array repeat exprs do not check the array type is well formed

[BoxyUwU]

I tried this code:

trait Foo {
    const ASSOC: [u8];
}

fn bar<T: Foo>() {
    let a = [T::ASSOC; 2];
}

fn main() {}

I expected to see this happen: It should not compile as the local variable a has type [[u8]; 2] which is not well formed

Instead, this happened: it compiled 😬

Meta

playground version:

Nightly channel

Build using the Nightly version: 1.71.0-nightly

(2023-04-30 9ecda8de85ce893cc3fc)

Backtrace

<backtrace>

[asquared31415]

I am pretty sure bar can't be called, since Foo can't be implemented by any type, since the const has a type that's not Sized (maybe some nightly feature enables this?). Is it an issue that a trait can have a const with a type that's not Sized?

[apiraino]

@BoxyUwU I've tried bisecting this but I can't find a previous version where compiling with rustc returns an error. Is this unsoundness always been there or can we bisect to a previous version that it didn't?

[BoxyUwU]

I imagine its likely that this always was broken lol