You quickly get into something similar the ship of theseus (or Trigger's broom) argument. You write some code that must link to a GPL library to functon; that code is now GPL because it's a derivative work of the library.
You rewrite that library under an MIT license, so now your code can link to that and run. Is your original code still a derivative work?
Your original code is never a derivative work. You retain copyright to the code you wrote yourself, even if it's combined with GPL later. GPL even contains this interesting clause:
> You are not required to accept this License, since you have not signed it.
So to answer your question: no, unless you've copied bits of GPL library into your code (or similar that would be judged as a copyright violation).
There's also a crappy situation of Oracle vs Google that made APIs copyrightable, so now it's not entirely clear if your code + your rewrite of library is still yours if it uses an API of the GPL library.
> Your original code is never a derivative work[...]
> > You are not required to accept this License, since you have not signed it.
> So to answer your question: no, unless you've copied bits of GPL library into your code (or similar that would be judged as a copyright violation).
Actually that clears a lot up for me, and I'd have considered myself reasonably knowledgeable when it comes to copyright in general; I think I had a few conflicting ideas about what it means to be an original work. Thank you.
> The license is abundantly clear about this and answers all your questions.
The GPL is emphatically not clear about anything. It's a legal minefield precisely because no one has any idea what it means, and everyone has their own interpretation.
> It matters who is doing the rewriting and how they got the code in the first place.
I think one of the matters that confused me about it was the CLISP question. IIRC, CLISP linked to readline, but was released under a non-GPL license.
RMS contacted them, and asked them to relicense. They suggested either reimplementing a stub readline-library, or rewriting their line editing code against another lib instead. RMS insisted that they would still be a GPL-derivative, resulting in the current license situation.
I may be misremembering the recount of this, as this was way before my time.
RMS may have believed or wanted that, but it is my understanding (IANAL!) that the case law has been settled differently. If you are found in violation of the GPL due to a dependency you weren't aware was released under the GPL, you can fix that violation by rewriting your application to avoid the GPL dependency.
CLISP et al cannot be forced to distribute their code under the GPL. It's their code and their choice; contract law cannot compel someone who has never entered into the contract to do something against their will -- CLISP didn't knowingly distribute GPL code, so that distribution doesn't trigger acceptance of the GPL terms. They just have to make the situation right once they're made aware of the violation.
It's more nuanced. If you've included GPL code and modified or redistributed it, then you either have to comply with the GPL to have permission for that use, or you've potentially committed a copyright violation.
To comply with the GPL you only need to publish the one specific snapshot of source code you've combined and redistributed with GPL code, but you don't need to permanently relicense your project if it doesn't contain any code you don't have rights to use. The "tainted" version will be granted as GPLed forever, but other earlier or later versions that don't use any GPL code don't have to.
Or you can go the copyright way, and claim it wasn't a copyright violation (because it was a fair use, or non-copyrightable code) or settle the matter in whatever way the law lets you get away with.
That isn’t any different from what I said though? If someone points out you violated their copyright then you need to (1) fix the issue, and (2) pay appropriate damages. But for open source software the damages are nil, so fixing the violation is the only thing you need to do. And you can do that by either releasing the code as GPL, or removing the dependency. Either would be an acceptable remedy, in the eyes of the law.
Apparently the situation was that CLISP was distributed as `lisp.a` and `libreadline.a` (with source for Readline included) and the end-user linked them together. Haible offered to write a `libnoreadline.a` library, exporting Readline's function but not providing their functionality, but RMS insisted that the result would still be a derived work of Readline.
I’m not a lawyer, but my understanding is that the GPL requires you to make source available upon request to users of your software.
So I guess if someone asks you for the source code, you can require them to prove that they actually have a copy of the GPL version, and not the new one.
You rewrite that library under an MIT license, so now your code can link to that and run. Is your original code still a derivative work?