`array::map` and `array::try_map` do not drop ZSTs properly

[theemathas]

array::map and array::try_map do not drop ZST elements properly if the closure panics.

Additionally, array::try_map does not drop ZST elements properly if the closure "exits the loop" early.

In both cases, the elements that the closure didn't get to are never dropped at all.

Panicking in array::map

struct LoudDrop;
impl Drop for LoudDrop {
    fn drop(&mut self) {
         println!("drop");
    }
}

// this prints "drop" only once instead of twice
fn main() {
    let _ = [LoudDrop, LoudDrop].map(|_| panic!());
}

Panicking in array::try_map

#![feature(array_try_map)]

struct LoudDrop;
impl Drop for LoudDrop {
    fn drop(&mut self) {
         println!("drop");
    }
}

// this prints "drop" only once instead of twice
fn main() {
    let _ = [LoudDrop, LoudDrop].try_map(|_| panic!() as Result<(), ()>);
}

Early exit in array::try_map

#![feature(array_try_map)]

struct LoudDrop;
impl Drop for LoudDrop {
    fn drop(&mut self) {
         println!("drop");
    }
}

// this prints "drop" only once instead of twice
fn main() {
    let _ = [LoudDrop, LoudDrop].try_map(|_| Err::<(), ()>(()));
}

Relevant code:

rust/library/core/src/array/drain.rs

Lines 92 to 108 in a3ceeeb

	impl<T: [const] Destruct, const N: usize, F> const Drop for Drain<'_, '_, T, N, F> {
	fn drop(&mut self) {
	if !T::IS_ZST {
	// SAFETY: we cant read more than N elements
	let slice = unsafe {
	from_raw_parts_mut::<[T]>(
	self.ptr.as_ptr(),
	// SAFETY: `start <= end`
	self.end.offset_from_unsigned(self.ptr.as_ptr()),
	)
	};
	// SAFETY: By the type invariant, we're allowed to drop all these. (we own it, after all)
	unsafe { drop_in_place(slice) }
	}
	}
	}

Meta

Reproducible on the playground with version 1.95.0-nightly (2026-02-05 f889772d6500faebcac5)

[eggyal]

@rustbot claim