instantiating an opaque with another opaque stops being an error

[lcnr]

#![feature(type_alias_impl_trait)]

type Tait = impl Sized;
type Tait2 = impl Sized;

fn mk<T>() -> T { todo!() }

fn main() {
    let x: Tait = 1u32;
    let y: Tait2 = x;
}

cc rust-lang/rust#112076

the current solver intentionally hard errors when it encounters this situation https://github.com/rust-lang/rust/blob/fd9bf594366e73efb1a26a023e0b4de8eff82b94/compiler/rustc_infer/src/infer/opaque_types.rs#L152-L167

the behavior feels fairly straightforward and how I'd expect it to happen, so this is fine to me