when using CanvasItem as the base class, the class does not appear in Godot editor picker

[AlexOkafor]

Hello,

I ran across this when trying to move a base class of Node to something more specific (CanvasItem). My current workaround has been to use Control instead.

#[derive(GodotClass)]
#[class(base=CanvasItem)]
pub struct TestItem {
    #[base]
    base: Base<CanvasItem>,
}

#[godot_api]
impl CanvasItemVirtual for TestItem {
    fn init(base: Base<CanvasItem>) -> Self {
        Self { base }
    }
}

#[godot_api]
impl TestItem {}

When using the above snippet, the class doesn't appear in the godot editor. Also if I refactor a class to use CanvasItem as a base class the editor will show errors like so:

ERROR: Class 'TestItem' or its base class cannot be instantiated.
   at: (core/object/class_db.cpp:341)

I did see that CanvasItem is an abstract base class so I wasn't sure if that's related, a technical limitation of the GDext bindings, or this is working as designed w.r.t. GD extensions.

[Bromeon]

Thanks for reporting!

I wonder if we need to do something specific for abstract base classes 🤔 this should be possible.

[PgBiel]

This seems to be on the Godot side: godotengine/godot#67510 and godotengine/godot#67512

[aaronfranke]

This is working as intended, the intention is that you are not allowed to extend abstract types. So you are not allowed to make your own CanvasItem-derived type. See the reasoning here: godotengine/godot#67510 (comment)

[Bromeon]

Thanks a lot @aaronfranke for clarifying!
Since this is an upstream design decision, I'll close this.