ResourceSaver duplicates items in all arrays

[JonathanPicques]

Godot version:
3.1

OS/device including version:
Windows 10

Issue description:
ResourceSaver duplicates items in all arrays upon saving

Minimal reproduction script:

extends Node2D

class Save:
	extends Resource

	export var version : String = "1.0"
	export var save_name : String = "Whatever"
    
	export var arr1: Array = []
	export var arr2: Array = []
	export var arr3: Array = []

func _ready():
	var save := Save.new()
	
	save.arr1.push_back({"name": "Plane"})
	save.arr2.push_back({"name": "Human"})
	save.arr3.push_back({"name": "Cat"})
	
	ResourceSaver.save("res://test.tres", save)

test.tres:

[gd_resource type="Resource" load_steps=2 format=2]

[sub_resource type="GDScript" id=1]

[resource]
script = SubResource( 1 )
version = "1.0"
save_name = "Whatever"
arr1 = [ {
"name": "Plane"
}, {
"name": "Human"
}, {
"name": "Cat"
} ]
arr2 = [ {
"name": "Plane"
}, {
"name": "Human"
}, {
"name": "Cat"
} ]
arr3 = [ {
"name": "Plane"
}, {
"name": "Human"
}, {
"name": "Cat"
} ]

[KoBeWi]

The actual problem here is that each exported array is the same instance. I remember it being mentioned/reported somewhere (like this related issue #20436), but not sure if there was some proper fix/workaround.

btw, this makes Resources almost useless for saving game progress, because you often need to use arrays in complex games.

[PetePete1984]

The erroneous sharing between typed arrays and dictionaries should be fixed in 3.2, see #24134
In the meantime, if you give your Save class an _init function, you should be able to bypass this (heavy emphasis on should because I haven't tried saving exported arrays since v306):

func _init():
    arr1 = []
    arr2 = []
    arr3 = []

[JonathanPicques]

Hey, thanks for the heads up @PetePete1984

I ended up using

class Save:
	extends Resource

	export var version : String = "1.0"
	export var save_name : String = "Whatever"
	export var save_data = {
		"nodes": [],
		"connections": []
	}

[nicktgn]

The erroneous sharing between typed arrays and dictionaries should be fixed in 3.2, see #24134
In the meantime, if you give your Save class an _init function, you should be able to bypass this (heavy emphasis on should because I haven't tried saving exported arrays since v306):

func _init():
    arr1 = []
    arr2 = []
    arr3 = []

Stumbled upon the same issue. Can confirm, @PetePete1984's workaround suggestion works.

[KoBeWi]

The erroneous sharing between typed arrays and dictionaries should be fixed in 3.2, see #24134

Tested in 4493957 and the problem still exists.

[KoBeWi]

So, another way to avoid this is not initializing the arrays:

export var arr1: Array
export var arr2: Array
export var arr3: Array

They are initialized automatically to unique references.

[ghost]

The issues related to this mentioned that dictionaries also had this problem; in my own experiments, the dictionaries were fine, but the arrays would still share the same instance. Not initializing them does the trick.

[KoBeWi]

Eh, if someone is interested, export var arr = [] executes code blocks at these lines:

godot/modules/gdscript/gdscript_parser.cpp

Line 927 in 4ee8ecd

} else if (tokenizer->get_token() == GDScriptTokenizer::TK_BRACKET_OPEN) {

godot/modules/gdscript/gdscript_parser.cpp

Line 1619 in 4ee8ecd

case Node::TYPE_ARRAY: {

Same operation for dictionaries uses exactly the same code, so not sure where is the part that makes arrays shared (but probably there are some parts I'm not aware of and these might differ. Dunno). I used #28603 to get a clue where to look, but then got stuck :/

[KoBeWi]

Still valid in a609b30

I'm surprised that GDScript 2.0 still has this problem.

[MGilleronFJ]

Would it be because arrays were made to be compared by value (even though they are ref types), therefore making them under the same key if indexed in a map or hashmap? If dictionaries also get compared by value they might end up with the same problem

[KoBeWi]

Except property name is the key in hashmap, not its value.