branchcache: add a "pure topological head" fast path
In a narrow but actually quick common case, all topological heads are all on
the same branch and all open. In this case, computing the branch map is very
simple. We can quickly detect situation where this situation will not change.
So we update the V3 format to be able to express this situation and upgrade the
update code to detect we remains in that mode.
The branch cache is populated with the actual value when the branch map is
accessed, but the update_disk method can do the update without needing to
populate it.
$ cat << EOF >> $HGRCPATH
> [extensions]
> rebase=
> [alias]
> tglog = log -G -T "{rev} '{desc}'\n"
> EOF
$ hg init
$ echo a > a; hg add a; hg ci -m a
$ echo b > b; hg add b; hg ci -m b1
$ hg up 0 -q
$ echo b > b; hg add b; hg ci -m b2 -q
$ hg tglog
@ 2 'b2'
|
| o 1 'b1'
|/
o 0 'a'
With rewrite.empty-successor=skip, b2 is skipped because it would become empty.
$ hg rebase -s 2 -d 1 --config rewrite.empty-successor=skip --dry-run
starting dry-run rebase; repository will not be changed
rebasing 2:6e2aad5e0f3c tip "b2"
note: not rebasing 2:6e2aad5e0f3c tip "b2", its destination already has all its changes
dry-run rebase completed successfully; run without -n/--dry-run to perform this rebase
With rewrite.empty-successor=keep, b2 will be recreated although it became empty.
$ hg rebase -s 2 -d 1 --config rewrite.empty-successor=keep
rebasing 2:6e2aad5e0f3c tip "b2"
note: created empty successor for 2:6e2aad5e0f3c tip "b2", its destination already has all its changes
saved backup bundle to $TESTTMP/.hg/strip-backup/6e2aad5e0f3c-7d7c8801-rebase.hg
$ hg tglog
@ 2 'b2'
|
o 1 'b1'
|
o 0 'a'