impl Trait missed bound should hint if underlying type could satisfy the bound

Code

use core::fmt::Debug;

fn accepts_copy(_x: impl Copy + Debug) {}

fn create_copyable() -> impl Debug { 42i32 }

fn main() {
    accepts_copy(create_copyable());
}

Current output

error[E0277]: the trait bound `impl Debug: std::marker::Copy` is not satisfied
 --> src/main.rs:8:19
  |
8 |     accepts_copy(create_copyable());
  |     ------------ ^^^^^^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `impl Debug`
  |     |
  |     required by a bound introduced by this call
  |
note: required by a bound in `accepts_clone`
 --> src/main.rs:3:26
  |
3 | fn accepts_copy(_x: impl Copy + Debug) {}
  |                          ^^^^ required by this bound in `accepts_clone`

For more information about this error, try `rustc --explain E0277`.

Desired output

error[E0277]: the trait bound `impl Debug: std::marker::Copy` is not satisfied
 --> src/main.rs:8:19
  |
8 |     accepts_copy(create_copyable());
  |     ------------ ^^^^^^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `impl Debug`
  |     |
  |     required by a bound introduced by this call
  |
note: required by a bound in `accepts_clone`
 --> src/main.rs:3:26
  |
3 | fn accepts_copy(x: impl Copy + Debug) {}
  |                         ^^^^ required by this bound in `accepts_clone`
  |
note: underlying type `i32` implements `Copy`, consider changing the bound
  |
5 | fn create_copyable() -> impl Debug + Copy { 42i32 }
                                      +++++++

Rationale and extra context

I was inspired to report this by this issue.

In cases where the originator of the impl Trait type is 'owned' by the consumer (i.e: is in the same crate/workspace) and the underlying type is found to implement the required trait, a note that explains how to express this syntactically would be very useful.

This might even be a useful diagnostic even when the underlying type does not implement the required trait, although this is much more debatable.

Other cases

Rust Version

1.92.0-nightly (2025-09-14 52618eb338609df44978)

Anything else?

No response

Reproduce the diagnostic using the Rust code in the issue, starting with src/main.rs and the shown rustc output. Trace the compiler diagnostic path for an impl Trait bound failure and determine how the underlying type and suggested bound can be identified. Done means the diagnostic adds the requested note and source suggestion when the underlying type satisfies the missing bound, with suitable compiler tests.