> Surely the person doing so would be responsible for doing so, but are they doing anything wrong?
You're perfectly at liberty to relicense public domain code if you wish.
The only thing you can't do is enforce the new license against people who obtain the code independently - either from the same source you did, or from a different source that doesn't carry your license.
This is correct, and it's not limited to code. I can take the story of Cinderella, create something new out of it, copyright my new work, but Cinderella remains public domain for someone else to do something with.
If I use public domain code in a project under a license, the whole work remains under the license, but not the public domain code.
I'm not sure what the hullabaloo is about.
If someone else uses your exact same prompt to generate the exact same code, can you claim copyright infringement against them? If the output is possible to copyright, then you could claim their prompt is infringement (just like if it reproduced Harry Potter). If it isn’t copyrightable, then the kernel would not have legal standing to enforce the GPL on those lines of code against any future AI reproduction of them. The developers might need to show that the code is licensed under GPL and only GPL, otherwise there is the possibility the same original contributor (eg the AI) did permit the copy. The GPL is an imposed restriction on what the kernel can legally do with any code contributions. That seems legally complicated for some projects—probably not the kernel with the large amount of pre-AI code, but maybe it spells trouble for smaller newer projects if they want to sue over infringement. IANAL.
> If someone else uses your exact same prompt to generate the exact same code, can you claim copyright infringement against them?
No, because they've independently obtained it from the same source that you did, so their copy is "upstream" of your imposing of a new license.
Realistically, adding a license to public domain work is only really meaningful when you've used it as a starting point for something else, and want to apply your license to the derivative work.
Copyright infringement is triggered by the act of copying, not by having the same bytes.
Be careful here - you cannot copyright a story, only the specific tangible form of the story.
Which is why I used precise language: "copyright my new *work*."