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rust-dirstate-status: add first Rust implementation of `dirstate.status`...
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
Raphaël Gomès -
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Mercurial Rust Code

This directory contains various Rust code for the Mercurial project.

The top-level Cargo.toml file defines a workspace containing all primary Mercurial crates.

Building

To build the Rust components:

$ cargo build

If you prefer a non-debug / release configuration:

$ cargo build --release

Features

The following Cargo features are available:

localdev (default)

Produce files that work with an in-source-tree build.

In this mode, the build finds and uses a python2.7 binary from PATH. The hg binary assumes it runs from rust/target/<target>hg and it finds Mercurial files at dirname($0)/../../../.

Build Mechanism

The produced hg binary is bound to a CPython installation. The binary links against and loads a CPython library that is discovered at build time (by a build.rs Cargo build script). The Python standard library defined by this CPython installation is also used.

Finding the appropriate CPython installation to use is done by the python27-sys crate's build.rs. Its search order is:

  1. PYTHON_SYS_EXECUTABLE environment variable.
  2. python executable on PATH
  3. python2 executable on PATH
  4. python2.7 executable on PATH

Additional verification of the found Python will be performed by our build.rs to ensure it meets Mercurial's requirements.

Details about the build-time configured Python are built into the produced hg binary. This means that a built hg binary is only suitable for a specific, well-defined role. These roles are controlled by Cargo features (see above).

Running

The hgcli crate produces an hg binary. You can run this binary via cargo run:

$ cargo run --manifest-path hgcli/Cargo.toml

Or directly:

$ target/debug/hg
$ target/release/hg

You can also run the test harness with this binary:

$ ./run-tests.py --with-hg ../rust/target/debug/hg

Note

Integration with the test harness is still preliminary. Remember to cargo build after changes because the test harness doesn't yet automatically build Rust code.