Regression in return type error quality with impl trait

[sophiajt]

In playing with impl trait this morning, I noticed that if you do the classic "oops, I left a ; after my return value" error, instead of the helpful message asking if you meant to have the semi-colon, you get this:

We should definitely try to cover this case too with the same improved error messages we have for other return types.

[sophiajt]

Test case

trait Bar {}
impl Bar for bool {}

fn baz() -> impl Bar {
    true;
}

fn main() {
    baz();
}

[larsluthman]

The same error message appears if your function body consists of 'unimplemented!()' or 'panic!()'. In that case it should probably say something like 'Failed to infer return type' instead.

[estebank]

Current output:

error[E0277]: the trait bound `(): Bar` is not satisfied
 --> src/main.rs:4:13
  |
4 | fn baz() -> impl Bar {
  |             ^^^^^^^^ the trait `Bar` is not implemented for `()`
5 |     true;
  |         - consider removing this semicolon
  |
  = note: the return type of a function must have a statically known size

It does not check wether the type actually impl Bar.