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diff --git a/engine/SCons/Node/__init__.py b/engine/SCons/Node/__init__.py
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+"""SCons.Node
+
+The Node package for the SCons software construction utility.
+
+This is, in many ways, the heart of SCons.
+
+A Node is where we encapsulate all of the dependency information about
+any thing that SCons can build, or about any thing which SCons can use
+to build some other thing.  The canonical "thing," of course, is a file,
+but a Node can also represent something remote (like a web page) or
+something completely abstract (like an Alias).
+
+Each specific type of "thing" is specifically represented by a subclass
+of the Node base class:  Node.FS.File for files, Node.Alias for aliases,
+etc.  Dependency information is kept here in the base class, and
+information specific to files/aliases/etc. is in the subclass.  The
+goal, if we've done this correctly, is that any type of "thing" should
+be able to depend on any other type of "thing."
+
+"""
+
+#
+# Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 The SCons Foundation
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be included
+# in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
+# KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+# 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
+# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+#
+
+__revision__ = "src/engine/SCons/Node/__init__.py 4577 2009/12/27 19:43:56 scons"
+
+import copy
+from itertools import chain, izip
+import string
+import UserList
+
+from SCons.Debug import logInstanceCreation
+import SCons.Executor
+import SCons.Memoize
+import SCons.Util
+
+from SCons.Debug import Trace
+
+def classname(obj):
+    return string.split(str(obj.__class__), '.')[-1]
+
+# Node states
+#
+# These are in "priority" order, so that the maximum value for any
+# child/dependency of a node represents the state of that node if
+# it has no builder of its own.  The canonical example is a file
+# system directory, which is only up to date if all of its children
+# were up to date.
+no_state = 0
+pending = 1
+executing = 2
+up_to_date = 3
+executed = 4
+failed = 5
+
+StateString = {
+    0 : "no_state",
+    1 : "pending",
+    2 : "executing",
+    3 : "up_to_date",
+    4 : "executed",
+    5 : "failed",
+}
+
+# controls whether implicit dependencies are cached:
+implicit_cache = 0
+
+# controls whether implicit dep changes are ignored:
+implicit_deps_unchanged = 0
+
+# controls whether the cached implicit deps are ignored:
+implicit_deps_changed = 0
+
+# A variable that can be set to an interface-specific function be called
+# to annotate a Node with information about its creation.
+def do_nothing(node): pass
+
+Annotate = do_nothing
+
+# Classes for signature info for Nodes.
+
+class NodeInfoBase:
+    """
+    The generic base class for signature information for a Node.
+
+    Node subclasses should subclass NodeInfoBase to provide their own
+    logic for dealing with their own Node-specific signature information.
+    """
+    current_version_id = 1
+    def __init__(self, node):
+        # Create an object attribute from the class attribute so it ends up
+        # in the pickled data in the .sconsign file.
+        self._version_id = self.current_version_id
+    def update(self, node):
+        try:
+            field_list = self.field_list
+        except AttributeError:
+            return
+        for f in field_list:
+            try:
+                delattr(self, f)
+            except AttributeError:
+                pass
+            try:
+                func = getattr(node, 'get_' + f)
+            except AttributeError:
+                pass
+            else:
+                setattr(self, f, func())
+    def convert(self, node, val):
+        pass
+    def merge(self, other):
+        self.__dict__.update(other.__dict__)
+    def format(self, field_list=None, names=0):
+        if field_list is None:
+            try:
+                field_list = self.field_list
+            except AttributeError:
+                field_list = self.__dict__.keys()
+                field_list.sort()
+        fields = []
+        for field in field_list:
+            try:
+                f = getattr(self, field)
+            except AttributeError:
+                f = None
+            f = str(f)
+            if names:
+                f = field + ': ' + f
+            fields.append(f)
+        return fields
+
+class BuildInfoBase:
+    """
+    The generic base class for build information for a Node.
+
+    This is what gets stored in a .sconsign file for each target file.
+    It contains a NodeInfo instance for this node (signature information
+    that's specific to the type of Node) and direct attributes for the
+    generic build stuff we have to track:  sources, explicit dependencies,
+    implicit dependencies, and action information.
+    """
+    current_version_id = 1
+    def __init__(self, node):
+        # Create an object attribute from the class attribute so it ends up
+        # in the pickled data in the .sconsign file.
+        self._version_id = self.current_version_id
+        self.bsourcesigs = []
+        self.bdependsigs = []
+        self.bimplicitsigs = []
+        self.bactsig = None
+    def merge(self, other):
+        self.__dict__.update(other.__dict__)
+
+class Node:
+    """The base Node class, for entities that we know how to
+    build, or use to build other Nodes.
+    """
+
+    if SCons.Memoize.use_memoizer:
+        __metaclass__ = SCons.Memoize.Memoized_Metaclass
+
+    memoizer_counters = []
+
+    class Attrs:
+        pass
+
+    def __init__(self):
+        if __debug__: logInstanceCreation(self, 'Node.Node')
+        # Note that we no longer explicitly initialize a self.builder
+        # attribute to None here.  That's because the self.builder
+        # attribute may be created on-the-fly later by a subclass (the
+        # canonical example being a builder to fetch a file from a
+        # source code system like CVS or Subversion).
+
+        # Each list of children that we maintain is accompanied by a
+        # dictionary used to look up quickly whether a node is already
+        # present in the list.  Empirical tests showed that it was
+        # fastest to maintain them as side-by-side Node attributes in
+        # this way, instead of wrapping up each list+dictionary pair in
+        # a class.  (Of course, we could always still do that in the
+        # future if we had a good reason to...).
+        self.sources = []       # source files used to build node
+        self.sources_set = set()
+        self._specific_sources = False
+        self.depends = []       # explicit dependencies (from Depends)
+        self.depends_set = set()
+        self.ignore = []        # dependencies to ignore
+        self.ignore_set = set()
+        self.prerequisites = SCons.Util.UniqueList()
+        self.implicit = None    # implicit (scanned) dependencies (None means not scanned yet)
+        self.waiting_parents = set()
+        self.waiting_s_e = set()
+        self.ref_count = 0
+        self.wkids = None       # Kids yet to walk, when it's an array
+
+        self.env = None
+        self.state = no_state
+        self.precious = None
+        self.noclean = 0
+        self.nocache = 0
+        self.always_build = None
+        self.includes = None
+        self.attributes = self.Attrs() # Generic place to stick information about the Node.
+        self.side_effect = 0 # true iff this node is a side effect
+        self.side_effects = [] # the side effects of building this target
+        self.linked = 0 # is this node linked to the variant directory?
+
+        self.clear_memoized_values()
+
+        # Let the interface in which the build engine is embedded
+        # annotate this Node with its own info (like a description of
+        # what line in what file created the node, for example).
+        Annotate(self)
+
+    def disambiguate(self, must_exist=None):
+        return self
+
+    def get_suffix(self):
+        return ''
+
+    memoizer_counters.append(SCons.Memoize.CountValue('get_build_env'))
+
+    def get_build_env(self):
+        """Fetch the appropriate Environment to build this node.
+        """
+        try:
+            return self._memo['get_build_env']
+        except KeyError:
+            pass
+        result = self.get_executor().get_build_env()
+        self._memo['get_build_env'] = result
+        return result
+
+    def get_build_scanner_path(self, scanner):
+        """Fetch the appropriate scanner path for this node."""
+        return self.get_executor().get_build_scanner_path(scanner)
+
+    def set_executor(self, executor):
+        """Set the action executor for this node."""
+        self.executor = executor
+
+    def get_executor(self, create=1):
+        """Fetch the action executor for this node.  Create one if
+        there isn't already one, and requested to do so."""
+        try:
+            executor = self.executor
+        except AttributeError:
+            if not create:
+                raise
+            try:
+                act = self.builder.action
+            except AttributeError:
+                executor = SCons.Executor.Null(targets=[self])
+            else:
+                executor = SCons.Executor.Executor(act,
+                                                   self.env or self.builder.env,
+                                                   [self.builder.overrides],
+                                                   [self],
+                                                   self.sources)
+            self.executor = executor
+        return executor
+
+    def executor_cleanup(self):
+        """Let the executor clean up any cached information."""
+        try:
+            executor = self.get_executor(create=None)
+        except AttributeError:
+            pass
+        else:
+            executor.cleanup()
+
+    def reset_executor(self):
+        "Remove cached executor; forces recompute when needed."
+        try:
+            delattr(self, 'executor')
+        except AttributeError:
+            pass
+
+    def push_to_cache(self):
+        """Try to push a node into a cache
+        """
+        pass
+
+    def retrieve_from_cache(self):
+        """Try to retrieve the node's content from a cache
+
+        This method is called from multiple threads in a parallel build,
+        so only do thread safe stuff here. Do thread unsafe stuff in
+        built().
+
+        Returns true iff the node was successfully retrieved.
+        """
+        return 0
+
+    #
+    # Taskmaster interface subsystem
+    #
+
+    def make_ready(self):
+        """Get a Node ready for evaluation.
+
+        This is called before the Taskmaster decides if the Node is
+        up-to-date or not.  Overriding this method allows for a Node
+        subclass to be disambiguated if necessary, or for an implicit
+        source builder to be attached.
+        """
+        pass
+
+    def prepare(self):
+        """Prepare for this Node to be built.
+
+        This is called after the Taskmaster has decided that the Node
+        is out-of-date and must be rebuilt, but before actually calling
+        the method to build the Node.
+
+        This default implementation checks that explicit or implicit
+        dependencies either exist or are derived, and initializes the
+        BuildInfo structure that will hold the information about how
+        this node is, uh, built.
+
+        (The existence of source files is checked separately by the
+        Executor, which aggregates checks for all of the targets built
+        by a specific action.)
+
+        Overriding this method allows for for a Node subclass to remove
+        the underlying file from the file system.  Note that subclass
+        methods should call this base class method to get the child
+        check and the BuildInfo structure.
+        """
+        for d in self.depends:
+            if d.missing():
+                msg = "Explicit dependency `%s' not found, needed by target `%s'."
+                raise SCons.Errors.StopError, msg % (d, self)
+        if self.implicit is not None:
+            for i in self.implicit:
+                if i.missing():
+                    msg = "Implicit dependency `%s' not found, needed by target `%s'."
+                    raise SCons.Errors.StopError, msg % (i, self)
+        self.binfo = self.get_binfo()
+
+    def build(self, **kw):
+        """Actually build the node.
+
+        This is called by the Taskmaster after it's decided that the
+        Node is out-of-date and must be rebuilt, and after the prepare()
+        method has gotten everything, uh, prepared.
+
+        This method is called from multiple threads in a parallel build,
+        so only do thread safe stuff here. Do thread unsafe stuff
+        in built().
+
+        """
+        try:
+            apply(self.get_executor(), (self,), kw)
+        except SCons.Errors.BuildError, e:
+            e.node = self
+            raise
+
+    def built(self):
+        """Called just after this node is successfully built."""
+
+        # Clear the implicit dependency caches of any Nodes
+        # waiting for this Node to be built.
+        for parent in self.waiting_parents:
+            parent.implicit = None
+
+        self.clear()
+
+        self.ninfo.update(self)
+
+    def visited(self):
+        """Called just after this node has been visited (with or
+        without a build)."""
+        try:
+            binfo = self.binfo
+        except AttributeError:
+            # Apparently this node doesn't need build info, so
+            # don't bother calculating or storing it.
+            pass
+        else:
+            self.ninfo.update(self)
+            self.store_info()
+
+    #
+    #
+    #
+
+    def add_to_waiting_s_e(self, node):
+        self.waiting_s_e.add(node)
+
+    def add_to_waiting_parents(self, node):
+        """
+        Returns the number of nodes added to our waiting parents list:
+        1 if we add a unique waiting parent, 0 if not.  (Note that the
+        returned values are intended to be used to increment a reference
+        count, so don't think you can "clean up" this function by using
+        True and False instead...)
+        """
+        wp = self.waiting_parents
+        if node in wp:
+            return 0
+        wp.add(node)
+        return 1
+
+    def postprocess(self):
+        """Clean up anything we don't need to hang onto after we've
+        been built."""
+        self.executor_cleanup()
+        self.waiting_parents = set()
+
+    def clear(self):
+        """Completely clear a Node of all its cached state (so that it
+        can be re-evaluated by interfaces that do continuous integration
+        builds).
+        """
+        # The del_binfo() call here isn't necessary for normal execution,
+        # but is for interactive mode, where we might rebuild the same
+        # target and need to start from scratch.
+        self.del_binfo()
+        self.clear_memoized_values()
+        self.ninfo = self.new_ninfo()
+        self.executor_cleanup()
+        try:
+            delattr(self, '_calculated_sig')
+        except AttributeError:
+            pass
+        self.includes = None
+
+    def clear_memoized_values(self):
+        self._memo = {}
+
+    def builder_set(self, builder):
+        self.builder = builder
+        try:
+            del self.executor
+        except AttributeError:
+            pass
+
+    def has_builder(self):
+        """Return whether this Node has a builder or not.
+
+        In Boolean tests, this turns out to be a *lot* more efficient
+        than simply examining the builder attribute directly ("if
+        node.builder: ..."). When the builder attribute is examined
+        directly, it ends up calling __getattr__ for both the __len__
+        and __nonzero__ attributes on instances of our Builder Proxy
+        class(es), generating a bazillion extra calls and slowing
+        things down immensely.
+        """
+        try:
+            b = self.builder
+        except AttributeError:
+            # There was no explicit builder for this Node, so initialize
+            # the self.builder attribute to None now.
+            b = self.builder = None
+        return b is not None
+
+    def set_explicit(self, is_explicit):
+        self.is_explicit = is_explicit
+
+    def has_explicit_builder(self):
+        """Return whether this Node has an explicit builder
+
+        This allows an internal Builder created by SCons to be marked
+        non-explicit, so that it can be overridden by an explicit
+        builder that the user supplies (the canonical example being
+        directories)."""
+        try:
+            return self.is_explicit
+        except AttributeError:
+            self.is_explicit = None
+            return self.is_explicit
+
+    def get_builder(self, default_builder=None):
+        """Return the set builder, or a specified default value"""
+        try:
+            return self.builder
+        except AttributeError:
+            return default_builder
+
+    multiple_side_effect_has_builder = has_builder
+
+    def is_derived(self):
+        """
+        Returns true iff this node is derived (i.e. built).
+
+        This should return true only for nodes whose path should be in
+        the variant directory when duplicate=0 and should contribute their build
+        signatures when they are used as source files to other derived files. For
+        example: source with source builders are not derived in this sense,
+        and hence should not return true.
+        """
+        return self.has_builder() or self.side_effect
+
+    def alter_targets(self):
+        """Return a list of alternate targets for this Node.
+        """
+        return [], None
+
+    def get_found_includes(self, env, scanner, path):
+        """Return the scanned include lines (implicit dependencies)
+        found in this node.
+
+        The default is no implicit dependencies.  We expect this method
+        to be overridden by any subclass that can be scanned for
+        implicit dependencies.
+        """
+        return []
+
+    def get_implicit_deps(self, env, scanner, path):
+        """Return a list of implicit dependencies for this node.
+
+        This method exists to handle recursive invocation of the scanner
+        on the implicit dependencies returned by the scanner, if the
+        scanner's recursive flag says that we should.
+        """
+        if not scanner:
+            return []
+
+        # Give the scanner a chance to select a more specific scanner
+        # for this Node.
+        #scanner = scanner.select(self)
+
+        nodes = [self]
+        seen = {}
+        seen[self] = 1
+        deps = []
+        while nodes:
+            n = nodes.pop(0)
+            d = filter(lambda x, seen=seen: not seen.has_key(x),
+                       n.get_found_includes(env, scanner, path))
+            if d:
+                deps.extend(d)
+                for n in d:
+                    seen[n] = 1
+                nodes.extend(scanner.recurse_nodes(d))
+
+        return deps
+
+    def get_env_scanner(self, env, kw={}):
+        return env.get_scanner(self.scanner_key())
+
+    def get_target_scanner(self):
+        return self.builder.target_scanner
+
+    def get_source_scanner(self, node):
+        """Fetch the source scanner for the specified node
+
+        NOTE:  "self" is the target being built, "node" is
+        the source file for which we want to fetch the scanner.
+
+        Implies self.has_builder() is true; again, expect to only be
+        called from locations where this is already verified.
+
+        This function may be called very often; it attempts to cache
+        the scanner found to improve performance.
+        """
+        scanner = None
+        try:
+            scanner = self.builder.source_scanner
+        except AttributeError:
+            pass
+        if not scanner:
+            # The builder didn't have an explicit scanner, so go look up
+            # a scanner from env['SCANNERS'] based on the node's scanner
+            # key (usually the file extension).
+            scanner = self.get_env_scanner(self.get_build_env())
+        if scanner:
+            scanner = scanner.select(node)
+        return scanner
+
+    def add_to_implicit(self, deps):
+        if not hasattr(self, 'implicit') or self.implicit is None:
+            self.implicit = []
+            self.implicit_set = set()
+            self._children_reset()
+        self._add_child(self.implicit, self.implicit_set, deps)
+
+    def scan(self):
+        """Scan this node's dependents for implicit dependencies."""
+        # Don't bother scanning non-derived files, because we don't
+        # care what their dependencies are.
+        # Don't scan again, if we already have scanned.
+        if self.implicit is not None:
+            return
+        self.implicit = []
+        self.implicit_set = set()
+        self._children_reset()
+        if not self.has_builder():
+            return
+
+        build_env = self.get_build_env()
+        executor = self.get_executor()
+
+        # Here's where we implement --implicit-cache.
+        if implicit_cache and not implicit_deps_changed:
+            implicit = self.get_stored_implicit()
+            if implicit is not None:
+                # We now add the implicit dependencies returned from the
+                # stored .sconsign entry to have already been converted
+                # to Nodes for us.  (We used to run them through a
+                # source_factory function here.)
+
+                # Update all of the targets with them.  This
+                # essentially short-circuits an N*M scan of the
+                # sources for each individual target, which is a hell
+                # of a lot more efficient.
+                for tgt in executor.get_all_targets():
+                    tgt.add_to_implicit(implicit)
+
+                if implicit_deps_unchanged or self.is_up_to_date():
+                    return
+                # one of this node's sources has changed,
+                # so we must recalculate the implicit deps:
+                self.implicit = []
+                self.implicit_set = set()
+
+        # Have the executor scan the sources.
+        executor.scan_sources(self.builder.source_scanner)
+
+        # If there's a target scanner, have the executor scan the target
+        # node itself and associated targets that might be built.
+        scanner = self.get_target_scanner()
+        if scanner:
+            executor.scan_targets(scanner)
+
+    def scanner_key(self):
+        return None
+
+    def select_scanner(self, scanner):
+        """Selects a scanner for this Node.
+
+        This is a separate method so it can be overridden by Node
+        subclasses (specifically, Node.FS.Dir) that *must* use their
+        own Scanner and don't select one the Scanner.Selector that's
+        configured for the target.
+        """
+        return scanner.select(self)
+
+    def env_set(self, env, safe=0):
+        if safe and self.env:
+            return
+        self.env = env
+
+    #
+    # SIGNATURE SUBSYSTEM
+    #
+
+    NodeInfo = NodeInfoBase
+    BuildInfo = BuildInfoBase
+
+    def new_ninfo(self):
+        ninfo = self.NodeInfo(self)
+        return ninfo
+
+    def get_ninfo(self):
+        try:
+            return self.ninfo
+        except AttributeError:
+            self.ninfo = self.new_ninfo()
+            return self.ninfo
+
+    def new_binfo(self):
+        binfo = self.BuildInfo(self)
+        return binfo
+
+    def get_binfo(self):
+        """
+        Fetch a node's build information.
+
+        node - the node whose sources will be collected
+        cache - alternate node to use for the signature cache
+        returns - the build signature
+
+        This no longer handles the recursive descent of the
+        node's children's signatures.  We expect that they're
+        already built and updated by someone else, if that's
+        what's wanted.
+        """
+        try:
+            return self.binfo
+        except AttributeError:
+            pass
+
+        binfo = self.new_binfo()
+        self.binfo = binfo
+
+        executor = self.get_executor()
+        ignore_set = self.ignore_set
+
+        if self.has_builder():
+            binfo.bact = str(executor)
+            binfo.bactsig = SCons.Util.MD5signature(executor.get_contents())
+
+        if self._specific_sources:
+            sources = []
+            for s in self.sources:
+                if s not in ignore_set:
+                    sources.append(s)
+        else:
+            sources = executor.get_unignored_sources(self, self.ignore)
+        seen = set()
+        bsources = []
+        bsourcesigs = []
+        for s in sources:
+            if not s in seen:
+                seen.add(s)
+                bsources.append(s)
+                bsourcesigs.append(s.get_ninfo())
+        binfo.bsources = bsources
+        binfo.bsourcesigs = bsourcesigs
+
+        depends = self.depends
+        dependsigs = []
+        for d in depends:
+            if d not in ignore_set:
+                dependsigs.append(d.get_ninfo())
+        binfo.bdepends = depends
+        binfo.bdependsigs = dependsigs
+
+        implicit = self.implicit or []
+        implicitsigs = []
+        for i in implicit:
+            if i not in ignore_set:
+                implicitsigs.append(i.get_ninfo())
+        binfo.bimplicit = implicit
+        binfo.bimplicitsigs = implicitsigs
+
+        return binfo
+
+    def del_binfo(self):
+        """Delete the build info from this node."""
+        try:
+            delattr(self, 'binfo')
+        except AttributeError:
+            pass
+
+    def get_csig(self):
+        try:
+            return self.ninfo.csig
+        except AttributeError:
+            ninfo = self.get_ninfo()
+            ninfo.csig = SCons.Util.MD5signature(self.get_contents())
+            return self.ninfo.csig
+
+    def get_cachedir_csig(self):
+        return self.get_csig()
+
+    def store_info(self):
+        """Make the build signature permanent (that is, store it in the
+        .sconsign file or equivalent)."""
+        pass
+
+    def do_not_store_info(self):
+        pass
+
+    def get_stored_info(self):
+        return None
+
+    def get_stored_implicit(self):
+        """Fetch the stored implicit dependencies"""
+        return None
+
+    #
+    #
+    #
+
+    def set_precious(self, precious = 1):
+        """Set the Node's precious value."""
+        self.precious = precious
+
+    def set_noclean(self, noclean = 1):
+        """Set the Node's noclean value."""
+        # Make sure noclean is an integer so the --debug=stree
+        # output in Util.py can use it as an index.
+        self.noclean = noclean and 1 or 0
+
+    def set_nocache(self, nocache = 1):
+        """Set the Node's nocache value."""
+        # Make sure nocache is an integer so the --debug=stree
+        # output in Util.py can use it as an index.
+        self.nocache = nocache and 1 or 0
+
+    def set_always_build(self, always_build = 1):
+        """Set the Node's always_build value."""
+        self.always_build = always_build
+
+    def exists(self):
+        """Does this node exists?"""
+        # All node exist by default:
+        return 1
+
+    def rexists(self):
+        """Does this node exist locally or in a repositiory?"""
+        # There are no repositories by default:
+        return self.exists()
+
+    def missing(self):
+        return not self.is_derived() and \
+               not self.linked and \
+               not self.rexists()
+
+    def remove(self):
+        """Remove this Node:  no-op by default."""
+        return None
+
+    def add_dependency(self, depend):
+        """Adds dependencies."""
+        try:
+            self._add_child(self.depends, self.depends_set, depend)
+        except TypeError, e:
+            e = e.args[0]
+            if SCons.Util.is_List(e):
+                s = map(str, e)
+            else:
+                s = str(e)
+            raise SCons.Errors.UserError("attempted to add a non-Node dependency to %s:\n\t%s is a %s, not a Node" % (str(self), s, type(e)))
+
+    def add_prerequisite(self, prerequisite):
+        """Adds prerequisites"""
+        self.prerequisites.extend(prerequisite)
+        self._children_reset()
+
+    def add_ignore(self, depend):
+        """Adds dependencies to ignore."""
+        try:
+            self._add_child(self.ignore, self.ignore_set, depend)
+        except TypeError, e:
+            e = e.args[0]
+            if SCons.Util.is_List(e):
+                s = map(str, e)
+            else:
+                s = str(e)
+            raise SCons.Errors.UserError("attempted to ignore a non-Node dependency of %s:\n\t%s is a %s, not a Node" % (str(self), s, type(e)))
+
+    def add_source(self, source):
+        """Adds sources."""
+        if self._specific_sources:
+            return
+        try:
+            self._add_child(self.sources, self.sources_set, source)
+        except TypeError, e:
+            e = e.args[0]
+            if SCons.Util.is_List(e):
+                s = map(str, e)
+            else:
+                s = str(e)
+            raise SCons.Errors.UserError("attempted to add a non-Node as source of %s:\n\t%s is a %s, not a Node" % (str(self), s, type(e)))
+
+    def _add_child(self, collection, set, child):
+        """Adds 'child' to 'collection', first checking 'set' to see if it's
+        already present."""
+        #if type(child) is not type([]):
+        #    child = [child]
+        #for c in child:
+        #    if not isinstance(c, Node):
+        #        raise TypeError, c
+        added = None
+        for c in child:
+            if c not in set:
+                set.add(c)
+                collection.append(c)
+                added = 1
+        if added:
+            self._children_reset()
+
+    def set_specific_source(self, source):
+        self.add_source(source)
+        self._specific_sources = True
+
+    def add_wkid(self, wkid):
+        """Add a node to the list of kids waiting to be evaluated"""
+        if self.wkids is not None:
+            self.wkids.append(wkid)
+
+    def _children_reset(self):
+        self.clear_memoized_values()
+        # We need to let the Executor clear out any calculated
+        # build info that it's cached so we can re-calculate it.
+        self.executor_cleanup()
+
+    memoizer_counters.append(SCons.Memoize.CountValue('_children_get'))
+
+    def _children_get(self):
+        try:
+            return self._memo['children_get']
+        except KeyError:
+            pass
+
+        # The return list may contain duplicate Nodes, especially in
+        # source trees where there are a lot of repeated #includes
+        # of a tangle of .h files.  Profiling shows, however, that
+        # eliminating the duplicates with a brute-force approach that
+        # preserves the order (that is, something like:
+        #
+        #       u = []
+        #       for n in list:
+        #           if n not in u:
+        #               u.append(n)"
+        #
+        # takes more cycles than just letting the underlying methods
+        # hand back cached values if a Node's information is requested
+        # multiple times.  (Other methods of removing duplicates, like
+        # using dictionary keys, lose the order, and the only ordered
+        # dictionary patterns I found all ended up using "not in"
+        # internally anyway...)
+        if self.ignore_set:
+            if self.implicit is None:
+                iter = chain(self.sources,self.depends)
+            else:
+                iter = chain(self.sources, self.depends, self.implicit)
+
+            children = []
+            for i in iter:
+                if i not in self.ignore_set:
+                    children.append(i)
+        else:
+            if self.implicit is None:
+                children = self.sources + self.depends
+            else:
+                children = self.sources + self.depends + self.implicit
+
+        self._memo['children_get'] = children
+        return children
+
+    def all_children(self, scan=1):
+        """Return a list of all the node's direct children."""
+        if scan:
+            self.scan()
+
+        # The return list may contain duplicate Nodes, especially in
+        # source trees where there are a lot of repeated #includes
+        # of a tangle of .h files.  Profiling shows, however, that
+        # eliminating the duplicates with a brute-force approach that
+        # preserves the order (that is, something like:
+        #
+        #       u = []
+        #       for n in list:
+        #           if n not in u:
+        #               u.append(n)"
+        #
+        # takes more cycles than just letting the underlying methods
+        # hand back cached values if a Node's information is requested
+        # multiple times.  (Other methods of removing duplicates, like
+        # using dictionary keys, lose the order, and the only ordered
+        # dictionary patterns I found all ended up using "not in"
+        # internally anyway...)
+        if self.implicit is None:
+            return self.sources + self.depends
+        else:
+            return self.sources + self.depends + self.implicit
+
+    def children(self, scan=1):
+        """Return a list of the node's direct children, minus those
+        that are ignored by this node."""
+        if scan:
+            self.scan()
+        return self._children_get()
+
+    def set_state(self, state):
+        self.state = state
+
+    def get_state(self):
+        return self.state
+
+    def state_has_changed(self, target, prev_ni):
+        return (self.state != SCons.Node.up_to_date)
+
+    def get_env(self):
+        env = self.env
+        if not env:
+            import SCons.Defaults
+            env = SCons.Defaults.DefaultEnvironment()
+        return env
+
+    def changed_since_last_build(self, target, prev_ni):
+        """
+
+        Must be overridden in a specific subclass to return True if this
+        Node (a dependency) has changed since the last time it was used
+        to build the specified target.  prev_ni is this Node's state (for
+        example, its file timestamp, length, maybe content signature)
+        as of the last time the target was built.
+
+        Note that this method is called through the dependency, not the
+        target, because a dependency Node must be able to use its own
+        logic to decide if it changed.  For example, File Nodes need to
+        obey if we're configured to use timestamps, but Python Value Nodes
+        never use timestamps and always use the content.  If this method
+        were called through the target, then each Node's implementation
+        of this method would have to have more complicated logic to
+        handle all the different Node types on which it might depend.
+        """
+        raise NotImplementedError
+
+    def Decider(self, function):
+        SCons.Util.AddMethod(self, function, 'changed_since_last_build')
+
+    def changed(self, node=None):
+        """
+        Returns if the node is up-to-date with respect to the BuildInfo
+        stored last time it was built.  The default behavior is to compare
+        it against our own previously stored BuildInfo, but the stored
+        BuildInfo from another Node (typically one in a Repository)
+        can be used instead.
+
+        Note that we now *always* check every dependency.  We used to
+        short-circuit the check by returning as soon as we detected
+        any difference, but we now rely on checking every dependency
+        to make sure that any necessary Node information (for example,
+        the content signature of an #included .h file) is updated.
+        """
+        t = 0
+        if t: Trace('changed(%s [%s], %s)' % (self, classname(self), node))
+        if node is None:
+            node = self
+
+        result = False
+
+        bi = node.get_stored_info().binfo
+        then = bi.bsourcesigs + bi.bdependsigs + bi.bimplicitsigs
+        children = self.children()
+
+        diff = len(children) - len(then)
+        if diff:
+            # The old and new dependency lists are different lengths.
+            # This always indicates that the Node must be rebuilt.
+            # We also extend the old dependency list with enough None
+            # entries to equal the new dependency list, for the benefit
+            # of the loop below that updates node information.
+            then.extend([None] * diff)
+            if t: Trace(': old %s new %s' % (len(then), len(children)))
+            result = True
+
+        for child, prev_ni in izip(children, then):
+            if child.changed_since_last_build(self, prev_ni):
+                if t: Trace(': %s changed' % child)
+                result = True
+
+        contents = self.get_executor().get_contents()
+        if self.has_builder():
+            import SCons.Util
+            newsig = SCons.Util.MD5signature(contents)
+            if bi.bactsig != newsig:
+                if t: Trace(': bactsig %s != newsig %s' % (bi.bactsig, newsig))
+                result = True
+
+        if not result:
+            if t: Trace(': up to date')
+
+        if t: Trace('\n')
+
+        return result
+
+    def is_up_to_date(self):
+        """Default check for whether the Node is current: unknown Node
+        subtypes are always out of date, so they will always get built."""
+        return None
+
+    def children_are_up_to_date(self):
+        """Alternate check for whether the Node is current:  If all of
+        our children were up-to-date, then this Node was up-to-date, too.
+
+        The SCons.Node.Alias and SCons.Node.Python.Value subclasses
+        rebind their current() method to this method."""
+        # Allow the children to calculate their signatures.
+        self.binfo = self.get_binfo()
+        if self.always_build:
+            return None
+        state = 0
+        for kid in self.children(None):
+            s = kid.get_state()
+            if s and (not state or s > state):
+                state = s
+        return (state == 0 or state == SCons.Node.up_to_date)
+
+    def is_literal(self):
+        """Always pass the string representation of a Node to
+        the command interpreter literally."""
+        return 1
+
+    def render_include_tree(self):
+        """
+        Return a text representation, suitable for displaying to the
+        user, of the include tree for the sources of this node.
+        """
+        if self.is_derived() and self.env:
+            env = self.get_build_env()
+            for s in self.sources:
+                scanner = self.get_source_scanner(s)
+                if scanner:
+                    path = self.get_build_scanner_path(scanner)
+                else:
+                    path = None
+                def f(node, env=env, scanner=scanner, path=path):
+                    return node.get_found_includes(env, scanner, path)
+                return SCons.Util.render_tree(s, f, 1)
+        else:
+            return None
+
+    def get_abspath(self):
+        """
+        Return an absolute path to the Node.  This will return simply
+        str(Node) by default, but for Node types that have a concept of
+        relative path, this might return something different.
+        """
+        return str(self)
+
+    def for_signature(self):
+        """
+        Return a string representation of the Node that will always
+        be the same for this particular Node, no matter what.  This
+        is by contrast to the __str__() method, which might, for
+        instance, return a relative path for a file Node.  The purpose
+        of this method is to generate a value to be used in signature
+        calculation for the command line used to build a target, and
+        we use this method instead of str() to avoid unnecessary
+        rebuilds.  This method does not need to return something that
+        would actually work in a command line; it can return any kind of
+        nonsense, so long as it does not change.
+        """
+        return str(self)
+
+    def get_string(self, for_signature):
+        """This is a convenience function designed primarily to be
+        used in command generators (i.e., CommandGeneratorActions or
+        Environment variables that are callable), which are called
+        with a for_signature argument that is nonzero if the command
+        generator is being called to generate a signature for the
+        command line, which determines if we should rebuild or not.
+
+        Such command generators should use this method in preference
+        to str(Node) when converting a Node to a string, passing
+        in the for_signature parameter, such that we will call
+        Node.for_signature() or str(Node) properly, depending on whether
+        we are calculating a signature or actually constructing a
+        command line."""
+        if for_signature:
+            return self.for_signature()
+        return str(self)
+
+    def get_subst_proxy(self):
+        """
+        This method is expected to return an object that will function
+        exactly like this Node, except that it implements any additional
+        special features that we would like to be in effect for
+        Environment variable substitution.  The principle use is that
+        some Nodes would like to implement a __getattr__() method,
+        but putting that in the Node type itself has a tendency to kill
+        performance.  We instead put it in a proxy and return it from
+        this method.  It is legal for this method to return self
+        if no new functionality is needed for Environment substitution.
+        """
+        return self
+
+    def explain(self):
+        if not self.exists():
+            return "building `%s' because it doesn't exist\n" % self
+
+        if self.always_build:
+            return "rebuilding `%s' because AlwaysBuild() is specified\n" % self
+
+        old = self.get_stored_info()
+        if old is None:
+            return None
+
+        old = old.binfo
+        old.prepare_dependencies()
+
+        try:
+            old_bkids    = old.bsources    + old.bdepends    + old.bimplicit
+            old_bkidsigs = old.bsourcesigs + old.bdependsigs + old.bimplicitsigs
+        except AttributeError:
+            return "Cannot explain why `%s' is being rebuilt: No previous build information found\n" % self
+
+        new = self.get_binfo()
+
+        new_bkids    = new.bsources    + new.bdepends    + new.bimplicit
+        new_bkidsigs = new.bsourcesigs + new.bdependsigs + new.bimplicitsigs
+
+        osig = dict(izip(old_bkids, old_bkidsigs))
+        nsig = dict(izip(new_bkids, new_bkidsigs))
+
+        # The sources and dependencies we'll want to report are all stored
+        # as relative paths to this target's directory, but we want to
+        # report them relative to the top-level SConstruct directory,
+        # so we only print them after running them through this lambda
+        # to turn them into the right relative Node and then return
+        # its string.
+        def stringify( s, E=self.dir.Entry ) :
+            if hasattr( s, 'dir' ) :
+                return str(E(s))
+            return str(s)
+
+        lines = []
+
+        removed = filter(lambda x, nk=new_bkids: not x in nk, old_bkids)
+        if removed:
+            removed = map(stringify, removed)
+            fmt = "`%s' is no longer a dependency\n"
+            lines.extend(map(lambda s, fmt=fmt: fmt % s, removed))
+
+        for k in new_bkids:
+            if not k in old_bkids:
+                lines.append("`%s' is a new dependency\n" % stringify(k))
+            elif k.changed_since_last_build(self, osig[k]):
+                lines.append("`%s' changed\n" % stringify(k))
+
+        if len(lines) == 0 and old_bkids != new_bkids:
+            lines.append("the dependency order changed:\n" +
+                         "%sold: %s\n" % (' '*15, map(stringify, old_bkids)) +
+                         "%snew: %s\n" % (' '*15, map(stringify, new_bkids)))
+
+        if len(lines) == 0:
+            def fmt_with_title(title, strlines):
+                lines = string.split(strlines, '\n')
+                sep = '\n' + ' '*(15 + len(title))
+                return ' '*15 + title + string.join(lines, sep) + '\n'
+            if old.bactsig != new.bactsig:
+                if old.bact == new.bact:
+                    lines.append("the contents of the build action changed\n" +
+                                 fmt_with_title('action: ', new.bact))
+                else:
+                    lines.append("the build action changed:\n" +
+                                 fmt_with_title('old: ', old.bact) +
+                                 fmt_with_title('new: ', new.bact))
+
+        if len(lines) == 0:
+            return "rebuilding `%s' for unknown reasons\n" % self
+
+        preamble = "rebuilding `%s' because" % self
+        if len(lines) == 1:
+            return "%s %s"  % (preamble, lines[0])
+        else:
+            lines = ["%s:\n" % preamble] + lines
+            return string.join(lines, ' '*11)
+
+try:
+    [].extend(UserList.UserList([]))
+except TypeError:
+    # Python 1.5.2 doesn't allow a list to be extended by list-like
+    # objects (such as UserList instances), so just punt and use
+    # real lists.
+    def NodeList(l):
+        return l
+else:
+    class NodeList(UserList.UserList):
+        def __str__(self):
+            return str(map(str, self.data))
+
+def get_children(node, parent): return node.children()
+def ignore_cycle(node, stack): pass
+def do_nothing(node, parent): pass
+
+class Walker:
+    """An iterator for walking a Node tree.
+
+    This is depth-first, children are visited before the parent.
+    The Walker object can be initialized with any node, and
+    returns the next node on the descent with each next() call.
+    'kids_func' is an optional function that will be called to
+    get the children of a node instead of calling 'children'.
+    'cycle_func' is an optional function that will be called
+    when a cycle is detected.
+
+    This class does not get caught in node cycles caused, for example,
+    by C header file include loops.
+    """
+    def __init__(self, node, kids_func=get_children,
+                             cycle_func=ignore_cycle,
+                             eval_func=do_nothing):
+        self.kids_func = kids_func
+        self.cycle_func = cycle_func
+        self.eval_func = eval_func
+        node.wkids = copy.copy(kids_func(node, None))
+        self.stack = [node]
+        self.history = {} # used to efficiently detect and avoid cycles
+        self.history[node] = None
+
+    def next(self):
+        """Return the next node for this walk of the tree.
+
+        This function is intentionally iterative, not recursive,
+        to sidestep any issues of stack size limitations.
+        """
+
+        while self.stack:
+            if self.stack[-1].wkids:
+                node = self.stack[-1].wkids.pop(0)
+                if not self.stack[-1].wkids:
+                    self.stack[-1].wkids = None
+                if self.history.has_key(node):
+                    self.cycle_func(node, self.stack)
+                else:
+                    node.wkids = copy.copy(self.kids_func(node, self.stack[-1]))
+                    self.stack.append(node)
+                    self.history[node] = None
+            else:
+                node = self.stack.pop()
+                del self.history[node]
+                if node:
+                    if self.stack:
+                        parent = self.stack[-1]
+                    else:
+                        parent = None
+                    self.eval_func(node, parent)
+                return node
+        return None
+
+    def is_done(self):
+        return not self.stack
+
+
+arg2nodes_lookups = []
+
+# Local Variables:
+# tab-width:4
+# indent-tabs-mode:nil
+# End:
+# vim: set expandtab tabstop=4 shiftwidth=4: