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// run-pass
//
// Test that we can handle unsized types with an extern type tail part.
// Regression test for issue #91827.
#![feature(extern_types)]
use std::ptr::addr_of;
extern "C" {
type Opaque;
}
unsafe impl Sync for Opaque {}
#[repr(C)]
pub struct List<T> {
len: usize,
data: [T; 0],
tail: Opaque,
}
#[repr(C)]
pub struct ListImpl<T, const N: usize> {
len: usize,
data: [T; N],
}
impl<T> List<T> {
const fn as_slice(&self) -> &[T] {
unsafe {
let ptr = addr_of!(self.tail) as *const T;
std::slice::from_raw_parts(ptr, self.len)
}
}
}
impl<T, const N: usize> ListImpl<T, N> {
const fn as_list(&self) -> &List<T> {
unsafe { std::mem::transmute(self) }
}
}
pub static A: ListImpl<u128, 3> = ListImpl {
len: 3,
data: [5, 6, 7],
};
pub static A_REF: &'static List<u128> = A.as_list();
pub static A_TAIL_OFFSET: isize = tail_offset(A.as_list());
const fn tail_offset<T>(list: &List<T>) -> isize {
unsafe { (addr_of!(list.tail) as *const u8).offset_from(list as *const List<T> as *const u8) }
}
fn main() {
assert_eq!(A_REF.as_slice(), &[5, 6, 7]);
// Check that interpreter and code generation agree about the position of the tail field.
assert_eq!(A_TAIL_OFFSET, tail_offset(A_REF));
}
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