Cycle E0391 error with polymorphize

[leonardo-m]

rustc (v.1.54.0-nightly 1025db84a 2021-05-14) compiles this code normally, even with optimizations:

#![feature(const_generics, const_evaluatable_checked, const_option)]
#![allow(incomplete_features, dead_code)]

struct Collection<T, const N: usize>
where [(); N.checked_next_power_of_two().unwrap()]: {
    arr: [T; N.checked_next_power_of_two().unwrap()],
    start: usize,
}

impl<T: Copy + Default, const N: usize> Collection<T, N>
where [(); N.checked_next_power_of_two().unwrap()]: {
    fn new() -> Self {
        Self {
            arr: [T::default(); N.checked_next_power_of_two().unwrap()],
            start: 0,
        }
    }
}

fn main() {
    let _ = Collection::<u32, 52>::new();
}

If I compile it with rustc -Z polymorphize=y, it raises errors:

error[E0391]: cycle detected when determining which generic parameters are unused by `<impl at test.rs:10:1: 18:2>::{constant#0}`
  --> test.rs:11:12
   |
11 | where [(); N.checked_next_power_of_two().unwrap()]: {
   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: ...which again requires determining which generic parameters are unused by `<impl at test.rs:10:1: 18:2>::{constant#0}`, completing the cycle
note: cycle used when determining which generic parameters are unused by `<impl at test.rs:10:1: 18:2>::new::{constant#0}`
  --> test.rs:14:33
   |
14 |             arr: [T::default(); N.checked_next_power_of_two().unwrap()],
   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

I don't know much about that polymorphize option, so I am not sure if this is a compiler problem.

[tgnottingham]

This can be closed. Works as of nightly-2021-10-18 (well, with updates to changed feature names). Most likely fixed by #89514.