fix (howto-launch): namespace on IncludeLaunchDescription

[krsche]

Following the documentation for including another launch file under a specific namespace I encountered an error.
Code:

pChannel = "vcan0"

ld.add_entity(
        GroupAction(
            actions=[
                PushRosNamespace(LaunchConfiguration(pChannel)), # < -- HERE IS THE ERROR! It has to be: PushRosNamespace(pChannel)
                IncludeLaunchDescription(
                    PythonLaunchDescriptionSource(
                        os.path.join(get_package_share_directory('ros2_socketcan'), 'launch/socket_can_receiver.launch.py')),
                    launch_arguments={
                        'interface': pChannel,
                        'interval_sec': '0.001'
                    }.items(),
                ),
            ]
        ),
    )

Error when launching:

[ERROR] [launch]: Caught exception in launch (see debug for traceback): launch configuration 'vcan0' does not exist

Resolution:
Looking at other code I noticed that people are using it differently instaed and the implementation of PushRosNamespace suggests to me that this is they way to go.

[kscottz]

This looks fine to me, but I want a second opinion. @audrow can you confirm?

Sorry, jet lag, more review coming soon.

[audrow]

Thanks for the PR @krsche. I think this should be retargeted to rolling and then backported to humble, since the error is also in rolling. Would you mind rebasing this commit on rolling?

[sumedhreddy90]

Reviewing LaunchConfiguration() and its interaction with PushRosNamespace

[sumedhreddy90]

Possible Solution:
setting the default_value of the DeclareLaunchArgument to the LaunchConfiguration value according to following modification:
namespace = LaunchConfiguration('namespace')

... Other code goes here....

DeclareLaunchArgument(
'namespace', default_value=namespace,
description='Top-level namespace'),
2. Adding PushRosNamespace(namespace=namespace) to the LaunchDescription in example.launch.py

[krsche]

I'm not sure what you mean. For me passing a string directly to PushRosNamespace works, can you elaborate what you're suggesting?

[krsche]

@audrow changed the target to rolling :) How would the backporting work? Manually by opening other PRs targeting those branches after this PR has been merged?

[clalancette]

@audrow changed the target to rolling :) How would the backporting work? Manually by opening other PRs targeting those branches after this PR has been merged?

We have a bot for it, so not to worry.

[audrow]

Thanks for the PR @krsche!