How to use

index

method

in

org.antlr.v4.runtime.CommonTokenStream

private Integer newlineOrEOF(List<Token> hidden){
  Optional<Token> newline = IntStream.range(0, hidden.size())
      .mapToObj(hidden::get)
      .filter(h -> h.getText().equals("\n") || h.getTokenIndex() == tokens.index() - 1)
      .findFirst();
  return newline.isPresent() ? hidden.indexOf(newline.get()) + 1 : null;
}