Implement Display for user-provided Gd<T>

Author: Bromeon

godot-core/src/obj/gd.rs

@@ -649,14 +649,7 @@ impl<T: GodotClass> PartialEq for Gd<T> {
 
 impl<T: GodotClass> Eq for Gd<T> {}
 
-impl<T> Display for Gd<T>
-where
-    T: GodotClass<Declarer = dom::EngineDomain>,
-{
-    // TODO support for user objects? should it return the engine repr, or a custom <T as Display>::fmt()?
-    // If the latter, we would need to do something like impl<T> Display for Gd<T> where T: Display,
-    // and thus implement it for each class separately (or blanket GodotClass/EngineClass/...).
-
+impl<T: GodotClass> Display for Gd<T> {
     fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
         engine::display_string(self, f)
     }

itest/rust/src/object_test.rs

@@ -115,7 +115,17 @@ fn object_engine_roundtrip() {
 }
 
 #[itest]
-fn object_display() {
+fn object_user_display() {
+    let obj = Gd::new(ObjPayload { value: 774 });
+
+    let actual = format!(".:{obj}:.");
+    let expected = ".:value=774:.".to_string();
+
+    assert_eq!(actual, expected);
+}
+
+#[itest]
+fn object_engine_display() {
     let obj = Node3D::new_alloc();
     let id = obj.instance_id();
 
@@ -631,7 +641,6 @@ fn user_object() -> Gd<ObjPayload> {
 }
 
 #[derive(GodotClass, Debug, Eq, PartialEq)]
-//#[class(init)]
 pub struct ObjPayload {
     value: i16,
 }
@@ -641,6 +650,10 @@ impl RefCountedVirtual for ObjPayload {
     fn init(_base: Base<Self::Base>) -> Self {
         Self { value: 111 }
     }
+
+    fn to_string(&self) -> GodotString {
+        format!("value={}", self.value).into()
+    }
 }
 
 // ----------------------------------------------------------------------------------------------------------------------------------------------