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diff --git a/site_scons/site_tools/environment_tools.py b/site_scons/site_tools/environment_tools.py
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+#!/usr/bin/python2.4
+# Copyright 2008, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Set up tools for environments for for software construction toolkit.
+
+This module is a SCons tool which should be include in all environments.  It
+will automatically be included by the component_setup tool.
+"""
+
+
+import SCons
+
+
+#------------------------------------------------------------------------------
+
+
+def FilterOut(self, **kw):
+  """Removes values from existing construction variables in an Environment.
+
+  The values to remove should be a list.  For example:
+
+  self.FilterOut(CPPDEFINES=['REMOVE_ME', 'ME_TOO'])
+
+  Args:
+    self: Environment to alter.
+    kw: (Any other named arguments are values to remove).
+  """
+
+  kw = SCons.Environment.copy_non_reserved_keywords(kw)
+  for key, val in kw.items():
+    envval = self.get(key, None)
+    if envval is None:
+      # No existing variable in the environment, so nothing to delete.
+      continue
+
+    for vremove in val:
+      if vremove in envval:
+        envval.remove(vremove)
+
+    self[key] = envval
+
+    # TODO(sgk): SCons.Environment.Append() has much more logic to deal
+    # with various types of values.  We should handle all those cases in here
+    # too.
+
+#------------------------------------------------------------------------------
+
+
+def Overlap(self, values1, values2):
+  """Checks for overlap between the values.
+
+  Args:
+    self: Environment to use for variable substitution.
+    values1: First value(s) to compare.  May be a string or list of strings.
+    values2: Second value(s) to compare.  May be a string or list of strings.
+
+  Returns:
+    The list of values in common after substitution, or an empty list if
+    the values do no overlap.
+
+  Converts the values to a set of plain strings via self.subst() before
+  comparison, so SCons $ variables are evaluated.
+  """
+
+  set1 = set()
+  for v in self.Flatten(values1):
+    set1.add(self.subst(v))
+
+  set2 = set()
+  for v in self.Flatten(values2):
+    set2.add(self.subst(v))
+
+  return list(set1.intersection(set2))
+
+
+#------------------------------------------------------------------------------
+
+
+def ApplySConscript(self, sconscript_file):
+  """Applies a SConscript to the current environment.
+
+  Args:
+    self: Environment to modify.
+    sconscript_file: Name of SConscript file to apply.
+
+  Returns:
+    The return value from the call to SConscript().
+
+  ApplySConscript() should be used when an existing SConscript which sets up an
+  environment gets too large, or when there is common setup between multiple
+  environments which can't be reduced into a parent environment which the
+  multiple child environments Clone() from.  The latter case is necessary
+  because env.Clone() only enables single inheritance for environments.
+
+  ApplySConscript() is NOT intended to replace the Tool() method.  If you need
+  to add methods or builders to one or more environments, do that as a tool
+  (and write unit tests for them).
+
+  ApplySConscript() is equivalent to the following SCons call:
+      SConscript(sconscript_file, exports={'env':self})
+
+  The called SConscript should import the 'env' variable to get access to the
+  calling environment:
+      Import('env')
+
+  Changes made to env in the called SConscript will be applied to the
+  environment calling ApplySConscript() - that is, env in the called SConscript
+  is a reference to the calling environment.
+
+  If you need to export multiple variables to the called SConscript, or return
+  variables from it, use the existing SConscript() function.
+  """
+  return SCons.Script.SConscript(sconscript_file, exports={'env':self})
+
+#------------------------------------------------------------------------------
+
+
+def BuildSConscript(self, sconscript_file):
+  """Builds a SConscript based on the current environment.
+
+  Args:
+    self: Environment to clone and pass to the called SConscript.
+    sconscript_file: Name of SConscript file to build.  If this is a directory,
+        this method will look for sconscript_file+'/build.scons', and if that
+        is not found, sconscript_file+'/SConscript'.
+
+  Returns:
+    The return value from the call to SConscript().
+
+  BuildSConscript() should be used when an existing SConscript which builds a
+  project gets too large, or when a group of SConscripts are logically related
+  but should not directly affect each others' environments (for example, a
+  library might want to build a number of unit tests which exist in
+  subdirectories, but not allow those tests' SConscripts to affect/pollute the
+  library's environment.
+
+  BuildSConscript() is NOT intended to replace the Tool() method.  If you need
+  to add methods or builders to one or more environments, do that as a tool
+  (and write unit tests for them).
+
+  BuildSConscript() is equivalent to the following SCons call:
+      SConscript(sconscript_file, exports={'env':self.Clone()})
+  or if sconscript_file is a directory:
+      SConscript(sconscript_file+'/build.scons', exports={'env':self.Clone()})
+
+  The called SConscript should import the 'env' variable to get access to the
+  calling environment:
+      Import('env')
+
+  Changes made to env in the called SConscript will NOT be applied to the
+  environment calling BuildSConscript() - that is, env in the called SConscript
+  is a clone/copy of the calling environment, not a reference to that
+  environment.
+
+  If you need to export multiple variables to the called SConscript, or return
+  variables from it, use the existing SConscript() function.
+  """
+  # Need to look for the source node, since by default SCons will look for the
+  # entry in the variant_dir, which won't exist (and thus won't be a directory
+  # or a file).  This isn't a problem in BuildComponents(), since the variant
+  # dir is only set inside its call to SConscript().
+  if self.Entry(sconscript_file).srcnode().isdir():
+    # Building a subdirectory, so look for build.scons or SConscript
+    script_file = sconscript_file + '/build.scons'
+    if not self.File(script_file).srcnode().exists():
+      script_file = sconscript_file + '/SConscript'
+  else:
+    script_file = sconscript_file
+
+  self.SConscript(script_file, exports={'env':self.Clone()})
+
+#------------------------------------------------------------------------------
+
+
+def generate(env):
+  # NOTE: SCons requires the use of this name, which fails gpylint.
+  """SCons entry point for this tool."""
+
+  # Add methods to environment
+  env.AddMethod(ApplySConscript)
+  env.AddMethod(BuildSConscript)
+  env.AddMethod(FilterOut)
+  env.AddMethod(Overlap)