Duplicating Resource scripts breaks the inspector when attaching the duplicate script to a .tres file

[jamesridley]

Tested versions

Godot Engine v4.2.stable.official

System information

Godot v4.2.stable - Windows 10.0.22631 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3070 Ti (NVIDIA; 31.0.15.4601) - AMD Ryzen 7 5700X 8-Core Processor (16 Threads)

Issue description

Duplicating a script that inherits from a custom resource, then attaching that script to an "instance" (not sure what to call it) of a resource causes the inspector to stop showing any exported variables from the resource. This only seems to happen when there is a difference in exported variables between the two sibling scripts but I'm not sure. The steps to reproduce should make it a lot clearer.

This happened to me when I was duplicating a script because I knew the next script would have similar code, so I think it's kinda common for this to happen. This was fixed by deleting the script, then making a new one without duplicating anything, and copy pasting manually.

I couldn't find any duplicates (haha) of this issue that specifically come from duplicating scripts, but it's possible that #83343 fixes this. I'm not sure though, since I don't have that version of Godot, nor do I know how to find that version of Godot.

Steps to reproduce

1. Create a new script test_resource.gd that extends Resource
2. Paste the following:

class_name TestResource
extends Resource

@export var member_variable: int

3. Create a new script inherited_resource.gd that extends TestResource
4. Paste the following

extends TestResource

@export inherited_member_variable: int

5. Create a new resource new_test_resource.tres. Select TestResource to be the "instancer" (still don't know what to call it)
6. Right-click then duplicate inherited_resource.gd. Name it inherited_resource2.gd
7. Replace the script body with the following:

extends TestResource

@export var duplicate_member_variable: int

8. Double click on new_test_resource.tres
9. Drag and drop inherited_resource2.gd to the script of new_test_resource in the inspector
10. Then drag and drop inherited_resource.gd to replace the duplicate
11. Watch all the variables in the inspector disappear! It should look like this:
    

Minimal reproduction project (MRP)

resource_duplication_bug.zip

Inspecting the .tres file should show no exported variables after opening the project, since reloading the project did not fix this for me.