mercurial/merge.py

worker: avoid potential partial write of pickled data

Previously, the code wrote the pickled data using os.write(). However,
os.write() can write less bytes than passed to it. To trigger the problem, the
pickled data had to be larger than 2147479552 bytes on my system.

Instead, open a file object and pass it to pickle.dump(). This also has the
advantage that it doesn’t buffer the whole pickled data in memory.

Note that the opened file must be buffered because pickle doesn’t support
unbuffered streams because unbuffered streams’ write() method might write less
bytes than passed to it (like os.write()) but pickle.dump() relies on that all
bytes are written (see https://github.com/python/cpython/issues/93050).

The side effect of using a file object and a with statement is that wfd is
explicitly closed now while it seems like before it was implicitly closed by
process exit.

# 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.


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,
    policy,
    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])
        msg = _(b"%s.%s not valid ('%s' is none of %s)")
        msg %= (section, name, config, validstr)
        raise error.ConfigError(msg)
    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:
    """
    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:
            msg = _(b"case-folding collision between %s and %s")
            msg %= (f, foldmap[fold])
            raise error.StateError(msg)
        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
            msg = _(b"case-folding collision between %s and directory of %s")
            msg %= (lastfull, f)
            raise error.StateError(msg)
        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, b'r'),
                    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.
    """
    # 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].no_op:
            mresult.removefile(f)  # merge does not affect file
        elif action[0].narrow_safe:
            if not f.endswith(b'/'):
                mresult.removefile(f)  # merge won't affect on-disk files

                mresult.addcommitinfo(
                    f, b'outside-narrow-merge-action', action[0].changes
                )
            else:  # TODO: handle the tree case
                msg = _(
                    b'merge affects file \'%s\' outside narrow, '
                    b'which is not yet supported'
                )
                hint = _(b'merging in the other direction may work')
                raise error.Abort(msg % f, hint=hint)
        else:
            msg = _(b'conflict in file \'%s\' is outside narrow clone')
            raise error.StateError(msg % f)


class mergeresult:
    """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 self._actionmapping[a].items():
                    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(self._filemapping.items()):
                yield key, val
        else:
            for key, val in self._filemapping.items():
                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 self._actionmapping.items():
            for f, (args, msg) in d.items():
                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 self._filemapping.items():
            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 not a.no_op
            ):
                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 branch_copies1.copy.items():
            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 diff.items():
        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.__bytes__()))
                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.__bytes__()))
            # 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.__bytes__())
                    )
                    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.__bytes__()))
            # 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.__bytes__())
            )
            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:
    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 mresult.commitinfo.items():
        # 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)

    num_no_op = mresult.len(mergestatemod.MergeAction.NO_OP_ACTIONS)
    numupdates = mresult.len() - num_no_op
    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.MergeAction.NO_OP_ACTIONS:
        for f, args, msg in mresult.getactions((a,), sort=True):
            repo.ui.debug(b" %s: %s -> %s\n" % (f, msg, a.__bytes__()))
            # 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:
        for f, args, msg in mergeactions:
            repo.ui.debug(b" %s: %s -> m\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()
            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
    dirstate_rustmod = policy.importrust("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 local, other, and base
    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
        okay = (UPDATECHECK_NONE, UPDATECHECK_LINEAR, UPDATECHECK_NO_CONFLICT)
        if updatecheck not in okay:
            msg = r'Invalid updatecheck %r (can accept %r)'
            msg %= (updatecheck, okay)
            raise ValueError(msg)
    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():
                msg = _(b"outstanding merge conflicts")
                hint = _(b"use 'hg resolve' to resolve")
                raise error.StateError(msg, hint=hint)
        if branchmerge:
            m_a = _(b"merging with a working directory ancestor has no effect")
            if pas == [p2]:
                raise error.Abort(m_a)
            elif pas == [p1]:
                if not mergeancestor and wc.branch() == p2.branch():
                    msg = _(b"nothing to merge")
                    hint = _(b"use 'hg update' or check 'hg heads'")
                    raise error.Abort(msg, hint=hint)
            if not force and (wc.files() or wc.deleted()):
                msg = _(b"uncommitted changes")
                hint = _(b"use 'hg status' to list changes")
                raise error.StateError(msg, hint=hint)
            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(mresult.diverge.items()):
            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(mresult.renamedelete.items()):
            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 extraactions.items():
                    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():
                ### Filter Filedata
                #
                # We gathered "cache" information for the clean file while
                # updating them: mtime, size and mode.
                #
                # At the time this comment is written, they are various issues
                # with how we gather the `mode` and `mtime` information (see
                # the comment in `batchget`).
                #
                # We are going to smooth one of this issue here : mtime ambiguity.
                #
                # i.e. even if the mtime gathered during `batchget` was
                # correct[1] a change happening right after it could change the
                # content while keeping the same mtime[2].
                #
                # When we reach the current code, the "on disk" part of the
                # update operation is finished. We still assume that no other
                # process raced that "on disk" part, but we want to at least
                # prevent later file change to alter the content of the file
                # right after the update operation. So quickly that the same
                # mtime is record for the operation.
                # To prevent such ambiguity to happens, we will only keep the
                # "file data" for files with mtime that are stricly in the past,
                # i.e. whose mtime is strictly lower than the current time.
                #
                # This protect us from race conditions from operation that could
                # run right after this one, especially other Mercurial
                # operation that could be waiting for the wlock to touch files
                # content and the dirstate.
                #
                # In an ideal world, we could only get reliable information in
                # `getfiledata` (from `getbatch`), however the current approach
                # have been a successful compromise since many years.
                #
                # At the time this comment is written, not using any "cache"
                # file data at all here would not be viable. As it would result is
                # a very large amount of work (equivalent to the previous `hg
                # update` during the next status after an update).
                #
                # [1] the current code cannot grantee that the `mtime` and
                # `mode` are correct, but the result is "okay in practice".
                # (see the comment in `batchget`).                #
                #
                # [2] using nano-second precision can greatly help here because
                # it makes the "different write with same mtime" issue
                # virtually vanish. However, dirstate v1 cannot store such
                # precision and a bunch of python-runtime, operating-system and
                # filesystem does not provide use with such precision, so we
                # have to operate as if it wasn't available.
                if getfiledata:
                    ambiguous_mtime = {}
                    now = timestamp.get_fs_now(repo.vfs)
                    if now is None:
                        # we can't write to the FS, so we won't actually update
                        # the dirstate content anyway, no need to put cache
                        # information.
                        getfiledata = None
                    else:
                        now_sec = now[0]
                        for f, m in getfiledata.items():
                            if m is not None and m[2][0] >= now_sec:
                                ambiguous_mtime[f] = (m[0], m[1], None)
                        for f, m in ambiguous_mtime.items():
                            getfiledata[f] = m

                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', b'working copy parent'],
        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:
            msg = b"must specify parent of merge commit to back out"
            raise error.ProgrammingError(msg)
        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_unknown = len(status.unknown)
            if nb_unknown and nb_ignored:
                msg = _(b"permanently delete %d unknown and %d ignored files?")
                msg %= (nb_unknown, nb_ignored)
            elif nb_unknown:
                msg = _(b"permanently delete %d unknown files?")
                msg %= nb_unknown
            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