error[E0072]: recursive type `S` has infinite size
  --> $DIR/issue-3779.rs:1:1
   |
LL | struct S {
   | ^^^^^^^^
LL |
LL |     element: Option<S>
   |                     - recursive without indirection
   |
help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle
   |
LL |     element: Option<Box<S>>
   |                     ++++ +

error: aborting due to previous error

For more information about this error, try `rustc --explain E0072`.