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

set -e

echo "[extensions]" >> $HGRCPATH
echo "hbisect=" >> $HGRCPATH

echo % init
hg init

echo % committing changes
count=0
echo > a
while test $count -lt 32 ; do
    echo 'a' >> a
    test $count -eq 0 && hg add
    hg ci -m "msg $count" -d "$count 0"
    echo % committed changeset $count
    count=`expr $count + 1`
done

echo % log
hg log

echo % hg up -C
hg up -C

echo % bisect test
hg bisect init
hg bisect bad
hg bisect good 1
hg bisect good
hg bisect good
hg bisect good
hg bisect bad
hg bisect good