Note when opaque future from `async fn` is involved in a type mismatch is unclear

[SNCPlay42]

fn foo() -> u8 {
    async fn async_fn() -> () {}
    
    async_fn()
}

emits

error[E0308]: mismatched types
 --> src/lib.rs:4:5
  |
1 | fn foo() -> u8 {
  |             -- expected `u8` because of return type
2 |     async fn async_fn() -> () {}
  |                            -- the `Output` of this `async fn`'s found opaque type
3 |
4 |     async_fn()
  |     ^^^^^^^^^^ expected `u8`, found opaque type
  |
  = note:     expected type `u8`
          found opaque type `impl Future`

The note "the Output of this async fn's found opaque type" is kind of hard to understand. If the return type of async_fn isn't explicitly given, it doesn't even point at a type:

2 |     async fn async_fn() {}
  |                         - the `Output` of this `async fn`'s found opaque type

Perhaps the note should instead look like this:

2 |     async fn async_fn() {}
  |     ----- the found opaque type is the `impl Future` returned by this `async fn`

@rustbot label A-async-await A-diagnostics D-confusing T-compiler

[nellshamrell]

Looks like #66463 touched areas of code that are relevant to this issue (not to say that it caused the issue, only that it provides a potential pointer to the parts of the code related to generating this error message)

[tmandry]

@nellshamrell Are you still planning to work on this? If not no worries, feel free to release your assignment.

[henryboisdequin]

Can't this issue be closed (#82165) or is there still more work to be done?