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
# Test issue 746: renaming files brought by the
# second parent of a merge was broken.
echo % create source repository
hg init t
cd t
echo a > a
hg ci -Am a
cd ..
echo % fork source repository
hg clone t t2
cd t2
echo b > b
hg ci -Am b
echo % update source repository
cd ../t
echo a >> a
hg ci -m a2
echo % merge repositories
hg pull ../t2
hg merge
echo % rename b as c
hg mv b c
hg st
echo % rename back c as b
hg mv c b
hg st