git_cl: Add reverse issue lookup.

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 1455 matching lines @@
   lines = CMDstatus.__doc__.splitlines()
   CMDstatus.__doc__ = '\n'.join(colorize_line(l) for l in lines)
 
 
 @subcommand.usage('[issue_number]')
 def CMDissue(parser, args):
   """Sets or displays the current code review issue number.
 
   Pass issue number 0 to clear the current issue.
   """
-  _, args = parser.parse_args(args)
+  parser.add_option('-r', '--reverse', action='store_true',
+                    help='Lookup the branch(es) for the specified issues. If '
+                         'no issues are specified, all branches with mapped '
+                         'issues will be listed.')
+  options, args = parser.parse_args(args)
 
-  cl = Changelist()
-  if len(args) > 0:
-    try:
-      issue = int(args[0])
-    except ValueError:
-      DieWithError('Pass a number to set the issue or none to list it.\n'
-          'Maybe you want to run git cl status?')
-    cl.SetIssue(issue)
-  print 'Issue number: %s (%s)' % (cl.GetIssue(), cl.GetIssueURL())
+  if options.reverse:
+    branches = RunGit(['for-each-ref', 'refs/heads',
+                       '--format=%(refname:short)']).splitlines()
+
+    # Reverse issue lookup.
+    issue_branch_map = {}
+    for branch in branches:
+      cl = Changelist(branchref=branch)
+      issue_branch_map.setdefault(cl.GetIssue(), []).append(branch)
+    if not args:
+      args = sorted(issue_branch_map.iterkeys())
+    for issue in args:
+      if not issue:
+        continue
+      print 'Branch for issue number %s: %s' % (
+          issue, ', '.join(issue_branch_map.get(int(issue)) or ('None',)))
+  else:
+    cl = Changelist()
+    if len(args) > 0:
+      try:
+        issue = int(args[0])
+      except ValueError:
+        DieWithError('Pass a number to set the issue or none to list it.\n'
+            'Maybe you want to run git cl status?')
+      cl.SetIssue(issue)
+    print 'Issue number: %s (%s)' % (cl.GetIssue(), cl.GetIssueURL())
   return 0
 
 
 def CMDcomments(parser, args):
   """Shows or posts review comments for any changelist."""
   parser.add_option('-a', '--add-comment', dest='comment',
                     help='comment to add to an issue')
   parser.add_option('-i', dest='issue',
                     help="review issue id (defaults to current issue)")
   options, args = parser.parse_args(args)
@@ skipping 1597 matching lines @@
 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()
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)