Even when setState returns null, it calls cDU lifecycle.

[Ailrun]

Describe the bug
In React, if setState returns null, cDU is not called and so following does not make infinite loop even after cDU is called. (You can check it on this codesandbox by typing text on the input. It prints only one console log at a time.)

export class TestComponent extends Component {
  constructor(props) {
    super(props);

    this.state = {};
  }

  componentDidUpdate() {
    this.setState(() => {
      return null;
    });
  }

  render() {
    return null;
  }
}

However, in enzyme, when I update component, i.e., invoking cDU with above component, will gives me infinite loop like

      at withSetStateAllowed (node_modules/enzyme/build/Utils.js:296:21)
      at ShallowWrapper.<anonymous> (node_modules/enzyme/build/ShallowWrapper.js:511:42)
      at ShallowWrapper.single (node_modules/enzyme/build/ShallowWrapper.js:1735:25)
      at ShallowWrapper.setState (node_modules/enzyme/build/ShallowWrapper.js:510:14)
      at TestComponent.ShallowWrapper.instance.setState (node_modules/enzyme/build/ShallowWrapper.js:190:35)
      at TestComponent.setState [as componentDidUpdate] (TestComponent.js:11:10)
      at node_modules/enzyme/build/ShallowWrapper.js:548:28
      at withSetStateAllowed (node_modules/enzyme/build/Utils.js:300:3)
      at ShallowWrapper.<anonymous> (node_modules/enzyme/build/ShallowWrapper.js:511:42)
      at ShallowWrapper.single (node_modules/enzyme/build/ShallowWrapper.js:1735:25)
      at ShallowWrapper.setState (node_modules/enzyme/build/ShallowWrapper.js:510:14)
      at TestComponent.ShallowWrapper.instance.setState (node_modules/enzyme/build/ShallowWrapper.js:190:35)
      at TestComponent.setState [as componentDidUpdate] (TestComponent.js:11:10)
      at node_modules/enzyme/build/ShallowWrapper.js:548:28
      // and repeat from line 1 to line 7

To Reproduce

1. git clone https://github.com/Ailrun/enzyme-issue1783
2. npm i
3. npm test

Expected behavior
Does not give infinite loop.

Desktop (please complete the following information):

• OS: Manjaro
• Browser: is not used
• Version: >=3.4.2, specifically, after Fix to call cDU when an instance calls setState #1742.

[ljharb]

I had no idea the return value of setState mattered at all. cc @koba04

Thanks, I’ll get a fix for this in soon.

[ljharb]

@Ailrun in that code sandbox, when i type a single letter, i get a single console log - but i get the same even if i comment out the return null line inside the setState callback. However, when I add return {} or return false, it infinitely loops - indicating that this is the correct behavior - except for null/undefined.

Thanks for the report.

[Ailrun]

@ljharb yes, it also ignores undefined too. I missed that part. Thank you.

[koba04]

Thanks to open the issue! I’ll working on this.

[ljharb]

@koba04 i'm about to restructure all the lifecycle method tests, so you may want to hold off for an hour or so :-)

[Ailrun]

@ljharb That sounds great! I cannot wait to use fixed lifecycles 😃

[ljharb]

@koba04 k, go for it :-D

[koba04]

I've created a PR to fix this. #1785