Recursive Trait Hang in rustc

[braxtoncuneo]

The code below, as the sole content of main.rs, should reproduce the error:

pub trait Indexed {
    type Index;
}

pub trait At<Address> {
    type AtItem;
    fn at(&self, address: Address`) -> &Self::AtItem;
}

impl <T, U> At<(T::Index,U)> for T
where
    Self: At<T::Index>,
    <T as At<T::Index>>::AtItem : At<U>,
    T : Indexed,
{
    type AtItem = <<T as At<T::Index>>::AtItem as At<U>>::AtItem;

    fn at(&self, address: (T::Index,U)) -> &<<T as At<T::Index>>::AtItem as At<U>>::AtItem {
        let (x,y) = address;
        At::<U>::at( self.at(x), y)
    }
}

fn main() {
    ().at(())
}

It pegs a CPU at 100%, and begins to consume progressively more memory (over 10 GB). It does not identify that Unit does not implement trait At

This issue is present in rustc 1.48.0-nightly (d006f57 2020-08-28).

[LeSeulArtichaut]

Assigning P-medium as discussed as part of the Prioritization WG procedure.

Also it looks like this regressed in 1.31.0