git cl: add python implementation of Change-Id generation.

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 2130 matching lines @@
   log_desc = options.message or CreateDescriptionFromLog(args)
   git_command = ['commit', '--amend', '-m', log_desc]
   RunGit(git_command)
   new_log_desc = CreateDescriptionFromLog(args)
   if CHANGE_ID in new_log_desc:
     print 'git-cl: Added Change-Id to commit message.'
   else:
     print >> sys.stderr, 'ERROR: Gerrit commit-msg hook not available.'
 
 
+def GenerateGerritChangeId(message):
+  """Returns Ixxxxxx...xxx change id.
+
+  Works the same way as
+  https://gerrit-review.googlesource.com/tools/hooks/commit-msg
+  but can be called on demand on all platforms.
+
+  The basic idea is to generate git hash of a state of the tree, original commit
+  message, author/committer info and timestamps.
+  """
+  lines = []
+  tree_hash = RunGitSilent(['write-tree'])
+  lines.append('tree %s' % tree_hash.strip())
+  code, parent = RunGitWithCode(['rev-parse', 'HEAD~0'], suppress_stderr=False)
+  if code == 0:
+    lines.append('parent %s' % parent.strip())
+  author = RunGitSilent(['var', 'GIT_AUTHOR_IDENT'])
+  lines.append('author %s' % author.strip())
+  committer = RunGitSilent(['var', 'GIT_COMMITTER_IDENT'])
+  lines.append('committer %s' % committer.strip())
+  lines.append('')
+  # Note: Gerrit's commit-hook actually cleans message of some lines and
+  # whitespace. This code is not doing this, but it clearly won't decrease
+  # entropy.
+  lines.append(message)
+  change_hash = RunCommand(['git', 'hash-object', '-t', 'commit', '--stdin'],
+                           stdin='\n'.join(lines))
+  return 'I%s' % change_hash.strip()
+
+
 def GerritUpload(options, args, cl, change):
   """upload the current branch to gerrit."""
   # We assume the remote called "origin" is the one we want.
   # It is probably not worthwhile to support different workflows.
   gerrit_remote = 'origin'
 
   remote, remote_branch = cl.GetRemoteBranch()
   branch = GetTargetRef(remote, remote_branch, options.target_branch,
                         pending_prefix='')
 
@@ skipping 1790 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)