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 a
cd a
echo 'root' >root
hg add root
hg commit -d '0 0' -u test -m "Adding root node"

echo 'a' >a
hg add a
hg branch a
hg commit -d '1 0' -u test -m "Adding a branch"

hg update -C 0
echo 'b' >b
hg add b
hg branch b
hg commit -d '2 0' -u test -m "Adding b branch"

echo 'bh1' >bh1
hg add bh1
hg commit -d '3 0' -u test -m "Adding b branch head 1"

hg update -C 2
echo 'bh2' >bh2
hg add bh2
hg commit -d '4 0' -u test -m "Adding b branch head 2"

echo 'c' >c
hg add c
hg branch c
hg commit -d '5 0' -u test -m "Adding c branch"

hg branches
echo '-------'
hg branches -a