'depends on')
-            return self.menu_dep is not None and \
-                   self.config._expr_depends_on(self.menu_dep, on)
+            if sc.env_var is not None:
+                indent_add('option env="{}"'.format(sc.env_var))
 
-        for _, cond_expr in self.prompts:
-            if self.config._expr_depends_on(cond_expr, on):
-                return True
+            if sc is sc.kconfig.modules:
+                indent_add("option modules")
 
-        return False
+            for low, high, cond in self.orig_ranges:
+                indent_add_cond(
+                    "range {} {}".format(sc_expr_str_fn(low),
+                                         sc_expr_str_fn(high)),
+                    cond)
 
-class Menu(Item):
+        for default, cond in self.orig_defaults:
+            indent_add_cond("default " + expr_str(default, sc_expr_str_fn),
+                            cond)
 
-    """Represents a menu statement."""
+        if sc.__class__ is Choice and sc.is_optional:
+            indent_add("optional")
 
-    #
-    # Public interface
-    #
+        if sc.__class__ is Symbol:
+            for select, cond in self.orig_selects:
+                indent_add_cond("select " + sc_expr_str_fn(select), cond)
 
-    def get_config(self):
-        """Return the Config instance this menu is from."""
-        return self.config
+            for imply, cond in self.orig_implies:
+                indent_add_cond("imply " + sc_expr_str_fn(imply), cond)
 
-    def get_title(self):
-        """Returns the title text of the menu."""
-        return self.title
+        if self.dep is not sc.kconfig.y:
+            indent_add("depends on " + expr_str(self.dep, sc_expr_str_fn))
 
-    def get_parent(self):
-        """Returns the menu or choice statement that contains the menu, or
-        None if the menu is at the top level. Note that if statements are
-        treated as syntactic sugar and do not have an explicit class
-        representation."""
-        return self.parent
+        if self.help is not None:
+            indent_add("help")
+            for line in self.help.splitlines():
+                indent_add("  " + line)
 
-    def get_location(self):
-        """Returns the location of the menu as a (filename, linenr) tuple,
-        where filename is a string and linenr an int."""
-        return (self.filename, self.linenr)
+        return "\n".join(lines)
 
-    def get_items(self, recursive=False):
-        """Returns a list containing the items (symbols, menus, choice
-        statements and comments) in in the menu, in the same order that the
-        items appear within the menu.
+    def _strip_dep(self, expr):
+        # Helper function for removing MenuNode.dep from 'expr'. Uses two
+        # pieces of internal knowledge: (1) Expressions are reused rather than
+        # copied, and (2) the direct dependencies always appear at the end.
 
-        recursive (default: False): True if items contained in items within the
-           menu should be included recursively (preorder)."""
+        # ... if dep -> ... if y
+        if self.dep is expr:
+            return self.kconfig.y
 
-        if not recursive:
-            return self.block
+        # (AND, X, dep) -> X
+        if expr.__class__ is tuple and expr[0] is AND and expr[2] is self.dep:
+            return expr[1]
 
-        res = []
-        for item in self.block:
-            res.append(item)
-            if isinstance(item, Menu):
-                res.extend(item.get_items(True))
-            elif isinstance(item, Choice):
-                res.extend(item.get_items())
-        return res
+        return expr
+
+
+class Variable(object):
+    """
+    Represents a preprocessor variable/function.
+
+    The following attributes are available:
+
+    name:
+      The name of the variable.
+
+    value:
+      The unexpanded value of the variable.
+
+    expanded_value:
+      The expanded value of the variable. For simple variables (those defined
+      with :=), this will equal 'value'. Accessing this property will raise a
+      KconfigError if the expansion seems to be stuck in a loop.
+
+      Accessing this field is the same as calling expanded_value_w_args() with
+      no arguments. I hadn't considered function arguments when adding it. It
+      is retained for backwards compatibility though.
+
+    is_recursive:
+      True if the variable is recursive (defined with =).
+    """
+    __slots__ = (
+        "_n_expansions",
+        "is_recursive",
+        "kconfig",
+        "name",
+        "value",
+    )
+
+    @property
+    def expanded_value(self):
+        """
+        See the class documentation.
+        """
+        return self.expanded_value_w_args()
+
+    def expanded_value_w_args(self, *args):
+        """
+        Returns the expanded value of the variable/function. Any arguments
+        passed will be substituted for $(1), $(2), etc.
 
-    def get_symbols(self, recursive=False):
-        """Returns a list containing the symbols in the menu, in the same order
-        that they appear within the menu.
+        Raises a KconfigError if the expansion seems to be stuck in a loop.
+        """
+        return self.kconfig._fn_val((self.name,) + args)
+
+    def __repr__(self):
+        return "<variable {}, {}, value '{}'>" \
+               .format(self.name,
+                       "recursive" if self.is_recursive else "immediate",
+                       self.value)
+
+
+class KconfigError(Exception):
+    """
+    Exception raised for Kconfig-related errors.
 
-        recursive (default: False): True if symbols contained in items within
-           the menu should be included recursively."""
+    KconfigError and KconfigSyntaxError are the same class. The
+    KconfigSyntaxError alias is only maintained for backwards compatibility.
+    """
 
-        return [item for item in self.get_items(recursive) if
-                isinstance(item, Symbol)]
+KconfigSyntaxError = KconfigError  # Backwards compatibility
 
-    def get_visibility(self):
-        """Returns the visibility of the menu. This also affects the visibility
-        of subitems. See also Symbol.get_visibility()."""
-        return self.config._eval_expr(self.dep_expr)
 
-    def get_visible_if_visibility(self):
-        """Returns the visibility the menu gets from its 'visible if'
-        condition. "y" if the menu has no 'visible if' condition."""
-        return self.config._eval_expr(self.visible_if_expr)
+class InternalError(Exception):
+    "Never raised. Kept around for backwards compatibility."
 
-    def get_referenced_symbols(self, refs_from_enclosing=False):
-        """See Symbol.get_referenced_symbols()."""
-        return self.all_referenced_syms if refs_from_enclosing else \
-               self.referenced_syms
+
+# Workaround:
+#
+# If 'errno' and 'strerror' are set on IOError, then __str__() always returns
+# "[Errno <errno>] <strerror>", ignoring any custom message passed to the
+# constructor. By defining our own subclass, we can use a custom message while
+# also providing 'errno', 'strerror', and 'filename' to scripts.
+class _KconfigIOError(IOError):
+    def __init__(self, ioerror, msg):
+        self.msg = msg
+        super(_KconfigIOError, self).__init__(
+            ioerror.errno, ioerror.strerror, ioerror.filename)
 
     def __str__(self):
-        """Returns a string containing various information about the menu."""
-        depends_on_str = self.config._expr_val_str(self.orig_deps,
-                                                   "(no dependencies)")
-        visible_if_str = self.config._expr_val_str(self.visible_if_expr,
-                                                   "(no dependencies)")
+        return self.msg
+
+
+#
+# Public functions
+#
 
-        additional_deps_str = " " + \
-          self.config._expr_val_str(self.deps_from_containing,
-                                    "(no additional dependencies)")
 
-        return _lines("Menu",
-                      "Title                     : " + self.title,
-                      "'depends on' dependencies : " + depends_on_str,
-                      "'visible if' dependencies : " + visible_if_str,
-                      "Additional dependencies from enclosing menus and "
-                        "ifs:",
-                      additional_deps_str,
-                      "Location: {0}:{1}".format(self.filename, self.linenr))
+def expr_value(expr):
+    """
+    Evaluates the expression 'expr' to a tristate value. Returns 0 (n), 1 (m),
+    or 2 (y).
 
-    #
-    # Private methods
+    'expr' must be an already-parsed expression from a Symbol, Choice, or
+    MenuNode property. To evaluate an expression represented as a string, use
+    Kconfig.eval_string().
+
+    Passing subexpressions of expressions to this function works as expected.
+    """
+    if expr.__class__ is not tuple:
+        return expr.tri_value
+
+    if expr[0] is AND:
+        v1 = expr_value(expr[1])
+        # Short-circuit the n case as an optimization (~5% faster
+        # allnoconfig.py and allyesconfig.py, as of writing)
+        return 0 if not v1 else min(v1, expr_value(expr[2]))
+
+    if expr[0] is OR:
+        v1 = expr_value(expr[1])
+        # Short-circuit the y case as an optimization
+        return 2 if v1 == 2 else max(v1, expr_value(expr[2]))
+
+    if expr[0] is NOT:
+        return 2 - expr_value(expr[1])
+
+    # Relation
     #
+    # Implements <, <=, >, >= comparisons as well. These were added to
+    # kconfig in 31847b67 (kconfig: allow use of relations other than
+    # (in)equality).
 
-    def __init__(self):
-        """Menu constructor -- not intended to be called directly by
-        Kconfiglib clients."""
+    rel, v1, v2 = expr
+
+    # If both operands are strings...
+    if v1.orig_type is STRING and v2.orig_type is STRING:
+        # ...then compare them lexicographically
+        comp = _strcmp(v1.str_value, v2.str_value)
+    else:
+        # Otherwise, try to compare them as numbers
+        try:
+            comp = _sym_to_num(v1) - _sym_to_num(v2)
+        except ValueError:
+            # Fall back on a lexicographic comparison if the operands don't
+            # parse as numbers
+            comp = _strcmp(v1.str_value, v2.str_value)
 
-        self.title = None
-        self.dep_expr = None
-        self.visible_if_expr = None
-        self.block = [] # List of contained items
-        self.config = None
-        self.parent = None
+    return 2*(comp == 0 if rel is EQUAL else
+              comp != 0 if rel is UNEQUAL else
+              comp <  0 if rel is LESS else
+              comp <= 0 if rel is LESS_EQUAL else
+              comp >  0 if rel is GREATER else
+              comp >= 0)
 
-        # Dependency expression without dependencies from enclosing menus and
-        # ifs propagated
-        self.orig_deps = None
 
-        # Dependencies inherited from containing menus and ifs
-        self.deps_from_containing = None
-        # The set of symbols referenced by this menu (see
-        # get_referenced_symbols())
-        self.referenced_syms = set()
-        # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and ifs
-        self.all_referenced_syms = None
+def standard_sc_expr_str(sc):
+    """
+    Standard symbol/choice printing function. Uses plain Kconfig syntax, and
+    displays choices as <choice> (or <choice NAME>, for named choices).
 
-        self.filename = None
-        self.linenr = None
+    See expr_str().
+    """
+    if sc.__class__ is Symbol:
+        if sc.is_constant and sc.name not in STR_TO_TRI:
+            return '"{}"'.format(escape(sc.name))
+        return sc.name
 
-    def _make_conf(self, append_fn):
-        if self.config._eval_expr(self.dep_expr) != "n" and \
-           self.config._eval_expr(self.visible_if_expr) != "n":
-            append_fn("\n#\n# {0}\n#".format(self.title))
-        _make_block_conf(self.block, append_fn)
+    return "<choice {}>".format(sc.name) if sc.name else "<choice>"
 
-class Choice(Item):
 
-    """Represents a choice statement. A choice can be in one of three modes:
+def expr_str(expr, sc_expr_str_fn=standard_sc_expr_str):
+    """
+    Returns the string representation of the expression 'expr', as in a Kconfig
+    file.
 
-    "n" - The choice is not visible and no symbols can be selected.
+    Passing subexpressions of expressions to this function works as expected.
 
-    "m" - Any number of symbols can be set to "m". The rest will be "n". This
-          is safe since potentially conflicting options don't actually get
-          compiled into the kernel simultaneously with "m".
+    sc_expr_str_fn (default: standard_sc_expr_str):
+      This function is called for every symbol/choice (hence "sc") appearing in
+      the expression, with the symbol/choice as the argument. It is expected to
+      return a string to be used for the symbol/choice.
 
-    "y" - One symbol will be "y" while the rest are "n".
+      This can be used e.g. to turn symbols/choices into links when generating
+      documentation, or for printing the value of each symbol/choice after it.
 
-    Only tristate choices can be in "m" mode, and the visibility of the choice
-    is an upper bound on the mode, so that e.g. a choice that depends on a
-    symbol with value "m" will be in "m" mode.
+      Note that quoted values are represented as constants symbols
+      (Symbol.is_constant == True).
+    """
+    if expr.__class__ is not tuple:
+        return sc_expr_str_fn(expr)
 
-    The mode changes automatically when a value is assigned to a symbol within
-    the choice.
+    if expr[0] is AND:
+        return "{} && {}".format(_parenthesize(expr[1], OR, sc_expr_str_fn),
+                                 _parenthesize(expr[2], OR, sc_expr_str_fn))
 
-    See Symbol.get_visibility() too."""
+    if expr[0] is OR:
+        # This turns A && B || C && D into "(A && B) || (C && D)", which is
+        # redundant, but more readable
+        return "{} || {}".format(_parenthesize(expr[1], AND, sc_expr_str_fn),
+                                 _parenthesize(expr[2], AND, sc_expr_str_fn))
 
-    #
-    # Public interface
+    if expr[0] is NOT:
+        if expr[1].__class__ is tuple:
+            return "!({})".format(expr_str(expr[1], sc_expr_str_fn))
+        return "!" + sc_expr_str_fn(expr[1])  # Symbol
+
+    # Relation
     #
+    # Relation operands are always symbols (quoted strings are constant
+    # symbols)
+    return "{} {} {}".format(sc_expr_str_fn(expr[1]), REL_TO_STR[expr[0]],
+                             sc_expr_str_fn(expr[2]))
+
 
-    def get_config(self):
-        """Returns the Config instance this choice is from."""
-        return self.config
+def expr_items(expr):
+    """
+    Returns a set() of all items (symbols and choices) that appear in the
+    expression 'expr'.
+
+    Passing subexpressions of expressions to this function works as expected.
+    """
+    res = set()
 
-    def get_name(self):
-        """For named choices, returns the name. Returns None for unnamed
-        choices. No named choices appear anywhere in the kernel Kconfig files
-        as of Linux 3.7.0-rc8."""
-        return self.name
+    def rec(subexpr):
+        if subexpr.__class__ is tuple:
+            # AND, OR, NOT, or relation
 
-    def get_type(self):
-        """Returns the type of the choice. See Symbol.get_type()."""
-        return self.type
+            rec(subexpr[1])
 
-    def get_prompts(self):
-        """Returns a list of prompts defined for the choice, in the order they
-        appear in the configuration files. Returns the empty list for choices
-        with no prompt.
+            # NOTs only have a single operand
+            if subexpr[0] is not NOT:
+                rec(subexpr[2])
 
-        This list will have a single entry for the vast majority of choices
-        having prompts, but having multiple prompts for a single choice is
-        possible through having multiple 'choice' entries for it (though I'm
-        not sure if that ever happens in practice)."""
-        return [prompt for prompt, _ in self.orig_prompts]
+        else:
+            # Symbol or choice
+            res.add(subexpr)
 
-    def get_help(self):
-        """Returns the help text of the choice, or None if the choice has no
-        help text."""
-        return self.help
+    rec(expr)
+    return res
 
-    def get_parent(self):
-        """Returns the menu or choice statement that contains the choice, or
-        None if the choice is at the top level. Note that if statements are
-        treated as syntactic sugar and do not have an explicit class
-        representation."""
-        return self.parent
 
-    def get_def_locations(self):
-        """Returns a list of (filename, linenr) tuples, where filename (string)
-        and linenr (int) represent a location where the choice is defined. For
-        the vast majority of choices (all of them as of Linux 3.7.0-rc8) this
-        list will only contain one element, but its possible for named choices
-        to be defined in multiple locations."""
-        return self.def_locations
+def split_expr(expr, op):
+    """
+    Returns a list containing the top-level AND or OR operands in the
+    expression 'expr', in the same (left-to-right) order as they appear in
+    the expression.
 
-    def get_selection(self):
-        """Returns the symbol selected (either by the user or through
-        defaults), or None if either no symbol is selected or the mode is not
-        "y"."""
-        if self.cached_selection is not None:
-            if self.cached_selection == NO_SELECTION:
-                return None
-            return self.cached_selection
+    This can be handy e.g. for splitting (weak) reverse dependencies
+    from 'select' and 'imply' into individual selects/implies.
 
-        if self.get_mode() != "y":
-            return self._cache_ret(None)
+    op:
+      Either AND to get AND operands, or OR to get OR operands.
 
-        # User choice available?
-        if self.user_val is not None and _get_visibility(self.user_val) == "y":
-            return self._cache_ret(self.user_val)
+      (Having this as an operand might be more future-safe than having two
+      hardcoded functions.)
 
-        if self.optional:
-            return self._cache_ret(None)
 
-        return self._cache_ret(self.get_selection_from_defaults())
+    Pseudo-code examples:
 
-    def get_selection_from_defaults(self):
-        """Like Choice.get_selection(), but acts as if no symbol has been
-        selected by the user and no 'optional' flag is in effect."""
+      split_expr( A                    , OR  )  ->  [A]
+      split_expr( A && B               , OR  )  ->  [A && B]
+      split_expr( A || B               , OR  )  ->  [A, B]
+      split_expr( A || B               , AND )  ->  [A || B]
+      split_expr( A || B || (C && D)   , OR  )  ->  [A, B, C && D]
 
-        if not self.actual_symbols:
-            return None
+      # Second || is not at the top level
+      split_expr( A || (B && (C || D)) , OR )  ->  [A, B && (C || D)]
 
-        for symbol, cond_expr in self.def_exprs:
-            if self.config._eval_expr(cond_expr) != "n":
-                chosen_symbol = symbol
-                break
+      # Parentheses don't matter as long as we stay at the top level (don't
+      # encounter any non-'op' nodes)
+      split_expr( (A || B) || C        , OR )  ->  [A, B, C]
+      split_expr( A || (B || C)        , OR )  ->  [A, B, C]
+    """
+    res = []
+
+    def rec(subexpr):
+        if subexpr.__class__ is tuple and subexpr[0] is op:
+            rec(subexpr[1])
+            rec(subexpr[2])
         else:
-            chosen_symbol = self.actual_symbols[0]
+            res.append(subexpr)
 
-        # Is the chosen symbol visible?
-        if _get_visibility(chosen_symbol) != "n":
-            return chosen_symbol
-        # Otherwise, pick the first visible symbol
-        for sym in self.actual_symbols:
-            if _get_visibility(sym) != "n":
-                return sym
-        return None
+    rec(expr)
+    return res
 
-    def get_user_selection(self):
-        """If the choice is in "y" mode and has a user-selected symbol, returns
-        that symbol. Otherwise, returns None."""
-        return self.user_val
 
-    def get_items(self):
-        """Gets all items contained in the choice in the same order as within
-        the configuration ("items" instead of "symbols" since choices and
-        comments might appear within choices. This only happens in one place as
-        of Linux 3.7.0-rc8, in drivers/usb/gadget/Kconfig)."""
-        return self.block
+def escape(s):
+    r"""
+    Escapes the string 's' in the same fashion as is done for display in
+    Kconfig format and when writing strings to a .config file. " and \ are
+    replaced by \" and \\, respectively.
+    """
+    # \ must be escaped before " to avoid double escaping
+    return s.replace("\\", r"\\").replace('"', r'\"')
 
-    def get_symbols(self):
-        """Returns a list containing the choice's symbols.
 
-        A quirk (perhaps a bug) of Kconfig is that you can put items within a
-        choice that will not be considered members of the choice insofar as
-        selection is concerned. This happens for example if one symbol within a
-        choice 'depends on' the symbol preceding it, or if you put non-symbol
-        items within choices.
+def unescape(s):
+    r"""
+    Unescapes the string 's'. \ followed by any character is replaced with just
+    that character. Used internally when reading .config files.
+    """
+    return _unescape_sub(r"\1", s)
 
-        As of Linux 3.7.0-rc8, this seems to be used intentionally in one
-        place: drivers/usb/gadget/Kconfig.
+# unescape() helper
+_unescape_sub = re.compile(r"\\(.)").sub
 
-        This function returns the "proper" symbols of the choice in the order
-        they appear in the choice, excluding such items. If you want all items
-        in the choice, use get_items()."""
-        return self.actual_symbols
 
-    def get_referenced_symbols(self, refs_from_enclosing=False):
-        """See Symbol.get_referenced_symbols()."""
-        return self.all_referenced_syms if refs_from_enclosing else \
-               self.referenced_syms
+def standard_kconfig():
+    """
+    Helper for tools. Loads the top-level Kconfig specified as the first
+    command-line argument, or "Kconfig" if there are no command-line arguments.
+    Returns the Kconfig instance.
 
-    def get_visibility(self):
-        """Returns the visibility of the choice statement: one of "n", "m" or
-        "y". This acts as an upper limit on the mode of the choice (though bool
-        choices can only have the mode "y"). See the class documentation for an
-        explanation of modes."""
-        return _get_visibility(self)
+    Exits with sys.exit() (which raises a SystemExit exception) and prints a
+    usage note to stderr if more than one command-line argument is passed.
+    """
+    if len(sys.argv) > 2:
+        sys.exit("usage: {} [Kconfig]".format(sys.argv[0]))
 
-    def get_mode(self):
-        """Returns the mode of the choice. See the class documentation for
-        an explanation of modes."""
-        minimum_mode = "n" if self.optional else "m"
-        mode = self.user_mode if self.user_mode is not None else minimum_mode
-        mode = self.config._eval_min(mode, _get_visibility(self))
+    # Only show backtraces for unexpected exceptions
+    try:
+        return Kconfig("Kconfig" if len(sys.argv) < 2 else sys.argv[1])
+    except (EnvironmentError, KconfigError) as e:
+        # Some long exception messages have extra newlines for better
+        # formatting when reported as an unhandled exception. Strip them here.
+        sys.exit(str(e).strip())
 
-        # Promote "m" to "y" for boolean choices
-        if mode == "m" and self.type == BOOL:
-            return "y"
 
-        return mode
+def standard_config_filename():
+    """
+    Helper for tools. Returns the value of KCONFIG_CONFIG (which specifies the
+    .config file to load/save) if it is set, and ".config" otherwise.
 
-    def is_optional(self):
-        """Returns True if the choice has the 'optional' flag set (and so will
-        default to "n" mode)."""
-        return self.optional
+    Calling load_config() with filename=None might give the behavior you want,
+    without having to use this function.
+    """
+    return os.getenv("KCONFIG_CONFIG", ".config")
 
-    def __str__(self):
-        """Returns a string containing various information about the choice
-        statement."""
-        return self.config._get_sym_or_choice_str(self)
 
-    #
-    # Private methods
-    #
+def load_allconfig(kconf, filename):
+    """
+    Helper for all*config. Loads (merges) the configuration file specified by
+    KCONFIG_ALLCONFIG, if any. See Documentation/kbuild/kconfig.txt in the
+    Linux kernel.
 
-    def __init__(self):
-        """Choice constructor -- not intended to be called directly by
-        Kconfiglib clients."""
+    Disables warnings for duplicated assignments within configuration files for
+    the duration of the call (kconf.warn_assign_override/warn_assign_redun = False),
+    and restores the previous warning settings at the end. The
+    KCONFIG_ALLCONFIG configuration file is expected to override symbols.
 
-        self.name = None # Yes, choices can be named
-        self.type = UNKNOWN
-        self.prompts = []
-        self.def_exprs = [] # 'default' properties
-        self.help = None # Help text
-        self.block = [] # List of contained items
-        self.config = None
-        self.parent = None
+    Exits with sys.exit() (which raises a SystemExit exception) and prints an
+    error to stderr if KCONFIG_ALLCONFIG is set but the configuration file
+    can't be opened.
 
-        self.user_val = None
-        self.user_mode = None
+    kconf:
+      Kconfig instance to load the configuration in.
 
-        # We need to filter out symbols that appear within the choice block but
-        # are not considered choice items (see
-        # Choice._determine_actual_symbols()) This list holds the "actual"
-        # choice items.
-        self.actual_symbols = []
+    filename:
+      Command-specific configuration filename - "allyes.config",
+      "allno.config", etc.
+    """
+    allconfig = os.getenv("KCONFIG_ALLCONFIG")
+    if allconfig is None:
+        return
 
-        # The prompts and default values without any dependencies from
-        # enclosing menus and ifs propagated
-        self.orig_prompts = []
-        self.orig_def_exprs = []
+    def std_msg(e):
+        # "Upcasts" a _KconfigIOError to an IOError, removing the custom
+        # __str__() message. The standard message is better here.
+        #
+        # This might also convert an OSError to an IOError in obscure cases,
+        # but it's probably not a big deal. The distinction is shaky (see
+        # PEP-3151).
+        return IOError(e.errno, e.strerror, e.filename)
 
-        # Dependencies inherited from containing menus and ifs
-        self.deps_from_containing = None
-        # The set of symbols referenced by this choice (see
-        # get_referenced_symbols())
-        self.referenced_syms = set()
-        # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and ifs
-        self.all_referenced_syms = set()
+    old_warn_assign_override = kconf.warn_assign_override
+    old_warn_assign_redun = kconf.warn_assign_redun
+    kconf.warn_assign_override = kconf.warn_assign_redun = False
 
-        # See Choice.get_def_locations()
-        self.def_locations = []
+    if allconfig in ("", "1"):
+        try:
+            print(kconf.load_config(filename, False))
+        except EnvironmentError as e1:
+            try:
+                print(kconf.load_config("all.config", False))
+            except EnvironmentError as e2:
+                sys.exit("error: KCONFIG_ALLCONFIG is set, but neither {} "
+                         "nor all.config could be opened: {}, {}"
+                         .format(filename, std_msg(e1), std_msg(e2)))
+    else:
+        try:
+            print(kconf.load_config(allconfig, False))
+        except EnvironmentError as e:
+            sys.exit("error: KCONFIG_ALLCONFIG is set to '{}', which "
+                     "could not be opened: {}"
+                     .format(allconfig, std_msg(e)))
 
-        # Cached values
-        self.cached_selection = None
-        self.cached_visibility = None
+    kconf.warn_assign_override = old_warn_assign_override
+    kconf.warn_assign_redun = old_warn_assign_redun
 
-        self.optional = False
 
-    def _determine_actual_symbols(self):
-        """If a symbol's visibility depends on the preceding symbol within a
-        choice, it is no longer viewed as a choice item. (This is quite
-        possibly a bug, but some things consciously use it... ugh. It stems
-        from automatic submenu creation.) In addition, it's possible to have
-        choices and comments within choices, and those shouldn't be considered
-        choice items either. Only drivers/usb/gadget/Kconfig seems to depend on
-        any of this. This method computes the "actual" items in the choice and
-        sets the is_choice_sym flag on them (retrieved via is_choice_symbol()).
+#
+# Internal functions
+#
 
-        Don't let this scare you: an earlier version simply checked for a
-        sequence of symbols where all symbols after the first appeared in the
-        'depends on' expression of the first, and that worked fine.  The added
-        complexity is to be future-proof in the event that
-        drivers/usb/gadget/Kconfig turns even more sinister. It might very well
-        be overkilling things (especially if that file is refactored ;)."""
 
-        # Items might depend on each other in a tree structure, so we need a
-        # stack to keep track of the current tentative parent
-        stack = []
+def _visibility(sc):
+    # Symbols and Choices have a "visibility" that acts as an upper bound on
+    # the values a user can set for them, corresponding to the visibility in
+    # e.g. 'make menuconfig'. This function calculates the visibility for the
+    # Symbol or Choice 'sc' -- the logic is nearly identical.
 
-        for item in self.block:
-            if not isinstance(item, Symbol):
-                stack = []
-                continue
+    vis = 0
 
-            while stack:
-                if item._has_auto_menu_dep_on(stack[-1]):
-                    # The item should not be viewed as a choice item, so don't
-                    # set item.is_choice_sym
-                    stack.append(item)
-                    break
-                else:
-                    stack.pop()
-            else:
-                item.is_choice_sym = True
-                self.actual_symbols.append(item)
-                stack.append(item)
+    for node in sc.nodes:
+        if node.prompt:
+            vis = max(vis, expr_value(node.prompt[1]))
 
-    def _cache_ret(self, selection):
-        # As None is used to indicate the lack of a cached value we can't use
-        # that to cache the fact that the choice has no selection. Instead, we
-        # use the symbolic constant NO_SELECTION.
-        if selection is None:
-            self.cached_selection = NO_SELECTION
-        else:
-            self.cached_selection = selection
+    if sc.__class__ is Symbol and sc.choice:
+        if sc.choice.orig_type is TRISTATE and \
+           sc.orig_type is not TRISTATE and sc.choice.tri_value != 2:
+            # Non-tristate choice symbols are only visible in y mode
+            return 0
 
-        return selection
+        if sc.orig_type is TRISTATE and vis == 1 and sc.choice.tri_value == 2:
+            # Choice symbols with m visibility are not visible in y mode
+            return 0
 
-    def _invalidate(self):
-        self.cached_selection = None
-        self.cached_visibility = None
+    # Promote m to y if we're dealing with a non-tristate (possibly due to
+    # modules being disabled)
+    if vis == 1 and sc.type is not TRISTATE:
+        return 2
 
-    def _unset_user_value(self):
-        self._invalidate()
-        self.user_val = None
-        self.user_mode = None
+    return vis
 
-    def _make_conf(self, append_fn):
-        _make_block_conf(self.block, append_fn)
 
-class Comment(Item):
+def _make_depend_on(sc, expr):
+    # Adds 'sc' (symbol or choice) as a "dependee" to all symbols in 'expr'.
+    # Constant symbols in 'expr' are skipped as they can never change value
+    # anyway.
 
-    """Represents a comment statement."""
+    if expr.__class__ is tuple:
+        # AND, OR, NOT, or relation
 
-    #
-    # Public interface
-    #
+        _make_depend_on(sc, expr[1])
 
-    def get_config(self):
-        """Returns the Config instance this comment is from."""
-        return self.config
+        # NOTs only have a single operand
+        if expr[0] is not NOT:
+            _make_depend_on(sc, expr[2])
 
-    def get_text(self):
-        """Returns the text of the comment."""
-        return self.text
+    elif not expr.is_constant:
+        # Non-constant symbol, or choice
+        expr._dependents.add(sc)
 
-    def get_parent(self):
-        """Returns the menu or choice statement that contains the comment, or
-        None if the comment is at the top level. Note that if statements are
-        treated as syntactic sugar and do not have an explicit class
-        representation."""
-        return self.parent
 
-    def get_location(self):
-        """Returns the location of the comment as a (filename, linenr) tuple,
-        where filename is a string and linenr an int."""
-        return (self.filename, self.linenr)
+def _parenthesize(expr, type_, sc_expr_str_fn):
+    # expr_str() helper. Adds parentheses around expressions of type 'type_'.
 
-    def get_visibility(self):
-        """Returns the visibility of the comment. See also
-        Symbol.get_visibility()."""
-        return self.config._eval_expr(self.dep_expr)
+    if expr.__class__ is tuple and expr[0] is type_:
+        return "({})".format(expr_str(expr, sc_expr_str_fn))
+    return expr_str(expr, sc_expr_str_fn)
 
-    def get_referenced_symbols(self, refs_from_enclosing=False):
-        """See Symbol.get_referenced_symbols()."""
-        return self.all_referenced_syms if refs_from_enclosing else \
-               self.referenced_syms
 
-    def __str__(self):
-        """Returns a string containing various information about the
-        comment."""
-        dep_str = self.config._expr_val_str(self.orig_deps,
-                                            "(no dependencies)")
+def _ordered_unique(lst):
+    # Returns 'lst' with any duplicates removed, preserving order. This hacky
+    # version seems to be a common idiom. It relies on short-circuit evaluation
+    # and set.add() returning None, which is falsy.
 
-        additional_deps_str = " " + \
-          self.config._expr_val_str(self.deps_from_containing,
-                                    "(no additional dependencies)")
+    seen = set()
+    seen_add = seen.add
+    return [x for x in lst if x not in seen and not seen_add(x)]
 
-        return _lines("Comment",
-                      "Text: "         + str(self.text),
-                      "Dependencies: " + dep_str,
-                      "Additional dependencies from enclosing menus and "
-                        "ifs:",
-                      additional_deps_str,
-                      "Location: {0}:{1}".format(self.filename, self.linenr))
 
-    #
-    # Private methods
+def _is_base_n(s, n):
+    try:
+        int(s, n)
+        return True
+    except ValueError:
+        return False
+
+
+def _strcmp(s1, s2):
+    # strcmp()-alike that returns -1, 0, or 1
+
+    return (s1 > s2) - (s1 < s2)
+
+
+def _sym_to_num(sym):
+    # expr_value() helper for converting a symbol to a number. Raises
+    # ValueError for symbols that can't be converted.
+
+    # For BOOL and TRISTATE, n/m/y count as 0/1/2. This mirrors 9059a3493ef
+    # ("kconfig: fix relational operators for bool and tristate symbols") in
+    # the C implementation.
+    return sym.tri_value if sym.orig_type in _BOOL_TRISTATE else \
+           int(sym.str_value, _TYPE_TO_BASE[sym.orig_type])
+
+
+def _touch_dep_file(path, sym_name):
+    # If sym_name is MY_SYM_NAME, touches my/sym/name.h. See the sync_deps()
+    # docstring.
+
+    sym_path = path + os.sep + sym_name.lower().replace("_", os.sep) + ".h"
+    sym_path_dir = dirname(sym_path)
+    if not exists(sym_path_dir):
+        os.makedirs(sym_path_dir, 0o755)
+
+    # A kind of truncating touch, mirroring the C tools
+    os.close(os.open(
+        sym_path, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o644))
+
+
+def _save_old(path):
+    # See write_config()
+
+    def copy(src, dst):
+        # Import as needed, to save some startup time
+        import shutil
+        shutil.copyfile(src, dst)
+
+    if islink(path):
+        # Preserve symlinks
+        copy_fn = copy
+    elif hasattr(os, "replace"):
+        # Python 3 (3.3+) only. Best choice when available, because it
+        # removes <filename>.old on both *nix and Windows.
+        copy_fn = os.replace
+    elif os.name == "posix":
+        # Removes <filename>.old on POSIX systems
+        copy_fn = os.rename
+    else:
+        # Fall back on copying
+        copy_fn = copy
+
+    try:
+        copy_fn(path, path + ".old")
+    except Exception:
+        # Ignore errors from 'path' missing as well as other errors.
+        # <filename>.old file is usually more of a nice-to-have, and not worth
+        # erroring out over e.g. if <filename>.old happens to be a directory or
+        # <filename> is something like /dev/null.
+        pass
+
+
+def _name_and_loc(sc):
+    # Helper for giving the symbol/choice name and location(s) in e.g. warnings
+
+    # Reuse the expression format. That way choices show up as
+    # '<choice (name, if any)>'
+    name = standard_sc_expr_str(sc)
+
+    if not sc.nodes:
+        return name + " (undefined)"
+
+    return "{} (defined at {})".format(
+        name,
+        ", ".join("{}:{}".format(node.filename, node.linenr)
+                  for node in sc.nodes))
+
+
+# Menu manipulation
+
+
+def _expr_depends_on(expr, sym):
+    # Reimplementation of expr_depends_symbol() from mconf.c. Used to determine
+    # if a submenu should be implicitly created. This also influences which
+    # items inside choice statements are considered choice items.
+
+    if expr.__class__ is not tuple:
+        return expr is sym
+
+    if expr[0] in _EQUAL_UNEQUAL:
+        # Check for one of the following:
+        # sym = m/y, m/y = sym, sym != n, n != sym
+
+        left, right = expr[1:]
+
+        if right is sym:
+            left, right = right, left
+        elif left is not sym:
+            return False
+
+        return (expr[0] is EQUAL and right is sym.kconfig.m or
+                                     right is sym.kconfig.y) or \
+               (expr[0] is UNEQUAL and right is sym.kconfig.n)
+
+    return expr[0] is AND and \
+           (_expr_depends_on(expr[1], sym) or
+            _expr_depends_on(expr[2], sym))
+
+
+def _auto_menu_dep(node1, node2):
+    # Returns True if node2 has an "automatic menu dependency" on node1. If
+    # node2 has a prompt, we check its condition. Otherwise, we look directly
+    # at node2.dep.
+
+    return _expr_depends_on(node2.prompt[1] if node2.prompt else node2.dep,
+                            node1.item)
+
+
+def _flatten(node):
+    # "Flattens" menu nodes without prompts (e.g. 'if' nodes and non-visible
+    # symbols with children from automatic menu creation) so that their
+    # children appear after them instead. This gives a clean menu structure
+    # with no unexpected "jumps" in the indentation.
     #
+    # Do not flatten promptless choices (which can appear "legitimately" if a
+    # named choice is defined in multiple locations to add on symbols). It
+    # looks confusing, and the menuconfig already shows all choice symbols if
+    # you enter the choice at some location with a prompt.
 
-    def __init__(self):
-        """Comment constructor -- not intended to be called directly by
-        Kconfiglib clients."""
+    while node:
+        if node.list and not node.prompt and \
+           node.item.__class__ is not Choice:
 
-        self.text = None
-        self.dep_expr = None
-        self.config = None
-        self.parent = None
+            last_node = node.list
+            while 1:
+                last_node.parent = node.parent
+                if not last_node.next:
+                    break
+                last_node = last_node.next
 
-        # Dependency expression without dependencies from enclosing menus and
-        # ifs propagated
-        self.orig_deps = None
+            last_node.next = node.next
+            node.next = node.list
+            node.list = None
 
-        # Dependencies inherited from containing menus and ifs
-        self.deps_from_containing = None
-        # The set of symbols referenced by this comment (see
-        # get_referenced_symbols())
-        self.referenced_syms = set()
-        # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and ifs
-        self.all_referenced_syms = None
+        node = node.next
 
-        self.filename = None
-        self.linenr = None
 
-    def _make_conf(self, append_fn):
-        if self.config._eval_expr(self.dep_expr) != "n":
-            append_fn("\n#\n# {0}\n#".format(self.text))
+def _remove_ifs(node):
+    # Removes 'if' nodes (which can be recognized by MenuNode.item being None),
+    # which are assumed to already have been flattened. The C implementation
+    # doesn't bother to do this, but we expose the menu tree directly, and it
+    # makes it nicer to work with.
 
-class Kconfig_Syntax_Error(Exception):
-    """Exception raised for syntax errors."""
-    pass
+    cur = node.list
+    while cur and not cur.item:
+        cur = cur.next
 
-class Internal_Error(Exception):
-    """Exception raised for internal errors."""
-    pass
+    node.list = cur
 
-#
-# Public functions
-#
+    while cur:
+        next = cur.next
+        while next and not next.item:
+            next = next.next
 
-def tri_less(v1, v2):
-    """Returns True if the tristate v1 is less than the tristate v2, where "n",
-    "m" and "y" are ordered from lowest to highest."""
-    return TRI_TO_INT[v1] < TRI_TO_INT[v2]
+        # Equivalent to
+        #
+        #   cur.next = next
+        #   cur = next
+        #
+        # due to tricky Python semantics. The order matters.
+        cur.next = cur = next
 
-def tri_less_eq(v1, v2):
-    """Returns True if the tristate v1 is less than or equal to the tristate
-    v2, where "n", "m" and "y" are ordered from lowest to highest."""
-    return TRI_TO_INT[v1] <= TRI_TO_INT[v2]
 
-def tri_greater(v1, v2):
-    """Returns True if the tristate v1 is greater than the tristate v2, where
-    "n", "m" and "y" are ordered from lowest to highest."""
-    return TRI_TO_INT[v1] > TRI_TO_INT[v2]
+def _finalize_choice(node):
+    # Finalizes a choice, marking each symbol whose menu node has the choice as
+    # the parent as a choice symbol, and automatically determining types if not
+    # specified.
 
-def tri_greater_eq(v1, v2):
-    """Returns True if the tristate v1 is greater than or equal to the tristate
-    v2, where "n", "m" and "y" are ordered from lowest to highest."""
-    return TRI_TO_INT[v1] >= TRI_TO_INT[v2]
+    choice = node.item
 
-#
-# Internal classes
-#
+    cur = node.list
+    while cur:
+        if cur.item.__class__ is Symbol:
+            cur.item.choice = choice
+            choice.syms.append(cur.item)
+        cur = cur.next
 
-class _Feed(object):
+    # If no type is specified for the choice, its type is that of
+    # the first choice item with a specified type
+    if not choice.orig_type:
+        for item in choice.syms:
+            if item.orig_type:
+                choice.orig_type = item.orig_type
+                break
 
-    """Class for working with sequences in a stream-like fashion; handy for
-    tokens."""
+    # Each choice item of UNKNOWN type gets the type of the choice
+    for sym in choice.syms:
+        if not sym.orig_type:
+            sym.orig_type = choice.orig_type
 
-    # This would be more helpful on the item classes, but would remove some
-    # flexibility
-    __slots__ = ['items', 'length', 'i']
 
-    def __init__(self, items):
-        self.items = items
-        self.length = len(self.items)
-        self.i = 0
+def _check_dep_loop_sym(sym, ignore_choice):
+    # Detects dependency loops using depth-first search on the dependency graph
+    # (which is calculated earlier in Kconfig._build_dep()).
+    #
+    # Algorithm:
+    #
+    #  1. Symbols/choices start out with _visited = 0, meaning unvisited.
+    #
+    #  2. When a symbol/choice is first visited, _visited is set to 1, meaning
+    #     "visited, potentially part of a dependency loop". The recursive
+    #     search then continues from the symbol/choice.
+    #
+    #  3. If we run into a symbol/choice X with _visited already set to 1,
+    #     there's a dependency loop. The loop is found on the call stack by
+    #     recording symbols while returning ("on the way back") until X is seen
+    #     again.
+    #
+    #  4. Once a symbol/choice and all its dependencies (or dependents in this
+    #     case) have been checked recursively without detecting any loops, its
+    #     _visited is set to 2, meaning "visited, not part of a dependency
+    #     loop".
+    #
+    #     This saves work if we run into the symbol/choice again in later calls
+    #     to _check_dep_loop_sym(). We just return immediately.
+    #
+    # Choices complicate things, as every choice symbol depends on every other
+    # choice symbol in a sense. When a choice is "entered" via a choice symbol
+    # X, we visit all choice symbols from the choice except X, and prevent
+    # immediately revisiting the choice with a flag (ignore_choice).
+    #
+    # Maybe there's a better way to handle this (different flags or the
+    # like...)
 
-    def get_next(self):
-        if self.i >= self.length:
-            return None
-        item = self.items[self.i]
-        self.i += 1
-        return item
+    if not sym._visited:
+        # sym._visited == 0, unvisited
 
-    def peek_next(self):
-        return None if self.i >= self.length else self.items[self.i]
+        sym._visited = 1
 
-    def check(self, token):
-        """Check if the next token is 'token'. If so, remove it from the token
-        feed and return True. Otherwise, leave it in and return False."""
-        if self.i < self.length and self.items[self.i] == token:
-            self.i += 1
-            return True
-        return False
+        for dep in sym._dependents:
+            # Choices show up in Symbol._dependents when the choice has the
+            # symbol in a 'prompt' or 'default' condition (e.g.
+            # 'default ... if SYM').
+            #
+            # Since we aren't entering the choice via a choice symbol, all
+            # choice symbols need to be checked, hence the None.
+            loop = _check_dep_loop_choice(dep, None) \
+                   if dep.__class__ is Choice \
+                   else _check_dep_loop_sym(dep, False)
 
-    def unget_all(self):
-        self.i = 0
+            if loop:
+                # Dependency loop found
+                return _found_dep_loop(loop, sym)
 
-class _FileFeed(object):
+        if sym.choice and not ignore_choice:
+            loop = _check_dep_loop_choice(sym.choice, sym)
+            if loop:
+                # Dependency loop found
+                return _found_dep_loop(loop, sym)
 
-    """Feeds lines from a file. Keeps track of the filename and current line
-    number. Joins any line ending in \\ with the following line. We need to be
-    careful to get the line number right in the presence of continuation
-    lines."""
+        # The symbol is not part of a dependency loop
+        sym._visited = 2
 
-    __slots__ = ['filename', 'lines', 'length', 'linenr']
+        # No dependency loop found
+        return None
 
-    def __init__(self, filename):
-        self.filename = _clean_up_path(filename)
-        with open(filename, "r") as f:
-            # No interleaving of I/O and processing yet. Don't know if it would
-            # help.
-            self.lines = f.readlines()
-        self.length = len(self.lines)
-        self.linenr = 0
+    if sym._visited == 2:
+        # The symbol was checked earlier and is already known to not be part of
+        # a dependency loop
+        return None
 
-    def get_next(self):
-        if self.linenr >= self.length:
-            return None
-        line = self.lines[self.linenr]
-        self.linenr += 1
-        while line.endswith("\\\n"):
-            line = line[:-2] + self.lines[self.linenr]
-            self.linenr += 1
-        return line
+    # sym._visited == 1, found a dependency loop. Return the symbol as the
+    # first element in it.
+    return (sym,)
 
-    def peek_next(self):
-        linenr = self.linenr
-        if linenr >= self.length:
-            return None
-        line = self.lines[linenr]
-        while line.endswith("\\\n"):
-            linenr += 1
-            line = line[:-2] + self.lines[linenr]
-        return line
 
-    def unget(self):
-        self.linenr -= 1
-        while self.lines[self.linenr].endswith("\\\n"):
-            self.linenr -= 1
+def _check_dep_loop_choice(choice, skip):
+    if not choice._visited:
+        # choice._visited == 0, unvisited
 
-    def next_nonblank(self):
-        """Removes lines up to and including the next non-blank (not all-space)
-        line and returns it. Returns None if there are no more non-blank
-        lines."""
-        while 1:
-            line = self.get_next()
-            if line is None or not line.isspace():
-                return line
+        choice._visited = 1
 
-#
-# Internal functions
-#
+        # Check for loops involving choice symbols. If we came here via a
+        # choice symbol, skip that one, as we'd get a false positive
+        # '<sym FOO> -> <choice> -> <sym FOO>' loop otherwise.
+        for sym in choice.syms:
+            if sym is not skip:
+                # Prevent the choice from being immediately re-entered via the
+                # "is a choice symbol" path by passing True
+                loop = _check_dep_loop_sym(sym, True)
+                if loop:
+                    # Dependency loop found
+                    return _found_dep_loop(loop, choice)
 
-def _get_visibility(sc):
-    """Symbols and Choices have a "visibility" that acts as an upper bound on
-    the values a user can set for them, corresponding to the visibility in e.g.
-    'make menuconfig'. This function calculates the visibility for the Symbol
-    or Choice 'sc' -- the logic is nearly identical."""
-    if sc.cached_visibility is None:
-        vis = "n"
-        for _, cond_expr in sc.prompts:
-            vis = sc.config._eval_max(vis, cond_expr)
+        # The choice is not part of a dependency loop
+        choice._visited = 2
 
-        if isinstance(sc, Symbol) and sc.is_choice_sym:
-            if sc.type == TRISTATE and vis == "m" and \
-               sc.parent.get_mode() == "y":
-                # Choice symbols with visibility "m" are not visible if the
-                # choice has mode "y"
-                vis = "n"
-            else:
-                vis = sc.config._eval_min(vis, _get_visibility(sc.parent))
+        # No dependency loop found
+        return None
 
-        # Promote "m" to "y" if we're dealing with a non-tristate
-        if vis == "m" and sc.type != TRISTATE:
-            vis = "y"
+    if choice._visited == 2:
+        # The choice was checked earlier and is already known to not be part of
+        # a dependency loop
+        return None
 
-        sc.cached_visibility = vis
+    # choice._visited == 1, found a dependency loop. Return the choice as the
+    # first element in it.
+    return (choice,)
 
-    return sc.cached_visibility
 
-def _make_and(e1, e2):
-    """Constructs an AND (&&) expression. Performs trivial simplification.
-    Nones equate to 'y'.
+def _found_dep_loop(loop, cur):
+    # Called "on the way back" when we know we have a loop
 
-    Note: returns None if e1 == e2 == None."""
-    if e1 is None or e1 == "y":
-        return e2
-    if e2 is None or e2 == "y":
-        return e1
+    # Is the symbol/choice 'cur' where the loop started?
+    if cur is not loop[0]:
+        # Nope, it's just a part of the loop
+        return loop + (cur,)
 
-    # Prefer to merge argument lists if possible to reduce the number of nodes
+    # Yep, we have the entire loop. Throw an exception that shows it.
 
-    if isinstance(e1, tuple) and e1[0] == AND:
-        if isinstance(e2, tuple) and e2[0] == AND:
-            return (AND, e1[1] + e2[1])
-        return (AND, e1[1] + [e2])
+    msg = "\nDependency loop\n" \
+            "===============\n\n"
 
-    if isinstance(e2, tuple) and e2[0] == AND:
-        return (AND, e2[1] + [e1])
+    for item in loop:
+        if item is not loop[0]:
+            msg += "...depends on "
+            if item.__class__ is Symbol and item.choice:
+                msg += "the choice symbol "
 
-    return (AND, [e1, e2])
+        msg += "{}, with definition...\n\n{}\n\n" \
+               .format(_name_and_loc(item), item)
 
-def _make_or(e1, e2):
-    """Constructs an OR (||) expression. Performs trivial simplification and
-    avoids Nones. Nones equate to 'y', which is usually what we want, but needs
-    to be kept in mind."""
+        # Small wart: Since we reuse the already calculated
+        # Symbol/Choice._dependents sets for recursive dependency detection, we
+        # lose information on whether a dependency came from a 'select'/'imply'
+        # condition or e.g. a 'depends on'.
+        #
+        # This might cause selecting symbols to "disappear". For example,
+        # a symbol B having 'select A if C' gives a direct dependency from A to
+        # C, since it corresponds to a reverse dependency of B && C.
+        #
+        # Always print reverse dependencies for symbols that have them to make
+        # sure information isn't lost. I wonder if there's some neat way to
+        # improve this.
 
-    # Perform trivial simplification and avoid None's (which
-    # correspond to y's)
-    if e1 is None or e2 is None or e1 == "y" or e2 == "y":
-        return "y"
-    if e1 == "n":
-        return e2
+        if item.__class__ is Symbol:
+            if item.rev_dep is not item.kconfig.n:
+                msg += "(select-related dependencies: {})\n\n" \
+                       .format(expr_str(item.rev_dep))
 
-    # Prefer to merge argument lists if possible to reduce the number of nodes
+            if item.weak_rev_dep is not item.kconfig.n:
+                msg += "(imply-related dependencies: {})\n\n" \
+                       .format(expr_str(item.rev_dep))
 
-    if isinstance(e1, tuple) and e1[0] == OR:
-        if isinstance(e2, tuple) and e2[0] == OR:
-            return (OR, e1[1] + e2[1])
-        return (OR, e1[1] + [e2])
+    msg += "...depends again on {}".format(_name_and_loc(loop[0]))
 
-    if isinstance(e2, tuple) and e2[0] == OR:
-        return (OR, e2[1] + [e1])
+    raise KconfigError(msg)
 
-    return (OR, [e1, e2])
 
-def _get_expr_syms_rec(expr, res):
-    """_get_expr_syms() helper. Recurses through expressions."""
-    if isinstance(expr, Symbol):
-        res.add(expr)
-    elif isinstance(expr, str):
-        return
-    elif expr[0] == AND or expr[0] == OR:
-        for term in expr[1]:
-            _get_expr_syms_rec(term, res)
-    elif expr[0] == NOT:
-        _get_expr_syms_rec(expr[1], res)
-    elif expr[0] == EQUAL or expr[0] == UNEQUAL:
-        if isinstance(expr[1], Symbol):
-            res.add(expr[1])
-        if isinstance(expr[2], Symbol):
-            res.add(expr[2])
-    else:
-        _internal_error("Internal error while fetching symbols from an "
-                        "expression with token stream {0}.".format(expr))
+def _decoding_error(e, filename, macro_linenr=None):
+    # Gives the filename and context for UnicodeDecodeError's, which are a pain
+    # to debug otherwise. 'e' is the UnicodeDecodeError object.
+    #
+    # If the decoding error is for the output of a $(shell,...) command,
+    # macro_linenr holds the line number where it was run (the exact line
+    # number isn't available for decoding errors in files).
 
-def _get_expr_syms(expr):
-    """Returns the set() of symbols appearing in expr."""
-    res = set()
-    if expr is not None:
-        _get_expr_syms_rec(expr, res)
-    return res
+    raise KconfigError(
+        "\n"
+        "Malformed {} in {}\n"
+        "Context: {}\n"
+        "Problematic data: {}\n"
+        "Reason: {}".format(
+            e.encoding,
+            "'{}'".format(filename) if macro_linenr is None else
+                "output from macro at {}:{}".format(filename, macro_linenr),
+            e.object[max(e.start - 40, 0):e.end + 40],
+            e.object[e.start:e.end],
+            e.reason))
 
-def _str_val(obj):
-    """Returns the value of obj as a string. If obj is not a string (constant
-    symbol), it must be a Symbol."""
-    return obj if isinstance(obj, str) else obj.get_value()
 
-def _make_block_conf(block, append_fn):
-    """Returns a list of .config strings for a block (list) of items."""
+def _warn_verbose_deprecated(fn_name):
+    sys.stderr.write(
+        "Deprecation warning: {0}()'s 'verbose' argument has no effect. Since "
+        "Kconfiglib 12.0.0, the message is returned from {0}() instead, "
+        "and is always generated. Do e.g. print(kconf.{0}()) if you want to "
+        "want to show a message like \"Loaded configuration '.config'\" on "
+        "stdout. The old API required ugly hacks to reuse messages in "
+        "configuration interfaces.\n".format(fn_name))
 
-    # Collect the substrings in a list and later use join() instead of += to
-    # build the final .config contents. With older Python versions, this yields
-    # linear instead of quadratic complexity.
-    for item in block:
-        item._make_conf(append_fn)
 
-def _sym_str_string(sym_or_str):
-    if isinstance(sym_or_str, str):
-        return '"' + sym_or_str + '"'
-    return sym_or_str.name
+# Predefined preprocessor functions
 
-def _intersperse(lst, op):
-    """_expr_to_str() helper. Gets the string representation of each expression
-    in lst and produces a list where op has been inserted between the
-    elements."""
-    if not lst:
-        return ""
 
-    res = []
+def _filename_fn(kconf, _):
+    return kconf.filename
 
-    def handle_sub_expr(expr):
-        no_parens = isinstance(expr, (str, Symbol)) or \
-                    expr[0] in (EQUAL, UNEQUAL) or \
-                    PRECEDENCE[op] <= PRECEDENCE[expr[0]]
-        if not no_parens:
-            res.append("(")
-        res.extend(_expr_to_str_rec(expr))
-        if not no_parens:
-            res.append(")")
 
-    op_str = OP_TO_STR[op]
+def _lineno_fn(kconf, _):
+    return str(kconf.linenr)
 
-    handle_sub_expr(lst[0])
-    for expr in lst[1:]:
-        res.append(op_str)
-        handle_sub_expr(expr)
 
-    return res
+def _info_fn(kconf, _, msg):
+    print("{}:{}: {}".format(kconf.filename, kconf.linenr, msg))
 
-def _expr_to_str_rec(expr):
-    if expr is None:
-        return [""]
+    return ""
 
-    if isinstance(expr, (Symbol, str)):
-        return [_sym_str_string(expr)]
 
-    if expr[0] in (AND, OR):
-        return _intersperse(expr[1], expr[0])
+def _warning_if_fn(kconf, _, cond, msg):
+    if cond == "y":
+        kconf._warn(msg, kconf.filename, kconf.linenr)
 
-    if expr[0] == NOT:
-        need_parens = not isinstance(expr[1], (str, Symbol))
+    return ""
 
-        res = ["!"]
-        if need_parens:
-            res.append("(")
-        res.extend(_expr_to_str_rec(expr[1]))
-        if need_parens:
-            res.append(")")
-        return res
 
-    if expr[0] in (EQUAL, UNEQUAL):
-        return [_sym_str_string(expr[1]),
-                OP_TO_STR[expr[0]],
-                _sym_str_string(expr[2])]
+def _error_if_fn(kconf, _, cond, msg):
+    if cond == "y":
+        raise KconfigError("{}:{}: {}".format(
+            kconf.filename, kconf.linenr, msg))
 
-def _expr_to_str(expr):
-    return "".join(_expr_to_str_rec(expr))
+    return ""
 
-def _indentation(line):
-    """Returns the length of the line's leading whitespace, treating tab stops
-    as being spaced 8 characters apart."""
-    line = line.expandtabs()
-    return len(line) - len(line.lstrip())
 
-def _deindent(line, indent):
-    """Deindent 'line' by 'indent' spaces."""
-    line = line.expandtabs()
-    if len(line) <= indent:
-        return line
-    return line[indent:]
+def _shell_fn(kconf, _, command):
+    # Only import as needed, to save some startup time
+    import subprocess
 
-def _is_base_n(s, n):
-    try:
-        int(s, n)
-        return True
-    except ValueError:
-        return False
+    stdout, stderr = subprocess.Popen(
+        command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE
+    ).communicate()
 
-def _lines(*args):
-    """Returns a string consisting of all arguments, with newlines inserted
-    between them."""
-    return "\n".join(args)
+    if not _IS_PY2:
+        try:
+            stdout = stdout.decode(kconf._encoding)
+            stderr = stderr.decode(kconf._encoding)
+        except UnicodeDecodeError as e:
+            _decoding_error(e, kconf.filename, kconf.linenr)
 
-def _comment(s):
-    """Returns a new string with "#" inserted before each line in 's'."""
-    if not s:
-        return "#"
-    res = "".join(["#" + line for line in s.splitlines(True)])
-    if s.endswith("\n"):
-        return res + "#"
-    return res
+    if stderr:
+        kconf._warn("'{}' wrote to stderr: {}".format(
+                        command, "\n".join(stderr.splitlines())),
+                    kconf.filename, kconf.linenr)
 
-def _clean_up_path(path):
-    """Strips an initial "./" and any trailing slashes from 'path'."""
-    if path.startswith("./"):
-        path = path[2:]
-    return path.rstrip("/")
+    # Universal newlines with splitlines() (to prevent e.g. stray \r's in
+    # command output on Windows), trailing newline removal, and
+    # newline-to-space conversion.
+    #
+    # On Python 3 versions before 3.6, it's not possible to specify the
+    # encoding when passing universal_newlines=True to Popen() (the 'encoding'
+    # parameter was added in 3.6), so we do this manual version instead.
+    return "\n".join(stdout.splitlines()).rstrip("\n").replace("\n", " ")
+
+#
+# Global constants
+#
 
-def _build_msg(msg, filename, linenr):
-    if filename is not None:
-        msg = "{0}:{1}: ".format(_clean_up_path(filename), linenr) + msg
-    return msg
+TRI_TO_STR = {
+    0: "n",
+    1: "m",
+    2: "y",
+}
 
-def _stderr_msg(msg, filename, linenr):
-    sys.stderr.write(_build_msg(msg, filename, linenr) + "\n")
+STR_TO_TRI = {
+    "n": 0,
+    "m": 1,
+    "y": 2,
+}
 
-def _tokenization_error(s, filename, linenr):
-    loc = "" if filename is None else "{0}:{1}: ".format(filename, linenr)
-    raise Kconfig_Syntax_Error("{0}Couldn't tokenize '{1}'"
-                               .format(loc, s.strip()))
+# Constant representing that there's no cached choice selection. This is
+# distinct from a cached None (no selection). Any object that's not None or a
+# Symbol will do. We test this with 'is'.
+_NO_CACHED_SELECTION = 0
 
-def _parse_error(s, msg, filename, linenr):
-    loc = "" if filename is None else "{0}:{1}: ".format(filename, linenr)
-    raise Kconfig_Syntax_Error("{0}Couldn't parse '{1}'{2}"
-                               .format(loc, s.strip(),
-                                       "." if msg is None else ": " + msg))
+# Are we running on Python 2?
+_IS_PY2 = sys.version_info[0] < 3
 
-def _internal_error(msg):
-    raise Internal_Error(msg +
-      "\nSorry! You may want to send an email to ulfalizer a.t Google's "
-      "email service to tell me about this. Include the message above and the "
-      "stack trace and describe what you were doing.")
+try:
+    _UNAME_RELEASE = os.uname()[2]
+except AttributeError:
+    # Only import as needed, to save some startup time
+    import platform
+    _UNAME_RELEASE = platform.uname()[2]
 
+# The token and type constants below are safe to test with 'is', which is a bit
+# faster (~30% faster on my machine, and a few % faster for total parsing
+# time), even without assuming Python's small integer optimization (which
+# caches small integer objects). The constants end up pointing to unique
+# integer objects, and since we consistently refer to them via the names below,
+# we always get the same object.
 #
-# Internal global constants
+# Client code should use == though.
+
+# Tokens, with values 1, 2, ... . Avoiding 0 simplifies some checks by making
+# all tokens except empty strings truthy.
+(
+    _T_ALLNOCONFIG_Y,
+    _T_AND,
+    _T_BOOL,
+    _T_CHOICE,
+    _T_CLOSE_PAREN,
+    _T_COMMENT,
+    _T_CONFIG,
+    _T_DEFAULT,
+    _T_DEFCONFIG_LIST,
+    _T_DEF_BOOL,
+    _T_DEF_HEX,
+    _T_DEF_INT,
+    _T_DEF_STRING,
+    _T_DEF_TRISTATE,
+    _T_DEPENDS,
+    _T_ENDCHOICE,
+    _T_ENDIF,
+    _T_ENDMENU,
+    _T_ENV,
+    _T_EQUAL,
+    _T_GREATER,
+    _T_GREATER_EQUAL,
+    _T_HELP,
+    _T_HEX,
+    _T_IF,
+    _T_IMPLY,
+    _T_INT,
+    _T_LESS,
+    _T_LESS_EQUAL,
+    _T_MAINMENU,
+    _T_MENU,
+    _T_MENUCONFIG,
+    _T_MODULES,
+    _T_NOT,
+    _T_ON,
+    _T_OPEN_PAREN,
+    _T_OPTION,
+    _T_OPTIONAL,
+    _T_OR,
+    _T_ORSOURCE,
+    _T_OSOURCE,
+    _T_PROMPT,
+    _T_RANGE,
+    _T_RSOURCE,
+    _T_SELECT,
+    _T_SOURCE,
+    _T_STRING,
+    _T_TRISTATE,
+    _T_UNEQUAL,
+    _T_VISIBLE,
+) = range(1, 51)
+
+# Keyword to token map, with the get() method assigned directly as a small
+# optimization
+_get_keyword = {
+    "---help---":     _T_HELP,
+    "allnoconfig_y":  _T_ALLNOCONFIG_Y,
+    "bool":           _T_BOOL,
+    "boolean":        _T_BOOL,
+    "choice":         _T_CHOICE,
+    "comment":        _T_COMMENT,
+    "config":         _T_CONFIG,
+    "def_bool":       _T_DEF_BOOL,
+    "def_hex":        _T_DEF_HEX,
+    "def_int":        _T_DEF_INT,
+    "def_string":     _T_DEF_STRING,
+    "def_tristate":   _T_DEF_TRISTATE,
+    "default":        _T_DEFAULT,
+    "defconfig_list": _T_DEFCONFIG_LIST,
+    "depends":        _T_DEPENDS,
+    "endchoice":      _T_ENDCHOICE,
+    "endif":          _T_ENDIF,
+    "endmenu":        _T_ENDMENU,
+    "env":            _T_ENV,
+    "grsource":       _T_ORSOURCE,  # Backwards compatibility
+    "gsource":        _T_OSOURCE,   # Backwards compatibility
+    "help":           _T_HELP,
+    "hex":            _T_HEX,
+    "if":             _T_IF,
+    "imply":          _T_IMPLY,
+    "int":            _T_INT,
+    "mainmenu":       _T_MAINMENU,
+    "menu":           _T_MENU,
+    "menuconfig":     _T_MENUCONFIG,
+    "modules":        _T_MODULES,
+    "on":             _T_ON,
+    "option":         _T_OPTION,
+    "optional":       _T_OPTIONAL,
+    "orsource":       _T_ORSOURCE,
+    "osource":        _T_OSOURCE,
+    "prompt":         _T_PROMPT,
+    "range":          _T_RANGE,
+    "rsource":        _T_RSOURCE,
+    "select":         _T_SELECT,
+    "source":         _T_SOURCE,
+    "string":         _T_STRING,
+    "tristate":       _T_TRISTATE,
+    "visible":        _T_VISIBLE,
+}.get
+
+# The constants below match the value of the corresponding tokens to remove the
+# need for conversion
+
+# Node types
+MENU    = _T_MENU
+COMMENT = _T_COMMENT
+
+# Expression types
+AND           = _T_AND
+OR            = _T_OR
+NOT           = _T_NOT
+EQUAL         = _T_EQUAL
+UNEQUAL       = _T_UNEQUAL
+LESS          = _T_LESS
+LESS_EQUAL    = _T_LESS_EQUAL
+GREATER       = _T_GREATER
+GREATER_EQUAL = _T_GREATER_EQUAL
+
+REL_TO_STR = {
+    EQUAL:         "=",
+    UNEQUAL:       "!=",
+    LESS:          "<",
+    LESS_EQUAL:    "<=",
+    GREATER:       ">",
+    GREATER_EQUAL: ">=",
+}
+
+# Symbol/choice types. UNKNOWN is 0 (falsy) to simplify some checks.
+# Client code shouldn't rely on it though, as it was non-zero in
+# older versions.
+UNKNOWN  = 0
+BOOL     = _T_BOOL
+TRISTATE = _T_TRISTATE
+STRING   = _T_STRING
+INT      = _T_INT
+HEX      = _T_HEX
+
+TYPE_TO_STR = {
+    UNKNOWN:  "unknown",
+    BOOL:     "bool",
+    TRISTATE: "tristate",
+    STRING:   "string",
+    INT:      "int",
+    HEX:      "hex",
+}
+
+# Used in comparisons. 0 means the base is inferred from the format of the
+# string.
+_TYPE_TO_BASE = {
+    HEX:      16,
+    INT:      10,
+    STRING:   0,
+    UNKNOWN:  0,
+}
+
+# def_bool -> BOOL, etc.
+_DEF_TOKEN_TO_TYPE = {
+    _T_DEF_BOOL:     BOOL,
+    _T_DEF_HEX:      HEX,
+    _T_DEF_INT:      INT,
+    _T_DEF_STRING:   STRING,
+    _T_DEF_TRISTATE: TRISTATE,
+}
+
+# Tokens after which strings are expected. This is used to tell strings from
+# constant symbol references during tokenization, both of which are enclosed in
+# quotes.
 #
+# Identifier-like lexemes ("missing quotes") are also treated as strings after
+# these tokens. _T_CHOICE is included to avoid symbols being registered for
+# named choices.
+_STRING_LEX = frozenset({
+    _T_BOOL,
+    _T_CHOICE,
+    _T_COMMENT,
+    _T_HEX,
+    _T_INT,
+    _T_MAINMENU,
+    _T_MENU,
+    _T_ORSOURCE,
+    _T_OSOURCE,
+    _T_PROMPT,
+    _T_RSOURCE,
+    _T_SOURCE,
+    _T_STRING,
+    _T_TRISTATE,
+})
+
+# Various sets for quick membership tests. Gives a single global lookup and
+# avoids creating temporary dicts/tuples.
+
+_TYPE_TOKENS = frozenset({
+    _T_BOOL,
+    _T_TRISTATE,
+    _T_INT,
+    _T_HEX,
+    _T_STRING,
+})
+
+_SOURCE_TOKENS = frozenset({
+    _T_SOURCE,
+    _T_RSOURCE,
+    _T_OSOURCE,
+    _T_ORSOURCE,
+})
+
+_REL_SOURCE_TOKENS = frozenset({
+    _T_RSOURCE,
+    _T_ORSOURCE,
+})
+
+# Obligatory (non-optional) sources
+_OBL_SOURCE_TOKENS = frozenset({
+    _T_SOURCE,
+    _T_RSOURCE,
+})
 
-# Tokens
-(T_AND, T_OR, T_NOT,
- T_OPEN_PAREN, T_CLOSE_PAREN,
- T_EQUAL, T_UNEQUAL,
- T_MAINMENU, T_MENU, T_ENDMENU,
- T_SOURCE, T_CHOICE, T_ENDCHOICE,
- T_COMMENT, T_CONFIG, T_MENUCONFIG,
- T_HELP, T_IF, T_ENDIF, T_DEPENDS, T_ON,
- T_OPTIONAL, T_PROMPT, T_DEFAULT,
- T_BOOL, T_TRISTATE, T_HEX, T_INT, T_STRING,
- T_DEF_BOOL, T_DEF_TRISTATE,
- T_SELECT, T_IMPLY, T_RANGE, T_OPTION, T_ALLNOCONFIG_Y, T_ENV,
- T_DEFCONFIG_LIST, T_MODULES, T_VISIBLE) = range(40)
+_BOOL_TRISTATE = frozenset({
+    BOOL,
+    TRISTATE,
+})
 
-# The leading underscore before the function assignments below prevent pydoc
-# from listing them. The constants could be hidden too, but they're fairly
-# obviously internal anyway, so don't bother spamming the code.
+_BOOL_TRISTATE_UNKNOWN = frozenset({
+    BOOL,
+    TRISTATE,
+    UNKNOWN,
+})
 
-# Keyword to token map. Note that the get() method is assigned directly as a
-# small optimization.
-_get_keyword = \
-  {"mainmenu": T_MAINMENU, "menu": T_MENU, "endmenu": T_ENDMENU,
-   "endif": T_ENDIF, "endchoice": T_ENDCHOICE, "source": T_SOURCE,
-   "choice": T_CHOICE, "config": T_CONFIG, "comment": T_COMMENT,
-   "menuconfig": T_MENUCONFIG, "help": T_HELP, "if": T_IF,
-   "depends": T_DEPENDS, "on": T_ON, "optional": T_OPTIONAL,
-   "prompt": T_PROMPT, "default": T_DEFAULT, "bool": T_BOOL, "boolean": T_BOOL,
-   "tristate": T_TRISTATE, "int": T_INT, "hex": T_HEX, "def_bool": T_DEF_BOOL,
-   "def_tristate": T_DEF_TRISTATE, "string": T_STRING, "select": T_SELECT,
-   "imply" : T_IMPLY, "range": T_RANGE, "option": T_OPTION,
-   "allnoconfig_y": T_ALLNOCONFIG_Y, "env": T_ENV,
-   "defconfig_list": T_DEFCONFIG_LIST, "modules": T_MODULES,
-   "visible": T_VISIBLE}.get
+_INT_HEX = frozenset({
+    INT,
+    HEX,
+})
 
-# Strings to use for True and False
-BOOL_STR = {False: "false", True: "true"}
+_SYMBOL_CHOICE = frozenset({
+    Symbol,
+    Choice,
+})
 
-# Tokens after which identifier-like lexemes are treated as strings. T_CHOICE
-# is included to avoid symbols being registered for named choices.
-STRING_LEX = frozenset((T_BOOL, T_TRISTATE, T_INT, T_HEX, T_STRING, T_CHOICE,
-                        T_PROMPT, T_MENU, T_COMMENT, T_SOURCE, T_MAINMENU))
+_MENU_COMMENT = frozenset({
+    MENU,
+    COMMENT,
+})
 
-# Matches the initial token on a line; see _tokenize(). Also eats trailing
-# whitespace as an optimization.
-_initial_token_re_match = re.compile(r"[^\w]*(\w+)\s*").match
+_EQUAL_UNEQUAL = frozenset({
+    EQUAL,
+    UNEQUAL,
+})
 
-# Matches an identifier/keyword optionally preceded by whitespace. Also eats
-# trailing whitespace as an optimization.
-_id_keyword_re_match = re.compile(r"\s*([\w./-]+)\s*").match
+_RELATIONS = frozenset({
+    EQUAL,
+    UNEQUAL,
+    LESS,
+    LESS_EQUAL,
+    GREATER,
+    GREATER_EQUAL,
+})
 
-# Regular expression for finding $-references to symbols in strings
-_sym_ref_re_search = re.compile(r"\$[A-Za-z0-9_]+").search
+# Helper functions for getting compiled regular expressions, with the needed
+# matching function returned directly as a small optimization.
+#
+# Use ASCII regex matching on Python 3. It's already the default on Python 2.
+
+
+def _re_match(regex):
+    return re.compile(regex, 0 if _IS_PY2 else re.ASCII).match
+
 
-# Integers representing symbol types
-UNKNOWN, BOOL, TRISTATE, STRING, HEX, INT = range(6)
+def _re_search(regex):
+    return re.compile(regex, 0 if _IS_PY2 else re.ASCII).search
 
-# Strings to use for types
-TYPENAME = {UNKNOWN: "unknown", BOOL: "bool", TRISTATE: "tristate",
-            STRING: "string", HEX: "hex", INT: "int"}
 
-# Token to type mapping
-TOKEN_TO_TYPE = {T_BOOL: BOOL, T_TRISTATE: TRISTATE, T_STRING: STRING,
-                 T_INT: INT, T_HEX: HEX}
+# Various regular expressions used during parsing
 
-# Default values for symbols of different types (the value the symbol gets if
-# it is not assigned a user value and none of its 'default' clauses kick in)
-DEFAULT_VALUE = {BOOL: "n", TRISTATE: "n", STRING: "", INT: "", HEX: ""}
+# The initial token on a line. Also eats leading and trailing whitespace, so
+# that we can jump straight to the next token (or to the end of the line if
+# there is only one token).
+#
+# This regex will also fail to match for empty lines and comment lines.
+#
+# '$' is included to detect preprocessor variable assignments with macro
+# expansions in the left-hand side.
+_command_match = _re_match(r"\s*([A-Za-z0-9_$-]+)\s*")
+
+# An identifier/keyword after the first token. Also eats trailing whitespace.
+# '$' is included to detect identifiers containing macro expansions.
+_id_keyword_match = _re_match(r"([A-Za-z0-9_$/.-]+)\s*")
+
+# A fragment in the left-hand side of a preprocessor variable assignment. These
+# are the portions between macro expansions ($(foo)). Macros are supported in
+# the LHS (variable name).
+_assignment_lhs_fragment_match = _re_match("[A-Za-z0-9_-]*")
 
-# Indicates that no item is selected in a choice statement
-NO_SELECTION = 0
+# The assignment operator and value (right-hand side) in a preprocessor
+# variable assignment
+_assignment_rhs_match = _re_match(r"\s*(=|:=|\+=)\s*(.*)")
 
-# Integers representing expression types
-AND, OR, NOT, EQUAL, UNEQUAL = range(5)
+# Special characters/strings while expanding a macro (')', ',', and '$(')
+_macro_special_search = _re_search(r"\)|,|\$\(")
 
-# Map from tristate values to integers
-TRI_TO_INT = {"n": 0, "m": 1, "y": 2}
+# Special characters/strings while expanding a string (quotes, '\', and '$(')
+_string_special_search = _re_search(r'"|\'|\\|\$\(')
 
-# Printing-related stuff
+# Special characters/strings while expanding a symbol name. Also includes
+# end-of-line, in case the macro is the last thing on the line.
+_name_special_search = _re_search(r'[^A-Za-z0-9_$/.-]|\$\(|$')
 
-OP_TO_STR = {AND: " && ", OR: " || ", EQUAL: " = ", UNEQUAL: " != "}
-PRECEDENCE = {OR: 0, AND: 1, NOT: 2}
+# A valid right-hand side for an assignment to a string symbol in a .config
+# file, including escaped characters. Extracts the contents.
+_conf_string_match = _re_match(r'"((?:[^\\"]|\\.)*)"')