In what sense? It is completely in the spirit of the GPL to reimplement a GPL tool from scratch with the same behavior and a different license. After all, that's how the free Unixes came about (though admittedly those were BSD licensed typically).
Kinda? Historically there were indeed concerns about reimplementation and copyright. One of the ways that the GNU Project tried to fight claims was to reimplement the tools using dynamically-allocated memory (instead of Unix's traditional fixed-size buffers) to make sure the implementation was sufficiently different. Other ways were making the implementation Posixly correct, adding internationalization or trying to pick different approaches (like using more modern algorithms for sorting). The GNU tools were better, not just direct ports, and that's why it was common to install them in systems like Solaris or HP-UX.
> Kinda? Historically there were indeed concerns about reimplementation and copyright.
Free software projects should welcome multiple implementations and interoperability, because these are the mother's milk of free software. It's frankly incoherent, given values of free software, that a reimplementation of, for example, Unix coreutils (GNU) would find fault with a reimplementation of itself (uutils).
Notwithstanding how philosophically incoherent it is, a desire, now that Linux and free software have some market power, to be a bully back, to grasp for monopoly power, to play AT&T, is really distasteful. What's exciting about free software is not the artifact, Linux or coreutils or sudo, but that anyone can create new and interesting alternatives. That users get to make choices about which implementation to use. The existence of FreeBSD does not make Linux worse. It makes it better! The "solution" to an MIT licensed coreutils is a GNU licensed fork which is 10x better. Instead, we get complaints which amount to a kind of free software entitlement, an endless pissing and moaning about how other people won't do new things your way.
This is a major problem in the way that most normies view the GNU and the GPL. In the past, I may not have chosen the GPL for my own projects, but I'd be pleased to contribute to a GPL project. Now, I'd have a hard contributing to a GPL project, because of just how toxic this attitude (no other license matters but ours) is.
The fact that it is free software shouldn't make things different since it's a matter of copyright law. It's fine to copy the interface - the implementation not really. There would certainly be NO problem if a close reimplementation was under the GNU GPL (as a derivive work). But a close reimplementation can't have a different license.
This was a discussion of the philosophical/meta/attitudinal issues, and why this is kinda a bizarre attitude for a free software project to hold.
Legally -- implicit in your comment are unstated assumptions about what is copied from the implementation. Suffice to say -- I disagree that a so-called "clean room" implementation is always required re: software published on the internet, or that the act of simply reading GPL code taints one forever, re: that code. The reason why is the reason why reading a book does not taint one forever and prevent one from writing one's own book -- "You should have used a while loop instead of a for loop here, now you're going to copyright prison." See, and pay close attention to the "Merger Doctrine": https://en.wikipedia.org/wiki/Idea–expression_distinction
It's my view that copyright is a rather weak IP protection, and GPL-type advocates have misconstrued the law of copyright for years, especially "derivative works". Mostly because they've been misinformed about the law by mendacious FOSS leadership cough like the FSF and SFC.
Now I'd agree with you, if there is something especially clever/creative about the GNU implementation that the reimplementation copies, that might be an issue, but again, even then, it seems especially rich for a reimplementation to find fault with another reimplementation.
a reimplementation that copies the interface has no need to copy the license. GPL people just get scared because they know their license can't prevent people from rewriting their own software (of course, such an idea is ridiculous).
the GPL is not a perfect license, there is no such thing.
Arguably writing in Rust will force a similar magnitude difference to those examples. For example, you'll probably replace that modern sorting algorithm with a call to .sort
I'm really not certain this is enough to be a copyright problem.
For instance, GNU and POSIX both publish their specs for the coreutils. If a coder were to take a look at the actual GNU code (which BTW is published for everyone to see), copyright law has a well trodden distinction between the idea and the expression -- that is, ideas are not copyrightable. If the "idea" simply amounts to what would be a more a detailed specification, I'm not sure there is a problem, like ... GNU uses this kernel facility for X. The problem would be vast amounts of "expression", especially "creative expression", directly copied and reimplemented in Rust. If the code is meat and potatoes, not 10xer galaxy brain fare ("I wrote a custom allocator which is suspiciously like the custom allocator implemented by GNU"), there shouldn't be an issue.
Think about what copyright to a play, or a novel, or a screenplay is. Now imagine a comment in the text/source: "This is how Toni Morrison did her characterizations in Beloved". This obviously isn't a copyright violation, unless you're copying the actual expression or a translation of the actual expression found in Beloved.
