Store empty (default) branch in branch cache, too.
Operations on this branch don't work otherwise.
Reading branches.cache had to be adjusted to allow an empty label.
Adjusted reading of the cache tip for symmetry, no functional change here.
#!/bin/sh
hg init t
cd t
hg branches
echo foo > a
hg add a
hg ci -m "initial" -d "1000000 0"
hg branch foo
hg branch
hg ci -m "add branch name" -d "1000000 0"
hg branch bar
hg ci -m "change branch name" -d "1000000 0"
hg branch ""
hg ci -m "clear branch name" -d "1000000 0"
hg co foo
hg branch
echo bleah > a
hg ci -m "modify a branch" -d "1000000 0"
hg merge
hg branch
hg ci -m "merge" -d "1000000 0"
hg log
hg branches
hg branches -q
echo % test for invalid branch cache
hg rollback
cp .hg/branches.cache .hg/bc-invalid
hg log -r foo
cp .hg/bc-invalid .hg/branches.cache
hg --debug log -r foo
rm .hg/branches.cache
echo corrupted > .hg/branches.cache
hg log -qr foo
cat .hg/branches.cache