annotate mercurial/filemerge.py @ 45972:8b99c473aae2

copies-rust: move is_ancestor caching within the rust code

Now that the OrdMap merging is fast, smaller things start to matters.

We move the caching of `is_ancestor` call within the Rust code. This avoid
round-trip to Python and help us to shave more time on our slower case:

Repo            Cases                                 Source-Rev   Dest-Rev         Old-Time      New-Time     Difference   Factor
------------------------------------------------------------------------------------------------------------------------------------
pypy            x0000_revs_x_added_0_copies           d1defd0dc478 c9cb1334cc78 :   2.780174 s,   2.137894 s,  -0.642280 s, × 0.7690
mozilla-try     x0000_revs_xx000_added_x000_copies    89294cd501d9 7ccb2fc7ccb5 :   9.843481 s,   8.100385 s,  -1.743096 s, × 0.8229


Note: I would happily have used native code for ancestors computation, however
I failed (did not tried hard) to created a rust version that goes as fast as
the current C version.

Below are full tables for:
- this change compared to the previous change
- this change compared to filelog performance

Repo            Cases                                 Source-Rev   Dest-Rev         Old-Time      New-Time     Difference   Factor
------------------------------------------------------------------------------------------------------------------------------------
mercurial       x_revs_x_added_0_copies               ad6b123de1c7 39cfcef4f463 :   0.000049 s,   0.000047 s,  -0.000002 s, × 0.9592
mercurial       x_revs_x_added_x_copies               2b1c78674230 0c1d10351869 :   0.000182 s,   0.000181 s,  -0.000001 s, × 0.9945
mercurial       x000_revs_x000_added_x_copies         81f8ff2a9bf2 dd3267698d84 :   0.005872 s,   0.005852 s,  -0.000020 s, × 0.9966
pypy            x_revs_x_added_0_copies               aed021ee8ae8 099ed31b181b :   0.000229 s,   0.000229 s,  +0.000000 s, × 1.0000
pypy            x_revs_x000_added_0_copies            4aa4e1f8e19a 359343b9ac0e :   0.000058 s,   0.000058 s,  +0.000000 s, × 1.0000
pypy            x_revs_x_added_x_copies               ac52eb7bbbb0 72e022663155 :   0.000148 s,   0.000146 s,  -0.000002 s, × 0.9865
pypy            x_revs_x00_added_x_copies             c3b14617fbd7 ace7255d9a26 :   0.001205 s,   0.001206 s,  +0.000001 s, × 1.0008
pypy            x_revs_x000_added_x000_copies         df6f7a526b60 a83dc6a2d56f :   0.025662 s,   0.025275 s,  -0.000387 s, × 0.9849
pypy            x000_revs_xx00_added_0_copies         89a76aede314 2f22446ff07e :   0.080113 s,   0.080303 s,  +0.000190 s, × 1.0024
pypy            x000_revs_x000_added_x_copies         8a3b5bfd266e 2c68e87c3efe :   0.153030 s,   0.152641 s,  -0.000389 s, × 0.9975
pypy            x000_revs_x000_added_x000_copies      89a76aede314 7b3dda341c84 :   0.098774 s,   0.099107 s,  +0.000333 s, × 1.0034
pypy            x0000_revs_x_added_0_copies           d1defd0dc478 c9cb1334cc78 :   2.780174 s,   2.137894 s,  -0.642280 s, × 0.7690
pypy            x0000_revs_xx000_added_0_copies       bf2c629d0071 4ffed77c095c :   0.022218 s,   0.022202 s,  -0.000016 s, × 0.9993
pypy            x0000_revs_xx000_added_x000_copies    08ea3258278e d9fa043f30c0 :   0.252125 s,   0.228946 s,  -0.023179 s, × 0.9081
netbeans        x_revs_x_added_0_copies               fb0955ffcbcd a01e9239f9e7 :   0.000186 s,   0.000186 s,  +0.000000 s, × 1.0000
netbeans        x_revs_x000_added_0_copies            6f360122949f 20eb231cc7d0 :   0.000133 s,   0.000133 s,  +0.000000 s, × 1.0000
netbeans        x_revs_x_added_x_copies               1ada3faf6fb6 5a39d12eecf4 :   0.000320 s,   0.000320 s,  +0.000000 s, × 1.0000
netbeans        x_revs_x00_added_x_copies             35be93ba1e2c 9eec5e90c05f :   0.001336 s,   0.001339 s,  +0.000003 s, × 1.0022
netbeans        x000_revs_xx00_added_0_copies         eac3045b4fdd 51d4ae7f1290 :   0.015573 s,   0.015694 s,  +0.000121 s, × 1.0078
netbeans        x000_revs_x000_added_x_copies         e2063d266acd 6081d72689dc :   0.018667 s,   0.018457 s,  -0.000210 s, × 0.9888
netbeans        x000_revs_x000_added_x000_copies      ff453e9fee32 411350406ec2 :   0.112534 s,   0.111691 s,  -0.000843 s, × 0.9925
netbeans        x0000_revs_xx000_added_x000_copies    588c2d1ced70 1aad62e59ddd :   1.231869 s,   1.166017 s,  -0.065852 s, × 0.9465
mozilla-central x_revs_x_added_0_copies               3697f962bb7b 7015fcdd43a2 :   0.000197 s,   0.000197 s,  +0.000000 s, × 1.0000
mozilla-central x_revs_x000_added_0_copies            dd390860c6c9 40d0c5bed75d :   0.000637 s,   0.000626 s,  -0.000011 s, × 0.9827
mozilla-central x_revs_x_added_x_copies               8d198483ae3b 14207ffc2b2f :   0.000303 s,   0.000303 s,  +0.000000 s, × 1.0000
mozilla-central x_revs_x00_added_x_copies             98cbc58cc6bc 446a150332c3 :   0.001663 s,   0.001679 s,  +0.000016 s, × 1.0096
mozilla-central x_revs_x000_added_x000_copies         3c684b4b8f68 0a5e72d1b479 :   0.007008 s,   0.006947 s,  -0.000061 s, × 0.9913
mozilla-central x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :   0.127385 s,   0.133070 s,  +0.005685 s, × 1.0446
mozilla-central x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :   0.008740 s,   0.008705 s,  -0.000035 s, × 0.9960
mozilla-central x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :   0.005783 s,   0.005913 s,  +0.000130 s, × 1.0225
mozilla-central x000_revs_x000_added_x000_copies      7c97034feb78 4407bd0c6330 :   0.102184 s,   0.101373 s,  -0.000811 s, × 0.9921
mozilla-central x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :   0.046220 s,   0.046526 s,  +0.000306 s, × 1.0066
mozilla-central x0000_revs_xx000_added_x000_copies    f78c615a656c 96a38b690156 :   0.315271 s,   0.313954 s,  -0.001317 s, × 0.9958
mozilla-central x00000_revs_x0000_added_x0000_copies  6832ae71433c 4c222a1d9a00 :   3.478747 s,   3.367395 s,  -0.111352 s, × 0.9680
mozilla-central x00000_revs_x00000_added_x000_copies  76caed42cf7c 1daa622bbe42 :   4.766435 s,   4.691820 s,  -0.074615 s, × 0.9843
mozilla-try     x_revs_x_added_0_copies               aaf6dde0deb8 9790f499805a :   0.001214 s,   0.001199 s,  -0.000015 s, × 0.9876
mozilla-try     x_revs_x000_added_0_copies            d8d0222927b4 5bb8ce8c7450 :   0.001221 s,   0.001216 s,  -0.000005 s, × 0.9959
mozilla-try     x_revs_x_added_x_copies               092fcca11bdb 936255a0384a :   0.000613 s,   0.000613 s,  +0.000000 s, × 1.0000
mozilla-try     x_revs_x00_added_x_copies             b53d2fadbdb5 017afae788ec :   0.001904 s,   0.001906 s,  +0.000002 s, × 1.0011
mozilla-try     x_revs_x000_added_x000_copies         20408ad61ce5 6f0ee96e21ad :   0.093000 s,   0.092766 s,  -0.000234 s, × 0.9975
mozilla-try     x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :   0.132194 s,   0.136074 s,  +0.003880 s, × 1.0294
mozilla-try     x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :   0.009069 s,   0.009067 s,  -0.000002 s, × 0.9998
mozilla-try     x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :   0.006169 s,   0.006243 s,  +0.000074 s, × 1.0120
mozilla-try     x000_revs_x000_added_x000_copies      1346fd0130e4 4c65cbdabc1f :   0.115540 s,   0.114463 s,  -0.001077 s, × 0.9907
mozilla-try     x0000_revs_x_added_0_copies           63519bfd42ee a36a2a865d92 :   0.435381 s,   0.433683 s,  -0.001698 s, × 0.9961
mozilla-try     x0000_revs_x_added_x_copies           9fe69ff0762d bcabf2a78927 :   0.415461 s,   0.411278 s,  -0.004183 s, × 0.9899
mozilla-try     x0000_revs_xx000_added_x_copies       156f6e2674f2 4d0f2c178e66 :   0.155946 s,   0.155133 s,  -0.000813 s, × 0.9948
mozilla-try     x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :   0.048521 s,   0.048933 s,  +0.000412 s, × 1.0085
mozilla-try     x0000_revs_xx000_added_x000_copies    89294cd501d9 7ccb2fc7ccb5 :   9.843481 s,   8.100385 s,  -1.743096 s, × 0.8229
mozilla-try     x0000_revs_x0000_added_x0000_copies   e928c65095ed e951f4ad123a :   1.465128 s,   1.446720 s,  -0.018408 s, × 0.9874
mozilla-try     x00000_revs_x00000_added_0_copies     dc8a3ca7010e d16fde900c9c :   1.374283 s,   1.369537 s,  -0.004746 s, × 0.9965
mozilla-try     x00000_revs_x0000_added_x0000_copies  8d3fafa80d4b eb884023b810 :   5.255158 s,   5.186079 s,  -0.069079 s, × 0.9869

Repo            Case                                  Source-Rev   Dest-Rev        filelog     sidedata     Difference    Factor
--------------------------------------------------------------------------------------------------------------------------------------
mercurial       x_revs_x_added_0_copies               ad6b123de1c7 39cfcef4f463 :  0.000892 s, 0.000047 s,  -0.000845 s,    × 0.052691
mercurial       x_revs_x_added_x_copies               2b1c78674230 0c1d10351869 :  0.001823 s, 0.000181 s,  -0.001642 s,    × 0.099287
mercurial       x000_revs_x000_added_x_copies         81f8ff2a9bf2 dd3267698d84 :  0.018063 s, 0.005852 s,  -0.012211 s,    × 0.323977
pypy            x_revs_x_added_0_copies               aed021ee8ae8 099ed31b181b :  0.001505 s, 0.000229 s,  -0.001276 s,    × 0.152159
pypy            x_revs_x000_added_0_copies            4aa4e1f8e19a 359343b9ac0e :  0.205895 s, 0.000058 s,  -0.205837 s,    × 0.000282
pypy            x_revs_x_added_x_copies               ac52eb7bbbb0 72e022663155 :  0.017021 s, 0.000146 s,  -0.016875 s,    × 0.008578
pypy            x_revs_x00_added_x_copies             c3b14617fbd7 ace7255d9a26 :  0.019422 s, 0.001206 s,  -0.018216 s,    × 0.062095
pypy            x_revs_x000_added_x000_copies         df6f7a526b60 a83dc6a2d56f :  0.767740 s, 0.025275 s,  -0.742465 s,    × 0.032921
pypy            x000_revs_xx00_added_0_copies         89a76aede314 2f22446ff07e :  1.188515 s, 0.080303 s,  -1.108212 s,    × 0.067566
pypy            x000_revs_x000_added_x_copies         8a3b5bfd266e 2c68e87c3efe :  1.251968 s, 0.152641 s,  -1.099327 s,    × 0.121921
pypy            x000_revs_x000_added_x000_copies      89a76aede314 7b3dda341c84 :  1.616799 s, 0.099107 s,  -1.517692 s,    × 0.061298
pypy            x0000_revs_x_added_0_copies           d1defd0dc478 c9cb1334cc78 :  0.001057 s, 2.137894 s,  +2.136837 s, × 2022.605487
pypy            x0000_revs_xx000_added_0_copies       bf2c629d0071 4ffed77c095c :  1.069485 s, 0.022202 s,  -1.047283 s,    × 0.020760
pypy            x0000_revs_xx000_added_x000_copies    08ea3258278e d9fa043f30c0 :  1.350162 s, 0.228946 s,  -1.121216 s,    × 0.169569
netbeans        x_revs_x_added_0_copies               fb0955ffcbcd a01e9239f9e7 :  0.028008 s, 0.000186 s,  -0.027822 s,    × 0.006641
netbeans        x_revs_x000_added_0_copies            6f360122949f 20eb231cc7d0 :  0.132281 s, 0.000133 s,  -0.132148 s,    × 0.001005
netbeans        x_revs_x_added_x_copies               1ada3faf6fb6 5a39d12eecf4 :  0.025311 s, 0.000320 s,  -0.024991 s,    × 0.012643
netbeans        x_revs_x00_added_x_copies             35be93ba1e2c 9eec5e90c05f :  0.052957 s, 0.001339 s,  -0.051618 s,    × 0.025285
netbeans        x000_revs_xx00_added_0_copies         eac3045b4fdd 51d4ae7f1290 :  0.038011 s, 0.015694 s,  -0.022317 s,    × 0.412880
netbeans        x000_revs_x000_added_x_copies         e2063d266acd 6081d72689dc :  0.198639 s, 0.018457 s,  -0.180182 s,    × 0.092917
netbeans        x000_revs_x000_added_x000_copies      ff453e9fee32 411350406ec2 :  0.955713 s, 0.111691 s,  -0.844022 s,    × 0.116867
netbeans        x0000_revs_xx000_added_x000_copies    588c2d1ced70 1aad62e59ddd :  3.838886 s, 1.166017 s,  -2.672869 s,    × 0.303738
mozilla-central x_revs_x_added_0_copies               3697f962bb7b 7015fcdd43a2 :  0.024548 s, 0.000197 s,  -0.024351 s,    × 0.008025
mozilla-central x_revs_x000_added_0_copies            dd390860c6c9 40d0c5bed75d :  0.143394 s, 0.000626 s,  -0.142768 s,    × 0.004366
mozilla-central x_revs_x_added_x_copies               8d198483ae3b 14207ffc2b2f :  0.026046 s, 0.000303 s,  -0.025743 s,    × 0.011633
mozilla-central x_revs_x00_added_x_copies             98cbc58cc6bc 446a150332c3 :  0.085440 s, 0.001679 s,  -0.083761 s,    × 0.019651
mozilla-central x_revs_x000_added_x000_copies         3c684b4b8f68 0a5e72d1b479 :  0.195656 s, 0.006947 s,  -0.188709 s,    × 0.035506
mozilla-central x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :  2.190874 s, 0.133070 s,  -2.057804 s,    × 0.060738
mozilla-central x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :  0.090208 s, 0.008705 s,  -0.081503 s,    × 0.096499
mozilla-central x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :  0.747367 s, 0.005913 s,  -0.741454 s,    × 0.007912
mozilla-central x000_revs_x000_added_x000_copies      7c97034feb78 4407bd0c6330 :  1.152863 s, 0.101373 s,  -1.051490 s,    × 0.087932
mozilla-central x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :  6.598336 s, 0.046526 s,  -6.551810 s,    × 0.007051
mozilla-central x0000_revs_xx000_added_x000_copies    f78c615a656c 96a38b690156 :  3.255015 s, 0.313954 s,  -2.941061 s,    × 0.096452
mozilla-central x00000_revs_x0000_added_x0000_copies  6832ae71433c 4c222a1d9a00 : 15.668041 s, 3.367395 s, -12.300646 s,    × 0.214921
mozilla-central x00000_revs_x00000_added_x000_copies  76caed42cf7c 1daa622bbe42 : 20.439638 s, 4.691820 s, -15.747818 s,    × 0.229545
mozilla-try     x_revs_x_added_0_copies               aaf6dde0deb8 9790f499805a :  0.080923 s, 0.001199 s,  -0.079724 s,    × 0.014817
mozilla-try     x_revs_x000_added_0_copies            d8d0222927b4 5bb8ce8c7450 :  0.498456 s, 0.001216 s,  -0.497240 s,    × 0.002440
mozilla-try     x_revs_x_added_x_copies               092fcca11bdb 936255a0384a :  0.020798 s, 0.000613 s,  -0.020185 s,    × 0.029474
mozilla-try     x_revs_x00_added_x_copies             b53d2fadbdb5 017afae788ec :  0.226930 s, 0.001906 s,  -0.225024 s,    × 0.008399
mozilla-try     x_revs_x000_added_x000_copies         20408ad61ce5 6f0ee96e21ad :  1.113005 s, 0.092766 s,  -1.020239 s,    × 0.083347
mozilla-try     x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :  2.230671 s, 0.136074 s,  -2.094597 s,    × 0.061001
mozilla-try     x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :  0.089672 s, 0.009067 s,  -0.080605 s,    × 0.101113
mozilla-try     x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :  0.740221 s, 0.006243 s,  -0.733978 s,    × 0.008434
mozilla-try     x000_revs_x000_added_x000_copies      1346fd0130e4 4c65cbdabc1f :  1.185881 s, 0.114463 s,  -1.071418 s,    × 0.096521
mozilla-try     x0000_revs_x_added_0_copies           63519bfd42ee a36a2a865d92 :  0.086072 s, 0.433683 s,  +0.347611 s,    × 5.038607
mozilla-try     x0000_revs_x_added_x_copies           9fe69ff0762d bcabf2a78927 :  0.081321 s, 0.411278 s,  +0.329957 s,    × 5.057464
mozilla-try     x0000_revs_xx000_added_x_copies       156f6e2674f2 4d0f2c178e66 :  7.528370 s, 0.155133 s,  -7.373237 s,    × 0.020606
mozilla-try     x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :  6.757368 s, 0.048933 s,  -6.708435 s,    × 0.007241
mozilla-try     x0000_revs_xx000_added_x000_copies    89294cd501d9 7ccb2fc7ccb5 :  7.643752 s, 8.100385 s,  +0.456633 s,    × 1.059739
mozilla-try     x0000_revs_x0000_added_x0000_copies   e928c65095ed e951f4ad123a :  9.704242 s, 1.446720 s,  -8.257522 s,    × 0.149081
mozilla-try     x00000_revs_x_added_0_copies          6a320851d377 1ebb79acd503 :  0.092845 s, killed
mozilla-try     x00000_revs_x00000_added_0_copies     dc8a3ca7010e d16fde900c9c : 26.626870 s, 1.369537 s, -25.257333 s,    × 0.051434
mozilla-try     x00000_revs_x_added_x_copies          5173c4b6f97c 95d83ee7242d :  0.092953 s, killed
mozilla-try     x00000_revs_x000_added_x_copies       9126823d0e9c ca82787bb23c :  0.227131 s, killed
mozilla-try     x00000_revs_x0000_added_x0000_copies  8d3fafa80d4b eb884023b810 : 18.884666 s, 5.186079 s, -13.698587 s,    × 0.274619
mozilla-try     x00000_revs_x00000_added_x0000_copies 1b661134e2ca 1ae03d022d6d : 21.451622 s, killed
mozilla-try     x00000_revs_x00000_added_x000_copies  9b2a99adc05e 8e29777b48e6 : 25.152558 s, killed

Differential Revision: https://phab.mercurial-scm.org/D9303

# filemerge.py - file-level merge handling for Mercurial
#
# Copyright 2006, 2007, 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 contextlib
import os
import re
import shutil

from .i18n import _
from .node import (
    hex,
    nullid,
    short,
)
from .pycompat import (
    getattr,
    open,
)

from . import (
    encoding,
    error,
    formatter,
    match,
    pycompat,
    registrar,
    scmutil,
    simplemerge,
    tagmerge,
    templatekw,
    templater,
    templateutil,
    util,
)

from .utils import (
    procutil,
    stringutil,
)


def _toolstr(ui, tool, part, *args):
    return ui.config(b"merge-tools", tool + b"." + part, *args)


def _toolbool(ui, tool, part, *args):
    return ui.configbool(b"merge-tools", tool + b"." + part, *args)


def _toollist(ui, tool, part):
    return ui.configlist(b"merge-tools", tool + b"." + part)


internals = {}
# Merge tools to document.
internalsdoc = {}

internaltool = registrar.internalmerge()

# internal tool merge types
nomerge = internaltool.nomerge
mergeonly = internaltool.mergeonly  # just the full merge, no premerge
fullmerge = internaltool.fullmerge  # both premerge and merge

# IMPORTANT: keep the last line of this prompt very short ("What do you want to
# do?") because of issue6158, ideally to <40 English characters (to allow other
# languages that may take more columns to still have a chance to fit in an
# 80-column screen).
_localchangedotherdeletedmsg = _(
    b"file '%(fd)s' was deleted in other%(o)s but was modified in local%(l)s.\n"
    b"You can use (c)hanged version, (d)elete, or leave (u)nresolved.\n"
    b"What do you want to do?"
    b"$$ &Changed $$ &Delete $$ &Unresolved"
)

_otherchangedlocaldeletedmsg = _(
    b"file '%(fd)s' was deleted in local%(l)s but was modified in other%(o)s.\n"
    b"You can use (c)hanged version, leave (d)eleted, or leave (u)nresolved.\n"
    b"What do you want to do?"
    b"$$ &Changed $$ &Deleted $$ &Unresolved"
)


class absentfilectx(object):
    """Represents a file that's ostensibly in a context but is actually not
    present in it.

    This is here because it's very specific to the filemerge code for now --
    other code is likely going to break with the values this returns."""

    def __init__(self, ctx, f):
        self._ctx = ctx
        self._f = f

    def __bytes__(self):
        return b'absent file %s@%s' % (self._f, self._ctx)

    def path(self):
        return self._f

    def size(self):
        return None

    def data(self):
        return None

    def filenode(self):
        return nullid

    _customcmp = True

    def cmp(self, fctx):
        """compare with other file context

        returns True if different from fctx.
        """
        return not (
            fctx.isabsent()
            and fctx.changectx() == self.changectx()
            and fctx.path() == self.path()
        )

    def flags(self):
        return b''

    def changectx(self):
        return self._ctx

    def isbinary(self):
        return False

    def isabsent(self):
        return True


def _findtool(ui, tool):
    if tool in internals:
        return tool
    cmd = _toolstr(ui, tool, b"executable", tool)
    if cmd.startswith(b'python:'):
        return cmd
    return findexternaltool(ui, tool)


def _quotetoolpath(cmd):
    if cmd.startswith(b'python:'):
        return cmd
    return procutil.shellquote(cmd)


def findexternaltool(ui, tool):
    for kn in (b"regkey", b"regkeyalt"):
        k = _toolstr(ui, tool, kn)
        if not k:
            continue
        p = util.lookupreg(k, _toolstr(ui, tool, b"regname"))
        if p:
            p = procutil.findexe(p + _toolstr(ui, tool, b"regappend", b""))
            if p:
                return p
    exe = _toolstr(ui, tool, b"executable", tool)
    return procutil.findexe(util.expandpath(exe))


def _picktool(repo, ui, path, binary, symlink, changedelete):
    strictcheck = ui.configbool(b'merge', b'strict-capability-check')

    def hascapability(tool, capability, strict=False):
        if tool in internals:
            return strict and internals[tool].capabilities.get(capability)
        return _toolbool(ui, tool, capability)

    def supportscd(tool):
        return tool in internals and internals[tool].mergetype == nomerge

    def check(tool, pat, symlink, binary, changedelete):
        tmsg = tool
        if pat:
            tmsg = _(b"%s (for pattern %s)") % (tool, pat)
        if not _findtool(ui, tool):
            if pat:  # explicitly requested tool deserves a warning
                ui.warn(_(b"couldn't find merge tool %s\n") % tmsg)
            else:  # configured but non-existing tools are more silent
                ui.note(_(b"couldn't find merge tool %s\n") % tmsg)
        elif symlink and not hascapability(tool, b"symlink", strictcheck):
            ui.warn(_(b"tool %s can't handle symlinks\n") % tmsg)
        elif binary and not hascapability(tool, b"binary", strictcheck):
            ui.warn(_(b"tool %s can't handle binary\n") % tmsg)
        elif changedelete and not supportscd(tool):
            # the nomerge tools are the only tools that support change/delete
            # conflicts
            pass
        elif not procutil.gui() and _toolbool(ui, tool, b"gui"):
            ui.warn(_(b"tool %s requires a GUI\n") % tmsg)
        else:
            return True
        return False

    # internal config: ui.forcemerge
    # forcemerge comes from command line arguments, highest priority
    force = ui.config(b'ui', b'forcemerge')
    if force:
        toolpath = _findtool(ui, force)
        if changedelete and not supportscd(toolpath):
            return b":prompt", None
        else:
            if toolpath:
                return (force, _quotetoolpath(toolpath))
            else:
                # mimic HGMERGE if given tool not found
                return (force, force)

    # HGMERGE takes next precedence
    hgmerge = encoding.environ.get(b"HGMERGE")
    if hgmerge:
        if changedelete and not supportscd(hgmerge):
            return b":prompt", None
        else:
            return (hgmerge, hgmerge)

    # then patterns

    # whether binary capability should be checked strictly
    binarycap = binary and strictcheck

    for pat, tool in ui.configitems(b"merge-patterns"):
        mf = match.match(repo.root, b'', [pat])
        if mf(path) and check(tool, pat, symlink, binarycap, changedelete):
            if binary and not hascapability(tool, b"binary", strict=True):
                ui.warn(
                    _(
                        b"warning: check merge-patterns configurations,"
                        b" if %r for binary file %r is unintentional\n"
                        b"(see 'hg help merge-tools'"
                        b" for binary files capability)\n"
                    )
                    % (pycompat.bytestr(tool), pycompat.bytestr(path))
                )
            toolpath = _findtool(ui, tool)
            return (tool, _quotetoolpath(toolpath))

    # then merge tools
    tools = {}
    disabled = set()
    for k, v in ui.configitems(b"merge-tools"):
        t = k.split(b'.')[0]
        if t not in tools:
            tools[t] = int(_toolstr(ui, t, b"priority"))
        if _toolbool(ui, t, b"disabled"):
            disabled.add(t)
    names = tools.keys()
    tools = sorted(
        [(-p, tool) for tool, p in tools.items() if tool not in disabled]
    )
    uimerge = ui.config(b"ui", b"merge")
    if uimerge:
        # external tools defined in uimerge won't be able to handle
        # change/delete conflicts
        if check(uimerge, path, symlink, binary, changedelete):
            if uimerge not in names and not changedelete:
                return (uimerge, uimerge)
            tools.insert(0, (None, uimerge))  # highest priority
    tools.append((None, b"hgmerge"))  # the old default, if found
    for p, t in tools:
        if check(t, None, symlink, binary, changedelete):
            toolpath = _findtool(ui, t)
            return (t, _quotetoolpath(toolpath))

    # internal merge or prompt as last resort
    if symlink or binary or changedelete:
        if not changedelete and len(tools):
            # any tool is rejected by capability for symlink or binary
            ui.warn(_(b"no tool found to merge %s\n") % path)
        return b":prompt", None
    return b":merge", None


def _eoltype(data):
    """Guess the EOL type of a file"""
    if b'\0' in data:  # binary
        return None
    if b'\r\n' in data:  # Windows
        return b'\r\n'
    if b'\r' in data:  # Old Mac
        return b'\r'
    if b'\n' in data:  # UNIX
        return b'\n'
    return None  # unknown


def _matcheol(file, back):
    """Convert EOL markers in a file to match origfile"""
    tostyle = _eoltype(back.data())  # No repo.wread filters?
    if tostyle:
        data = util.readfile(file)
        style = _eoltype(data)
        if style:
            newdata = data.replace(style, tostyle)
            if newdata != data:
                util.writefile(file, newdata)


@internaltool(b'prompt', nomerge)
def _iprompt(repo, mynode, orig, fcd, fco, fca, toolconf, labels=None):
    """Asks the user which of the local `p1()` or the other `p2()` version to
    keep as the merged version."""
    ui = repo.ui
    fd = fcd.path()
    uipathfn = scmutil.getuipathfn(repo)

    # Avoid prompting during an in-memory merge since it doesn't support merge
    # conflicts.
    if fcd.changectx().isinmemory():
        raise error.InMemoryMergeConflictsError(
            b'in-memory merge does not support file conflicts'
        )

    prompts = partextras(labels)
    prompts[b'fd'] = uipathfn(fd)
    try:
        if fco.isabsent():
            index = ui.promptchoice(_localchangedotherdeletedmsg % prompts, 2)
            choice = [b'local', b'other', b'unresolved'][index]
        elif fcd.isabsent():
            index = ui.promptchoice(_otherchangedlocaldeletedmsg % prompts, 2)
            choice = [b'other', b'local', b'unresolved'][index]
        else:
            # IMPORTANT: keep the last line of this prompt ("What do you want to
            # do?") very short, see comment next to _localchangedotherdeletedmsg
            # at the top of the file for details.
            index = ui.promptchoice(
                _(
                    b"file '%(fd)s' needs to be resolved.\n"
                    b"You can keep (l)ocal%(l)s, take (o)ther%(o)s, or leave "
                    b"(u)nresolved.\n"
                    b"What do you want to do?"
                    b"$$ &Local $$ &Other $$ &Unresolved"
                )
                % prompts,
                2,
            )
            choice = [b'local', b'other', b'unresolved'][index]

        if choice == b'other':
            return _iother(repo, mynode, orig, fcd, fco, fca, toolconf, labels)
        elif choice == b'local':
            return _ilocal(repo, mynode, orig, fcd, fco, fca, toolconf, labels)
        elif choice == b'unresolved':
            return _ifail(repo, mynode, orig, fcd, fco, fca, toolconf, labels)
    except error.ResponseExpected:
        ui.write(b"\n")
        return _ifail(repo, mynode, orig, fcd, fco, fca, toolconf, labels)


@internaltool(b'local', nomerge)
def _ilocal(repo, mynode, orig, fcd, fco, fca, toolconf, labels=None):
    """Uses the local `p1()` version of files as the merged version."""
    return 0, fcd.isabsent()


@internaltool(b'other', nomerge)
def _iother(repo, mynode, orig, fcd, fco, fca, toolconf, labels=None):
    """Uses the other `p2()` version of files as the merged version."""
    if fco.isabsent():
        # local changed, remote deleted -- 'deleted' picked
        _underlyingfctxifabsent(fcd).remove()
        deleted = True
    else:
        _underlyingfctxifabsent(fcd).write(fco.data(), fco.flags())
        deleted = False
    return 0, deleted


@internaltool(b'fail', nomerge)
def _ifail(repo, mynode, orig, fcd, fco, fca, toolconf, labels=None):
    """
    Rather than attempting to merge files that were modified on both
    branches, it marks them as unresolved. The resolve command must be
    used to resolve these conflicts."""
    # for change/delete conflicts write out the changed version, then fail
    if fcd.isabsent():
        _underlyingfctxifabsent(fcd).write(fco.data(), fco.flags())
    return 1, False


def _underlyingfctxifabsent(filectx):
    """Sometimes when resolving, our fcd is actually an absentfilectx, but
    we want to write to it (to do the resolve). This helper returns the
    underyling workingfilectx in that case.
    """
    if filectx.isabsent():
        return filectx.changectx()[filectx.path()]
    else:
        return filectx


def _premerge(repo, fcd, fco, fca, toolconf, files, labels=None):
    tool, toolpath, binary, symlink, scriptfn = toolconf
    if symlink or fcd.isabsent() or fco.isabsent():
        return 1
    unused, unused, unused, back = files

    ui = repo.ui

    validkeep = [b'keep', b'keep-merge3']

    # do we attempt to simplemerge first?
    try:
        premerge = _toolbool(ui, tool, b"premerge", not binary)
    except error.ConfigError:
        premerge = _toolstr(ui, tool, b"premerge", b"").lower()
        if premerge not in validkeep:
            _valid = b', '.join([b"'" + v + b"'" for v in validkeep])
            raise error.ConfigError(
                _(b"%s.premerge not valid ('%s' is neither boolean nor %s)")
                % (tool, premerge, _valid)
            )

    if premerge:
        if premerge == b'keep-merge3':
            if not labels:
                labels = _defaultconflictlabels
            if len(labels) < 3:
                labels.append(b'base')
        r = simplemerge.simplemerge(ui, fcd, fca, fco, quiet=True, label=labels)
        if not r:
            ui.debug(b" premerge successful\n")
            return 0
        if premerge not in validkeep:
            # restore from backup and try again
            _restorebackup(fcd, back)
    return 1  # continue merging


def _mergecheck(repo, mynode, orig, fcd, fco, fca, toolconf):
    tool, toolpath, binary, symlink, scriptfn = toolconf
    uipathfn = scmutil.getuipathfn(repo)
    if symlink:
        repo.ui.warn(
            _(b'warning: internal %s cannot merge symlinks for %s\n')
            % (tool, uipathfn(fcd.path()))
        )
        return False
    if fcd.isabsent() or fco.isabsent():
        repo.ui.warn(
            _(
                b'warning: internal %s cannot merge change/delete '
                b'conflict for %s\n'
            )
            % (tool, uipathfn(fcd.path()))
        )
        return False
    return True


def _merge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels, mode):
    """
    Uses the internal non-interactive simple merge algorithm for merging
    files. It will fail if there are any conflicts and leave markers in
    the partially merged file. Markers will have two sections, one for each side
    of merge, unless mode equals 'union' which suppresses the markers."""
    ui = repo.ui

    r = simplemerge.simplemerge(ui, fcd, fca, fco, label=labels, mode=mode)
    return True, r, False


@internaltool(
    b'union',
    fullmerge,
    _(
        b"warning: conflicts while merging %s! "
        b"(edit, then use 'hg resolve --mark')\n"
    ),
    precheck=_mergecheck,
)
def _iunion(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
    """
    Uses the internal non-interactive simple merge algorithm for merging
    files. It will use both left and right sides for conflict regions.
    No markers are inserted."""
    return _merge(
        repo, mynode, orig, fcd, fco, fca, toolconf, files, labels, b'union'
    )


@internaltool(
    b'merge',
    fullmerge,
    _(
        b"warning: conflicts while merging %s! "
        b"(edit, then use 'hg resolve --mark')\n"
    ),
    precheck=_mergecheck,
)
def _imerge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
    """
    Uses the internal non-interactive simple merge algorithm for merging
    files. It will fail if there are any conflicts and leave markers in
    the partially merged file. Markers will have two sections, one for each side
    of merge."""
    return _merge(
        repo, mynode, orig, fcd, fco, fca, toolconf, files, labels, b'merge'
    )


@internaltool(
    b'merge3',
    fullmerge,
    _(
        b"warning: conflicts while merging %s! "
        b"(edit, then use 'hg resolve --mark')\n"
    ),
    precheck=_mergecheck,
)
def _imerge3(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
    """
    Uses the internal non-interactive simple merge algorithm for merging
    files. It will fail if there are any conflicts and leave markers in
    the partially merged file. Marker will have three sections, one from each
    side of the merge and one for the base content."""
    if not labels:
        labels = _defaultconflictlabels
    if len(labels) < 3:
        labels.append(b'base')
    return _imerge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels)


def _imergeauto(
    repo,
    mynode,
    orig,
    fcd,
    fco,
    fca,
    toolconf,
    files,
    labels=None,
    localorother=None,
):
    """
    Generic driver for _imergelocal and _imergeother
    """
    assert localorother is not None
    r = simplemerge.simplemerge(
        repo.ui, fcd, fca, fco, label=labels, localorother=localorother
    )
    return True, r


@internaltool(b'merge-local', mergeonly, precheck=_mergecheck)
def _imergelocal(*args, **kwargs):
    """
    Like :merge, but resolve all conflicts non-interactively in favor
    of the local `p1()` changes."""
    success, status = _imergeauto(localorother=b'local', *args, **kwargs)
    return success, status, False


@internaltool(b'merge-other', mergeonly, precheck=_mergecheck)
def _imergeother(*args, **kwargs):
    """
    Like :merge, but resolve all conflicts non-interactively in favor
    of the other `p2()` changes."""
    success, status = _imergeauto(localorother=b'other', *args, **kwargs)
    return success, status, False


@internaltool(
    b'tagmerge',
    mergeonly,
    _(
        b"automatic tag merging of %s failed! "
        b"(use 'hg resolve --tool :merge' or another merge "
        b"tool of your choice)\n"
    ),
)
def _itagmerge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
    """
    Uses the internal tag merge algorithm (experimental).
    """
    success, status = tagmerge.merge(repo, fcd, fco, fca)
    return success, status, False


@internaltool(b'dump', fullmerge, binary=True, symlink=True)
def _idump(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
    """
    Creates three versions of the files to merge, containing the
    contents of local, other and base. These files can then be used to
    perform a merge manually. If the file to be merged is named
    ``a.txt``, these files will accordingly be named ``a.txt.local``,
    ``a.txt.other`` and ``a.txt.base`` and they will be placed in the
    same directory as ``a.txt``.

    This implies premerge. Therefore, files aren't dumped, if premerge
    runs successfully. Use :forcedump to forcibly write files out.
    """
    a = _workingpath(repo, fcd)
    fd = fcd.path()

    from . import context

    if isinstance(fcd, context.overlayworkingfilectx):
        raise error.InMemoryMergeConflictsError(
            b'in-memory merge does not support the :dump tool.'
        )

    util.writefile(a + b".local", fcd.decodeddata())
    repo.wwrite(fd + b".other", fco.data(), fco.flags())
    repo.wwrite(fd + b".base", fca.data(), fca.flags())
    return False, 1, False


@internaltool(b'forcedump', mergeonly, binary=True, symlink=True)
def _forcedump(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
    """
    Creates three versions of the files as same as :dump, but omits premerge.
    """
    return _idump(
        repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=labels
    )


def _xmergeimm(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
    # In-memory merge simply raises an exception on all external merge tools,
    # for now.
    #
    # It would be possible to run most tools with temporary files, but this
    # raises the question of what to do if the user only partially resolves the
    # file -- we can't leave a merge state. (Copy to somewhere in the .hg/
    # directory and tell the user how to get it is my best idea, but it's
    # clunky.)
    raise error.InMemoryMergeConflictsError(
        b'in-memory merge does not support external merge tools'
    )


def _describemerge(ui, repo, mynode, fcl, fcb, fco, env, toolpath, args):
    tmpl = ui.config(b'command-templates', b'pre-merge-tool-output')
    if not tmpl:
        return

    mappingdict = templateutil.mappingdict
    props = {
        b'ctx': fcl.changectx(),
        b'node': hex(mynode),
        b'path': fcl.path(),
        b'local': mappingdict(
            {
                b'ctx': fcl.changectx(),
                b'fctx': fcl,
                b'node': hex(mynode),
                b'name': _(b'local'),
                b'islink': b'l' in fcl.flags(),
                b'label': env[b'HG_MY_LABEL'],
            }
        ),
        b'base': mappingdict(
            {
                b'ctx': fcb.changectx(),
                b'fctx': fcb,
                b'name': _(b'base'),
                b'islink': b'l' in fcb.flags(),
                b'label': env[b'HG_BASE_LABEL'],
            }
        ),
        b'other': mappingdict(
            {
                b'ctx': fco.changectx(),
                b'fctx': fco,
                b'name': _(b'other'),
                b'islink': b'l' in fco.flags(),
                b'label': env[b'HG_OTHER_LABEL'],
            }
        ),
        b'toolpath': toolpath,
        b'toolargs': args,
    }

    # TODO: make all of this something that can be specified on a per-tool basis
    tmpl = templater.unquotestring(tmpl)

    # Not using cmdutil.rendertemplate here since it causes errors importing
    # things for us to import cmdutil.
    tres = formatter.templateresources(ui, repo)
    t = formatter.maketemplater(
        ui, tmpl, defaults=templatekw.keywords, resources=tres
    )
    ui.status(t.renderdefault(props))


def _xmerge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels):
    tool, toolpath, binary, symlink, scriptfn = toolconf
    uipathfn = scmutil.getuipathfn(repo)
    if fcd.isabsent() or fco.isabsent():
        repo.ui.warn(
            _(b'warning: %s cannot merge change/delete conflict for %s\n')
            % (tool, uipathfn(fcd.path()))
        )
        return False, 1, None
    unused, unused, unused, back = files
    localpath = _workingpath(repo, fcd)
    args = _toolstr(repo.ui, tool, b"args")

    with _maketempfiles(
        repo, fco, fca, repo.wvfs.join(back.path()), b"$output" in args
    ) as temppaths:
        basepath, otherpath, localoutputpath = temppaths
        outpath = b""
        mylabel, otherlabel = labels[:2]
        if len(labels) >= 3:
            baselabel = labels[2]
        else:
            baselabel = b'base'
        env = {
            b'HG_FILE': fcd.path(),
            b'HG_MY_NODE': short(mynode),
            b'HG_OTHER_NODE': short(fco.changectx().node()),
            b'HG_BASE_NODE': short(fca.changectx().node()),
            b'HG_MY_ISLINK': b'l' in fcd.flags(),
            b'HG_OTHER_ISLINK': b'l' in fco.flags(),
            b'HG_BASE_ISLINK': b'l' in fca.flags(),
            b'HG_MY_LABEL': mylabel,
            b'HG_OTHER_LABEL': otherlabel,
            b'HG_BASE_LABEL': baselabel,
        }
        ui = repo.ui

        if b"$output" in args:
            # read input from backup, write to original
            outpath = localpath
            localpath = localoutputpath
        replace = {
            b'local': localpath,
            b'base': basepath,
            b'other': otherpath,
            b'output': outpath,
            b'labellocal': mylabel,
            b'labelother': otherlabel,
            b'labelbase': baselabel,
        }
        args = util.interpolate(
            br'\$',
            replace,
            args,
            lambda s: procutil.shellquote(util.localpath(s)),
        )
        if _toolbool(ui, tool, b"gui"):
            repo.ui.status(
                _(b'running merge tool %s for file %s\n')
                % (tool, uipathfn(fcd.path()))
            )
        if scriptfn is None:
            cmd = toolpath + b' ' + args
            repo.ui.debug(b'launching merge tool: %s\n' % cmd)
            _describemerge(ui, repo, mynode, fcd, fca, fco, env, toolpath, args)
            r = ui.system(
                cmd, cwd=repo.root, environ=env, blockedtag=b'mergetool'
            )
        else:
            repo.ui.debug(
                b'launching python merge script: %s:%s\n' % (toolpath, scriptfn)
            )
            r = 0
            try:
                # avoid cycle cmdutil->merge->filemerge->extensions->cmdutil
                from . import extensions

                mod = extensions.loadpath(toolpath, b'hgmerge.%s' % tool)
            except Exception:
                raise error.Abort(
                    _(b"loading python merge script failed: %s") % toolpath
                )
            mergefn = getattr(mod, scriptfn, None)
            if mergefn is None:
                raise error.Abort(
                    _(b"%s does not have function: %s") % (toolpath, scriptfn)
                )
            argslist = procutil.shellsplit(args)
            # avoid cycle cmdutil->merge->filemerge->hook->extensions->cmdutil
            from . import hook

            ret, raised = hook.pythonhook(
                ui, repo, b"merge", toolpath, mergefn, {b'args': argslist}, True
            )
            if raised:
                r = 1
        repo.ui.debug(b'merge tool returned: %d\n' % r)
        return True, r, False


def _formatconflictmarker(ctx, template, label, pad):
    """Applies the given template to the ctx, prefixed by the label.

    Pad is the minimum width of the label prefix, so that multiple markers
    can have aligned templated parts.
    """
    if ctx.node() is None:
        ctx = ctx.p1()

    props = {b'ctx': ctx}
    templateresult = template.renderdefault(props)

    label = (b'%s:' % label).ljust(pad + 1)
    mark = b'%s %s' % (label, templateresult)

    if mark:
        mark = mark.splitlines()[0]  # split for safety

    # 8 for the prefix of conflict marker lines (e.g. '<<<<<<< ')
    return stringutil.ellipsis(mark, 80 - 8)


_defaultconflictlabels = [b'local', b'other']


def _formatlabels(repo, fcd, fco, fca, labels, tool=None):
    """Formats the given labels using the conflict marker template.

    Returns a list of formatted labels.
    """
    cd = fcd.changectx()
    co = fco.changectx()
    ca = fca.changectx()

    ui = repo.ui
    template = ui.config(b'command-templates', b'mergemarker')
    if tool is not None:
        template = _toolstr(ui, tool, b'mergemarkertemplate', template)
    template = templater.unquotestring(template)
    tres = formatter.templateresources(ui, repo)
    tmpl = formatter.maketemplater(
        ui, template, defaults=templatekw.keywords, resources=tres
    )

    pad = max(len(l) for l in labels)

    newlabels = [
        _formatconflictmarker(cd, tmpl, labels[0], pad),
        _formatconflictmarker(co, tmpl, labels[1], pad),
    ]
    if len(labels) > 2:
        newlabels.append(_formatconflictmarker(ca, tmpl, labels[2], pad))
    return newlabels


def partextras(labels):
    """Return a dictionary of extra labels for use in prompts to the user

    Intended use is in strings of the form "(l)ocal%(l)s".
    """
    if labels is None:
        return {
            b"l": b"",
            b"o": b"",
        }

    return {
        b"l": b" [%s]" % labels[0],
        b"o": b" [%s]" % labels[1],
    }


def _restorebackup(fcd, back):
    # TODO: Add a workingfilectx.write(otherfilectx) path so we can use
    # util.copy here instead.
    fcd.write(back.data(), fcd.flags())


def _makebackup(repo, ui, wctx, fcd, premerge):
    """Makes and returns a filectx-like object for ``fcd``'s backup file.

    In addition to preserving the user's pre-existing modifications to `fcd`
    (if any), the backup is used to undo certain premerges, confirm whether a
    merge changed anything, and determine what line endings the new file should
    have.

    Backups only need to be written once (right before the premerge) since their
    content doesn't change afterwards.
    """
    if fcd.isabsent():
        return None
    # TODO: Break this import cycle somehow. (filectx -> ctx -> fileset ->
    # merge -> filemerge). (I suspect the fileset import is the weakest link)
    from . import context

    back = scmutil.backuppath(ui, repo, fcd.path())
    inworkingdir = back.startswith(repo.wvfs.base) and not back.startswith(
        repo.vfs.base
    )
    if isinstance(fcd, context.overlayworkingfilectx) and inworkingdir:
        # If the backup file is to be in the working directory, and we're
        # merging in-memory, we must redirect the backup to the memory context
        # so we don't disturb the working directory.
        relpath = back[len(repo.wvfs.base) + 1 :]
        if premerge:
            wctx[relpath].write(fcd.data(), fcd.flags())
        return wctx[relpath]
    else:
        if premerge:
            # Otherwise, write to wherever path the user specified the backups
            # should go. We still need to switch based on whether the source is
            # in-memory so we can use the fast path of ``util.copy`` if both are
            # on disk.
            if isinstance(fcd, context.overlayworkingfilectx):
                util.writefile(back, fcd.data())
            else:
                a = _workingpath(repo, fcd)
                util.copyfile(a, back)
        # A arbitraryfilectx is returned, so we can run the same functions on
        # the backup context regardless of where it lives.
        return context.arbitraryfilectx(back, repo=repo)


@contextlib.contextmanager
def _maketempfiles(repo, fco, fca, localpath, uselocalpath):
    """Writes out `fco` and `fca` as temporary files, and (if uselocalpath)
    copies `localpath` to another temporary file, so an external merge tool may
    use them.
    """
    tmproot = None
    tmprootprefix = repo.ui.config(b'experimental', b'mergetempdirprefix')
    if tmprootprefix:
        tmproot = pycompat.mkdtemp(prefix=tmprootprefix)

    def maketempfrompath(prefix, path):
        fullbase, ext = os.path.splitext(path)
        pre = b"%s~%s" % (os.path.basename(fullbase), prefix)
        if tmproot:
            name = os.path.join(tmproot, pre)
            if ext:
                name += ext
            f = open(name, "wb")
        else:
            fd, name = pycompat.mkstemp(prefix=pre + b'.', suffix=ext)
            f = os.fdopen(fd, "wb")
        return f, name

    def tempfromcontext(prefix, ctx):
        f, name = maketempfrompath(prefix, ctx.path())
        data = repo.wwritedata(ctx.path(), ctx.data())
        f.write(data)
        f.close()
        return name

    b = tempfromcontext(b"base", fca)
    c = tempfromcontext(b"other", fco)
    d = localpath
    if uselocalpath:
        # We start off with this being the backup filename, so remove the .orig
        # to make syntax-highlighting more likely.
        if d.endswith(b'.orig'):
            d, _ = os.path.splitext(d)
        f, d = maketempfrompath(b"local", d)
        with open(localpath, b'rb') as src:
            f.write(src.read())
        f.close()

    try:
        yield b, c, d
    finally:
        if tmproot:
            shutil.rmtree(tmproot)
        else:
            util.unlink(b)
            util.unlink(c)
            # if not uselocalpath, d is the 'orig'/backup file which we
            # shouldn't delete.
            if d and uselocalpath:
                util.unlink(d)


def _filemerge(premerge, repo, wctx, mynode, orig, fcd, fco, fca, labels=None):
    """perform a 3-way merge in the working directory

    premerge = whether this is a premerge
    mynode = parent node before merge
    orig = original local filename before merge
    fco = other file context
    fca = ancestor file context
    fcd = local file context for current/destination file

    Returns whether the merge is complete, the return value of the merge, and
    a boolean indicating whether the file was deleted from disk."""

    if not fco.cmp(fcd):  # files identical?
        return True, None, False

    ui = repo.ui
    fd = fcd.path()
    uipathfn = scmutil.getuipathfn(repo)
    fduipath = uipathfn(fd)
    binary = fcd.isbinary() or fco.isbinary() or fca.isbinary()
    symlink = b'l' in fcd.flags() + fco.flags()
    changedelete = fcd.isabsent() or fco.isabsent()
    tool, toolpath = _picktool(repo, ui, fd, binary, symlink, changedelete)
    scriptfn = None
    if tool in internals and tool.startswith(b'internal:'):
        # normalize to new-style names (':merge' etc)
        tool = tool[len(b'internal') :]
    if toolpath and toolpath.startswith(b'python:'):
        invalidsyntax = False
        if toolpath.count(b':') >= 2:
            script, scriptfn = toolpath[7:].rsplit(b':', 1)
            if not scriptfn:
                invalidsyntax = True
            # missing :callable can lead to spliting on windows drive letter
            if b'\\' in scriptfn or b'/' in scriptfn:
                invalidsyntax = True
        else:
            invalidsyntax = True
        if invalidsyntax:
            raise error.Abort(_(b"invalid 'python:' syntax: %s") % toolpath)
        toolpath = script
    ui.debug(
        b"picked tool '%s' for %s (binary %s symlink %s changedelete %s)\n"
        % (
            tool,
            fduipath,
            pycompat.bytestr(binary),
            pycompat.bytestr(symlink),
            pycompat.bytestr(changedelete),
        )
    )

    if tool in internals:
        func = internals[tool]
        mergetype = func.mergetype
        onfailure = func.onfailure
        precheck = func.precheck
        isexternal = False
    else:
        if wctx.isinmemory():
            func = _xmergeimm
        else:
            func = _xmerge
        mergetype = fullmerge
        onfailure = _(b"merging %s failed!\n")
        precheck = None
        isexternal = True

    toolconf = tool, toolpath, binary, symlink, scriptfn

    if mergetype == nomerge:
        r, deleted = func(repo, mynode, orig, fcd, fco, fca, toolconf, labels)
        return True, r, deleted

    if premerge:
        if orig != fco.path():
            ui.status(
                _(b"merging %s and %s to %s\n")
                % (uipathfn(orig), uipathfn(fco.path()), fduipath)
            )
        else:
            ui.status(_(b"merging %s\n") % fduipath)

    ui.debug(b"my %s other %s ancestor %s\n" % (fcd, fco, fca))

    if precheck and not precheck(repo, mynode, orig, fcd, fco, fca, toolconf):
        if onfailure:
            if wctx.isinmemory():
                raise error.InMemoryMergeConflictsError(
                    b'in-memory merge does not support merge conflicts'
                )
            ui.warn(onfailure % fduipath)
        return True, 1, False

    back = _makebackup(repo, ui, wctx, fcd, premerge)
    files = (None, None, None, back)
    r = 1
    try:
        internalmarkerstyle = ui.config(b'ui', b'mergemarkers')
        if isexternal:
            markerstyle = _toolstr(ui, tool, b'mergemarkers')
        else:
            markerstyle = internalmarkerstyle

        if not labels:
            labels = _defaultconflictlabels
        formattedlabels = labels
        if markerstyle != b'basic':
            formattedlabels = _formatlabels(
                repo, fcd, fco, fca, labels, tool=tool
            )

        if premerge and mergetype == fullmerge:
            # conflict markers generated by premerge will use 'detailed'
            # settings if either ui.mergemarkers or the tool's mergemarkers
            # setting is 'detailed'. This way tools can have basic labels in
            # space-constrained areas of the UI, but still get full information
            # in conflict markers if premerge is 'keep' or 'keep-merge3'.
            premergelabels = labels
            labeltool = None
            if markerstyle != b'basic':
                # respect 'tool's mergemarkertemplate (which defaults to
                # command-templates.mergemarker)
                labeltool = tool
            if internalmarkerstyle != b'basic' or markerstyle != b'basic':
                premergelabels = _formatlabels(
                    repo, fcd, fco, fca, premergelabels, tool=labeltool
                )

            r = _premerge(
                repo, fcd, fco, fca, toolconf, files, labels=premergelabels
            )
            # complete if premerge successful (r is 0)
            return not r, r, False

        needcheck, r, deleted = func(
            repo,
            mynode,
            orig,
            fcd,
            fco,
            fca,
            toolconf,
            files,
            labels=formattedlabels,
        )

        if needcheck:
            r = _check(repo, r, ui, tool, fcd, files)

        if r:
            if onfailure:
                if wctx.isinmemory():
                    raise error.InMemoryMergeConflictsError(
                        b'in-memory merge '
                        b'does not support '
                        b'merge conflicts'
                    )
                ui.warn(onfailure % fduipath)
            _onfilemergefailure(ui)

        return True, r, deleted
    finally:
        if not r and back is not None:
            back.remove()


def _haltmerge():
    msg = _(b'merge halted after failed merge (see hg resolve)')
    raise error.InterventionRequired(msg)


def _onfilemergefailure(ui):
    action = ui.config(b'merge', b'on-failure')
    if action == b'prompt':
        msg = _(b'continue merge operation (yn)?$$ &Yes $$ &No')
        if ui.promptchoice(msg, 0) == 1:
            _haltmerge()
    if action == b'halt':
        _haltmerge()
    # default action is 'continue', in which case we neither prompt nor halt


def hasconflictmarkers(data):
    return bool(
        re.search(b"^(<<<<<<< .*|=======|>>>>>>> .*)$", data, re.MULTILINE)
    )


def _check(repo, r, ui, tool, fcd, files):
    fd = fcd.path()
    uipathfn = scmutil.getuipathfn(repo)
    unused, unused, unused, back = files

    if not r and (
        _toolbool(ui, tool, b"checkconflicts")
        or b'conflicts' in _toollist(ui, tool, b"check")
    ):
        if hasconflictmarkers(fcd.data()):
            r = 1

    checked = False
    if b'prompt' in _toollist(ui, tool, b"check"):
        checked = True
        if ui.promptchoice(
            _(b"was merge of '%s' successful (yn)?$$ &Yes $$ &No")
            % uipathfn(fd),
            1,
        ):
            r = 1

    if (
        not r
        and not checked
        and (
            _toolbool(ui, tool, b"checkchanged")
            or b'changed' in _toollist(ui, tool, b"check")
        )
    ):
        if back is not None and not fcd.cmp(back):
            if ui.promptchoice(
                _(
                    b" output file %s appears unchanged\n"
                    b"was merge successful (yn)?"
                    b"$$ &Yes $$ &No"
                )
                % uipathfn(fd),
                1,
            ):
                r = 1

    if back is not None and _toolbool(ui, tool, b"fixeol"):
        _matcheol(_workingpath(repo, fcd), back)

    return r


def _workingpath(repo, ctx):
    return repo.wjoin(ctx.path())


def premerge(repo, wctx, mynode, orig, fcd, fco, fca, labels=None):
    return _filemerge(
        True, repo, wctx, mynode, orig, fcd, fco, fca, labels=labels
    )


def filemerge(repo, wctx, mynode, orig, fcd, fco, fca, labels=None):
    return _filemerge(
        False, repo, wctx, mynode, orig, fcd, fco, fca, labels=labels
    )


def loadinternalmerge(ui, extname, registrarobj):
    """Load internal merge tool from specified registrarobj"""
    for name, func in pycompat.iteritems(registrarobj._table):
        fullname = b':' + name
        internals[fullname] = func
        internals[b'internal:' + name] = func
        internalsdoc[fullname] = func

        capabilities = sorted([k for k, v in func.capabilities.items() if v])
        if capabilities:
            capdesc = b"    (actual capabilities: %s)" % b', '.join(
                capabilities
            )
            func.__doc__ = func.__doc__ + pycompat.sysstr(b"\n\n%s" % capdesc)

    # to put i18n comments into hg.pot for automatically generated texts

    # i18n: "binary" and "symlink" are keywords
    # i18n: this text is added automatically
    _(b"    (actual capabilities: binary, symlink)")
    # i18n: "binary" is keyword
    # i18n: this text is added automatically
    _(b"    (actual capabilities: binary)")
    # i18n: "symlink" is keyword
    # i18n: this text is added automatically
    _(b"    (actual capabilities: symlink)")


# load built-in merge tools explicitly to setup internalsdoc
loadinternalmerge(None, None, internaltool)

# tell hggettext to extract docstrings from these functions:
i18nfunctions = internals.values()