rust-dirstate: call rust dirstatemap from Python
Since Rust-backed Python classes cannot be used as baseclasses (for
rust-cpython anyway), we use composition rather than inheritance.
This also allows us to keep the IO operations in the Python side, removing
(for now) the need to rewrite VFS in Rust, which would be a heavy undertaking.
Differential Revision: https://phab.mercurial-scm.org/D6634
Ancestors of 5
4 2 0
Ancestors of 6 and 5
4 3 2 1 0
Ancestors of 5 and 4
4 2 0
Ancestors of 7, stop at 6
6
Ancestors of 7, including revs
7 6 5 4 3 2 1 0
Ancestors of 7, 5 and 3, including revs
7 6 5 4 3 2 1 0
Descendants of 5
7 8
Descendants of 5 and 3
6 7 8
Descendants of 5 and 4
5 7 8