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
hg init
cat > .hg/hgrc <<EOF
[encode]
*.gz = gunzip
[decode]
*.gz = gzip
EOF
echo "this is a test" | gzip > a.gz
hg add a.gz
hg ci -m "test" -d "1000000 0"
echo %% no changes
hg status
touch a.gz
echo %% no changes
hg status
echo %% uncompressed contents in repo
hg debugdata .hg/store/data/a.gz.d 0
echo %% uncompress our working dir copy
gunzip < a.gz
rm a.gz
hg co
echo %% uncompress our new working dir copy
gunzip < a.gz