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
# 0-2-4
# \ \ \
# 1-3-5
#
# rename in #1, content change in #4.
hg init t
cd t
touch 1
touch 2
hg commit -Am init -d "0 0" # 0
hg rename 1 1a
hg commit -m rename -d "0 0" # 1
hg co -C 0
echo unrelated >> 2
hg ci -m unrelated1 -d "0 0" # 2
hg merge --debug 1
hg ci -m merge1 -d "0 0" # 3
hg co -C 2
echo hello >> 1
hg ci -m unrelated2 -d "0 0" # 4
hg co -C 3
hg merge -y --debug 4
hg co -C 4
hg merge -y --debug 3