`Cargo Build` gets stuck compiling my code

While writing some code I wanted to see if it compiled, and instead cargo build just hung, either forever or longer than I was willing to late. It's a bug either way. I think I got it stuck in an infinite loop resolving traits

Code is here. I was editing mask.rs when I encountered the issue.

I think the problem code is

pub trait Maskable<T>: Copy {
    type Mask: Mask;

    fn set_masked<R: Splat<Self>>(&mut self, mask: Self::Mask, value: R);
}

impl<T, const N: usize> Maskable<T> for Col<T, N>
where
    T: Copy,
{
    type Mask = Col<bool, N>;

    fn set_masked<R: Splat<Self>>(&mut self, mask: Self::Mask, value: R) {
        let value: Self = value.splat();
        for (i, &m) in mask.iter().enumerate() {
            if m {
                self[i] = value[i]
            }
        }
    }
}

impl<S: Copy, T: Copy, const H: usize, const W: usize> Maskable<T> for Mat<S, W, H>
where
    Col<S, W>: Copy + Maskable<T>,
{
    type Mask = Col<Col<S, W>::Mask, H>;

    fn set_masked<R: Splat<Self>>(&mut self, mask: Self::Mask, value: R) {
        let value: Self = value.splat();
        for (i, &m) in mask.iter().enumerate() {
            self[i].set_masked(m, value[i]);
        }
    }
}

(this code is bad and wrong but it probably shouldn't do this)

I cant include a backtrace because Cargo never terminates

Reproduce the hang with the trait definitions from mask.rs using cargo build, then inspect the compiler's trait-resolution behavior for the Maskable and Splat bounds. Done means compilation terminates with an appropriate result or diagnostic instead of hanging indefinitely.