License Precision: GPLv3 only or extended?

[Sigmanificient]

Hi, I am currently trying to ship Ragnar into the nixpkgs.

My proposition for a derivation as been reviewed, and within the changes requested lies a question about the license. Nix distinguishes between gpl "only" and "plus", and we need to know in which this project is.

The ambiguous gpl3 attribute is sorta-outdated, we prefer clarifying if it's gpl3Only (without the "or (at your option) any later version" bit) or gpl3Plus (with it).

The license text expects the developer to include the GPL notice at the start of their code files. If the aforementioned line is included in these, then the license says that code may be "upgraded" to any later GPL version.