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.

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#!/bin/sh

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#

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# Corrupt an hg repo with two pulls.

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#

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# create one repo with a long history

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hg init source1

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cd source1

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touch foo

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hg add foo

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for i in 1 2 3 4 5 6 7 8 9 10; do

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    echo $i >> foo

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    hg ci -m $i

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done

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cd ..

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# create one repo with a shorter history

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hg clone -r 0 source1 source2

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cd source2

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echo a >> foo

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hg ci -m a

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cd ..

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# create a third repo to pull both other repos into it

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hg init corrupted

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cd corrupted

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# use a hook to make the second pull start while the first one is still running

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echo '[hooks]' >> .hg/hgrc

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echo 'prechangegroup = sleep 5' >> .hg/hgrc

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# start a pull...

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hg pull ../source1 &

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# ... and start another pull before the first one has finished

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sleep 1

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hg pull ../source2 2>/dev/null

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# see the result

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wait

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hg verify

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