No line number printed with the compile error

[grantslatton]

I found a case in which no line number is printed where it is known:

https://play.rust-lang.org/?version=stable&mode=debug&edition=2015&gist=b993c1bf0ecd17c5c8a3e3bc826bea26

Code:

trait Foo {
    type T;
    fn foo(&self, t: Self::T);
}

impl Foo for u32 {
    type T = ();
    
    fn foo(&self, t: impl Clone) {}
}

fn main() {}

Output:

   Compiling playground v0.0.1 (file:///playground)
error[E0049]: method `foo` has 1 type parameter but its trait declaration has 0 type parameters

error: aborting due to previous error

For more information about this error, try `rustc --explain E0049`.
error: Could not compile `playground`.

To learn more, run the command again with --verbose.

[estebank]

This is caused by improper handling of impl Trait in argument position in diagnostics, with code assuming that if the type parameters don't match is purely due to generics. I have a small patch that will fix this issue, but we'll have to rework how we get spans for generic arguments so that all diagnostics can handle impl Trait in arg position.