error: usage of `Arc<T>` where `T` is not `Send` or `Sync`
  --> $DIR/arc_with_non_send_sync.rs:19:13
   |
LL |     let b = Arc::new(RefCell::new(42));
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: consider using `Rc<T>` instead or wrapping `T` in a std::sync type like `Mutex<T>`
   = note: `-D clippy::arc-with-non-send-sync` implied by `-D warnings`

error: aborting due to previous error