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 the 'check-commit' script
==============================
A fine patch:
$ cat > patch-with-long-header.diff << EOF
> # HG changeset patch
> # User timeless <timeless@mozdev.org>
> # Date 1448911706 0
> # Mon Nov 30 19:28:26 2015 +0000
> # Node ID c41cb6d2b7dbd62b1033727f8606b8c09fc4aa88
> # Parent 42aa0e570eaa364a622bc4443b0bcb79b1100a58
> # ClownJoke This is a veryly long header that should not be warned about because its not the description
> bundle2: use Oxford comma (issue123) (BC)
>
> diff --git a/hgext/transplant.py b/hgext/transplant.py
> --- a/hgext/transplant.py
> +++ b/hgext/transplant.py
> @@ -599,7 +599,7 @@
> return
> if not (opts.get('source') or revs or
> opts.get('merge') or opts.get('branch')):
> - raise error.Abort(_('no source URL, branch revision or revision '
> + raise error.Abort(_('no source URL, branch revision, or revision '
> 'list provided'))
> if opts.get('all'):
>
> + def blahblah(x):
> + pass
> EOF
$ cat patch-with-long-header.diff | $TESTDIR/../contrib/check-commit
This would normally be against the rules, but it's okay because that's
what tagging and signing looks like:
$ cat > creates-a-tag.diff << EOF
> # HG changeset patch
> # User Augie Fackler <raf@durin42.com>
> # Date 1484787778 18000
> # Wed Jan 18 20:02:58 2017 -0500
> # Branch stable
> # Node ID c177635e4acf52923bc3aa9f72a5b1ad1197b173
> # Parent a1dd2c0c479e0550040542e392e87bc91262517e
> Added tag 4.1-rc for changeset a1dd2c0c479e
>
> diff --git a/.hgtags b/.hgtags
> --- a/.hgtags
> +++ b/.hgtags
> @@ -150,3 +150,4 @@ 438173c415874f6ac653efc1099dec9c9150e90f
> eab27446995210c334c3d06f1a659e3b9b5da769 4.0
> b3b1ae98f6a0e14c1e1ba806a6c18e193b6dae5c 4.0.1
> e69874dc1f4e142746ff3df91e678a09c6fc208c 4.0.2
> +a1dd2c0c479e0550040542e392e87bc91262517e 4.1-rc
> EOF
$ $TESTDIR/../contrib/check-commit < creates-a-tag.diff
A patch with lots of errors:
$ cat > patch-with-long-header.diff << EOF
> # HG changeset patch
> # User timeless
> # Date 1448911706 0
> # Mon Nov 30 19:28:26 2015 +0000
> # Node ID c41cb6d2b7dbd62b1033727f8606b8c09fc4aa88
> # Parent 42aa0e570eaa364a622bc4443b0bcb79b1100a58
> # ClownJoke This is a veryly long header that should not be warned about because its not the description
> transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
>
> diff --git a/hgext/transplant.py b/hgext/transplant.py
> --- a/hgext/transplant.py
> +++ b/hgext/transplant.py
> @@ -599,7 +599,7 @@
> return
> if not (opts.get('source') or revs or
> opts.get('merge') or opts.get('branch')):
> - raise error.Abort(_('no source URL, branch revision or revision '
> + raise error.Abort(_('no source URL, branch revision, or revision '
> 'list provided'))
> if opts.get('all'):
> EOF
$ cat patch-with-long-header.diff | $TESTDIR/../contrib/check-commit
1: username is not an email address
# User timeless
7: summary keyword should be most user-relevant one-word command or topic
transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
7: (BC) needs to be uppercase
transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
7: use (issueDDDD) instead of bug
transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
7: no space allowed between issue and number
transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
7: summary line too long (limit is 78)
transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
[1]
A patch with other errors:
$ cat > patch-with-long-header.diff << EOF
> # HG changeset patch
> # User timeless
> # Date 1448911706 0
> # Mon Nov 30 19:28:26 2015 +0000
> # Node ID c41cb6d2b7dbd62b1033727f8606b8c09fc4aa88
> # Parent 42aa0e570eaa364a622bc4443b0bcb79b1100a58
> # ClownJoke This is a veryly long header that should not be warned about because its not the description
> This has no topic and ends with a period.
>
> diff --git a/hgext/transplant.py b/hgext/transplant.py
> --- a/hgext/transplant.py
> +++ b/hgext/transplant.py
> @@ -599,7 +599,7 @@
> if opts.get('all'):
>
>
> +
> + some = otherjunk
> +
> +
> + def blah_blah(x):
> + pass
> +
>
> EOF
$ cat patch-with-long-header.diff | $TESTDIR/../contrib/check-commit
1: username is not an email address
# User timeless
7: don't capitalize summary lines
This has no topic and ends with a period.
7: summary line doesn't start with 'topic: '
This has no topic and ends with a period.
7: don't add trailing period on summary line
This has no topic and ends with a period.
[1]