Tracking issue for minimum supported Rust version (RFC 2495)

[djc]

RFC: https://github.com/rust-lang/rfcs/blob/master/text/2495-min-rust-version.md
Rust tracking issue: rust-lang/rust#65262
Initial implementation: #8037
Documentation: https://doc.rust-lang.org/cargo/reference/manifest.html#the-rust-version-field

Concise description of the implementation:

• An optional rust-version field in the Cargo.toml package section, which can contain a version number like "1.43.1" or "1.56". It must be a single version number, with no semver operator(s) or pre-release identifier. The version must be equal to or newer than the version that first introduces support for the configured edition.
• If specified, Cargo versions newer than the one stabilizing this feature will start to fail any compile-like commands with an error referring to the specified rust-version if the crate is compiled with an older version of the compiler. Pre-release identifiers for the active compilers are ignored for purposed of comparison.
• The rust-version field may be ignored using the --ignore-rust-version option.

[djc]

My call for testing in https://users.rust-lang.org/t/call-for-testing-unstable-cargo-support-for-rust-version/59386/4 has not yielded any explicit feedback (other than likes on the post). What should we do next? Would be nice to have this stabilized (the edition coming up is also one reason why this might start being more useful).

[ehuss]

I think stabilizing would be fine. Just need to submit a PR, updating the documentation, and write a clear description of what is being stabilized.

[djc]

What is being stabilized:

• An optional rust-version field in the Cargo.toml package section, which can contain a version number like "1.43.1" or "1.56". It must be a single version number, with no semver operator(s) or pre-release identifier. The version must be equal to or newer than the version that first introduces support for the configured edition.
• If specified, Cargo versions newer than the one stabilizing this feature will start to fail any compile-like commands with an error referring to the specified rust-version if the crate is compiled with an older version of the compiler. Pre-release identifiers for the active compilers are ignored for purposed of comparison.
• The rust-version field may be ignored using the --ignore-rust-version option.

[ehuss]

Closing as this has been stabilized in #9732.

[djc]

Shouldn't cargo tracking issue FCPs get tracked in This Week in Rust?

[est31]

List of issues in rust related tooling to provide support for the new feature:

• use minimal supported rust version rust-version from Cargo.toml actions-rs/toolchain#206
• Support the rust-version field in Cargo.toml to specify the MSRV rust-clippy#7765
• Allow cargo +rust-version build|test|... rustup#2925