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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echo % init foo-base

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hg init foo-base

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echo % create alpha in first repo

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cd foo-base

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echo 'alpha' > alpha

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hg ci -A -m 'add alpha' -d '1 0'

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cd ..

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echo % clone foo-base to foo-work

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hg clone foo-base foo-work

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echo % create beta in second repo

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cd foo-work

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echo 'beta' > beta

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hg ci -A -m 'add beta' -d '2 0'

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cd ..

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echo % create gamma in first repo

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cd foo-base

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echo 'gamma' > gamma

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hg ci -A -m 'add gamma' -d '3 0'

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cd ..

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echo % pull into work and merge

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cd foo-work

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hg pull -q

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hg merge

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echo % revert to changeset 1 to simulate a failed merge

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rm alpha beta gamma

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hg up -C 1