ICE with impl_trait_in_bindings

[JohnTitor]

Code

This snippet is found in #60473.

Reduced:

#![feature(impl_trait_in_bindings)]
#![allow(incomplete_features)]

struct A<'a>(&'a ());

trait Trait<T> {}

impl<T> Trait<T> for () {}

pub fn foo<'a>() {
    let _x: impl Trait<A<'a>> = ();
}

fn main() {}

playground

playground (original)

Meta

rustc --version --verbose:

1.43.0-nightly (823ff8cf1 2020-03-07)

Error output

error: internal compiler error: opaque type with non-universal region substs
  --> src/main.rs:10:1
   |
10 | / pub fn foo<'a>() {
11 | |     let _x: impl Trait<A<'a>> = ();
12 | | }
   | |_^

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:355:17

[hellow554]

Nitpick: There's no need to put the two let _x into different functions, you can put them both in foo.

[CDirkx]

Like #70971, when using an anonymous binding (_), the above code compiles:

let _: impl Trait<A<'a>> = ();

[Alexendoo]

No longer ICEs since #72080