New callable_mp macro, for signals to call method pointers directly.

[reduz]

Implemented the callable_mp macro (simple on appearance and extremely complex under the hood).

Allows signals to call method pointers directly via Callable (using custom data). Should improve performance as well as not requiring internal methods to be registered in order to receive signals.

[reduz]

Behold the power of Voodoo below..
Making a straw doll gain life and dance is probably simpler than this.

[kuruk-mm]

I don't know if there is a debate, but with this signal rework are you going to implement lambdas in GDScript?

[akien-mga]

This one raises a warning with GCC 8:

In file included from editor/inspector_dock.cpp:33:
./core/callable_method_pointer.h: In instantiation of 'void call_with_variant_args_helper(T*, void (T::*)(P ...), const Variant**, Callable::CallError&, IndexSequence<Is ...>) [with T = InspectorDock; P = {}; long unsigned int ...Is = {}]':
./core/callable_method_pointer.h:125:40:   required from 'void call_with_variant_args(T*, void (T::*)(P ...), const Variant**, int, Callable::CallError&) [with T = InspectorDock; P = {}]'
./core/callable_method_pointer.h:141:25:   required from 'void CallableCustomMethodPointer<T, P>::call(const Variant**, int, Variant&, Callable::CallError&) const [with T = InspectorDock; P = {}]'
./core/callable_method_pointer.h:139:15:   required from here
./core/callable_method_pointer.h:96:94: error: parameter 'p_args' set but not used [-Werror=unused-but-set-parameter]
   96 | void call_with_variant_args_helper(T *p_instance, void (T::*p_method)(P...), const Variant **p_args, Callable::CallError &r_error, IndexSequence<Is...>) {
      |         

[akien-mga]

I ended up adding a #pragma to selectively disable this warning around this method for GCC.

@reduz thinks that it's likely a false positive, I copied the rationale he exposed in the above comment.

WDYT @marxin?

[marxin]

I reported a GCC PR:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93999

[akien-mga]

Rebased to fix style and silence a likely GCC false positive warning, should be good to merge now provided CI passes.

[Calinou]

Shouldn't it be CALLABLE_MP (uppercase) since it's a macro? Or did we settle on using lowercase macros from now on?

[akien-mga]

Shouldn't it be CALLABLE_MP (uppercase) since it's a macro? Or did we settle on using lowercase macros from now on?

14:24 <Akien> reduz: Calinou asks if we shouldn't use uppercase CALLABLE_MP instead of callable_mp. I also wondered about it. No strong opinion either way but I think so far we've mostly used uppercase macros for bindings.
14:26 <Akien> Could also be CallableMP if we want to show that it creates a Callable
14:31 <reduz> as you wish, i think its probably more readable lowercase because its actually a function
14:31 <reduz> otherwise people might misunderstand it to be a class
14:32 <reduz> if its lowercase, you will understand it to be a function. The only reason its a macro is to get the name of the function as a string in debug

[akien-mga]

Thanks!

[kuruk-mm]

@akien-mga Now with C++17 we can use [[maybe_unused]]

https://en.cppreference.com/w/cpp/language/attributes/maybe_unused

[akien-mga]

Thanks, that could be used indeed. Though in this case it does look like a GCC bug, so we might want to keep the compiler-specific hack, at least until we know more about the issue.
If it turns out that GCC is correct and that other compilers simply don't catch the issue, we can use [[maybe_unused]] indeed for p_args.