ICE: fictitious type <&'static str as AsOwned>::R in sizing_type_of()

[WildCryptoFox]

The following code causes a compiler panic.

trait AsOwned { type R; }
impl<'a> AsOwned for &'a str { type R = String; }
fn as_owned<'a>(a: &'a str) -> <&'a str as AsOwned>::R { a.to_owned() }

This should resolve to a concrete type but instead panics with: play.rust-lang.org

error: internal compiler error: fictitious type <&'static str as AsOwned>::R in
sizing_type_of()

[eddyb]

cc @jroesch @nikomatsakis This looks like should've been normalized quite early, what's stopping it, the 'a lifetime param?

[arielb1]

@eddyb

Right. I had a branch fixing this, but it was killed due to rebase damage.