Sandbox: https://codesandbox.io/s/cranky-kapitsa-op3jh

Repro: type "a" and then after a second "b"

Expected: Eventually you'll see "ab" in all fields. Pending "..." indicator goes away.

Actual: You'll keep seeing "a" in low pri field. Pending "..." indicator is stuck.
if (!is(newState, hook.memoizedState)) {
      markWorkInProgressReceivedUpdate();
    }
    hook.memoizedState = newState;
    
    
    
    
    if (hook.baseQueue === null) {
      hook.baseState = newState;
    }
    queue.lastRenderedState = newState;
  }
  return [newState, dispatch];
}
type MutableSourceMemoizedState<Source, Snapshot> = {|
  refs: {
    getSnapshot: MutableSourceGetSnapshotFn<Source, Snapshot>,
    setSnapshot: Snapshot => void,
  },
  source: MutableSource<any>,
  subscribe: MutableSourceSubscribeFn<Source, Snapshot>,
|};
function readFromUnsubcribedMutableSource<Source, Snapshot>(
  root: FiberRoot,
  source: MutableSource<Source>,
  getSnapshot: MutableSourceGetSnapshotFn<Source, Snapshot>,
): Snapshot {