Following the discussion we had this morning about the question :"Can a company take the rights from a contribution even if the project is under GPL ?", I would like to share the example that led me to ask this question :
https://github.com/tobspr-games/shapez.io/blob/master/CONTRIBUTING.md
Point 4 states : "Grant of Copyright License Subject to the terms and conditions of this Agreement, You hereby grant to the Company and to recipients of software distributed by the Company a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Your Contributions and such derivative works. You agree that your changes/additions are incorporated into the source code under a GPL-3 license. You agree that the Company is free to use its code without a GPL-3 license as closed source in any context, including for commercial purposes, without any license whatsoever"
If I'm not mistaken, this answers the question and is a great illustration of this morning's discussion.