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
mkdir t
cd t
hg init
echo This is file a1 > a
echo This is file b1 > b
hg add a b
hg commit -m "commit #0" -d "1000000 0"
echo This is file b22 > b
hg commit -m"comment #1" -d "1000000 0"
hg update 0
rm b
hg commit -A -m"comment #2" -d "1000000 0"
# in theory, we shouldn't need the "-y" below, but it prevents
# this test from hanging when "hg update" erroneously prompts the
# user for "keep or delete"
hg update -y 1
exit 0