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// Check that constants with interior mutability inside unions are rejected
// during validation.
//
// Note that this test case relies on undefined behaviour to construct a
// constant with interior mutability that is "invisible" to the static checks.
// If for some reason this approach no longer works, it is should be fine to
// remove the test case.
//
// build-fail
// stderr-per-bitwidth
#![feature(const_mut_refs)]
use std::cell::Cell;
use std::mem::ManuallyDrop;
#[repr(C)]
struct S {
x: u32,
y: E,
}
#[repr(u32)]
enum E {
A,
B(U)
}
union U {
cell: ManuallyDrop<Cell<u32>>,
}
const C: S = {
let s = S { x: 0, y: E::A };
// Go through an &u32 reference which is definitely not allowed to mutate anything.
let p = &s.x as *const u32 as *mut u32;
// Change enum tag to E::B.
unsafe { *p.add(1) = 1 };
s
};
fn main() { //~ ERROR it is undefined behavior to use this value
let _: &'static _ = &C; //~ ERROR erroneous constant used
//~^ WARN this was previously accepted
}
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