Handle missing instance binding callbacks by finding the closest parent

Author: dsnopek

src/core/class_db.cpp

@@ -310,7 +310,18 @@ GDExtensionClassCallVirtual ClassDB::get_virtual_func(void *p_userdata, GDExtens
 
 const GDExtensionInstanceBindingCallbacks *ClassDB::get_instance_binding_callbacks(const StringName &p_class) {
 std::unordered_map<StringName, const GDExtensionInstanceBindingCallbacks *>::iterator callbacks_it = instance_binding_callbacks.find(p_class);
-ERR_FAIL_COND_V_MSG(callbacks_it == instance_binding_callbacks.end(), nullptr, String("Cannot find instance binding callbacks for class '{0}'.").format(Array::make(p_class)));
+if (likely(callbacks_it != instance_binding_callbacks.end())) {
+return callbacks_it->second;
+}
+
+// If we don't have an instance binding callback for the given class, find the closest parent where we do.
+StringName class_name = p_class;
+do {
+class_name = get_parent_class(class_name);
+ERR_FAIL_COND_V_MSG(class_name == StringName(), nullptr, String("Cannot find instance binding callbacks for class '{0}'.").format(Array::make(p_class)));
+callbacks_it = instance_binding_callbacks.find(class_name);
+} while (callbacks_it == instance_binding_callbacks.end());
+
 return callbacks_it->second;
 }