> but if there's a python GPL project, and it's tests (spec) were used to rewrite specs in rust, and then an implementation in rust, can the second project be legally MIT, or any other?

Isn't that what https://github.com/uutils/coreutils is? GNU coreutils spec and test suite, used to produce a rust MIT implementation. (Granted, by humans AFAIK)

Its very important to understand the "how" it was done. The GPL hands the "compile" step, and the result is still GPL. The clean Room process uses 2 teams, separated by a specification. So you would have to

1. Generate specification on what the system does. 2. Pass to another "clean" system 3. Second clean system implements based just on the specification, without any information on the original.

That 3rd step is the hardest, especially for well known projects.

Treating an AI-assisted rewrite as a legal bypass for the GPL is wishful thinking. A defensible path is a documented clean-room reimplementation where a team that never saw the GPL source writes independent specs and tests, and a separate team implements from those specs using black-box characterization and differential testing while you document the chain of custody.

AI muddies the water because large models trained on public repos can reproduce GPL snippets verbatim, so prompting with tests that mirror the original risks contamination and a court could find substantial similarity. To reduce risk use black-box fuzzing and property-based tools, have humans review and scrub model outputs, run similarity scans, and budget for legal review before calling anything MIT.

No, GPL still holds even if you transform the source code from one language to another language.