Godot: An inner class cannot be extended out of its script file

[Geequlim]

Operating system or device - Godot version:
Godot 3.0 alpha1

Issue description:

I cannot inherit a inner class in other script files.

The file named ItemListEnhanced.gd with a inner class ListItemProvider as below:

tool
extends ItemList

class ListItemProvider:
    func sort(p_item, p_item):
        return true

    func item_fit_filter(p_item, p_filter):
        return true

    func get_item_text(p_item):
        return str(p_item)

    func get_item_color(p_item):
        return Color(0, 0, 0, 0)

The editor complains Parser Error: Unknown class 'ListItemProvider' with the script code below

extends 'ItemListEnhanced.gd'

class MyItemProvider extends ListItemProvider:
    func get_item_text(p_item):
        return p_item.name

May #4472 related?

[leonkrause]

ListItemProvider exists in the scope of the file ItemListEnhanced.gd, so you'll have to reference it like this:

class MyItemProvider extends 'ItemListEnhanced.gd'.ListItemProvider:

[Geequlim]

This grammar is really strange.

[Geequlim]

Just like a string with a member ListItemProvider

[bojidar-bg]

@eska014 I think that the problem in this issue is that the script in the question
extends 'ItemListEnhanced.gd', and thus should have inherited the other scripts's scope as well.

[akien-mga]

Fixed by #12507.