Does #including (non-trivial) Qt headers make your software a derivative work? IIRC there is a decent amount of actual code in some of the headers. Seems like a very grey area.
It does not, and with significantly complex header files (like the SIGNAL/SLOT macros Qt includes) this can seem like a grey area, but the LGPL specifically splits code into object & specification code, if your code directly references and links against publicly defined specification code you're in the clear... if you are doing this with knowledge of how specific object code works and manipulating that object code using your own code (i.e. intentionally overwriting a stake frame) I think that does become more of a grey area, but the intent of the license is very straightforward about allowing non-contagious use of interface specifications, that is what specifically makes it LGPL instead of GPL (the latter lacks that distinction and does not allow the use you're asking about among some other uses).
This is of course complicated by SaaS and all that is covered in more detail in Affero license and in that field I'm out of my depth.
Oh also, I am not a lawyer, if you're developing something commercially or otherwise reading this for advice please take a moment to consult a professional.
Thanks, what you said makes sense, or licensing Qt under LGPL in addition to GPL would make no sense.
> Oh also, I am not a lawyer, if you're developing something commercially or otherwise reading this for advice please take a moment to consult a professional.
