Groovy + Java = disaster?

I’m trying to use Groovy now. It’s a maven project with sub modules where each of them is Java and Groovy mixed. I have groovy eclipse plugin for kepler installed.

The Groovy feature is not working. It’s fine, I don’t care. The problem is eclipse’s Java features. I can’t use Call/Type hierarchy, auto-suggestion, and my folders are not treated as sources. Changing the facet to Java will only break Groovy compilation. So, any idea?

Note: you’ll be questioning why it must be like this. Look how I bold above thing showing how desperate I am, and how disastrous it is ;D Short answer: I inherit someone’s project.