1 error[E0072]: recursive type `ListNode` has infinite size
7 LL | tail: Option<ListNode>,
8 | -------- recursive without indirection
10 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle
12 LL | tail: Option<Box<ListNode>>,
15 error: aborting due to previous error
17 For more information about this error, try `rustc --explain E0072`.