bisect: avoid copying ancestor list for non-merge commits
During a bisection, hg needs to compute a list of all ancestors for every
candidate commit. This is accomplished via a bottom-up traversal of the set of
candidates, during which each revision's ancestor list is populated using the
ancestor list of its parent(s). Previously, this involved copying the entire
list, which could be very long in if the bisection range was large.
To help improve this, we can observe that each candidate commit is visited
exactly once, at which point its ancestor list is copied into its children's
lists and then dropped. In the case of non-merge commits, a commit's ancestor
list consists exactly of its parent's list plus itself. This means that we can
trivially reuse the parent's existing list for one of its non-merge children,
which avoids copying entirely if that commit is the parent's only child. This
makes bisections over linear ranges of commits much faster.
During some informal testing in the large publicly-available `mozilla-central`
repository, this noticeably sped up bisections over large ranges of history:
Setup:
$ cd mozilla-central
$ hg bisect --reset
$ hg bisect --good 0
$ hg log -r tip -T '{rev}\n'
628417
Test:
$ time hg bisect --bad tip --noupdate
Before:
real 3m35.927s
user 3m35.553s
sys 0m0.319s
After:
real 1m41.142s
user 1m40.810s
sys 0m0.285s
#!/usr/bin/env python3
import getopt
import sys
import hgdemandimport
hgdemandimport.enable()
from mercurial.i18n import _
from mercurial import (
context,
error,
fancyopts,
simplemerge,
ui as uimod,
util,
)
from mercurial.utils import procutil, stringutil
options = [
(b'L', b'label', [], _(b'labels to use on conflict markers')),
(b'a', b'text', None, _(b'treat all files as text')),
(b'p', b'print', None, _(b'print results instead of overwriting LOCAL')),
(b'', b'no-minimal', None, _(b'no effect (DEPRECATED)')),
(b'h', b'help', None, _(b'display help and exit')),
(b'q', b'quiet', None, _(b'suppress output')),
]
usage = _(
b'''simplemerge [OPTS] LOCAL BASE OTHER
Simple three-way file merge utility with a minimal feature set.
Apply to LOCAL the changes necessary to go from BASE to OTHER.
By default, LOCAL is overwritten with the results of this operation.
'''
)
class ParseError(Exception):
"""Exception raised on errors in parsing the command line."""
def showhelp():
procutil.stdout.write(usage)
procutil.stdout.write(b'\noptions:\n')
out_opts = []
for shortopt, longopt, default, desc in options:
out_opts.append(
(
b'%2s%s'
% (
shortopt and b'-%s' % shortopt,
longopt and b' --%s' % longopt,
),
b'%s' % desc,
)
)
opts_len = max([len(opt[0]) for opt in out_opts])
for first, second in out_opts:
procutil.stdout.write(b' %-*s %s\n' % (opts_len, first, second))
def _verifytext(input, ui, quiet=False, allow_binary=False):
"""verifies that text is non-binary (unless opts[text] is passed,
then we just warn)"""
if stringutil.binary(input.text()):
msg = _(b"%s looks like a binary file.") % input.fctx.path()
if not quiet:
ui.warn(_(b'warning: %s\n') % msg)
if not allow_binary:
sys.exit(1)
try:
for fp in (sys.stdin, procutil.stdout, sys.stderr):
procutil.setbinary(fp)
opts = {}
try:
bargv = [a.encode('utf8') for a in sys.argv[1:]]
args = fancyopts.fancyopts(bargv, options, opts)
except getopt.GetoptError as e:
raise ParseError(e)
if opts[b'help']:
showhelp()
sys.exit(0)
if len(args) != 3:
raise ParseError(_(b'wrong number of arguments').decode('utf8'))
mode = b'merge'
if len(opts[b'label']) > 2:
mode = b'merge3'
local, base, other = args
overrides = opts[b'label']
if len(overrides) > 3:
raise error.InputError(b'can only specify three labels.')
labels = [local, other, base]
labels[: len(overrides)] = overrides
local_input = simplemerge.MergeInput(
context.arbitraryfilectx(local), labels[0]
)
other_input = simplemerge.MergeInput(
context.arbitraryfilectx(other), labels[1]
)
base_input = simplemerge.MergeInput(
context.arbitraryfilectx(base), labels[2]
)
quiet = opts.get(b'quiet')
allow_binary = opts.get(b'text')
ui = uimod.ui.load()
_verifytext(local_input, ui, quiet=quiet, allow_binary=allow_binary)
_verifytext(base_input, ui, quiet=quiet, allow_binary=allow_binary)
_verifytext(other_input, ui, quiet=quiet, allow_binary=allow_binary)
merged_text, conflicts = simplemerge.simplemerge(
local_input,
base_input,
other_input,
mode,
allow_binary=allow_binary,
)
if opts.get(b'print'):
ui.fout.write(merged_text)
else:
util.writefile(local, merged_text)
sys.exit(1 if conflicts else 0)
except ParseError as e:
e = stringutil.forcebytestr(e)
procutil.stdout.write(b"%s: %s\n" % (sys.argv[0].encode('utf8'), e))
showhelp()
sys.exit(1)
except error.Abort as e:
procutil.stderr.write(b"abort: %s\n" % e)
sys.exit(255)
except KeyboardInterrupt:
sys.exit(255)