forbid-foreign-prop-types should allow another component's propTypes in a propTypes definition

[iansu]

Currently this results in a warning but shouldn't:

Button.propTypes = {
  ...Touchable.propTypes,
  color: PropTypes.string
}

The error message could also be improved to explain why using another component's propTypes is bad. For example: "Using propTypes from another component is not safe because they may be removed in production builds".

Comments via @gaearon on this issue: facebook/create-react-app#3818

[ljharb]

I think that by default, it definitely should warn on it; however, I'd be open to adding an option that explicitly allowed this case.

[iansu]

Something like allowPropTypesInPropTypes? Or is that too confusing?

[iansu]

allowPropTypesComposition?

Also, how do you feel about softening the error message a bit?

[ljharb]

I wouldn't call it "softening"; just making it more accurate :-) but yes, I'm also open to that.

For an option name, allowInPropTypes? (since it's already a subset of "foreign propTypes")

[iansu]

Sounds good to me. I'll work on implementing this change.