Rule proposal: Check for unused propTypes

[EvHaus]

While refactoring code you may remove the use of some props but forget to remove them from the propTypes. It would nice if ESLint could alert you with:

`foo` propType is defined but not used.

Similar to the unused vars rule.

[FirstWhack]

+1 this seems necessary since we check for props missing a proptype definition we should also check for proptypes never being used

[ljharb]

All +1's should now be in the form of reactions on the first post - I'll clean up the ones here, and any future ones. Thanks for everyone's interest!

[EvHaus]

I'm going to take a stab at writing this rule. Will submit a PR.

[lo1tuma]

What should happen if the whole props object is passed to an external third party function? Or if you are using the spread operator to pass-through all props to a child component? I guess in such cases the rule should not warn.

[silvenon]

Yeah, unfortunately I think this rule is prone to false-positives.

[jamesdwilson]

Maybe we could just have it have options to issue warning or not if props object is passed to a third party function or using a spread operator? Instead of throwing the baby with the bathwater.

[EvHaus]

I've done a first pass at this here: #611 (Instructions on how to test and install are in the PR).

Still hunting down false positives, but early feedback would be highly appreciated.

[mattdell]

Any update on this? Is there something preventing this from being merged?

[CrazyAlvaro]

@EvNaverniouk Thank you for add this rule here, Evgueni. During our development here, we found that this rule checks propType used under this.props but not under nextProps. In some cases we only need to update specific props by using nextProps.foo. Would it be nice if we could check on both this.props and nextProps?