On Mon, 30 May 2016 14:06:04 +1200, Peter Reutemann wrote:
For instance, imagine a GPL plugin-framework (eg image processing pipeline) which requires you only to implement an interface to make your plugin usable in the framework (eg FFT filter). Then just implementing (or "using") the interface would be considered "fair use" and commercial derivatives would no longer be considered derivative work.
I never thought they were. It has been a long-standing assumption among open-source developers that APIs are not copyrightable. Examples: 1) The Linux kernel developers never considered code using the userland Linux APIs to be “derivative works”. 2) The FSF has long resisted adding a plugin API to GCC, precisely because they were worried it would be used to evade the GPL on GCC itself.