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.
$ . "$TESTDIR/narrow-library.sh"
$ hg init repo
$ cd repo
$ cat << EOF > .hg/store/narrowspec
> [include]
> path:foo
> [exclude]
> EOF
$ cp .hg/store/narrowspec .hg/narrowspec.dirstate
$ echo treemanifest >> .hg/requires
$ echo narrowhg-experimental >> .hg/requires
$ mkdir -p foo/bar
$ echo b > foo/f
$ echo c > foo/bar/f
$ hg commit -Am hi
adding foo/bar/f
adding foo/f
$ hg debugindex -m
rev linkrev nodeid p1-nodeid p2-nodeid
0 0 14a5d056d75a 000000000000 000000000000
$ hg debugindex --dir foo
rev linkrev nodeid p1-nodeid p2-nodeid
0 0 e635c7857aef 000000000000 000000000000
$ hg debugindex --dir foo/
rev linkrev nodeid p1-nodeid p2-nodeid
0 0 e635c7857aef 000000000000 000000000000
$ hg debugindex --dir foo/bar
rev linkrev nodeid p1-nodeid p2-nodeid
0 0 e091d4224761 000000000000 000000000000
$ hg debugindex --dir foo/bar/
rev linkrev nodeid p1-nodeid p2-nodeid
0 0 e091d4224761 000000000000 000000000000
$ hg debugdata -m 0
foo\x00e635c7857aef92ac761ce5741a99da159abbbb24t (esc)
$ hg debugdata --dir foo 0
bar\x00e091d42247613adff5d41b67f15fe7189ee97b39t (esc)
f\x001e88685f5ddec574a34c70af492f95b6debc8741 (esc)
$ hg debugdata --dir foo/ 0
bar\x00e091d42247613adff5d41b67f15fe7189ee97b39t (esc)
f\x001e88685f5ddec574a34c70af492f95b6debc8741 (esc)
$ hg debugdata --dir foo/bar 0
f\x00149da44f2a4e14f488b7bd4157945a9837408c00 (esc)
$ hg debugdata --dir foo/bar/ 0
f\x00149da44f2a4e14f488b7bd4157945a9837408c00 (esc)