error[E0072]: recursive types `ObjectType` and `TypeSignature` have infinite size
  --> $DIR/issue-57271.rs:7:1
   |
LL | pub enum ObjectType {
   | ^^^^^^^^^^^^^^^^^^^
LL |     Class(ClassTypeSignature),
LL |     Array(TypeSignature),
   |           ------------- recursive without indirection
...
LL | pub enum TypeSignature {
   | ^^^^^^^^^^^^^^^^^^^^^^
LL |     Base(BaseType),
LL |     Object(ObjectType),
   |            ---------- recursive without indirection
   |
help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle
   |
LL ~     Array(Box<TypeSignature>),
LL |     TypeVariable(()),
 ...
LL |     Base(BaseType),
LL ~     Object(Box<ObjectType>),
   |

error: aborting due to previous error

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