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
$ hg init
$ echo a > a
$ hg commit -A -ma
adding a
$ echo b >> a
$ hg commit -mb
$ echo c >> a
$ hg commit -mc
$ hg up 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo d >> a
$ hg commit -md
created new head
$ hg up 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo e >> a
$ hg commit -me
created new head
$ hg up 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
Should fail because not at a head:
$ hg merge
abort: working directory not at a head revision
(use 'hg update' or merge with an explicit revision)
[255]
$ hg up
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
updated to "f25cbe84d8b3: e"
2 other heads for branch "default"
Should fail because > 2 heads:
$ HGMERGE=internal:other; export HGMERGE
$ hg merge
abort: branch 'default' has 3 heads - please merge with an explicit rev
(run 'hg heads .' to see heads, specify rev with -r)
[255]
Should succeed (we're specifying commands.merge.require-rev=True just to test
that it allows merge to succeed if we specify a revision):
$ hg merge 2 --config commands.merge.require-rev=True
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg id -Tjson
[
{
"bookmarks": [],
"branch": "default",
"dirty": "+",
"id": "f25cbe84d8b320e298e7703f18a25a3959518c23+2d95304fed5d89bc9d70b2a0d02f0d567469c3ab+",
"node": "ffffffffffffffffffffffffffffffffffffffff",
"parents": ["f25cbe84d8b320e298e7703f18a25a3959518c23", "2d95304fed5d89bc9d70b2a0d02f0d567469c3ab"],
"tags": ["tip"]
}
]
$ hg commit -mm1
Should fail because we didn't specify a revision (even though it would have
succeeded without this):
$ hg merge --config commands.merge.require-rev=True
abort: configuration requires specifying revision to merge with
[10]
Should succeed - 2 heads:
$ hg merge -P
changeset: 3:ea9ff125ff88
parent: 1:1846eede8b68
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: d
$ hg merge
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg commit -mm2
$ hg id -r 1 -Tjson
[
{
"bookmarks": [],
"branch": "default",
"id": "1846eede8b6886d8cc8a88c96a687b7fe8f3b9d1",
"node": "1846eede8b6886d8cc8a88c96a687b7fe8f3b9d1",
"tags": []
}
]
Should fail because we didn't specify a revision (even though it would have
failed without this due to being on tip, but this check comes first):
$ hg merge --config commands.merge.require-rev=True
abort: configuration requires specifying revision to merge with
[10]
Should fail because at tip:
$ hg merge
abort: nothing to merge
[255]
$ hg up 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
Should fail because there is only one head:
$ hg merge
abort: nothing to merge
(use 'hg update' instead)
[255]
$ hg up 3
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo f >> a
$ hg branch foobranch
marked working directory as branch foobranch
(branches are permanent and global, did you want a bookmark?)
$ hg commit -mf
Should fail because merge with other branch:
$ hg merge
abort: branch 'foobranch' has one head - please merge with an explicit rev
(run 'hg heads' to see all heads, specify rev with -r)
[255]
Test for issue2043: ensure that 'merge -P' shows ancestors of 6 that
are not ancestors of 7, regardless of where their common ancestors are.
Merge preview not affected by common ancestor:
$ hg up -q 7
$ hg merge -q -P 6
2:2d95304fed5d
4:f25cbe84d8b3
5:a431fabd6039
6:e88e33f3bf62
Test experimental destination revset
$ hg log -r '_destmerge()'
abort: branch 'foobranch' has one head - please merge with an explicit rev
(run 'hg heads' to see all heads, specify rev with -r)
[255]
(on a branch with a two heads)
$ hg up 5
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo f >> a
$ hg commit -mf
created new head
$ hg log -r '_destmerge()'
changeset: 6:e88e33f3bf62
parent: 5:a431fabd6039
parent: 3:ea9ff125ff88
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: m2
(from the other head)
$ hg log -r '_destmerge(e88e33f3bf62)'
changeset: 8:b613918999e2
tag: tip
parent: 5:a431fabd6039
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: f
(from unrelated branch)
$ hg log -r '_destmerge(foobranch)'
abort: branch 'foobranch' has one head - please merge with an explicit rev
(run 'hg heads' to see all heads, specify rev with -r)
[255]