tests/ui/mir/issue-46845.rs

//@ run-pass
// To work around #46855
//@ compile-flags: -Z mir-opt-level=0
// Regression test for the inhabitedness of unions with uninhabited variants, issue #46845

use std::mem;

#[derive(Copy, Clone)]
enum Never { }

// A single uninhabited variant shouldn't make the whole union uninhabited.
union Foo {
    a: u64,
    _b: Never
}

// If all the variants are uninhabited, however, the union should be uninhabited.
// NOTE(#49298) the union being uninhabited shouldn't change its size.
union Bar {
    _a: (Never, u64),
    _b: (u64, Never)
}

fn main() {
    assert_eq!(mem::size_of::<Foo>(), 8);
    // See the note on `Bar`'s definition for why this isn't `0`.
    assert_eq!(mem::size_of::<Bar>(), 8);

    let f = [Foo { a: 42 }, Foo { a: 10 }];
    println!("{}", unsafe { f[0].a });
    assert_eq!(unsafe { f[1].a }, 10);
}