branchcache: skip entries that are topological heads in the on disk file In the majority of cases, topological heads are also branch heads. We have efficient way to get the topological heads and efficient way to retrieve their branch information. So there is little value in putting them in the branch cache file explicitly. On the contrary, writing them explicitly tend to create very large cache file that are inefficient to read and update. So the branch cache v3 format is no longer including them. This changeset focus on the format aspect and have no focus on the performance aspect. We will cover that later.

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Test null revisions (node 0000000000000000000000000000000000000000, aka rev -1)

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in various circumstances.

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Make an empty repo:

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  $ hg init a

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  $ cd a

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  $ hg files -r 0000000000000000000000000000000000000000

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  [1]

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  $ hg files -r .

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  [1]

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Add an empty commit (this makes the changelog refer to a null manifest node):

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  $ hg commit -m "init" --config ui.allowemptycommit=true

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  $ hg files -r .

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  [1]

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Strip that empty commit (this makes the changelog file empty, as opposed to missing):

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  $ hg --config 'extensions.strip=' strip . > /dev/null

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  $ hg files -r .

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  [1]