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

echo "[extensions]" >> $HGRCPATH
echo "imerge=" >> $HGRCPATH
HGMERGE=true
export HGMERGE

hg init base
cd base

echo foo > foo
echo bar > bar
hg ci -Am0 -d '0 0'

hg mv foo foo2
echo foo >> foo2
hg ci -m1 -d '1 0'

hg up -C 0
echo bar >> foo
echo bar >> bar
hg ci -m2 -d '2 0'

echo % start imerge
hg imerge

cat foo2
cat bar

echo % status -v
hg -v imerge st

echo % next
hg imerge next

echo % merge next
hg --traceback imerge

echo % unresolve
hg imerge unres foo

echo % merge foo
hg imerge merge foo

echo % save
echo foo > foo2
hg imerge save ../savedmerge

echo % load
hg up -C 0
hg imerge --traceback load ../savedmerge
cat foo2

hg ci -m'merged' -d '3 0'
hg tip -v

echo % nothing to merge -- tip
hg imerge

hg up 0
echo % nothing to merge
hg imerge

exit 0