Fix refcount of callables being erroneously decremented when received…

… as argument

godot-core/src/builtin/callable.rs

@@ -250,6 +250,10 @@ impl Callable {
     pub fn as_inner(&self) -> inner::InnerCallable {
         inner::InnerCallable::from_outer(self)
     }
+
+    fn inc_ref(&self) {
+        std::mem::forget(self.clone())
+    }
 }
 
 impl_builtin_traits! {
@@ -270,7 +274,18 @@ impl_builtin_traits! {
 // The `opaque` in `Callable` is just a pair of pointers, and requires no special initialization or cleanup
 // beyond what is done in `from_opaque` and `drop`. So using `*mut Opaque` is safe.
 unsafe impl GodotFfi for Callable {
-    ffi_methods! { type sys::GDExtensionTypePtr = *mut Opaque; .. }
+    ffi_methods! { type sys::GDExtensionTypePtr = *mut Opaque;
+        fn from_sys;
+        fn sys;
+        fn from_sys_init;
+        fn move_return_ptr;
+    }
+
+    unsafe fn from_arg_ptr(ptr: sys::GDExtensionTypePtr, _call_type: sys::PtrcallType) -> Self {
+        let callable = Self::from_sys(ptr);
+        callable.inc_ref();
+        callable
+    }
 
     unsafe fn from_sys_init_default(init_fn: impl FnOnce(sys::GDExtensionTypePtr)) -> Self {
         let mut result = Self::invalid();

itest/godot/ManualFfiTests.gd

@@ -326,3 +326,15 @@ func test_gd_self_reference_succeeds():
 	gd_self_reference.update_internal_signal.connect(update_self_reference)
 
 	assert_eq(gd_self_reference.succeed_at_updating_internal_value(10), 10)
+
+func sample_func():
+	pass
+
+func test_callable_refcount():
+	var test_obj: CallableRefcountTest = CallableRefcountTest.new()
+	for i in range(10):
+		var method := Callable(self, "sample_func")
+		test_obj.accept_callable(method)
+	var method := Callable(self, "sample_func")
+	assert(method.is_valid())
+	test_obj.free()

itest/rust/src/builtin_tests/containers/callable_test.rs

@@ -126,6 +126,18 @@ fn callable_call_engine() {
     obj.free();
 }
 
+// Testing https://github.com/godot-rust/gdext/issues/410
+
+#[derive(GodotClass)]
+#[class(init, base = Node)]
+pub struct CallableRefcountTest {}
+
+#[godot_api]
+impl CallableRefcountTest {
+    #[func]
+    fn accept_callable(&self, _call: Callable) {}
+}
+
 // ----------------------------------------------------------------------------------------------------------------------------------------------
 // Tests and infrastructure for custom callables