Object: Add tests about the safety of tail destruction

core/object/object.cpp

@@ -53,7 +53,7 @@ struct _ObjectDebugLock {
 	}
 	~_ObjectDebugLock() {
 		Object *obj_ptr = ObjectDB::get_instance(obj_id);
-		if (likely(obj_ptr)) {
+		if (obj_ptr) {
 			obj_ptr->_lock_index.unref();
 		}
 	}

tests/core/object/test_object.h

@@ -37,6 +37,16 @@
 
 #include "tests/test_macros.h"
 
+#ifdef SANITIZERS_ENABLED
+#ifdef __has_feature
+#if __has_feature(address_sanitizer) || __has_feature(thread_sanitizer)
+#define ASAN_OR_TSAN_ENABLED
+#endif
+#elif defined(__SANITIZE_ADDRESS__) || defined(__SANITIZE_THREAD__)
+#define ASAN_OR_TSAN_ENABLED
+#endif
+#endif
+
 // Declared in global namespace because of GDCLASS macro warning (Windows):
 // "Unqualified friend declaration referring to type outside of the nearest enclosing namespace
 // is a Microsoft extension; add a nested name specifier".
@@ -524,6 +534,68 @@ TEST_CASE("[Object] Notification order") { // GH-52325
 	memdelete(test_notification_object);
 }
 
+TEST_CASE("[Object] Destruction at the end of the call chain is safe") {
+	Object *object = memnew(Object);
+	ObjectID obj_id = object->get_instance_id();
+
+	class _SelfDestroyingScriptInstance : public _MockScriptInstance {
+		Object *self = nullptr;
+
+		// This has to be static because ~Object() also destroys the script instance.
+		static void free_self(Object *p_self) {
+			memdelete(p_self);
+#if !defined(ASAN_OR_TSAN_ENABLED)
+			// Without asan/tsan, try at least to force a crash by replacing the otherwise seemingly good data with zeroes.
+			// Operations such as dereferencing pointers or decreasing a refcount would fail.
+			memset((void *)p_self, 0, sizeof(Object));
+#endif
+		}
+
+	public:
+		Variant callp(const StringName &p_method, const Variant **p_args, int p_argcount, Callable::CallError &r_error) override {
+			free_self(self);
+			return Variant();
+		}
+		Variant call_const(const StringName &p_method, const Variant **p_args, int p_argcount, Callable::CallError &r_error) override {
+			free_self(self);
+			return Variant();
+		}
+		bool has_method(const StringName &p_method) const override {
+			return p_method == "some_method";
+		}
+
+	public:
+		_SelfDestroyingScriptInstance(Object *p_self) :
+				self(p_self) {}
+	};
+
+	_SelfDestroyingScriptInstance *script_instance = memnew(_SelfDestroyingScriptInstance(object));
+	object->set_script_instance(script_instance);
+
+	SUBCASE("Within callp()") {
+		SUBCASE("Through call()") {
+			object->call("some_method");
+		}
+		SUBCASE("Through callv()") {
+			object->callv("some_method", Array());
+		}
+	}
+	SUBCASE("Within call_const()") {
+		Callable::CallError call_error;
+		object->call_const("some_method", nullptr, 0, call_error);
+	}
+	SUBCASE("Within signal handling (from emit_signalp(), through emit_signal())") {
+		Object emitter;
+		emitter.add_user_signal(MethodInfo("some_signal"));
+		emitter.connect("some_signal", Callable(object, "some_method"));
+		emitter.emit_signal("some_signal");
+	}
+
+	CHECK_MESSAGE(
+			ObjectDB::get_instance(obj_id) == nullptr,
+			"Object was tail-deleted without crashes.");
+}
+
 } // namespace TestObject
 
 #endif // TEST_OBJECT_H