--hint-msrv=version option so the compiler can take MSRV into account when linting · Issue #772 · rust-lang/compiler-team (original) (raw)

Proposal

Add a --hint-msrv=version command-line option to rustc, which cargo would then pass in based on the rust-version option in Cargo.toml.

The rationale for this is the same reason clippy wants to know rust-version: it allows smarter linting and suggestions. For instance, we could avoid making fix suggestions that would raise MSRV, or alternatively we could emit some metadata saying we'd increase MSRV so that cargo fix could automatically increase MSRV.

As an additional rationale, when we have a cfg for the compiler version, having the MSRV would let us determine if the cfg is always true or always false: rust-lang/rust#64796 (comment)

I'm proposing that the initial implementation of this just validate that its argument is a valid version number (accepting exactly what rust-version accepts), and otherwise ignore it; this would be enough for cargo to start passing it to compilers that support it. Any additional functionality would come later.

The name --hint-msrv helps make it clear that this isn't intended to be load-bearing, and is best-effort.

(Until this is stable, it'll require -Zunstable-options.)

Mentors or Reviewers

I don't have a specific mentor/reviewer in mind here.

Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.