tests/test-abort-checkin.t

bundle2: don't assume ordering of heads checked after push

Usually, the heads will have the same ordering in handlecheckheads. Insisting
on the same ordering is however an unnecessary constraint that in some custom
cases can cause pushes to fail even though the actual heads didn't change. This
caused production issues for us in combination with the current version of
https://bitbucket.org/Unity-Technologies/hgwebcachingproxy/ .

  $ cat > abortcommit.py <<EOF
  > from mercurial import error
  > def hook(**args):
  >     raise error.Abort("no commits allowed")
  > def reposetup(ui, repo):
  >     repo.ui.setconfig("hooks", "pretxncommit.nocommits", hook)
  > EOF
  $ abspath=`pwd`/abortcommit.py

  $ cat <<EOF >> $HGRCPATH
  > [extensions]
  > mq =
  > abortcommit = $abspath
  > EOF

  $ hg init foo
  $ cd foo
  $ echo foo > foo
  $ hg add foo

mq may keep a reference to the repository so __del__ will not be
called and .hg/journal.dirstate will not be deleted:

  $ hg ci -m foo
  error: pretxncommit.nocommits hook failed: no commits allowed
  transaction abort!
  rollback completed
  abort: no commits allowed
  [255]
  $ hg ci -m foo
  error: pretxncommit.nocommits hook failed: no commits allowed
  transaction abort!
  rollback completed
  abort: no commits allowed
  [255]

  $ cd ..