GPL copyleft with regards to this library about catkin_virtualenv

[androiddrew]

So, I talked to a build expert from a company that basically manages it's own distro. She had directed me to https://www.gnu.org/licenses/gpl-faq.en.html which not so conveniently spells out a lot of "what you can and cannot do" in various scenarios regarding the GPL. I summarized her take on it back in the original ROS answers thread you referenced.

You can use catkin_virtualenv though without importing it into your python code. It is a build dependency specified in your package.xml file, no different than using debhelper or some other GPL build dependency tool. Even if it is modifying your code, that is it's purpose, and it's output is not immediately subject to the GPL, called out here . I did not do an exhaustive investigation into the tool's under the hood workings, but it is simply modifying shebang lines and copying code to a virtualenv. As far as I can tell it is not copying any code that was copyrighted using the GPL from itself into your package, which I think is where a lot of people start to get worried. If you do find that this is modifying the output with it's own GPL content LocusRobotics can specify that as an acceptation much like the GCC example I listed above.

[paulbovbel]

That's a fantastic explanation @androiddrew, thanks a lot for taking the type to put that together! I'm not a licensing expert but I came to similar conclusions (though with less certainty). catkin_virtualenv keeps the GPL license because of it's origins with https://github.com/spotify/dh-virtualenv, but as it's pretty squarely in the infrastructure/tooling category, I don't feel like it should interfere with anyone's internal code and commercial business, unless your business is ROS infrastructure :)

[androiddrew]

@Doomerdinger I think you are referring to the misconception of the "virality" of licenses. If you create a derived work off of catkin_virtualenv yeah you are pretty much stuck with using GPL terms yourself. That is "did you modify the source code of catkin_virtualenv for your own purposes?" If so, then you are obligated to provide those changes to "the users" of your derived work under the same terms. It does not necessarily obligate you to make your changes public, but those users can't be limited by any of the protections the license grants them. So even if you have someone paying you for your GPL'd software they have the same rights as before like being able to freely download it, modify it etc.

Use of a GPL licensed dependency does not virally make anything it touches GPL'd software. The GNU Compiler is GPL, granted it does make an explicit exception for header files in its corpus that may be compiled into your binaries. Catkin virtualenv isn't being compiled into your code. It is creating a wrapper around a virtualenv it maintains. It is not modifying your work. If you distribute any part of catkin_virtualenv you have to provide the user with the same license and rights to modify that code (the wrapper in this case). Open up an Android phone and you can find a laundry list of licenses for different parts of what you "the user" received.

Of course, I'm not a lawyer, but also you have to ask yourself what is the likelihood that Locusrobotics is going to take you to court? Ultimately, these terms and licenses are all about dispute resolution. 🤷

Edit: Let me put it in other terms. The MIT license is compatible with GPL. That means you can use an MIT-licensed work, with a GPL-licensed work, and produce new work (which yeah probably GPL unless you actually get into the nitty-gritty of things like making sure your stuff runs in a different address space and all that). The point is "What are you distributing?" If it's code that runs without catkin_virtualenv I'm going to say you don't have anything to worry about. I can take aiorospy, make sure its 3 dependencies are in my system python and still use it even without catkin_virtualenv. Your work doesn't need to be GPL even if it's intended to be combined with other GPL code. Just make sure your license is GPL compatible and you're fine.

[Doomerdinger]

I was under the impression that the argument is made (correct or not I believe the jury is out on that one) that with python code since when you run a library you "include" the entire source and it is interpreted that it is technically within the project.
Of course it could be a different library with the same name and a replicated API, but I know that can be a gray area as well.

How you have described it is how I hoped it worked to begin with, but really digging around the topic made me less sure.

Essentially we have a ros melodic system where we need to make use of some python 3 stuff, and I think it'd be slick to use catkin_virtualenv for that. The package could run without it if the system satisfied all the dependencies on its own, but technically once we add it as a dependency to cmake and the launch process, and the installation process of our project, I'd imagine that changes things somewhat. 🤷‍♀️

I'll seek some legal council on this just to be sure. I'll leave this open if you have any further comments, but if you do not feel free to close it.