`expect` on struct does not cover the derives

[joshtriplett]

Minimal reproducer:

#[expect(clippy::derived_hash_with_manual_eq)]
#[derive(Hash)]
pub struct Thing;

impl PartialEq<Thing> for Thing {
    fn eq(&self, _other: &Thing) -> bool {
        true
    }
}

I ran cargo clippy, and I expected the expect to suppress the clippy::derived_hash_with_manual_eq lint. Instead, I got the following:

error: you are deriving `Hash` but have implemented `PartialEq` explicitly
 --> src/lib.rs:2:10
  |
2 | #[derive(Hash)]
  |          ^^^^
  |
note: `PartialEq` implemented here
 --> src/lib.rs:5:1
  |
5 | impl PartialEq<Thing> for Thing {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#derived_hash_with_manual_eq
  = note: `#[deny(clippy::derived_hash_with_manual_eq)]` on by default
  = note: this error originates in the derive macro `Hash` (in Nightly builds, run with -Z macro-backtrace for more info)

warning: this lint expectation is unfulfilled
 --> src/lib.rs:1:10
  |
1 | #[expect(clippy::derived_hash_with_manual_eq)]
  |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unfulfilled_lint_expectations)]` on by default

I haven't found any way to apply the expect to the derive except by putting it on the containing module.

Note, however, that replacing the expect with an allow does successfully suppress the warning. This seems particularly surprising, and violates the expectation that replacing an allow with an expect should always work.

Meta

rustc --version --verbose:

rustc 1.81.0 (eeb90cda1 2024-09-04)
binary: rustc
commit-hash: eeb90cda1969383f56a2637cbd3037bdf598841c
commit-date: 2024-09-04
host: x86_64-unknown-linux-gnu
release: 1.81.0
LLVM version: 18.1.7

[joshtriplett]

Highlighting the particularly surprising part of this: Note that replacing the expect with an allow does successfully suppress the warning.

[Urgau]

cc @xFrednet

[xFrednet]

I believe there are two issues here:

1. More generally speaking: My understanding is that derives create a new item that is not affected by lint levels set on the struct.
2. Clippy has several lints that check for explicit allow's on the struct itself. Since this is a clippy lint, I'm fairly certain, that the lint simply needs to be updated, to account for both lint levels.

Problem one, is a macro / language design issue. Problem 2 is a Clippy bug.

Edit: I created rust-lang/rust-clippy#13356 to fix this specific lint (Problem 2).