skyfaller
commented
5 years ago Nevermind, after some cursory research, I think this would be an unmanageable headache for Wordpress themes unless Wordpress itself upgrades to GPLv3, because it appears both GPLv3 code and AGPLv3 code would be incompatible with GPLv2. You can upgrade the Wordpress license to GPLv3, but then you have to redistribute Wordpress yourself, or maybe get any end user who installs your theme to upgrade the Wordpress license, which seems too annoying. I'll quote from https://wordpress.stackexchange.com/questions/5/am-i-allowed-to-license-my-wordpress-theme-under-the-agpl
By licensing their work under GPLv2 (or later), which I will refer to in this email as GPLv2+, the copyright holders of Wordpress have explicitly permitted you to further distribute their work under any later version of the GPL. By upgrading you can further distribute their work under GPLv3, GPLv3+, GPLv4 (doesn't exist yet, but if it did you could choose it), GPLv4+, etc. This is spelled out in section 9 of GPLv2 and section 14 of GPLv3.
Once you've upgraded the work to GPLv3 (you update the license version number and include a copy of GPLv3, add your own copyright notices as needed, but otherwise keep the original copyright notices and license notices intact), two things will happen: First, the work becomes incompatible with GPLv2-only code; both GPLv2 and GPLv3 are strong copyleft licenses and they cannot both be satisfied at the same time. Second, and more important for you is that under section 13 of GPLv3, and section 13 of AGPLv3, you will now have a narrow compatibility with works licensed under AGPLv3. Which is to say that while you cannot re-license the work, as a whole, from GPLv3 to AGPLv3, you will be able to further distribute the combination of GPLv3 code (the upgraded Wordpress code) and AGPLv3 code (your additional code).
Yoni Rabkin, volunteer at the FSF GPL Compliance Lab
I spoke to Yoni some more in the FSF's IRC channel, and he said "generally speaking, when contributing to a project it is typically good to contribute back to the project with the same free software license the project uses", which seems like good advice.
I realize this may be low priority, but have you considered licensing your theme under AGPLv3 instead of GPLv2?
If you are concerned about distributing your theme with Wordpress's GPLv2 licensed code, it appears that since the GPLv2 allows you to use any later version of the license, and the GPLv3 is explicitly compatible with AGPLv3, you can upgrade GPLv2 to v3 and then distribute with AGPLv3 code. So I don't think there are any legal obstacles.
It seems to me that the AGPL is a better form of copyleft for code that is only served on a webpage, like a Wordpress theme, and never truly redistributed.