Re: LGPL v3 compatibilty (original) (raw)

Anthony W. Youngman wrote:

If your GPLv2 program links to an LGPLv3 library, then you don't need to give a monkeys.

The whole point behind LGPL is that the LGPL library must be independently distributable, and independently upgradeable. If your program is GPL (any version), then it is compatible with any LGPL library (any version).

I don't think that's correct.

Clearly, as you say, there's no problem from the LGPL library's point of view. However, the GPL2'd program says that any code that is part of the program needs to be under the GPL2. Now there are various licenses held to be compatible with the GPL2, in that their provisions are a subset of the GPL2s - such as the BSD licence family. So libraries under those are no problem. And the LGPLv2 can be converted to the GPLv2 via a clause in it, so LGPLv2 libraries are OK too. But if, for example, your library is MPLed, you are stuck. There's no way to make MPLed code compatible with GPLv2. And the same is true of LGPLv3, which can also not be made compatible with the GPLv2 (because it has extra restrictions over and above those in GPLv2, and GPLv2 forbids extra restrictions).

Of course, if you own the copyright on the GPLv2 program, you can add a license exception for linking with the LGPLv3 library.

Gerv

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