The toolchain_build git cache is now referenced as a git-alternate.

toolchain_build/substituter.py

 #!/usr/bin/python
 # Copyright (c) 2013 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import multiprocessing
 import os
 import sys
 
 
@@ skipping 55 matching lines @@
     self.SetUpPathVariables()
 
   def SetUpPathVariables(self):
     """Create the internal mappings for all path variables.
 
     Paths are calculated relative to the current working directory.
     """
     self._variables = self._nonpaths.copy()
     self._variables['cwd'] = FixPath(os.path.abspath(self._cwd))
     for key, value in self._paths.iteritems():
-      self._variables['abs_' + key] = FixPath(os.path.abspath(value))
-      self._variables[key] = FixPath(os.path.relpath(value, self._cwd))
+      if value:
+        abs_path = FixPath(os.path.abspath(value))
+        key_path = FixPath(os.path.relpath(value, self._cwd))
+      else:
+        abs_path = value
+        key_path = value
+
+      self._variables['abs_' + key] = abs_path
+      self._variables[key] = key_path
 
   def Substitute(self, template):
     """ Substitute the %-variables in 'template' """
     return template % self._variables
 
   def SubstituteAbsPaths(self, template):
     """Substitute the %-variables in 'template'.
 
     All variables in the template must be paths, and if the values are relative
     paths, they are resolved relative to cwd and returned as absolute paths.
     """
-    return AbsPath(self.Substitute(template), self._cwd)
+    path = self.Substitute(template)
+    if path:
+      path = AbsPath(path, self._cwd)
+    return path
 
   def _SetUpCommonNonPaths(self):
     try:
       self._nonpaths['cores'] = multiprocessing.cpu_count()
     except NotImplementedError:
       self._nonpaths['cores'] = 4  # Assume 4 if we can't measure.