Add standalone executable for Servo server node

[schornakj]

Description

Previously the servo_server node was only available as a component node. This adds a new executable to run the servo_server as a standalone node.

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[tylerjw]

Looks really good and useful. Thank you. Only thing I'd add is an example launch file for it but it is so similar to the component node I'm not sure that's worth it. I hope this is helpful in debugging the issues you've seen with component nodes.

[tylerjw]

In the future I hope we can get away from this by declaring all the parameters in a better way with nicer validation. I'm working on that.

[AndyZe]

TBH I'm still fuzzy on the finer differences between component nodes and standalone nodes.

The PR looks good. I'll prob give it a thumbs up after testing.

[codecov]

Codecov Report

Merging #621 (eab5e3a) into main (09406c1) will not change coverage.
The diff coverage is n/a.

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##             main     #621   +/-   ##
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  Coverage   54.38%   54.38%           
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  Files         191      191           
  Lines       20100    20100           
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  Hits        10929    10929           
  Misses       9171     9171           

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[AndyZe]

@schornakj do you have a launch file to test with? My simple modification of moveit2_tutorials/docs/realtime_servo/launch/servo_teleop.launch.py did not work. I'm guessing the parameters were loaded in the wrong namespace.

servo_teleop.launch.py.txt

[schornakj]

@schornakj do you have a launch file to test with? My simple modification of moveit2_tutorials/docs/realtime_servo/launch/servo_teleop.launch.py did not work. I'm guessing the parameters were loaded in the wrong namespace.

servo_teleop.launch.py.txt

I'll add a standalone launch file for this equivalent to the one we provide for the Servo component node.

[henningkayser]

Looks good to me. In general, would it be bad practice to add a main function to source files of component nodes directly? Say, add it to servo_server.cpp below registering the component node, or alternatively add the RCLCPP_COMPONENTS_REGISTER_NODE macro to servo_server_node.cpp? Also, the source file naming is really confusing, we have servo.cpp (main servo class), servo_server.cpp (node implementation) and servo_server_node.cpp which is the now added main function to run ServoServer as node executable. Out of scope of this PR, but we should clear that up.

[AndyZe]

Agree that the naming is starting to be confusing.

[tylerjw]

Agree that the naming is starting to be confusing.

I created a PR because I feel the same way: #649

[AndyZe]

blocking merge until I can test it

[AndyZe]

@schornakj I updated the example launch file to:

• launch RViz
• include a commented example of launching Servo as a component, so that documentation is all in one place

I think the tutorial can now use this launch file rather than a completely separate one 👍

Let me know if that bugs you for some reason and we can revert the commits.