`RefCounted` releases itself if it is referenced in `NOTIFICATION_POSTINITIALIZE`

[beicause]

Tested versions

4.5

System information

Linux

Issue description

See godot-rust/gdext#1211 (comment)

In GDExtension, referencing RefCounted in postinitialize will cause the count not to increase correctly. The reference count is lower than expected by 1, leading to releasing itself.

This also occurs in constructor.

Steps to reproduce

Run https://github.com/godotengine/godot-cpp-template with following code:

#include "example_class.h"

void ExampleClass::_bind_methods() {
	godot::ClassDB::bind_method(D_METHOD("print_type", "variant"), &ExampleClass::print_type);
}

void ExampleClass::_notification(int p_what) {
	if (p_what == NOTIFICATION_POSTINITIALIZE) {
		UtilityFunctions::print("refcount: ", get_reference_count());
		Ref<ExampleClass> a = this;
		UtilityFunctions::print("refcount: ", get_reference_count());
		Ref<ExampleClass> b = this;
		UtilityFunctions::print("refcount: ", get_reference_count());
		Ref<ExampleClass> c = this;
		UtilityFunctions::print("refcount: ", get_reference_count());
		Ref<ExampleClass> d = this;
		UtilityFunctions::print("refcount: ", get_reference_count());
	}
}

void ExampleClass::print_type(const Variant &p_variant) const {
	print_line(vformat("Type: %d", p_variant.get_type()));
}

extends Node


func _ready() -> void:
	var example := ExampleClass.new()
	example.print_type(example)

Output:

refcount: 1
refcount: 1
refcount: 2
refcount: 3
refcount: 4
SCRIPT ERROR: Cannot call method 'print_type' on a null value.
          at: _ready (res://example.gd:6)
          GDScript backtrace (most recent call first):
              [0] _ready (res://example.gd:6)

Minimal reproduction project (MRP)

See above

[AThousandShips]

Checked the code and this is likely an issue in core, as the post-initialization is called before the object reference is returned, and therefore before it has any chance of being referenced

This might also be a GDScript issue, would be good to check what happens if this is constructed on the C++ side, but probably the same result

I'm not sure this can be supported though, I can't see any reasonable way to handle this as the ref it is put into isn't constructed yet

One possible solution would be to somehow have some check while it is being initialized to ensure it has a valid reference lying around, but that might cause various problems on its own, perhaps instead it would be best to add a check or something to fail if a ref counted is referenced like this in this case

[beicause]

extends RefCounted
class_name Rc

func _notification(what: int) -> void:
    if what == NOTIFICATION_POSTINITIALIZE:
        print("post init")
        print(get_reference_count())
        var a = self
        print(a.get_reference_count())

        var b = self
        print(b.get_reference_count())

I also tested NOTIFICATION_POSTINITIALIZE in gdscript, but it didn't receive postinitialize at all and there was no output.

And refcount works correctly in gdscript's _init:

func _init() -> void:
        print("init")
        print(get_reference_count())
        var a = self
        print(a.get_reference_count())

        var b = self
        print(b.get_reference_count())

init
2
3
4
1
--- Debugging process stopped ---

Edit:
😅This is as expected as docs said:

Notification received when the object is initialized, before its script is attached. Used internally.

[beicause]

I do see postinit executes immediately after the instance is constructed, at which point the RefCounted::refcount_init has not been initialized. That is to say, the behavior of postinit is similar to constructor.
This seems unsolvable, I don't see how RefCounted can distinguish whether it is being referenced within postinit/constructor or externally

So closing.