Bugfix: Ease AsArg<Option<Gd<T>>> bounds to make it usable with signals.

[Yarwin]

Long story short AsArg<Option<Gd<T>> bounds were too restrictive which made it unusable with user-defined classes (despite Option<Gd<MyClass>> being totally valid).

In other words, this did not compile:

#[derive(GodotClass)]
#[class(init, base = Node)]
struct MyClass {
    base: Base<Node>
}

#[godot_api]
impl MyClass {
    #[signal]
    fn my_signal(arg: Option<Gd<MyClass>>);

    #[func]
    fn foo(&mut self) {
        let obj = self.to_gd();
        self.signals().my_signal().emit(&obj);
        let smth: Option<Gd<MyClass>> = None;
        self.signals().my_signal().emit(smth.as_ref());
    }
}

compile error

error[E0271]: type mismatch resolving `<MyClass as Bounds>::Declarer == DeclEngine`
  --> src/lib.rs:27:41
   |
27 |         self.signals().my_signal().emit(&obj);
   |                                    ---- ^^^^ type mismatch resolving `<MyClass as Bounds>::Declarer == DeclEngine`
   |                                    |
   |                                    required by a bound introduced by this call
   |
note: expected this to be `DeclEngine`
  --> src/lib.rs:8:10
   |
 8 | #[derive(GodotClass)]
   |          ^^^^^^^^^^
   = note: required for `&godot::prelude::Gd<MyClass>` to implement `AsArg<Option<godot::prelude::Gd<MyClass>>>`
note: required by a bound in `__godot_Signal_MyClass_my_signal::<'_, C>::emit`
  --> src/lib.rs:14:1
   |
14 | #[godot_api]
   | ^^^^^^^^^^^^ required by this bound in `__godot_Signal_MyClass_my_signal::<'_, C>::emit`
   = note: this error originates in the derive macro `GodotClass` which comes from the expansion of the attribute macro `godot_api` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0271]: type mismatch resolving `<MyClass as Bounds>::Declarer == DeclEngine`
  --> src/lib.rs:29:41
   |
29 |         self.signals().my_signal().emit(smth.as_ref());
   |                                    ---- ^^^^^^^^^^^^^ type mismatch resolving `<MyClass as Bounds>::Declarer == DeclEngine`
   |                                    |
   |                                    required by a bound introduced by this call
   |
note: expected this to be `DeclEngine`
  --> src/lib.rs:8:10
   |
 8 | #[derive(GodotClass)]
   |          ^^^^^^^^^^
   = note: required for `Option<&godot::prelude::Gd<MyClass>>` to implement `AsArg<Option<godot::prelude::Gd<MyClass>>>`
note: required by a bound in `__godot_Signal_MyClass_my_signal::<'_, C>::emit`
  --> src/lib.rs:14:1
   |
14 | #[godot_api]
   | ^^^^^^^^^^^^ required by this bound in `__godot_Signal_MyClass_my_signal::<'_, C>::emit`
   = note: this error originates in the derive macro `GodotClass` which comes from the expansion of the attribute macro `godot_api` (in Nightly builds, run with -Z macro-backtrace for more info)

Since it is compilation error only I covered it with doctests (I'm pretty sure doctest works because it failed on me three times due to typos and whatnot).

Gd:null_arg remains unchanged (idk what to think about it - let arg: Option<Gd<MyClass> = None; ain't that bad).

---

Reported by Iride Lombardi on discord (thanks!): https://discord.com/channels/723850269347283004/1429013604258025554/1429013604258025554

[GodotRust]

API docs are being generated and will be shortly available at: https://godot-rust.github.io/docs/gdext/pr-1371

[Bromeon]

Thanks! The logic error here was likely that base would be strictly a base class, but the Inherits bound is also implemented for the class itself.

[Bromeon]

This only tests as_ref() doing &Option<T> -> Option<&T>, which isn't godot-rust specific.

[Yarwin]

true, testing it is silly.

[Bromeon]

Also here?

What do you mean with "restricted", could you clarify?

[Yarwin]

Limited to engine classes