Original elisp algorithm. While using the original elisp source as a guideline might result in less idiomatic Rust code...
Seems to be a pretty direct translation (without reading the sources of both).
Now, if they took the original source and used it to implement a grammar then based the rust code off said grammar they might have a case -- which, I believe, is what a "clean room" implementation would do, preferably with two different people doing either task.
IMHO this is a clear copyright violation else you could just "reimplement" your way out of any license.
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Seems to be a pretty direct translation (without reading the sources of both).
Now, if they took the original source and used it to implement a grammar then based the rust code off said grammar they might have a case -- which, I believe, is what a "clean room" implementation would do, preferably with two different people doing either task.
IMHO this is a clear copyright violation else you could just "reimplement" your way out of any license.
AIUI clean room implementation isn't required, just good practice to avoid
- Accidentally copying copyrighted material (past what fair use allows)
- Expensive lawsuits where you have to actually argue that "no we didn't copy copyrighted elements"
We're talking about two open source projects here, the latter anyways doesn't really matter.