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

# Just exercize debugindexdot
# Create a short file history including a merge.
hg init t
cd t
echo a > a
hg ci -qAm t1 -d '0 0'
echo a >> a
hg ci -m t2 -d '1 0'
hg up -qC 0
echo b >> a
hg ci -m t3 -d '2 0'
HGMERGE=true hg merge -q
hg ci -m merge -d '3 0'

hg debugindexdot .hg/store/data/a.i