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.
Test admin::verify
$ hg init admin-verify
$ cd admin-verify
Test normal output
$ hg admin::verify -c dirstate
running 1 checks
running working-copy.dirstate
checking dirstate
Quiet works
$ hg admin::verify -c dirstate --quiet
Test no check no options
$ hg admin::verify
abort: `checks` required
[255]
Test single check without options
$ hg admin::verify -c working-copy.dirstate
running 1 checks
running working-copy.dirstate
checking dirstate
Test single check (alias) without options
$ hg admin::verify -c dirstate
running 1 checks
running working-copy.dirstate
checking dirstate
Test wrong check name without options
$ hg admin::verify -c working-copy.dir
abort: unknown check working-copy.dir
(did you mean working-copy.dirstate?)
[10]
Test wrong alias without options
$ hg admin::verify -c dir
abort: unknown check dir
[10]