[C++] Builder would ub when AppendValues called with empty vector

[mapleFU]

Describe the enhancement requested

When AppendValues called with empty vector, this would cause memcpy

  /// \brief Append a sequence of elements in one shot
  /// \param[in] values a contiguous C array of values
  /// \param[in] length the number of values to append
  /// \param[in] is_valid an std::vector<bool> indicating valid (1) or null
  /// (0). Equal in length to values
  /// \return Status
  Status AppendValues(const value_type* values, int64_t length,
                      const std::vector<bool>& is_valid) {
    ARROW_RETURN_NOT_OK(Reserve(length));
    data_builder_.UnsafeAppend(values, length);
    // length_ is update by these
    ArrayBuilder::UnsafeAppendToBitmap(is_valid);
    return Status::OK();
  }

  /// \brief Append a sequence of elements in one shot
  /// \param[in] values a std::vector of values
  /// \param[in] is_valid an std::vector<bool> indicating valid (1) or null
  /// (0). Equal in length to values
  /// \return Status
  Status AppendValues(const std::vector<value_type>& values,
                      const std::vector<bool>& is_valid) {
    return AppendValues(values.data(), static_cast<int64_t>(values.size()), is_valid);
  }

In this case, unsafe append directly memcpy, and when size == 0, it would be a undefined behavior

Component(s)

C++