code: protected void enterTypevars(Type t) {
          if (t.getEnclosingType() != null && t.getEnclosingType().hasTag(CLASS))
              enterTypevars(t.getEnclosingType());
          for (List<Type> xs = t.getTypeArguments(); xs.nonEmpty(); xs = xs.tail)
              typevars.enter(xs.head.tsym);
      }
docs: Enter type variables of this classtype and all enclosing ones in
  `typevars'.