`super let` with `&mut [T; 0]` in `const` has inconsistent borrow-checking behavior

[theemathas]

It is possible to create a &mut reference pointing to specifically an empty array in const. See #140126.

In the following code, the constants TUPLE, REBORROW, and INFER are slight variations of the constant FAILS.

#![feature(super_let)]

type Ref = &'static mut [i32; 0];

const fn make() -> Ref {
    &mut []
}

const FAILS: [Ref; 2] = {
    super let x: Ref = make();
    [x, x]
};

const TUPLE: (Ref, Ref) = {
    super let x: Ref = make();
    (x, x)
};

const REBORROW: [Ref; 2] = {
    super let x: Ref = make();
    [x, &mut *x]
};

const INFER: [Ref; 2] = {
    // Don't annotate as 'static
    super let x: &mut [i32; 0] = make();
    [x, x]
};

I expected all four constants to either all compile or all produce an error. Instead, the FAILS constant produces an error, but the other three compile fine.

error[E0505]: cannot move out of `x` because it is borrowed
  --> src/lib.rs:11:9
   |
10 |     super let x: Ref = make();
   |               - binding `x` declared here
11 |     [x, x]
   |     ----^-
   |     ||  |
   |     ||  move out of `x` occurs here
   |     |borrow of `*x` occurs here
   |     using this value as a constant requires that `*x` is borrowed for `'static`

For more information about this error, try `rustc --explain E0505`.
error: could not compile `playground` (lib) due to 1 previous error

Maybe related to #142607.

Meta

Reproducible on the playground with version 1.89.0-nightly (2025-06-11 e703dff8fe220b78195c)

@rustbot labels +F-super_let +A-const-eval +A-borrow-checker