I found this with the following code:

#![allow(incomplete_features)]
#![feature(min_generic_const_args)]

pub trait Foo {
    #[cfg_attr(feature = "some_feature", type_const)]
    const N: usize;
}

impl Foo for u32 {
    #[cfg_attr(feature = "some_feature", type_const)]
    const N: usize = 99;
}

fn main() {}

If one gets rid of the cfg_attr to just #[type_const] builds just fine. Also no issue if the feature flag is off.

Build Command:
rustc test.rs --cfg 'feature="some_feature"'

rustc-ice-2026-01-17T22_27_14-1367133.txt

@rustbot label +F-min_generic_const_args +C-bug +I-ICE +T-compiler +requires-debug-assertions