convert: add a mode where mercurial_sink skips empty revisions.
The getchanges function of some converter_source classes can return
some false positives. I.e. they sometimes claim that a file "foo"
was changed in some revision, even though its contents are still the
same.
convert_svn is particularly bad, but I think this can also happen with
convert_cvs and, at least in theory, with mercurial_source.
For regular conversions this is not really a problem - as long as
getfile returns the right contents, we'll get a converted revision
with the right contents. But when we use --filemap, this could lead
to superfluous revisions being converted.
Instead of fixing every converter_source, I decided to change
mercurial_sink to work around this problem.
When --filemap is used, we're interested only in revisions that touch
some specific files. If a revision doesn't change any of these files,
then we're not interested in it (at least for revisions with a single
parent; merges are special).
For mercurial_sink, we abuse this property and rollback a commit if
the manifest text hasn't changed. This avoids duplicating the logic
from localrepo.filecommit to detect unchanged files.
#!/bin/sh
#
# Corrupt an hg repo with two pulls.
#
# create one repo with a long history
hg init source1
cd source1
touch foo
hg add foo
for i in 1 2 3 4 5 6 7 8 9 10; do
echo $i >> foo
hg ci -m $i
done
cd ..
# create one repo with a shorter history
hg clone -r 0 source1 source2
cd source2
echo a >> foo
hg ci -m a
cd ..
# create a third repo to pull both other repos into it
hg init corrupted
cd corrupted
# use a hook to make the second pull start while the first one is still running
echo '[hooks]' >> .hg/hgrc
echo 'prechangegroup = sleep 5' >> .hg/hgrc
# start a pull...
hg pull ../source1 &
# ... and start another pull before the first one has finished
sleep 1
hg pull ../source2 2>/dev/null
# see the result
wait
hg verify