annotate mercurial/copies.py @ 43252:32187ae9eeb3

copies: simplify the handling of merges

Instead of stacking copies for both parent on the head, we move copies outside
of the heap into a dedicated dictionary. The two side of merge can we merged
sooner, making the algorithm simpler.

This simplicity reflect in the heap structure and speed up the execution for
copies involving a large amount of merges.

Here are timing for perfpathcopies of multiple revision pairs.
- filelog: timing using filelog (with the introrev condition dropped)
- base:    this series base
- before:  the parent of this changeset
- after:   this changeset

revision: large amount; added files: large amount; rename small amount; c3b14617fbd7 9ba6ab77fd29
filelog: ! wall 3.679613 comb 3.680000 user 3.580000 sys 0.100000 (median of 3)
base:    ! wall 8.884369 comb 8.880000 user 8.850000 sys 0.030000 (median of 3)
before:  ! wall 8.443747 comb 8.420000 user 8.410000 sys 0.010000 (median of 3)
after:   ! wall 4.697917 comb 4.690000 user 4.660000 sys 0.030000 (median of 3)
revision: large amount; added files: small amount; rename small amount; c3b14617fbd7 f650a9b140d2
filelog: ! wall 0.003357 comb 0.010000 user 0.010000 sys 0.000000 (median of 781)
base:    ! wall 12.398524 comb 12.400000 user 12.330000 sys 0.070000 (median of 3)
before:  ! wall 10.852593 comb 10.850000 user 10.800000 sys 0.050000 (median of 3)
after:   ! wall 6.750832 comb 6.750000 user 6.640000 sys 0.110000 (median of 3)
revision: large amount; added files: large amount; rename large amount; 08ea3258278e d9fa043f30c0
filelog: ! wall 2.754687 comb 2.760000 user 2.650000 sys 0.110000 (median of 4)
base:    ! wall 1.423166 comb 1.420000 user 1.400000 sys 0.020000 (median of 8)
before:  ! wall 1.068041 comb 1.060000 user 1.050000 sys 0.010000 (median of 10)
after:   ! wall 1.045916 comb 1.050000 user 1.040000 sys 0.010000 (median of 10)
revision: small amount; added files: large amount; rename large amount; df6f7a526b60 a83dc6a2d56f
filelog: ! wall 1.552293 comb 1.550000 user 1.510000 sys 0.040000 (median of 6
base:    ! wall 0.022662 comb 0.020000 user 0.020000 sys 0.000000 (median of 128)
before:  ! wall 0.021111 comb 0.020000 user 0.020000 sys 0.000000 (median of 139)
after:   ! wall 0.021577 comb 0.020000 user 0.020000 sys 0.000000 (median of 138)
revision: small amount; added files: large amount; rename small amount; 4aa4e1f8e19a 169138063d63
filelog: ! wall 1.500983 comb 1.500000 user 1.420000 sys 0.080000 (median of 7)
base:    ! wall 0.006956 comb 0.010000 user 0.010000 sys 0.000000 (median of 392)
before:  ! wall 0.004356 comb 0.010000 user 0.010000 sys 0.000000 (median of 675)
after:   ! wall 0.004329 comb 0.000000 user 0.000000 sys 0.000000 (median of 682)
revision: small amount; added files: small amount; rename small amount; 4bc173b045a6 964879152e2e
filelog: ! wall 0.011745 comb 0.020000 user 0.020000 sys 0.000000 (median of 250)
base:    ! wall 0.000156 comb 0.000000 user 0.000000 sys 0.000000 (median of 17180)
before:  ! wall 0.000100 comb 0.000000 user 0.000000 sys 0.000000 (median of 26912)
after:   ! wall 0.000105 comb 0.000000 user 0.000000 sys 0.000000 (median of 25689)
revision: medium amount; added files: large amount; rename medium amount; c95f1ced15f2 2c68e87c3efe
filelog: ! wall 3.228230 comb 3.230000 user 3.110000 sys 0.120000 (median of 4)
base:    ! wall 0.997640 comb 1.000000 user 0.980000 sys 0.020000 (median of 10)
before:  ! wall 0.778291 comb 0.780000 user 0.780000 sys 0.000000 (median of 13)
after:   ! wall 0.706594 comb 0.710000 user 0.710000 sys 0.000000 (median of 15)
revision: medium amount; added files: medium amount; rename small amount; d343da0c55a8 d7746d32bf9d
filelog: ! wall 1.052501 comb 1.060000 user 1.040000 sys 0.020000 (median of 10
base:    ! wall 0.214519 comb 0.220000 user 0.220000 sys 0.000000 (median of 45)
before:  ! wall 0.160804 comb 0.160000 user 0.160000 sys 0.000000 (median of 62)
after:   ! wall 0.163736 comb 0.160000 user 0.160000 sys 0.000000 (median of 60)

Differential Revision: https://phab.mercurial-scm.org/D7069

# 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 heapq
import os

from .i18n import _


from .revlogutils.flagutil import REVIDX_SIDEDATA

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

from .revlogutils import sidedata as sidedatamod

from .utils import stringutil


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(a, b):
    """chain two sets of copies 'a' and 'b'"""
    t = a.copy()
    for k, v in pycompat.iteritems(b):
        if v in t:
            t[k] = t[v]
        else:
            t[k] = v
    return t


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

    repo = a.repo()
    children = {}
    cl = repo.changelog
    missingrevs = cl.findmissingrevs(common=[a.rev()], heads=[b.rev()])
    for r in missingrevs:
        for p in cl.parentrevs(r):
            if p == node.nullrev:
                continue
            if p not in children:
                children[p] = [r]
            else:
                children[p].append(r)

    roots = set(children) - set(missingrevs)
    work = list(roots)
    all_copies = {r: {} for r in roots}
    heapq.heapify(work)
    alwaysmatch = match.always()
    while work:
        r = heapq.heappop(work)
        copies = all_copies.pop(r)
        if r == b.rev():
            return copies
        for i, c in enumerate(children[r]):
            childctx = repo[c]
            if r == childctx.p1().rev():
                parent = 1
                childcopies = childctx.p1copies()
            else:
                assert r == childctx.p2().rev()
                parent = 2
                childcopies = childctx.p2copies()
            if not alwaysmatch:
                childcopies = {
                    dst: src for dst, src in childcopies.items() if match(dst)
                }
            # Copy the dict only if later iterations will also need it
            if i != len(children[r]) - 1:
                newcopies = copies.copy()
            else:
                newcopies = copies
            if childcopies:
                newcopies = _chain(newcopies, childcopies)
            for f in childctx.filesremoved():
                if f in newcopies:
                    del newcopies[f]
            othercopies = all_copies.get(c)
            if othercopies is None:
                heapq.heappush(work, c)
                all_copies[c] = newcopies
            else:
                # we are the second parent to work on c, we need to merge our
                # work with the other.
                #
                # Unlike when copies are stored in the filelog, we consider
                # it a copy even if the destination already existed on the
                # other branch. It's simply too expensive to check if the
                # file existed in the manifest.
                #
                # 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:
                    othercopies.update(newcopies)
                else:
                    newcopies.update(othercopies)
                    all_copies[c] = newcopies
    assert False


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 {}
    a = y.ancestor(x)
    if a == x:
        if debug:
            repo.ui.debug(b'debug.copies: search mode: forward\n')
        if y.rev() is None and x == y.p1():
            # short-circuit to avoid issues with merge states
            return _dirstatecopies(repo, match)
        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() != node.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 five dicts: "copy", "movewithdir", "diverge", "renamedelete" and
    "dirmove".

    "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.

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

    "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.

    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 {}, {}, {}, {}, {}

    narrowmatch = c1.repo().narrowmatch()

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

    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 {}, {}, {}, {}, {}

    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 m2[src] != mb[src]:
        if not _related(c2[src], base[src]):
            return
        # modified on side 2
        for dst in dsts1:
            if dst not in m2:
                # dst not added on side 2 (handle as regular
                # "both created" case in manifestmerge otherwise)
                copy[dst] = src


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)

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

    copy = {}
    diverge = {}
    renamedelete = {}
    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:
                        copy[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:
                    copy[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, copy, renamedelete
            )
        elif dsts2:
            # copied/renamed only on side 2
            _checksinglesidecopies(
                src, dsts2, m2, m1, mb, c1, base, copy, renamedelete
            )

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

    # find interesting file sets from manifests
    addedinm1 = m1.filesnotin(mb, repo.narrowmatch())
    addedinm2 = m2.filesnotin(mb, repo.narrowmatch())
    u1 = sorted(addedinm1 - addedinm2)
    u2 = sorted(addedinm2 - addedinm1)

    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)))

    fullcopy = copies1.copy()
    fullcopy.update(copies2)
    if not fullcopy:
        return copy, {}, diverge, renamedelete, {}

    if repo.ui.debugflag:
        repo.ui.debug(
            b"  all copies found (* = to merge, ! = divergent, "
            b"% = renamed and deleted):\n"
        )
        for f in sorted(fullcopy):
            note = b""
            if f in copy:
                note += b"*"
            if f in divergeset:
                note += b"!"
            if f in renamedeleteset:
                note += b"%"
            repo.ui.debug(
                b"   src: '%s' -> dst: '%s' %s\n" % (fullcopy[f], f, note)
            )
    del divergeset

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

    # generate a directory move map
    d1, d2 = c1.dirs(), c2.dirs()
    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 dsrc in d1 and ddst in d1:
            # directory wasn't entirely moved locally
            invalid.add(dsrc)
        elif dsrc in d2 and ddst in d2:
            # directory wasn't entirely moved remotely
            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 d1, d2, invalid

    if not dirmove:
        return copy, {}, diverge, renamedelete, {}

    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 u1 + u2:
        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 copy, movewithdir, diverge, renamedelete, dirmove


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()

    copies = {}

    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()

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

    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
                    copies[candidate] = f

    return copies, {}, {}, {}, {}


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 duplicatecopies(repo, wctx, rev, fromrev, skiprev=None):
    """reproduce copies from fromrev to rev in the dirstate

    If skiprev is specified, it's a revision that should be used to
    filter copy records. Any copies that occur between fromrev and
    skiprev will not be duplicated, even if they appear in the set of
    copies between fromrev and rev.
    """
    exclude = {}
    ctraceconfig = repo.ui.config(b'experimental', b'copytrace')
    bctrace = stringutil.parsebool(ctraceconfig)
    if skiprev is not None and (
        ctraceconfig == b'heuristics' or bctrace or bctrace is None
    ):
        # copytrace='off' skips this line, but not the entire function because
        # the line below is O(size of the repo) during a rebase, while the rest
        # of the function is much faster (and is required for carrying copy
        # metadata across the rebase anyway).
        exclude = pathcopies(repo[fromrev], repo[skiprev])
    for dst, src in pycompat.iteritems(pathcopies(repo[fromrev], repo[rev])):
        if dst in exclude:
            continue
        if dst in wctx:
            wctx[dst].markcopied(src)


def computechangesetfilesadded(ctx):
    """return the list of files added in a changeset
    """
    added = []
    for f in ctx.files():
        if not any(f in p for p in ctx.parents()):
            added.append(f)
    return added


def computechangesetfilesremoved(ctx):
    """return the list of files removed in a changeset
    """
    removed = []
    for f in ctx.files():
        if f not in ctx:
            removed.append(f)
    return removed


def computechangesetcopies(ctx):
    """return the copies data for a changeset

    The copies data are returned as a pair of dictionnary (p1copies, p2copies).

    Each dictionnary are in the form: `{newname: oldname}`
    """
    p1copies = {}
    p2copies = {}
    p1 = ctx.p1()
    p2 = ctx.p2()
    narrowmatch = ctx._repo.narrowmatch()
    for dst in ctx.files():
        if not narrowmatch(dst) or dst not in ctx:
            continue
        copied = ctx[dst].renamed()
        if not copied:
            continue
        src, srcnode = copied
        if src in p1 and p1[src].filenode() == srcnode:
            p1copies[dst] = src
        elif src in p2 and p2[src].filenode() == srcnode:
            p2copies[dst] = src
    return p1copies, p2copies


def encodecopies(files, copies):
    items = []
    for i, dst in enumerate(files):
        if dst in copies:
            items.append(b'%d\0%s' % (i, copies[dst]))
    if len(items) != len(copies):
        raise error.ProgrammingError(
            b'some copy targets missing from file list'
        )
    return b"\n".join(items)


def decodecopies(files, data):
    try:
        copies = {}
        if not data:
            return copies
        for l in data.split(b'\n'):
            strindex, src = l.split(b'\0')
            i = int(strindex)
            dst = files[i]
            copies[dst] = src
        return copies
    except (ValueError, IndexError):
        # Perhaps someone had chosen the same key name (e.g. "p1copies") and
        # used different syntax for the value.
        return None


def encodefileindices(files, subset):
    subset = set(subset)
    indices = []
    for i, f in enumerate(files):
        if f in subset:
            indices.append(b'%d' % i)
    return b'\n'.join(indices)


def decodefileindices(files, data):
    try:
        subset = []
        if not data:
            return subset
        for strindex in data.split(b'\n'):
            i = int(strindex)
            if i < 0 or i >= len(files):
                return None
            subset.append(files[i])
        return subset
    except (ValueError, IndexError):
        # Perhaps someone had chosen the same key name (e.g. "added") and
        # used different syntax for the value.
        return None


def _getsidedata(srcrepo, rev):
    ctx = srcrepo[rev]
    filescopies = computechangesetcopies(ctx)
    filesadded = computechangesetfilesadded(ctx)
    filesremoved = computechangesetfilesremoved(ctx)
    sidedata = {}
    if any([filescopies, filesadded, filesremoved]):
        sortedfiles = sorted(ctx.files())
        p1copies, p2copies = filescopies
        p1copies = encodecopies(sortedfiles, p1copies)
        p2copies = encodecopies(sortedfiles, p2copies)
        filesadded = encodefileindices(sortedfiles, filesadded)
        filesremoved = encodefileindices(sortedfiles, filesremoved)
        if p1copies:
            sidedata[sidedatamod.SD_P1COPIES] = p1copies
        if p2copies:
            sidedata[sidedatamod.SD_P2COPIES] = p2copies
        if filesadded:
            sidedata[sidedatamod.SD_FILESADDED] = filesadded
        if filesremoved:
            sidedata[sidedatamod.SD_FILESREMOVED] = filesremoved
    return sidedata


def getsidedataadder(srcrepo, destrepo):
    def sidedatacompanion(revlog, rev):
        sidedata = {}
        if util.safehasattr(revlog, 'filteredrevs'):  # this is a changelog
            sidedata = _getsidedata(srcrepo, rev)
        return False, (), sidedata

    return sidedatacompanion


def getsidedataremover(srcrepo, destrepo):
    def sidedatacompanion(revlog, rev):
        f = ()
        if util.safehasattr(revlog, 'filteredrevs'):  # this is a changelog
            if revlog.flags(rev) & REVIDX_SIDEDATA:
                f = (
                    sidedatamod.SD_P1COPIES,
                    sidedatamod.SD_P2COPIES,
                    sidedatamod.SD_FILESADDED,
                    sidedatamod.SD_FILESREMOVED,
                )
        return False, f, {}

    return sidedatacompanion