ICE: index out of bounds: the len is 0 but the index is 0

[Keith-Cancel]

Here is the example code that I found:

#![allow(incomplete_features)]
#![feature(min_generic_const_args)]
pub struct A;

impl A {
    #[type_const]
    const LEN: usize = 4;

    #[allow(unused_braces)]
    fn arr() -> [u8; const { Self::LEN }] {
        return [0u8; const { Self::LEN }];
    }
}


fn main() {
    let _ = A::arr();
}

This bit of code should compile with no issue, but instead panics with:

thread 'rustc' (2378376) panicked at compiler/rustc_middle/src/ty/generic_args.rs:54:14:
index out of bounds: the len is 0 but the index is 0

I discovered this when working on PR: #150799. I did find a fix, but it would have been too localized from what was described to me, and is more related to the fact that that one of the steps for mGCA #132980 is incomplete:

• Make inherent associated constants behave correctly

I am making this issue as requested by @BoxyUwU here: #150799 (comment)

rustc-ice-2026-01-11T09_57_00-2380279.txt

@rustbot label +F-associated_const_equality +F-min_generic_const_args +I-ICE +T-compiler

[rustbot]

Error: Parsing relabel command in comment failed: ...'s +I-ICE +' | error: empty label at >| ' T-compile'...

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[reddevilmidzy]

While the ICE message is different, I believe the core cause is the same for this #138226.