react/no-unused-state triggered when optional chaining is used

[gustavolaux]

eslint: 6.5.1
eslint-plugin-react: 7.16.0
babel-eslint: 10.0.3

in constructor:

this.state = {
  downloading: false,
}

but when this.state?.downloading is used i got this message:

[ljharb]

Presumably you're using babel-eslint since optional chaining just got stage 4 within the last 10 hours; it seems reasonable to modify all the rules that check for dotted and bracketed things to also check for optionally dotted and bracketed things.

[gustavolaux]

edited with babel-eslint version

[JoshuaKGoldberg]

Sorry to nitpick, but is this an enhancement or a bug?

[ljharb]

Actually I'm not sure it's either.

this.state?.downloading doesn't make any sense to me - when would this.state be nullish?

[JoshuaKGoldberg]

State is null by default, so this is something you need to do if you don't give it an initial value.

https://codesandbox.io/s/react-state-null-initially-ui5rp:

class App extends React.Component {
  render() {
    return (
      <div>{JSON.stringify(this.state)}</div>
    );
  }
}

[ljharb]

well sure, but you're always supposed to give it an initial value - does this.setState even work if you don't?

[JoshuaKGoldberg]

Yup, it works! React doesn't give any warning or indication, so I'd assume there are many (like me) who relied on the behavior.

[ljharb]

Oof, that sounds awful :-/ hopefully #2588 will resolve this, either way.