Hello,

You are right, we broke API compatibility between Gazebo 1.2 and Gazebo 1.3
without a proper tick-tock. Version 1.2 of Gazebo marked when Gazebo first
started to adopt the tick-tock model, and we obviously missed a function.
We have since improved our efforts, and there is a person looking into
maintaining API and ABI compatibility within Gazebo.

Thank you for your report and concern. We'll do our best to prevent future
occurrences.

-nate


On Thu, Jan 31, 2013 at 8:44 AM, Jack O'Quin <jack.oquin@gmail.com> wrote:

> I remember hearing that Groovy released with gazebo 1.2, but would be
> "upgrading" to 1.3 later on. I presumed that those two versions must be
> compatible, so I didn't think much about it.
>
> Now, it appears I was wrong, those versions are *not* compatible, after
> all. Some of the code we are using for a class at the University of Texas
> broke recently:
>
> math::Pose pose = this->parent->GetState().GetPose();
>
>
> Becomes:
>
> math::Pose pose = this->parent->GetWorldPose();
>
>
> That seems trivial on an individual basis, but it is causing trouble for
> our students who are trying to complete a class assignment today. Some
> installed ROS Groovy on their personal laptops. Others use departmental
> machines on which Groovy was installed at the beginning of the semester.
>
> Those using their own machines broke when recent
> ros-groovy-simulator-gazebo updates were applied. Computer Science
> department policy is not to apply non-security package updates in the
> middle of the semester, so those machines continue working correctly.
>
> This kind of change breaks the most basic concept of a ROS distribution:
>
> Much like Linux distributions, they make it much easier for developers to
> target a consistent set of libraries to develop and test on. Also, we are
> providing patches for distributions so that developers are not forced to
> switch to bleeding edge, unstable code just to incorporate important bug
> fixes.[1]
>
> [1] http://www.ros.org/wiki/Distributions#What_is_a_Distribution.3F
>
> Package maintainers are supposed to provide *binary* (ABI) as well as
> *source* (API) compatibility after a distribution is released. Those things
> may only change *before* the next release becomes final. After that, only
> bug fixes should be made.
>
> Furthermore, API changes between releases should provide at least one
> tick-tock release cycle, in which both the new and the (deprecated) old
> versions are provided.
>
> Gazebo is an excellent simulator, heavily used by many projects.
> Therefore, it needs to be especially sensitive to these stability issues.
> --
>  joq
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