error[E0072]: recursive type `Foo` has infinite size --> $DIR/issue-17431-1.rs:1:1 | LL | struct Foo { foo: Option<Option<Foo>> } | ^^^^^^^^^^ --- recursive without indirection | help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle | LL | struct Foo { foo: Option<Option<Box<Foo>>> } | ++++ + error: aborting due to previous error For more information about this error, try `rustc --explain E0072`.