code: def _target_classes(self, target):
      
      target_classes = set()
      contents = ClasspathUtil.classpath_contents((target,), self.runtime_classpath)
      for f in contents:
        classname = ClasspathUtil.classname_for_rel_classfile(f)
        if classname:
          target_classes.add(classname)
      return target_classes
docs: Set of target's provided classes.
  
      Call at the target level is to memoize efficiently.