Cyclic dependencies in resource arrays turn null on loading with ResourceLoader

[mmyumu]

Tested versions

Reproducible in Godot 4.2.1 stable.
This issue does not occur in versions prior to 4.2, as cyclic dependencies in resources were not functional.

System information

Godot v4.2.1.stable - Windows 10.0.22621 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 2080 (NVIDIA; 31.0.15.4601) - Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz (8 Threads)

Issue description

I am working with two resource types: RefA and RefB.
Within the RefA resource, I have an array containing elements of type RefB, declared as @export var ref_b_list: Array[RefB].
In the RefB resource, there's a simple reference to RefA, declared as @export var ref_a: RefA.

I use ResourceSaver to serialize the RefA resource. However, when I load this resource back using ResourceLoader, the ref_a reference in the RefB objects within the ref_b_list array is set to null.

This issue seems to be specific to the usage of an Array. If I replace the Array[RefB] with a single instance of RefB, the serialization and subsequent loading maintain the ref_a reference correctly.

Steps to reproduce

1. Create a ref_a.gd script :

class_name RefA extends Resource

@export var ref_b_list: Array[RefB]

2. Create a ref_b.gd script:

class_name RefB extends Resource

@export var ref_a: RefA

3. Create a main scene (Node) with attached script:

extends Node

func _ready():
	var ref_b: RefB = RefB.new()
	
	var ref_a: RefA = RefA.new()
	ref_a.ref_b_list.append(ref_b)
	ref_b.ref_a = ref_a
	
	var result = ResourceSaver.save(ref_a, "user://test_data.res")
	var loaded_ref_a = ResourceLoader.load("user://test_data.res")
	
	print("ref_a.ref_b_list[0].ref_a=%s"% ref_a.ref_b_list[0].ref_a)
	print("loaded_ref_a.ref_b_list[0].ref_a=%s"% loaded_ref_a.ref_b_list[0].ref_a)

4. Run the main scene and checks the output:

ref_a.ref_b_list[0].ref_a=<Resource#-9223372009776347953>
loaded_ref_a.ref_b_list[0].ref_a=<null>

Minimal reproduction project (MRP)

bug_cross_reference.zip

The project basically contains what is described in step reproduction except I added a single ref_b variable as a sanity check.
When executing it you will see in the output something like :

ref_a.ref_b=<Resource#-9223372009793125170>
ref_a.ref_b_list[0].ref_a=<Resource#-9223372009776347953>
loaded_ref_a.ref_b=<Resource#-9223372009575021357>
loaded_ref_a.ref_b_list[0].ref_a=<null>

[AThousandShips]

This is not supported, and shouldn't IMO be used as it introduces memory management breaking behavior

Since this isn't supported and by design I'm closing this in favor of a proposal which suggests supporting this, I suggest adding your support there

• Allow circular dependencies/references for resources in export var godot-proposals#7363

Thank you for your report