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
hg init rep; cd rep
touch empty-file
python -c 'for x in range(10000): print x' > large-file
hg addremove
hg commit -m A
rm large-file empty-file
python -c 'for x in range(10,10000): print x' > another-file
hg addremove -s50
hg commit -m B
echo % comparing two empty files caused ZeroDivisionError in the past
hg update -C 0
rm empty-file
touch another-empty-file
hg addremove -s50
cd ..
hg init rep2; cd rep2
python -c 'for x in range(10000): print x' > large-file
python -c 'for x in range(50): print x' > tiny-file
hg addremove
hg commit -m A
python -c 'for x in range(70): print x' > small-file
rm tiny-file
rm large-file
hg addremove -s50
hg commit -m B
echo % should all fail
hg addremove -s foo
hg addremove -s -1
hg addremove -s 1e6
true