src/test/ui/issues/issue-46845.rs

   1 // run-pass
   2 // To work around #46855
   3 // compile-flags: -Z mir-opt-level=0
   4 // Regression test for the inhabitedness of unions with uninhabited variants, issue #46845
   5
   6 use std::mem;
   7
   8 #[derive(Copy, Clone)]
   9 enum Never { }
  10
  11 // A single uninhabited variant shouldn't make the whole union uninhabited.
  12 union Foo {
  13     a: u64,
  14     _b: Never
  15 }
  16
  17 // If all the variants are uninhabited, however, the union should be uninhabited.
  18 // NOTE(#49298) the union being uninhabited shouldn't change its size.
  19 union Bar {
  20     _a: (Never, u64),
  21     _b: (u64, Never)
  22 }
  23
  24 fn main() {
  25     assert_eq!(mem::size_of::<Foo>(), 8);
  26     // See the note on `Bar`'s definition for why this isn't `0`.
  27     assert_eq!(mem::size_of::<Bar>(), 8);
  28
  29     let f = [Foo { a: 42 }, Foo { a: 10 }];
  30     println!("{}", unsafe { f[0].a });
  31     assert_eq!(unsafe { f[1].a }, 10);
  32 }