$(arg) is overwritten when including multiple launch files

[h-ohta]

Bug report ?

Required Info:

• Operating System:
  • Ubuntu20.04
• Installation type:
  • galactic binaries
• Version or commit hash:
  • up to date
• DDS implementation:
  • irrelevant
• Client library (if applicable):
  • irrelevant

Steps to reproduce issue

• Create three files

# outside.launch.xml

<launch>
    <include file="inside1.launch.xml"></include>
    <include file="inside2.launch.xml"></include>
</launch>

#include1.launch.xml

<launch>
    <arg name="test_arg" default="1"/>
    <log message="include1 has $(var test_arg)"/>
</launch>

#include2.launch.xml

<launch>
    <arg name="test_arg" default="2"/>
    <log message="include2 has $(var test_arg)"/>
</launch>

• Run outside.launch.xml

Expected behavior

$ ros2 launch outside.launch.xml 
[INFO] [launch]: All log files can be found below /home/hrkota/.ros/log/2022-06-16-14-28-00-475031-npc2103034-543336
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [launch.user]: include1 has 1
[INFO] [launch.user]: include2 has 2

Actual behavior

$ ros2 launch outside.launch.xml 
[INFO] [launch]: All log files can be found below /home/hrkota/.ros/log/2022-06-16-14-28-00-475031-npc2103034-543336
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [launch.user]: include1 has 1
[INFO] [launch.user]: include2 has 1

Additional information

Now, I can avoid this problem by using <group> tag.

# outside.launch.xml

<launch>
    <group>
        <include file="inside1.launch.xml"></include>
    </group>

    <group>
        <include file="inside2.launch.xml"></include>
    </group>
</launch>

# result

$ ros2 launch outside.launch.xml 
[INFO] [launch]: All log files can be found below /home/hrkota/.ros/log/2022-06-16-14-30-35-485185-npc2103034-543607
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [launch.user]: include1 has 1
[INFO] [launch.user]: include2 has 2

Is it bug or correct behavior?
I can't get some information about it.

---

Feature request

Feature description

Implementation considerations

[h-ohta]

@clalancette Could you confirm this? Thank you.

[hidmic]

@h-ohta include actions don't scope (almost no action does), only group actions do. #618 is somewhat related.

[h-ohta]

@hidmic Thank you for your response!
I understand that this issue is correct behavior and I have to use <group> to scope any actions.
Could you close If you don't have any problems?

[peci1]

This is really a hard hit when migrating from ROS 1. I know it is described in the migration guide, but for people who don't know ROS 2 well (yet), the formulation does not seem to be warning them enough:

Available in ROS 1, included content was scoped. In ROS 2, it’s not. Nest includes in group tags to scope them.

This basically means that migrating ROS 1 launch files into ROS 2 is <include> -> <group><include>. What about providing an <include scoped="1"> attribute or something similar that would ease that transition?

[christophebedard]

What about providing an <include scoped="1"> attribute or something similar that would ease that transition?

See #801 and #841