Feature request

This is a feature request to implement a declarative markup (XML, YAML, TOML, etc.) front-end for launch descriptions. Acceptance criteria is limited to TBD.

Feature description

• Optionally narrow down feature set for a first iteration.
• Draft a format standardization document in https://github.com/ros2/design.
• Gather feedback from potential users (i.e. community and customers).
• Implement parser, from markup based description into LaunchDescription instances.
• Update ros2launch CLI to also understand declarative launchfiles using the parser.

Implementation considerations

ros2launch

Consider refactoring to ease extension through integration of external parsers (using Python modules?).

launch_[markup_fmt]

Weigh different markup formats. Some tentative XML can be found in ros2/design#163. Some draft YAML can be found here.

With the current launch API being already quite declarative, a 1-on-1 mapping may be possible (though this is still a conjecture).