rust: hooking into Python code We introduce a new class called 'rustlazyancestors' in the ancestors module, which is used only if parsers.rustlazyancestors does exist. The implementation of __contains__ stays unchanged, but is now backed by the Rust iterator. It would probably be a good candidate for further development, though, as it is mostly looping, and duplicates the 'seen' set. The Rust code could be further optimized, however it already gives rise to performance improvements: median timing from hg perfancestors: - on pypy: before: 0.077566s after: 0.016676s -79% - on mozilla central: before: 0.190037s after: 0.082225s -58% - on a private repository (about one million revisions): before: 0.567085s after: 0.108816s -80% - on another private repository (about 400 000 revisions): before: 1.440918s after: 0.290116s -80% median timing for hg perfbranchmap base - on pypy: before: 1.383413s after: 0.507993s -63% - on mozilla central: before: 2.821940s after: 1.258902s -55% - on a private repository (about one million revisions): before: 77.065076s after: 16.158475s -80% - on another private repository (about 401 000 revisions): before: 7.835503s after: 3.545331s -54%