Support Object.assign in propTypes definition

In my React App, I have components which pass receive properties but just pass them as is to their child component. The parent component sort of extends the child component properties, so I'm using Object.assign to avoid code duplication. Unfortunately, recat-docgen doesn't seem to handle propTypes values which are evaluated from a function.

For example, let's say I have a component named ParentComponent and a component named ChildComponent.

The render function of the ParentComponent looks like this:

render() {
  return (
    <ChildComponent childPropA="SomeValue" childPropB="AnotherValue" />
  );
}

When I render the ParentComponent my code looks like this:

<ParentComponent parentPropA="Value" childPropA="SomeValue" childPropB="AnotherValue" />

Therefore, I use Object.assign for setting ParentComponent.propTypes:

ParentComponent.propTypes = Object.assign({}, ChildComponent.propTypes, {
  parentPropA: React.PropTypes.string
});

No source file or test is named. Start by tracing how react-docgen evaluates component propTypes, then reproduce the Object.assign example from the issue. Done means inherited and locally defined propTypes are both extracted correctly, with a regression test covering the example.