undocumented_unsafe_blocks does not trigger on unsafe trait impls

[djkoloski]

Summary

missing_safety_doc and undocumented_unsafe_blocks complement each other to provide full safety documentation coverage. While missing_safety_doc triggers on unsafe trait definitions and warn that safety docs must be provided, undocumented_unsafe_blocks does not trigger on unsafe trait implementations.

Lint Name

undocumented_unsafe_blocks

Reproducer

I tried this code:

#![warn(clippy::undocumented_unsafe_blocks)]

/// # Safety
///
/// The implementor must justify with a safety comment.
unsafe trait Foo {}

unsafe impl Foo for () {}

/// # Safety
///
/// The caller must justify with a safety comment.
unsafe fn foo() {}

fn main() {
    // SAFETY: It's justified.
    unsafe {
        foo();
    }
}

I expected to see this happen:

warning: unsafe impl missing a safety comment
  --> src/main.rs:8:1

Instead, this happened:

No lint triggered for the unsafe impl.

Version

rustc 1.59.0 (9d1b2106e 2022-02-23)
binary: rustc
commit-hash: 9d1b2106e23b1abd32fce1f17267604a5102f57a
commit-date: 2022-02-23
host: x86_64-apple-darwin
release: 1.59.0
LLVM version: 13.0.0

[tamaroning]

@rustbot claim

[tamaroning]

I'm gonna tackle with this after #8450 is merged

[repi]

Would love to see this! We are using undocumented_unsafe_blocks by default and this is an important gap in its coverage