Symbol symbol = tree.symbol(); assert symbol != null && symbol.isTerm(): show(tree); assert !symbol.isMethod(): show(tree);
    public boolean location(Tree tree) {        switch (tree) {        case Select(_, _):            Symbol symbol = tree.symbol();            assert symbol != null && symbol.isTerm(): show(tree);            assert !symbol.isMethod(): show(tree);            return selection(tree);        case Ident(_):            Symbol symbol = tree.symbol();            assert symbol != null && symbol.isTerm(): show(tree);            if (symbol.isModule()) return true;            assert vvars.contains(symbol): show(tree);            return true;        default:            throw Debug.abort("illegal case", tree);        }    }