annotate mercurial/copies.py @ 45892:06b64fabf91c

copies: cache the ancestor checking call when tracing copy

A good share of the time spent in this function is spent doing ancestors
checking. To avoid spending time in duplicated call, we cache the result of
calls.

In the slower case, this provide a quite significant performance boost. Below
are the result for a set of selected pairs (many of them pathological):

(And further down is another table that summarize the current state of filelog
based vs changeset base copy tracing)


The benchmark have been configured to be killed after 6 minutes of runtime,
which mean that any detect slower than 2 minutes will be marked as "killed".
This drop some useful information about how much slower these case are… but also
prevent 99% of the benchmark time to be spent on case that can be labelled "very
slow" anyway.


Repo            Case                                  Source-Rev   Dest-Rev         Old-Time      New-Time     Difference   Factor
------------------------------------------------------------------------------------------------------------------------------------
mercurial       x_revs_x_added_0_copies               ad6b123de1c7 39cfcef4f463 :   0.000044 s,   0.000044 s,  +0.000000 s, × 1.0000
mercurial       x_revs_x_added_x_copies               2b1c78674230 0c1d10351869 :   0.000138 s,   0.000138 s,  +0.000000 s, × 1.0000
mercurial       x000_revs_x000_added_x_copies         81f8ff2a9bf2 dd3267698d84 :   0.005067 s,   0.005052 s,  -0.000015 s, × 0.9970
pypy            x_revs_x_added_0_copies               aed021ee8ae8 099ed31b181b :   0.000218 s,   0.000219 s,  +0.000001 s, × 1.0046
pypy            x_revs_x000_added_0_copies            4aa4e1f8e19a 359343b9ac0e :   0.000053 s,   0.000055 s,  +0.000002 s, × 1.0377
pypy            x_revs_x_added_x_copies               ac52eb7bbbb0 72e022663155 :   0.000125 s,   0.000128 s,  +0.000003 s, × 1.0240
pypy            x_revs_x00_added_x_copies             c3b14617fbd7 ace7255d9a26 :   0.001098 s,   0.001089 s,  -0.000009 s, × 0.9918
pypy            x_revs_x000_added_x000_copies         df6f7a526b60 a83dc6a2d56f :   0.017546 s,   0.017407 s,  -0.000139 s, × 0.9921
pypy            x000_revs_xx00_added_0_copies         89a76aede314 2f22446ff07e :   0.096723 s,   0.094175 s,  -0.002548 s, × 0.9737
pypy            x000_revs_x000_added_x_copies         8a3b5bfd266e 2c68e87c3efe :   0.271796 s,   0.238009 s,  -0.033787 s, × 0.8757
pypy            x000_revs_x000_added_x000_copies      89a76aede314 7b3dda341c84 :   0.128602 s,   0.125876 s,  -0.002726 s, × 0.9788
pypy            x0000_revs_x_added_0_copies           d1defd0dc478 c9cb1334cc78 :   7.086742 s,   3.581556 s,  -3.505186 s, × 0.5054
pypy            x0000_revs_xx000_added_0_copies       bf2c629d0071 4ffed77c095c :   0.016634 s,   0.016721 s,  +0.000087 s, × 1.0052
pypy            x0000_revs_xx000_added_x000_copies    08ea3258278e d9fa043f30c0 :   0.254225 s,   0.242367 s,  -0.011858 s, × 0.9534
netbeans        x_revs_x_added_0_copies               fb0955ffcbcd a01e9239f9e7 :   0.000166 s,   0.000165 s,  -0.000001 s, × 0.9940
netbeans        x_revs_x000_added_0_copies            6f360122949f 20eb231cc7d0 :   0.000118 s,   0.000114 s,  -0.000004 s, × 0.9661
netbeans        x_revs_x_added_x_copies               1ada3faf6fb6 5a39d12eecf4 :   0.000296 s,   0.000296 s,  +0.000000 s, × 1.0000
netbeans        x_revs_x00_added_x_copies             35be93ba1e2c 9eec5e90c05f :   0.001137 s,   0.001124 s,  -0.000013 s, × 0.9886
netbeans        x000_revs_xx00_added_0_copies         eac3045b4fdd 51d4ae7f1290 :   0.014133 s,   0.013060 s,  -0.001073 s, × 0.9241
netbeans        x000_revs_x000_added_x_copies         e2063d266acd 6081d72689dc :   0.016988 s,   0.017112 s,  +0.000124 s, × 1.0073
netbeans        x000_revs_x000_added_x000_copies      ff453e9fee32 411350406ec2 :   0.676361 s,   0.660350 s,  -0.016011 s, × 0.9763
netbeans        x0000_revs_xx000_added_x000_copies    588c2d1ced70 1aad62e59ddd :  12.515149 s,  10.032499 s,  -2.482650 s, × 0.8016
mozilla-central x_revs_x_added_0_copies               3697f962bb7b 7015fcdd43a2 :   0.000186 s,   0.000189 s,  +0.000003 s, × 1.0161
mozilla-central x_revs_x000_added_0_copies            dd390860c6c9 40d0c5bed75d :   0.000459 s,   0.000462 s,  +0.000003 s, × 1.0065
mozilla-central x_revs_x_added_x_copies               8d198483ae3b 14207ffc2b2f :   0.000273 s,   0.000270 s,  -0.000003 s, × 0.9890
mozilla-central x_revs_x00_added_x_copies             98cbc58cc6bc 446a150332c3 :   0.001503 s,   0.001474 s,  -0.000029 s, × 0.9807
mozilla-central x_revs_x000_added_x000_copies         3c684b4b8f68 0a5e72d1b479 :   0.004862 s,   0.004806 s,  -0.000056 s, × 0.9885
mozilla-central x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :   0.088291 s,   0.085150 s,  -0.003141 s, × 0.9644
mozilla-central x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :   0.007113 s,   0.007064 s,  -0.000049 s, × 0.9931
mozilla-central x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :   0.004687 s,   0.004741 s,  +0.000054 s, × 1.0115
mozilla-central x000_revs_x000_added_x000_copies      7c97034feb78 4407bd0c6330 :   0.198710 s,   0.190133 s,  -0.008577 s, × 0.9568
mozilla-central x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :   0.036068 s,   0.035651 s,  -0.000417 s, × 0.9884
mozilla-central x0000_revs_xx000_added_x000_copies    f78c615a656c 96a38b690156 :   0.465362 s,   0.440694 s,  -0.024668 s, × 0.9470
mozilla-central x00000_revs_x0000_added_x0000_copies  6832ae71433c 4c222a1d9a00 :  24.519684 s,  18.454163 s,  -6.065521 s, × 0.7526
mozilla-central x00000_revs_x00000_added_x000_copies  76caed42cf7c 1daa622bbe42 :  42.711897 s,  31.562719 s, -11.149178 s, × 0.7390
mozilla-try     x_revs_x_added_0_copies               aaf6dde0deb8 9790f499805a :   0.001201 s,   0.001189 s,  -0.000012 s, × 0.9900
mozilla-try     x_revs_x000_added_0_copies            d8d0222927b4 5bb8ce8c7450 :   0.001216 s,   0.001204 s,  -0.000012 s, × 0.9901
mozilla-try     x_revs_x_added_x_copies               092fcca11bdb 936255a0384a :   0.000595 s,   0.000586 s,  -0.000009 s, × 0.9849
mozilla-try     x_revs_x00_added_x_copies             b53d2fadbdb5 017afae788ec :   0.001856 s,   0.001845 s,  -0.000011 s, × 0.9941
mozilla-try     x_revs_x000_added_x000_copies         20408ad61ce5 6f0ee96e21ad :   0.064936 s,   0.063822 s,  -0.001114 s, × 0.9828
mozilla-try     x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :   0.090601 s,   0.088038 s,  -0.002563 s, × 0.9717
mozilla-try     x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :   0.007510 s,   0.007389 s,  -0.000121 s, × 0.9839
mozilla-try     x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :   0.004911 s,   0.004868 s,  -0.000043 s, × 0.9912
mozilla-try     x000_revs_x000_added_x000_copies      1346fd0130e4 4c65cbdabc1f :   0.233231 s,   0.222450 s,  -0.010781 s, × 0.9538
mozilla-try     x0000_revs_x_added_0_copies           63519bfd42ee a36a2a865d92 :   0.419989 s,   0.370675 s,  -0.049314 s, × 0.8826
mozilla-try     x0000_revs_x_added_x_copies           9fe69ff0762d bcabf2a78927 :   0.401521 s,   0.358020 s,  -0.043501 s, × 0.8917
mozilla-try     x0000_revs_xx000_added_x_copies       156f6e2674f2 4d0f2c178e66 :   0.179555 s,   0.145235 s,  -0.034320 s, × 0.8089
mozilla-try     x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :   0.038004 s,   0.037606 s,  -0.000398 s, × 0.9895
mozilla-try     x0000_revs_xx000_added_x000_copies    89294cd501d9 7ccb2fc7ccb5 :  52.838482 s,   7.382439 s, -45.456043 s, × 0.1397
mozilla-try     x0000_revs_x0000_added_x0000_copies   e928c65095ed e951f4ad123a :   8.705874 s,   7.273506 s,  -1.432368 s, × 0.8355
mozilla-try     x00000_revs_x00000_added_0_copies     dc8a3ca7010e d16fde900c9c :   1.126708 s,   1.074593 s,  -0.052115 s, × 0.9537
mozilla-try     x00000_revs_x0000_added_x0000_copies  8d3fafa80d4b eb884023b810 :  83.854020 s,  27.746195 s, -56.107825 s, × 0.3309


Below is a table comparing the runtime of the current "filelog centric"
algorithm, with the "changeset centric" one, we just modified.

The changeset centric algorithm is a significant win in many scenario, but they
are still various cases where it is quite slower. When many revision  has to be
considered the cost of retrieving the copy information, creating new
dictionaries, merging dictionaries and checking if revision are ancestors of
each other can slow things down.

The rest of this series, will introduce a rust version of the copy tracing code
to deal with most of theses issues.


Repo            Case                                  Source-Rev   Dest-Rev         filelog     sidedata      Difference       Factor
---------------------------------------------------------------------------------------------------------------------------------------
mercurial       x_revs_x_added_0_copies               ad6b123de1c7 39cfcef4f463 :  0.000914 s,  0.000044 s, - 0.000870 s,    × 0.048140
mercurial       x_revs_x_added_x_copies               2b1c78674230 0c1d10351869 :  0.001812 s,  0.000138 s, - 0.001674 s,    × 0.076159
mercurial       x000_revs_x000_added_x_copies         81f8ff2a9bf2 dd3267698d84 :  0.017954 s,  0.005052 s, - 0.012902 s,    × 0.281386
pypy            x_revs_x_added_0_copies               aed021ee8ae8 099ed31b181b :  0.001509 s,  0.000219 s, - 0.001290 s,    × 0.145129
pypy            x_revs_x000_added_0_copies            4aa4e1f8e19a 359343b9ac0e :  0.206881 s,  0.000055 s, - 0.206826 s,    × 0.000266
pypy            x_revs_x_added_x_copies               ac52eb7bbbb0 72e022663155 :  0.016951 s,  0.000128 s, - 0.016823 s,    × 0.007551
pypy            x_revs_x00_added_x_copies             c3b14617fbd7 ace7255d9a26 :  0.019096 s,  0.001089 s, - 0.018007 s,    × 0.057028
pypy            x_revs_x000_added_x000_copies         df6f7a526b60 a83dc6a2d56f :  0.762506 s,  0.017407 s, - 0.745099 s,    × 0.022829
pypy            x000_revs_xx00_added_0_copies         89a76aede314 2f22446ff07e :  1.179211 s,  0.094175 s, - 1.085036 s,    × 0.079863
pypy            x000_revs_x000_added_x_copies         8a3b5bfd266e 2c68e87c3efe :  1.249058 s,  0.238009 s, - 1.011049 s,    × 0.190551
pypy            x000_revs_x000_added_x000_copies      89a76aede314 7b3dda341c84 :  1.614107 s,  0.125876 s, - 1.488231 s,    × 0.077985
pypy            x0000_revs_x_added_0_copies           d1defd0dc478 c9cb1334cc78 :  0.001064 s,  3.581556 s, + 3.580492 s, × 3366.124060
pypy            x0000_revs_xx000_added_0_copies       bf2c629d0071 4ffed77c095c :  1.061275 s,  0.016721 s, - 1.044554 s,    × 0.015756
pypy            x0000_revs_xx000_added_x000_copies    08ea3258278e d9fa043f30c0 :  1.341119 s,  0.242367 s, - 1.098752 s,    × 0.180720
netbeans        x_revs_x_added_0_copies               fb0955ffcbcd a01e9239f9e7 :  0.027803 s,  0.000165 s, - 0.027638 s,    × 0.005935
netbeans        x_revs_x000_added_0_copies            6f360122949f 20eb231cc7d0 :  0.130014 s,  0.000114 s, - 0.129900 s,    × 0.000877
netbeans        x_revs_x_added_x_copies               1ada3faf6fb6 5a39d12eecf4 :  0.024990 s,  0.000296 s, - 0.024694 s,    × 0.011845
netbeans        x_revs_x00_added_x_copies             35be93ba1e2c 9eec5e90c05f :  0.052201 s,  0.001124 s, - 0.051077 s,    × 0.021532
netbeans        x000_revs_xx00_added_0_copies         eac3045b4fdd 51d4ae7f1290 :  0.037642 s,  0.013060 s, - 0.024582 s,    × 0.346953
netbeans        x000_revs_x000_added_x_copies         e2063d266acd 6081d72689dc :  0.197086 s,  0.017112 s, - 0.179974 s,    × 0.086825
netbeans        x000_revs_x000_added_x000_copies      ff453e9fee32 411350406ec2 :  0.935148 s,  0.660350 s, - 0.274798 s,    × 0.706145
netbeans        x0000_revs_xx000_added_x000_copies    588c2d1ced70 1aad62e59ddd :  3.920674 s, 10.032499 s, + 6.111825 s,    × 2.558871
mozilla-central x_revs_x_added_0_copies               3697f962bb7b 7015fcdd43a2 :  0.024232 s,  0.000189 s, - 0.024043 s,    × 0.007800
mozilla-central x_revs_x000_added_0_copies            dd390860c6c9 40d0c5bed75d :  0.141483 s,  0.000462 s, - 0.141021 s,    × 0.003265
mozilla-central x_revs_x_added_x_copies               8d198483ae3b 14207ffc2b2f :  0.025775 s,  0.000270 s, - 0.025505 s,    × 0.010475
mozilla-central x_revs_x00_added_x_copies             98cbc58cc6bc 446a150332c3 :  0.084922 s,  0.001474 s, - 0.083448 s,    × 0.017357
mozilla-central x_revs_x000_added_x000_copies         3c684b4b8f68 0a5e72d1b479 :  0.194784 s,  0.004806 s, - 0.189978 s,    × 0.024673
mozilla-central x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :  2.161103 s,  0.085150 s, - 2.075953 s,    × 0.039401
mozilla-central x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :  0.089347 s,  0.007064 s, - 0.082283 s,    × 0.079063
mozilla-central x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :  0.732171 s,  0.004741 s, - 0.727430 s,    × 0.006475
mozilla-central x000_revs_x000_added_x000_copies      7c97034feb78 4407bd0c6330 :  1.157287 s,  0.190133 s, - 0.967154 s,    × 0.164292
mozilla-central x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :  6.726568 s,  0.035651 s, - 6.690917 s,    × 0.005300
mozilla-central x0000_revs_xx000_added_x000_copies    f78c615a656c 96a38b690156 :  3.266229 s,  0.440694 s, - 2.825535 s,    × 0.134924
mozilla-central x00000_revs_x0000_added_x0000_copies  6832ae71433c 4c222a1d9a00 : 15.860534 s, 18.454163 s, + 2.593629 s,    × 1.163527
mozilla-central x00000_revs_x00000_added_x000_copies  76caed42cf7c 1daa622bbe42 : 20.450475 s, 31.562719 s, +11.112244 s,    × 1.543373
mozilla-try     x_revs_x_added_0_copies               aaf6dde0deb8 9790f499805a :  0.080442 s,  0.001189 s, - 0.079253 s,    × 0.014781
mozilla-try     x_revs_x000_added_0_copies            d8d0222927b4 5bb8ce8c7450 :  0.497672 s,  0.001204 s, - 0.496468 s,    × 0.002419
mozilla-try     x_revs_x_added_x_copies               092fcca11bdb 936255a0384a :  0.021183 s,  0.000586 s, - 0.020597 s,    × 0.027664
mozilla-try     x_revs_x00_added_x_copies             b53d2fadbdb5 017afae788ec :  0.230991 s,  0.001845 s, - 0.229146 s,    × 0.007987
mozilla-try     x_revs_x000_added_x000_copies         20408ad61ce5 6f0ee96e21ad :  1.118461 s,  0.063822 s, - 1.054639 s,    × 0.057062
mozilla-try     x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :  2.206083 s,  0.088038 s, - 2.118045 s,    × 0.039907
mozilla-try     x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :  0.089404 s,  0.007389 s, - 0.082015 s,    × 0.082647
mozilla-try     x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :  0.733043 s,  0.004868 s, - 0.728175 s,    × 0.006641
mozilla-try     x000_revs_x000_added_x000_copies      1346fd0130e4 4c65cbdabc1f :  1.163367 s,  0.222450 s, - 0.940917 s,    × 0.191212
mozilla-try     x0000_revs_x_added_0_copies           63519bfd42ee a36a2a865d92 :  0.085456 s,  0.370675 s, + 0.285219 s,    × 4.337612
mozilla-try     x0000_revs_x_added_x_copies           9fe69ff0762d bcabf2a78927 :  0.083601 s,  0.358020 s, + 0.274419 s,    × 4.282485
mozilla-try     x0000_revs_xx000_added_x_copies       156f6e2674f2 4d0f2c178e66 :  7.366614 s,  0.145235 s, - 7.221379 s,    × 0.019715
mozilla-try     x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :  6.664464 s,  0.037606 s, - 6.626858 s,    × 0.005643
mozilla-try     x0000_revs_xx000_added_x000_copies    89294cd501d9 7ccb2fc7ccb5 :  7.467836 s,  7.382439 s, - 0.085397 s,    × 0.988565
mozilla-try     x0000_revs_x0000_added_x0000_copies   e928c65095ed e951f4ad123a :  9.801294 s,  7.273506 s, - 2.527788 s,    × 0.742097
mozilla-try     x00000_revs_x_added_0_copies          6a320851d377 1ebb79acd503 :  0.091886 s, killed
mozilla-try     x00000_revs_x00000_added_0_copies     dc8a3ca7010e d16fde900c9c : 26.491140 s,  1.074593 s, -25.416547 s,    × 0.040564
mozilla-try     x00000_revs_x_added_x_copies          5173c4b6f97c 95d83ee7242d :  0.092863 s, killed
mozilla-try     x00000_revs_x000_added_x_copies       9126823d0e9c ca82787bb23c :  0.226823 s, killed
mozilla-try     x00000_revs_x0000_added_x0000_copies  8d3fafa80d4b eb884023b810 : 18.914630 s, 27.746195 s, + 8.831565 s,    × 1.466917
mozilla-try     x00000_revs_x00000_added_x0000_copies 1b661134e2ca 1ae03d022d6d : 21.198903 s, killed
mozilla-try     x00000_revs_x00000_added_x000_copies  9b2a99adc05e 8e29777b48e6 : 24.952268 s, killed

Differential Revision: https://phab.mercurial-scm.org/D9296

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


from .utils import stringutil

from .revlogutils import flagutil


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() == 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):
    """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 = {}

    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 != node.nullrev and p2 != node.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 (node.nullrev, b.rev()):
        return {}

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

    cl = repo.changelog
    isancestor = cached_is_ancestor(cl.isancestorrev)
    missingrevs = cl.findmissingrevs(common=[a.rev()], heads=[b.rev()])
    mrset = set(missingrevs)
    roots = set()
    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)
            if p not in mrset:
                roots.add(p)
    if not roots:
        # no common revision to track copies from
        return {}
    min_root = min(roots)

    from_head = set(
        cl.reachableroots(min_root, [b.rev()], list(roots), includepath=True)
    )

    iterrevs = set(from_head)
    iterrevs &= mrset
    iterrevs.update(roots)
    iterrevs.remove(b.rev())
    revs = sorted(iterrevs)

    if repo.filecopiesmode == b'changeset-sidedata':
        revinfo = _revinfo_getter(repo)
        return _combine_changeset_copies(
            revs, children, b.rev(), revinfo, match, isancestor
        )
    else:
        revinfo = _revinfo_getter_extra(repo)
        return _combine_changeset_copies_extra(
            revs, children, b.rev(), revinfo, match, isancestor
        )


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

    revs: sorted iterable of revision to visit
    children: a {parent: [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`.
    """
    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, changes = revinfo(c)
            childcopies = {}
            if r == p1:
                parent = 1
                if changes is not None:
                    childcopies = changes.copied_from_p1
            else:
                assert r == p2
                parent = 2
                if changes is not None:
                    childcopies = changes.copied_from_p2
            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
            if changes is not None:
                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] = (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(
                        othercopies, newcopies, isancestor, changes
                    )
                else:
                    _merge_copies_dict(
                        newcopies, othercopies, isancestor, changes
                    )
                    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(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,
    """
    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


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 != node.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() != 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 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
    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)))

    if repo.ui.debugflag:
        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, u2)
    dirmove2, movewithdir1 = _dir_renames(repo, c2, copy2, copies2, u1)

    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, addedfiles):
    """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
    addedfiles: added files on the other side (compared to ctx)
    """
    # generate a directory move map
    d = ctx.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 d and ddst in d:
            # 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 d, 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 addedfiles:
        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)