[ICE] with conservative_impl_trait and universal_impl_trait

[leonardo-m]

#![feature(conservative_impl_trait, universal_impl_trait)]
fn foo(bar: impl Iterator<Item=&str>) -> impl Iterator<Item=u8> {
    bar.map(|_| b'x')
}
fn main() {}

Gives:

note: rustc 1.24.0-nightly (f9b0897c5 2017-12-02) running on x86_64-pc-windows-gnu

thread 'rustc' panicked at 'assertion failed: match *region { ty::ReLateBound(..) => false, _ => true, }', src\librustc\infer\higher_ranked\mod.rs:471:8

[cramertj]

It's sort of hidden, but I'm pretty sure this is the ICE due to impl Trait return position not properly supporting lifetime elision. The elided lifetime in the argument is still present in the output iterator.

[cramertj]

This is #46685.

[ghost]

This wasn't closed automatically.

[cramertj]

This is fixed.