error[E0072]: recursive type `U` has infinite size --> $DIR/union-nonrepresentable.rs:1:1 | LL | union U { | ^^^^^^^ recursive type has infinite size LL | a: u8, LL | b: std::mem::ManuallyDrop, | ------------------------- recursive without indirection | help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `U` representable | LL | b: Box>, | ++++ + error: aborting due to previous error For more information about this error, try `rustc --explain E0072`.