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 children command

cat <<EOF >> $HGRCPATH
[extensions]
hgext.children=
EOF

echo "% init"
hg init t
cd t

echo "% no working directory"
hg children

echo % setup
echo 0 > file0
hg ci -qAm 0 -d '0 0'

echo 1 > file1
hg ci -qAm 1 -d '1 0'

echo 2 >> file0
hg ci -qAm 2 -d '2 0'

hg co null
echo 3 > file3
hg ci -qAm 3 -d '3 0'

echo "% hg children at revision 3 (tip)"
hg children

hg co null
echo "% hg children at nullrev (should be 0 and 3)"
hg children

hg co 1
echo "% hg children at revision 1 (should be 2)"
hg children

hg co 2
echo "% hg children at revision 2 (other head)"
hg children

for i in null 0 1 2 3; do
  echo "% hg children -r $i"
  hg children -r $i
done

echo "% hg children -r 0 file0 (should be 2)"
hg children -r 0 file0

echo "% hg children -r 1 file0 (should be 2)"
hg children -r 1 file0

hg co 0
echo "% hg children file0 at revision 0 (should be 2)"
hg children file0