react/no-unused-prop-types false positives when passing props as an argument

[barakyosi]

In this scenario something is marked as unused although it is used.

class Hello extends Component {
  constructor (props) {
    super(props);
    this.doSomething(this.props);
  }
  doSomething(props) {
    if (props.something) {
      return true;
    }
  }
}
Hello.propTypes = {
  something: PropTypes.bool
}

It's similar to #855, but here the code is part of the class.

[ljharb]

This isn't really something we can statically analyze - in general, you shouldn't be passing around the entire props (or state) object. If you destructure props in the constructor, and pass something in explicitly, it should work fine.

[barakyosi]

I thought about detecting method calls with props argument, then look inside the method body and check usage.
Started to work on it but wasn't sure how to get the method body from the call expression.
Would be happy to know whether this check can be done (and if not what's the limitation)

[ljharb]

In your specific simple case, it could certainly be done - but, anyone from outside the file could call doSomething with an object that's not the props - so it's simply impossible to statically know it for all circumstances, only for a subset of usage patterns.

I don't think it's worth the complexity to try to target only some of the patterns, when the entire thing can be avoided by not having the antipattern of passing the props object around.

[barakyosi]

Sometimes passing all props makes it easier to follow. Especially when you need more than one prop and need to call it in different lifecycle methods.
I understand it's impossible to catch all scenarios. Would love to see a solution covering this one :)

[ljharb]

I'm sure it's subjective, but I would argue that in that case, you'd want to do this:

const { a, b, c } = props;
doSomething({ a, b, c });

You can still pass an object, but it's not the actual props object, it's an explicit object you created.

[barakyosi]

I agree your solution is better for this scenario, but if you need it in more than one place (in constructor & CWRP), or use many props inside doSomething - when adding a new prop you might forget to add it everywhere.

[ljharb]

I see that as a feature, not a bug, since if you do forget, your tests will fail :-)

[ljharb]

This seems answered - don't pass the props or state objects anywhere.