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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hg init a

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cd a

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touch empty1

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hg add empty1

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hg commit -m 'add empty1' -d '1000000 0'

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touch empty2

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hg add empty2

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hg commit -m 'add empty2' -d '1000000 0'

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hg up -C 0

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touch empty3

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hg add empty3

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hg commit -m 'add empty3' -d '1000000 0'

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hg heads

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hg merge 1

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# before changeset 05257fd28591, we didn't notice the

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# empty file that came from rev 1.

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hg status

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hg commit -m merge -d '1000000 0'

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hg manifest --debug tip