GDScript "Parse Error: Script export type must be a global class." regression in HungryProton Scatter plugin

[akien-mga]

Tested versions

• Reproducible in 4.3.beta (71699e0)
• Also reproducible after merging Fix loading of cyclic scenes from GDScript #92326 locally, which I hoped might fix it as it sounds related
• Not reproducible in 4.3.beta1, so it's a recent regression, needs bisecting

System information

Fedora Linux 40 (KDE Plasma) - Wayland - Vulkan (Forward+) - dedicated AMD Radeon RX 7600M XT (RADV NAVI33) - AMD Ryzen 7 7840HS w/ Radeon 780M Graphics (16 Threads)

Issue description

When opening a project using the https://github.com/HungryProton/scatter addon (installed from the asset lib), the following errors are printed:

SCRIPT ERROR: Parse Error: Script export type must be a global class.
          at: GDScript::reload (res://addons/proton_scatter/src/stack/modifier_stack.gd:15)
SCRIPT ERROR: Compile Error: 
          at: GDScript::reload (res://addons/proton_scatter/src/scatter.gd:-1)
SCRIPT ERROR: Parse Error: Script export type must be a global class.
          at: GDScript::reload (res://addons/proton_scatter/src/stack/modifier_stack.gd:15)
SCRIPT ERROR: Compile Error: 
          at: GDScript::reload (res://addons/proton_scatter/src/common/scatter_util.gd:-1)
SCRIPT ERROR: Compile Error: 
          at: GDScript::reload (res://addons/proton_scatter/src/scatter_shape.gd:-1)
SCRIPT ERROR: Compile Error: 
          at: GDScript::reload (res://addons/proton_scatter/src/shapes/gizmos_plugin/components/path_panel.gd:-1)
ERROR: Failed to load script "res://addons/proton_scatter/src/shapes/gizmos_plugin/components/path_panel.gd" with error "Compilation failed".
   at: load (./modules/gdscript/gdscript.cpp:2943)
SCRIPT ERROR: Invalid call. Nonexistent function 'selection_changed' in base 'MarginContainer (path_panel.gd)'.
          at: _on_selection_changed (res://addons/proton_scatter/plugin.gd:137)

This is a recent regression which doesn't appear in 4.3-beta1.

Steps to reproduce

• Create new project
• Install and enabled HungryProton scatter addon

Minimal reproduction project (MRP)

testscatter.zip

[dalexeev]

• See Register the export info correctly when a script is used as the variable type for Node #90487.

This is intentional, the inspector only supports global classes. Previously in GDScript there was an inconsistency between SCRIPT and CLASS datatypes.

Also, it's documented:

Note: Custom resources and nodes must be registered as global classes using class_name.

Alternatively, we could use a native class instead, if the script is not a global class.

[akien-mga]

I confirm that the following change fixes the issue for the Scatter plugin:

diff --git a/addons/proton_scatter/src/modifiers/base_modifier.gd b/addons/proton_scatter/src/modifiers/base_modifier.gd
index 244d465..3c30edb 100644
--- a/addons/proton_scatter/src/modifiers/base_modifier.gd
+++ b/addons/proton_scatter/src/modifiers/base_modifier.gd
@@ -1,4 +1,5 @@
 @tool
+class_name BaseModifier
 extends Resource
 
 # Modifiers place transforms. They create, edit or remove transforms in a list,
diff --git a/addons/proton_scatter/src/stack/modifier_stack.gd b/addons/proton_scatter/src/stack/modifier_stack.gd
index 3b46123..65c2afe 100644
--- a/addons/proton_scatter/src/stack/modifier_stack.gd
+++ b/addons/proton_scatter/src/stack/modifier_stack.gd
@@ -9,7 +9,6 @@ signal transforms_ready
 
 const ProtonScatter := preload("../scatter.gd")
 const TransformList := preload("../common/transform_list.gd")
-const BaseModifier := preload("../modifiers/base_modifier.gd")
 
 
 @export var stack: Array[BaseModifier] = []

There main problem I see is that plugins tend to avoid using class_name to avoid polluting the game's namespace with plugin-internal classes. I suppose this is why @HungryProton used preloads for these instead of class_name.

I suspect we'll find more addons with similar broken compatibility with 4.3 after this change. I'm not sure telling all the plugin authors to use class_name instead will be a satisfactory option for all.

For example @shakesoda already mentioned that the Spatial Gardener plugin seems to have the same issue.

[HungryProton]

If there were a way to tell Godot that a class is not meant to be exposed to the end user, I'd be more than happy to use global class names everywhere.

I avoid class_names for nodes because I don't want them to show up in the Create new node window unless the plugin is actually enabled (otherwise these nodes don't work properly).

This one is an exported resource so I guess I can make the fix on my end.