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

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 (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	Comma-separated list of Rustup toolchain specifier e.g. stable, nightly, 1.42.0. The last version is the default.	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-directories	Propagates the value to Swatinem/rust-cache
cache-workspaces	Propagates the value to Swatinem/rust-cache
cache-on-failure	Propagates the value to Swatinem/rust-cache	true
cache-key	Propagates the value to Swatinem/rust-cache as key
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"
override	Setup the last installed toolchain as the default via rustup override	true

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.