Add Gerrit's Change-Id handling to git_footers.

git_footers.py

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 import argparse
 import re
 import sys
 
 from collections import defaultdict
@@ skipping 44 matching lines @@
   message = git.run('log', '-1', '--format=%B', branch)
   footers = parse_footers(message)
   git_svn_id = get_unique(footers, 'git-svn-id')
   if git_svn_id:
     match = GIT_SVN_ID_PATTERN.match(git_svn_id)
     if match:
       svn_id = match.group(1)
   return svn_id
 
 
+def get_footer_change_id(message):
+  """Returns a list of Gerrit's ChangeId from given commit message."""
+  return parse_footers(message).get(normalize_name('Change-Id'), [])
+
+
+def add_footer_change_id(message, change_id):
+  """Returns message with Change-ID footer in it.
+
+  Assumes that Change-Id is not yet in footers, which is then
+  inserted after any of these footers: Bug|Issue|Test|Feature.
+  """
+  assert 0 == len(get_footer_change_id(message))
+  change_id_line = 'Change-Id: %s' % change_id
+  # This code does the same as parse_footers, but keeps track of line
+  # numbers so that ChangeId is inserted in the right place.
+  lines = message.splitlines()
+  footer_lines = []
+  for line in reversed(lines):
+    if line == '' or line.isspace():
+      break
+    footer_lines.append(line)
+  # footers order is from end to start of the message.
+  footers = map(parse_footer, footer_lines)
+  if not all(footers):
+    lines.append('')
+    lines.append(change_id_line)
+  else:
+    after = set(map(normalize_name, ['Bug', 'Issue', 'Test', 'Feature']))
+    for i, (key, _) in enumerate(footers):
+      if normalize_name(key) in after:
+        insert_at = len(lines) - i
+        break
+    else:
+      insert_at = len(lines) - len(footers)
+    lines.insert(insert_at, change_id_line)
+  return '\n'.join(lines)
+
+
 def get_unique(footers, key):
   key = normalize_name(key)
   values = footers[key]
   assert len(values) <= 1, 'Multiple %s footers' % key
   if values:
     return values[0]
   else:
     return None
 
 
@@ skipping 80 matching lines @@
         print '%s: %s' % (k, v)
   return 0
 
 
 if __name__ == '__main__':
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)