Fix to Flow Maximum Callstack exceeded error on recursive generic structs

[FermiDirak]

Resolves #427

Nested structs using generics currently cause a maximum callstack exceeded error. This PR resolves the issue by short-circuiting the recursion when the type resolves to a generic.

This approach has a shortcoming where the below example will resolve the prop prop as T instead of as string. But this is currently the same behavior seen when switching to typescript and should be fine since it's an an overall improvement to docgen erroring.

import * as React from "react";

type Identity<T> = T;

type Props<T> = {
  prop: Identity<T>;
}

export default function Test(props: Props<string>) {
  return <div />;
}

I'm happy to iterate on this PR, let me know if you need me to change anything.

[elicwhite]

We are running into a similar problem at Facebook on 5.1.0. I haven't gotten it down to a minimal repro yet, but our stack trace looks like this:

RangeError: Maximum call stack size exceeded
        at Object.hasOwnProperty (<anonymous>)

      at defFromValue (node_modules/ast-types/lib/types.js:339:24)
      at DefImpl.check (node_modules/ast-types/lib/types.js:362:24)
      at PredicateType.predicate (node_modules/ast-types/lib/types.js:351:109)
      at PredicateType.Object.<anonymous>.PredicateType.check (node_modules/ast-types/lib/types.js:122:27)
      at Object.handleGenericTypeAnnotation [as GenericTypeAnnotation] (node_modules/react-docgen/dist/utils/getFlowType.js:109:52)
      at getFlowTypeWithResolvedTypes (node_modules/react-docgen/dist/utils/getFlowType.js:296:33)
      at Object.handleGenericTypeAnnotation [as GenericTypeAnnotation] (node_modules/react-docgen/dist/utils/getFlowType.js:135:12)
      at getFlowTypeWithResolvedTypes (node_modules/react-docgen/dist/utils/getFlowType.js:296:33)
      at Object.handleGenericTypeAnnotation [as GenericTypeAnnotation] (node_modules/react-docgen/dist/utils/getFlowType.js:135:12)

Does this line up with the stack trace that this PR is fixing?

Edit:
Yep, my minimal repro got down to this with the same error.

type Props<T> = {
  segments: Array<T>,
};

export default class FBSegments<T> extends React.Component<Props<T>> {
  render(): React.Node {
    return null;
  }

  foo(props: Props<T>) {}
}

Interestingly, if I remove foo, it doesn't error. @FermiDirak, can you include a class example with a method like this in your test fixtures?

[FermiDirak]

@TheSavior I've added the minimal repo you've listed which confirms the fix works for class components as well.

https://github.com/reactjs/react-docgen/pull/428/files#diff-a415f878f867f9bdce185d67c4407d86R1520-R1579

[danez]

Thanks for the fix.