[Fix] no-unused-state: avoid a crash

[WillyLiaoWH]

Try to fix #3240 with the smallest change.

[ljharb]

Thanks; but first we'd need a test case that fails without the fix.

[WillyLiaoWH]

Unfortunately, I cannot reproduce it in the test environments. But the error still occurs in my working environment. Here is the sample code that failed in my working environment. The key point is that if I don't declare it in the arrow function form, it would be fine. It would be great if you could spend a few minutes checking the problem. You can just close the PR if you cannot find the root cause either. Thanks for your work again.

import React, { PureComponent } from 'react';

class TestNoUnusedState {
  constructor(props) {
    super(props);
    this.state = {
      id: null,
    };
  }

  static getDerivedStateFromProps = (props, state) => {
    if (state.id !== props.id) {
      return {
        id: props.id,
      };
    }

    return null;
  };

  render() {
    return <h1>{this.state.id}</h1>;
  }
}

export default TestNoUnusedState;

[ljharb]

Your test case reveals another problem, but it passes without your change.

[ljharb]

oops, it does fail in older node versions :-) i'll update this PR.

[codecov-commenter]

Codecov Report

Merging #3258 (4876d54) into master (b9b1bee) will increase coverage by 0.01%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #3258      +/-   ##
==========================================
+ Coverage   97.68%   97.69%   +0.01%     
==========================================
  Files         121      121              
  Lines        8584     8586       +2     
  Branches     3117     3118       +1     
==========================================
+ Hits         8385     8388       +3     
+ Misses        199      198       -1     

Impacted Files	Coverage Δ
lib/rules/no-unused-state.js	99.23% <66.66%> (+0.39%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b9b1bee...4876d54. Read the comment docs.

[WillyLiaoWH]

Thanks for the fix 🙏