tests/test-context-metadata.t

merge: add `--abort` flag which can abort the merge

Currently we don't have a good functionality to abort the merge and tell user to
do `hg update -C .` which can leads to different results if user missed the '.'
and moreover does not align with other abort functionalities like rebase, shelve
etc.

This patch adds `hg merge --abort` which will abort the ongoing merge and take
us back to the chagneset where we started from. Works in both cases when merge
resulted in conflicts and when there were no conflicts.

.. feature::

    A `--abort` flag to merge command to abort the ongoing merge.

Differential Revision: https://phab.mercurial-scm.org/D1829

Tests about metadataonlyctx

  $ hg init
  $ echo A > A
  $ hg commit -A A -m 'Add A'
  $ echo B > B
  $ hg commit -A B -m 'Add B'
  $ hg rm A
  $ echo C > C
  $ echo B2 > B
  $ hg add C -q
  $ hg commit -m 'Remove A'

  $ cat > metaedit.py <<EOF
  > from __future__ import absolute_import
  > from mercurial import context, registrar
  > cmdtable = {}
  > command = registrar.command(cmdtable)
  > @command('metaedit')
  > def metaedit(ui, repo, arg):
  >     # Modify commit message to "FOO"
  >     with repo.wlock(), repo.lock(), repo.transaction('metaedit'):
  >         old = repo['.']
  >         kwargs = dict(s.split('=', 1) for s in arg.split(';'))
  >         if 'parents' in kwargs:
  >             kwargs['parents'] = kwargs['parents'].split(',')
  >         new = context.metadataonlyctx(repo, old, **kwargs)
  >         new.commit()
  > EOF
  $ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'text=Changed'
  $ hg log -r tip
  changeset:   3:ad83e9e00ec9
  tag:         tip
  parent:      1:3afb7afe6632
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Changed
  
  $ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'parents=0' 2>&1 | egrep '^RuntimeError'
  RuntimeError: can't reuse the manifest: its p1 doesn't match the new ctx p1

  $ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'user=foo <[e-mail]>'
  $ hg log -r tip
  changeset:   4:1f86eaeca92b
  tag:         tip
  parent:      1:3afb7afe6632
  user:        foo <[e-mail]>
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Remove A