useEffect + setState panics with RefCell already borrowed on macOS ARM64

[tomkennedy22]

Hey! Humongous fan of perry!

Been playing around with perry-react today and hit a crash that I think is also responsible for the weather-app demo crashing on launch.
Calling a state setter inside useEffect panics every time:

function App() {
  const [status, setStatus] = useState("idle")

  useEffect(() => {
    setStatus("started")
  }, [])

  return <div><h1>Status: {status}</h1></div>
}

thread '<unnamed>' panicked at crates/perry-ui-macos/src/state.rs:382:13:
RefCell already borrowed

My guess is the useEffect fires and triggers a re-render while the initial render is still holding a borrow on the state RefCell.

I initially found this when cloning & testing the weather-app and it crashes on launch with the same abort — pretty sure it's the same root cause since it calls setState from inside a fetch callback on startup. I couldn't get weather-app working so started a new react repo and ultimately hit this error

macOS ARM64, built from source, perry-react from PerryTS/react.

[proggeramlug]

Hey Thomas, thanks for the detailed report — your diagnosis was spot on.

Perry-react is admittedly the least tested part of our current UI surface, so really appreciate you putting it through its paces and taking the time to file this.

Root cause: state_set() held an immutable borrow on the ON_CHANGE_CALLBACKS RefCell while iterating and invoking user closures via js_closure_call1. In perry-react, useEffect fires synchronously during the initial render — so when setStatus("started") triggers state_set → onChange callback → _scheduleRerender → component re-render → any new useState calls sig.onChange() → state_on_change() tries borrow_mut() on the same RefCell → panic.

Fix: state_set() now snapshots the callback list into a local Vec before invoking any closures, releasing the RefCell borrow first. Same treatment applied to FOR_EACH_BINDINGS (which also calls user closures). Fixed across all 5 platform crates (macOS, iOS, GTK4, Windows, Android).

Fixed in b521064.

[tomkennedy22]

Awesome! Amazing response time, much appreciated. I'll test it out more on Saturday