Controller requiring robot_description parameter does not load anymore after switch to loading robot_description from topic

[firesurfer]

Describe the bug

Please see the related issue in the cartesian controllers repository: fzi-forschungszentrum-informatik/cartesian_controllers#179

I recently (tried) to switch from passing the robot_description as a parameter to loading it from the corresponding topic.
The cartesian controllers apparently depend on obtaining the robot_description from the respective parameter.

This issue is rather a question than a pure bug report: What is the intended way of accessing the robot description inside a controller?

a) Via the robot_description parameter
b) Load it yourself from the topic
c) A different way (e.g. ros2control provides the URDF ready to use to the controller?)

To Reproduce

1. Configure ros2control to load the robot_description from the topic
2. Try to load any of the cartesian controllers

Environment (please complete the following information):

• I am currently using the fixed branch from @saikishor https://github.com/saikishor/ros2_control/tree/fix/iron/missing/resources_lock

[christophfroehlich]

The URDF is already a member of the base class:

ros2_control/controller_interface/include/controller_interface/controller_interface_base.hpp

Line 253 in 20e01d8

std::string urdf_ = "";

[firesurfer]

Ah great to know. Do you also plan on backporting this to iron/humble ?

[christophfroehlich]

No, I don't think so because #1088 would break API (init is not a method used by users, but still at least breaks ABI for controllers.)

We will stop backporting such changes, and motivate users to build the latest rolling version for their distros from source.

[saikishor]

I agree with @christophfroehlich backporting it will break API and ABI. It's recommended from now on to use the rolling version to use the main features