fix: merged ref behavior in react 19

[jquense]

React 19 supports clean up functions, which we need to handle. This also ensures that the current behavior of not returning a callback still results in them being called/set with null

[kyletsang]

Does this need a react 19 check? Could it return the cleanup function regardless of version, which would be ignored in R18 and actually work in R19?

[jquense]

I don't know. I think there are react warnings if you return stuff

[kyletsang]

Ah ok - in that case, this code is missing the return handler for anything below R19

[jquense]

ya but that is the same as now right? no return for < 19

[kyletsang]

Sorry I meant the mergeRefs function. mergeRefs currently doesn't return a function on R18 and below

You meant to do this right?

export function mergeRefs<T>(refA?: Ref<T> | null, refB?: Ref<T> | null) {
  const refASetter = toFnRef(refA);
  const refBSetter = toFnRef(refB);

  return (value: T | null) => {
    const cleanupA = refASetter?.(value);
    const cleanupB = refBSetter?.(value);

    if (isReact19) {  // <--- This moved inside
      return () => {
        cleanUp(cleanupA, refASetter);
        cleanUp(cleanupB, refBSetter);
      };
    }
  };
}