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
Path conflict checking is currently disabled by default because of issue5716.
Turn it on for this test.
$ cat >> $HGRCPATH << EOF
> [experimental]
> merge.checkpathconflicts=True
> EOF
$ hg init repo
$ cd repo
$ echo base > base
$ hg add base
$ hg commit -m "base"
$ hg bookmark -i base
$ echo 1 > a
$ hg add a
$ hg commit -m "file"
$ hg bookmark -i file
$ echo 2 > a
$ hg commit -m "file2"
$ hg bookmark -i file2
$ hg up -q 0
$ mkdir a
$ echo 2 > a/b
$ hg add a/b
$ hg commit -m "dir"
created new head
$ hg bookmark -i dir
Basic merge - local file conflicts with remote directory
$ hg up -q file
$ hg bookmark -i
$ hg merge --verbose dir
resolving manifests
a: path conflict - a file or link has the same name as a directory
the local file has been renamed to a~853701544ac3
resolve manually then use 'hg resolve --mark a'
moving a to a~853701544ac3
getting a/b
1 files updated, 0 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
[1]
$ hg update --clean .
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ rm a~853701544ac3
Basic update - local directory conflicts with remote file
$ hg up -q 0
$ mkdir a
$ echo 3 > a/b
$ hg up file
a: untracked directory conflicts with file
abort: untracked files in working directory differ from files in requested revision
[20]
$ hg up --clean file
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(activating bookmark file)
Repo state is ok
$ hg sum
parent: 1:853701544ac3
file
branch: default
bookmarks: *file
commit: (clean)
update: 2 new changesets (update)
phases: 4 draft
Basic update - untracked file conflicts with remote directory
$ hg up -q 0
$ echo untracked > a
$ hg up --config merge.checkunknown=warn dir
a: replacing untracked file
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(activating bookmark dir)
$ cat a.orig
untracked
$ rm -f a.orig
Basic clean update - local directory conflicts with changed remote file
$ hg up -q file
$ rm a
$ mkdir a
$ echo 4 > a/b
$ hg up file2
abort: *: *$TESTTMP/repo/a* (glob)
[255]
$ hg up --clean file2
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(activating bookmark file2)
Repo state is ok
$ hg sum
parent: 2:f64e09fac717
file2
branch: default
bookmarks: *file2
commit: (clean)
update: 1 new changesets, 2 branch heads (merge)
phases: 4 draft