This is a follow-up question for: Multiple Ruby modules under one directory

What happens if these extensions include each other? For example, you have the following structure:

ext/foo
ext/bar

In ext/bar/bar.h, you have a

#include "foo.h"

foo.h and foo.cpp compile to form foo.o, to make life a little more complicated.

Finally, it is necessary that foo and bar be separate extensions.

How is this managed? I can't figure out how to add ../foo to the search path for bar.h, primarily. Symbolic links seem hack-ish.