// run-pass #[repr(packed)] struct Packed<T: Copy>(#[allow(unused_tuple_struct_fields)] T); impl<T: Copy> Copy for Packed<T> {} impl<T: Copy> Clone for Packed<T> { fn clone(&self) -> Self { *self } } fn sanity_check_size<T: Copy>(one: T) { let two = [one, one]; let stride = (&two[1] as *const _ as usize) - (&two[0] as *const _ as usize); let (size, align) = (std::mem::size_of::<T>(), std::mem::align_of::<T>()); assert_eq!(stride, size); assert_eq!(size % align, 0); } fn main() { // This can fail if rustc and LLVM disagree on the size of a type. // In this case, `Option<Packed<(&(), u32)>>` was erroneously not // marked as packed despite needing alignment `1` and containing // its `&()` discriminant, which has alignment larger than `1`. sanity_check_size((Some(Packed((&(), 0))), true)); // In #46769, `Option<(Packed<&()>, bool)>` was found to have // pointer alignment, without actually being aligned in size. // e.g., on 64-bit platforms, it had alignment `8` but size `9`. type PackedRefAndBool<'a> = (Packed<&'a ()>, bool); sanity_check_size::<Option<PackedRefAndBool>>(Some((Packed(&()), true))); // Make sure we don't pay for the enum optimization in size, // e.g., we shouldn't need extra padding after the packed data. assert_eq!(std::mem::align_of::<Option<PackedRefAndBool>>(), 1); assert_eq!(std::mem::size_of::<Option<PackedRefAndBool>>(), std::mem::size_of::<PackedRefAndBool>()); }