error[E0072]: recursive type `E2` has infinite size
  --> $DIR/issue-3008-3.rs:4:1
   |
LL | enum E2<T> { V2(E2<E1>, marker::PhantomData<T>), }
   | ^^^^^^^^^^      ------ recursive without indirection
   |
help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle
   |
LL | enum E2<T> { V2(Box<E2<E1>>, marker::PhantomData<T>), }
   |                 ++++      +

error: aborting due to 1 previous error

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