A subclass of an GDExtension subclass of EditorPlugin cannot be used as an editor plugin

[andreymal]

Godot version

4.1.3

System information

Linux

Issue description

I'm trying to make an editor plugin on Rust:

#[derive(GodotClass)]
#[class(tool, editor_plugin, init, base=EditorPlugin)]
pub struct MyEditorPluginBase {}

But due to some limitations, I still have to use GDScript for some specific things.

So I tried to make a subclass of this Rust class:

@tool
class_name MyEditorPlugin
extends MyEditorPluginBase

This would work if MyEditorPluginBase was a GDScript class, but since it's a GDExtension class in my case, it doesn't work:

Unable to load addon script from path: 'res://addons/my_addon/my_editor_plugin.gd' Base type is not EditorPlugin.

But it obviously IS EditorPlugin!

If I understand correctly, this behavior is caused by this function, which checks some mysterious "instance base type" instead of real inheritance:

godot/editor/editor_node.cpp

Lines 3456 to 3458 in fa4a653

	// Plugin init scripts must inherit from EditorPlugin and be tools.
	if (String(scr->get_instance_base_type()) != "EditorPlugin") {
	show_warning(vformat(TTR("Unable to load addon script from path: '%s' Base type is not EditorPlugin."), script_path));

godot/modules/gdscript/gdscript.cpp

Lines 260 to 263 in fa4a653

	StringName GDScript::get_instance_base_type() const {
	if (native.is_valid()) {
	return native->get_name();
	}

Since the documentation doesn't say that the script must be a direct subclass of EditorPlugin (and an indirect subclass works fine in GDScript), I interpret this behavior as a Godot bug.

Steps to reproduce

See above

Minimal reproduction project

gdext_editor_plugin_test.zip

[AThousandShips]

Please provide a minimum project, there may be many different aspects of how you've set this up that might cause this

[andreymal]

@AThousandShips ok added

[YuriSizov]

get_instance_base_type is used correctly, but the check itself should likely be ClassDB::is_parent_class(instance_base_type, "EditorPlugin");.

Edit: Looks like a few places need to be updated. I'll make a PR.

[dsnopek]

FYI, it is also possible to directly register an EditorPlugin from GDExtension, you don't need to make an addon which necessitates the workaround you're using here, where you have a GDScript that extends your GDExtension class.

I don't know the API for how it's done from Rust, but in godot-cpp, you can have code like:

void register_my_extension(ModuleInitializationLevel p_level) {
#if defined(TOOLS_ENABLED) || defined(DEBUG_ENABLED)
	if (p_level == MODULE_INITIALIZATION_LEVEL_EDITOR) {
		GDREGISTER_CLASS(MyEditorPlugin);

		EditorPlugins::add_by_type<MyEditorPlugin>();
	}
#endif
}

This will cause the editor plugin to be registered as soon as the GDExtension is loaded.

There's probably a way to do this from Rust as well!

[andreymal]

@dsnopek I can't because of a godot-rust bug godot-rust/gdext#494

(which can't be painlessly fixed until godotengine/godot-proposals#2241 is implemented)

[andreymal]

There is another error in 4.2.1.rc1:

ERROR: Script inherits from native type 'MyEditorPluginBase', so it can't be assigned to an object of type 'EditorPlugin'.
   at: instance_create (modules/gdscript/gdscript.cpp:390)

Should I create a separate issue about this?

[YuriSizov]

@andreymal It may be is just a continuation of this one, but feel free to open a new report. I would also appreciate if you could make an MRP that uses godot-cpp at least. It's unlikely that many contributors, myself included, have a Rust environment set up to reproduce and validate your report as it stands.