tryserver recipe_module: Add get_tags.

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 json
 import re
 import sys
 
 from collections import defaultdict
 
 import git_common as git
 
 
 FOOTER_PATTERN = re.compile(r'^\s*([\w-]+): (.*)$')
 CHROME_COMMIT_POSITION_PATTERN = re.compile(r'^([\w/-]+)@{#(\d+)}$')
@@ skipping 139 matching lines @@
       # svn commit numbers do not map to branches.
       return ('refs/branch-heads/%s' % branch_match.group(1), None)
 
   raise ValueError('Unable to infer commit position from footers')
 
 
 def main(args):
   parser = argparse.ArgumentParser(
     formatter_class=argparse.ArgumentDefaultsHelpFormatter
   )
-  parser.add_argument('ref')
+  parser.add_argument('ref', nargs='?', help="Git ref to retrieve footers from."
+                      " Omit to parse stdin.")
 
   g = parser.add_mutually_exclusive_group()
   g.add_argument('--key', metavar='KEY',
                  help='Get all values for the given footer name, one per '
                  'line (case insensitive)')
   g.add_argument('--position', action='store_true')
   g.add_argument('--position-ref', action='store_true')
   g.add_argument('--position-num', action='store_true')
+  g.add_argument('--json', help="filename to dump JSON serialized headers to.")
 
 
   opts = parser.parse_args(args)
 
-  message = git.run('log', '-1', '--format=%B', opts.ref)
+  if opts.ref:
+    message = git.run('log', '-1', '--format=%B', opts.ref)
+  else:
+    message = '\n'.join(l for l in sys.stdin)
+
   footers = parse_footers(message)
 
   if opts.key:
     for v in footers.get(normalize_name(opts.key), []):
       print v
   elif opts.position:
     pos = get_position(footers)
     print '%s@{#%s}' % (pos[0], pos[1] or '?')
   elif opts.position_ref:
     print get_position(footers)[0]
   elif opts.position_num:
     pos = get_position(footers)
     assert pos[1], 'No valid position for commit'
     print pos[1]
+  elif opts.json:
+    with open(opts.json, 'w') as f:
+      json.dump(footers, f)
   else:
     for k in footers.keys():
       for v in footers[k]:
         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)