py3: buildbot spotted more passing tests Differential Revision: https://phab.mercurial-scm.org/D5501

tests: add lots of b prefix goo to test-fastannotate-revmap.py All the paths are now bytes, so now things work correctly. # skip-blame just bytes/str issues in this test Differential Revision: https://phab.mercurial-scm.org/D5500

fastannotate: add a missing b prefix Spotted while debugging a test failure, but this wasn't the problem. # skip-blame b prefix Differential Revision: https://phab.mercurial-scm.org/D5499

rust-cpython: using the new bindings from Python The Python callers detect if we have cpython or direct-ffi bindings and fallback to the Python implementation if none is present. This intermediate state allows to compare the three possibilities. Differential Revision: https://phab.mercurial-scm.org/D5442

rust-cpython: binding for LazyAncestors The `mercurial.rustext.ancestor` module will not in the foreseeable future be a drop-in replacement for the pure `mercurial.ancestor`, because the Rust variants take the index at instantiation whereas the Python ones take a parents function. From the Python side, using the index from `ancestor` would leak internal details out of `mercurial.revlog`, and that's unwanted. Therefore, given that classes defined in `rust-cpython` have the same names in both language, we keep the Rust naming convention (CamelCase). Eventually, though, the ancestor module can be placed under control of `mercurial.policy`, but it will still be up to `revlog` to be aware of that and play the role of a factory for instantiation. Differential Revision: https://phab.mercurial-scm.org/D5441

discovery: move common heads computation inside partialdiscovery object This remove one of the private attribute access. In additions, head tracking and computation is a typical operation we can speed up using Rust.