Since in the recent past more and more PRs have been discussed (and some of them merged) which do break ABI compatibility I would like to establish a rule (or a set of rules) which we follow in the future in order to avoid having the same discussion on every patch. The possible range goes from:

• most conservative: any patch which breaks ABI will only be considered for future ROS distros and will not be merged into already released ROS distros
• <anything in between>
• no restriction: patches which break ABI can be merged into the latest already released distro, probably even be considered for backporting into e.g. an LTS ROS distro.

What I certainly want to avoid is a rule like "it can be done but it depends on <some undefined or fuzzy criteria>". @ros/ros_comm-maintainers @ros/ros_team Please comment with your opinion on this and describe the criteria when a patch should be considered as specific / detailed as possible.