rustc doesn't suggest missing .await before a `?`

[jimblandy]

When I compile the following code:

async fn fallible() -> Result<(), ()> { Ok(()) }

async fn caller() -> Result<(), ()> {
    fallible() /* mising .await */ ?;
    Ok(())
}

fn main() -> Result<(), ()> {
    futures::executor::block_on(caller())
}

rustc says:

error[E0277]: the `?` operator can only be applied to values that implement `std::ops::Try`
 --> src/main.rs:4:5
  |
4 |     fallible() /* mising .await */ ?;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `impl core::future::future::Future`
  |
  = help: the trait `std::ops::Try` is not implemented for `impl core::future::future::Future`
  = note: required by `std::ops::Try::into_result`

I think it should notice that the program is trying to apply ? to a future, and suggest awaiting it.

(If there is an existing issue for this, it is not labeled A-async-await and A-suggestion-diagnostics.)

[jimblandy]

Related: #61076