[roslaunch] --ros-args option fails in noetic

[xaver-k]

Short description

Running roslaunch with the option --ros-args under ROS noetic fails.

Expected behavior

Print the arguments of the launch file like under ROS melodic.
As an example, getting the arguments of roslaunch's own example launch-file via

docker run --rm -it ros:melodic-robot roslaunch roslaunch example.launch --ros-args

gives

Optional Arguments:
  commandline_true_arg (default "true"): undocumented

Acutual behavior

Running any of the below commands

docker run --rm -it ros:noetic-robot roslaunch roslaunch example.launch --ros-args
docker run --rm -it ros:noetic-robot roslaunch --ros-args roslaunch example.launch
docker run --rm -it ros:noetic-robot roslaunch /opt/ros/noetic/share/roslaunch/resources/example.launch --ros-args
docker run --rm -it ros:noetic-robot roslaunch --ros-args /opt/ros/noetic/share/roslaunch/resources/example.launch

Gives

Traceback (most recent call last):
  File "/opt/ros/noetic/lib/python3/dist-packages/roslaunch/__init__.py", line 275, in main
    import arg_dump as roslaunch_arg_dump
ModuleNotFoundError: No module named 'arg_dump'

Thoughts

I suspect that

ros_comm/tools/roslaunch/src/roslaunch/__init__.py

Line 277 in 7ee09ea

import arg_dump as roslaunch_arg_dump

should be

from . import arg_dump as roslaunch_arg_dump 

because of the switch to python 3.

[dirk-thomas]

Please create a pull request with the proposed change.