correction: factually CQ stopped committing changes, but the reason may be different

from cq logs

[D2017-03-31T11:59:43.325357-07:00 30107 140610691032896 utils.rietveld:450] POSTing to https://codereview.chromium.org/api/2666423002?messages=true, args {'payload': None, 'timeout': 15}.
[D2017-03-31T11:59:43.371799-07:00 30107 140610509989632 checkouts:489] adding git number with parent u'aef3329cadaa6cc1a8d2f558cd33cce6caa95278' msg("Move all of csswg-test to wpt/css and temporarily disable all css tests.\n\nI intend to directly land this CL, so what's shown in Rietvel
d isn't a reflection of the true contents of the patch, which changes more than 6000 files.\n\nThis commit will include:\n An import of just wpt/css from wpt@a810200e6e1b0b98527bd1fd791fa110646cfb91\n Removal of external/csswg-test\n Updates to the expectation files to temporarily disabl
e the tests\n\nNOEXPORT=true\nTBR=kojii\nTBR_REASON=preparing for follow-up CLs which enable the tests; I expect this CL to be low-risk since it disables all of the affected tests.\nBUG=706118\n\nReview-Url: https://codereview.chromium.org/2793583002 .\nCr-Commit-Position: refs/heads/mas
ter@{#461177}\n\nwarning: inexact rename detection was skipped due to too many files.\nwarning: you may want to set your diff.renameLimit variable to at least 6027 and retry the command.") destined for refs/heads/master
[E2017-03-31T11:59:43.373450-07:00 30107 140610509989632 errors:174] Transient error: Unable to get commit position from footers
  File "/usr/lib/python2.7/threading.py", line 783, in __bootstrap
    self.__bootstrap_inner()
  File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
    self.run()
  File "/usr/lib/python2.7/threading.py", line 763, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/b/infra_internal/commit_queue/pending_manager/base.py", line 464, in _work
    self._commit_patch(pending)
  File "/b/infra_internal/commit_queue/pending_manager/rietveld.py", line 451, in _commit_patch
    self._commit_to_checkout(pending)
  File "/b/infra_internal/commit_queue/pending_manager/rietveld.py", line 404, in _commit_to_checkout
    pre_push_cb=lambda cr, pr: pending._publish_intent_to_push(
  File "/b/infra_internal/commit_queue/checkouts.py", line 585, in amend_and_push
    original_description, target_remote_ref)
  File "/b/infra_internal/commit_queue/checkouts.py", line 526, in _add_git_number
    description, parent_rev, parent_msg.rstrip(), target_remote_ref)
  File "/b/infra_internal/commit_queue/errors.py", line 213, in wrapper
    return func(obj, *args, **kwargs), None
  File "/usr/lib/python2.7/contextlib.py", line 35, in __exit__
    self.gen.throw(type, value, traceback)
  File "/b/infra_internal/commit_queue/errors.py", line 172, in track_exceptions
    self.stacktrace = (''.join(traceback.format_stack()) +
Traceback (most recent call last):
  File "/b/infra_internal/commit_queue/errors.py", line 169, in track_exceptions
    yield ctx
  File "/b/infra_internal/commit_queue/errors.py", line 213, in wrapper
    return func(obj, *args, **kwargs), None
  File "/b/infra_internal/commit_queue/checkouts.py", line 492, in _add_git_number_footers
    parent_rev, parent_msg, target_remote_ref)
  File "/b/infra_internal/commit_queue/utils/git_cl.py", line 169, in update_with_git_number_footers
    parent_position = git_footers.get_position(parent_footer_map)
  File "/b/infra_internal/commit_queue/utils/git_footers.py", line 143, in get_position
    raise ValueError('Unable to get commit position from footers')
ValueError: Unable to get commit position from footers

I think I've found the cause:

CQ tried to get commit messages of the parent commit
$ git show -s --format=%B HEAD~1

And receives:
"""
Move all of csswg-test to wpt/css and temporarily disable all css tests.

I intend to directly land this CL, so what's shown in Rietveld isn't a reflection of the true contents of the patch, which changes more than 6000 files.

This commit will include:
 An import of just wpt/css from wpt@a810200e6e1b0b98527bd1fd791fa110646cfb91
 Removal of external/csswg-test
 Updates to the expectation files to temporarily disable the tests

NOEXPORT=true
TBR=kojii
TBR_REASON=preparing for follow-up CLs which enable the tests; I expect this CL to be low-risk since it disables all of the affected tests.
BUG= 706118 

Review-Url: https://codereview.chromium.org/2793583002 .
Cr-Commit-Position: refs/heads/master@{#461177}

warning: inexact rename detection was skipped due to too many files.
warning: you may want to set your diff.renameLimit variable to at least 6027 and retry the command.
"""

Nothing warnings at the end.

This confuses git_footers.py parser.

As emergency solution I set "git config diff.renameLimit 10000" in chromium/src checkout. It "fixed" the commit message output. I hope it will unwedge the CQ.

This fix unblocked the CQ.

Lowering priority and assigning to Andrii for a more permanent fix.

Nodir thanks for detecting! Vadim, thanks for temporary fix!
Here is a CL to fix this for real: https://chrome-internal-review.googlesource.com/347383 

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/infra/infra_internal/+/20de264ce7037bf8137db09be5eced8b70df60e6

commit 20de264ce7037bf8137db09be5eced8b70df60e6
Author: Andrii Shyshkalov <tandrii@chromium.org>
Date: Wed Apr 05 12:56:36 2017

Issue 707315 has been merged into this issue.