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ci: add a runner for Windows 10...
ci: add a runner for Windows 10 This is currently only manually invoked, and allows for failure because we only have a single runner that takes over 2h for a full run, and there are a handful of flakey tests, plus 3 known failing tests. The system being used here is running MSYS, Python, Visual Studio, etc, as installed by `install-windows-dependencies.ps1`. This script installs everything to a specific directory instead of using the defaults, so we adjust the MinGW shell path to compensate. Additionally, the script doesn't install the launcher `py.exe`. It is possible to adjust the script to install it, but it's an option to an existing python install (instead of a standalone installer), and I've had the whole python install fail and rollback when requested to install the launcher if it detects a newer one is already installed. In short, it is a point of failure for a feature we don't (yet?) need. Unlike other systems where the intepreter name includes the version, everything here is `python.exe`, so they can't all exist on `PATH` and let the script choose the desired one. (The `py.exe` launcher would accomplish, using the registry instead of `PATH`, but that wouldn't allow for venv installs.) Because of this, switch to the absolute path of the python interpreter to be used (in this case a venv created from the py39 install, which is old, but what both pyoxidizer and TortoiseHg currently use). The `RUNTEST_ARGS` hardcodes `-j8` because this system has 4 cores, and therefore runs 4 parallel tests by default. However on Windows, using more parallel tests than cores results in better performance for whatever reason. I don't have an optimal value yet (ideally the runner itself can make the adjustment on Windows), but this results in saving ~15m on a full run that otherwise takes ~2.5h. I'm also not concerned about how it would affect other Windows machines, because we don't have any at this point, and I have no idea when we can get more. As far as system setup goes, the CI is run by a dedicated user that lacks admin rights. The install script was run by an admin user, and then the standard user was configured to use it. If I set this up again, I'd probably give the dedicated user admin rights to run the install script, and reset to standard user rights when done. The python intepreter failed in weird ways when run by the standard user until it was manually reinstalled by the standard user: Fatal Python error: init_fs_encoding: failed to get the Python codec of the filesystem encoding Additionally, changing the environment through the Windows UI prompts to escalate to an admin user, and then setting the user level environment variables like `TEMP` and `PATH` (to try to avoid exceeding the 260 character path limit) didn't actually change the user's environment. (Likely it changed the admin user's environment, but I didn't confirm that.) I ended up having to use the registry editor for the standard user to make those changes.
Matt Harbison -
r53049:8766d47e stable
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Mercurial Rust Code

This directory contains various Rust code for the Mercurial project. Rust is not required to use (or build) Mercurial, but using it improves performance in some areas.

There are currently four independent Rust projects:

  • chg. An implementation of chg, in Rust instead of C.
  • hgcli. A project that provides a (mostly) self-contained "hg" binary, for ease of deployment and a bit of speed, using PyOxidizer. See hgcli/README.md.
  • hg-core (and hg-cpython): implementation of some functionality of mercurial in Rust, e.g. ancestry computations in revision graphs, status or pull discovery. The top-level Cargo.toml file defines a workspace containing these crates.
  • rhg: a pure Rust implementation of Mercurial, with a fallback mechanism for unsupported invocations. It reuses the logic hg-core but completely forgoes interaction with Python. See rust/rhg/README.md for more details.

Using Rust code

Local use (you need to clean previous build artifacts if you have built without rust previously):

$ make PURE=--rust local # to use ./hg
$ ./tests/run-tests.py --rust # to run all tests
$ ./hg debuginstall | grep -i rust # to validate rust is in use
checking Rust extensions (installed)
checking module policy (rust+c-allow)

If the environment variable HGWITHRUSTEXT=cpython is set, the Rust extension will be used by default unless --no-rust.

One day we may use this environment variable to switch to new experimental binding crates like a hypothetical HGWITHRUSTEXT=hpy.

Special features

In the future, compile-time opt-ins may be added to the features section in hg-cpython/Cargo.toml.

To use features from the Makefile, use the HG_RUST_FEATURES environment variable: for instance HG_RUST_FEATURES="some-feature other-feature".

Profiling

Setting the environment variable RUST_LOG=trace will make hg print a few high level rust-related performance numbers. It can also indicate why the rust code cannot be used (say, using lookarounds in hgignore).

Creating a .cargo/config file with the following content enables debug information in optimized builds. This make profiles more informative with source file name and line number for Rust stack frames and (in some cases) stack frames for Rust functions that have been inlined:

[profile.release]
debug = true

py-spy (https://github.com/benfred/py-spy) can be used to construct a single profile with rust functions and python functions (as opposed to hg --profile, which attributes time spent in rust to some unlucky python code running shortly after the rust code, and as opposed to tools for native code like perf, which attribute time to the python interpreter instead of python functions).

Example usage:

$ make PURE=--rust local # Don't forget to recompile after a code change
$ py-spy record --native --output /tmp/profile.svg -- ./hg ...

Developing Rust

Minimum Supported Rust Version

The minimum supported rust version (MSRV) is specified in the Clippy configuration file at rust/clippy.toml. It is set to be 1.79.0 as of this writing, but keep in mind that the authoritative value is the one from the configuration file.

We bump it from time to time, with the general rule being that our MSRV should not be greater that the version of the Rust toolchain shipping with Debian testing, so that the Rust enhanced Mercurial can be eventually packaged in Debian.

To ensure that you are not depending on features introduced in later versions, you can issue rustup override set x.y.z at the root of the repository.

Build and development

Go to the hg-cpython folder:

$ cd rust/hg-cpython

Or, only the hg-core folder. Be careful not to break compatibility:

$ cd rust/hg-core

Simply run:

$ cargo build --release

It is possible to build without --release, but it is not recommended if performance is of any interest: there can be an order of magnitude of degradation when removing --release.

For faster builds, you may want to skip code generation:

$ cargo check

For even faster typing:

$ cargo c

You can run only the rust-specific tests (as opposed to tests of mercurial as a whole) with:

$ cargo test --all

Formatting the code

We use rustfmt to keep the code formatted at all times. For now, we are using the nightly version because it has been stable enough and provides comment folding.

Our CI enforces that the code does not need reformatting. Before submitting your changes, please format the entire Rust workspace by running:

$ cargo +nightly fmt

This requires you to have the nightly toolchain installed.

Linting: code sanity

We're using Clippy, the standard code diagnosis tool of the Rust community.

Our CI enforces that the code is free of Clippy warnings, so you might want to run it on your side before submitting your changes. Simply do:

% cargo clippy

from the top of the Rust workspace. Clippy is part of the default rustup install, so it should work right away. In case it would not, you can install it with rustup component add.