error[E0277]: `?` couldn't convert the error to `impl Debug`
  --> $DIR/cross-return-site-inference.rs:32:18
   |
LL | fn muh() -> Result<(), impl std::fmt::Debug> {
   |             -------------------------------- expected `impl Debug` because of this
LL |     Err("whoops")?;
   |                  ^ the trait `From<&str>` is not implemented for `impl Debug`
   |
   = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
   = help: the trait `FromResidual<Result<Infallible, E>>` is implemented for `Result<T, F>`
   = note: required because of the requirements on the impl of `FromResidual<Result<Infallible, &str>>` for `Result<(), impl Debug>`

error[E0277]: the trait bound `impl Debug: From<&str>` is not satisfied
  --> $DIR/cross-return-site-inference.rs:37:16
   |
LL |     return Err(From::from("foo"));
   |                ^^^^^^^^^^ the trait `From<&str>` is not implemented for `impl Debug`

error[E0277]: the trait bound `impl Debug: From<&str>` is not satisfied
  --> $DIR/cross-return-site-inference.rs:42:9
   |
LL |     Err(From::from("foo"))
   |         ^^^^^^^^^^ the trait `From<&str>` is not implemented for `impl Debug`

error: aborting due to 3 previous errors

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