Use static_assertions to verify the safety of init_type_hierarchy

Author: coolreader18

Cargo.lock

@@ -79,6 +79,7 @@ cfg-if = "0.1.10"
 timsort = "0.1"
 thiserror = "1.0"
 atty = "0.2"
+static_assertions = "1.1"
 
 ## unicode stuff
 unicode_names2 = "0.4"

vm/Cargo.toml

@@ -410,6 +410,11 @@ pub(crate) fn init_type_hierarchy() -> (PyTypeRef, PyTypeRef) {
         type PyTypeObj = PyObject<PyType>;
         type UninitRef<T> = PyRwLock<PyRc<MaybeUninit<PyInner<T>>>>;
 
+        // We cast between these 2 types, so make sure (at compile time) that there's no change in
+        // layout when we wrap PyInner<PyTypeObj> in MaybeUninit<>
+        static_assertions::assert_eq_size!(MaybeUninit<PyInner<PyTypeObj>>, PyInner<PyTypeObj>);
+        static_assertions::assert_eq_align!(MaybeUninit<PyInner<PyTypeObj>>, PyInner<PyTypeObj>);
+
         let type_payload = PyType {
             name: PyTypeRef::NAME.to_owned(),
             base: None,