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, pycompat, registrar

  > cmdtable = {}

  > command = registrar.command(cmdtable)

  > @command(b'metaedit')

  > def metaedit(ui, repo, arg):

  >     # Modify commit message to "FOO"

  >     with repo.wlock(), repo.lock(), repo.transaction(b'metaedit'):

  >         old = repo[b'.']

  >         kwargs = dict(s.split(b'=', 1) for s in arg.split(b';'))

  >         if b'parents' in kwargs:

  >             kwargs[b'parents'] = map(int, kwargs[b'parents'].split(b','))

  >         new = context.metadataonlyctx(repo, old,

  >                                       **pycompat.strkwargs(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 <foo@example.com>'

  $ hg log -r tip

  changeset:   4:1f86eaeca92b

  tag:         tip

  parent:      1:3afb7afe6632

  user:        foo <foo@example.com>

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     Remove A