Missing support for Flow Unions

react-docgen doesn't recognize the props if it's an union type:

type BaseProps = {|
  label: string,
|};

type LinkButtonProps = {|
  ...BaseProps,
  href: string,
  target?: string,
  rel?: string,
|};

type ButtonProps = {|
  ...BaseProps,
  type?: 'button' | 'submit',
|};

type Props = ButtonProps | LinkButtonProps;

class MyButton extends React.Component<Props> {
  render() {
     // conditionally render `<a>` or `<button>` based on props...
  }
}

I don't want users to pass props that are specific to <a> at the same time as some props that are specific to <button> - I know this kind of pattern of having a single component render to <a> or <button> is "weird", but some of our legacy components use it...

For now I need to define a single type that includes all the props and mark them all as optional - which is "fine", I guess..

More info about unions here: https://flow.org/en/docs/types/unions/

tested on v3.0.0-beta10

Reproduce the example from the issue using react-docgen v3.0.0-beta10 and compare the result with the expected props for the union. Read the linked Flow unions documentation and trace the parser entry point that handles component props. Done means union members are recognized without requiring users to flatten all props into one optional type.