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

cat >findbranch.py <<EOF
import re, sys

head_re = re.compile('^#(?:(?:\\s+([A-Za-z][A-Za-z0-9_]*)(?:\\s.*)?)|(?:\\s*))$')

for line in sys.stdin:
    hmatch = head_re.match(line)
    if not hmatch:
        sys.exit(1)
    if hmatch.group(1) == 'Branch':
        sys.exit(0)
sys.exit(1)
EOF
hg init a
cd a
echo "Rev 1" >rev
hg add rev
hg commit -m "No branch."
hg branch abranch
echo "Rev  2" >rev
hg commit -m "With branch."
if hg export 0 | python ../findbranch.py; then
    echo "Export of default branch revision has Branch header" 1>&2
    exit 1
fi
if hg export 1 | python ../findbranch.py; then
    :  # Do nothing
else
    echo "Export of branch revision is missing Branch header" 1>&2
    exit 1
fi
# Make sure import still works with branch information in patches.
cd ..
hg init b
cd b
hg -R ../a export 0 | hg import -
hg -R ../a export 1 | hg import -
cd ..
rm -rf b
hg init b
cd b
hg -R ../a export 0 | hg import --exact -
hg -R ../a export 1 | hg import --exact -