#[class(no_init)] makes extension non-reloadable

[snatvb]

Note

Edit bromeon: updated problem description.

When disabling the default constructor via #[class(no_init)], the class can no longer be reloaded. Godot uses this as a reason to disable reloading for the entire extension, with the following error:

Extension marked as reloadable, but attempted to register class 'MyClass' which doesn't support reloading. Perhaps your language binding don't support it? Reloading disabled for this extension.

It looks like the problem arises in the following part:

gdext/godot-macros/src/class/derive_godot_class.rs

Lines 78 to 105 in 6e6889a

	let mut create_fn = quote! { None };
	let mut recreate_fn = quote! { None };
	let mut is_instantiable = true;
	match struct_cfg.init_strategy {
	InitStrategy::Generated => {
	godot_init_impl = make_godot_init_impl(class_name, &fields);
	create_fn = quote! { Some(#prv::callbacks::create::<#class_name>) };
	if cfg!(since_api = "4.2") {
	recreate_fn = quote! { Some(#prv::callbacks::recreate::<#class_name>) };
	}
	}
	InitStrategy::UserDefined => {
	let fn_name = format_ident!("class_{}_must_have_an_init_method", class_name);
	init_expecter = quote! {
	#[allow(non_snake_case)]
	fn #fn_name() {
	fn __type_check<T: ::godot::obj::cap::GodotDefault>() {}
	__type_check::<#class_name>();
	}
	}
	}
	InitStrategy::Absent => {
	is_instantiable = false;
	}
	};

If no_init is specified, the init strategy will be Absent, and neither create nor recreate functions are set. I think particularly the latter causes problems, although this needs to be confirmed. The class is also marked abstract, but I'm not sure if that interferes with it.

We would need to see how we can enable reloading in the absence of a default constructor. If there are no instances of a class to be reloaded, there shouldn't be a problem -- so maybe Godot is overzealous at forbidding reloading if there is no constructor?

Update: there's now an upstream issue to enable this workflow in Godot:

• GDExtension: Classes without default constructor break reloading godotengine/godot#96823

---

Original message:

Hello,

I've noticed that when I've updated gdext and godot on 4.3 I got broken reload. I used gdext_coroutines. After disable this part on another project that I've created for testing - reloadable starts work fine. After I read the library and didn't notice any specific cases and tried to add imports coroutines into my extenstion directrly and got same issue.

Reproduce:

1. Use nightly rust (coroutines is unstable feature)
2. Add #![feature(coroutines, coroutine_trait)]
3. Add use std::ops::{Coroutine, CoroutineState};

Read more: Houtamelo/gdext_coroutines#2
showcase.zip

[Bromeon]

Your project has a ton of dependencies, that's not really helpful. Please really come up with a minimal complete example, a single Rust file + if relevant, Cargo.toml and .gdextension file. Avoid any dependencies that are not necessary. In particular, see if you can somehow trigger the problem without gdext_coroutines (but still using Rust coroutines).

Also, ZIPs are nice -- but additionally, please add the above-mentioned files as inline snippets here (make sure they're short and do not contain irrelevant info). This is more accessible for anyone joining the discussion, and lets people try out things without first downloading and unpacking an archive.

[snatvb]

iteresting, I got error when I started it from scratch:

core/extension/gdextension.cpp:508 - Extension marked as reloadable, but attempted to register class 'SpireCoroutine' which doesn't support reloading. Perhaps your language binding don't support it? Reloading disabled for this extension.

I think that it's issue on the lib side, if it so, please, close this issue(just I am not sure):
Houtamelo/gdext_coroutines#2 (comment)

[Bromeon]

So it looks like this has nothing to do with coroutines, but rather #[class(no_init)]. I'll edit the issue description.

[Bromeon]

Confirmed to be a limitation in Godot: godotengine/godot#96823