*  @param env               The environment current at the reference.
     *  @param classExpected     true if only a class is expected here.
     *  @param interfaceExpected true if only an interface is expected here.
     */
    Type attribBase(JCTree tree,
                    Env<AttrContext> env,
                    boolean classExpected,
                    boolean interfaceExpected,
                    boolean checkExtensible) {
        Type t = attribType(tree, env);
        return checkBase(t, tree, env, classExpected, interfaceExpected, checkExtensible);
    }