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
Test temp file used with an editor has the expected suffix.
$ hg init
Create an editor that writes its arguments to stdout and set it to $HGEDITOR.
$ cat > editor.sh << EOF
> echo "\$@"
> exit 1
> EOF
$ hg add editor.sh
$ HGEDITOR="sh $TESTTMP/editor.sh"
$ export HGEDITOR
Verify that the path for a commit editor has the expected suffix.
$ hg commit
*.commit.hg.txt (glob)
abort: edit failed: sh exited with status 1
[250]
Verify that the path for a histedit editor has the expected suffix.
$ cat >> $HGRCPATH <<EOF
> [extensions]
> rebase=
> histedit=
> EOF
$ hg commit --message 'At least one commit for histedit.'
$ hg histedit
*.histedit.hg.txt (glob)
abort: edit failed: sh exited with status 1
[250]
Verify that when performing an action that has the side-effect of creating an
editor for a diff, the file ends in .diff.
$ echo 1 > one
$ echo 2 > two
$ hg add
adding one
adding two
$ hg commit --interactive --config ui.interactive=true --config ui.interface=text << EOF
> y
> e
> q
> EOF
diff --git a/one b/one
new file mode 100644
examine changes to 'one'?
(enter ? for help) [Ynesfdaq?] y
@@ -0,0 +1,1 @@
+1
record change 1/2 to 'one'?
(enter ? for help) [Ynesfdaq?] e
*.diff (glob)
editor exited with exit code 1
record change 1/2 to 'one'?
(enter ? for help) [Ynesfdaq?] q
abort: user quit
[250]