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
#
# Corrupt an hg repo with a pull started during an aborted commit
#
# Create two repos, so that one of them can pull from the other one.
hg init source
cd source
touch foo
hg add foo
hg ci -m 'add foo'
hg clone . ../corrupted
echo >> foo
hg ci -m 'change foo'
# Add a hook to wait 5 seconds and then abort the commit
cd ../corrupted
echo '[hooks]' >> .hg/hgrc
echo 'pretxncommit = sleep 5; exit 1' >> .hg/hgrc
# start a commit...
touch bar
hg add bar
hg ci -m 'add bar' &
# ... and start a pull while the commit is still running
sleep 1
hg pull ../source 2>/dev/null
# see what happened
wait
hg verify