Deduplication of warning messages in nested updates (#11081)

[imanushree]

@gaearon I have added flags for preventing duplication of both the warning messages so they print only once now.
But I noticed that the error related to 'Maximum update depth exceeded .... ' was going in infinite loop. Not sure if its an issue or I am missing something.

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[gaearon]

Thanks for the PR!

But I noticed that the error related to 'Maximum update depth exceeded .... ' was going in infinite loop.

Can you give me more details about this? How was this problem manifesting itself?

[imanushree]

I wrote this component to recreate the warnings:

 class App extends Component {
  constructor() {
    super();
    this.state = {
      value: null,
    };
  }

  render() {
    this.setState({
      value: 'test',
    });

    return <div />;
  }
}

And in the process found that this error came up:

'Uncaught Error: Maximum update depth exceeded. This can happen when a component repeatedly
calls setState inside componentWillUpdate or componentDidUpdate. React limits the number of
nested updates to prevent infinite loops.'

But the execution did not stop. It was going in an infinite loop and printing 2 variants of the same error one after another. I tested it in older versions of react and this problem is not present there. Please let me know if you want me to file an issue for this @gaearon .

Screenshot for your reference:

[imanushree]

I have created issue #11136 for this. Please take a look.

[gaearon]

Do you think you could add a separate test that verifies the warning is deduplicated? We typically do this by writing some test causing it to fire twice, and then asserting there has only been one warning call.

[gaearon]

This looks good to me. The test isn't super important tbh, as we don't test deduplication everywhere, and the code is pretty trivial.

[gaearon]

Thanks!

[imanushree]

@gaearon Thanks a lot Dan for merging my first PR to react ! :)