Linking this partly because I just realized every snippet on stackoverflow is effectively gpl

It requires hyperlinking each of stackoverflow, the question page, the authors, AND those links are not to be nofollow

https://stackoverflow.blog/2009/06/25/attribution-required/

Also: ""Stack Exchange Inc; user contributions licensed under cc by-sa 4.0 with attribution required.""

cc by-sa 4.0 is viral/copyleft, and gpl compatible, see:

https://wiki.creativecommons.org/wiki/ShareAlike_compatibili...