Tracking issue for MCP 950: Add flag to pass MSRV/`package.rust-version` for use by lints

[rustbot]

This is a tracking issue for MCP "Add flag to pass MSRV/package.rust-version for use by lints" (rust-lang/compiler-team#950).

Note

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Steps

• Implement the MCP
• Adjust the documentation
  • In the Rust Compiler Development Guide if applicable (e.g., for refactorings)
  • In the Rust Forge if applicable (e.g., for policy changes)
  • In the rustc book if applicable (e.g., for target tier or CLI changes)
  • In the Unstable Book if applicable (e.g., for unstable CLI changes)

Unresolved questions

None so far.

Implementation history

• Flag and lint machinery implementation: Introduce -Z lint-rust-version #157707

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@clubby789, consider @rustbot claim'ing the work.

[joshtriplett]

It seems we had two different approved MCPs proposing essentially the same thing:

• MCP 950, proposing -Z lint-rust-version
• MCP 772, proposing --hint-msrv.

Both went through essentially the same discussion over again: people identified that this shouldn't be used as anything more than a hint, and thus that got encoded in the name. For MCP 950, this changed it from -Z msrv=... to -Z lint-rustc-version=.... For MCP 772, this added "hint" to change it to --hint-msrv.

Proposal: could we consolidate these two, around the name --hint-msrv? Rationale:

• This is about the minimum supported Rust version (MSRV), and rustc-version doesn't specify "minimum supported".
• "hint" makes it semantically clearer that this should not be used for anything load-bearing.