rust-lang / rust-lang/rust-clippy

Regression: `undocumented_unsafe_blocks` false positive on a multi-line attribute between // SAFETY and `unsafe`

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#15,915 3 comments 1 reaction 0 assignees View on GitHub

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C-bug I-false-positive
Dominant language
Rust
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Description

Summary

Seems to be a recent regression. I'm not sure what the release cycle for clippy is, but it has appreared in rustup's nightly within the last week. Maybe due to #15678?

Lint Name

undocumented_unsafe_blocks

Reproducer

I tried this code:

#![warn(clippy::undocumented_unsafe_blocks)]

unsafe fn f() {}

fn main() {
    // SAFETY: trust me
    #[allow(
        unused // can be any lint
    )]
    unsafe {
        f();
    }
}

I saw this happen:

warning: unsafe block missing a safety comment
  --> src/main.rs:10:5
   |
10 |     unsafe {
   |     ^^^^^^^^
   |
   = help: consider adding a safety comment on the preceding line
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#undocumented_unsafe_blocks
note: the lint level is defined here
  --> src/main.rs:1:9
   |
 1 | #![warn(clippy::undocumented_unsafe_blocks)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I expected to see this happen:

no warning

Version
clippy 0.1.92 (f04e3dfc87 2025-10-19)
Additional Labels

No response

Contributor guide

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First steps

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the provided reproducer in src/main.rs with Clippy's undocumented_unsafe_blocks lint enabled. Investigate how the lint handles the multi-line #[allow(...)] attribute between the // SAFETY comment and unsafe block, then add coverage showing that this case produces no warning.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
tooling
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
55/100

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