rust-dirstate-status: add first Rust implementation of `dirstate.status` Note: This patch also added the rayon crate as a Cargo dependency. It will help us immensely in making Rust code parallel and easy to maintain. It is a stable, well-known, and supported crate maintained by people on the Rust team. The current `dirstate.status` method has grown over the years through bug reports and new features to the point where it got too big and too complex. This series does not yet improve the logic, but adds a Rust fast-path to speed up certain cases. Tested on mozilla-try-2019-02-18 with zstd compression: - `hg diff` on an empty working copy: - c: 1.64(+-)0.04s - rust+c before this change: 2.84(+-)0.1s - rust+c: 849(+-)40ms - `hg commit` when creating a file: - c: 5.960s - rust+c before this change: 5.828s - rust+c: 4.668s - `hg commit` when updating a file: - c: 4.866s - rust+c before this change: 4.371s - rust+c: 3.855s - `hg status -mard` - c: 1.82(+-)0.04s - rust+c before this change: 2.64(+-)0.1s - rust+c: 896(+-)30ms The numbers are clear: the current Rust `dirstatemap` implementation is super slow, its performance needs to be addressed. This will be done in a future series, immediately after this one, with the goal of getting Rust to be at least to the speed of the Python + C implementation in all cases before the 5.2 freeze. At worse, we gate dirstatemap to only be used in those cases. Cases where the fast-path is not executed: - for commands that need ignore support (`status`, for example) - if subrepos are found (should not be hard to add, but winter is coming) - any other matcher than an `alwaysmatcher`, like patterns, etc. - with extensions like `sparse` and `fsmonitor` The next step after this is to rethink the logic to be closer to Jane Street's Valentin Gatien-Baron's Rust fast-path which does a lot less work when possible. Differential Revision: https://phab.mercurial-scm.org/D7058