Suppose a developer receives software from XX with a license permitting unlimited modification and redistribution as well as full ownership of any original content. The only restriction being no selling/monetizing anything which packages XX's code.
So that other developers could build off of the functionality of XX’s code without packaging it and becoming limited in their commercial usage, this developer creates a wrapper for indirectly interfacing with XX's software and distributes it with a GNU GPLv3 license.
Downstream users now have GPL licensed software containing XX’s code. If they fork it, the GPL which comes with the software would indicate that they could sell their fork for a price. However, XX’s software license (while not requiring that the license itself it be transmitted with the software) still asserts that selling content containing their code is forbidden.
My understanding is that this is effectively an "inferred" dual license, since the developer of the interface cannot simply re-license XX’s code under the GPL which permits commercial usage.
Since the GPL allows commercial usage and XX’s code does not, and since the GPL forbids "further restrictions" not permitted by section 7’s a—f, I believe the two licenses are incompatible, and thus downstream conveyers of the software must choose one license or the other to adopt for their derivatives.
Is this correct?
If my understanding of dual licensing is correct; then if they choose to create and distribute a derivative containing XX’s code, they MUST adopt XX’s license and not the GPL. However, if they choose to create and distribute a derivative not containing XX’s code, they have the option of adopting either the GPL or XX’s license.
Have I erred in this conclusion?