>Would using a GPL test suite with an MIT implementation make the whole GPL?
Absolutely not. MIT is a FSF-approved GPL-compatible license and you're free to use it with whatever GPL-licensed packages you wish[0].
However, if you package and distribute the Rust coreutils with the GPL test suite, then the users of the package are obliged to either use GPL, MIT, or some other FSF-approved OS license.
But it's simple enough to package the Rust coreutils without the test suite, which puts the Rust coreutils users under no GPL obligations.
GPL2 is all about the distributing of software, not how you use it.
I do agree that any use of a GPL package will make some folks using this package in commercial software nervous, given the very few (none?) actual court cases that have decided these issues.
> However, if you package and distribute the Rust coreutils with the GPL test suite, then the users of the package are obliged to either use GPL, MIT, or some other FSF-approved OS license.
I don't think this is right. The programs in question are the test suite, and there's can certainly distribute complete programs licensed under the GPL alongside with programs under even non-free licenses (otherwise Mac OS X couldn't ship).
Since the test suite doesn't link against the individual utilities, it won't affect them, license-wise.
It is well understood that the GPL doesn't cross executable boundaries (again, otherwise Mac OS X is in trouble).
IANAL, but AFAIK as long as the test suite is not distributed as part of the package, it does not affect the licensing of the package as a whole; whereas if the test suite is distributed with the package, then the whole package can only be distributed under GPL, but the original sources the package authors wrote need not be relicensed. So, the sources will be MIT, the test suite will be GPL, and the whole package, including both the test suite and the sources will have to be GPL.
Nor am I a lawyer, but I'll point out that the GPL is only based in copyright, so if there's no chance of copyright infringement then the GPL terms don't apply.
I believe the relevant part of the GPLv3, regarding "whole package" is:
> A compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program, in or on a volume of a storage or distribution medium, is called an “aggregate” if the compilation and its resulting copyright are not used to limit the access or legal rights of the compilation's users beyond what the individual works permit. Inclusion of a covered work in an aggregate does not cause this License to apply to the other parts of the aggregate.
From my understanding, no. The tools are not linked by code.
I'm free to write a proprietary coreutils test suite and charge $100 for it, so long as it doesn't hook directly into the source of the tools. If it's only interacting with the product, so be it.
