error[E0072]: recursive type `ListNode` has infinite size --> $DIR/multiline-span-E0072.rs:2:1 | LL | / struct LL | | ListNode | |________^ ... LL | tail: Option, | -------- recursive without indirection | help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle | LL | tail: Option>, | ++++ + error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0072`.