src/test/run-pass/issue-46845.rs

   1 // Copyright 2017 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // To work around #46855
  12 // compile-flags: -Z mir-opt-level=0
  13 // Regression test for the inhabitedness of unions with uninhabited variants, issue #46845
  14
  15 use std::mem;
  16
  17 #[derive(Copy, Clone)]
  18 enum Never { }
  19
  20 // A single uninhabited variant shouldn't make the whole union uninhabited.
  21 union Foo {
  22     a: u64,
  23     _b: Never
  24 }
  25
  26 // If all the variants are uninhabited, however, the union should be uninhabited.
  27 // NOTE(#49298) the union being uninhabited shouldn't change its size.
  28 union Bar {
  29     _a: (Never, u64),
  30     _b: (u64, Never)
  31 }
  32
  33 fn main() {
  34     assert_eq!(mem::size_of::<Foo>(), 8);
  35     // See the note on `Bar`'s definition for why this isn't `0`.
  36     assert_eq!(mem::size_of::<Bar>(), 8);
  37
  38     let f = [Foo { a: 42 }, Foo { a: 10 }];
  39     println!("{}", unsafe { f[0].a });
  40     assert_eq!(unsafe { f[1].a }, 10);
  41 }