# Rules Rust

This repository provides rules for building [Rust][rust] projects with [Bazel][bazel].

[bazel]: https://bazel.build/
[rust]: http://www.rust-lang.org/

<!-- TODO: Render generated docs on the github pages site again, https://bazelbuild.github.io/rules_rust/ -->

<a name="setup"></a>

## Setup

The rules are released, and releases can be found on [the GitHub Releases page](https://github.com/bazelbuild/rules_rust/releases). We recommend using the latest release from that page.

To use `rules_rust` in a project, add the following to your `MODULE.bazel` file:

```python
bazel_dep(name = "rules_rust", version = "0.70.0")
```

Don't forget to substitute in your desired release's version number.

## Specifying Rust version

To use a particular version of the Rust compiler, pass that version to the `toolchain` method of the `rust` extension, like this:

```python
rust = use_extension("@rules_rust//rust:extensions.bzl", "rust")
rust.toolchain(
    edition = "2024",
    versions = [ "1.85.0" ],
)
```

As well as an exact version, `versions` can accept `nightly/{iso_date}` and `beta/{iso_date}` strings for toolchains from different release channels, as in

```python
rust.toolchain(
    edition = "2021",
    versions = [ "nightly/1.85.0" ],
)
```

By default, a `stable` and `nightly` toolchain will be registered if no `toolchain` method is called (and thus no specific versions are registered). However, if only 1 version is passed and it is from the `nightly` or `beta` release channels (i.e. __not__ `stable`), then the following build setting flag must be present, either on the command line or set in the project's `.bazelrc` file:

```text
build --@rules_rust//rust/toolchain/channel=nightly
```

Failure to do so will result in rules attempting to match a `stable` toolchain when one was not registered, thus raising an error.

## Supported bazel versions

The oldest version of Bazel the `main` branch is tested against is `7.4.1`. Previous versions may still be functional in certain environments, but this is the minimum version we strive to fully support.

We test these rules against the latest rolling releases of Bazel, and aim for compatibility with them, but prioritise stable releases over rolling releases where necessary.

## Supported platforms

We aim to support Linux and macOS.

We do not have sufficient maintainer expertise to support Windows. Most things probably work, but we have had to disable many tests in CI because we lack the expertise to fix them. We welcome contributions to help improve its support.