Can't return typed arrays from C# functions to GDScript

[TheSecondReal0]

Tested versions

Reproducible in 4.4dev5

System information

Windows 10, Godot v4.4dev5

Issue description

If I declare a function in C# like this:

public Godot.Collections.Array<Vector2> GetCoolPlaces() {
    return new Godot.Collections.Array<Vector2>(... some values);
}

I would expect to be able to put the result into a typed array variable in GDScript:

var cool_places: Array[Vector2] = CSharpObject.GetCoolPlaces()

But the above code will result in this runtime error:
Trying to assign an array of type "Array" to a variable of type "Array[Vector2i]".

It is possible to do by creating a new typed array from the result of the function like this:

var cool_places: Array[Vector2] = Array(CSharpObject.GetCoolPlaces(), TYPE_VECTOR2, "", null)

But this is really clunky and annoying to do, especially when it's a function you use often.

Note: Packed arrays would not be a solution here, as this is also a problem for custom classes (e.g. Resources).

Steps to reproduce

Create a function in C# that returns an array and try to put the result of that function into a typed array in GDScript. See MRP for example

Minimal reproduction project (MRP)

Reproduce by running this project:

CSharp Typed Arrays.zip

[adamscott]

cc. @raulsntos @paulloz

[raulsntos]

The C# type Godot.Collections.Array<T> is a wrapper over an untyped array, so it gets marshalled as an untyped array and that's what you'll get on the GDScript side. As you show in the MRP, you have to cast it to the array type you want:

var working: Array[Vector2] = Array(csharp.GetCoolPlaces(), TYPE_VECTOR2, "", null)

This issue is technically a duplicate of #74936, the root cause is the same: the array is untyped on the engine side. To fix it, we need to call set_typed on the underlying array, there's a PR for that:

• Fix generic arrays and dictionaries in .NET not calling set_typed #98545