annotate mercurial/copies.py @ 46149:294d5aca4ff5

copies: iterate over children directly (instead of parents)

Before this change we would gather all parent → child edges and iterate on
all parent, gathering copy information for children and aggregating them from
there.

They are not strict requirement for edges to be processed in that specific
order. We could also simply iterate over all "children" revision and aggregate
data from both parents at the same time. This patch does that.

It make various things simpler:

 * since both parents are processed at the same time, we no longer need to
   cache data for merge (see next changeset for details),

 * we no longer need nested loop to process data,

 * we no longer need to store partial merge data for a rev from distinct loop
   interaction to another when processing merges,

 * we no longer need to build a full parent -> children mapping (we only rely on
   a simpler "parent -> number of children" map (for memory efficiency),

 * the data access pattern is now simpler (from lower revisions to higher
   revisions) and entirely predicable. That predictability open the way to
   prefetching and parallel processing.

So that new iterations order requires simpler code and open the way to
interesting optimisation.

The effect on performance is quite good. In the worse case, we don't see any
significant negative impact. And in the best case, the reduction of roundtrip
to Python provide us with a significant speed. Some example below:

Repo            Case                                  Source-Rev   Dest-Rev      # of revisions  old time    new time      Difference    Factor    time per rev
---------------------------------------------------------------------------------------------------------------------------------------------------------------
mozilla-try     x00000_revs_x00000_added_0_copies     dc8a3ca7010e d16fde900c9c :  34414 revs,   0.962867 s,   0.502584 s,  -0.460283 s, × 0.5220,    14 µs/rev
mozilla-try     x0000_revs_xx000_added_x_copies       156f6e2674f2 4d0f2c178e66 :   8598 revs,   0.110717 s,   0.076323 s,  -0.034394 s, × 0.6894,     8 µs/rev



# full comparison between the previous changeset and this one

Repo            Case                                  Source-Rev   Dest-Rev      # of revisions  old time    new time      Difference    Factor    time per rev
---------------------------------------------------------------------------------------------------------------------------------------------------------------
mercurial       x_revs_x_added_0_copies               ad6b123de1c7 39cfcef4f463 :      1 revs,   0.000048 s,   0.000041 s,  -0.000007 s, × 0.8542,    41 µs/rev
mercurial       x_revs_x_added_x_copies               2b1c78674230 0c1d10351869 :      6 revs,   0.000153 s,   0.000102 s,  -0.000051 s, × 0.6667,    17 µs/rev
mercurial       x000_revs_x000_added_x_copies         81f8ff2a9bf2 dd3267698d84 :   1032 revs,   0.004209 s,   0.004254 s,  +0.000045 s, × 1.0107,     4 µs/rev
pypy            x_revs_x_added_0_copies               aed021ee8ae8 099ed31b181b :      9 revs,   0.000203 s,   0.000282 s,  +0.000079 s, × 1.3892,    31 µs/rev
pypy            x_revs_x000_added_0_copies            4aa4e1f8e19a 359343b9ac0e :      1 revs,   0.000059 s,   0.000048 s,  -0.000011 s, × 0.8136,    48 µs/rev
pypy            x_revs_x_added_x_copies               ac52eb7bbbb0 72e022663155 :      7 revs,   0.000194 s,   0.000211 s,  +0.000017 s, × 1.0876,    30 µs/rev
pypy            x_revs_x00_added_x_copies             c3b14617fbd7 ace7255d9a26 :      1 revs,   0.000380 s,   0.000375 s,  -0.000005 s, × 0.9868,   375 µs/rev
pypy            x_revs_x000_added_x000_copies         df6f7a526b60 a83dc6a2d56f :      6 revs,   0.010588 s,   0.010574 s,  -0.000014 s, × 0.9987,  1762 µs/rev
pypy            x000_revs_xx00_added_0_copies         89a76aede314 2f22446ff07e :   4785 revs,   0.048961 s,   0.049974 s,  +0.001013 s, × 1.0207,    10 µs/rev
pypy            x000_revs_x000_added_x_copies         8a3b5bfd266e 2c68e87c3efe :   6780 revs,   0.083612 s,   0.084300 s,  +0.000688 s, × 1.0082,    12 µs/rev
pypy            x000_revs_x000_added_x000_copies      89a76aede314 7b3dda341c84 :   5441 revs,   0.058579 s,   0.060128 s,  +0.001549 s, × 1.0264,    11 µs/rev
pypy            x0000_revs_x_added_0_copies           d1defd0dc478 c9cb1334cc78 :  43645 revs,   0.736783 s,   0.686542 s,  -0.050241 s, × 0.9318,    15 µs/rev
pypy            x0000_revs_xx000_added_0_copies       bf2c629d0071 4ffed77c095c :      2 revs,   0.022050 s,   0.009277 s,  -0.012773 s, × 0.4207,  4638 µs/rev
pypy            x0000_revs_xx000_added_x000_copies    08ea3258278e d9fa043f30c0 :  11316 revs,   0.120800 s,   0.114733 s,  -0.006067 s, × 0.9498,    10 µs/rev
netbeans        x_revs_x_added_0_copies               fb0955ffcbcd a01e9239f9e7 :      2 revs,   0.000140 s,   0.000081 s,  -0.000059 s, × 0.5786,    40 µs/rev
netbeans        x_revs_x000_added_0_copies            6f360122949f 20eb231cc7d0 :      2 revs,   0.000114 s,   0.000107 s,  -0.000007 s, × 0.9386,    53 µs/rev
netbeans        x_revs_x_added_x_copies               1ada3faf6fb6 5a39d12eecf4 :      3 revs,   0.000224 s,   0.000173 s,  -0.000051 s, × 0.7723,    57 µs/rev
netbeans        x_revs_x00_added_x_copies             35be93ba1e2c 9eec5e90c05f :      9 revs,   0.000723 s,   0.000698 s,  -0.000025 s, × 0.9654,    77 µs/rev
netbeans        x000_revs_xx00_added_0_copies         eac3045b4fdd 51d4ae7f1290 :   1421 revs,   0.009665 s,   0.009248 s,  -0.000417 s, × 0.9569,     6 µs/rev
netbeans        x000_revs_x000_added_x_copies         e2063d266acd 6081d72689dc :   1533 revs,   0.014820 s,   0.015446 s,  +0.000626 s, × 1.0422,    10 µs/rev
netbeans        x000_revs_x000_added_x000_copies      ff453e9fee32 411350406ec2 :   5750 revs,   0.076049 s,   0.074373 s,  -0.001676 s, × 0.9780,    12 µs/rev
netbeans        x0000_revs_xx000_added_x000_copies    588c2d1ced70 1aad62e59ddd :  66949 revs,   0.683603 s,   0.639870 s,  -0.043733 s, × 0.9360,     9 µs/rev
mozilla-central x_revs_x_added_0_copies               3697f962bb7b 7015fcdd43a2 :      2 revs,   0.000161 s,   0.000088 s,  -0.000073 s, × 0.5466,    44 µs/rev
mozilla-central x_revs_x000_added_0_copies            dd390860c6c9 40d0c5bed75d :      8 revs,   0.000234 s,   0.000199 s,  -0.000035 s, × 0.8504,    24 µs/rev
mozilla-central x_revs_x_added_x_copies               8d198483ae3b 14207ffc2b2f :      9 revs,   0.000247 s,   0.000171 s,  -0.000076 s, × 0.6923,    19 µs/rev
mozilla-central x_revs_x00_added_x_copies             98cbc58cc6bc 446a150332c3 :      7 revs,   0.000630 s,   0.000592 s,  -0.000038 s, × 0.9397,    84 µs/rev
mozilla-central x_revs_x000_added_x000_copies         3c684b4b8f68 0a5e72d1b479 :      3 revs,   0.003286 s,   0.003151 s,  -0.000135 s, × 0.9589,  1050 µs/rev
mozilla-central x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :      6 revs,   0.062441 s,   0.061612 s,  -0.000829 s, × 0.9867, 10268 µs/rev
mozilla-central x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :   1593 revs,   0.005423 s,   0.005381 s,  -0.000042 s, × 0.9923,     3 µs/rev
mozilla-central x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :     41 revs,   0.005919 s,   0.003742 s,  -0.002177 s, × 0.6322,    91 µs/rev
mozilla-central x000_revs_x000_added_x000_copies      7c97034feb78 4407bd0c6330 :   7839 revs,   0.062597 s,   0.061983 s,  -0.000614 s, × 0.9902,     7 µs/rev
mozilla-central x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :    615 revs,   0.043551 s,   0.019861 s,  -0.023690 s, × 0.4560,    32 µs/rev
mozilla-central x0000_revs_xx000_added_x000_copies    f78c615a656c 96a38b690156 :  30263 revs,   0.192475 s,   0.188101 s,  -0.004374 s, × 0.9773,     6 µs/rev
mozilla-central x00000_revs_x0000_added_x0000_copies  6832ae71433c 4c222a1d9a00 : 153721 revs,   1.955575 s,   1.806696 s,  -0.148879 s, × 0.9239,    11 µs/rev
mozilla-central x00000_revs_x00000_added_x000_copies  76caed42cf7c 1daa622bbe42 : 204976 revs,   2.886501 s,   2.682987 s,  -0.203514 s, × 0.9295,    13 µs/rev
mozilla-try     x_revs_x_added_0_copies               aaf6dde0deb8 9790f499805a :      2 revs,   0.001181 s,   0.000852 s,  -0.000329 s, × 0.7214,   426 µs/rev
mozilla-try     x_revs_x000_added_0_copies            d8d0222927b4 5bb8ce8c7450 :      2 revs,   0.001189 s,   0.000859 s,  -0.000330 s, × 0.7225,   429 µs/rev
mozilla-try     x_revs_x_added_x_copies               092fcca11bdb 936255a0384a :      4 revs,   0.000563 s,   0.000150 s,  -0.000413 s, × 0.2664,    37 µs/rev
mozilla-try     x_revs_x00_added_x_copies             b53d2fadbdb5 017afae788ec :      2 revs,   0.001548 s,   0.001158 s,  -0.000390 s, × 0.7481,   579 µs/rev
mozilla-try     x_revs_x000_added_x000_copies         20408ad61ce5 6f0ee96e21ad :      1 revs,   0.027782 s,   0.027240 s,  -0.000542 s, × 0.9805, 27240 µs/rev
mozilla-try     x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :      6 revs,   0.062781 s,   0.062824 s,  +0.000043 s, × 1.0007, 10470 µs/rev
mozilla-try     x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :   1593 revs,   0.005778 s,   0.005463 s,  -0.000315 s, × 0.9455,     3 µs/rev
mozilla-try     x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :     41 revs,   0.006192 s,   0.004238 s,  -0.001954 s, × 0.6844,   103 µs/rev
mozilla-try     x000_revs_x000_added_x000_copies      1346fd0130e4 4c65cbdabc1f :   6657 revs,   0.065391 s,   0.064113 s,  -0.001278 s, × 0.9805,     9 µs/rev
mozilla-try     x0000_revs_x_added_0_copies           63519bfd42ee a36a2a865d92 :  40314 revs,   0.317216 s,   0.294063 s,  -0.023153 s, × 0.9270,     7 µs/rev
mozilla-try     x0000_revs_x_added_x_copies           9fe69ff0762d bcabf2a78927 :  38690 revs,   0.303119 s,   0.281493 s,  -0.021626 s, × 0.9287,     7 µs/rev
mozilla-try     x0000_revs_xx000_added_x_copies       156f6e2674f2 4d0f2c178e66 :   8598 revs,   0.110717 s,   0.076323 s,  -0.034394 s, × 0.6894,     8 µs/rev
mozilla-try     x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :    615 revs,   0.045739 s,   0.020390 s,  -0.025349 s, × 0.4458,    33 µs/rev
mozilla-try     x0000_revs_xx000_added_x000_copies    89294cd501d9 7ccb2fc7ccb5 :  97052 revs,   3.098021 s,   3.023879 s,  -0.074142 s, × 0.9761,    31 µs/rev
mozilla-try     x0000_revs_x0000_added_x0000_copies   e928c65095ed e951f4ad123a :  52031 revs,   0.771480 s,   0.735549 s,  -0.035931 s, × 0.9534,    14 µs/rev
mozilla-try     x00000_revs_x_added_0_copies          6a320851d377 1ebb79acd503 : 363753 revs,  18.813422 s,  18.568900 s,  -0.244522 s, × 0.9870,    51 µs/rev
mozilla-try     x00000_revs_x00000_added_0_copies     dc8a3ca7010e d16fde900c9c :  34414 revs,   0.962867 s,   0.502584 s,  -0.460283 s, × 0.5220,    14 µs/rev
mozilla-try     x00000_revs_x_added_x_copies          5173c4b6f97c 95d83ee7242d : 362229 revs,  18.684923 s,  18.356645 s,  -0.328278 s, × 0.9824,    50 µs/rev
mozilla-try     x00000_revs_x000_added_x_copies       9126823d0e9c ca82787bb23c : 359344 revs,  18.296305 s,  18.250393 s,  -0.045912 s, × 0.9975,    50 µs/rev
mozilla-try     x00000_revs_x0000_added_x0000_copies  8d3fafa80d4b eb884023b810 : 192665 revs,   3.061887 s,   2.792459 s,  -0.269428 s, × 0.9120,    14 µs/rev
mozilla-try     x00000_revs_x00000_added_x0000_copies 1b661134e2ca 1ae03d022d6d : 228985 revs, 103.869641 s, 107.697264 s,  +3.827623 s, × 1.0369,   470 µs/rev
mozilla-try     x00000_revs_x00000_added_x000_copies  9b2a99adc05e 8e29777b48e6 : 382065 revs,  64.262957 s,  63.961040 s,  -0.301917 s, × 0.9953,   167 µs/rev

Differential Revision: https://phab.mercurial-scm.org/D9422

# coding: utf8
# copies.py - copy detection for Mercurial
#
# Copyright 2008 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import collections
import os

from .i18n import _
from .node import (
    nullid,
    nullrev,
)

from . import (
    match as matchmod,
    pathutil,
    policy,
    pycompat,
    util,
)


from .utils import stringutil

from .revlogutils import (
    flagutil,
    sidedata as sidedatamod,
)

rustmod = policy.importrust("copy_tracing")


def _filter(src, dst, t):
    """filters out invalid copies after chaining"""

    # When _chain()'ing copies in 'a' (from 'src' via some other commit 'mid')
    # with copies in 'b' (from 'mid' to 'dst'), we can get the different cases
    # in the following table (not including trivial cases). For example, case 2
    # is where a file existed in 'src' and remained under that name in 'mid' and
    # then was renamed between 'mid' and 'dst'.
    #
    # case src mid dst result
    #   1   x   y   -    -
    #   2   x   y   y   x->y
    #   3   x   y   x    -
    #   4   x   y   z   x->z
    #   5   -   x   y    -
    #   6   x   x   y   x->y
    #
    # _chain() takes care of chaining the copies in 'a' and 'b', but it
    # cannot tell the difference between cases 1 and 2, between 3 and 4, or
    # between 5 and 6, so it includes all cases in its result.
    # Cases 1, 3, and 5 are then removed by _filter().

    for k, v in list(t.items()):
        # remove copies from files that didn't exist
        if v not in src:
            del t[k]
        # remove criss-crossed copies
        elif k in src and v in dst:
            del t[k]
        # remove copies to files that were then removed
        elif k not in dst:
            del t[k]


def _chain(prefix, suffix):
    """chain two sets of copies 'prefix' and 'suffix'"""
    result = prefix.copy()
    for key, value in pycompat.iteritems(suffix):
        result[key] = prefix.get(value, value)
    return result


def _tracefile(fctx, am, basemf):
    """return file context that is the ancestor of fctx present in ancestor
    manifest am

    Note: we used to try and stop after a given limit, however checking if that
    limit is reached turned out to be very expensive. we are better off
    disabling that feature."""

    for f in fctx.ancestors():
        path = f.path()
        if am.get(path, None) == f.filenode():
            return path
        if basemf and basemf.get(path, None) == f.filenode():
            return path


def _dirstatecopies(repo, match=None):
    ds = repo.dirstate
    c = ds.copies().copy()
    for k in list(c):
        if ds[k] not in b'anm' or (match and not match(k)):
            del c[k]
    return c


def _computeforwardmissing(a, b, match=None):
    """Computes which files are in b but not a.
    This is its own function so extensions can easily wrap this call to see what
    files _forwardcopies is about to process.
    """
    ma = a.manifest()
    mb = b.manifest()
    return mb.filesnotin(ma, match=match)


def usechangesetcentricalgo(repo):
    """Checks if we should use changeset-centric copy algorithms"""
    if repo.filecopiesmode == b'changeset-sidedata':
        return True
    readfrom = repo.ui.config(b'experimental', b'copies.read-from')
    changesetsource = (b'changeset-only', b'compatibility')
    return readfrom in changesetsource


def _committedforwardcopies(a, b, base, match):
    """Like _forwardcopies(), but b.rev() cannot be None (working copy)"""
    # files might have to be traced back to the fctx parent of the last
    # one-side-only changeset, but not further back than that
    repo = a._repo

    if usechangesetcentricalgo(repo):
        return _changesetforwardcopies(a, b, match)

    debug = repo.ui.debugflag and repo.ui.configbool(b'devel', b'debug.copies')
    dbg = repo.ui.debug
    if debug:
        dbg(b'debug.copies:    looking into rename from %s to %s\n' % (a, b))
    am = a.manifest()
    basemf = None if base is None else base.manifest()

    # find where new files came from
    # we currently don't try to find where old files went, too expensive
    # this means we can miss a case like 'hg rm b; hg cp a b'
    cm = {}

    # Computing the forward missing is quite expensive on large manifests, since
    # it compares the entire manifests. We can optimize it in the common use
    # case of computing what copies are in a commit versus its parent (like
    # during a rebase or histedit). Note, we exclude merge commits from this
    # optimization, since the ctx.files() for a merge commit is not correct for
    # this comparison.
    forwardmissingmatch = match
    if b.p1() == a and b.p2().node() == nullid:
        filesmatcher = matchmod.exact(b.files())
        forwardmissingmatch = matchmod.intersectmatchers(match, filesmatcher)
    missing = _computeforwardmissing(a, b, match=forwardmissingmatch)

    ancestrycontext = a._repo.changelog.ancestors([b.rev()], inclusive=True)

    if debug:
        dbg(b'debug.copies:      missing files to search: %d\n' % len(missing))

    for f in sorted(missing):
        if debug:
            dbg(b'debug.copies:        tracing file: %s\n' % f)
        fctx = b[f]
        fctx._ancestrycontext = ancestrycontext

        if debug:
            start = util.timer()
        opath = _tracefile(fctx, am, basemf)
        if opath:
            if debug:
                dbg(b'debug.copies:          rename of: %s\n' % opath)
            cm[f] = opath
        if debug:
            dbg(
                b'debug.copies:          time: %f seconds\n'
                % (util.timer() - start)
            )
    return cm


def _revinfo_getter(repo, match):
    """returns a function that returns the following data given a <rev>"

    * p1: revision number of first parent
    * p2: revision number of first parent
    * changes: a ChangingFiles object
    """
    cl = repo.changelog
    parents = cl.parentrevs
    flags = cl.flags

    HASCOPIESINFO = flagutil.REVIDX_HASCOPIESINFO

    changelogrevision = cl.changelogrevision

    # A small cache to avoid doing the work twice for merges
    #
    # In the vast majority of cases, if we ask information for a revision
    # about 1 parent, we'll later ask it for the other. So it make sense to
    # keep the information around when reaching the first parent of a merge
    # and dropping it after it was provided for the second parents.
    #
    # It exists cases were only one parent of the merge will be walked. It
    # happens when the "destination" the copy tracing is descendant from a
    # new root, not common with the "source". In that case, we will only walk
    # through merge parents that are descendant of changesets common
    # between "source" and "destination".
    #
    # With the current case implementation if such changesets have a copy
    # information, we'll keep them in memory until the end of
    # _changesetforwardcopies. We don't expect the case to be frequent
    # enough to matters.
    #
    # In addition, it would be possible to reach pathological case, were
    # many first parent are met before any second parent is reached. In
    # that case the cache could grow. If this even become an issue one can
    # safely introduce a maximum cache size. This would trade extra CPU/IO
    # time to save memory.
    merge_caches = {}

    alwaysmatch = match.always()

    if rustmod is not None and alwaysmatch:

        def revinfo(rev):
            p1, p2 = parents(rev)
            value = None
            e = merge_caches.pop(rev, None)
            if e is not None:
                return e
            if flags(rev) & HASCOPIESINFO:
                raw = changelogrevision(rev)._sidedata.get(sidedatamod.SD_FILES)
            else:
                raw = None
            value = (p1, p2, raw)
            if p1 != nullrev and p2 != nullrev:
                # XXX some case we over cache, IGNORE
                merge_caches[rev] = value
            return value

    else:

        def revinfo(rev):
            p1, p2 = parents(rev)
            value = None
            e = merge_caches.pop(rev, None)
            if e is not None:
                return e
            changes = None
            if flags(rev) & HASCOPIESINFO:
                changes = changelogrevision(rev).changes
            value = (p1, p2, changes)
            if p1 != nullrev and p2 != nullrev:
                # XXX some case we over cache, IGNORE
                merge_caches[rev] = value
            return value

    return revinfo


def cached_is_ancestor(is_ancestor):
    """return a cached version of is_ancestor"""
    cache = {}

    def _is_ancestor(anc, desc):
        if anc > desc:
            return False
        elif anc == desc:
            return True
        key = (anc, desc)
        ret = cache.get(key)
        if ret is None:
            ret = cache[key] = is_ancestor(anc, desc)
        return ret

    return _is_ancestor


def _changesetforwardcopies(a, b, match):
    if a.rev() in (nullrev, b.rev()):
        return {}

    repo = a.repo().unfiltered()
    children = {}

    cl = repo.changelog
    isancestor = cl.isancestorrev

    # To track rename from "A" to B, we need to gather all parent → children
    # edges that are contains in `::B` but not in `::A`.
    #
    #
    # To do so, we need to gather all revisions exclusive¹ to "B" (ie¹: `::b -
    # ::a`) and also all the "roots point", ie the parents of the exclusive set
    # that belong to ::a. These are exactly all the revisions needed to express
    # the parent → children we need to combine.
    #
    # [1] actually, we need to gather all the edges within `(::a)::b`, ie:
    # excluding paths that leads to roots that are not ancestors of `a`. We
    # keep this out of the explanation because it is hard enough without this special case..

    parents = cl._uncheckedparentrevs
    graph_roots = (nullrev, nullrev)

    ancestors = cl.ancestors([a.rev()], inclusive=True)
    revs = cl.findmissingrevs(common=[a.rev()], heads=[b.rev()])
    roots = set()
    has_graph_roots = False

    # iterate over `only(B, A)`
    for r in revs:
        ps = parents(r)
        if ps == graph_roots:
            has_graph_roots = True
        else:
            p1, p2 = ps

            # find all the "root points" (see larger comment above)
            if p1 != nullrev and p1 in ancestors:
                roots.add(p1)
            if p2 != nullrev and p2 in ancestors:
                roots.add(p2)
    if not roots:
        # no common revision to track copies from
        return {}
    if has_graph_roots:
        # this deal with the special case mentionned in the [1] footnotes. We
        # must filter out revisions that leads to non-common graphroots.
        roots = list(roots)
        m = min(roots)
        h = [b.rev()]
        roots_to_head = cl.reachableroots(m, h, roots, includepath=True)
        roots_to_head = set(roots_to_head)
        revs = [r for r in revs if r in roots_to_head]

    if repo.filecopiesmode == b'changeset-sidedata':
        # When using side-data, we will process the edges "from" the children.
        # We iterate over the childre, gathering previous collected data for
        # the parents. Do know when the parents data is no longer necessary, we
        # keep a counter of how many children each revision has.
        #
        # An interresting property of `children_count` is that it only contains
        # revision that will be relevant for a edge of the graph. So if a
        # children has parent not in `children_count`, that edges should not be
        # processed.
        children_count = dict((r, 0) for r in roots)
        for r in revs:
            for p in cl.parentrevs(r):
                if p == nullrev:
                    continue
                children_count[r] = 0
                if p in children_count:
                    children_count[p] += 1
        revinfo = _revinfo_getter(repo, match)
        return _combine_changeset_copies(
            revs, children_count, b.rev(), revinfo, match, isancestor
        )
    else:
        # When not using side-data, we will process the edges "from" the parent.
        # so we need a full mapping of the parent -> children relation.
        children = dict((r, []) for r in roots)
        for r in revs:
            for p in cl.parentrevs(r):
                if p == nullrev:
                    continue
                children[r] = []
                if p in children:
                    children[p].append(r)
        x = revs.pop()
        assert x == b.rev()
        revs.extend(roots)
        revs.sort()

        revinfo = _revinfo_getter_extra(repo)
        return _combine_changeset_copies_extra(
            revs, children, b.rev(), revinfo, match, isancestor
        )


def _combine_changeset_copies(
    revs, children_count, targetrev, revinfo, match, isancestor
):
    """combine the copies information for each item of iterrevs

    revs: sorted iterable of revision to visit
    children_count: a {parent: <number-of-relevant-children>} mapping.
    targetrev: the final copies destination revision (not in iterrevs)
    revinfo(rev): a function that return (p1, p2, p1copies, p2copies, removed)
    match: a matcher

    It returns the aggregated copies information for `targetrev`.
    """

    alwaysmatch = match.always()

    if rustmod is not None and alwaysmatch:
        return rustmod.combine_changeset_copies(
            list(revs), children_count, targetrev, revinfo, isancestor
        )

    isancestor = cached_is_ancestor(isancestor)

    all_copies = {}
    # iterate over all the "children" side of copy tracing "edge"
    for current_rev in revs:
        p1, p2, changes = revinfo(current_rev)
        current_copies = None

        # iterate over all parents to chain the existing data with the
        # data from the parent → child edge.
        for parent, parent_rev in ((1, p1), (2, p2)):
            if parent_rev == nullrev:
                continue
            remaining_children = children_count.get(parent_rev)
            if remaining_children is None:
                continue
            remaining_children -= 1
            children_count[parent_rev] = remaining_children
            if remaining_children:
                copies = all_copies.get(parent_rev, None)
            else:
                copies = all_copies.pop(parent_rev, None)

            if copies is None:
                # this is a root
                copies = {}

            newcopies = copies
            # chain the data in the edge with the existing data
            if changes is not None:
                childcopies = {}
                if parent == 1:
                    childcopies = changes.copied_from_p1
                elif parent == 2:
                    childcopies = changes.copied_from_p2

                if not alwaysmatch:
                    childcopies = {
                        dst: src
                        for dst, src in childcopies.items()
                        if match(dst)
                    }
                if childcopies:
                    newcopies = copies.copy()
                    for dest, source in pycompat.iteritems(childcopies):
                        prev = copies.get(source)
                        if prev is not None and prev[1] is not None:
                            source = prev[1]
                        newcopies[dest] = (current_rev, source)
                    assert newcopies is not copies
                if changes.removed:
                    if newcopies is copies:
                        newcopies = copies.copy()
                    for f in changes.removed:
                        if f in newcopies:
                            if newcopies is copies:
                                # copy on write to avoid affecting potential other
                                # branches.  when there are no other branches, this
                                # could be avoided.
                                newcopies = copies.copy()
                            newcopies[f] = (current_rev, None)

            # check potential need to combine the data from another parent (for
            # that child). See comment below for details.
            if current_copies is None:
                current_copies = newcopies
            elif current_copies is newcopies:
                # nothing to merge:
                pass
            else:
                # we are the second parent to work on c, we need to merge our
                # work with the other.
                #
                # In case of conflict, parent 1 take precedence over parent 2.
                # This is an arbitrary choice made anew when implementing
                # changeset based copies. It was made without regards with
                # potential filelog related behavior.
                assert parent == 2
                current_copies = _merge_copies_dict(
                    newcopies, current_copies, isancestor, changes
                )
        all_copies[current_rev] = current_copies

    # filter out internal details and return a {dest: source mapping}
    final_copies = {}
    for dest, (tt, source) in all_copies[targetrev].items():
        if source is not None:
            final_copies[dest] = source
    return final_copies


def _merge_copies_dict(minor, major, isancestor, changes):
    """merge two copies-mapping together, minor and major

    In case of conflict, value from "major" will be picked.

    - `isancestors(low_rev, high_rev)`: callable return True if `low_rev` is an
                                        ancestors of `high_rev`,

    - `ismerged(path)`: callable return True if `path` have been merged in the
                        current revision,

    return the resulting dict (in practice, the "minor" object, updated)
    """
    for dest, value in major.items():
        other = minor.get(dest)
        if other is None:
            minor[dest] = value
        else:
            new_tt = value[0]
            other_tt = other[0]
            if value[1] == other[1]:
                continue
            # content from "major" wins, unless it is older
            # than the branch point or there is a merge
            if new_tt == other_tt:
                minor[dest] = value
            elif (
                changes is not None
                and value[1] is None
                and dest in changes.salvaged
            ):
                pass
            elif (
                changes is not None
                and other[1] is None
                and dest in changes.salvaged
            ):
                minor[dest] = value
            elif changes is not None and dest in changes.merged:
                minor[dest] = value
            elif not isancestor(new_tt, other_tt):
                if value[1] is not None:
                    minor[dest] = value
                elif isancestor(other_tt, new_tt):
                    minor[dest] = value
    return minor


def _revinfo_getter_extra(repo):
    """return a function that return multiple data given a <rev>"i

    * p1: revision number of first parent
    * p2: revision number of first parent
    * p1copies: mapping of copies from p1
    * p2copies: mapping of copies from p2
    * removed: a list of removed files
    * ismerged: a callback to know if file was merged in that revision
    """
    cl = repo.changelog
    parents = cl.parentrevs

    def get_ismerged(rev):
        ctx = repo[rev]

        def ismerged(path):
            if path not in ctx.files():
                return False
            fctx = ctx[path]
            parents = fctx._filelog.parents(fctx._filenode)
            nb_parents = 0
            for n in parents:
                if n != nullid:
                    nb_parents += 1
            return nb_parents >= 2

        return ismerged

    def revinfo(rev):
        p1, p2 = parents(rev)
        ctx = repo[rev]
        p1copies, p2copies = ctx._copies
        removed = ctx.filesremoved()
        return p1, p2, p1copies, p2copies, removed, get_ismerged(rev)

    return revinfo


def _combine_changeset_copies_extra(
    revs, children, targetrev, revinfo, match, isancestor
):
    """version of `_combine_changeset_copies` that works with the Google
    specific "extra" based storage for copy information"""
    all_copies = {}
    alwaysmatch = match.always()
    for r in revs:
        copies = all_copies.pop(r, None)
        if copies is None:
            # this is a root
            copies = {}
        for i, c in enumerate(children[r]):
            p1, p2, p1copies, p2copies, removed, ismerged = revinfo(c)
            if r == p1:
                parent = 1
                childcopies = p1copies
            else:
                assert r == p2
                parent = 2
                childcopies = p2copies
            if not alwaysmatch:
                childcopies = {
                    dst: src for dst, src in childcopies.items() if match(dst)
                }
            newcopies = copies
            if childcopies:
                newcopies = copies.copy()
                for dest, source in pycompat.iteritems(childcopies):
                    prev = copies.get(source)
                    if prev is not None and prev[1] is not None:
                        source = prev[1]
                    newcopies[dest] = (c, source)
                assert newcopies is not copies
            for f in removed:
                if f in newcopies:
                    if newcopies is copies:
                        # copy on write to avoid affecting potential other
                        # branches.  when there are no other branches, this
                        # could be avoided.
                        newcopies = copies.copy()
                    newcopies[f] = (c, None)
            othercopies = all_copies.get(c)
            if othercopies is None:
                all_copies[c] = newcopies
            else:
                # we are the second parent to work on c, we need to merge our
                # work with the other.
                #
                # In case of conflict, parent 1 take precedence over parent 2.
                # This is an arbitrary choice made anew when implementing
                # changeset based copies. It was made without regards with
                # potential filelog related behavior.
                if parent == 1:
                    _merge_copies_dict_extra(
                        othercopies, newcopies, isancestor, ismerged
                    )
                else:
                    _merge_copies_dict_extra(
                        newcopies, othercopies, isancestor, ismerged
                    )
                    all_copies[c] = newcopies

    final_copies = {}
    for dest, (tt, source) in all_copies[targetrev].items():
        if source is not None:
            final_copies[dest] = source
    return final_copies


def _merge_copies_dict_extra(minor, major, isancestor, ismerged):
    """version of `_merge_copies_dict` that works with the Google
    specific "extra" based storage for copy information"""
    for dest, value in major.items():
        other = minor.get(dest)
        if other is None:
            minor[dest] = value
        else:
            new_tt = value[0]
            other_tt = other[0]
            if value[1] == other[1]:
                continue
            # content from "major" wins, unless it is older
            # than the branch point or there is a merge
            if (
                new_tt == other_tt
                or not isancestor(new_tt, other_tt)
                or ismerged(dest)
            ):
                minor[dest] = value


def _forwardcopies(a, b, base=None, match=None):
    """find {dst@b: src@a} copy mapping where a is an ancestor of b"""

    if base is None:
        base = a
    match = a.repo().narrowmatch(match)
    # check for working copy
    if b.rev() is None:
        cm = _committedforwardcopies(a, b.p1(), base, match)
        # combine copies from dirstate if necessary
        copies = _chain(cm, _dirstatecopies(b._repo, match))
    else:
        copies = _committedforwardcopies(a, b, base, match)
    return copies


def _backwardrenames(a, b, match):
    if a._repo.ui.config(b'experimental', b'copytrace') == b'off':
        return {}

    # Even though we're not taking copies into account, 1:n rename situations
    # can still exist (e.g. hg cp a b; hg mv a c). In those cases we
    # arbitrarily pick one of the renames.
    # We don't want to pass in "match" here, since that would filter
    # the destination by it. Since we're reversing the copies, we want
    # to filter the source instead.
    f = _forwardcopies(b, a)
    r = {}
    for k, v in sorted(pycompat.iteritems(f)):
        if match and not match(v):
            continue
        # remove copies
        if v in a:
            continue
        r[v] = k
    return r


def pathcopies(x, y, match=None):
    """find {dst@y: src@x} copy mapping for directed compare"""
    repo = x._repo
    debug = repo.ui.debugflag and repo.ui.configbool(b'devel', b'debug.copies')
    if debug:
        repo.ui.debug(
            b'debug.copies: searching copies from %s to %s\n' % (x, y)
        )
    if x == y or not x or not y:
        return {}
    if y.rev() is None and x == y.p1():
        if debug:
            repo.ui.debug(b'debug.copies: search mode: dirstate\n')
        # short-circuit to avoid issues with merge states
        return _dirstatecopies(repo, match)
    a = y.ancestor(x)
    if a == x:
        if debug:
            repo.ui.debug(b'debug.copies: search mode: forward\n')
        copies = _forwardcopies(x, y, match=match)
    elif a == y:
        if debug:
            repo.ui.debug(b'debug.copies: search mode: backward\n')
        copies = _backwardrenames(x, y, match=match)
    else:
        if debug:
            repo.ui.debug(b'debug.copies: search mode: combined\n')
        base = None
        if a.rev() != nullrev:
            base = x
        copies = _chain(
            _backwardrenames(x, a, match=match),
            _forwardcopies(a, y, base, match=match),
        )
    _filter(x, y, copies)
    return copies


def mergecopies(repo, c1, c2, base):
    """
    Finds moves and copies between context c1 and c2 that are relevant for
    merging. 'base' will be used as the merge base.

    Copytracing is used in commands like rebase, merge, unshelve, etc to merge
    files that were moved/ copied in one merge parent and modified in another.
    For example:

    o          ---> 4 another commit
    |
    |   o      ---> 3 commit that modifies a.txt
    |  /
    o /        ---> 2 commit that moves a.txt to b.txt
    |/
    o          ---> 1 merge base

    If we try to rebase revision 3 on revision 4, since there is no a.txt in
    revision 4, and if user have copytrace disabled, we prints the following
    message:

    ```other changed <file> which local deleted```

    Returns a tuple where:

    "branch_copies" an instance of branch_copies.

    "diverge" is a mapping of source name -> list of destination names
    for divergent renames.

    This function calls different copytracing algorithms based on config.
    """
    # avoid silly behavior for update from empty dir
    if not c1 or not c2 or c1 == c2:
        return branch_copies(), branch_copies(), {}

    narrowmatch = c1.repo().narrowmatch()

    # avoid silly behavior for parent -> working dir
    if c2.node() is None and c1.node() == repo.dirstate.p1():
        return (
            branch_copies(_dirstatecopies(repo, narrowmatch)),
            branch_copies(),
            {},
        )

    copytracing = repo.ui.config(b'experimental', b'copytrace')
    if stringutil.parsebool(copytracing) is False:
        # stringutil.parsebool() returns None when it is unable to parse the
        # value, so we should rely on making sure copytracing is on such cases
        return branch_copies(), branch_copies(), {}

    if usechangesetcentricalgo(repo):
        # The heuristics don't make sense when we need changeset-centric algos
        return _fullcopytracing(repo, c1, c2, base)

    # Copy trace disabling is explicitly below the node == p1 logic above
    # because the logic above is required for a simple copy to be kept across a
    # rebase.
    if copytracing == b'heuristics':
        # Do full copytracing if only non-public revisions are involved as
        # that will be fast enough and will also cover the copies which could
        # be missed by heuristics
        if _isfullcopytraceable(repo, c1, base):
            return _fullcopytracing(repo, c1, c2, base)
        return _heuristicscopytracing(repo, c1, c2, base)
    else:
        return _fullcopytracing(repo, c1, c2, base)


def _isfullcopytraceable(repo, c1, base):
    """Checks that if base, source and destination are all no-public branches,
    if yes let's use the full copytrace algorithm for increased capabilities
    since it will be fast enough.

    `experimental.copytrace.sourcecommitlimit` can be used to set a limit for
    number of changesets from c1 to base such that if number of changesets are
    more than the limit, full copytracing algorithm won't be used.
    """
    if c1.rev() is None:
        c1 = c1.p1()
    if c1.mutable() and base.mutable():
        sourcecommitlimit = repo.ui.configint(
            b'experimental', b'copytrace.sourcecommitlimit'
        )
        commits = len(repo.revs(b'%d::%d', base.rev(), c1.rev()))
        return commits < sourcecommitlimit
    return False


def _checksinglesidecopies(
    src, dsts1, m1, m2, mb, c2, base, copy, renamedelete
):
    if src not in m2:
        # deleted on side 2
        if src not in m1:
            # renamed on side 1, deleted on side 2
            renamedelete[src] = dsts1
    elif src not in mb:
        # Work around the "short-circuit to avoid issues with merge states"
        # thing in pathcopies(): pathcopies(x, y) can return a copy where the
        # destination doesn't exist in y.
        pass
    elif mb[src] != m2[src] and not _related(c2[src], base[src]):
        return
    elif mb[src] != m2[src] or mb.flags(src) != m2.flags(src):
        # modified on side 2
        for dst in dsts1:
            copy[dst] = src


class branch_copies(object):
    """Information about copies made on one side of a merge/graft.

    "copy" is a mapping from destination name -> source name,
    where source is in c1 and destination is in c2 or vice-versa.

    "movewithdir" is a mapping from source name -> destination name,
    where the file at source present in one context but not the other
    needs to be moved to destination by the merge process, because the
    other context moved the directory it is in.

    "renamedelete" is a mapping of source name -> list of destination
    names for files deleted in c1 that were renamed in c2 or vice-versa.

    "dirmove" is a mapping of detected source dir -> destination dir renames.
    This is needed for handling changes to new files previously grafted into
    renamed directories.
    """

    def __init__(
        self, copy=None, renamedelete=None, dirmove=None, movewithdir=None
    ):
        self.copy = {} if copy is None else copy
        self.renamedelete = {} if renamedelete is None else renamedelete
        self.dirmove = {} if dirmove is None else dirmove
        self.movewithdir = {} if movewithdir is None else movewithdir

    def __repr__(self):
        return '<branch_copies\n  copy=%r\n  renamedelete=%r\n  dirmove=%r\n  movewithdir=%r\n>' % (
            self.copy,
            self.renamedelete,
            self.dirmove,
            self.movewithdir,
        )


def _fullcopytracing(repo, c1, c2, base):
    """The full copytracing algorithm which finds all the new files that were
    added from merge base up to the top commit and for each file it checks if
    this file was copied from another file.

    This is pretty slow when a lot of changesets are involved but will track all
    the copies.
    """
    m1 = c1.manifest()
    m2 = c2.manifest()
    mb = base.manifest()

    copies1 = pathcopies(base, c1)
    copies2 = pathcopies(base, c2)

    if not (copies1 or copies2):
        return branch_copies(), branch_copies(), {}

    inversecopies1 = {}
    inversecopies2 = {}
    for dst, src in copies1.items():
        inversecopies1.setdefault(src, []).append(dst)
    for dst, src in copies2.items():
        inversecopies2.setdefault(src, []).append(dst)

    copy1 = {}
    copy2 = {}
    diverge = {}
    renamedelete1 = {}
    renamedelete2 = {}
    allsources = set(inversecopies1) | set(inversecopies2)
    for src in allsources:
        dsts1 = inversecopies1.get(src)
        dsts2 = inversecopies2.get(src)
        if dsts1 and dsts2:
            # copied/renamed on both sides
            if src not in m1 and src not in m2:
                # renamed on both sides
                dsts1 = set(dsts1)
                dsts2 = set(dsts2)
                # If there's some overlap in the rename destinations, we
                # consider it not divergent. For example, if side 1 copies 'a'
                # to 'b' and 'c' and deletes 'a', and side 2 copies 'a' to 'c'
                # and 'd' and deletes 'a'.
                if dsts1 & dsts2:
                    for dst in dsts1 & dsts2:
                        copy1[dst] = src
                        copy2[dst] = src
                else:
                    diverge[src] = sorted(dsts1 | dsts2)
            elif src in m1 and src in m2:
                # copied on both sides
                dsts1 = set(dsts1)
                dsts2 = set(dsts2)
                for dst in dsts1 & dsts2:
                    copy1[dst] = src
                    copy2[dst] = src
            # TODO: Handle cases where it was renamed on one side and copied
            # on the other side
        elif dsts1:
            # copied/renamed only on side 1
            _checksinglesidecopies(
                src, dsts1, m1, m2, mb, c2, base, copy1, renamedelete1
            )
        elif dsts2:
            # copied/renamed only on side 2
            _checksinglesidecopies(
                src, dsts2, m2, m1, mb, c1, base, copy2, renamedelete2
            )

    # find interesting file sets from manifests
    cache = []

    def _get_addedfiles(idx):
        if not cache:
            addedinm1 = m1.filesnotin(mb, repo.narrowmatch())
            addedinm2 = m2.filesnotin(mb, repo.narrowmatch())
            u1 = sorted(addedinm1 - addedinm2)
            u2 = sorted(addedinm2 - addedinm1)
            cache.extend((u1, u2))
        return cache[idx]

    u1fn = lambda: _get_addedfiles(0)
    u2fn = lambda: _get_addedfiles(1)
    if repo.ui.debugflag:
        u1 = u1fn()
        u2 = u2fn()

        header = b"  unmatched files in %s"
        if u1:
            repo.ui.debug(
                b"%s:\n   %s\n" % (header % b'local', b"\n   ".join(u1))
            )
        if u2:
            repo.ui.debug(
                b"%s:\n   %s\n" % (header % b'other', b"\n   ".join(u2))
            )

        renamedeleteset = set()
        divergeset = set()
        for dsts in diverge.values():
            divergeset.update(dsts)
        for dsts in renamedelete1.values():
            renamedeleteset.update(dsts)
        for dsts in renamedelete2.values():
            renamedeleteset.update(dsts)

        repo.ui.debug(
            b"  all copies found (* = to merge, ! = divergent, "
            b"% = renamed and deleted):\n"
        )
        for side, copies in ((b"local", copies1), (b"remote", copies2)):
            if not copies:
                continue
            repo.ui.debug(b"   on %s side:\n" % side)
            for f in sorted(copies):
                note = b""
                if f in copy1 or f in copy2:
                    note += b"*"
                if f in divergeset:
                    note += b"!"
                if f in renamedeleteset:
                    note += b"%"
                repo.ui.debug(
                    b"    src: '%s' -> dst: '%s' %s\n" % (copies[f], f, note)
                )
        del renamedeleteset
        del divergeset

    repo.ui.debug(b"  checking for directory renames\n")

    dirmove1, movewithdir2 = _dir_renames(repo, c1, copy1, copies1, u2fn)
    dirmove2, movewithdir1 = _dir_renames(repo, c2, copy2, copies2, u1fn)

    branch_copies1 = branch_copies(copy1, renamedelete1, dirmove1, movewithdir1)
    branch_copies2 = branch_copies(copy2, renamedelete2, dirmove2, movewithdir2)

    return branch_copies1, branch_copies2, diverge


def _dir_renames(repo, ctx, copy, fullcopy, addedfilesfn):
    """Finds moved directories and files that should move with them.

    ctx: the context for one of the sides
    copy: files copied on the same side (as ctx)
    fullcopy: files copied on the same side (as ctx), including those that
              merge.manifestmerge() won't care about
    addedfilesfn: function returning added files on the other side (compared to
                  ctx)
    """
    # generate a directory move map
    invalid = set()
    dirmove = {}

    # examine each file copy for a potential directory move, which is
    # when all the files in a directory are moved to a new directory
    for dst, src in pycompat.iteritems(fullcopy):
        dsrc, ddst = pathutil.dirname(src), pathutil.dirname(dst)
        if dsrc in invalid:
            # already seen to be uninteresting
            continue
        elif ctx.hasdir(dsrc) and ctx.hasdir(ddst):
            # directory wasn't entirely moved locally
            invalid.add(dsrc)
        elif dsrc in dirmove and dirmove[dsrc] != ddst:
            # files from the same directory moved to two different places
            invalid.add(dsrc)
        else:
            # looks good so far
            dirmove[dsrc] = ddst

    for i in invalid:
        if i in dirmove:
            del dirmove[i]
    del invalid

    if not dirmove:
        return {}, {}

    dirmove = {k + b"/": v + b"/" for k, v in pycompat.iteritems(dirmove)}

    for d in dirmove:
        repo.ui.debug(
            b"   discovered dir src: '%s' -> dst: '%s'\n" % (d, dirmove[d])
        )

    movewithdir = {}
    # check unaccounted nonoverlapping files against directory moves
    for f in addedfilesfn():
        if f not in fullcopy:
            for d in dirmove:
                if f.startswith(d):
                    # new file added in a directory that was moved, move it
                    df = dirmove[d] + f[len(d) :]
                    if df not in copy:
                        movewithdir[f] = df
                        repo.ui.debug(
                            b"   pending file src: '%s' -> dst: '%s'\n"
                            % (f, df)
                        )
                    break

    return dirmove, movewithdir


def _heuristicscopytracing(repo, c1, c2, base):
    """Fast copytracing using filename heuristics

    Assumes that moves or renames are of following two types:

    1) Inside a directory only (same directory name but different filenames)
    2) Move from one directory to another
                    (same filenames but different directory names)

    Works only when there are no merge commits in the "source branch".
    Source branch is commits from base up to c2 not including base.

    If merge is involved it fallbacks to _fullcopytracing().

    Can be used by setting the following config:

        [experimental]
        copytrace = heuristics

    In some cases the copy/move candidates found by heuristics can be very large
    in number and that will make the algorithm slow. The number of possible
    candidates to check can be limited by using the config
    `experimental.copytrace.movecandidateslimit` which defaults to 100.
    """

    if c1.rev() is None:
        c1 = c1.p1()
    if c2.rev() is None:
        c2 = c2.p1()

    changedfiles = set()
    m1 = c1.manifest()
    if not repo.revs(b'%d::%d', base.rev(), c2.rev()):
        # If base is not in c2 branch, we switch to fullcopytracing
        repo.ui.debug(
            b"switching to full copytracing as base is not "
            b"an ancestor of c2\n"
        )
        return _fullcopytracing(repo, c1, c2, base)

    ctx = c2
    while ctx != base:
        if len(ctx.parents()) == 2:
            # To keep things simple let's not handle merges
            repo.ui.debug(b"switching to full copytracing because of merges\n")
            return _fullcopytracing(repo, c1, c2, base)
        changedfiles.update(ctx.files())
        ctx = ctx.p1()

    copies2 = {}
    cp = _forwardcopies(base, c2)
    for dst, src in pycompat.iteritems(cp):
        if src in m1:
            copies2[dst] = src

    # file is missing if it isn't present in the destination, but is present in
    # the base and present in the source.
    # Presence in the base is important to exclude added files, presence in the
    # source is important to exclude removed files.
    filt = lambda f: f not in m1 and f in base and f in c2
    missingfiles = [f for f in changedfiles if filt(f)]

    copies1 = {}
    if missingfiles:
        basenametofilename = collections.defaultdict(list)
        dirnametofilename = collections.defaultdict(list)

        for f in m1.filesnotin(base.manifest()):
            basename = os.path.basename(f)
            dirname = os.path.dirname(f)
            basenametofilename[basename].append(f)
            dirnametofilename[dirname].append(f)

        for f in missingfiles:
            basename = os.path.basename(f)
            dirname = os.path.dirname(f)
            samebasename = basenametofilename[basename]
            samedirname = dirnametofilename[dirname]
            movecandidates = samebasename + samedirname
            # f is guaranteed to be present in c2, that's why
            # c2.filectx(f) won't fail
            f2 = c2.filectx(f)
            # we can have a lot of candidates which can slow down the heuristics
            # config value to limit the number of candidates moves to check
            maxcandidates = repo.ui.configint(
                b'experimental', b'copytrace.movecandidateslimit'
            )

            if len(movecandidates) > maxcandidates:
                repo.ui.status(
                    _(
                        b"skipping copytracing for '%s', more "
                        b"candidates than the limit: %d\n"
                    )
                    % (f, len(movecandidates))
                )
                continue

            for candidate in movecandidates:
                f1 = c1.filectx(candidate)
                if _related(f1, f2):
                    # if there are a few related copies then we'll merge
                    # changes into all of them. This matches the behaviour
                    # of upstream copytracing
                    copies1[candidate] = f

    return branch_copies(copies1), branch_copies(copies2), {}


def _related(f1, f2):
    """return True if f1 and f2 filectx have a common ancestor

    Walk back to common ancestor to see if the two files originate
    from the same file. Since workingfilectx's rev() is None it messes
    up the integer comparison logic, hence the pre-step check for
    None (f1 and f2 can only be workingfilectx's initially).
    """

    if f1 == f2:
        return True  # a match

    g1, g2 = f1.ancestors(), f2.ancestors()
    try:
        f1r, f2r = f1.linkrev(), f2.linkrev()

        if f1r is None:
            f1 = next(g1)
        if f2r is None:
            f2 = next(g2)

        while True:
            f1r, f2r = f1.linkrev(), f2.linkrev()
            if f1r > f2r:
                f1 = next(g1)
            elif f2r > f1r:
                f2 = next(g2)
            else:  # f1 and f2 point to files in the same linkrev
                return f1 == f2  # true if they point to the same file
    except StopIteration:
        return False


def graftcopies(wctx, ctx, base):
    """reproduce copies between base and ctx in the wctx

    Unlike mergecopies(), this function will only consider copies between base
    and ctx; it will ignore copies between base and wctx. Also unlike
    mergecopies(), this function will apply copies to the working copy (instead
    of just returning information about the copies). That makes it cheaper
    (especially in the common case of base==ctx.p1()) and useful also when
    experimental.copytrace=off.

    merge.update() will have already marked most copies, but it will only
    mark copies if it thinks the source files are related (see
    merge._related()). It will also not mark copies if the file wasn't modified
    on the local side. This function adds the copies that were "missed"
    by merge.update().
    """
    new_copies = pathcopies(base, ctx)
    _filter(wctx.p1(), wctx, new_copies)
    for dst, src in pycompat.iteritems(new_copies):
        wctx[dst].markcopied(src)