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 1

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echo '[ui]' >> 1/.hg/hgrc

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echo 'timeout = 10' >> 1/.hg/hgrc

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echo foo > 1/foo

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hg --cwd 1 ci -A -m foo

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hg clone 1 2

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hg clone 2 3

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echo '[hooks]' >> 2/.hg/hgrc

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echo 'changegroup.push = hg push -qf ../1' >> 2/.hg/hgrc

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echo bar >> 3/foo

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hg --cwd 3 ci -m bar

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hg --cwd 3 push ../2