fix(python): type object 'InterfaceDynamicProxy' has no attribute '__…

…jsii_type__' (#4209)

In the odd case where an opaque reference is returned (FQN is `Object`) and no interfaces are registered, the `InterfaceDynamicProxy` instance created to represent the value in Python did not have any delegate, resulting it in not having any visible properties; including a `__jsii_type__` value on the `__class__`, or the `__jsii_ref__` property, both of which are required for the vlaue to be able to correctly make it back to JavaScript.



---

By submitting this pull request, I confirm that my contribution is made under the terms of the [Apache 2.0 license].

[Apache 2.0 license]: https://www.apache.org/licenses/LICENSE-2.0

packages/@jsii/python-runtime/src/jsii/_reference_map.py

@@ -1,7 +1,8 @@
 # This module exists to break an import cycle between jsii.runtime and jsii.kernel
 import inspect
 
-from typing import Any, Iterable, Mapping, MutableMapping, Type
+from typing import Any, Iterable, List, Mapping, MutableMapping, Type
+from ._kernel.types import ObjRef
 
 
 _types = {}
@@ -32,15 +33,15 @@ def __init__(self, ref: str) -> None:
 
 
 class _ReferenceMap:
-    def __init__(self, types):
+    def __init__(self, types: Mapping[str, Type]) -> None:
         # We are using a real dictionary here instead of a WeakValueDictionary because
         # the nature of the JSII is such that we can never free the memory of JSII
         # objects ever, because we have no idea how many references exist on the *other*
         # side.
-        self._refs = {}
+        self._refs: MutableMapping[str, Any] = {}
         self._types = types
 
-    def register(self, inst: Any):
+    def register(self, inst: Any) -> None:
         self._refs[inst.__jsii_ref__.ref] = inst
 
     def resolve(self, kernel, ref):
@@ -129,18 +130,34 @@ def resolve(self, kernel, ref):
         else:
             raise ValueError(f"Unknown type: {class_fqn}")
 
-    def resolve_id(self, id):
+    def resolve_id(self, id: str) -> Any:
         return self._refs[id]
 
-    def build_interface_proxies_for_ref(self, ref):
+    def build_interface_proxies_for_ref(self, ref: ObjRef) -> List[Any]:
         ifaces = [_interfaces[fqn] for fqn in ref.interfaces or []]
         classes = [iface.__jsii_proxy_class__() for iface in ifaces]
+
+        # If there's no classes, use an Opaque reference to make sure the
+        # __jsii_ref__ property is visible through the InterfaceDynamicProxy.
+        if len(classes) == 0:
+            return [Opaque(ref)]
+
         insts = [klass.__new__(klass) for klass in classes]
         for inst in insts:
             inst.__jsii_ref__ = ref
         return insts
 
 
+class Opaque:
+    def __init__(self, ref: ObjRef) -> None:
+        # Set the __jsii_type__ property on the class if it's not there already
+        if getattr(self.__class__, "__jsii_type__", None) is None:
+            setattr(self.__class__, "__jsii_type__", "Object")
+
+        # Track the jsii reference
+        self.__jsii_ref__ = ref
+
+
 class InterfaceDynamicProxy(object):
     def __init__(self, delegates):
         self._delegates = delegates