GDScript 2.0: Subclass member with type of another script's subclass does not get assigned correctly

[estroBiologist]

Godot version

v4.0.alpha8.official [cc3ed63]

System information

Windows 10

Issue description

(I tried my best with the title, I swear.)

In GDScript 2.0, attempting to assign to a subclass member variable with a type of another script's subclass quietly fails, resulting in a null value instead.

Steps to reproduce

A minimal example project is provided. In addition, here are the steps used to manually reproduce the issue:

• Create a project in the latest alpha build of Godot 4.0.
• Create two scripts, AScript.gd and BScript.gd, with these contents, respectively:

# AScript.gd

class_name AScript

class ASubClass:
	var data := 4.0

# BScript.gd

extends Node # Assign this script to the main scene to reproduce

class BSubClass:
	# The type annotation here is what triggers the bug - without it, no problem
	var a := AScript.ASubClass.new()
	
func _ready():
	# Lone ASubClass, works as expected.
	
	var lone_a := AScript.ASubClass.new()
	print(lone_a.data)
	
	# BSubClass.new() initializes correctly, `a` is valid, as is `data`
	
	var b := BSubClass.new()
	print(b.a.data)
	
	# Here's where it gets weird - despite being functionally identical 
	# to line 10, `a` is `null` after this statement
	
	b.a = AScript.ASubClass.new()
	print(b.a)
	# print(b.a.data) 	Error, `a` is null

The console output of this project is:

4
4
null

(Given that removing the type annotation from BSubClass resolves this, it seems like a type checking issue. I've used this to work around the bug in my own project.)

Minimal reproduction project

GDScriptBugTest.zip

[rune-scape]

just checked that #68374 fixes this