_init with parameters breaks when used with scene tree editor

[ishax-kos]

Godot version

4.0.2

System information

Windows 10

Issue description

I was exploring whether I should instantiate a number of slot node from an exported count parameter, or collect the manually added nodes in said parameter. I had created an _init function to properly initialize these slots, when my static typing seemed to hit this error.

Steps to reproduce

The problem is demonstrated in the provided project with an assert. Note that the problem goes away if there are no parameters in _init for the test_class.gd script. Additionally, a cpp exception is emitted.

Minimal reproduction project

Bug_report_class_name.zip

[gotnospirit]

https://godotengine.org/qa/4786/how-to-pass-parameters-when-instantiating-a-node?show=4827#c4827

[dalexeev]

You should not create node classes with required constructor parameters, they cannot be instantiated from the scene editor. Also, when adding a node from code, MyNodeClass.new() will only create the root of the scene, not the entire scene. Instead, you can add a static method that creates a node or instantiates a scene.

extends Node
class_name MyNodeClass

var param: String

static func create(p_param: String) -> MyNodeClass:
    var packed_scene: PackedScene = load("res://my_node_class.tscn")
    var node: MyNodeClass = packed_scene.instantiate()
    node.param = p_param
    return node

Usage:

var node := MyNodeClass.create("test")
add_child(node)

Related:

• Exporting resource whose _init takes a parameter results in resource being null in scene startup #67059
• Make it possible to pass arguments to PackedScene.instance() godot-proposals#1513
• Add scene binding for optional tight-coupling between Node-extending Scripts and PackedScene resources godot-proposals#1935
• Inform the users that non-default-constructible nodes are a bad thing godot-proposals#5899

I also remember that there was a proposal/comment about adding the ability to specify node/resource parameters when creating in the editor (but IMO this unnecessarily complicates things).

[ishax-kos]

It's definitely not a great thing to do, but the engine, instead of having a sensible error, will proceed without informing the user what is happening. It's failing with errors that don't give the user the information they need. Not to mention having unusual side effects. The program should not run.

[Calinou]

• Duplicate of Inform the users that non-default-constructible nodes are a bad thing godot-proposals#5899.