Register reference/unreference callbacks for RefCounted classes

Author: Bromeon

godot-core/src/obj/bounds.rs

@@ -152,7 +152,11 @@ pub use crate::implement_godot_bounds;
 // Memory bounds
 
 /// Specifies the memory strategy of the static type.
-pub trait Memory: Sealed {}
+pub trait Memory: Sealed {
+    /// True for everything inheriting `RefCounted`, false for `Object` and all other classes.
+    #[doc(hidden)]
+    const IS_REF_COUNTED: bool;
+}
 
 /// Specifies the memory strategy of the dynamic type.
 ///
@@ -205,7 +209,9 @@ pub trait DynMemory: Sealed {
 /// This is used for `RefCounted` classes and derived.
 pub struct MemRefCounted {}
 impl Sealed for MemRefCounted {}
-impl Memory for MemRefCounted {}
+impl Memory for MemRefCounted {
+    const IS_REF_COUNTED: bool = true;
+}
 impl DynMemory for MemRefCounted {
     fn maybe_init_ref<T: GodotClass>(obj: &mut RawGd<T>) {
         out!("  MemRefc::init:  {obj:?}");
@@ -327,7 +333,9 @@ impl DynMemory for MemDynamic {
 /// This is used for all `Object` derivates, which are not `RefCounted`. `Object` itself is also excluded.
 pub struct MemManual {}
 impl Sealed for MemManual {}
-impl Memory for MemManual {}
+impl Memory for MemManual {
+    const IS_REF_COUNTED: bool = false;
+}
 impl DynMemory for MemManual {
     fn maybe_init_ref<T: GodotClass>(_obj: &mut RawGd<T>) {}
     fn maybe_inc_ref<T: GodotClass>(_obj: &mut RawGd<T>) {}

godot-core/src/registry/class.rs

@@ -136,8 +136,8 @@ impl ClassRegistrationInfo {
 }
 
 /// Registers a class with static type information.
-// Currently dead code, but will be needed for builder API. Don't remove.
-pub fn register_class<
+#[expect(dead_code)] // Will be needed for builder API. Don't remove.
+pub(crate) fn register_class<
     T: cap::GodotDefault
         + cap::ImplementsGodotVirtual
         + cap::GodotToString
@@ -427,6 +427,8 @@ fn fill_class_info(item: PluginItem, c: &mut ClassRegistrationInfo) {
             is_instantiable,
             #[cfg(all(since_api = "4.3", feature = "register-docs"))]
                 docs: _,
+            reference_fn,
+            unreference_fn,
         }) => {
             c.parent_class_name = Some(base_class_name);
             c.default_virtual_fn = default_get_virtual_fn;
@@ -443,6 +445,8 @@ fn fill_class_info(item: PluginItem, c: &mut ClassRegistrationInfo) {
             // See also: https://github.com/godotengine/godot/pull/58972
             c.godot_params.is_abstract = sys::conv::bool_to_sys(!is_instantiable);
             c.godot_params.free_instance_func = Some(free_fn);
+            c.godot_params.reference_func = reference_fn;
+            c.godot_params.unreference_func = unreference_fn;
 
             fill_into(
                 &mut c.godot_params.create_instance_func,

godot-core/src/registry/plugin.rs

@@ -167,6 +167,12 @@ pub struct Struct {
     /// Callback to library-generated function which registers properties in the `struct` definition.
     pub(crate) register_properties_fn: ErasedRegisterFn,
 
+    /// Callback on refc-increment. Only for `RefCounted` classes.
+    pub(crate) reference_fn: sys::GDExtensionClassReference,
+
+    /// Callback on refc-decrement. Only for `RefCounted` classes.
+    pub(crate) unreference_fn: sys::GDExtensionClassUnreference,
+
     /// Function called by Godot when an object of this class is freed.
     ///
     /// Always implemented as [`callbacks::free`].
@@ -200,6 +206,8 @@ impl Struct {
     pub fn new<T: GodotClass + cap::ImplementsGodotExports>(
         #[cfg(all(since_api = "4.3", feature = "register-docs"))] docs: StructDocs,
     ) -> Self {
+        let refcounted = <T::Memory as bounds::Memory>::IS_REF_COUNTED;
+
         Self {
             base_class_name: T::Base::class_name(),
             generated_create_fn: None,
@@ -215,6 +223,9 @@ impl Struct {
             is_instantiable: false,
             #[cfg(all(since_api = "4.3", feature = "register-docs"))]
             docs,
+            // While Godot doesn't do anything with these callbacks for non-RefCounted classes, we can avoid instantiating them in Rust.
+            reference_fn: refcounted.then_some(callbacks::reference::<T>),
+            unreference_fn: refcounted.then_some(callbacks::unreference::<T>),
         }
     }