Currently, if you define `shouldComponentUpdate` on `React.PureComponent` nothing bad happens and it acts like `React.Component` https://jsfiddle.net/jekmdfva/

We should probably warn in dev since it defaults the point of `PureComponent`
'likely caused by a bug in React. Please file an issue.',
      );
    }
    const oldContext = instance.context;
    const newUnmaskedContext = getUnmaskedContext(workInProgress);
    const newContext = getMaskedContext(workInProgress, newUnmaskedContext);
    
    
    
    if (oldProps !== newProps || oldContext !== newContext) {
      if (typeof instance.componentWillReceiveProps === 'function') {
        if (__DEV__) {
          startPhaseTimer(workInProgress, 'componentWillReceiveProps');
        }
        instance.componentWillReceiveProps(newProps, newContext);
        if (__DEV__) {
          stopPhaseTimer();
        }
        if (instance.state !== workInProgress.memoizedState) {
          if (__DEV__) {
            warning(
              false,
              '%s.componentWillReceiveProps(): Assigning directly to ' +
                "this.state is deprecated (except inside a component's " +
                'constructor). Use setState instead.',
              getComponentName(workInProgress),
            );
          }
          updater.enqueueReplaceState(instance, instance.state, null);
        }