`unnecessary_safety_comment` and `undocumented_unsafe_blocks` won't find `SAFETY` comments between attributes

[teofr]

Summary

unnecessary_safety_comment and undocumented_unsafe_blocks have an accept-comment-above-attributes configuration, signaling that SAFETY comments can be accepted or looked for above attributes. However, this changes the semantics of the lint, only looking for comments above the topmost attribute.

For example, the following code only lints if accept-comment-above-attributes is false:

fn foo() {
    #[doc(hidden)]
    // SAFETY: ...
    let x = 34;
}

As far as I understand, that's a bug rather than the config indicating that SAFETY comments are only looked for above attributes, since if that were the case there's code that won't lint in any configuration:

fn foo() {
    #[doc(hidden)]
    // SAFETY: ...
    #[must_use]
    let x = 34;
}

Reproducer

I tried this code:

fn foo() {
    #[doc(hidden)]
    // SAFETY: ...
    let x = 34;
}

I expected to see this happen:

A lint indicating an unnecessary_safety_comment occured.

Instead, this happened:

No lint

https://godbolt.org/z/v7xTozs6h

Version

rustc 1.92.0-nightly (4645a7988 2025-09-17)
binary: rustc
commit-hash: 4645a7988177c286f61609cc667ecae4c571a2e8
commit-date: 2025-09-17
host: aarch64-apple-darwin
release: 1.92.0-nightly
LLVM version: 21.1.1

Additional Labels

No response

[teofr]

@rustbot claim

[teofr]

Just a note, on undocumented_unsafe_blocks the lint happens when it shouldn't (since it can't find the SAFETY comment above the attributes). So we have both a false positive and a false negative

@rustbot label +I-false-positive
@rustbot label +I-false-negative

[rustbot]

Unknown labels: l-false-negative