Feature request

Feature description

Follow up of #730 (see #730 (comment)). Currently, the user don't have a way of ignoring a parameter override.

My suggestion is to change:

  RCLCPP_PUBLIC
  const rclcpp::ParameterValue &
  declare_parameter(
    const std::string & name,
    const rclcpp::ParameterValue & default_value = rclcpp::ParameterValue(),
    const rcl_interfaces::msg::ParameterDescriptor & parameter_descriptor =
    rcl_interfaces::msg::ParameterDescriptor());

to

  RCLCPP_PUBLIC
  const rclcpp::ParameterValue &
  declare_parameter(
    const std::string & name,
    const rclcpp::ParameterValue & default_value = rclcpp::ParameterValue(),
    const rcl_interfaces::msg::ParameterDescriptor & parameter_descriptor =
    rcl_interfaces::msg::ParameterDescriptor()
    bool ignore_override = false,
  );

and maybe, also add:

  RCLCPP_PUBLIC
  const rclcpp::ParameterValue &
  declare_parameter(
    const std::string & name,
    const rclcpp::ParameterValue & default_value = rclcpp::ParameterValue(),
    bool ignore_override = false,
  );

When undeclared parameters are allowed and automatically_declare_parameter_overrides is false, the first set_parameter call does not actually set the parameter but it takes the override value (see the second example here).

I don't see much usage of that feature, and I think it's a little confusing. I suggest always ignoring the parameter override in that case. That last change would be an api break, but of something with not much use cases. I don't see much value on adding a ignore_override argument to set_parameter method.

Note: Maybe, we could also add a node option for ignoring all the overrides. But I don't see much usage of that.

Implementation considerations

Should be fairly easy to implement. An equivalent would be needed in rclpy.