Clean room is sufficient, but not necessary to avoid the accusations of license violation.
a2mark has to demonstrate that v7 is "a work containing the v6 or a portion of it, either verbatim or with modifications and/or translated straightforwardly into another language", which is different from demanding a clean-room reimplementation.
Theoretically, the existence of a publicly available commit that is half v6 code and half v7 can be used to show that this part of v7 code has been infected by LGPL and must thus infect the rest of v7, but that's IMO going against the spirit of the [L]GPL.
Please don't use loaded terms like "infect". The license does not infect, it has provisions and requirements. If you want to interact with it, you either accept them or don't use the project. In this case, the author of v7 is trying to steal the copyrighted work of other authors by re-licensing it illegally.
Is their work present in v7?
Yes. The AI operator posted this as the prompt: https://github.com/chardet/chardet/commit/f51f523506a73f89f0...
which, minimally instructs it to directly examine the test suite: `4. High encoding accuracy on the chardet test suite`
So what? Is reading code the same as copying code or modifying existing code?
If you want to prove you did not make a derivative work, yes it helps if you never read the source code. Hence so call "clean room" implementations.
Why should I prove that? Let those who claim the violation prove that.
There is plenty of evidence already. The claim has been substantiated.
You can't just dismiss it then say the claimant has to provide proof.
Yes. Commits clearly show in progress where both LGPL and MIT code was working together. This clearly show they are a derivative work and MUST follow the original license.
Plus the argument put forth is that they can re-license the project. It's not a new one made from scratch.
Did they eventually remove/replace all the LGPL code?
So, if these commits were private and squashed together before 7.0 was published there would be no violation?
The commits being public or not does not change the fact the developement was made as a derivative work of the original version.
They would be concealing the violation.
Consider TCC relicensing. They identified the files touched by contributors that wanted to keep the GPL license and reimplemented them. No team A/team B clean room approach used. The same happened here, but at a different scale. All files now have a new author and this author is free to change the license of his work.