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rust

How to allow and expect a compiler warning in Rust?

Sometimes during development I would like to allow warnings. For example, for dead_code. Yet, in CI and pre_commit git hooks, I have RUSTFLAGS="--deny warnings".

So I'm thinking that what I would like is an attribute such as

#[expect(dead_code)]
fn foo() {
    todo!();
}

It would work similar to TypesScript's @ts-expect-error and yet be more specific, expecting a specific list of warnings.

Not sure whether it would make sense for expecting errors, as well.

Solution

  • This is supported since Rust 1.81.0. The RFC is called Lint Reasons. The form is exactly what you would expect: #[expect(lint)].

    #[expect(dead_code)]
fn foo() {
    todo!();
}

    Playground.

    If the expectation is not fulfilled, a warning is raised. You can #[deny(unfulfilled_lint_expectations)] to make it into an error.

    If you only want to allow the warning (but not warn when it is not raised), use #[allow(lint)]:

    #[allow(dead_code)]
fn foo() {
    todo!();
}

    Playground.