tests/ui/transmutability/unions/repr/should_handle_align.rs

   1 // check-pass
   2 //! The presence of an `align(X)` annotation must be accounted for.
   3
   4 #![crate_type = "lib"]
   5 #![feature(transmutability)]
   6 #![allow(dead_code, incomplete_features, non_camel_case_types)]
   7
   8 mod assert {
   9     use std::mem::{Assume, BikeshedIntrinsicFrom};
  10     pub struct Context;
  11
  12     pub fn is_maybe_transmutable<Src, Dst>()
  13     where
  14         Dst: BikeshedIntrinsicFrom<Src, Context, {
  15             Assume {
  16                 alignment: true,
  17                 lifetimes: true,
  18                 safety: true,
  19                 validity: true,
  20             }
  21         }>
  22     {}
  23 }
  24
  25 fn should_pad_explicitly_aligned_field() {
  26     #[derive(Clone, Copy)] #[repr(u8)] enum V0u8 { V = 0 }
  27     #[derive(Clone, Copy)] #[repr(u8)] enum V1u8 { V = 1 }
  28
  29     #[repr(C)]
  30     pub union Uninit {
  31         a: (),
  32         b: V1u8,
  33     }
  34
  35     #[repr(C, align(2))]
  36     pub union align_2 {
  37         a: V0u8,
  38     }
  39
  40     #[repr(C)] struct ImplicitlyPadded(align_2, V0u8);
  41     #[repr(C)] struct ExplicitlyPadded(V0u8, Uninit, V0u8);
  42
  43     // An implementation that (incorrectly) does not place a padding byte after
  44     // `align_2` will, incorrectly, reject the following transmutations.
  45     assert::is_maybe_transmutable::<ImplicitlyPadded, ExplicitlyPadded>();
  46     assert::is_maybe_transmutable::<ExplicitlyPadded, ImplicitlyPadded>();
  47 }