src/test/ui/transmutability/enums/should_pad_variants.rs

   1 //! The variants of an enum must be padded with uninit bytes such that they have
   2 //! the same length (in bytes).
   3
   4 #![crate_type = "lib"]
   5 #![feature(transmutability)]
   6 #![allow(dead_code)]
   7
   8 mod assert {
   9     use std::mem::BikeshedIntrinsicFrom;
  10
  11     pub fn is_transmutable<Src, Dst, Context>()
  12     where
  13         Dst: BikeshedIntrinsicFrom<Src, Context, true, true, true, true>
  14     {}
  15 }
  16
  17 #[derive(Clone, Copy)]
  18 #[repr(C)] struct Zst;
  19
  20 #[derive(Clone, Copy)]
  21 #[repr(u8)] enum V0 { V = 0 }
  22
  23 #[derive(Clone, Copy)]
  24 #[repr(u8)] enum V2 { V = 2 }
  25
  26 #[repr(C, u8)]
  27 enum Lopsided {
  28     Smol(Zst),
  29     Lorg(V0),
  30 }
  31
  32 #[repr(C)] struct Src(V0, Zst, V2);
  33 #[repr(C)] struct Dst(Lopsided, V2);
  34
  35 fn should_pad_variants() {
  36     struct Context;
  37     // If the implementation (incorrectly) fails to pad `Lopsided::Smol` with
  38     // an uninitialized byte, this transmutation might be (wrongly) accepted:
  39     assert::is_transmutable::<Src, Dst, Context>(); //~ ERROR cannot be safely transmuted
  40 }