match: strengthen visit_children_set invariant, Recursive means "all files" My previous interpretation of "Recursive" was too relaxed: I thought it instructed the caller to do something like this: > you can stop calling `visit_children_set` because you'll need to descend into > every directory recursively, but you should still check every file if it > matches or not Whereas the real instruction seems to be: > I guarantee that everything in this subtree matches, you can stop > querying the matcher for all files and dirs altogether. The evidence to support this: - the test actually passes with the stronger invariant, revealing no exceptions from this rule - the implementation of `visit_children_set` for `DifferenceMatcher` clearly relies on this requirement, so it must hold for that not to lead to bugs.

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Set up

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  $ hg init repo

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  $ cd repo

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  $ echo a > a

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  $ hg add a

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  $ hg commit -m a

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Try to import an empty patch

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  $ hg import --no-commit - <<EOF

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  > EOF

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  applying patch from stdin

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  abort: stdin: no diffs found

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  [10]

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No dirstate backups are left behind

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  $ ls .hg/dirstate* | sort

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  .hg/dirstate

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