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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# 0-2-4

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#  \ \ \

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#   1-3-5

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#

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# rename in #1, content change in #4.

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hg init t

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cd t

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touch 1

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touch 2

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hg commit -Am init -d "0 0"  # 0

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hg rename 1 1a

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hg commit -m rename -d "0 0" # 1

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hg co -C 0

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echo unrelated >> 2

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hg ci -m unrelated1 -d "0 0"  # 2

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hg merge --debug 1

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hg ci -m merge1 -d "0 0" # 3

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hg co -C 2

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echo hello >> 1

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hg ci -m unrelated2 -d "0 0" # 4

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hg co -C 3

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hg merge -y --debug 4

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hg co -C 4

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hg merge -y --debug 3

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