setup-rust-toolchain/README.md

# 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@v3
      - 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@v3
      # 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, it takes precedence.
All input values are ignored if a toolchain file exists.

| 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` |         |

## 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` |

## 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