Fix signal parameter type not propagated to editor

gdnative-core/src/export/class_builder.rs

@@ -30,11 +30,11 @@
 //! For full examples, see [`examples`](https://github.com/godot-rust/godot-rust/tree/master/examples)
 //! in the godot-rust repository.
 
-use crate::core_types::GodotString;
 use std::ffi::CString;
 use std::marker::PhantomData;
 use std::ptr;
 
+use crate::core_types::{GodotString, VariantType};
 use crate::export::*;
 use crate::object::NewRef;
 use crate::private::get_api;
@@ -199,13 +199,13 @@ impl<C: NativeClass> ClassBuilder<C> {
 
             let mut sys_args = args_and_hints
                 .iter()
-                .map(|(arg, hint_string)| sys::godot_signal_argument {
-                    name: arg.name.to_sys(),
-                    type_: arg.default.get_type() as i32,
-                    hint: arg.export_info.hint_kind,
+                .map(|(param, hint_string)| sys::godot_signal_argument {
+                    name: param.name.to_sys(),
+                    type_: Self::get_param_type(param) as i32,
+                    hint: param.export_info.hint_kind,
                     hint_string: hint_string.to_sys(),
-                    usage: arg.usage.to_sys(),
-                    default_value: arg.default.to_sys(),
+                    usage: param.usage.to_sys(),
+                    default_value: param.default.to_sys(),
                 })
                 .collect::<Vec<_>>();
 
@@ -223,6 +223,16 @@ impl<C: NativeClass> ClassBuilder<C> {
         }
     }
 
+    /// Returns the declared parameter type, or the default value's type, or Nil (in that order)
+    fn get_param_type(arg: &SignalParam) -> VariantType {
+        let export_type = arg.export_info.variant_type;
+        if export_type != VariantType::Nil {
+            export_type
+        } else {
+            arg.default.get_type()
+        }
+    }
+
     pub(crate) fn add_method(&self, method: ScriptMethod) {
         let method_name = CString::new(method.name).unwrap();