dirstate: add a comment about a racy piece of code during updates

This is a bit that is not really correct but works "fine" in practice. Let us
write the details down so that people stop wondering how that logic might be
correct… It is not.

Differential Revision: https://phab.mercurial-scm.org/D11781

mercurial/merge.py

@@ -1,2434 +1,2462 b''
 # merge.py - directory-level update/merge handling for Mercurial
 #
 # Copyright 2006, 2007 Olivia Mackall <[e-mail]>
 #
 # 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
 
 import collections
 import errno
 import struct
 
 from .i18n import _
 from .node import nullrev
 from .thirdparty import attr
 from .utils import stringutil
 from .dirstateutils import timestamp
 from . import (
     copies,
     encoding,
     error,
     filemerge,
     match as matchmod,
     mergestate as mergestatemod,
     obsutil,
     pathutil,
     pycompat,
     scmutil,
     subrepoutil,
     util,
     worker,
 )
 
 _pack = struct.pack
 _unpack = struct.unpack
 
 
 def _getcheckunknownconfig(repo, section, name):
     config = repo.ui.config(section, name)
     valid = [b'abort', b'ignore', b'warn']
     if config not in valid:
         validstr = b', '.join([b"'" + v + b"'" for v in valid])
         raise error.ConfigError(
             _(b"%s.%s not valid ('%s' is none of %s)")
             % (section, name, config, validstr)
         )
     return config
 
 
 def _checkunknownfile(repo, wctx, mctx, f, f2=None):
     if wctx.isinmemory():
         # Nothing to do in IMM because nothing in the "working copy" can be an
         # unknown file.
         #
         # Note that we should bail out here, not in ``_checkunknownfiles()``,
         # because that function does other useful work.
         return False
 
     if f2 is None:
         f2 = f
     return (
         repo.wvfs.audit.check(f)
         and repo.wvfs.isfileorlink(f)
         and repo.dirstate.normalize(f) not in repo.dirstate
         and mctx[f2].cmp(wctx[f])
     )
 
 
 class _unknowndirschecker(object):
     """
     Look for any unknown files or directories that may have a path conflict
     with a file.  If any path prefix of the file exists as a file or link,
     then it conflicts.  If the file itself is a directory that contains any
     file that is not tracked, then it conflicts.
 
     Returns the shortest path at which a conflict occurs, or None if there is
     no conflict.
     """
 
     def __init__(self):
         # A set of paths known to be good.  This prevents repeated checking of
         # dirs.  It will be updated with any new dirs that are checked and found
         # to be safe.
         self._unknowndircache = set()
 
         # A set of paths that are known to be absent.  This prevents repeated
         # checking of subdirectories that are known not to exist. It will be
         # updated with any new dirs that are checked and found to be absent.
         self._missingdircache = set()
 
     def __call__(self, repo, wctx, f):
         if wctx.isinmemory():
             # Nothing to do in IMM for the same reason as ``_checkunknownfile``.
             return False
 
         # Check for path prefixes that exist as unknown files.
         for p in reversed(list(pathutil.finddirs(f))):
             if p in self._missingdircache:
                 return
             if p in self._unknowndircache:
                 continue
             if repo.wvfs.audit.check(p):
                 if (
                     repo.wvfs.isfileorlink(p)
                     and repo.dirstate.normalize(p) not in repo.dirstate
                 ):
                     return p
                 if not repo.wvfs.lexists(p):
                     self._missingdircache.add(p)
                     return
                 self._unknowndircache.add(p)
 
         # Check if the file conflicts with a directory containing unknown files.
         if repo.wvfs.audit.check(f) and repo.wvfs.isdir(f):
             # Does the directory contain any files that are not in the dirstate?
             for p, dirs, files in repo.wvfs.walk(f):
                 for fn in files:
                     relf = util.pconvert(repo.wvfs.reljoin(p, fn))
                     relf = repo.dirstate.normalize(relf, isknown=True)
                     if relf not in repo.dirstate:
                         return f
         return None
 
 
 def _checkunknownfiles(repo, wctx, mctx, force, mresult, mergeforce):
     """
     Considers any actions that care about the presence of conflicting unknown
     files. For some actions, the result is to abort; for others, it is to
     choose a different action.
     """
     fileconflicts = set()
     pathconflicts = set()
     warnconflicts = set()
     abortconflicts = set()
     unknownconfig = _getcheckunknownconfig(repo, b'merge', b'checkunknown')
     ignoredconfig = _getcheckunknownconfig(repo, b'merge', b'checkignored')
     pathconfig = repo.ui.configbool(
         b'experimental', b'merge.checkpathconflicts'
     )
     if not force:
 
         def collectconflicts(conflicts, config):
             if config == b'abort':
                 abortconflicts.update(conflicts)
             elif config == b'warn':
                 warnconflicts.update(conflicts)
 
         checkunknowndirs = _unknowndirschecker()
         for f in mresult.files(
             (
                 mergestatemod.ACTION_CREATED,
                 mergestatemod.ACTION_DELETED_CHANGED,
             )
         ):
             if _checkunknownfile(repo, wctx, mctx, f):
                 fileconflicts.add(f)
             elif pathconfig and f not in wctx:
                 path = checkunknowndirs(repo, wctx, f)
                 if path is not None:
                     pathconflicts.add(path)
         for f, args, msg in mresult.getactions(
             [mergestatemod.ACTION_LOCAL_DIR_RENAME_GET]
         ):
             if _checkunknownfile(repo, wctx, mctx, f, args[0]):
                 fileconflicts.add(f)
 
         allconflicts = fileconflicts | pathconflicts
         ignoredconflicts = {c for c in allconflicts if repo.dirstate._ignore(c)}
         unknownconflicts = allconflicts - ignoredconflicts
         collectconflicts(ignoredconflicts, ignoredconfig)
         collectconflicts(unknownconflicts, unknownconfig)
     else:
         for f, args, msg in list(
             mresult.getactions([mergestatemod.ACTION_CREATED_MERGE])
         ):
             fl2, anc = args
             different = _checkunknownfile(repo, wctx, mctx, f)
             if repo.dirstate._ignore(f):
                 config = ignoredconfig
             else:
                 config = unknownconfig
 
             # The behavior when force is True is described by this table:
             #  config  different  mergeforce  |    action    backup
             #    *         n          *       |      get        n
             #    *         y          y       |     merge       -
             #   abort      y          n       |     merge       -   (1)
             #   warn       y          n       |  warn + get     y
             #  ignore      y          n       |      get        y
             #
             # (1) this is probably the wrong behavior here -- we should
             #     probably abort, but some actions like rebases currently
             #     don't like an abort happening in the middle of
             #     merge.update.
             if not different:
                 mresult.addfile(
                     f,
                     mergestatemod.ACTION_GET,
                     (fl2, False),
                     b'remote created',
                 )
             elif mergeforce or config == b'abort':
                 mresult.addfile(
                     f,
                     mergestatemod.ACTION_MERGE,
                     (f, f, None, False, anc),
                     b'remote differs from untracked local',
                 )
             elif config == b'abort':
                 abortconflicts.add(f)
             else:
                 if config == b'warn':
                     warnconflicts.add(f)
                 mresult.addfile(
                     f,
                     mergestatemod.ACTION_GET,
                     (fl2, True),
                     b'remote created',
                 )
 
     for f in sorted(abortconflicts):
         warn = repo.ui.warn
         if f in pathconflicts:
             if repo.wvfs.isfileorlink(f):
                 warn(_(b"%s: untracked file conflicts with directory\n") % f)
             else:
                 warn(_(b"%s: untracked directory conflicts with file\n") % f)
         else:
             warn(_(b"%s: untracked file differs\n") % f)
     if abortconflicts:
         raise error.StateError(
             _(
                 b"untracked files in working directory "
                 b"differ from files in requested revision"
             )
         )
 
     for f in sorted(warnconflicts):
         if repo.wvfs.isfileorlink(f):
             repo.ui.warn(_(b"%s: replacing untracked file\n") % f)
         else:
             repo.ui.warn(_(b"%s: replacing untracked files in directory\n") % f)
 
     for f, args, msg in list(
         mresult.getactions([mergestatemod.ACTION_CREATED])
     ):
         backup = (
             f in fileconflicts
             or f in pathconflicts
             or any(p in pathconflicts for p in pathutil.finddirs(f))
         )
         (flags,) = args
         mresult.addfile(f, mergestatemod.ACTION_GET, (flags, backup), msg)
 
 
 def _forgetremoved(wctx, mctx, branchmerge, mresult):
     """
     Forget removed files
 
     If we're jumping between revisions (as opposed to merging), and if
     neither the working directory nor the target rev has the file,
     then we need to remove it from the dirstate, to prevent the
     dirstate from listing the file when it is no longer in the
     manifest.
 
     If we're merging, and the other revision has removed a file
     that is not present in the working directory, we need to mark it
     as removed.
     """
 
     m = mergestatemod.ACTION_FORGET
     if branchmerge:
         m = mergestatemod.ACTION_REMOVE
     for f in wctx.deleted():
         if f not in mctx:
             mresult.addfile(f, m, None, b"forget deleted")
 
     if not branchmerge:
         for f in wctx.removed():
             if f not in mctx:
                 mresult.addfile(
                     f,
                     mergestatemod.ACTION_FORGET,
                     None,
                     b"forget removed",
                 )
 
 
 def _checkcollision(repo, wmf, mresult):
     """
     Check for case-folding collisions.
     """
     # If the repo is narrowed, filter out files outside the narrowspec.
     narrowmatch = repo.narrowmatch()
     if not narrowmatch.always():
         pmmf = set(wmf.walk(narrowmatch))
         if mresult:
             for f in list(mresult.files()):
                 if not narrowmatch(f):
                     mresult.removefile(f)
     else:
         # build provisional merged manifest up
         pmmf = set(wmf)
 
     if mresult:
         # KEEP and EXEC are no-op
         for f in mresult.files(
             (
                 mergestatemod.ACTION_ADD,
                 mergestatemod.ACTION_ADD_MODIFIED,
                 mergestatemod.ACTION_FORGET,
                 mergestatemod.ACTION_GET,
                 mergestatemod.ACTION_CHANGED_DELETED,
                 mergestatemod.ACTION_DELETED_CHANGED,
             )
         ):
             pmmf.add(f)
         for f in mresult.files((mergestatemod.ACTION_REMOVE,)):
             pmmf.discard(f)
         for f, args, msg in mresult.getactions(
             [mergestatemod.ACTION_DIR_RENAME_MOVE_LOCAL]
         ):
             f2, flags = args
             pmmf.discard(f2)
             pmmf.add(f)
         for f in mresult.files((mergestatemod.ACTION_LOCAL_DIR_RENAME_GET,)):
             pmmf.add(f)
         for f, args, msg in mresult.getactions([mergestatemod.ACTION_MERGE]):
             f1, f2, fa, move, anc = args
             if move:
                 pmmf.discard(f1)
             pmmf.add(f)
 
     # check case-folding collision in provisional merged manifest
     foldmap = {}
     for f in pmmf:
         fold = util.normcase(f)
         if fold in foldmap:
             raise error.StateError(
                 _(b"case-folding collision between %s and %s")
                 % (f, foldmap[fold])
             )
         foldmap[fold] = f
 
     # check case-folding of directories
     foldprefix = unfoldprefix = lastfull = b''
     for fold, f in sorted(foldmap.items()):
         if fold.startswith(foldprefix) and not f.startswith(unfoldprefix):
             # the folded prefix matches but actual casing is different
             raise error.StateError(
                 _(b"case-folding collision between %s and directory of %s")
                 % (lastfull, f)
             )
         foldprefix = fold + b'/'
         unfoldprefix = f + b'/'
         lastfull = f
 
 
 def _filesindirs(repo, manifest, dirs):
     """
     Generator that yields pairs of all the files in the manifest that are found
     inside the directories listed in dirs, and which directory they are found
     in.
     """
     for f in manifest:
         for p in pathutil.finddirs(f):
             if p in dirs:
                 yield f, p
                 break
 
 
 def checkpathconflicts(repo, wctx, mctx, mresult):
     """
     Check if any actions introduce path conflicts in the repository, updating
     actions to record or handle the path conflict accordingly.
     """
     mf = wctx.manifest()
 
     # The set of local files that conflict with a remote directory.
     localconflicts = set()
 
     # The set of directories that conflict with a remote file, and so may cause
     # conflicts if they still contain any files after the merge.
     remoteconflicts = set()
 
     # The set of directories that appear as both a file and a directory in the
     # remote manifest.  These indicate an invalid remote manifest, which
     # can't be updated to cleanly.
     invalidconflicts = set()
 
     # The set of directories that contain files that are being created.
     createdfiledirs = set()
 
     # The set of files deleted by all the actions.
     deletedfiles = set()
 
     for f in mresult.files(
         (
             mergestatemod.ACTION_CREATED,
             mergestatemod.ACTION_DELETED_CHANGED,
             mergestatemod.ACTION_MERGE,
             mergestatemod.ACTION_CREATED_MERGE,
         )
     ):
         # This action may create a new local file.
         createdfiledirs.update(pathutil.finddirs(f))
         if mf.hasdir(f):
             # The file aliases a local directory.  This might be ok if all
             # the files in the local directory are being deleted.  This
             # will be checked once we know what all the deleted files are.
             remoteconflicts.add(f)
     # Track the names of all deleted files.
     for f in mresult.files((mergestatemod.ACTION_REMOVE,)):
         deletedfiles.add(f)
     for (f, args, msg) in mresult.getactions((mergestatemod.ACTION_MERGE,)):
         f1, f2, fa, move, anc = args
         if move:
             deletedfiles.add(f1)
     for (f, args, msg) in mresult.getactions(
         (mergestatemod.ACTION_DIR_RENAME_MOVE_LOCAL,)
     ):
         f2, flags = args
         deletedfiles.add(f2)
 
     # Check all directories that contain created files for path conflicts.
     for p in createdfiledirs:
         if p in mf:
             if p in mctx:
                 # A file is in a directory which aliases both a local
                 # and a remote file.  This is an internal inconsistency
                 # within the remote manifest.
                 invalidconflicts.add(p)
             else:
                 # A file is in a directory which aliases a local file.
                 # We will need to rename the local file.
                 localconflicts.add(p)
         pd = mresult.getfile(p)
         if pd and pd[0] in (
             mergestatemod.ACTION_CREATED,
             mergestatemod.ACTION_DELETED_CHANGED,
             mergestatemod.ACTION_MERGE,
             mergestatemod.ACTION_CREATED_MERGE,
         ):
             # The file is in a directory which aliases a remote file.
             # This is an internal inconsistency within the remote
             # manifest.
             invalidconflicts.add(p)
 
     # Rename all local conflicting files that have not been deleted.
     for p in localconflicts:
         if p not in deletedfiles:
             ctxname = bytes(wctx).rstrip(b'+')
             pnew = util.safename(p, ctxname, wctx, set(mresult.files()))
             porig = wctx[p].copysource() or p
             mresult.addfile(
                 pnew,
                 mergestatemod.ACTION_PATH_CONFLICT_RESOLVE,
                 (p, porig),
                 b'local path conflict',
             )
             mresult.addfile(
                 p,
                 mergestatemod.ACTION_PATH_CONFLICT,
                 (pnew, b'l'),
                 b'path conflict',
             )
 
     if remoteconflicts:
         # Check if all files in the conflicting directories have been removed.
         ctxname = bytes(mctx).rstrip(b'+')
         for f, p in _filesindirs(repo, mf, remoteconflicts):
             if f not in deletedfiles:
                 m, args, msg = mresult.getfile(p)
                 pnew = util.safename(p, ctxname, wctx, set(mresult.files()))
                 if m in (
                     mergestatemod.ACTION_DELETED_CHANGED,
                     mergestatemod.ACTION_MERGE,
                 ):
                     # Action was merge, just update target.
                     mresult.addfile(pnew, m, args, msg)
                 else:
                     # Action was create, change to renamed get action.
                     fl = args[0]
                     mresult.addfile(
                         pnew,
                         mergestatemod.ACTION_LOCAL_DIR_RENAME_GET,
                         (p, fl),
                         b'remote path conflict',
                     )
                 mresult.addfile(
                     p,
                     mergestatemod.ACTION_PATH_CONFLICT,
                     (pnew, mergestatemod.ACTION_REMOVE),
                     b'path conflict',
                 )
                 remoteconflicts.remove(p)
                 break
 
     if invalidconflicts:
         for p in invalidconflicts:
             repo.ui.warn(_(b"%s: is both a file and a directory\n") % p)
         raise error.StateError(
             _(b"destination manifest contains path conflicts")
         )
 
 
 def _filternarrowactions(narrowmatch, branchmerge, mresult):
     """
     Filters out actions that can ignored because the repo is narrowed.
 
     Raise an exception if the merge cannot be completed because the repo is
     narrowed.
     """
     # TODO: handle with nonconflicttypes
     nonconflicttypes = {
         mergestatemod.ACTION_ADD,
         mergestatemod.ACTION_ADD_MODIFIED,
         mergestatemod.ACTION_CREATED,
         mergestatemod.ACTION_CREATED_MERGE,
         mergestatemod.ACTION_FORGET,
         mergestatemod.ACTION_GET,
         mergestatemod.ACTION_REMOVE,
         mergestatemod.ACTION_EXEC,
     }
     # We mutate the items in the dict during iteration, so iterate
     # over a copy.
     for f, action in mresult.filemap():
         if narrowmatch(f):
             pass
         elif not branchmerge:
             mresult.removefile(f)  # just updating, ignore changes outside clone
         elif action[0] in mergestatemod.NO_OP_ACTIONS:
             mresult.removefile(f)  # merge does not affect file
         elif action[0] in nonconflicttypes:
             raise error.Abort(
                 _(
                     b'merge affects file \'%s\' outside narrow, '
                     b'which is not yet supported'
                 )
                 % f,
                 hint=_(b'merging in the other direction may work'),
             )
         else:
             raise error.StateError(
                 _(b'conflict in file \'%s\' is outside narrow clone') % f
             )
 
 
 class mergeresult(object):
     """An object representing result of merging manifests.
 
     It has information about what actions need to be performed on dirstate
     mapping of divergent renames and other such cases."""
 
     def __init__(self):
         """
         filemapping: dict of filename as keys and action related info as values
         diverge: mapping of source name -> list of dest name for
                  divergent renames
         renamedelete: mapping of source name -> list of destinations for files
                       deleted on one side and renamed on other.
         commitinfo: dict containing data which should be used on commit
                     contains a filename -> info mapping
         actionmapping: dict of action names as keys and values are dict of
                        filename as key and related data as values
         """
         self._filemapping = {}
         self._diverge = {}
         self._renamedelete = {}
         self._commitinfo = collections.defaultdict(dict)
         self._actionmapping = collections.defaultdict(dict)
 
     def updatevalues(self, diverge, renamedelete):
         self._diverge = diverge
         self._renamedelete = renamedelete
 
     def addfile(self, filename, action, data, message):
         """adds a new file to the mergeresult object
 
         filename: file which we are adding
         action: one of mergestatemod.ACTION_*
         data: a tuple of information like fctx and ctx related to this merge
         message: a message about the merge
         """
         # if the file already existed, we need to delete it's old
         # entry form _actionmapping too
         if filename in self._filemapping:
             a, d, m = self._filemapping[filename]
             del self._actionmapping[a][filename]
 
         self._filemapping[filename] = (action, data, message)
         self._actionmapping[action][filename] = (data, message)
 
     def getfile(self, filename, default_return=None):
         """returns (action, args, msg) about this file
 
         returns default_return if the file is not present"""
         if filename in self._filemapping:
             return self._filemapping[filename]
         return default_return
 
     def files(self, actions=None):
         """returns files on which provided action needs to perfromed
 
         If actions is None, all files are returned
         """
         # TODO: think whether we should return renamedelete and
         # diverge filenames also
         if actions is None:
             for f in self._filemapping:
                 yield f
 
         else:
             for a in actions:
                 for f in self._actionmapping[a]:
                     yield f
 
     def removefile(self, filename):
         """removes a file from the mergeresult object as the file might
         not merging anymore"""
         action, data, message = self._filemapping[filename]
         del self._filemapping[filename]
         del self._actionmapping[action][filename]
 
     def getactions(self, actions, sort=False):
         """get list of files which are marked with these actions
         if sort is true, files for each action is sorted and then added
 
         Returns a list of tuple of form (filename, data, message)
         """
         for a in actions:
             if sort:
                 for f in sorted(self._actionmapping[a]):
                     args, msg = self._actionmapping[a][f]
                     yield f, args, msg
             else:
                 for f, (args, msg) in pycompat.iteritems(
                     self._actionmapping[a]
                 ):
                     yield f, args, msg
 
     def len(self, actions=None):
         """returns number of files which needs actions
 
         if actions is passed, total of number of files in that action
         only is returned"""
 
         if actions is None:
             return len(self._filemapping)
 
         return sum(len(self._actionmapping[a]) for a in actions)
 
     def filemap(self, sort=False):
         if sorted:
             for key, val in sorted(pycompat.iteritems(self._filemapping)):
                 yield key, val
         else:
             for key, val in pycompat.iteritems(self._filemapping):
                 yield key, val
 
     def addcommitinfo(self, filename, key, value):
         """adds key-value information about filename which will be required
         while committing this merge"""
         self._commitinfo[filename][key] = value
 
     @property
     def diverge(self):
         return self._diverge
 
     @property
     def renamedelete(self):
         return self._renamedelete
 
     @property
     def commitinfo(self):
         return self._commitinfo
 
     @property
     def actionsdict(self):
         """returns a dictionary of actions to be perfomed with action as key
         and a list of files and related arguments as values"""
         res = collections.defaultdict(list)
         for a, d in pycompat.iteritems(self._actionmapping):
             for f, (args, msg) in pycompat.iteritems(d):
                 res[a].append((f, args, msg))
         return res
 
     def setactions(self, actions):
         self._filemapping = actions
         self._actionmapping = collections.defaultdict(dict)
         for f, (act, data, msg) in pycompat.iteritems(self._filemapping):
             self._actionmapping[act][f] = data, msg
 
     def hasconflicts(self):
         """tells whether this merge resulted in some actions which can
         result in conflicts or not"""
         for a in self._actionmapping.keys():
             if (
                 a
                 not in (
                     mergestatemod.ACTION_GET,
                     mergestatemod.ACTION_EXEC,
                     mergestatemod.ACTION_REMOVE,
                     mergestatemod.ACTION_PATH_CONFLICT_RESOLVE,
                 )
                 and self._actionmapping[a]
                 and a not in mergestatemod.NO_OP_ACTIONS
             ):
                 return True
 
         return False
 
 
 def manifestmerge(
     repo,
     wctx,
     p2,
     pa,
     branchmerge,
     force,
     matcher,
     acceptremote,
     followcopies,
     forcefulldiff=False,
 ):
     """
     Merge wctx and p2 with ancestor pa and generate merge action list
 
     branchmerge and force are as passed in to update
     matcher = matcher to filter file lists
     acceptremote = accept the incoming changes without prompting
 
     Returns an object of mergeresult class
     """
     mresult = mergeresult()
     if matcher is not None and matcher.always():
         matcher = None
 
     # manifests fetched in order are going to be faster, so prime the caches
     [
         x.manifest()
         for x in sorted(wctx.parents() + [p2, pa], key=scmutil.intrev)
     ]
 
     branch_copies1 = copies.branch_copies()
     branch_copies2 = copies.branch_copies()
     diverge = {}
     # information from merge which is needed at commit time
     # for example choosing filelog of which parent to commit
     # TODO: use specific constants in future for this mapping
     if followcopies:
         branch_copies1, branch_copies2, diverge = copies.mergecopies(
             repo, wctx, p2, pa
         )
 
     boolbm = pycompat.bytestr(bool(branchmerge))
     boolf = pycompat.bytestr(bool(force))
     boolm = pycompat.bytestr(bool(matcher))
     repo.ui.note(_(b"resolving manifests\n"))
     repo.ui.debug(
         b" branchmerge: %s, force: %s, partial: %s\n" % (boolbm, boolf, boolm)
     )
     repo.ui.debug(b" ancestor: %s, local: %s, remote: %s\n" % (pa, wctx, p2))
 
     m1, m2, ma = wctx.manifest(), p2.manifest(), pa.manifest()
     copied1 = set(branch_copies1.copy.values())
     copied1.update(branch_copies1.movewithdir.values())
     copied2 = set(branch_copies2.copy.values())
     copied2.update(branch_copies2.movewithdir.values())
 
     if b'.hgsubstate' in m1 and wctx.rev() is None:
         # Check whether sub state is modified, and overwrite the manifest
         # to flag the change. If wctx is a committed revision, we shouldn't
         # care for the dirty state of the working directory.
         if any(wctx.sub(s).dirty() for s in wctx.substate):
             m1[b'.hgsubstate'] = repo.nodeconstants.modifiednodeid
 
     # Don't use m2-vs-ma optimization if:
     # - ma is the same as m1 or m2, which we're just going to diff again later
     # - The caller specifically asks for a full diff, which is useful during bid
     #   merge.
     # - we are tracking salvaged files specifically hence should process all
     #   files
     if (
         pa not in ([wctx, p2] + wctx.parents())
         and not forcefulldiff
         and not (
             repo.ui.configbool(b'experimental', b'merge-track-salvaged')
             or repo.filecopiesmode == b'changeset-sidedata'
         )
     ):
         # Identify which files are relevant to the merge, so we can limit the
         # total m1-vs-m2 diff to just those files. This has significant
         # performance benefits in large repositories.
         relevantfiles = set(ma.diff(m2).keys())
 
         # For copied and moved files, we need to add the source file too.
         for copykey, copyvalue in pycompat.iteritems(branch_copies1.copy):
             if copyvalue in relevantfiles:
                 relevantfiles.add(copykey)
         for movedirkey in branch_copies1.movewithdir:
             relevantfiles.add(movedirkey)
         filesmatcher = scmutil.matchfiles(repo, relevantfiles)
         matcher = matchmod.intersectmatchers(matcher, filesmatcher)
 
     diff = m1.diff(m2, match=matcher)
 
     for f, ((n1, fl1), (n2, fl2)) in pycompat.iteritems(diff):
         if n1 and n2:  # file exists on both local and remote side
             if f not in ma:
                 # TODO: what if they're renamed from different sources?
                 fa = branch_copies1.copy.get(
                     f, None
                 ) or branch_copies2.copy.get(f, None)
                 args, msg = None, None
                 if fa is not None:
                     args = (f, f, fa, False, pa.node())
                     msg = b'both renamed from %s' % fa
                 else:
                     args = (f, f, None, False, pa.node())
                     msg = b'both created'
                 mresult.addfile(f, mergestatemod.ACTION_MERGE, args, msg)
             elif f in branch_copies1.copy:
                 fa = branch_copies1.copy[f]
                 mresult.addfile(
                     f,
                     mergestatemod.ACTION_MERGE,
                     (f, fa, fa, False, pa.node()),
                     b'local replaced from %s' % fa,
                 )
             elif f in branch_copies2.copy:
                 fa = branch_copies2.copy[f]
                 mresult.addfile(
                     f,
                     mergestatemod.ACTION_MERGE,
                     (fa, f, fa, False, pa.node()),
                     b'other replaced from %s' % fa,
                 )
             else:
                 a = ma[f]
                 fla = ma.flags(f)
                 nol = b'l' not in fl1 + fl2 + fla
                 if n2 == a and fl2 == fla:
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_KEEP,
                         (),
                         b'remote unchanged',
                     )
                 elif n1 == a and fl1 == fla:  # local unchanged - use remote
                     if n1 == n2:  # optimization: keep local content
                         mresult.addfile(
                             f,
                             mergestatemod.ACTION_EXEC,
                             (fl2,),
                             b'update permissions',
                         )
                     else:
                         mresult.addfile(
                             f,
                             mergestatemod.ACTION_GET,
                             (fl2, False),
                             b'remote is newer',
                         )
                         if branchmerge:
                             mresult.addcommitinfo(
                                 f, b'filenode-source', b'other'
                             )
                 elif nol and n2 == a:  # remote only changed 'x'
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_EXEC,
                         (fl2,),
                         b'update permissions',
                     )
                 elif nol and n1 == a:  # local only changed 'x'
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_GET,
                         (fl1, False),
                         b'remote is newer',
                     )
                     if branchmerge:
                         mresult.addcommitinfo(f, b'filenode-source', b'other')
                 else:  # both changed something
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_MERGE,
                         (f, f, f, False, pa.node()),
                         b'versions differ',
                     )
         elif n1:  # file exists only on local side
             if f in copied2:
                 pass  # we'll deal with it on m2 side
             elif (
                 f in branch_copies1.movewithdir
             ):  # directory rename, move local
                 f2 = branch_copies1.movewithdir[f]
                 if f2 in m2:
                     mresult.addfile(
                         f2,
                         mergestatemod.ACTION_MERGE,
                         (f, f2, None, True, pa.node()),
                         b'remote directory rename, both created',
                     )
                 else:
                     mresult.addfile(
                         f2,
                         mergestatemod.ACTION_DIR_RENAME_MOVE_LOCAL,
                         (f, fl1),
                         b'remote directory rename - move from %s' % f,
                     )
             elif f in branch_copies1.copy:
                 f2 = branch_copies1.copy[f]
                 mresult.addfile(
                     f,
                     mergestatemod.ACTION_MERGE,
                     (f, f2, f2, False, pa.node()),
                     b'local copied/moved from %s' % f2,
                 )
             elif f in ma:  # clean, a different, no remote
                 if n1 != ma[f]:
                     if acceptremote:
                         mresult.addfile(
                             f,
                             mergestatemod.ACTION_REMOVE,
                             None,
                             b'remote delete',
                         )
                     else:
                         mresult.addfile(
                             f,
                             mergestatemod.ACTION_CHANGED_DELETED,
                             (f, None, f, False, pa.node()),
                             b'prompt changed/deleted',
                         )
                         if branchmerge:
                             mresult.addcommitinfo(
                                 f, b'merge-removal-candidate', b'yes'
                             )
                 elif n1 == repo.nodeconstants.addednodeid:
                     # This file was locally added. We should forget it instead of
                     # deleting it.
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_FORGET,
                         None,
                         b'remote deleted',
                     )
                 else:
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_REMOVE,
                         None,
                         b'other deleted',
                     )
                     if branchmerge:
                         # the file must be absent after merging,
                         # howeber the user might make
                         # the file reappear using revert and if they does,
                         # we force create a new node
                         mresult.addcommitinfo(
                             f, b'merge-removal-candidate', b'yes'
                         )
 
             else:  # file not in ancestor, not in remote
                 mresult.addfile(
                     f,
                     mergestatemod.ACTION_KEEP_NEW,
                     None,
                     b'ancestor missing, remote missing',
                 )
 
         elif n2:  # file exists only on remote side
             if f in copied1:
                 pass  # we'll deal with it on m1 side
             elif f in branch_copies2.movewithdir:
                 f2 = branch_copies2.movewithdir[f]
                 if f2 in m1:
                     mresult.addfile(
                         f2,
                         mergestatemod.ACTION_MERGE,
                         (f2, f, None, False, pa.node()),
                         b'local directory rename, both created',
                     )
                 else:
                     mresult.addfile(
                         f2,
                         mergestatemod.ACTION_LOCAL_DIR_RENAME_GET,
                         (f, fl2),
                         b'local directory rename - get from %s' % f,
                     )
             elif f in branch_copies2.copy:
                 f2 = branch_copies2.copy[f]
                 msg, args = None, None
                 if f2 in m2:
                     args = (f2, f, f2, False, pa.node())
                     msg = b'remote copied from %s' % f2
                 else:
                     args = (f2, f, f2, True, pa.node())
                     msg = b'remote moved from %s' % f2
                 mresult.addfile(f, mergestatemod.ACTION_MERGE, args, msg)
             elif f not in ma:
                 # local unknown, remote created: the logic is described by the
                 # following table:
                 #
                 # force  branchmerge  different  |  action
                 #   n         *           *      |   create
                 #   y         n           *      |   create
                 #   y         y           n      |   create
                 #   y         y           y      |   merge
                 #
                 # Checking whether the files are different is expensive, so we
                 # don't do that when we can avoid it.
                 if not force:
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_CREATED,
                         (fl2,),
                         b'remote created',
                     )
                 elif not branchmerge:
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_CREATED,
                         (fl2,),
                         b'remote created',
                     )
                 else:
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_CREATED_MERGE,
                         (fl2, pa.node()),
                         b'remote created, get or merge',
                     )
             elif n2 != ma[f]:
                 df = None
                 for d in branch_copies1.dirmove:
                     if f.startswith(d):
                         # new file added in a directory that was moved
                         df = branch_copies1.dirmove[d] + f[len(d) :]
                         break
                 if df is not None and df in m1:
                     mresult.addfile(
                         df,
                         mergestatemod.ACTION_MERGE,
                         (df, f, f, False, pa.node()),
                         b'local directory rename - respect move '
                         b'from %s' % f,
                     )
                 elif acceptremote:
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_CREATED,
                         (fl2,),
                         b'remote recreating',
                     )
                 else:
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_DELETED_CHANGED,
                         (None, f, f, False, pa.node()),
                         b'prompt deleted/changed',
                     )
                     if branchmerge:
                         mresult.addcommitinfo(
                             f, b'merge-removal-candidate', b'yes'
                         )
             else:
                 mresult.addfile(
                     f,
                     mergestatemod.ACTION_KEEP_ABSENT,
                     None,
                     b'local not present, remote unchanged',
                 )
                 if branchmerge:
                     # the file must be absent after merging
                     # however the user might make
                     # the file reappear using revert and if they does,
                     # we force create a new node
                     mresult.addcommitinfo(f, b'merge-removal-candidate', b'yes')
 
     if repo.ui.configbool(b'experimental', b'merge.checkpathconflicts'):
         # If we are merging, look for path conflicts.
         checkpathconflicts(repo, wctx, p2, mresult)
 
     narrowmatch = repo.narrowmatch()
     if not narrowmatch.always():
         # Updates "actions" in place
         _filternarrowactions(narrowmatch, branchmerge, mresult)
 
     renamedelete = branch_copies1.renamedelete
     renamedelete.update(branch_copies2.renamedelete)
 
     mresult.updatevalues(diverge, renamedelete)
     return mresult
 
 
 def _resolvetrivial(repo, wctx, mctx, ancestor, mresult):
     """Resolves false conflicts where the nodeid changed but the content
     remained the same."""
     # We force a copy of actions.items() because we're going to mutate
     # actions as we resolve trivial conflicts.
     for f in list(mresult.files((mergestatemod.ACTION_CHANGED_DELETED,))):
         if f in ancestor and not wctx[f].cmp(ancestor[f]):
             # local did change but ended up with same content
             mresult.addfile(
                 f, mergestatemod.ACTION_REMOVE, None, b'prompt same'
             )
 
     for f in list(mresult.files((mergestatemod.ACTION_DELETED_CHANGED,))):
         if f in ancestor and not mctx[f].cmp(ancestor[f]):
             # remote did change but ended up with same content
             mresult.removefile(f)  # don't get = keep local deleted
 
 
 def calculateupdates(
     repo,
     wctx,
     mctx,
     ancestors,
     branchmerge,
     force,
     acceptremote,
     followcopies,
     matcher=None,
     mergeforce=False,
 ):
     """
     Calculate the actions needed to merge mctx into wctx using ancestors
 
     Uses manifestmerge() to merge manifest and get list of actions required to
     perform for merging two manifests. If there are multiple ancestors, uses bid
     merge if enabled.
 
     Also filters out actions which are unrequired if repository is sparse.
 
     Returns mergeresult object same as manifestmerge().
     """
     # Avoid cycle.
     from . import sparse
 
     mresult = None
     if len(ancestors) == 1:  # default
         mresult = manifestmerge(
             repo,
             wctx,
             mctx,
             ancestors[0],
             branchmerge,
             force,
             matcher,
             acceptremote,
             followcopies,
         )
         _checkunknownfiles(repo, wctx, mctx, force, mresult, mergeforce)
 
     else:  # only when merge.preferancestor=* - the default
         repo.ui.note(
             _(b"note: merging %s and %s using bids from ancestors %s\n")
             % (
                 wctx,
                 mctx,
                 _(b' and ').join(pycompat.bytestr(anc) for anc in ancestors),
             )
         )
 
         # mapping filename to bids (action method to list af actions)
         # {FILENAME1 : BID1, FILENAME2 : BID2}
         # BID is another dictionary which contains
         # mapping of following form:
         # {ACTION_X : [info, ..], ACTION_Y : [info, ..]}
         fbids = {}
         mresult = mergeresult()
         diverge, renamedelete = None, None
         for ancestor in ancestors:
             repo.ui.note(_(b'\ncalculating bids for ancestor %s\n') % ancestor)
             mresult1 = manifestmerge(
                 repo,
                 wctx,
                 mctx,
                 ancestor,
                 branchmerge,
                 force,
                 matcher,
                 acceptremote,
                 followcopies,
                 forcefulldiff=True,
             )
             _checkunknownfiles(repo, wctx, mctx, force, mresult1, mergeforce)
 
             # Track the shortest set of warning on the theory that bid
             # merge will correctly incorporate more information
             if diverge is None or len(mresult1.diverge) < len(diverge):
                 diverge = mresult1.diverge
             if renamedelete is None or len(renamedelete) < len(
                 mresult1.renamedelete
             ):
                 renamedelete = mresult1.renamedelete
 
             # blindly update final mergeresult commitinfo with what we get
             # from mergeresult object for each ancestor
             # TODO: some commitinfo depends on what bid merge choose and hence
             # we will need to make commitinfo also depend on bid merge logic
             mresult._commitinfo.update(mresult1._commitinfo)
 
             for f, a in mresult1.filemap(sort=True):
                 m, args, msg = a
                 repo.ui.debug(b' %s: %s -> %s\n' % (f, msg, m))
                 if f in fbids:
                     d = fbids[f]
                     if m in d:
                         d[m].append(a)
                     else:
                         d[m] = [a]
                 else:
                     fbids[f] = {m: [a]}
 
         # Call for bids
         # Pick the best bid for each file
         repo.ui.note(
             _(b'\nauction for merging merge bids (%d ancestors)\n')
             % len(ancestors)
         )
         for f, bids in sorted(fbids.items()):
             if repo.ui.debugflag:
                 repo.ui.debug(b" list of bids for %s:\n" % f)
                 for m, l in sorted(bids.items()):
                     for _f, args, msg in l:
                         repo.ui.debug(b'   %s -> %s\n' % (msg, m))
             # bids is a mapping from action method to list af actions
             # Consensus?
             if len(bids) == 1:  # all bids are the same kind of method
                 m, l = list(bids.items())[0]
                 if all(a == l[0] for a in l[1:]):  # len(bids) is > 1
                     repo.ui.note(_(b" %s: consensus for %s\n") % (f, m))
                     mresult.addfile(f, *l[0])
                     continue
             # If keep is an option, just do it.
             if mergestatemod.ACTION_KEEP in bids:
                 repo.ui.note(_(b" %s: picking 'keep' action\n") % f)
                 mresult.addfile(f, *bids[mergestatemod.ACTION_KEEP][0])
                 continue
             # If keep absent is an option, just do that
             if mergestatemod.ACTION_KEEP_ABSENT in bids:
                 repo.ui.note(_(b" %s: picking 'keep absent' action\n") % f)
                 mresult.addfile(f, *bids[mergestatemod.ACTION_KEEP_ABSENT][0])
                 continue
             # ACTION_KEEP_NEW and ACTION_CHANGED_DELETED are conflicting actions
             # as one say that file is new while other says that file was present
             # earlier too and has a change delete conflict
             # Let's fall back to conflicting ACTION_CHANGED_DELETED and let user
             # do the right thing
             if (
                 mergestatemod.ACTION_CHANGED_DELETED in bids
                 and mergestatemod.ACTION_KEEP_NEW in bids
             ):
                 repo.ui.note(_(b" %s: picking 'changed/deleted' action\n") % f)
                 mresult.addfile(
                     f, *bids[mergestatemod.ACTION_CHANGED_DELETED][0]
                 )
                 continue
             # If keep new is an option, let's just do that
             if mergestatemod.ACTION_KEEP_NEW in bids:
                 repo.ui.note(_(b" %s: picking 'keep new' action\n") % f)
                 mresult.addfile(f, *bids[mergestatemod.ACTION_KEEP_NEW][0])
                 continue
             # ACTION_GET and ACTION_DELETE_CHANGED are conflicting actions as
             # one action states the file is newer/created on remote side and
             # other states that file is deleted locally and changed on remote
             # side. Let's fallback and rely on a conflicting action to let user
             # do the right thing
             if (
                 mergestatemod.ACTION_DELETED_CHANGED in bids
                 and mergestatemod.ACTION_GET in bids
             ):
                 repo.ui.note(_(b" %s: picking 'delete/changed' action\n") % f)
                 mresult.addfile(
                     f, *bids[mergestatemod.ACTION_DELETED_CHANGED][0]
                 )
                 continue
             # If there are gets and they all agree [how could they not?], do it.
             if mergestatemod.ACTION_GET in bids:
                 ga0 = bids[mergestatemod.ACTION_GET][0]
                 if all(a == ga0 for a in bids[mergestatemod.ACTION_GET][1:]):
                     repo.ui.note(_(b" %s: picking 'get' action\n") % f)
                     mresult.addfile(f, *ga0)
                     continue
             # TODO: Consider other simple actions such as mode changes
             # Handle inefficient democrazy.
             repo.ui.note(_(b' %s: multiple bids for merge action:\n') % f)
             for m, l in sorted(bids.items()):
                 for _f, args, msg in l:
                     repo.ui.note(b'  %s -> %s\n' % (msg, m))
             # Pick random action. TODO: Instead, prompt user when resolving
             m, l = list(bids.items())[0]
             repo.ui.warn(
                 _(b' %s: ambiguous merge - picked %s action\n') % (f, m)
             )
             mresult.addfile(f, *l[0])
             continue
         repo.ui.note(_(b'end of auction\n\n'))
         mresult.updatevalues(diverge, renamedelete)
 
     if wctx.rev() is None:
         _forgetremoved(wctx, mctx, branchmerge, mresult)
 
     sparse.filterupdatesactions(repo, wctx, mctx, branchmerge, mresult)
     _resolvetrivial(repo, wctx, mctx, ancestors[0], mresult)
 
     return mresult
 
 
 def _getcwd():
     try:
         return encoding.getcwd()
     except OSError as err:
         if err.errno == errno.ENOENT:
             return None
         raise
 
 
 def batchremove(repo, wctx, actions):
     """apply removes to the working directory
 
     yields tuples for progress updates
     """
     verbose = repo.ui.verbose
     cwd = _getcwd()
     i = 0
     for f, args, msg in actions:
         repo.ui.debug(b" %s: %s -> r\n" % (f, msg))
         if verbose:
             repo.ui.note(_(b"removing %s\n") % f)
         wctx[f].audit()
         try:
             wctx[f].remove(ignoremissing=True)
         except OSError as inst:
             repo.ui.warn(
                 _(b"update failed to remove %s: %s!\n")
                 % (f, stringutil.forcebytestr(inst.strerror))
             )
         if i == 100:
             yield i, f
             i = 0
         i += 1
     if i > 0:
         yield i, f
 
     if cwd and not _getcwd():
         # cwd was removed in the course of removing files; print a helpful
         # warning.
         repo.ui.warn(
             _(
                 b"current directory was removed\n"
                 b"(consider changing to repo root: %s)\n"
             )
             % repo.root
         )
 
 
 def batchget(repo, mctx, wctx, wantfiledata, actions):
     """apply gets to the working directory
 
     mctx is the context to get from
 
     Yields arbitrarily many (False, tuple) for progress updates, followed by
     exactly one (True, filedata). When wantfiledata is false, filedata is an
     empty dict. When wantfiledata is true, filedata[f] is a triple (mode, size,
     mtime) of the file f written for each action.
     """
     filedata = {}
     verbose = repo.ui.verbose
     fctx = mctx.filectx
     ui = repo.ui
     i = 0
     with repo.wvfs.backgroundclosing(ui, expectedcount=len(actions)):
         for f, (flags, backup), msg in actions:
             repo.ui.debug(b" %s: %s -> g\n" % (f, msg))
             if verbose:
                 repo.ui.note(_(b"getting %s\n") % f)
 
             if backup:
                 # If a file or directory exists with the same name, back that
                 # up.  Otherwise, look to see if there is a file that conflicts
                 # with a directory this file is in, and if so, back that up.
                 conflicting = f
                 if not repo.wvfs.lexists(f):
                     for p in pathutil.finddirs(f):
                         if repo.wvfs.isfileorlink(p):
                             conflicting = p
                             break
                 if repo.wvfs.lexists(conflicting):
                     orig = scmutil.backuppath(ui, repo, conflicting)
                     util.rename(repo.wjoin(conflicting), orig)
             wfctx = wctx[f]
             wfctx.clearunknown()
             atomictemp = ui.configbool(b"experimental", b"update.atomic-file")
             size = wfctx.write(
                 fctx(f).data(),
                 flags,
                 backgroundclose=True,
                 atomictemp=atomictemp,
             )
             if wantfiledata:
+                # XXX note that there is a race window between the time we
+                # write the clean data into the file and we stats it. So another
+                # writing process meddling with the file content right after we
+                # wrote it could cause bad stat data to be gathered.
+                #
+                # They are 2 data we gather here
+                # - the mode:
+                #       That we actually just wrote, we should not need to read
+                #       it from disk, (except not all mode might have survived
+                #       the disk round-trip, which is another issue: we should
+                #       not depends on this)
+                # - the mtime,
+                #       On system that support nanosecond precision, the mtime
+                #       could be accurate enough to tell the two writes appart.
+                #       However gathering it in a racy way make the mtime we
+                #       gather "unreliable".
+                #
+                # (note: we get the size from the data we write, which is sane)
+                #
+                # So in theory the data returned here are fully racy, but in
+                # practice "it works mostly fine".
+                #
+                # Do not be surprised if you end up reading this while looking
+                # for the causes of some buggy status. Feel free to improve
+                # this in the future, but we cannot simply stop gathering
+                # information. Otherwise `hg status` call made after a large `hg
+                # update` runs would have to redo a similar amount of work to
+                # restore and compare all files content.
                 s = wfctx.lstat()
                 mode = s.st_mode
                 mtime = timestamp.mtime_of(s)
                 # for dirstate.update_file's parentfiledata argument:
                 filedata[f] = (mode, size, mtime)
             if i == 100:
                 yield False, (i, f)
                 i = 0
             i += 1
     if i > 0:
         yield False, (i, f)
     yield True, filedata
 
 
 def _prefetchfiles(repo, ctx, mresult):
     """Invoke ``scmutil.prefetchfiles()`` for the files relevant to the dict
     of merge actions.  ``ctx`` is the context being merged in."""
 
     # Skipping 'a', 'am', 'f', 'r', 'dm', 'e', 'k', 'p' and 'pr', because they
     # don't touch the context to be merged in.  'cd' is skipped, because
     # changed/deleted never resolves to something from the remote side.
     files = mresult.files(
         [
             mergestatemod.ACTION_GET,
             mergestatemod.ACTION_DELETED_CHANGED,
             mergestatemod.ACTION_LOCAL_DIR_RENAME_GET,
             mergestatemod.ACTION_MERGE,
         ]
     )
 
     prefetch = scmutil.prefetchfiles
     matchfiles = scmutil.matchfiles
     prefetch(
         repo,
         [
             (
                 ctx.rev(),
                 matchfiles(repo, files),
             )
         ],
     )
 
 
 @attr.s(frozen=True)
 class updateresult(object):
     updatedcount = attr.ib()
     mergedcount = attr.ib()
     removedcount = attr.ib()
     unresolvedcount = attr.ib()
 
     def isempty(self):
         return not (
             self.updatedcount
             or self.mergedcount
             or self.removedcount
             or self.unresolvedcount
         )
 
 
 def applyupdates(
     repo,
     mresult,
     wctx,
     mctx,
     overwrite,
     wantfiledata,
     labels=None,
 ):
     """apply the merge action list to the working directory
 
     mresult is a mergeresult object representing result of the merge
     wctx is the working copy context
     mctx is the context to be merged into the working copy
 
     Return a tuple of (counts, filedata), where counts is a tuple
     (updated, merged, removed, unresolved) that describes how many
     files were affected by the update, and filedata is as described in
     batchget.
     """
 
     _prefetchfiles(repo, mctx, mresult)
 
     updated, merged, removed = 0, 0, 0
     ms = wctx.mergestate(clean=True)
     ms.start(wctx.p1().node(), mctx.node(), labels)
 
     for f, op in pycompat.iteritems(mresult.commitinfo):
         # the other side of filenode was choosen while merging, store this in
         # mergestate so that it can be reused on commit
         ms.addcommitinfo(f, op)
 
     numupdates = mresult.len() - mresult.len(mergestatemod.NO_OP_ACTIONS)
     progress = repo.ui.makeprogress(
         _(b'updating'), unit=_(b'files'), total=numupdates
     )
 
     if b'.hgsubstate' in mresult._actionmapping[mergestatemod.ACTION_REMOVE]:
         subrepoutil.submerge(repo, wctx, mctx, wctx, overwrite, labels)
 
     # record path conflicts
     for f, args, msg in mresult.getactions(
         [mergestatemod.ACTION_PATH_CONFLICT], sort=True
     ):
         f1, fo = args
         s = repo.ui.status
         s(
             _(
                 b"%s: path conflict - a file or link has the same name as a "
                 b"directory\n"
             )
             % f
         )
         if fo == b'l':
             s(_(b"the local file has been renamed to %s\n") % f1)
         else:
             s(_(b"the remote file has been renamed to %s\n") % f1)
         s(_(b"resolve manually then use 'hg resolve --mark %s'\n") % f)
         ms.addpathconflict(f, f1, fo)
         progress.increment(item=f)
 
     # When merging in-memory, we can't support worker processes, so set the
     # per-item cost at 0 in that case.
     cost = 0 if wctx.isinmemory() else 0.001
 
     # remove in parallel (must come before resolving path conflicts and getting)
     prog = worker.worker(
         repo.ui,
         cost,
         batchremove,
         (repo, wctx),
         list(mresult.getactions([mergestatemod.ACTION_REMOVE], sort=True)),
     )
     for i, item in prog:
         progress.increment(step=i, item=item)
     removed = mresult.len((mergestatemod.ACTION_REMOVE,))
 
     # resolve path conflicts (must come before getting)
     for f, args, msg in mresult.getactions(
         [mergestatemod.ACTION_PATH_CONFLICT_RESOLVE], sort=True
     ):
         repo.ui.debug(b" %s: %s -> pr\n" % (f, msg))
         (f0, origf0) = args
         if wctx[f0].lexists():
             repo.ui.note(_(b"moving %s to %s\n") % (f0, f))
             wctx[f].audit()
             wctx[f].write(wctx.filectx(f0).data(), wctx.filectx(f0).flags())
             wctx[f0].remove()
         progress.increment(item=f)
 
     # get in parallel.
     threadsafe = repo.ui.configbool(
         b'experimental', b'worker.wdir-get-thread-safe'
     )
     prog = worker.worker(
         repo.ui,
         cost,
         batchget,
         (repo, mctx, wctx, wantfiledata),
         list(mresult.getactions([mergestatemod.ACTION_GET], sort=True)),
         threadsafe=threadsafe,
         hasretval=True,
     )
     getfiledata = {}
     for final, res in prog:
         if final:
             getfiledata = res
         else:
             i, item = res
             progress.increment(step=i, item=item)
 
     if b'.hgsubstate' in mresult._actionmapping[mergestatemod.ACTION_GET]:
         subrepoutil.submerge(repo, wctx, mctx, wctx, overwrite, labels)
 
     # forget (manifest only, just log it) (must come first)
     for f, args, msg in mresult.getactions(
         (mergestatemod.ACTION_FORGET,), sort=True
     ):
         repo.ui.debug(b" %s: %s -> f\n" % (f, msg))
         progress.increment(item=f)
 
     # re-add (manifest only, just log it)
     for f, args, msg in mresult.getactions(
         (mergestatemod.ACTION_ADD,), sort=True
     ):
         repo.ui.debug(b" %s: %s -> a\n" % (f, msg))
         progress.increment(item=f)
 
     # re-add/mark as modified (manifest only, just log it)
     for f, args, msg in mresult.getactions(
         (mergestatemod.ACTION_ADD_MODIFIED,), sort=True
     ):
         repo.ui.debug(b" %s: %s -> am\n" % (f, msg))
         progress.increment(item=f)
 
     # keep (noop, just log it)
     for a in mergestatemod.NO_OP_ACTIONS:
         for f, args, msg in mresult.getactions((a,), sort=True):
             repo.ui.debug(b" %s: %s -> %s\n" % (f, msg, a))
             # no progress
 
     # directory rename, move local
     for f, args, msg in mresult.getactions(
         (mergestatemod.ACTION_DIR_RENAME_MOVE_LOCAL,), sort=True
     ):
         repo.ui.debug(b" %s: %s -> dm\n" % (f, msg))
         progress.increment(item=f)
         f0, flags = args
         repo.ui.note(_(b"moving %s to %s\n") % (f0, f))
         wctx[f].audit()
         wctx[f].write(wctx.filectx(f0).data(), flags)
         wctx[f0].remove()
 
     # local directory rename, get
     for f, args, msg in mresult.getactions(
         (mergestatemod.ACTION_LOCAL_DIR_RENAME_GET,), sort=True
     ):
         repo.ui.debug(b" %s: %s -> dg\n" % (f, msg))
         progress.increment(item=f)
         f0, flags = args
         repo.ui.note(_(b"getting %s to %s\n") % (f0, f))
         wctx[f].write(mctx.filectx(f0).data(), flags)
 
     # exec
     for f, args, msg in mresult.getactions(
         (mergestatemod.ACTION_EXEC,), sort=True
     ):
         repo.ui.debug(b" %s: %s -> e\n" % (f, msg))
         progress.increment(item=f)
         (flags,) = args
         wctx[f].audit()
         wctx[f].setflags(b'l' in flags, b'x' in flags)
 
     moves = []
 
     # 'cd' and 'dc' actions are treated like other merge conflicts
     mergeactions = list(
         mresult.getactions(
             [
                 mergestatemod.ACTION_CHANGED_DELETED,
                 mergestatemod.ACTION_DELETED_CHANGED,
                 mergestatemod.ACTION_MERGE,
             ],
             sort=True,
         )
     )
     for f, args, msg in mergeactions:
         f1, f2, fa, move, anc = args
         if f == b'.hgsubstate':  # merged internally
             continue
         if f1 is None:
             fcl = filemerge.absentfilectx(wctx, fa)
         else:
             repo.ui.debug(b" preserving %s for resolve of %s\n" % (f1, f))
             fcl = wctx[f1]
         if f2 is None:
             fco = filemerge.absentfilectx(mctx, fa)
         else:
             fco = mctx[f2]
         actx = repo[anc]
         if fa in actx:
             fca = actx[fa]
         else:
             # TODO: move to absentfilectx
             fca = repo.filectx(f1, fileid=nullrev)
         ms.add(fcl, fco, fca, f)
         if f1 != f and move:
             moves.append(f1)
 
     # remove renamed files after safely stored
     for f in moves:
         if wctx[f].lexists():
             repo.ui.debug(b"removing %s\n" % f)
             wctx[f].audit()
             wctx[f].remove()
 
     # these actions updates the file
     updated = mresult.len(
         (
             mergestatemod.ACTION_GET,
             mergestatemod.ACTION_EXEC,
             mergestatemod.ACTION_LOCAL_DIR_RENAME_GET,
             mergestatemod.ACTION_DIR_RENAME_MOVE_LOCAL,
         )
     )
 
     try:
         # premerge
         tocomplete = []
         for f, args, msg in mergeactions:
             repo.ui.debug(b" %s: %s -> m (premerge)\n" % (f, msg))
             ms.addcommitinfo(f, {b'merged': b'yes'})
             progress.increment(item=f)
             if f == b'.hgsubstate':  # subrepo states need updating
                 subrepoutil.submerge(
                     repo, wctx, mctx, wctx.ancestor(mctx), overwrite, labels
                 )
                 continue
             wctx[f].audit()
             complete, r = ms.preresolve(f, wctx)
             if not complete:
                 numupdates += 1
                 tocomplete.append((f, args, msg))
 
         # merge
         for f, args, msg in tocomplete:
             repo.ui.debug(b" %s: %s -> m (merge)\n" % (f, msg))
             ms.addcommitinfo(f, {b'merged': b'yes'})
             progress.increment(item=f, total=numupdates)
             ms.resolve(f, wctx)
 
     except error.InterventionRequired:
         # If the user has merge.on-failure=halt, catch the error and close the
         # merge state "properly".
         pass
     finally:
         ms.commit()
 
     unresolved = ms.unresolvedcount()
 
     msupdated, msmerged, msremoved = ms.counts()
     updated += msupdated
     merged += msmerged
     removed += msremoved
 
     extraactions = ms.actions()
 
     progress.complete()
     return (
         updateresult(updated, merged, removed, unresolved),
         getfiledata,
         extraactions,
     )
 
 
 def _advertisefsmonitor(repo, num_gets, p1node):
     # Advertise fsmonitor when its presence could be useful.
     #
     # We only advertise when performing an update from an empty working
     # directory. This typically only occurs during initial clone.
     #
     # We give users a mechanism to disable the warning in case it is
     # annoying.
     #
     # We only allow on Linux and MacOS because that's where fsmonitor is
     # considered stable.
     fsmonitorwarning = repo.ui.configbool(b'fsmonitor', b'warn_when_unused')
     fsmonitorthreshold = repo.ui.configint(
         b'fsmonitor', b'warn_update_file_count'
     )
     # avoid cycle dirstate -> sparse -> merge -> dirstate
     from . import dirstate
 
     if dirstate.rustmod is not None:
         # When using rust status, fsmonitor becomes necessary at higher sizes
         fsmonitorthreshold = repo.ui.configint(
             b'fsmonitor',
             b'warn_update_file_count_rust',
         )
 
     try:
         # avoid cycle: extensions -> cmdutil -> merge
         from . import extensions
 
         extensions.find(b'fsmonitor')
         fsmonitorenabled = repo.ui.config(b'fsmonitor', b'mode') != b'off'
         # We intentionally don't look at whether fsmonitor has disabled
         # itself because a) fsmonitor may have already printed a warning
         # b) we only care about the config state here.
     except KeyError:
         fsmonitorenabled = False
 
     if (
         fsmonitorwarning
         and not fsmonitorenabled
         and p1node == repo.nullid
         and num_gets >= fsmonitorthreshold
         and pycompat.sysplatform.startswith((b'linux', b'darwin'))
     ):
         repo.ui.warn(
             _(
                 b'(warning: large working directory being used without '
                 b'fsmonitor enabled; enable fsmonitor to improve performance; '
                 b'see "hg help -e fsmonitor")\n'
             )
         )
 
 
 UPDATECHECK_ABORT = b'abort'  # handled at higher layers
 UPDATECHECK_NONE = b'none'
 UPDATECHECK_LINEAR = b'linear'
 UPDATECHECK_NO_CONFLICT = b'noconflict'
 
 
 def _update(
     repo,
     node,
     branchmerge,
     force,
     ancestor=None,
     mergeancestor=False,
     labels=None,
     matcher=None,
     mergeforce=False,
     updatedirstate=True,
     updatecheck=None,
     wc=None,
 ):
     """
     Perform a merge between the working directory and the given node
 
     node = the node to update to
     branchmerge = whether to merge between branches
     force = whether to force branch merging or file overwriting
     matcher = a matcher to filter file lists (dirstate not updated)
     mergeancestor = whether it is merging with an ancestor. If true,
       we should accept the incoming changes for any prompts that occur.
       If false, merging with an ancestor (fast-forward) is only allowed
       between different named branches. This flag is used by rebase extension
       as a temporary fix and should be avoided in general.
     labels = labels to use for base, local and other
     mergeforce = whether the merge was run with 'merge --force' (deprecated): if
       this is True, then 'force' should be True as well.
 
     The table below shows all the behaviors of the update command given the
     -c/--check and -C/--clean or no options, whether the working directory is
     dirty, whether a revision is specified, and the relationship of the parent
     rev to the target rev (linear or not). Match from top first. The -n
     option doesn't exist on the command line, but represents the
     experimental.updatecheck=noconflict option.
 
     This logic is tested by test-update-branches.t.
 
     -c  -C  -n  -m  dirty  rev  linear  |  result
      y   y   *   *    *     *     *     |    (1)
      y   *   y   *    *     *     *     |    (1)
      y   *   *   y    *     *     *     |    (1)
      *   y   y   *    *     *     *     |    (1)
      *   y   *   y    *     *     *     |    (1)
      *   *   y   y    *     *     *     |    (1)
      *   *   *   *    *     n     n     |     x
      *   *   *   *    n     *     *     |    ok
      n   n   n   n    y     *     y     |   merge
      n   n   n   n    y     y     n     |    (2)
      n   n   n   y    y     *     *     |   merge
      n   n   y   n    y     *     *     |  merge if no conflict
      n   y   n   n    y     *     *     |  discard
      y   n   n   n    y     *     *     |    (3)
 
     x = can't happen
     * = don't-care
     1 = incompatible options (checked in commands.py)
     2 = abort: uncommitted changes (commit or update --clean to discard changes)
     3 = abort: uncommitted changes (checked in commands.py)
 
     The merge is performed inside ``wc``, a workingctx-like objects. It defaults
     to repo[None] if None is passed.
 
     Return the same tuple as applyupdates().
     """
     # Avoid cycle.
     from . import sparse
 
     # This function used to find the default destination if node was None, but
     # that's now in destutil.py.
     assert node is not None
     if not branchmerge and not force:
         # TODO: remove the default once all callers that pass branchmerge=False
         # and force=False pass a value for updatecheck. We may want to allow
         # updatecheck='abort' to better suppport some of these callers.
         if updatecheck is None:
             updatecheck = UPDATECHECK_LINEAR
         if updatecheck not in (
             UPDATECHECK_NONE,
             UPDATECHECK_LINEAR,
             UPDATECHECK_NO_CONFLICT,
         ):
             raise ValueError(
                 r'Invalid updatecheck %r (can accept %r)'
                 % (
                     updatecheck,
                     (
                         UPDATECHECK_NONE,
                         UPDATECHECK_LINEAR,
                         UPDATECHECK_NO_CONFLICT,
                     ),
                 )
             )
     if wc is not None and wc.isinmemory():
         maybe_wlock = util.nullcontextmanager()
     else:
         maybe_wlock = repo.wlock()
     with maybe_wlock:
         if wc is None:
             wc = repo[None]
         pl = wc.parents()
         p1 = pl[0]
         p2 = repo[node]
         if ancestor is not None:
             pas = [repo[ancestor]]
         else:
             if repo.ui.configlist(b'merge', b'preferancestor') == [b'*']:
                 cahs = repo.changelog.commonancestorsheads(p1.node(), p2.node())
                 pas = [repo[anc] for anc in (sorted(cahs) or [repo.nullid])]
             else:
                 pas = [p1.ancestor(p2, warn=branchmerge)]
 
         fp1, fp2, xp1, xp2 = p1.node(), p2.node(), bytes(p1), bytes(p2)
 
         overwrite = force and not branchmerge
         ### check phase
         if not overwrite:
             if len(pl) > 1:
                 raise error.StateError(_(b"outstanding uncommitted merge"))
             ms = wc.mergestate()
             if ms.unresolvedcount():
                 raise error.StateError(
                     _(b"outstanding merge conflicts"),
                     hint=_(b"use 'hg resolve' to resolve"),
                 )
         if branchmerge:
             if pas == [p2]:
                 raise error.Abort(
                     _(
                         b"merging with a working directory ancestor"
                         b" has no effect"
                     )
                 )
             elif pas == [p1]:
                 if not mergeancestor and wc.branch() == p2.branch():
                     raise error.Abort(
                         _(b"nothing to merge"),
                         hint=_(b"use 'hg update' or check 'hg heads'"),
                     )
             if not force and (wc.files() or wc.deleted()):
                 raise error.StateError(
                     _(b"uncommitted changes"),
                     hint=_(b"use 'hg status' to list changes"),
                 )
             if not wc.isinmemory():
                 for s in sorted(wc.substate):
                     wc.sub(s).bailifchanged()
 
         elif not overwrite:
             if p1 == p2:  # no-op update
                 # call the hooks and exit early
                 repo.hook(b'preupdate', throw=True, parent1=xp2, parent2=b'')
                 repo.hook(b'update', parent1=xp2, parent2=b'', error=0)
                 return updateresult(0, 0, 0, 0)
 
             if updatecheck == UPDATECHECK_LINEAR and pas not in (
                 [p1],
                 [p2],
             ):  # nonlinear
                 dirty = wc.dirty(missing=True)
                 if dirty:
                     # Branching is a bit strange to ensure we do the minimal
                     # amount of call to obsutil.foreground.
                     foreground = obsutil.foreground(repo, [p1.node()])
                     # note: the <node> variable contains a random identifier
                     if repo[node].node() in foreground:
                         pass  # allow updating to successors
                     else:
                         msg = _(b"uncommitted changes")
                         hint = _(b"commit or update --clean to discard changes")
                         raise error.UpdateAbort(msg, hint=hint)
                 else:
                     # Allow jumping branches if clean and specific rev given
                     pass
 
         if overwrite:
             pas = [wc]
         elif not branchmerge:
             pas = [p1]
 
         # deprecated config: merge.followcopies
         followcopies = repo.ui.configbool(b'merge', b'followcopies')
         if overwrite:
             followcopies = False
         elif not pas[0]:
             followcopies = False
         if not branchmerge and not wc.dirty(missing=True):
             followcopies = False
 
         ### calculate phase
         mresult = calculateupdates(
             repo,
             wc,
             p2,
             pas,
             branchmerge,
             force,
             mergeancestor,
             followcopies,
             matcher=matcher,
             mergeforce=mergeforce,
         )
 
         if updatecheck == UPDATECHECK_NO_CONFLICT:
             if mresult.hasconflicts():
                 msg = _(b"conflicting changes")
                 hint = _(b"commit or update --clean to discard changes")
                 raise error.StateError(msg, hint=hint)
 
         # Prompt and create actions. Most of this is in the resolve phase
         # already, but we can't handle .hgsubstate in filemerge or
         # subrepoutil.submerge yet so we have to keep prompting for it.
         vals = mresult.getfile(b'.hgsubstate')
         if vals:
             f = b'.hgsubstate'
             m, args, msg = vals
             prompts = filemerge.partextras(labels)
             prompts[b'f'] = f
             if m == mergestatemod.ACTION_CHANGED_DELETED:
                 if repo.ui.promptchoice(
                     _(
                         b"local%(l)s changed %(f)s which other%(o)s deleted\n"
                         b"use (c)hanged version or (d)elete?"
                         b"$$ &Changed $$ &Delete"
                     )
                     % prompts,
                     0,
                 ):
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_REMOVE,
                         None,
                         b'prompt delete',
                     )
                 elif f in p1:
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_ADD_MODIFIED,
                         None,
                         b'prompt keep',
                     )
                 else:
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_ADD,
                         None,
                         b'prompt keep',
                     )
             elif m == mergestatemod.ACTION_DELETED_CHANGED:
                 f1, f2, fa, move, anc = args
                 flags = p2[f2].flags()
                 if (
                     repo.ui.promptchoice(
                         _(
                             b"other%(o)s changed %(f)s which local%(l)s deleted\n"
                             b"use (c)hanged version or leave (d)eleted?"
                             b"$$ &Changed $$ &Deleted"
                         )
                         % prompts,
                         0,
                     )
                     == 0
                 ):
                     mresult.addfile(
                         f,
                         mergestatemod.ACTION_GET,
                         (flags, False),
                         b'prompt recreating',
                     )
                 else:
                     mresult.removefile(f)
 
         if not util.fscasesensitive(repo.path):
             # check collision between files only in p2 for clean update
             if not branchmerge and (
                 force or not wc.dirty(missing=True, branch=False)
             ):
                 _checkcollision(repo, p2.manifest(), None)
             else:
                 _checkcollision(repo, wc.manifest(), mresult)
 
         # divergent renames
         for f, fl in sorted(pycompat.iteritems(mresult.diverge)):
             repo.ui.warn(
                 _(
                     b"note: possible conflict - %s was renamed "
                     b"multiple times to:\n"
                 )
                 % f
             )
             for nf in sorted(fl):
                 repo.ui.warn(b" %s\n" % nf)
 
         # rename and delete
         for f, fl in sorted(pycompat.iteritems(mresult.renamedelete)):
             repo.ui.warn(
                 _(
                     b"note: possible conflict - %s was deleted "
                     b"and renamed to:\n"
                 )
                 % f
             )
             for nf in sorted(fl):
                 repo.ui.warn(b" %s\n" % nf)
 
         ### apply phase
         if not branchmerge:  # just jump to the new rev
             fp1, fp2, xp1, xp2 = fp2, repo.nullid, xp2, b''
         # If we're doing a partial update, we need to skip updating
         # the dirstate.
         always = matcher is None or matcher.always()
         updatedirstate = updatedirstate and always and not wc.isinmemory()
         if updatedirstate:
             repo.hook(b'preupdate', throw=True, parent1=xp1, parent2=xp2)
             # note that we're in the middle of an update
             repo.vfs.write(b'updatestate', p2.hex())
 
         _advertisefsmonitor(
             repo, mresult.len((mergestatemod.ACTION_GET,)), p1.node()
         )
 
         wantfiledata = updatedirstate and not branchmerge
         stats, getfiledata, extraactions = applyupdates(
             repo,
             mresult,
             wc,
             p2,
             overwrite,
             wantfiledata,
             labels=labels,
         )
 
         if updatedirstate:
             if extraactions:
                 for k, acts in pycompat.iteritems(extraactions):
                     for a in acts:
                         mresult.addfile(a[0], k, *a[1:])
                     if k == mergestatemod.ACTION_GET and wantfiledata:
                         # no filedata until mergestate is updated to provide it
                         for a in acts:
                             getfiledata[a[0]] = None
 
             assert len(getfiledata) == (
                 mresult.len((mergestatemod.ACTION_GET,)) if wantfiledata else 0
             )
             with repo.dirstate.parentchange():
                 repo.setparents(fp1, fp2)
                 mergestatemod.recordupdates(
                     repo, mresult.actionsdict, branchmerge, getfiledata
                 )
                 # update completed, clear state
                 util.unlink(repo.vfs.join(b'updatestate'))
 
                 if not branchmerge:
                     repo.dirstate.setbranch(p2.branch())
 
                 # If we're updating to a location, clean up any stale temporary includes
                 # (ex: this happens during hg rebase --abort).
                 if not branchmerge:
                     sparse.prunetemporaryincludes(repo)
 
     if updatedirstate:
         repo.hook(
             b'update', parent1=xp1, parent2=xp2, error=stats.unresolvedcount
         )
     return stats
 
 
 def merge(ctx, labels=None, force=False, wc=None):
     """Merge another topological branch into the working copy.
 
     force = whether the merge was run with 'merge --force' (deprecated)
     """
 
     return _update(
         ctx.repo(),
         ctx.rev(),
         labels=labels,
         branchmerge=True,
         force=force,
         mergeforce=force,
         wc=wc,
     )
 
 
 def update(ctx, updatecheck=None, wc=None):
     """Do a regular update to the given commit, aborting if there are conflicts.
 
     The 'updatecheck' argument can be used to control what to do in case of
     conflicts.
 
     Note: This is a new, higher-level update() than the one that used to exist
     in this module. That function is now called _update(). You can hopefully
     replace your callers to use this new update(), or clean_update(), merge(),
     revert_to(), or graft().
     """
     return _update(
         ctx.repo(),
         ctx.rev(),
         branchmerge=False,
         force=False,
         labels=[b'working copy', b'destination'],
         updatecheck=updatecheck,
         wc=wc,
     )
 
 
 def clean_update(ctx, wc=None):
     """Do a clean update to the given commit.
 
     This involves updating to the commit and discarding any changes in the
     working copy.
     """
     return _update(ctx.repo(), ctx.rev(), branchmerge=False, force=True, wc=wc)
 
 
 def revert_to(ctx, matcher=None, wc=None):
     """Revert the working copy to the given commit.
 
     The working copy will keep its current parent(s) but its content will
     be the same as in the given commit.
     """
 
     return _update(
         ctx.repo(),
         ctx.rev(),
         branchmerge=False,
         force=True,
         updatedirstate=False,
         matcher=matcher,
         wc=wc,
     )
 
 
 def graft(
     repo,
     ctx,
     base=None,
     labels=None,
     keepparent=False,
     keepconflictparent=False,
     wctx=None,
 ):
     """Do a graft-like merge.
 
     This is a merge where the merge ancestor is chosen such that one
     or more changesets are grafted onto the current changeset. In
     addition to the merge, this fixes up the dirstate to include only
     a single parent (if keepparent is False) and tries to duplicate any
     renames/copies appropriately.
 
     ctx - changeset to rebase
     base - merge base, or ctx.p1() if not specified
     labels - merge labels eg ['local', 'graft']
     keepparent - keep second parent if any
     keepconflictparent - if unresolved, keep parent used for the merge
 
     """
     # If we're grafting a descendant onto an ancestor, be sure to pass
     # mergeancestor=True to update. This does two things: 1) allows the merge if
     # the destination is the same as the parent of the ctx (so we can use graft
     # to copy commits), and 2) informs update that the incoming changes are
     # newer than the destination so it doesn't prompt about "remote changed foo
     # which local deleted".
     # We also pass mergeancestor=True when base is the same revision as p1. 2)
     # doesn't matter as there can't possibly be conflicts, but 1) is necessary.
     wctx = wctx or repo[None]
     pctx = wctx.p1()
     base = base or ctx.p1()
     mergeancestor = (
         repo.changelog.isancestor(pctx.node(), ctx.node())
         or pctx.rev() == base.rev()
     )
 
     stats = _update(
         repo,
         ctx.node(),
         True,
         True,
         base.node(),
         mergeancestor=mergeancestor,
         labels=labels,
         wc=wctx,
     )
 
     if keepconflictparent and stats.unresolvedcount:
         pother = ctx.node()
     else:
         pother = repo.nullid
         parents = ctx.parents()
         if keepparent and len(parents) == 2 and base in parents:
             parents.remove(base)
             pother = parents[0].node()
     # Never set both parents equal to each other
     if pother == pctx.node():
         pother = repo.nullid
 
     if wctx.isinmemory():
         wctx.setparents(pctx.node(), pother)
         # fix up dirstate for copies and renames
         copies.graftcopies(wctx, ctx, base)
     else:
         with repo.dirstate.parentchange():
             repo.setparents(pctx.node(), pother)
             repo.dirstate.write(repo.currenttransaction())
             # fix up dirstate for copies and renames
             copies.graftcopies(wctx, ctx, base)
     return stats
 
 
 def back_out(ctx, parent=None, wc=None):
     if parent is None:
         if ctx.p2() is not None:
             raise error.ProgrammingError(
                 b"must specify parent of merge commit to back out"
             )
         parent = ctx.p1()
     return _update(
         ctx.repo(),
         parent,
         branchmerge=True,
         force=True,
         ancestor=ctx.node(),
         mergeancestor=False,
     )
 
 
 def purge(
     repo,
     matcher,
     unknown=True,
     ignored=False,
     removeemptydirs=True,
     removefiles=True,
     abortonerror=False,
     noop=False,
     confirm=False,
 ):
     """Purge the working directory of untracked files.
 
     ``matcher`` is a matcher configured to scan the working directory -
     potentially a subset.
 
     ``unknown`` controls whether unknown files should be purged.
 
     ``ignored`` controls whether ignored files should be purged.
 
     ``removeemptydirs`` controls whether empty directories should be removed.
 
     ``removefiles`` controls whether files are removed.
 
     ``abortonerror`` causes an exception to be raised if an error occurs
     deleting a file or directory.
 
     ``noop`` controls whether to actually remove files. If not defined, actions
     will be taken.
 
     ``confirm`` ask confirmation before actually removing anything.
 
     Returns an iterable of relative paths in the working directory that were
     or would be removed.
     """
 
     def remove(removefn, path):
         try:
             removefn(path)
         except OSError:
             m = _(b'%s cannot be removed') % path
             if abortonerror:
                 raise error.Abort(m)
             else:
                 repo.ui.warn(_(b'warning: %s\n') % m)
 
     # There's no API to copy a matcher. So mutate the passed matcher and
     # restore it when we're done.
     oldtraversedir = matcher.traversedir
 
     res = []
 
     try:
         if removeemptydirs:
             directories = []
             matcher.traversedir = directories.append
 
         status = repo.status(match=matcher, ignored=ignored, unknown=unknown)
 
         if confirm:
             nb_ignored = len(status.ignored)
             nb_unkown = len(status.unknown)
             if nb_unkown and nb_ignored:
                 msg = _(b"permanently delete %d unkown and %d ignored files?")
                 msg %= (nb_unkown, nb_ignored)
             elif nb_unkown:
                 msg = _(b"permanently delete %d unkown files?")
                 msg %= nb_unkown
             elif nb_ignored:
                 msg = _(b"permanently delete %d ignored files?")
                 msg %= nb_ignored
             elif removeemptydirs:
                 dir_count = 0
                 for f in directories:
                     if matcher(f) and not repo.wvfs.listdir(f):
                         dir_count += 1
                 if dir_count:
                     msg = _(
                         b"permanently delete at least %d empty directories?"
                     )
                     msg %= dir_count
                 else:
                     # XXX we might be missing directory there
                     return res
             msg += b" (yN)$$ &Yes $$ &No"
             if repo.ui.promptchoice(msg, default=1) == 1:
                 raise error.CanceledError(_(b'removal cancelled'))
 
         if removefiles:
             for f in sorted(status.unknown + status.ignored):
                 if not noop:
                     repo.ui.note(_(b'removing file %s\n') % f)
                     remove(repo.wvfs.unlink, f)
                 res.append(f)
 
         if removeemptydirs:
             for f in sorted(directories, reverse=True):
                 if matcher(f) and not repo.wvfs.listdir(f):
                     if not noop:
                         repo.ui.note(_(b'removing directory %s\n') % f)
                         remove(repo.wvfs.rmdir, f)
                     res.append(f)
 
         return res
 
     finally:
         matcher.traversedir = oldtraversedir