VecDeque from Vec with ZST elements breaks internal invariants

[tmiasko]

fn main() {
    let n = 1 << (core::mem::size_of::<usize>() * 8 - 1);

    let mut v = Vec::<()>::new();
    assert!(v.capacity() >= n);
    unsafe { v.set_len(n) };

    let d = std::collections::VecDeque::from(v);
    assert_eq!(d.len(), n, "unexpected len");
}

I expected VecDeque constructed from Vec to either work correctly or construction to panic if it is not possible. Instead:

thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `0`,
 right: `2147483648`: unexpected len', a.rs:9:5

Introduced by #80003.

[camelid]

cc #78532

[camelid]

Not sure how severe this is, but figured that it's worth prioritizing.

[Stupremee]

@rustbot claim

[camelid]

Assigning P-high and removing I-prioritize as discussed in the prioritization working group.

[cuviper]

#83244 should fix this -- written before I saw this issue and @Stupremee's claim, so I'm sorry if you were still working on it.