Add option to read version from `rust-version` in `Cargo.toml`

[nik-rev]

I use nightly Rust in rust-toolchain.toml to get the nightly version of tools (clippy, rust-analyzer, rustfmt):

toolchain.channel = "nightly-2025-08-24"

But my project is supposed to build on stable rust 1.88. To do this, I set rust-version (MSRV) in Cargo.toml:

[package]
rust-version = "1.88"

In my CI I want to use toolchain of rust-version (stable) for these workflows:

• cargo check
• cargo test --workspace

And use the toolchain from rust-toolchain.toml for these workflows:

• cargo clippy -- -D warnings (rust-toolchain.toml)
• cargo fmt --check (rust-toolchain.toml)

To do that, I need to duplicate the entire components field from rust-toolchain.toml and I also duplicate the MSRV in the workflows. It would be nice to have a single source of truth for versions

Wanted behaviour

An input to the workflow to specify that I want the rust-version in Cargo.toml to override the version specified in rust-toolchain.toml. components field in rust-toolchain.toml should still be read.

I use your workflow in all of my projects, and I love it! Thanks for making it.

[xtqqczze]

@nik-rev You could probably achieve something like that with a composite action:

name: "Extract Rust MSRV"
description: "Reads rust-version from Cargo.toml and exports RUST_MIN_SRV"

runs:
  using: "composite"
  steps:
    - name: Extract MSRV from Cargo.toml
      shell: bash
      run: |
        MSRV=$(cargo metadata --no-deps --format-version 1 \
          | jq -r '.packages[0].rust_version')
        echo "RUST_MIN_SRV=$MSRV" >> "$GITHUB_ENV"

[jonasbb]

This already exists as an action just not as part of this one.
https://github.com/actions-rust-lang/msrv

[jonasbb]

Given that actions-rust-lang/msrv exist, this issue can be closed.