lastchange: don't use git rev-parse output when it fails

build/util/lastchange.py

 #!/usr/bin/env python
 # Copyright (c) 2010 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 lastchange.py -- Chromium revision fetching utility.
 """
 
 import optparse
@@ skipping 23 matching lines @@
   command = ['git', 'rev-parse', 'HEAD']
   if sys.platform in ('cygwin', 'win32'):
     command = ['sh', '-c', ' '.join(command)]
   try:
     proc = subprocess.Popen(command,
                             stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE,
                             cwd=directory)
   except OSError:
     return None
-  return VersionInfo('git', 'git', proc.stdout.read().strip()[:7])
+  output = proc.communicate()[0].strip()
+  if proc.returncode == 0 and output:
+    return VersionInfo('git', 'git', output[:7])
+  return None
 
 
 def FetchSVNRevision(directory):
   """
   Fetch the Subversion branch and revision for the a given directory.
 
   Errors are swallowed.
 
   Returns:
     a VersionInfo object or None on error.
@@ skipping 90 matching lines @@
     if out_file:
       WriteIfChanged(out_file, contents)
     else:
       sys.stdout.write(contents)
 
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())