Weird interaction between specialization and RPITITs

[compiler-errors]

#108203 didn't fully fix this. the bug still persists when using polymorphic indirection via specialization:

#![feature(async_fn_in_trait)]
#![feature(min_specialization)]

struct MyStruct;

trait MyTrait<T> {
	async fn foo(_: T);
}

impl<T> MyTrait<T> for MyStruct {
	default async fn foo(_: T) {
		println!("default");
	}
}

impl MyTrait<i32> for MyStruct {
	async fn foo(_: i32) {
		println!("specialized");
	}
}

#[tokio::main]
async fn main() {
	MyStruct::foo(42).await;
	indirection(42).await;
}

async fn indirection<T>(x: T) {
	//explicit type coercion is currently necessary because of https://github.com/rust-lang/rust/issues/67918
	<MyStruct as MyTrait<T>>::foo(x).await;
}

(note that <MyStruct as MyTrait<i32>>::foo(42).await works just fine, so #67918 probably isn't at fault)

output is

specialized
default

should be

specialized
specialized

Originally commented by @LastExceed em #107002 (comment)

[compiler-errors]

I'll look into this when I actually wake up in a few hours lol

[LastExceed]

why does this issue have the F-return_position_impl_trait_in_trait label ?

[compiler-errors]

Because async fn in trait is just return position impl trait in trait, and the specialization problems are equally as broken with the latter?