`self.to_gd()` in `drop()` causes (double) panic

[ttencate]

Maybe the inverse problem of #557.

#[derive(GodotClass)]
#[class(init, base=RefCounted)]
struct AccessGdOnDrop {
    base: Base<RefCounted>,
}

impl Drop for AccessGdOnDrop {
    fn drop(&mut self) {
        // This causes a panic.
        self.to_gd();
    }
}

#[itest]
fn access_gd_on_drop() {
    let obj = AccessGdOnDrop::new_gd();
    drop(obj);
}

This gives a panic (message copied from my actual game, the above seems to outright abort):

ERROR: [panic .../godot-core-0.3.1/src/obj/raw_gd.rs:201]
  object expected to inherit RefCounted

[Bromeon]

Thanks for reporting! Marked it now as "feature" since #557 is one too, but either way it would be nice to support this.

And if we can't, we should at least document it and ideally provide a better error message than the one you posted on Discord:

ERROR: [panic .../godot-core-0.3.1/src/obj/raw_gd.rs:201]
object expected to inherit RefCounted

[beicause]

Additionally, using NOTIFICATION_PREDELETE can't work around this issue:

#[derive(GodotClass)]
#[class(init)]
struct RefcPredelete {
    base: Base<RefCounted>,
}

#[godot_api]
impl IRefCounted for RefcPredelete {
    fn on_notification(&mut self, what: ObjectNotification) {
        if what == ObjectNotification::PREDELETE {
            println!("{:?}", self.base().get_meta("meta"));
            assert_eq!(self.base().get_meta("meta"), "value".to_variant());
        }
    }
}

#[itest]
fn base_predelete_refcounted() {
    let mut obj = RefcPredelete::new_gd();
    obj.set_meta("meta", &"value".to_variant());
}

This also panics, base() attempted to increase the reference count but failed.

[Yarwin]

It happens in gdscript too – there is an upstream issue: godotengine/godot#80834.

class GDScriptRefCounted:
	func _notification(what: int) -> void:
		if what == NOTIFICATION_PREDELETE:
			# Attempt to call function 'get_meta' in base 'null instance' on a null instance.
			print(self.get_meta("any_value"))

[Bromeon]

Very good observation!

Btw @beicause, today we might attend the GDExtension meeting (see RocketChat) at 23:30 CEST. Might be a bit early in your timezone (5:30 AM? please double-check) but of course, in case you'd like to join, feel free 🙂 otherwise we can try to bring up some of these points to Godot devs. If you can't attend and would like us to ask something on your behalf, let me know!