git cl replacing gnumbd: set correct committer timestamp.

BUG=642493
R=sergiyb@chromium.org

Change-Id: I5d8588f2b6f30368188aecab2d2c462a11aa6883
Reviewed-on: https://chromium-review.googlesource.com/414369
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>

git_cl.py

@@ -228,6 +228,26 @@ def _git_set_branch_config_value(key, value, branch=None, **kwargs):
   RunGit(args, **kwargs)
 
 
+def _get_committer_timestamp(commit):
+  """Returns unix timestamp as integer of a committer in a commit.
+
+  Commit can be whatever git show would recognize, such as HEAD, sha1 or ref.
+  """
+  # Git also stores timezone offset, but it only affects visual display,
+  # actual point in time is defined by this timestamp only.
+  return int(RunGit(['show', '-s', '--format=%ct', commit]).strip())
+
+
+def _git_amend_head(message, committer_timestamp):
+  """Amends commit with new message and desired committer_timestamp.
+
+  Sets committer timezone to UTC.
+  """
+  env = os.environ.copy()
+  env['GIT_COMMITTER_DATE'] = '%d+0000' % committer_timestamp
+  return RunGit(['commit', '--amend', '-m', message], env=env)
+
+
 def add_git_similarity(parser):
   parser.add_option(
       '--similarity', metavar='SIM', type=int, action='store',
@@ -4501,8 +4521,10 @@ def SendUpstream(parser, args, cmd):
         parent_msg = RunGit(['show', '-s', '--format=%B', merge_base]).strip()
         commit_desc.update_with_git_number_footers(merge_base, parent_msg,
                                                    branch)
-        # TODO(tandrii): timestamp handling is missing here.
-        RunGitSilent(['commit', '--amend', '-m', commit_desc.description])
+        # Ensure timestamps are monotonically increasing.
+        timestamp = max(1 + _get_committer_timestamp(merge_base),
+                        _get_committer_timestamp('HEAD'))
+        _git_amend_head(commit_desc.description, timestamp)
         change_desc = ChangeDescription(commit_desc.description)
         # If gnumbd is sitll ON and we ultimately push to branch with
         # pending_prefix, gnumbd will modify footers we've just inserted with

tests/git_cl_test.py

@@ -1066,9 +1066,17 @@ class TestGitCl(TestCase):
     git_cl.main(['land'])
 
   def test_land_rietveld_git_numberer(self):
-    self._land_rietveld_common()
+    self._land_rietveld_common(debug_stdout=False)
     self.mock(git_cl, 'ShouldGenerateGitNumberFooters',
               lambda *a: self._mocked_call(['ShouldGenerateGitNumberFooters']))
+
+    # Special mocks to check validity of timestamp.
+    original_git_amend_head = git_cl._git_amend_head
+    def _git_amend_head_mock(msg, tstamp):
+      self._mocked_call(['git_amend_head committer timestamp', tstamp])
+      return original_git_amend_head(msg, tstamp)
+    self.mock(git_cl, '_git_amend_head', _git_amend_head_mock)
+
     self.calls += [
       ((['git', 'config', 'rietveld.pending-ref-prefix'],), CERR1),
       ((['ShouldGenerateGitNumberFooters'],), True),
@@ -1078,7 +1086,12 @@ class TestGitCl(TestCase):
        '\n'
        'Cr-Commit-Position: refs/heads/master@{#543}\n'
        'Cr-Branched-From: refs/svn/2014@{#2208}'),
+      ((['git', 'show', '-s', '--format=%ct', 'fake_ancestor_sha'],),
+       '1480022355'),  # Committer's unix timestamp.
+      ((['git', 'show', '-s', '--format=%ct', 'HEAD'],),
+       '1480024000'),
 
+      ((['git_amend_head committer timestamp', 1480024000],), None),
       ((['git', 'commit', '--amend', '-m',
         'Issue: 123\n\nR=john@chromium.org\n'
         '\n'