setup-rust-toolchain/README.md
Iain Lane b01657d9bb
Add support for adding to cache key
When using this action in multiple matrix jobs in the same workflow, the
generated cache key is the same for all of them, because they all get
the same job ID. This means that all apart from the first job are unable
to save the cache, and subsequent runs might restore the wrong cache.

The `Swatinem/rust-cache` action which we use for caching has a `key`
input which it puts in its cache key. (It doesn't override the key, just
adds to it.) Providing this as an input here will allow us to generate a
unique cache key for each job in the matrix.
2024-07-13 07:31:43 +01:00

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# Install Rust Toolchain
This GitHub Action installs a Rust toolchain using rustup.
It further integrates into the ecosystem.
Caching for Rust tools and build artifacts is enabled.
Environment variables are set to optimize the cache hits.
[Problem Matchers] are provided for build messages (cargo, clippy) and formatting (rustfmt).
The action is heavily inspired by *dtolnay*'s <https://github.com/dtolnay/rust-toolchain> and extends it with further features.
## Example workflow
```yaml
name: "Test Suite"
on:
push:
pull_request:
jobs:
test:
name: cargo test
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v4
- uses: actions-rust-lang/setup-rust-toolchain@v1
- run: cargo test --all-features
# Check formatting with rustfmt
formatting:
name: cargo fmt
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v4
# Ensure rustfmt is installed and setup problem matcher
- uses: actions-rust-lang/setup-rust-toolchain@v1
with:
components: rustfmt
- name: Rustfmt Check
uses: actions-rust-lang/rustfmt@v1
```
## Inputs
All inputs are optional.
If a [toolchain file](https://rust-lang.github.io/rustup/overrides.html#the-toolchain-file) (i.e., `rust-toolchain` or `rust-toolchain.toml`) is found in the root of the repository and no `toolchain` value is provided, all items specified in the toolchain file will be installed.
If a `toolchain` value is provided, the toolchain file will be ignored.
If no `toolchain` value or toolchain file is present, it will default to `stable`.
First, all items specified in the toolchain file are installed.
Afterward, the `components` and `target` specified via inputs are installed in addition to the items from the toolchain file.
| Name | Description | Default |
|--------------------|----------------------------------------------------------------------------------------|---------------|
| `toolchain` | Rustup toolchain specifier e.g. `stable`, `nightly`, `1.42.0`. | stable |
| `target` | Additional target support to install e.g. `wasm32-unknown-unknown` | |
| `components` | Comma-separated string of additional components to install e.g. `clippy, rustfmt` | |
| `cache` | Automatically configure Rust cache (using [`Swatinem/rust-cache`]) | true |
| `cache-workspaces` | Propagates the value to [`Swatinem/rust-cache`] | |
| `cache-on-failure` | Propagates the value to [`Swatinem/rust-cache`] | true |
| `key` | Propagates the value to [`Swatinem/rust-cache`] | |
| `matcher` | Enable problem matcher to surface build messages and formatting issues | true |
| `rustflags` | Set the value of `RUSTFLAGS` (set to empty string to avoid overwriting existing flags) | "-D warnings" |
[`Swatinem/rust-cache`]: https://github.com/Swatinem/rust-cache
### RUSTFLAGS
By default, this action sets the `RUSTFLAGS` environment variable to `-D warnings`.
However, rustflags sources are mutually exclusive, so setting this environment variable omits any configuration through `target.*.rustflags` or `build.rustflags`.
* If `RUSTFLAGS` is already set, no modifications of the variable are made and the original value remains.
* If `RUSTFLAGS` is unset and the `rustflags` input is empty (i.e., the empty string), then it will remain unset.
Use this, if you want to prevent the value from being set because you make use of `target.*.rustflags` or `build.rustflags`.
* Otherwise, the environment variable `RUSTFLAGS` is set to the content of `rustflags`.
To prevent this from happening, set the `rustflags` input to an empty string, which will
prevent the action from setting `RUSTFLAGS` at all, keeping any existing preferences.
You can read more rustflags, and their load order, in the [Cargo reference].
## Outputs
| Name | Description |
| ---------------- | ------------------------------------------- |
| `rustc-version` | Version as reported by `rustc --version` |
| `cargo-version` | Version as reported by `cargo --version` |
| `rustup-version` | Version as reported by `rustup --version` |
| `cachekey` | A short hash of the installed rustc version |
## License
The scripts and documentation in this project are released under the [MIT
License].
[MIT License]: LICENSE
[Problem Matchers]: https://github.com/actions/toolkit/blob/main/docs/problem-matchers.md
[Cargo reference]: https://doc.rust-lang.org/cargo/reference/config.html?highlight=unknown#buildrustflags