File corruption when two scenes call preload on each other

[rsutton1]

Tested versions

Reproducible in

• 4.2.stable.official [46dc277]
• 4.1.1.stable
• 4.1.beta3.official [ada712e]
• 4.1.dev4.official [5c2295f]
• 4.1.dev3.official [a67d37f]

In these versions, there is no file corruption but the program behaves unexpectedly

• 4.1.dev2.official [668cf3c]
• 4.0.4.stable.official
• 4.0.stable.official

In this version, there is no file corruption and when attempting to Run the project I receive the following error:

• 3.6.beta3.official

E 0:00:00.426   load: Resource: 'res://scene_a.tscn' is already being loaded. Cyclic reference?
  <C++ Error>   Condition "!success" is true. Returned: RES()
  <C++ Source>  core/io/resource_loader.cpp:353 @ load()

System information

Godot v4.2.stable - Windows 10.0.19045 - GLES3 (Compatibility) - NVIDIA GeForce RTX 3060 (NVIDIA; 31.0.15.3742) - Intel(R) Core(TM) i7-7700K CPU @ 4.20GHz (8 Threads)

Issue description

Expected Behavior

When two scenes call "preload" on each other, I should be able to exit and reopen the project successfully.

Actual Behavior

When I exit and reload the project, I see the following error message:

It appears I cannot open scene_a anymore.

Steps to reproduce

How to reproduce with MRP

1. Import and open the project
2. You should see a pop-up window that says scene_a.tscn is invalid/corrupt:

How I created the MRP

Here are the steps I followed to create the MRP.

1. Open Godot
2. Create a scene scene_a.tscn
3. Create a Node in scene_a
4. Attach the "scene_a.gd" script to the Node
5. Create a scene scene_b.tscn
6. Create a Node in scene_b
7. Attach the "scene_b.gd" script to the Node

scene_a.gd:

extends Node

func _ready():
	preload("res://scene_b.tscn")

scene_b.gd:

extends Node

func _ready():
	preload("res://scene_a.tscn")

Minimal reproduction project (MRP)

SceneBugMRP.zip

[rsutton1]

It seems like Godot does not support two scenes loading each other with PackedScene.

If this is the case, I would advise the following:

1. In Godot 4, don't let the user run the project when trying to do this. (Godot 3 provides an error message and refuses to Run the project).
2. Update the docs on changing scenes to warn about this (I created a godot-docs issue here: The page on changing scenes should warn about cyclic dependencies godot-docs#8596 )

Because of this issue I lost about ~3 hours scratching my head at the unexpected behavior. When I tried to reload the project, my scene file was corrupted. I would prefer that Godot provide an error message to prevent me from running the unsupported behavior in the first place (and if the docs were up-to-date, I wouldn't have tried to do this at all -- but that's a discussion for the the Issue in godot-docs).