Const sanity checks skips uninhabited arrays

[RalfJung]

The following should be stopped by the const sanity check:

#![feature(never_type, const_transmute)]

use std::mem;

const TEST: [!; 1] = unsafe { mem::transmute(()) };

But it is not.

The issue is that the sanity check calls is_zst() to skip arrays that could be immediate, but some of those arrays are uninhabited...

Cc @oli-obk

[oli-obk]

lolwat. That should not even pass WF checks, right? Statics and constants should not be allowed to have uninhabited types.

[RalfJung]

That's just a bandaid though, WF checks won't catch the same thing wrapped in an Option (and Some).

[RalfJung]

I will fix this as part of my work for preparing validation for miri usage.