Ensure GDExtension class is the correct type for the Godot engine class

Author: dsnopek

binding_generator.py

@@ -128,6 +128,8 @@ def get_file_list(api_filepath, output_dir, headers=False, sources=False):
     if sources:
         utility_functions_source_path = source_gen_folder / "variant" / "utility_functions.cpp"
         files.append(str(utility_functions_source_path.as_posix()))
+        register_engine_classes_source_path = source_gen_folder / "register_engine_classes.cpp"
+        files.append(str(register_engine_classes_source_path.as_posix()))
 
     return files
 
@@ -1157,6 +1159,10 @@ def generate_engine_classes_bindings(api, output_dir, use_template_get_node):
                 generate_engine_class_source(class_api, used_classes, fully_used_classes, use_template_get_node)
             )
 
+    register_engine_classes_filename = Path(output_dir) / "src" / "register_engine_classes.cpp"
+    with register_engine_classes_filename.open("w+") as source_file:
+        source_file.write(generate_register_engine_classes_source(api))
+
     for native_struct in api["native_structures"]:
         struct_name = native_struct["name"]
         snake_struct_name = camel_to_snake(struct_name)
@@ -1551,6 +1557,38 @@ def generate_engine_class_source(class_api, used_classes, fully_used_classes, us
     return "\n".join(result)
 
 
+def generate_register_engine_classes_source(api):
+    includes = []
+    registrations = []
+
+    for class_api in api["classes"]:
+        if class_api["name"] == "ClassDB":
+            continue
+
+        class_name = class_api["name"]
+        snake_class_name = camel_to_snake(class_name)
+
+        includes.append(f"#include <godot_cpp/classes/{snake_class_name}.hpp>")
+        registrations.append(f"\tClassDB::register_engine_class<{class_name}>();")
+
+    result = []
+    add_header(f"register_engine_classes.cpp", result)
+
+    result.append("#include <godot_cpp/godot.hpp>")
+    result.append("")
+    result = result + includes
+    result.append("")
+    result.append("namespace godot {")
+    result.append("")
+    result.append("void GDExtensionBinding::register_engine_classes() {")
+    result = result + registrations
+    result.append("}")
+    result.append("")
+    result.append("} // namespace godot ")
+
+    return "\n".join(result)
+
+
 def generate_global_constants(api, output_dir):
     include_gen_folder = Path(output_dir) / "include" / "godot_cpp" / "classes"
     source_gen_folder = Path(output_dir) / "src" / "classes"

gdextension/gdextension_interface.h

@@ -573,6 +573,7 @@ typedef struct {
 
 	void (*object_set_instance)(GDExtensionObjectPtr p_o, GDExtensionConstStringNamePtr p_classname, GDExtensionClassInstancePtr p_instance); /* p_classname should be a registered extension class and should extend the p_o object's class. */
 
+	GDExtensionBool (*object_get_class_name)(GDExtensionConstObjectPtr p_object, GDExtensionStringNamePtr r_class_name);
 	GDExtensionObjectPtr (*object_cast_to)(GDExtensionConstObjectPtr p_object, void *p_class_tag);
 	GDExtensionObjectPtr (*object_get_instance_from_id)(GDObjectInstanceID p_instance_id);
 	GDObjectInstanceID (*object_get_instance_id)(GDExtensionConstObjectPtr p_object);

include/godot_cpp/core/class_db.hpp

@@ -104,6 +104,7 @@ class ClassDB {
 private:
 	// This may only contain custom classes, not Godot classes
 	static std::unordered_map<StringName, ClassInfo> classes;
+	static std::unordered_map<StringName, const GDExtensionInstanceBindingCallbacks *> instance_binding_callbacks;
 
 	static MethodBind *bind_methodfi(uint32_t p_flags, MethodBind *p_bind, const MethodDefinition &method_name, const void **p_defs, int p_defcount);
 	static void initialize_class(const ClassInfo &cl);
@@ -117,6 +118,8 @@ class ClassDB {
 	static void register_class(bool p_virtual = false);
 	template <class T>
 	static void register_abstract_class();
+	template <class T>
+	static void register_engine_class();
 
 	template <class N, class M, typename... VarArgs>
 	static MethodBind *bind_method(N p_method_name, M p_method, VarArgs... p_args);
@@ -137,6 +140,7 @@ class ClassDB {
 	static MethodBind *get_method(const StringName &p_class, const StringName &p_method);
 
 	static GDExtensionClassCallVirtual get_virtual_func(void *p_userdata, GDExtensionConstStringNamePtr p_name);
+	static const GDExtensionInstanceBindingCallbacks *get_instance_binding_callbacks(const StringName &p_class);
 
 	static void initialize(GDExtensionInitializationLevel p_level);
 	static void deinitialize(GDExtensionInitializationLevel p_level);
@@ -161,6 +165,8 @@ class ClassDB {
 
 template <class T, bool is_abstract>
 void ClassDB::_register_class(bool p_virtual) {
+	instance_binding_callbacks[T::get_class_static()] = &T::___binding_callbacks;
+
 	// Register this class within our plugin
 	ClassInfo cl;
 	cl.name = T::get_class_static();
@@ -213,6 +219,11 @@ void ClassDB::register_abstract_class() {
 	ClassDB::_register_class<T, true>();
 }
 
+template <class T>
+void ClassDB::register_engine_class() {
+	instance_binding_callbacks[T::get_class_static()] = &T::___binding_callbacks;
+}
+
 template <class N, class M, typename... VarArgs>
 MethodBind *ClassDB::bind_method(N p_method_name, M p_method, VarArgs... p_args) {
 	Variant args[sizeof...(p_args) + 1] = { p_args..., Variant() }; // +1 makes sure zero sized arrays are also supported.

include/godot_cpp/godot.hpp

@@ -51,6 +51,9 @@ enum ModuleInitializationLevel {
 };
 
 class GDExtensionBinding {
+private:
+	static void register_engine_classes();
+
 public:
 	using Callback = void (*)(ModuleInitializationLevel p_level);
 

src/core/class_db.cpp

@@ -40,6 +40,7 @@
 namespace godot {
 
 std::unordered_map<StringName, ClassDB::ClassInfo> ClassDB::classes;
+std::unordered_map<StringName, const GDExtensionInstanceBindingCallbacks *> ClassDB::instance_binding_callbacks;
 GDExtensionInitializationLevel ClassDB::current_level = GDEXTENSION_INITIALIZATION_CORE;
 
 MethodDefinition D_METHOD(StringName p_name) {
@@ -314,6 +315,12 @@ GDExtensionClassCallVirtual ClassDB::get_virtual_func(void *p_userdata, GDExtens
 	return nullptr;
 }
 
+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("Engine class '{0}' doesn't exist.").format(Array::make(p_class)));
+	return callbacks_it->second;
+}
+
 void ClassDB::bind_virtual_method(const StringName &p_class, const StringName &p_method, GDExtensionClassCallVirtual p_call) {
 	std::unordered_map<StringName, ClassInfo>::iterator type_it = classes.find(p_class);
 	ERR_FAIL_COND_MSG(type_it == classes.end(), String("Class '{0}' doesn't exist.").format(Array::make(p_class)));

src/godot.cpp

@@ -63,6 +63,7 @@ GDExtensionBool GDExtensionBinding::init(const GDExtensionInterface *p_interface
 	ERR_FAIL_COND_V_MSG(init_callback == nullptr, false, "Initialization callback must be defined.");
 
 	Variant::init_bindings();
+	register_engine_classes();
 
 	return true;
 }

src/variant/variant.cpp

@@ -33,6 +33,7 @@
 #include <godot_cpp/godot.hpp>
 
 #include <godot_cpp/core/binder_common.hpp>
+#include <godot_cpp/core/class_db.hpp>
 #include <godot_cpp/core/defs.hpp>
 
 #include <utility>
@@ -411,7 +412,16 @@ Variant::operator Object *() const {
 	if (obj == nullptr) {
 		return nullptr;
 	}
-	return reinterpret_cast<Object *>(internal::gde_interface->object_get_instance_binding(obj, internal::token, &Object::___binding_callbacks));
+
+	StringName class_name;
+	if (!internal::gde_interface->object_get_class_name(obj, reinterpret_cast<GDExtensionStringNamePtr>(class_name._native_ptr()))) {
+		ERR_FAIL_V_MSG(nullptr, "Unable to get object class name");
+	}
+
+	const GDExtensionInstanceBindingCallbacks *binding_callbacks = ClassDB::get_instance_binding_callbacks(class_name);
+	ERR_FAIL_COND_V(binding_callbacks == nullptr, nullptr);
+
+	return reinterpret_cast<Object *>(internal::gde_interface->object_get_instance_binding(obj, internal::token, binding_callbacks));
 }
 
 Variant::operator ObjectID() const {