mirror of
https://github.com/rust-lang/rust.git
synced 2024-11-23 23:34:48 +00:00
22 lines
997 B
Rust
22 lines
997 B
Rust
//@ run-pass
|
|
use std::ptr::addr_of;
|
|
|
|
// When the unsized tail is a `dyn Trait`, its alignments is only dynamically known. This means the
|
|
// packed(2) needs to be applied at runtime: the actual alignment of the field is `min(2,
|
|
// usual_alignment)`. Here we check that we do this right by comparing size, alignment, and field
|
|
// offset before and after unsizing.
|
|
fn main() {
|
|
#[repr(C, packed(2))]
|
|
struct Packed<T: ?Sized>(u8, core::mem::ManuallyDrop<T>);
|
|
|
|
let p = Packed(0, core::mem::ManuallyDrop::new(1));
|
|
let p: &Packed<usize> = &p;
|
|
let sized = (core::mem::size_of_val(p), core::mem::align_of_val(p));
|
|
let sized_offset = unsafe { addr_of!(p.1).cast::<u8>().offset_from(addr_of!(p.0)) };
|
|
let p: &Packed<dyn Send> = p;
|
|
let un_sized = (core::mem::size_of_val(p), core::mem::align_of_val(p));
|
|
let un_sized_offset = unsafe { addr_of!(p.1).cast::<u8>().offset_from(addr_of!(p.0)) };
|
|
assert_eq!(sized, un_sized);
|
|
assert_eq!(sized_offset, un_sized_offset);
|
|
}
|