[rustc.git] / src / test / ui / consts / issue-69488.rs

// run-pass

#![feature(const_ptr_write)]
#![feature(const_mut_refs)]

// Or, equivalently: `MaybeUninit`.
pub union BagOfBits<T: Copy> {
    uninit: (),
    _storage: T,
}

pub const fn make_1u8_bag<T: Copy>() -> BagOfBits<T> {
    assert!(core::mem::size_of::<T>() >= 1);
    let mut bag = BagOfBits { uninit: () };
    unsafe { (&mut bag as *mut _ as *mut u8).write(1); };
    bag
}

pub fn check_bag<T: Copy>(bag: &BagOfBits<T>) {
    let val = unsafe { (bag as *const _ as *const u8).read() };
    assert_eq!(val, 1);
}

fn main() {
    check_bag(&make_1u8_bag::<[usize; 1]>()); // Fine
    check_bag(&make_1u8_bag::<usize>()); // Fine

    const CONST_ARRAY_BAG: BagOfBits<[usize; 1]> = make_1u8_bag();
    check_bag(&CONST_ARRAY_BAG); // Fine.
    const CONST_USIZE_BAG: BagOfBits<usize> = make_1u8_bag();

    // Used to panic since CTFE would make the entire `BagOfBits<usize>` uninit
    check_bag(&CONST_USIZE_BAG);
}
Commit	Line	Data
04454e1e FG	1	// run-pass
	2
	3	#![feature(const_ptr_write)]
	4	#![feature(const_mut_refs)]
	5
	6	// Or, equivalently: `MaybeUninit`.
	7	pub union BagOfBits<T: Copy> {
	8	uninit: (),
	9	_storage: T,
	10	}
	11
	12	pub const fn make_1u8_bag<T: Copy>() -> BagOfBits<T> {
	13	assert!(core::mem::size_of::<T>() >= 1);
	14	let mut bag = BagOfBits { uninit: () };
	15	unsafe { (&mut bag as mut _ as mut u8).write(1); };
	16	bag
	17	}
	18
	19	pub fn check_bag<T: Copy>(bag: &BagOfBits<T>) {
	20	let val = unsafe { (bag as const _ as const u8).read() };
	21	assert_eq!(val, 1);
	22	}
	23
	24	fn main() {
	25	check_bag(&make_1u8_bag::<[usize; 1]>()); // Fine
	26	check_bag(&make_1u8_bag::<usize>()); // Fine
	27
	28	const CONST_ARRAY_BAG: BagOfBits<[usize; 1]> = make_1u8_bag();
	29	check_bag(&CONST_ARRAY_BAG); // Fine.
	30	const CONST_USIZE_BAG: BagOfBits<usize> = make_1u8_bag();
	31
	32	// Used to panic since CTFE would make the entire `BagOfBits<usize>` uninit
	33	check_bag(&CONST_USIZE_BAG);
	34	}