merge: make applyupdates() not mutate mresult argument We have an extension at work that overrides `merge.applyupdates()` to make it skip some writes and instead instruct the virtual filesystem we use to get a different version. That override doesn't work correctly when doing `hg co -m` and there's a modified file in the dirstate that's deleted in the destination. That's because `applyupdates()` mutates its `mresult` argument and our extension had passed in a modified copied of `mresult` to the overridden function, which resulted in the mutation not having any effect. This patch fixes that by letting the caller (i.e. `merge._update()`) update `mresult` with the extra actions instead. Besides fixing our internal extension, that seems cleaner to me anyway (better to not mutate `mresult` only in some cases and we can skip some of the logic if we're not going to update the dirstate anyway). Differential Revision: https://phab.mercurial-scm.org/D10830

# mergeutil.py - help for merge processing in mercurial
#
# Copyright 2005-2007 Olivia Mackall <olivia@selenic.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

from .i18n import _

from . import error


def checkunresolved(ms):
    if ms.unresolvedcount():
        raise error.StateError(
            _(b"unresolved merge conflicts (see 'hg help resolve')")
        )