[rustc.git] / src / test / ui / consts / invalid-union.rs

// 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)]
#![feature(untagged_unions)]
use std::cell::Cell;

#[repr(C)]
struct S {
    x: u32,
    y: E,
}

#[repr(u32)]
enum E {
    A,
    B(U)
}

union U {
    cell: 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
}
Commit	Line	Data
a2a8927a XL	1	// Check that constants with interior mutability inside unions are rejected
	2	// during validation.
	3	//
	4	// Note that this test case relies on undefined behaviour to construct a
	5	// constant with interior mutability that is "invisible" to the static checks.
	6	// If for some reason this approach no longer works, it is should be fine to
	7	// remove the test case.
	8	//
	9	// build-fail
	10	// stderr-per-bitwidth
	11	#![feature(const_mut_refs)]
a2a8927a XL	12	#![feature(untagged_unions)]
	13	use std::cell::Cell;
	14
	15	#[repr(C)]
	16	struct S {
	17	x: u32,
	18	y: E,
	19	}
	20
	21	#[repr(u32)]
	22	enum E {
	23	A,
	24	B(U)
	25	}
	26
	27	union U {
	28	cell: Cell<u32>,
	29	}
	30
	31	const C: S = {
	32	let s = S { x: 0, y: E::A };
	33	// Go through an &u32 reference which is definitely not allowed to mutate anything.
	34	let p = &s.x as const u32 as mut u32;
	35	// Change enum tag to E::B.
	36	unsafe { *p.add(1) = 1 };
	37	s
	38	};
	39
	40	fn main() { //~ ERROR it is undefined behavior to use this value
	41	let _: &'static _ = &C; //~ ERROR erroneous constant used
	42	//~^ WARN this was previously accepted
	43	}