Fix optional callback props implementation (#5225)

* fix optional event handler diffing

* add regression test

packages/core-macro/src/props/mod.rs

@@ -697,10 +697,14 @@ mod struct_info {
                 let name = field.name;
                 if optional {
                     quote! {
-                        // If the event handler is None, we don't need to update it
+                        // If both event handler are Some, update them in place
                         if let (Some(old_handler), Some(new_handler)) = (self.#name.as_mut(), new.#name.as_ref()) {
                             old_handler.__point_to(new_handler);
                         }
+                        // Otherwise just move the new handler into self
+                        else {
+                            self.#name = new.#name;
+                        }
                     }
                 } else {
                     quote! {

packages/core-macro/tests/values_memoize_in_place.rs

@@ -215,3 +215,28 @@ fn cloning_read_signal_components_work() {
     }
     dom.render_immediate(&mut dioxus_core::NoOpMutations);
 }
+
+// Regression test for https://github.com/DioxusLabs/dioxus/issues/5222
+#[tokio::test]
+async fn optional_event_handler_diff() {
+    use dioxus_core::Properties;
+
+    #[derive(Props, Clone, PartialEq)]
+    struct CompProps {
+        callback: Option<Callback>,
+    }
+
+    let dom = VirtualDom::new(|| rsx! {});
+
+    dom.in_scope(ScopeId::APP, || {
+        // Diffing from None to Some should be different and copy the callback
+        let mut props = CompProps::builder().callback(None).build();
+        assert!(!props.memoize(&CompProps::builder().callback(|_| {}).build()));
+        assert!(props.inner.callback.is_some());
+
+        // Diffing from Some to None should be different and remove the callback
+        let mut props = CompProps::builder().callback(|_| {}).build();
+        assert!(!props.memoize(&CompProps::builder().callback(None).build()));
+        assert!(props.inner.callback.is_none());
+    });
+}