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 rep; cd rep

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touch empty-file

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python -c 'for x in range(10000): print x' > large-file

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hg addremove

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hg commit -m A

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rm large-file empty-file

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python -c 'for x in range(10,10000): print x' > another-file

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hg addremove -s50

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hg commit -m B

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echo % comparing two empty files caused ZeroDivisionError in the past

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hg update -C 0

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rm empty-file

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touch another-empty-file

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hg addremove -s50

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cd ..

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hg init rep2; cd rep2

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python -c 'for x in range(10000): print x' > large-file

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python -c 'for x in range(50): print x' > tiny-file

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hg addremove

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hg commit -m A

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python -c 'for x in range(70): print x' > small-file

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rm tiny-file

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rm large-file

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hg addremove -s50

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hg commit -m B

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echo % should all fail

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hg addremove -s foo

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hg addremove -s -1

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hg addremove -s 1e6

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true