tests/failfilemerge.py

uncommit: leave empty commit if all files are uncommitted

We had instructions for our internal users to add copy information
after commit like this:

  hg uncommit <srcfile> <dstfile>
  hg cp --after <srcfile> <dstfile>
  hg amend

That usually works, but if the rename was the only change in that
commit, then the commit would get pruned. It's easy to fix the recipe:
just pass the --keep option. However, it seems too subtle, so I think
this is an indication that the commit should not be pruned if any
patterns were given.

Differential Revision: https://phab.mercurial-scm.org/D2862

# extension to emulate interrupting filemerge._filemerge

from __future__ import absolute_import

from mercurial import (
    error,
    extensions,
    filemerge,
)

def failfilemerge(filemergefn,
                  premerge, repo, wctx, mynode, orig, fcd, fco, fca,
                  labels=None):
    raise error.Abort("^C")
    return filemergefn(premerge, repo, mynode, orig, fcd, fco, fca, labels)

def extsetup(ui):
    extensions.wrapfunction(filemerge, '_filemerge',
                            failfilemerge)