tests: make python oneliner portable to python 3 in remotefilelog test Differential Revision: https://phab.mercurial-scm.org/D5602

remotefilelog: implement __bool__ as well as __nonzero__ for py3 Differential Revision: https://phab.mercurial-scm.org/D5601

remotefilelog: fix logging in retry decorator This still fails with an error about no exception being available to re-raise, but so it goes. Differential Revision: https://phab.mercurial-scm.org/D5600

basepack: avoid 'rbe' mode in Python 3 Differential Revision: https://phab.mercurial-scm.org/D5598

remotefilelog: do file IO in terms of bytes Differential Revision: https://phab.mercurial-scm.org/D5597

rust-cpython: using MissingAncestors from Python code As precedently done with LazyAncestors on cpython.rs, we test for the presence of the 'rustext' module. incrementalmissingrevs() has two callers within the Mercurial core: `setdiscovery.partialdiscovery` and the `only()` revset. This move shows a significant discovery performance improvement in cases where the baseline is slow: using perfdiscovery on the PyPy repos, prepared with `contrib/discovery-helper <repo> 50 100`, we get averaged medians of 403ms with the Rust version vs 742ms without (about 45% better). But there are still indications that performance can be worse in cases the baseline is fast, possibly due to the conversion from Python to Rust and back becoming the bottleneck. We could measure this on mozilla-central in cases were the delta is just a few changesets. This requires confirmation, but if that's the reason, then an upcoming `partialdiscovery` fully in Rust should solve the problem. Differential Revision: https://phab.mercurial-scm.org/D5551

rust: MissingAncestors.basesheads() This new API method on `MissingAncestors` leverages directly the Rust implementation for relative heads of a set, and also lowers the cost of returning the results to Python in the context of discovery. These interchange costs can probably be further reduced by implementing the `partialdiscovery` class in Rust, but that will be investigated in the 5.0 development cycle. Differential Revision: https://phab.mercurial-scm.org/D5584

discovery: using the new basesheads() Our ultimate goal is to switch eventually to a Rust implementation, but this move actually seems to increase the performance in a pure Python build. What follows is a quick measurement done on PyPy on repos prepared with `contrib/discovery-helper.sh 50 100`. Before: ! wall 0.894384 comb 0.890000 user 0.890000 sys 0.000000 (best of 11) ! wall 0.971199 comb 0.970000 user 0.950000 sys 0.020000 (max of 11) ! wall 0.927993 comb 0.925455 user 0.919091 sys 0.006364 (avg of 11) ! wall 0.921619 comb 0.920000 user 0.910000 sys 0.010000 (median of 11) After: ! wall 0.614278 comb 0.610000 user 0.610000 sys 0.000000 (best of 14) ! wall 0.789459 comb 0.790000 user 0.770000 sys 0.020000 (max of 14) ! wall 0.722765 comb 0.720000 user 0.715714 sys 0.004286 (avg of 14) ! wall 0.734448 comb 0.720000 user 0.720000 sys 0.000000 (median of 14) Differential Revision: https://phab.mercurial-scm.org/D5583

ancestor: incrementalmissingancestors.basesheads() This new method will avoid the need to access the `bases` attribute directly in `setdiscovery`, and to prefilter `nullrev` before passing it to the `heads()` revset. Being a method, it can transparently be reimplemented in a Rust (or any native) version. Differential Revision: https://phab.mercurial-scm.org/D5582

rust-cpython: set conversion for MissingAncestors.bases() Also I hope that the separate `py_set()` helper will help transition to proper `PySet` support in `rust-cpython` Took the opportunity to replace explict for loop with iteration and collect(). Differential Revision: https://phab.mercurial-scm.org/D5581