Copyleft-next and the kernel

> But what happens if there's a bug in the code you copied, and your patch for the bug happens to be the same as the way the original project fixed it and that code is still under copyleft? Your code is now a duplicate of copylefted code, and it doesn't matter legally if you arrived at the solution independently.

If you can convince a judge that your solution really was independent, and you didn't look at their solution, then it's unlikely to be copyright infringement under US law, because copyright infringement only happens when you do one of the things listed in 17 USC 106[1] without permission. "I came up with it independently" is not any one of those things. Of course, good luck proving that unless you're doing some kind of clean-room reimplementation. For larger and more complicated changes, you might be able to use intermediate Git commits as evidence of originality, so hopefully you're not one of those git squash people.

OTOH given that you really did come up with it independently, you may be able to argue that the similarity between your code and theirs is purely functional, and not subject to copyright protection in the first place.[2] This is especially likely to be the case for simple one-line bug fixes, where there's only one or two reasonable ways to fix it (e.g. "this loop is off by one, so switch the <= to <, or add/subtract one somewhere"). You might also raise a fair use, de minimis, or merger/scènes à faire defense, depending on the circumstances.

[1]: https://www.law.cornell.edu/uscode/text/17/106
[2]: See 17 USC 102(b): https://www.law.cornell.edu/uscode/text/17/102