Read `Cargo.toml` and `Cargo.lock` for automatically installing the environment

[TheRealBecks]

Problem you are trying to solve

I'm new to Rust and trying to initialize an existing Rust project (https://github.com/containers/podlet) on my machine. I already cloned the repository and then installed rustup and trying to install the Rust version and packages defined in the Cargo.toml and Cargo.lock. But I can't figure out how I need to use rustup to read these files. Maybe that's not yet implemented?

I had to manually gather the version 1.85 from the Cargo.toml to install the correct toolchain:

rustup toolchain install 1.85

Cargo.toml file:

[package]
name = "podlet"
edition = "2024"
rust-version = "1.85"
[...]

[dependencies]
clap = { version = "4.2", features = ["derive", "wrap_help"] }
[...]

Solution you'd like

I would like to run a command that reads the necessary files itself like:

rustup toolchain install --toml-file [Cargo.toml]

...defaulting to Cargo.toml.

Maybe also reading Cargo.lock makes sense?

Notes

No response

[rami3l]

@TheRealBecks Hi there! You are generally speaking NOT supposed to install the Rust version from Cargo.toml, since the spec says it's the minimal supported version.

Unlike Python or other languages that you might have used (esp. Python that breaks on minor updates), we break on major updates (and we have been on v1 since 10+ years ago), and thus encourage the user to just follow the latest "stable" version for regular dev, so if there is no rust-toolchain.toml to pin a toolchain version, just doing rustup default stable to install the latest stable will suffice. Enjoy!

[rami3l]

Aside: How did you install rustup? If it's via the official website https://rustup.rs, then a toolchain must have been downloaded for you upon installation.

If it's via Debian's APT or similar, the lack of guidance is a known issue and the responsibility should fall on their side since they have completely skipped the installation phase that we set up. See #4651 (comment) for more info on this if this is your case.

[TheRealBecks]

Good catch, I'm familiar with Python and the uv tool 😂 Therefore I thought that rustup will read the version in the Cargo.toml file by default if not specified by any other file or command line argument.

I already saw that I can set up a default toolchain with rustup default stable, but from my perspective I wanted to use what the project defines as minimal version as I want to stay conform to the project when I develop new features.

That being said: rustup default stable installed version 1.93 which is way newer than the project defined version 1.85. If I understood correctly this is not what I should use when developing for the example project that I linked earlier.

On the other side you wrote about the rust-toolchain.toml (docs) which is currently absent from the project. If I understand the documentation and your comment correctly I need to create that file containing the channel = "1.85" entry?

[Diggsey]

If I understood correctly this is not what I should use when developing for the example project that I linked earlier.

That would depend on the contributing guidelines for the project and your personal preference. The expectation is that the minimal rust version is tested in CI to ensure it compiles successfully, but that doesn't necessarily mean contributors need to use that version, and I would expect most contributors simply use the latest stable Rust. If projects want everyone to use a specific version they will generally commit a rust-toolchain.toml.

If you prefer to work directly in the minimal supported version, you can set a directory level override (See rustup override --help) so that rustup will use that exact version for any work you do in that project.

[TheRealBecks]

Thanks for your help, I now understand how that works! 🙂