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 sparse
$ cat >> $HGRCPATH << EOF
> [ui]
> username = nobody <no.reply@fb.com>
> [extensions]
> sparse=
> purge=
> strip=
> rebase=
> EOF
$ hg init myrepo
$ cd myrepo
$ echo a > index.html
$ echo x > data.py
$ echo z > readme.txt
$ cat > webpage.sparse <<EOF
> [include]
> *.html
> EOF
$ cat > backend.sparse <<EOF
> [include]
> *.py
> EOF
$ hg ci -Aqm 'initial'
$ cd ..
Verify local clone with a sparse profile works
$ hg clone --enable-profile webpage.sparse myrepo clone1
updating to branch default
warning: sparse profile 'webpage.sparse' not found in rev 000000000000 - ignoring it
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd clone1
$ ls -A
.hg
index.html
$ cd ..
Verify local clone with include works
$ hg clone --include *.sparse myrepo clone2
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd clone2
$ ls -A
.hg
backend.sparse
webpage.sparse
$ cd ..
Verify local clone with exclude works
$ hg clone --exclude data.py myrepo clone3
updating to branch default
4 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd clone3
$ ls -A
.hg
backend.sparse
index.html
readme.txt
webpage.sparse
$ cd ..
Verify sparse clone profile over ssh works
$ hg clone -q --enable-profile webpage.sparse ssh://user@dummy/myrepo clone4
warning: sparse profile 'webpage.sparse' not found in rev 000000000000 - ignoring it
$ cd clone4
$ ls -A
.hg
index.html
$ cd ..