text: #
  # Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007 The SCons Foundation
  #
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  # permit persons to whom the Software is furnished to do so, subject to
  # the following conditions:
  #
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  # WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  # NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  # LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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  # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  #
  
  __revision__ = "/home/scons/scons/branch.0/baseline/src/engine/SCons/PathList.py 0.97.D001 2007/05/17 11:35:19 knight"
  
  __doc__ = """SCons.PathList
  
  A module for handling lists of directory paths (the sort of things
  that get set as CPPPATH, LIBPATH, etc.) with as much caching of data and
  efficiency as we can while still keeping the evaluation delayed so that we
  Do the Right Thing (almost) regardless of how the variable is specified.
  
  """
  
  import os
  import string
  
  import SCons.Memoize
  import SCons.Node
  import SCons.Util
  
  #
  # Variables to specify the different types of entries in a PathList object:
  #
  
  TYPE_STRING_NO_SUBST = 0        # string with no '$'
  TYPE_STRING_SUBST = 1           # string containing '$'
  TYPE_OBJECT = 2                 # other object
  
  def node_conv(obj):
      """
      This is the "string conversion" routine that we have our substitutions
      use to return Nodes, not strings.  This relies on the fact that an
      EntryProxy object has a get() method that returns the underlying
      Node that it wraps, which is a bit of architectural dependence
      that we might need to break or modify in the future in response to
      additional requirements.
      """
      try:
          get = obj.get
      except AttributeError:
          if isinstance(obj, SCons.Node.Node):
              result = obj
          else:
              result = str(obj)
      else:
          result = get()
      return result
  
  class _PathList:
      """
      An actual PathList object.
      """
      def __init__(self, pathlist):
          """
          Initializes a PathList object, canonicalizing the input and
          pre-processing it for quicker substitution later.
  
          The stored representation of the PathList is a list of tuples
          containing (type, value), where the "type" is one of the TYPE_*
          variables defined above.  We distinguish between:
  
              strings that contain no '$' and therefore need no
              delayed-evaluation string substitution (we expect that there
              will be many of these and that we therefore get a pretty
              big win from avoiding string substitution)
  
              strings that contain '$' and therefore need substitution
              (the hard case is things like '${TARGET.dir}/include',
              which require re-evaluation for every target + source)
  
              other objects (which may be something like an EntryProxy
              that needs a method called to return a Node)
  
          Pre-identifying the type of each element in the PathList up-front
          and storing the type in the list of tuples is intended to reduce
          the amount of calculation when we actually do the substitution
          over and over for each target.
          """
          if SCons.Util.is_String(pathlist):
              pathlist = string.split(pathlist, os.pathsep)
          elif not SCons.Util.is_Sequence(pathlist):
              pathlist = [pathlist]
  
          pl = []
          for p in pathlist:
              try:
                  index = string.find(p, '$')
              except (AttributeError, TypeError):
                  type = TYPE_OBJECT
              else:
                  if index == -1:
                      type = TYPE_STRING_NO_SUBST
                  else:
                      type = TYPE_STRING_SUBST
              pl.append((type, p))
  
          self.pathlist = tuple(pl)
  
      def __len__(self): return len(self.pathlist)
  
      def __getitem__(self, i): return self.pathlist[i]
  
      def subst_path(self, env, target, source):
          """
          Performs construction variable substitution on a pre-digested
          PathList for a specific target and source.
          """
          result = []
          for type, value in self.pathlist:
              if type == TYPE_STRING_SUBST:
                  value = env.subst(value, target=target, source=source,
                                    conv=node_conv)
                  if SCons.Util.is_Sequence(value):
                      # It came back as a string or tuple, which in this
                      # case usually means some variable expanded to an
                      # actually Dir node.  Concatenate the values.
                      value = string.join(map(str, value), '')
              elif type == TYPE_OBJECT:
                  value = node_conv(value)
              result.append(value)
          return tuple(result)
  
  
  class PathListCache:
      """
      A class to handle caching of PathList lookups.
  
      This class gets instantiated once and then deleted from the namespace,
      so it's used as a Singleton (although we don't enforce that in the
      usual Pythonic ways).  We could have just made the cache a dictionary
      in the module namespace, but putting it in this class allows us to
      use the same Memoizer pattern that we use elsewhere to count cache
      hits and misses, which is very valuable.
  
      Lookup keys in the cache are computed by the _PathList_key() method.
      Cache lookup should be quick, so we don't spend cycles canonicalizing
      all forms of the same lookup key.  For example, 'x:y' and ['x',
      'y'] logically represent the same list, but we don't bother to
      split string representations and treat those two equivalently.
      (Note, however, that we do, treat lists and tuples the same.)
  
      The main type of duplication we're trying to catch will come from
      looking up the same path list from two different clones of the
      same construction environment.  That is, given
      
          env2 = env1.Clone()
  
      both env1 and env2 will have the same CPPPATH value, and we can
      cheaply avoid re-parsing both values of CPPPATH by using the
      common value from this cache.
      """
      if SCons.Memoize.use_memoizer:
          __metaclass__ = SCons.Memoize.Memoized_Metaclass
  
      memoizer_counters = []
  
      def __init__(self):
          self._memo = {}
  
      def _PathList_key(self, pathlist):
          """
          Returns the key for memoization of PathLists.
  
          Note that we want this to be pretty quick, so we don't completely
          canonicalize all forms of the same list.  For example,
          'dir1:$ROOT/dir2' and ['$ROOT/dir1', 'dir'] may logically
          represent the same list if you're executing from $ROOT, but
          we're not going to bother splitting strings into path elements,
          or massaging strings into Nodes, to identify that equivalence.
          We just want to eliminate obvious redundancy from the normal
          case of re-using exactly the same cloned value for a path.
          """
          if SCons.Util.is_Sequence(pathlist):
              pathlist = tuple(SCons.Util.flatten(pathlist))
          return pathlist
  
      memoizer_counters.append(SCons.Memoize.CountDict('PathList', _PathList_key))
  
      def PathList(self, pathlist):
          """
          Returns the cached _PathList object for the specified pathlist,
          creating and caching a new object as necessary.
          """
          pathlist = self._PathList_key(pathlist)
          try:
              memo_dict = self._memo['PathList']
          except KeyError:
              memo_dict = {}
              self._memo['PathList'] = memo_dict
          else:
              try:
                  return memo_dict[pathlist]
              except KeyError:
                  pass
  
          result = _PathList(pathlist)
  
          memo_dict[pathlist] = result
  
          return result
  
  PathList = PathListCache().PathList
  
  
  del PathListCache
  