rosparam with inline yaml and argument substitution not working

[matawed]

problem

mon launch reports Substitution error: $(arg traffic_topic_name_generic ): Unknown arg

input

for the following launch file:

<launch>
    <!--****************************************
    **********   Program Parameters   **********
    *****************************************-->

    <arg name="traffic_topic_name_generic" default="example_name"/>


    <!--*********************************
    **********   Launch Node   **********
    **********************************-->
        <node pkg="package" type="type" name="name" output="screen" >
            <rosparam param="topic_names" subst_value="true" command="load">
                traffic_topic_name_generic:        $(arg traffic_topic_name_generic       )
            </rosparam>
        </node>
</launch>

workaround

It seems that the trailing whitespaces after the arg name cause the problem, since the following line works
traffic_topic_name_generic: $(arg traffic_topic_name_generic)

rosmon version

2.0.2 ubuntu 18.04. ros melodic

[xqms]

Thanks for the report, I'll look into it. I guess this is one of the cases were roslaunch is more lenient than the spec, so we'll have to adapt.