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
#require execbit
b51a8138292a introduced a regression where we would mention in the
changelog executable files added by the second parent of a merge. Test
that that doesn't happen anymore
$ hg init repo
$ cd repo
$ echo foo > foo
$ hg ci -qAm 'add foo'
$ echo bar > bar
$ chmod +x bar
$ hg ci -qAm 'add bar'
manifest of p2:
$ hg manifest
bar
foo
$ hg up -qC 0
$ echo >> foo
$ hg ci -m 'change foo'
created new head
manifest of p1:
$ hg manifest
foo
$ hg merge
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ chmod +x foo
$ hg ci -m 'merge'
this should not mention bar but should mention foo:
$ hg tip -v
changeset: 3:c53d17ff3380
tag: tip
parent: 2:ed1b79f46b9a
parent: 1:d394a8db219b
user: test
date: Thu Jan 01 00:00:00 1970 +0000
files: foo
description:
merge
$ hg debugindex bar
rev linkrev nodeid p1-nodeid p2-nodeid
0 1 b004912a8510 000000000000 000000000000
$ cd ..