Typechecking failure with HRTBs and associated types

[arpj-rebola]

Rust fails to typecheck the following code:

trait Aaa: Sized where
	for<'a> &'a Self: AaaLt<'a, Self>
{}

trait AaaLt<'a, A: Aaa> where
	for<'b> &'b A: AaaLt<'b, A>
{
	type View;
}

trait AaaPlus: Aaa where
	for<'a> &'a Self: AaaLt<'a, Self>,
	for<'a> <&'a Self as AaaLt<'a, Self>>::View: Bbb
{}

trait Bbb {
}

struct Foo<'a> {
	x: &'a usize
}
impl<'a> Bbb for Foo<'a> {
}

struct Bar {
}
impl Aaa for Bar {
}
impl<'a> AaaLt<'a, Bar> for &'a Bar {
	type View = Foo<'a>;
}
impl AaaPlus for Bar {
}

with error: the trait bound for<'a> <&'a dirty::Bar as dirty::AaaLt<'a, dirty::Bar>>::View: dirty::Bbb is not satisfied.

What I am trying to do is the following. I want to have a marker trait Aaa that defines some associated types. One of those associated types View have lifetime parameters. But generic associated types are not currently allowed in stable Rust, so I define them as types associated to a lifetime-parameterized trait that every reference must satisfy; I use a higher-rank trait bound for this purpose.

For a specialization of the trait Aaa called AaaPlus, (each instantiation of) the type View must satisfy some other trait Bbb. Despite the corresponding traits being implemented for Bar: AaaPlus and Foo<'a>: Bbb, Rust is failing to typecheck this.

[jonas-schievink]

Yeah this is a known issue with HRTB projections, covered by older issues like #30472, so closing in favor of that.