Let git cl format be runnable outside of the root

git_cl.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld."""
 
 from distutils.version import LooseVersion
@@ skipping 2230 matching lines @@
 
 
 def CMDformat(parser, args):
   """Runs clang-format on the diff."""
   CLANG_EXTS = ['.cc', '.cpp', '.h']
   parser.add_option('--full', action='store_true', default=False)
   opts, args = parser.parse_args(args)
   if args:
     parser.error('Unrecognized args: %s' % ' '.join(args))
 
+  # git diff generates paths against the root of the repository.  Change
+  # to that directory so clang-format can find files even within subdirs.
+  rel_base_path = RunGit(['rev-parse', '--show-cdup']).strip()
+  if rel_base_path:
+    os.chdir(rel_base_path)
+
   # Generate diff for the current branch's changes.
   diff_cmd = ['diff', '--no-ext-diff', '--no-prefix']
   if opts.full:
     # Only list the names of modified files.
     diff_cmd.append('--name-only')
   else:
     # Only generate context-less patches.
     diff_cmd.append('-U0')
 
   # Grab the merge-base commit, i.e. the upstream commit of the current
@@ skipping 86 matching lines @@
         ('AppEngine is misbehaving and returned HTTP %d, again. Keep faith '
           'and retry or visit go/isgaeup.\n%s') % (e.code, str(e)))
 
 
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   colorama.init()
   sys.exit(main(sys.argv[1:]))