Is there a way to check for obsolete clippy allowances?

Question

Sometimes you want to suppress a clippy warning for the time being and you let clippy ignore a specific rule for a specific code block by adding lines like the following:

#[allow(dead_code)]

But as the project continues, it can actually happen that you remove the problem, without actually removing the allowing of the clippy lint. So is there a way to check for allowed clippy warnings that are actually not being used anymore? So in this example I'd like to be informed when I #[allow(dead_code)] but there is actually no dead code to be found in the given code block.

Answer 1

Since Rust 1.81, the #[expect] attribute can be used to allow the lint, but also warn if the lint is not detected.

#[expect(dead_code)]
fn foo() {}

fn main() {
    foo();
}

Output:

warning: this lint expectation is unfulfilled
 --> src/main.rs:3:10
  |
3 | #[expect(dead_code)]
  |          ^^^^^^^^^
  |
  = note: `#[warn(unfulfilled_lint_expectations)]` on by default