react-doctor/rerender-functional-setstate

Use the callback form: `setState(prev => prev + 1)` to always read the latest value

• Category: Performance
• Severity: warn
• Source: oxlint-plugin-react-doctor
• Framework: global
• Enabled when: always

Validation prompt

Use this to decide whether a fired diagnostic is real or a false positive.

Fires on setX(x + n), setX(x ** n), setX(++x), setX([...x, item]), or setX({ ...x, k: v }) where x is the state variable name derived from the setter (setCount → count). The derived-name check prevents false positives on patterns like setCount(1 + computedValue) where no operand structurally references the state.

Fix prompt

Use this once validation confirms the diagnostic is real.

Use the updater form so React reads the latest queued value: setCount(prev => prev + 1), setMessages(prev => [...prev, msg]), setUser(prev => ({ ...prev, name })). This is critical inside subscription handlers, setInterval callbacks, and batched event handlers where the captured value otherwise goes stale. See https://react.dev/reference/react/useState#updating-state-based-on-the-previous-state

Related rules

More Performance rules from the rules reference:

• react-doctor/rerender-lazy-ref-init: Lazy-init the ref: `const ref = useRef(null); if (ref.current === null) ref.current = expensiveCall()`
• react-doctor/rerender-lazy-state-init: Wrap in an arrow function so it only runs once: `useState(() => expensiveComputation())`
• react-doctor/rerender-memo-before-early-return: Extract the JSX into a memoized child component so the parent's early return short-circuits before the child renders
• react-doctor/rerender-memo-with-default-value: Move to module scope: `const EMPTY_ITEMS: Item[] = []` then use as the default value
• react-doctor/rerender-state-only-in-handlers: Replace useState with useRef when the value is only mutated and never read in render — `ref.current = ...` updates without re-rendering the component