Adapt to '--ros-args ... [--]'-based ROS args extraction

[hidmic]

Precisely what the title says. Connected to ros2/rcl#477.

[hidmic]

So, I'm having second thoughts about 3256ee2 too. I did it for consistency with rclcpp behaviour but it makes the API somewhat asymmetric compared to arguments provided to rclpy.init().

[wjwwood]

Again, I don't feel strongly about it, I don't mind the feature as long as it's documented and consistent.

it makes the API somewhat asymmetric compared to arguments provided to rclpy.init().

I don't really think this is an issue (especially if documented). Personally I think of the arguments to rclpy.init() as "argv" which traditionally the command line arguments, even if it does not have to be the command line arguments, and I think of the arguments to the node as "arguments for this node" which implies to me that it is probably a subset of the full command line arguments anyways.

[ivanpauno]

What if someone does:

cli_args=['asd', '--ros-args', ...]

?

[hidmic]

Same as in rclcpp, 'asd' will become an unparsed non-ROS arg.

[hidmic]

Hmm, but that doesn't match the docstring.

[hidmic]

Here, looks like that docstring is outdated though.

[ivanpauno]

So in the case above, asd is a non-ROS argument, and in the following:

cli_args=['asd']

It's a ros argument, because --ros-args is magically prepended.

I prefer a consistent and explicit behavior, i.e.: always add explicitly --ros-args when needed.
But if I'm the only with this feeling, I don't mind if we left this as-is.

[ivanpauno]

The same comment applies in rclcpp:
https://github.com/ros2/rclcpp/blob/69773838e2b229c79676897d080455113f10bc9e/rclcpp/src/rclcpp/node_options.cpp#L107-L109

[wjwwood]

We sort of discuss this here: ros2/rclcpp#816 (comment)

I can see the point of both sides. I would be fine requiring the user to explicitly use --ros-args with the NodeOptions.arguments if you guys think that would be less surprising. I don't expect it to be used in this way very often, so I think it's fine if it's not quite as convenient as it could be with implicitly added --ros-args.

[hidmic]

Always adding --ros-args is the least surprising alternative, but it is somewhat verbose. I don't have a strong opinion as to which we should prioritize.