private void addFunctionNamesCompletion() {
    extend(CompletionType.BASIC,
           psiElement().andOr(
             AFTER_OPERATOR_EXCEPT_IS,
             INSIDE_LIST,
             // NOTE: function calls can't be used as other functions arguments according to grammar
             AFTER_KEYWORD_IN_HISTORY_PREDICATE),
           new JqlFunctionCompletionProvider());
  }
private void addFunctionNamesCompletion()