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 se nombra ningún archivo fuente ni ninguna prueba. Empieza por seguir cómo react-docgen evalúa los propTypes de los componentes y, después, reproduce el ejemplo de Object.assign del issue. La tarea estará terminada cuando se extraigan correctamente tanto los propTypes heredados como los definidos localmente, con una prueba de regresión que cubra el ejemplo.