I am not sure whether it is still the case, but the Scala compiler used to have a dependency on Swing. The reason was that one of the potent -Y flags gave you a

I am not sure whether it is still the case, but the Scala compiler used to have a dependency on Swing. The reason was that one of the potent -Y flags gave you access to an AST browser after the phase of your choice. Very convenient tool for compiler plugin developers, but a questionable dependency for most. (Edit: seems to have been taken away at least as of 2.10)