diagnostic::on_unimplemented fails to trigger

[konnorandrews]

Code

#[diagnostic::on_unimplemented(
    message = "message",
)]
pub trait ProviderLt {}

pub trait ProviderExt {
    fn request<R>(&self) {
        todo!()
    }
}

impl<T: ?Sized + ProviderLt> ProviderExt for T {}

struct A<'a>(&'a ());

struct B; // works

fn main() {
    A(&()).request();
    
    B.request(); // works
}

Current output

error[E0599]: the method `request` exists for struct `A<'_>`, but its trait bounds were not satisfied
  --> src/main.rs:19:12
   |
14 | struct A<'a>(&'a ());
   | ------------ method `request` not found for this struct because it doesn't satisfy `A<'_>: ProviderExt` or `A<'_>: ProviderLt`
...
19 |     A(&()).request();
   |            ^^^^^^^ method cannot be called on `A<'_>` due to unsatisfied trait bounds
   |
note: trait bound `A<'_>: ProviderLt` was not satisfied
  --> src/main.rs:12:18
   |
12 | impl<T: ?Sized + ProviderLt> ProviderExt for T {}
   |                  ^^^^^^^^^^  -----------     -
   |                  |
   |                  unsatisfied trait bound introduced here
note: the trait `ProviderLt` must be implemented
  --> src/main.rs:4:1
   |
4  | pub trait ProviderLt {}
   | ^^^^^^^^^^^^^^^^^^^^
   = help: items from traits can only be used if the trait is implemented and in scope
note: `ProviderExt` defines an item `request`, perhaps you need to implement it
  --> src/main.rs:6:1
   |
6  | pub trait ProviderExt {
   | ^^^^^^^^^^^^^^^^^^^^^

error[E0599]: message
  --> src/main.rs:21:7
   |
16 | struct B; // works
   | -------- method `request` not found for this struct because it doesn't satisfy `B: ProviderExt` or `B: ProviderLt`
...
21 |     B.request(); // works
   |       ^^^^^^^ method cannot be called on `B` due to unsatisfied trait bounds
   |
note: trait bound `B: ProviderLt` was not satisfied
  --> src/main.rs:12:18
   |
12 | impl<T: ?Sized + ProviderLt> ProviderExt for T {}
   |                  ^^^^^^^^^^  -----------     -
   |                  |
   |                  unsatisfied trait bound introduced here
note: the trait `ProviderLt` must be implemented
  --> src/main.rs:4:1
   |
4  | pub trait ProviderLt {}
   | ^^^^^^^^^^^^^^^^^^^^
   = help: items from traits can only be used if the trait is implemented and in scope
note: `ProviderExt` defines an item `request`, perhaps you need to implement it
  --> src/main.rs:6:1
   |
6  | pub trait ProviderExt {
   | ^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0599`.

Desired output

The first error should also be using the "message" message like the second one.

Rationale and extra context

Playground link: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=f9313422f1b0da95507832b37b234c30

Other cases

No response

Rust Version

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

Anything else?

No response

[weiznich]

I think in the end this is quite similar to #125231, which means the compiler just sees the wild card impl and tries to prove that this one holds. In my opinion that's something that might be solveable by the crate author using the currently unstable #[diagonstic::do_not_recommend] on the wild card impl.

Also that sounds really similar to #130563