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

"$TESTDIR/hghave" symlink || exit 80

cleanpath()
{
    sed -e "s:/.*\(/test-symlink-basic/.*\):...\1:"
}

cat >> readlink.py <<EOF
import os
import sys

for f in sys.argv[1:]:
    print f, '->', os.readlink(f)
EOF

hg init a
cd a
ln -s nothing dangling
hg commit -m 'commit symlink without adding' -d '0 0' dangling 2>&1 | cleanpath
hg add dangling
hg commit -m 'add symlink' -d '0 0'

hg tip -v
hg manifest --debug
echo '% rev 0:'
python ../readlink.py dangling

rm dangling
ln -s void dangling
hg commit -m 'change symlink'
echo '% rev 1:'
python ../readlink.py dangling

echo '% modifying link'
rm dangling
ln -s empty dangling
python ../readlink.py dangling

echo '% reverting to rev 0:'
hg revert -r 0 -a
python ../readlink.py dangling

echo '% backups:'
python ../readlink.py *.orig

rm *.orig
hg up -C
echo '% copies'
hg cp -v dangling dangling2
hg st -Cmard
python ../readlink.py dangling dangling2