type CleanupProbe {
    marker: MutSpan<u8>,
    fn drop(self: mutref<Self>) -> Void {
        self.marker[0] = 1
    }
}

fn mark_defer(marker: MutSpan<u8>) -> Void {
    marker[1] = 1
}

pub fn main(world: World) -> Void raises {
    var marker: [2]u8 = [0, 0]
    if true {
        defer mark_defer(marker)
        let probe: owned<CleanupProbe> = CleanupProbe { marker: marker }
    }
    if marker[0] == 1 && marker[1] == 1 {
        check world.out.write("ownership cleanup ok\n")
    } else {
        check world.out.write("ownership cleanup failed\n")
    }
}