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//@ run-pass
#![feature(layout_for_ptr)]
use std::mem;
#[repr(packed(4))]
struct Slice(#[allow(dead_code)] [u32]);
#[repr(packed(2), C)]
struct PackedSized {
f: u8,
d: [u32; 4],
}
#[repr(packed(2), C)]
struct PackedUnsized {
f: u8,
d: Slice,
}
impl PackedSized {
fn unsize(&self) -> &PackedUnsized {
// We can't unsize via a generic type since then we get the error
// that packed structs with unsized tail don't work if the tail
// might need dropping.
let len = 4usize;
unsafe { mem::transmute((self, len)) }
}
}
fn main() { unsafe {
let p = PackedSized { f: 0, d: [1, 2, 3, 4] };
let p = p.unsize() as *const PackedUnsized;
// Make sure the size computation correctly adds exact 1 byte of padding
// in front of the `d` field.
assert_eq!(mem::size_of_val_raw(p), 1 + 1 + 4*4);
// And likewise for the offset computation.
let d = std::ptr::addr_of!((*p).d);
assert_eq!(d.cast::<u32>().read_unaligned(), 1);
} }
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