Include WPIcal GPL license

[sciencewhiz]

Fixes #7694

[Gold856]

I would say that WPIcal is distributed under the terms of GPLv3, but the code itself is not licensed under GPLv3. Because of the GPL dependency, the combined work needs to be distributed under the terms of GPLv3, but that doesn't mean WPIcal's own code has to be GPLv3 as well.

[sciencewhiz]

I would say that WPIcal is distributed under the terms of GPLv3, but the code itself is not licensed under GPLv3. Because of the GPL dependency, the combined work needs to be distributed under the terms of GPLv3, but that doesn't mean WPIcal's own code has to be GPLv3 as well.

IANAL, but I don't believe that's true. For example section 5 of GPLv3 says:

• c) You must license the entire work, as a whole, under this
  License to anyone who comes into possession of a copy. This
  License will therefore apply, along with any applicable section 7
  additional terms, to the whole of the work, and all its parts,
  regardless of how they are packaged. This License gives no
  permission to license the work in any other way, but it does not
  invalidate such permission if you have separately received it.

[ThadHouse]

As a whole would mean the binary in my eyes (And some other searches show that too). Its known that BSD/MIT licenses are usable from GPL programs. So the source code could all be BSD, its just the binary itself that needs to be GPL.

[sciencewhiz]

As a whole would mean the binary in my eyes (And some other searches show that too). Its known that BSD/MIT licenses are usable from GPL programs. So the source code could all be BSD, its just the binary itself that needs to be GPL.

I'm very curious about who says GPL only applies to the binaries and not the source, because that goes against the entire viral point of the GPL.

The FSF FAQ says

Can I release a modified version of a GPL-covered program in binary form only? (#ModifiedJustBinary)

No. The whole point of the GPL is that all modified versions must be free software—which means, in particular, that the source code of the modified version is available to the users.

I think this might be what people are confusing it with. The FSF FAQ says

If I add a module to a GPL-covered program, do I have to use the GPL as the license for my module? (#GPLModuleLicense)

The GPL says that the whole combined program has to be released under the GPL. So your module has to be available for use under the GPL.

But you can give additional permission for the use of your code. You can, if you wish, release your module under a license which is more lax than the GPL but compatible with the GPL. The license list page gives a partial list of GPL-compatible licenses.

So everything in WPIcal has to be licensed as GPL. We could additionally license the parts we wrote as BSD, but I don't think that actually buys anyone anything other then confusion.

[ThadHouse]

It gives us free implicit licensing back to BSD if/when we remove the GPL components.

"You can, if you wish, release your module under a license which is more lax than the GPL but compatible with the GPL"

That's basically what we'd be doing. Releasing the main code module under BSD, which is more lax but compatible with the GPL.

It's not really that only the binary has to be released under GPL. It's that BSD source code is compatible with a GPL binary. You can include BSD licensed code in a GPL binary without issue. Theres no reason to actually make the source code GPL.

Our BSD source code is still available, which satifies the license of the GPL. If it didn't, we couldn't include any wpiutil or glass code at all.

[sciencewhiz]

It's not really that only the binary has to be released under GPL. It's that BSD source code is compatible with a GPL binary. You can include BSD licensed code in a GPL binary without issue. Theres no reason to actually make the source code GPL.

Our BSD source code is still available, which satifies the license of the GPL. If it didn't, we couldn't include any wpiutil or glass code at all.

The fact that we distribute the source code is irrelevant. The GPL isn't viral if someone else could modify WPIcal and not distribute the BSD licensed source, which they'd have the ability to do if parts of the source code are only BSD. That's specifically why the FAQ says you can have multiple licenses, but you have to make the source GPL.

It gives us free implicit licensing back to BSD if/when we remove the GPL components.

It's my understanding that re-licensing can never be implicit, which is why I explicitly covered it. The only time it can be implicit is if all contributors grant the license rights, which some projects do, but we don't.

Can you explain exactly what should be done for what you're proposing? It sounds like you're suggesting a one liner that includes the GPL in licenseFiles, but it feels like I've heard a few different things.

[ThadHouse]

Basically, what I'm proposing is shipping the mrcal binary with a copy of the GPL license rather than the BSD or LGPL license. Nothing else needs to change.

If someone modifies the mrcal binary, they'd still have to ship the BSD source code. They'd have to ship all the source code used to compile the binary.

Remember that shipping the source code means all the source code must be available, including all libraries. The license makes no difference between library and app code. If BSD code wasn't allowed, then it wouldn't be a compatible license, and bsd code in general couldn't be used in GPL apps, unless it was explicitly dual licensed. Which is definitely not the case.

[sciencewhiz]

Closing in favor of wpilibsuite/thirdparty-ceres#10