Core: Allow methods of built-in Variant types to be used as Callables

[dalexeev]

• Closes GDScript: "Cannot find property emit on base Signal" #82251.
• Reverts Add note in Callable documentation about methods of native types (reverted) #78274.

Makes the following code work:

var array: Array = [1, 2, 3]
print(array) # [1, 2, 3]
var callable: Callable = array.clear
callable.call()
print(array) # []

Note that signals can still only be connected to Object-based callables. Fixed by #82695.

[dalexeev]

It makes sense to change the argument type in the constructor from Object to Variant, but I think it's hard to do with the current system. The only thing we can do is declare constructors for all Variant types. It might make sense to add a constructor only for the Dictionary, since it does not support methods as callables due to ambiguity with properties. Or add a static method, which is much easier to bind.

[akien-mga]

This is quite important IMO, as currently there is no proper type safe way to do call_deferred on built-in Variant type methods.

See #84046 (comment) for context, where currently a lambda needs to be used instead of doing some_signal.emit.call_deferred() to emit a signal from a thread.

BTW if this works in this PR, this could be worth adding as a unit test.

[RandomShaper]

No apparent issues to me. TIWAGOS, though.

[KoBeWi]

I found an issue with free() (#86706), which seems related to this PR, but it doesn't fix that bug.

Note that signals can still only be connected to Object-based callables.

Does not work with free().

[akien-mga]

Thanks!

[nlupugla]

Hi folks!

I ran into this commit while working on GDScript Structs #82198 and worried there might be an issue with this feature and built in Variants with dynamic properties, that is, Dictionaries and eventually Structs (which are just fancy arrays).

For example if I run

var dict: Dictionary = {&"clear" : "oops"}
var callable: Callable = dict.clear

The analyzer does not complain, but at runtime, I get "INTERNAL ERROR: Trying to assign value of type 'String' to a variable of type 'Callable'."

At the moment, my Struct branch is failing the unit test that was added for this feature:

var array: Array = [1, 2, 3]
print(array) # [1, 2, 3]
var callable: Callable = array.clear
callable.call()
print(array) # []

in the same way that the dictionary example I gave above fails as I have added named getters to arrays so that struct fields can be accessed like my_struct.my_field.

I'm not entirely sure what the best solution would be here, but one easy and temporary fix would be to change the test so that it tests using a method from a different Variant type as a callable, say, Vector2. For example,

var vec: Vector2 = Vector2(1.5, 2.5)
print(vec)
var callable: Callable = vec.ceil
print(callable.call())