text: #
  # 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:
  
   - 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.
  
  For the Linux kernel, scripts are run using
  
   $ make scriptconfig [ARCH=<arch>] SCRIPT=<path to script> [SCRIPT_ARG=<arg>]
  
  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].
  
  To get an interactive Python prompt with Kconfiglib preloaded and a Config
  object 'c' created, run
  
   $ make iscriptconfig [ARCH=<arch>]
  
  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.
  
  The examples/ directory contains short example scripts, which can be run with
  e.g.
  
   $ make scriptconfig SCRIPT=Kconfiglib/examples/print_tree.py
  
  or
  
   $ make scriptconfig SCRIPT=Kconfiglib/examples/help_grep.py SCRIPT_ARG=kernel
  
  testsuite.py contains the test suite. See the top of the script for how to run
  it.
  
  Credits: Written by Ulf "Ulfalizer" Magnusson
  
  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 re
  import sys
  
  # File layout:
  #
  # Public classes
  # Public functions
  # Internal classes
  # Internal functions
  # Internal global constants
  
  # Line length: 79 columns
  
  #
  # Public classes
  #
  
  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."""
  
      #
      # Public interface
      #
  
      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].
  
          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.
  
             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.
  
          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.
  
          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()."""
  
          # The set of all symbols, indexed by name (a string)
          self.syms = {}
          # Python 2/3 compatibility hack. This is the only one needed.
          if sys.version_info[0] >= 3:
              self.syms_iter = self.syms.values
          else:
              self.syms_iter = 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 = []
  
          # The set of all named choices (yes, choices can have names), indexed
          # by name (a string)
          self.named_choices = {}
  
          # Lists containing all choices, menus and comments in the configuration
          self.choices = []
          self.menus = []
          self.comments = []
  
          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", os.uname()[2])
  
          # The symbol with "option defconfig_list" set, containing a list of
          # default .config files
          self.defconfig_sym = None
  
          # See Symbol.get_(src)arch()
          self.arch = os.environ.get("ARCH")
          self.srcarch = os.environ.get("SRCARCH")
  
          # See Config.__init__(). We need this for get_defconfig_filename().
          self.srctree = os.environ.get("srctree")
          if self.srctree is None:
              self.srctree = "."
  
          self.filename = filename
          if base_dir is None:
              self.base_dir = self.srctree
          else:
              self.base_dir = os.path.expandvars(base_dir)
  
          # The 'mainmenu' text
          self.mainmenu_text = None
  
          # 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
  
          self.print_warnings = print_warnings
          self.print_undef_assign = print_undef_assign
  
          # 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
  
          # See the comment in _parse_expr().
          self._cur_item = None
          self._line = None
          self._filename = None
          self._linenr = None
          self._transform_m = None
  
          # Parse the Kconfig files
          self.top_block = self._parse_file(filename, None, None, None)
  
          # Build Symbol.dep for all symbols
          self._build_dep()
  
      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
  
      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
  
      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
  
      def get_kconfig_filename(self):
          """Returns the name of the (base) kconfig file this configuration was
          loaded from."""
          return self.filename
  
      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
  
      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. Does not start with "#"
          2. Has the form "# CONFIG_FOO is not set."
          """
          return self.config_header
  
      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)
  
      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.
  
          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__().
  
          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
  
      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)
  
      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]
  
      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
  
          for sym in config:
              ...
  
          which relies on Config implementing __iter__() and is equivalent to
  
          for sym in config.get_symbols(False):
              ...
  
          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
  
      def __iter__(self):
          """Convenience function for iterating over the set of all defined
          symbols in the configuration, used like
  
          for sym in conf:
              ...
  
          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)
  
      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
  
      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
  
      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
  
      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
  
      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 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.
  
          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."""
  
          # Put this first so that a missing file doesn't screw up our state
          filename = os.path.expandvars(filename)
          line_feeder = _FileFeed(filename)
  
          self.config_filename = filename
  
          #
          # Read header
          #
  
          def is_header_line(line):
              return line is not None and line.startswith("#") and \
                     not _unset_re_match(line)
  
          self.config_header = None
  
          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]
  
          #
          # 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)
  
          # 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()
  
          while 1:
              line = line_feeder.get_next()
              if line is None:
                  return
  
              line = line.rstrip()
  
              set_match = _set_re_match(line)
              if set_match:
                  name, val = set_match.groups()
  
                  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("\\\\", "\\")
  
                  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)
  
                      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)
  
                      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")
  
                          sym._set_user_value_no_invalidate("n", True)
  
      def write_config(self, filename, header=None):
          """Writes out symbol values in the familiar .config format.
  
          Kconfiglib makes sure the format matches what the C implementation
          would generate, down to whitespace. This eases testing.
  
          filename: The filename under which to save the configuration.
  
          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."""
  
          for sym in self.syms_iter():
              sym.already_written = False
  
          with open(filename, "w") as f:
              # Write header
              if header is not None:
                  f.write(_comment(header))
                  f.write("\n")
  
              # Build and write configuration
              conf_strings = []
              _make_block_conf(self.top_block, conf_strings.append)
              f.write("\n".join(conf_strings))
              f.write("\n")
  
      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'.
  
          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"
  
          This function always yields a tristate value. To get the value of
          non-bool, non-tristate symbols, use Symbol.get_value().
  
          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.
  
          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
  
      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()
  
      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.
  
          print_warnings: True if warnings should be printed."""
          self.print_warnings = print_warnings
  
      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.
  
          print_undef_assign: If True, such messages will be printed."""
          self.print_undef_assign = print_undef_assign
  
      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])
  
      #
      # Private methods
      #
  
      #
      # Kconfig parsing
      #
  
      def _parse_file(self, filename, parent, deps, visible_if_deps, res=None):
          """Parses the Kconfig file 'filename'. Returns a list with the Items in
          the file. See _parse_block() for the meaning of the parameters."""
          return self._parse_block(_FileFeed(filename), None, parent, deps,
                                   visible_if_deps, res)
  
      def _parse_block(self, line_feeder, end_marker, parent, deps,
                       visible_if_deps, res=None):
          """Parses a block, which is the contents of either a file or an if,
          menu, or choice statement. Returns a list with the Items in the block.
  
          line_feeder: A _FileFeed instance feeding lines from a file. The
            Kconfig language is line-based in practice.
  
          end_marker: The token that ends the block, e.g. T_ENDIF ("endif") for
             ifs. None for files.
  
          parent: The enclosing menu or choice, or None if we're at the top
             level.
  
          deps: Dependencies from enclosing menus, choices and ifs.
  
          visible_if_deps (default: None): 'visible if' dependencies from
             enclosing menus.
  
          res (default: None): The list to add items to. If None, a new list is
             created to hold the items."""
  
          block = [] if res is None else res
  
          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()
  
                  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 block
  
                  tokens = self._tokenize(line, False, line_feeder.filename,
                                          line_feeder.linenr)
  
              t0 = tokens.get_next()
              if t0 is None:
                  continue
  
              # Cases are ordered roughly by frequency, which speeds things up a
              # bit
  
              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
  
                  self.kconfig_syms.append(sym)
                  block.append(sym)
  
                  self._parse_properties(line_feeder, sym, deps, visible_if_deps)
  
              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)
  
              elif t0 == end_marker:
                  # We have reached the end of the block
                  return block
  
              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.
  
                  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)
  
              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.comments.append(comment)
                  block.append(comment)
  
                  self._parse_properties(line_feeder, comment, deps,
                                         visible_if_deps)
  
              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()
  
                  self.menus.append(menu)
                  block.append(menu)
  
                  # Parse properties and contents
                  self._parse_properties(line_feeder, menu, deps,
                                         visible_if_deps)
                  menu.block = self._parse_block(line_feeder, T_ENDMENU, menu,
                                                 menu.dep_expr,
                                                 _make_and(visible_if_deps,
                                                           menu.visible_if_expr))
  
              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)
  
                  choice.config = self
                  choice.parent = parent
  
                  choice.def_locations.append((line_feeder.filename,
                                               line_feeder.linenr))
  
                  # Parse properties and contents
                  self._parse_properties(line_feeder, choice, deps,
                                         visible_if_deps)
                  choice.block = self._parse_block(line_feeder, T_ENDCHOICE,
                                                   choice, deps, visible_if_deps)
  
                  choice._determine_actual_symbols()
  
                  # 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
  
                  # 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
  
                  block.append(choice)
  
              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
  
              else:
                  _parse_error(line, "unrecognized construct",
                               line_feeder.filename, line_feeder.linenr)
  
      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."""
  
          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."""
              val = self._parse_expr(tokens, stmt, line, filename, linenr, False)
              if tokens.check(T_IF):
                  return (val, self._parse_expr(tokens, stmt, line, filename,
                                                linenr))
              return (val, None)
  
          # In case the symbol is defined in multiple locations, we need to
          # remember what prompts, defaults, and selects are new for this
          # definition, as "depends on" should only apply to the local
          # definition.
          new_prompt = None
          new_def_exprs = []
          new_selects = []
  
          # Dependencies from 'depends on' statements
          depends_on_expr = None
  
          while 1:
              line = line_feeder.get_next()
              if line is None:
                  break
  
              filename = line_feeder.filename
              linenr = line_feeder.linenr
  
              tokens = self._tokenize(line, False, filename, linenr)
  
              t0 = tokens.get_next()
              if t0 is None:
                  continue
  
              # 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)
  
                  parsed_deps = self._parse_expr(tokens, stmt, line, filename,
                                                 linenr)
  
                  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
  
                  # 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
  
                  line_feeder.unget()
  
              elif t0 == T_SELECT or t0 == T_IMPLY:
                  target = tokens.get_next()
  
                  stmt.referenced_syms.add(target)
                  stmt.selected_syms.add(target)
  
                  if tokens.check(T_IF):
                      new_selects.append((target,
                                          self._parse_expr(tokens, stmt, line,
                                                           filename, linenr)))
                  else:
                      new_selects.append((target, None))
  
              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)
  
              elif t0 == T_DEFAULT:
                  new_def_exprs.append(parse_val_and_cond(tokens, line, filename,
                                                          linenr))
  
              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))
  
              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)
  
              elif t0 == T_RANGE:
                  low = tokens.get_next()
                  high = tokens.get_next()
                  stmt.referenced_syms.add(low)
                  stmt.referenced_syms.add(high)
  
                  if tokens.check(T_IF):
                      stmt.ranges.append((low, high,
                                          self._parse_expr(tokens, stmt, line,
                                                           filename, linenr)))
                  else:
                      stmt.ranges.append((low, high, None))
  
              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))
  
              elif t0 == T_OPTION:
                  if tokens.check(T_ENV) and tokens.check(T_EQUAL):
                      env_var = tokens.get_next()
  
                      stmt.is_special_ = True
                      stmt.is_from_env = True
  
                      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)
  
                          stmt.cached_val = ""
                      else:
                          stmt.cached_val = os.environ[env_var]
  
                  elif tokens.check(T_DEFCONFIG_LIST):
                      self.defconfig_sym = stmt
  
                  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)
  
                  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
  
                  else:
                      _parse_error(line, "unrecognized option", filename, linenr)
  
              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)
  
                  parsed_deps = self._parse_expr(tokens, stmt, line, filename,
                                                 linenr)
                  stmt.visible_if_expr = _make_and(stmt.visible_if_expr,
                                                   parsed_deps)
  
              elif t0 == T_OPTIONAL:
                  if not isinstance(stmt, Choice):
                      _parse_error(line,
                                   '"optional" is only valid for choices',
                                   filename,
                                   linenr)
                  stmt.optional = True
  
              else:
                  # See comment in Config.__init__()
                  self.end_line = line
                  self.end_line_tokens = tokens
                  break
  
          # Done parsing properties. Now propagate 'depends on' and enclosing
          # menu/if dependencies to expressions.
  
          # 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)
  
          # Save original dependencies from enclosing menus and ifs
          stmt.deps_from_containing = deps
  
          if isinstance(stmt, (Menu, Comment)):
              stmt.dep_expr = _make_and(stmt.orig_deps, deps)
          else:
              # Symbol or Choice
  
              # See comment for 'menu_dep'
              stmt.menu_dep = depends_on_expr
  
              # Propagate dependencies to prompts
  
              if new_prompt is not None:
                  # Propagate 'visible if' dependencies from enclosing menus
                  prompt, cond_expr = new_prompt
                  cond_expr = _make_and(cond_expr, visible_if_deps)
                  # Propagate 'depends on' dependencies
                  new_prompt = (prompt, _make_and(cond_expr, depends_on_expr))
                  # Save original
                  stmt.orig_prompts.append(new_prompt)
                  # Finalize with dependencies from enclosing menus and ifs
                  stmt.prompts.append((new_prompt[0],
                                       _make_and(new_prompt[1], deps)))
  
              # Propagate dependencies to defaults
  
              # 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])
  
              # Propagate dependencies to selects
  
              # Only symbols can select
              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]
                  # Save original
                  stmt.orig_selects.extend(new_selects)
                  # 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)))
  
      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.
  
          feed: _Feed instance containing the tokens for the expression.
  
          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.
  
          line: The line containing the expression being parsed.
  
          filename (default: None): The file containing the expression.
  
          linenr (default: None): The line number containing the expression.
  
          transform_m (default: False): Determines if 'm' should be rewritten to
             'm && MODULES' -- see parse_val_and_cond().
  
          Expression grammar, in decreasing order of precedence:
  
          <expr> -> <symbol>
                    <symbol> '=' <symbol>
                    <symbol> '!=' <symbol>
                    '(' <expr> ')'
                    '!' <expr>
                    <expr> '&&' <expr>
                    <expr> '||' <expr>"""
  
          # 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
  
          return self._parse_expr_rec(feed)
  
      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)
  
      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)
  
      def _parse_factor(self, feed):
          token = feed.get_next()
  
          if isinstance(token, (Symbol, str)):
              if self._cur_item is not None and isinstance(token, Symbol):
                  self._cur_item.referenced_syms.add(token)
  
              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
  
              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)
  
          if token == T_NOT:
              return (NOT, self._parse_factor(feed))
  
          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
  
          _parse_error(self._line, "malformed expression", self._filename,
                       self._linenr)
  
      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()).
  
          (I experimented with a pure regular expression implementation, but it
          came out slower, less readable, and wouldn't have been as flexible.)
  
          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."""
  
          s = s.strip()
          if s == "" or s[0] == "#":
              return _Feed([])
  
          if for_eval:
              previous = None # The previous token seen
              tokens = []
              i = 0 # The current index in the string being tokenized
  
          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)
  
              previous = keyword
              tokens = [keyword]
              # The current index in the string being tokenized
              i = initial_token_match.end()
  
          # _tokenize() is a hotspot during parsing, and this speeds things up a
          # bit
          strlen = len(s)
          append = tokens.append
  
          # 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()
  
                  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)
  
                      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))
  
                      append(sym)
  
              else:
                  # Not an identifier/keyword
  
                  while i < strlen and s[i].isspace():
                      i += 1
                  if i == strlen:
                      break
                  c = s[i]
                  i += 1
  
                  # 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
  
                  elif c == "&":
                      # Invalid characters are ignored
                      if i >= len(s) or s[i] != "&": continue
                      append(T_AND)
                      i += 1
  
                  elif c == "|":
                      # Invalid characters are ignored
                      if i >= len(s) or s[i] != "|": continue
                      append(T_OR)
                      i += 1
  
                  elif c == "!":
                      if i < len(s) and s[i] == "=":
                          append(T_UNEQUAL)
                          i += 1
                      else:
                          append(T_NOT)
  
                  elif c == "=": append(T_EQUAL)
                  elif c == "(": append(T_OPEN_PAREN)
                  elif c == ")": append(T_CLOSE_PAREN)
                  elif c == "#": break # Comment
  
                  else: continue # Invalid characters are ignored
  
              previous = tokens[-1]
  
          return _Feed(tokens)
  
      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]
  
          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
  
      #
      # Expression evaluation
      #
  
      def _eval_expr(self, expr):
          """Evaluates an expression to "n", "m", or "y"."""
  
          # Handles e.g. an "x if y" condition where the "if y" part is missing.
          if expr is None:
              return "y"
  
          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
  
      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()
  
          if isinstance(expr, str):
              return expr if (expr == "y" or expr == "m") else "n"
  
          # Ordered by frequency
  
          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
  
          if expr[0] == NOT:
              ev = self._eval_expr_rec(expr[1])
              if ev == "y":
                  return "n"
              return "y" if (ev == "n") else "m"
  
          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
  
          if expr[0] == EQUAL:
              return "y" if (_str_val(expr[1]) == _str_val(expr[2])) else "n"
  
          if expr[0] == UNEQUAL:
              return "y" if (_str_val(expr[1]) != _str_val(expr[2])) else "n"
  
          _internal_error("Internal error while evaluating expression: "
                          "unknown operation {0}.".format(expr[0]))
  
      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
  
      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
  
      #
      # Dependency tracking (for caching and invalidation)
      #
  
      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."""
  
          # 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)
  
          # The directly dependent symbols of a symbol are:
          #  - Any symbols whose prompts, default values, rev_dep (select
          #    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)
  
              for v, e in sym.def_exprs:
                  add_expr_deps(v, sym)
                  add_expr_deps(e, sym)
  
              add_expr_deps(sym.rev_dep, sym)
  
              for l, u, e in sym.ranges:
                  add_expr_deps(l, sym)
                  add_expr_deps(u, sym)
                  add_expr_deps(e, sym)
  
              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)
  
      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
  
          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
  
          left = transform_y_m_n(left)
          right = transform_y_m_n(right)
  
          # 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
  
      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
  
          def rec(expr):
              if isinstance(expr, str):
                  return False
              if isinstance(expr, Symbol):
                  return expr is sym
  
              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
  
          return rec(expr)
  
      def _invalidate_all(self):
          for sym in self.syms_iter():
              sym._invalidate()
  
      #
      # Printing and misc.
      #
  
      def _expand_sym_refs(self, s):
          """Expands $-references to symbols in 's' to symbol values, or to the
          empty string for undefined symbols."""
  
          while 1:
              sym_ref_match = _sym_ref_re_search(s)
              if sym_ref_match is None:
                  return s
  
              sym_name = sym_ref_match.group(0)[1:]
              sym = self.syms.get(sym_name)
              expansion = "" if sym is None else sym.get_value()
  
              s = s[:sym_ref_match.start()] + \
                  expansion + \
                  s[sym_ref_match.end():]
  
      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.
  
          no_value_str: String to return when 'expr' is missing (None).
  
          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."""
  
          if expr is None:
              return no_value_str
  
          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)
  
          return "{0} (value: {1})".format(_expr_to_str(expr), _expr_to_str(val))
  
      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"."""
  
          # As we deal a lot with string representations here, use some
          # convenient shorthand:
          s = _expr_to_str
  
          #
          # Common symbol/choice properties
          #
  
          user_val_str = "(no user value)" if sc.user_val is None else \
                         s(sc.user_val)
  
          # Build prompts string
          if not sc.prompts:
              prompts_str = " (no prompts)"
          else:
              prompts_str_rows = []
              for prompt, cond_expr in sc.orig_prompts:
                  if cond_expr is None:
                      prompts_str_rows.append(' "{0}"'.format(prompt))
                  else:
                      prompts_str_rows.append(
                        ' "{0}" if {1}'.format(prompt,
                                               self._expr_val_str(cond_expr)))
              prompts_str = "\n".join(prompts_str_rows)
  
          # Build locations string
          if not sc.def_locations:
              locations_str = "(no locations)"
          else:
              locations_str = " ".join(["{0}:{1}".format(filename, linenr) for
                                        (filename, linenr) in sc.def_locations])
  
          # Build additional-dependencies-from-menus-and-ifs string
          additional_deps_str = " " + \
            self._expr_val_str(sc.deps_from_containing,
                               "(no additional dependencies)")
  
          #
          # Symbol-specific stuff
          #
  
          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:
                          if cond_expr is None:
                              ranges_str_rows.append(" [{0}, {1}]".format(s(l),
                                                                          s(u)))
                          else:
                              ranges_str_rows.append(" [{0}, {1}] if {2}"
                                .format(s(l), s(u),
                                        self._expr_val_str(cond_expr)))
                      ranges_str = "\n".join(ranges_str_rows)
  
              # 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)
  
              # Build selects string
              if not sc.orig_selects:
                  selects_str = " (no selects)"
              else:
                  selects_str_rows = []
                  for target, cond_expr in sc.orig_selects:
                      if cond_expr is None:
                          selects_str_rows.append(" {0}".format(target.name))
                      else:
                          selects_str_rows.append(
                            " {0} if {1}".format(target.name,
                                                 self._expr_val_str(cond_expr)))
                  selects_str = "\n".join(selects_str_rows)
  
              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,
                            "Reverse (select-related) dependencies:",
                            " (no reverse dependencies)" if sc.rev_dep == "n"
                              else " " + self._expr_val_str(sc.rev_dep),
                            "Additional dependencies from enclosing menus "
                              "and ifs:",
                            additional_deps_str,
                            "Locations: " + locations_str)
  
              return res
  
          #
          # Choice-specific stuff
          #
  
          # Build selected symbol string
          sel = sc.get_selection()
          sel_str = "(no selection)" if sel is None else sel.name
  
          # 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:
                  if cond_expr is None:
                      defaults_str_rows.append(" {0}".format(sym.name))
                  else:
                      defaults_str_rows.append(" {0} if {1}".format(sym.name,
                                                  self._expr_val_str(cond_expr)))
              defaults_str = "\n".join(defaults_str_rows)
  
          # Build contained symbols string
          names = [sym.name for sym in sc.actual_symbols]
          syms_string = " ".join(names) if names else "(empty)"
  
          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)
  
      def _warn(self, msg, filename=None, linenr=None):
          """For printing warnings to stderr."""
          if self.print_warnings:
              _stderr_msg("warning: " + msg, filename, linenr)
  
  class Item(object):
  
      """Base class for symbols and other Kconfig constructs. Subclasses are
      Symbol, Choice, Menu, and Comment."""
  
      def is_symbol(self):
          """Returns True if the item is a symbol. Short for
          isinstance(item, kconfiglib.Symbol)."""
          return isinstance(self, Symbol)
  
      def is_choice(self):
          """Returns True if the item is a choice. Short for
          isinstance(item, kconfiglib.Choice)."""
          return isinstance(self, Choice)
  
      def is_menu(self):
          """Returns True if the item is a menu. Short for
          isinstance(item, kconfiglib.Menu)."""
          return isinstance(self, Menu)
  
      def is_comment(self):
          """Returns True if the item is a comment. Short for
          isinstance(item, kconfiglib.Comment)."""
          return isinstance(self, Comment)
  
  class Symbol(Item):
  
      """Represents a configuration symbol - e.g. FOO for
  
      config FOO
          ..."""
  
      #
      # Public interface
      #
  
      def get_config(self):
          """Returns the Config instance this symbol is from."""
          return self.config
  
      def get_name(self):
          """Returns the name of the symbol."""
          return self.name
  
      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
  
          if sym.get_type() == kconfiglib.STRING:
              ..."""
          return self.type
  
      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.
  
          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]
  
      def get_help(self):
          """Returns the help text of the symbol, or None if the symbol has no
          help text."""
          return self.help
  
      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
  
      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 *.
  
          config FOO *
              bool "foo prompt 1"
  
          config FOO *
              bool "foo prompt 2"
          """
          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:
  
          config A
              bool
              default BAR || FOO *
  
          config B
              tristate
              depends on FOO *
              default m if FOO *
  
          if FOO *
              config A
                  bool "A"
          endif
  
          config FOO (definition not included)
              bool
          """
          return self.ref_locations
  
      def get_value(self):
          """Calculate and return the value of the symbol. See also
          Symbol.set_user_value()."""
  
          if self.cached_val is not None:
              return self.cached_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
  
          new_val = DEFAULT_VALUE[self.type]
          vis = _get_visibility(self)
  
          # This is easiest to calculate together with the value
          self.write_to_conf = False
  
          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()
  
                      self.write_to_conf = (mode != "n")
  
                      if mode == "y":
                          if choice.get_selection() is self:
                              new_val = "y"
                          else:
                              new_val = "n"
                      elif mode == "m":
                          if self.user_val == "m" or self.user_val == "y":
                              new_val = "m"
  
              else:
                  # If the symbol is visible and has a user value, use that.
                  # Otherwise, look at defaults.
                  use_defaults = True
  
                  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 = False
  
                  if use_defaults:
                      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
  
                  # 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)
  
              # Promote "m" to "y" for booleans
              if new_val == "m" and self.type == BOOL:
                  new_val = "y"
  
          elif self.type == INT or self.type == HEX:
              has_active_range = False
              low = None
              high = None
              use_defaults = True
  
              base = 16 if self.type == HEX else 10
  
              for l, h, cond_expr in self.ranges:
                  if self.config._eval_expr(cond_expr) != "n":
                      has_active_range = True
  
                      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
  
                      break
  
              if vis != "n":
                  self.write_to_conf = True
  
                  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 the user value is OK, it is stored in exactly the same
                      # form as specified in the assignment (with or without
                      # "0x", etc).
  
                      use_defaults = False
                      new_val = self.user_val
  
              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
  
                          # 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.
  
                          new_val = _str_val(val_expr)
  
                          if _is_base_n(new_val, base):
                              new_val_num = int(new_val, base)
                              if has_active_range:
                                  clamped_val = None
  
                                  if new_val_num < low:
                                      clamped_val = low
                                  elif new_val_num > high:
                                      clamped_val = high
  
                                  if clamped_val is not None:
                                      new_val = (hex(clamped_val) if \
                                        self.type == HEX else str(clamped_val))
  
                              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))
  
          elif self.type == STRING:
              use_defaults = True
  
              if vis != "n":
                  self.write_to_conf = True
                  if self.user_val is not None:
                      new_val = self.user_val
                      use_defaults = False
  
              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
  
          self.cached_val = new_val
          return new_val
  
      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
  
      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.
  
          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.
  
          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
  
      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.
  
          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.
  
          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
  
      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.
  
          Otherwise, returns a list containing the user values that can be
          assigned to the symbol (that won't be truncated). Usage example:
  
          if "m" in sym.get_assignable_values():
              sym.set_user_value("m")
  
          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 []
  
      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.
  
          Example (assuming we're running with modules enabled -- i.e., MODULES
          set to 'y'):
  
          # Assume this has been assigned 'n'
          config N_SYM
              tristate "N_SYM"
  
          # Assume this has been assigned 'm'
          config M_SYM
              tristate "M_SYM"
  
          # Has visibility 'n'
          config A
              tristate "A"
              depends on N_SYM
  
          # Has visibility 'm'
          config B
              tristate "B"
              depends on M_SYM
  
          # Has visibility 'y'
          config C
              tristate "C"
  
          # Has no prompt, and hence visibility 'n'
          config D
              tristate
  
          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.
  
          You should probably look at get_lower/upper_bound(),
          get_assignable_values() and is_modifiable() before using this."""
          return _get_visibility(self)
  
      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
  
          config FOO
              bool
              prompt "foo" if A && B
              default C if D
              depends on E
              select F if G
  
          references the symbols A through G.
  
          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
  
      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
  
      def set_user_value(self, v):
          """Sets the user value of the symbol.
  
          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.
  
          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().
  
          Any symbols dependent on the symbol are (recursively) invalidated, so
          things will just work with regards to dependencies.
  
          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
  
          self._invalidate()
          self._invalidate_dependent()
  
      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()
  
      def is_modifiable(self):
          """Returns True if the value of the symbol could be modified by calling
          Symbol.set_user_value().
  
          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 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"
  
      def is_defined(self):
          """Returns False if the symbol is referred to in the Kconfig but never
          actually defined."""
          return self.is_defined_
  
      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_
  
      def is_from_environment(self):
          """Returns True if the symbol gets its value from the environment."""
          return self.is_from_env
  
      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)
  
      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
  
      def is_choice_selection(self):
          """Returns True if the symbol is contained in a choice statement and is
          the selected item. Equivalent to
  
          sym.is_choice_symbol() and sym.get_parent().get_selection() is sym"""
          return self.is_choice_sym and self.parent.get_selection() is self
  
      def is_allnoconfig_y(self):
          """Returns True if the symbol has the 'allnoconfig_y' option set."""
          return self.allnoconfig_y
  
      def __str__(self):
          """Returns a string containing various information about the symbol."""
          return self.config._get_sym_or_choice_str(self)
  
      #
      # Private methods
      #
  
      def __init__(self):
          """Symbol constructor -- not intended to be called directly by
          Kconfiglib clients."""
  
          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.config = None
          self.parent = None
  
          self.user_val = None # Value set by user
  
          # The prompt, default value and select conditions without any
          # dependencies from menus and ifs propagated to them
          self.orig_prompts = []
          self.orig_def_exprs = []
          self.orig_selects = []
  
          # 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()
          # Like 'referenced_syms', but includes symbols from
          # dependencies inherited from enclosing menus and ifs
          self.all_referenced_syms = set()
  
          # This records only dependencies specified with 'depends on'. Needed
          # when determining actual choice items (hrrrr...). See also
          # Choice._determine_actual_symbols().
          self.menu_dep = None
  
          # See Symbol.get_ref/def_locations().
          self.def_locations = []
          self.ref_locations = []
  
          # 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()
  
          # Cached values
  
          # 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
  
          # Flags
  
          # 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
  
      def _invalidate(self):
          if self.is_special_:
              return
  
          if self.is_choice_sym:
              self.parent._invalidate()
  
          self.cached_val = None
          self.cached_visibility = None
  
      def _invalidate_dependent(self):
          for sym in self._get_dependent():
              sym._invalidate()
  
      def _set_user_value_no_invalidate(self, v, suppress_load_warnings):
          """Like set_user_value(), but does not invalidate any symbols.
  
          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.
  
             Perhaps this could be made optional for load_config() instead."""
  
          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
  
          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
  
          # 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
  
          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))
  
          self.user_val = v
  
          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 _unset_user_value_no_recursive_invalidate(self):
          self._invalidate()
          self.user_val = None
  
          if self.is_choice_sym:
              self.parent._unset_user_value()
  
      def _make_conf(self, append_fn):
          if self.already_written:
              return
  
          self.already_written = True
  
          # Note: write_to_conf is determined in get_value()
          val = self.get_value()
          if not self.write_to_conf:
              return
  
          if self.type == BOOL or self.type == TRISTATE:
              if val == "y" or val == "m":
                  append_fn("CONFIG_{0}={1}".format(self.name, val))
              else:
                  append_fn("# CONFIG_{0} is not set".format(self.name))
  
          elif self.type == INT or self.type == HEX:
              append_fn("CONFIG_{0}={1}".format(self.name, val))
  
          elif self.type == STRING:
              # Escape \ and "
              append_fn('CONFIG_{0}="{1}"'
                        .format(self.name,
                                val.replace("\\", "\\\\").replace('"', '\\"')))
  
          else:
              _internal_error("Internal error while creating .config: unknown "
                              'type "{0}".'.format(self.type))
  
      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
  
          res = set(self.dep)
          for s in self.dep:
              res |= s._get_dependent()
  
          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()
  
          self.cached_deps = res
          return res
  
      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 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)
  
          for _, cond_expr in self.prompts:
              if self.config._expr_depends_on(cond_expr, on):
                  return True
  
          return False
  
  class Menu(Item):
  
      """Represents a menu statement."""
  
      #
      # Public interface
      #
  
      def get_config(self):
          """Return the Config instance this menu is from."""
          return self.config
  
      def get_title(self):
          """Returns the title text of the menu."""
          return self.title
  
      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
  
      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)
  
      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.
  
          recursive (default: False): True if items contained in items within the
             menu should be included recursively (preorder)."""
  
          if not recursive:
              return self.block
  
          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
  
      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.
  
          recursive (default: False): True if symbols contained in items within
             the menu should be included recursively."""
  
          return [item for item in self.get_items(recursive) if
                  isinstance(item, Symbol)]
  
      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)
  
      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 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)")
  
          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))
  
      #
      # Private methods
      #
  
      def __init__(self):
          """Menu constructor -- not intended to be called directly by
          Kconfiglib clients."""
  
          self.title = None
          self.dep_expr = None
          self.visible_if_expr = None
          self.block = None
          self.config = None
          self.parent = None
  
          # 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
  
          self.filename = None
          self.linenr = None
  
      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)
  
  class Choice(Item):
  
      """Represents a choice statement. A choice can be in one of three modes:
  
      "n" - The choice is not visible and no symbols can be selected.
  
      "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".
  
      "y" - One symbol will be "y" while the rest are "n".
  
      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.
  
      The mode changes automatically when a value is assigned to a symbol within
      the choice.
  
      See Symbol.get_visibility() too."""
  
      #
      # Public interface
      #
  
      def get_config(self):
          """Returns the Config instance this choice is from."""
          return self.config
  
      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 get_type(self):
          """Returns the type of the choice. See Symbol.get_type()."""
          return self.type
  
      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.
  
          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]
  
      def get_help(self):
          """Returns the help text of the choice, or None if the choice has no
          help text."""
          return self.help
  
      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 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
  
          if self.get_mode() != "y":
              return self._cache_ret(None)
  
          # User choice available?
          if self.user_val is not None and _get_visibility(self.user_val) == "y":
              return self._cache_ret(self.user_val)
  
          if self.optional:
              return self._cache_ret(None)
  
          return self._cache_ret(self.get_selection_from_defaults())
  
      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."""
  
          if not self.actual_symbols:
              return None
  
          for symbol, cond_expr in self.def_exprs:
              if self.config._eval_expr(cond_expr) != "n":
                  chosen_symbol = symbol
                  break
          else:
              chosen_symbol = self.actual_symbols[0]
  
          # 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
  
      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 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.
  
          As of Linux 3.7.0-rc8, this seems to be used intentionally in one
          place: drivers/usb/gadget/Kconfig.
  
          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 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)
  
      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))
  
          # Promote "m" to "y" for boolean choices
          if mode == "m" and self.type == BOOL:
              return "y"
  
          return mode
  
      def is_optional(self):
          """Returns True if the choice has the 'optional' flag set (and so will
          default to "n" mode)."""
          return self.optional
  
      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 __init__(self):
          """Choice constructor -- not intended to be called directly by
          Kconfiglib clients."""
  
          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 = None # List of contained items
          self.config = None
          self.parent = None
  
          self.user_val = None
          self.user_mode = None
  
          # 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 = []
  
          # The prompts and default values without any dependencies from
          # enclosing menus and ifs propagated
          self.orig_prompts = []
          self.orig_def_exprs = []
  
          # 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()
  
          # See Choice.get_def_locations()
          self.def_locations = []
  
          # Cached values
          self.cached_selection = None
          self.cached_visibility = None
  
          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()).
  
          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 = []
  
          for item in self.block:
              if not isinstance(item, Symbol):
                  stack = []
                  continue
  
              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)
  
      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
  
          return selection
  
      def _invalidate(self):
          self.cached_selection = None
          self.cached_visibility = None
  
      def _unset_user_value(self):
          self._invalidate()
          self.user_val = None
          self.user_mode = None
  
      def _make_conf(self, append_fn):
          _make_block_conf(self.block, append_fn)
  
  class Comment(Item):
  
      """Represents a comment statement."""
  
      #
      # Public interface
      #
  
      def get_config(self):
          """Returns the Config instance this comment is from."""
          return self.config
  
      def get_text(self):
          """Returns the text of the comment."""
          return self.text
  
      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 get_visibility(self):
          """Returns the visibility of the comment. See also
          Symbol.get_visibility()."""
          return self.config._eval_expr(self.dep_expr)
  
      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)")
  
          additional_deps_str = " " + \
            self.config._expr_val_str(self.deps_from_containing,
                                      "(no additional dependencies)")
  
          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 __init__(self):
          """Comment constructor -- not intended to be called directly by
          Kconfiglib clients."""
  
          self.text = None
          self.dep_expr = None
          self.config = None
          self.parent = None
  
          # 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 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
  
          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))
  
  class Kconfig_Syntax_Error(Exception):
      """Exception raised for syntax errors."""
      pass
  
  class Internal_Error(Exception):
      """Exception raised for internal errors."""
      pass
  
  #
  # Public functions
  #
  
  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]
  
  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 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]
  
  #
  # Internal classes
  #
  
  class _Feed(object):
  
      """Class for working with sequences in a stream-like fashion; handy for
      tokens."""
  
      # 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 get_next(self):
          if self.i >= self.length:
              return None
          item = self.items[self.i]
          self.i += 1
          return item
  
      def peek_next(self):
          return None if self.i >= self.length else self.items[self.i]
  
      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
  
      def unget_all(self):
          self.i = 0
  
  class _FileFeed(object):
  
      """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."""
  
      __slots__ = ['filename', 'lines', 'length', 'linenr']
  
      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
  
      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
  
      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 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
  
  #
  # Internal functions
  #
  
  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)
  
          if isinstance(sc, Symbol) and sc.is_choice_sym:
              vis = sc.config._eval_min(vis, _get_visibility(sc.parent))
  
          # Promote "m" to "y" if we're dealing with a non-tristate
          if vis == "m" and sc.type != TRISTATE:
              vis = "y"
  
          sc.cached_visibility = vis
  
      return sc.cached_visibility
  
  def _make_and(e1, e2):
      """Constructs an AND (&&) expression. Performs trivial simplification.
      Nones equate to 'y'.
  
      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
  
      # Prefer to merge argument lists if possible to reduce the number of nodes
  
      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])
  
      if isinstance(e2, tuple) and e2[0] == AND:
          return (AND, e2[1] + [e1])
  
      return (AND, [e1, e2])
  
  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."""
  
      # 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
  
      # Prefer to merge argument lists if possible to reduce the number of nodes
  
      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])
  
      if isinstance(e2, tuple) and e2[0] == OR:
          return (OR, e2[1] + [e1])
  
      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 _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
  
  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."""
  
      # 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
  
  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 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]
  
      handle_sub_expr(lst[0])
      for expr in lst[1:]:
          res.append(op_str)
          handle_sub_expr(expr)
  
      return res
  
  def _expr_to_str_rec(expr):
      if expr is None:
          return [""]
  
      if isinstance(expr, (Symbol, str)):
          return [_sym_str_string(expr)]
  
      if expr[0] in (AND, OR):
          return _intersperse(expr[1], expr[0])
  
      if expr[0] == NOT:
          need_parens = not isinstance(expr[1], (str, Symbol))
  
          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 _expr_to_str(expr):
      return "".join(_expr_to_str_rec(expr))
  
  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 _is_base_n(s, n):
      try:
          int(s, n)
          return True
      except ValueError:
          return False
  
  def _lines(*args):
      """Returns a string consisting of all arguments, with newlines inserted
      between them."""
      return "\n".join(args)
  
  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
  
  def _clean_up_path(path):
      """Strips an initial "./" and any trailing slashes from 'path'."""
      if path.startswith("./"):
          path = path[2:]
      return path.rstrip("/")
  
  def _stderr_msg(msg, filename, linenr):
      if filename is not None:
          sys.stderr.write("{0}:{1}: ".format(_clean_up_path(filename), linenr))
      sys.stderr.write(msg + "\n")
  
  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()))
  
  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))
  
  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.")
  
  #
  # Internal global constants
  #
  
  # 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)
  
  # 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.
  
  # 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
  
  # Strings to use for True and False
  BOOL_STR = {False: "false", True: "true"}
  
  # 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))
  
  # 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
  
  # 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
  
  # Regular expressions for parsing .config files
  _set_re_match = re.compile(r"CONFIG_(\w+)=(.*)").match
  _unset_re_match = re.compile(r"# CONFIG_(\w+) is not set").match
  
  # Regular expression for finding $-references to symbols in strings
  _sym_ref_re_search = re.compile(r"\$[A-Za-z0-9_]+").search
  
  # Integers representing symbol types
  UNKNOWN, BOOL, TRISTATE, STRING, HEX, INT = range(6)
  
  # 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}
  
  # 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: ""}
  
  # Indicates that no item is selected in a choice statement
  NO_SELECTION = 0
  
  # Integers representing expression types
  AND, OR, NOT, EQUAL, UNEQUAL = range(5)
  
  # Map from tristate values to integers
  TRI_TO_INT = {"n": 0, "m": 1, "y": 2}
  
  # Printing-related stuff
  
  OP_TO_STR = {AND: " && ", OR: " || ", EQUAL: " = ", UNEQUAL: " != "}
  PRECEDENCE = {OR: 0, AND: 1, NOT: 2}
  