Warn on connected functions without correct argument count

[N0hbdy]

Operating system or device, Godot version, GPU Model and driver (if graphics related):
MacOS, Godot 3.0 alpha

Issue description:

Connecting a signal to a function that doesn't have the correct number of arguments means that the function is never called (and I haven't seen any warnings in the debugger being called). Ideally, either the editor puts a lint warning up, or when attempting to call the function it complains that the function is invalid.

Steps to reproduce:
I connected a no-argument function to an animation_finished callback, which never is called. Can upload examples if needed!

Link to minimal example project:

Happy to make one if it helps; might poke around to see if I can cobble something together!

[mhilbrunner]

Maybe users should even be warned when overriding methods, e.g. defining _process(): without the delta argument.

[N0hbdy]

Any tips on where to start digging into this? I'd like to see if I can get this added :)

[bojidar-bg]

Some pointers which I guess might be useful, from core/object.cpp and modules/gdscript/gd_function.cpp.

Object::emit_signal, the lines related to calling the method:

godot/core/object.cpp

Lines 1116 to 1131 in 62a3dcd

	if (c.flags & CONNECT_DEFERRED) {
	MessageQueue::get_singleton()->push_call(target->get_instance_id(), c.method, args, argc, true);
	} else {
	Variant::CallError ce;
	target->call(c.method, args, argc, ce);
	if (ce.error != Variant::CallError::CALL_OK) {
	if (ce.error == Variant::CallError::CALL_ERROR_INVALID_METHOD && !ClassDB::class_exists(target->get_class_name())) {
	//most likely object is not initialized yet, do not throw error.
	} else {
	ERR_PRINTS("Error calling method from signal '" + String(p_name) + "': " + Variant::get_call_error_text(target, c.method, args, argc, ce));
	err = ERR_METHOD_NOT_FOUND;
	}
	}
	}

---

GDScript/GDInstance::call() correctly returns CALL_ERROR_TOO_FEW_ARGUMENTS:

godot/modules/gdscript/gd_function.cpp

Lines 285 to 287 in 62a3dcd

	} else if (p_argcount < _argument_count - _default_arg_count) {
	r_err.error = Variant::CallError::CALL_ERROR_TOO_FEW_ARGUMENTS;

---

Object::call directly returns the error returned by the script (by passing r_error to it, which is passed by reference):

godot/core/object.cpp

Lines 818 to 832 in 62a3dcd

	ret = script_instance->call(p_method, p_args, p_argcount, r_error);
	//force jumptable
	switch (r_error.error) {
	case Variant::CallError::CALL_OK:
	return ret;
	case Variant::CallError::CALL_ERROR_INVALID_METHOD:
	break;
	case Variant::CallError::CALL_ERROR_INVALID_ARGUMENT:
	case Variant::CallError::CALL_ERROR_TOO_MANY_ARGUMENTS:
	case Variant::CallError::CALL_ERROR_TOO_FEW_ARGUMENTS:
	return ret;
	case Variant::CallError::CALL_ERROR_INSTANCE_IS_NULL: {
	}
	}

---

_test_call_error, a debug-only helper function, which might be useful:

godot/core/object.cpp

Lines 600 to 618 in 62a3dcd

	static bool _test_call_error(const StringName &p_func, const Variant::CallError &error) {
	switch (error.error) {
	case Variant::CallError::CALL_OK:
	return true;
	case Variant::CallError::CALL_ERROR_INVALID_METHOD:
	return false;
	case Variant::CallError::CALL_ERROR_INVALID_ARGUMENT: {
	ERR_EXPLAIN("Error Calling Function: " + String(p_func) + " - Invalid type for argument " + itos(error.argument) + ", expected " + Variant::get_type_name(error.expected));
	ERR_FAIL_V(true);
	} break;
	case Variant::CallError::CALL_ERROR_TOO_MANY_ARGUMENTS: {
	ERR_EXPLAIN("Error Calling Function: " + String(p_func) + " - Too many arguments, expected " + itos(error.argument));
	ERR_FAIL_V(true);
	} break;

[robfram]

Has this issue being solved? I get an error in the debug window in this cases, and remember being that way since December at least. I don't know if the message shown is not enough and a better method to inform or alert the user is required.

[Nufflee]

I can try adding a lint message for this.

[jordgubben]

I've tinkered a bit now and I think I'm slowly getting somewhere. This is my first attempt to contribute to Godot, so I still need to spend a lot of time just browsing the source code.

I have one question: Is there any simple way to get the MethodInfo of a single method? Invoking Object::get_method_list() and iterating over an entire List<MethodInfo>seems a bit of a performance waste when it's already a hash-map behind the scenes?

[jordgubben]

So far I've managed to add a warning in the Connections dialogue. I need to rebase all the things before I submit a Draft-PR.

[Anutrix]

In current master it gives something like:

ERROR: Error calling from signal 'button_down' to callable: Node2D(Node2D.gd)::hello : Method expected 1 arguments, but called with 0..
   at: emit_signal (core\object.cpp:1088)

It does need a better warning.
I think we should disallow connecting to methods having non-matching number of arguments at signal connection window itself OR it should create new function with same name but signal's supplied number of arguments instead.