ICE with Const Generic expression inside array declaration

[sfleischman105]

Found an ICE with the following code:

pub struct Foo<const LEN: usize> {
    buf: [u8; {LEN * 2}]
}

Results in "no errors encountered even though delay_span_bug issued" on current nightly.

Playground link.

The ICE still happens regardless of the LEN * 2 being in a block, in parenthesis, or even as a standalone expression. Interestingly, refactoring out the array into a seperate struct solves the issue.

cc @varkor @yodaldevoid

[Centril]

Recommended: P-medium due to unstable incomplete feature.

[varkor]

Thanks for the report.

(This only ICEs with the feature gate, so there's no need to raise the priority on this.)

[hellow554]

(This only ICEs with the feature gate, so there's no need to raise the priority on this.)

Not on beta though, but I guess #60277 will land in beta soon-ish so it shouldn't ICE there anymore?

[yodaldevoid]

I'm currently looking into this. That said, if someone else wants to work on this, let me know.

[yodaldevoid]

This can also be reproduced with the following code:

pub struct Foo<const LEN: usize> {
    buf: [u8; {LEN}]
}

Due to this, I think that this is related to the const parameter being in braces in the array length.

[varkor]

If that's the case, it might be related to #60717.