branchcache: allow to detect "pure topological case" for branchmap We don't rum this detection every time we run the branchcache, that would be costly. However we now do it when running `hg debugupdatecache`. This will help existing repository to benefit from the fastpath when possible.

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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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