Add a features list to branches.cache to detect caches of old hg versions.
The leading space in the written file makes sure that the feature list never
can match an existing version, even if the first feature can be read as hex.
Additionally old hg versions display the id with --debug, too.
#!/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