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

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mkdir alpha

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touch alpha/one

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mkdir beta

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touch beta/two

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hg add alpha/one beta/two

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hg ci -m "start" -d "1000000 0"

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echo 1 > alpha/one

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echo 2 > beta/two

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echo EVERYTHING

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hg diff --nodates

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echo BETA ONLY

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hg diff --nodates beta

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echo INSIDE BETA

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cd beta

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hg diff --nodates .