* represented with nullable pointers could be misoptimized in some cases.
*/
-enum List<X> { Nil, Cons(X, Box<List<X>>) }
+enum List<X> { Nil, Cons(X, #[allow(unused_tuple_struct_fields)] Box<List<X>>) }
pub fn main() {
match List::Cons(10, Box::new(List::Nil)) {
List::Cons(10, _) => {}