I think honestly this is something other providers (Google code when it was around, gitlab now) are much better at.
That type of thing is why I think people need to choose one of: GPL, LGPL, MIT, BSD (isn't that essentially MIT?). I dont see the point in other "open source" licenses, they primarily create compatibility issues.
In Rust most code is dual licensed as MIT or Apache 2. You can pick which one to use although IIRC Apache 2 is considered the "primary license" because it provides protections from patent trolls and an explicit contribution licensing clause. However Apache 2 isn't compatible with GPL.
What are you talking about? Let say we have code A licensed as MIT and code B licensed GPL.
You can combine A with B and distribute it. You can combine B with A and distribute it. AB or BA is both a legal combination that a distributor can do. In both cases the distributor need to follow the condition of both MIT and GPL. You can not distribute AB and only follow GPL, or combine BA and only follow MIT.
There is two ways to look at copyright licenses. The slightly incorrect but slightly easier way is to see them as a contract. In order to distribute you need to follow the conditions. If you have two contracts then you have two sets of conditions. Three contracts and three sets of conditions.
The second way, which lawyers prefer as the more "true" perspective, is to see a copyright license as a list of permissions. Copyright law dictate that as a distributor you have no rights, so the license is the specific conditions in order to gain permission. It is like a airplane ticket where in order to travel you got to follow the rules and conditions or the airline. Countries can also have conditions and rules like visas, passports and enter/exiting laws. Thus in order to have permission to travel between countries you need to follow both sets of rules and conditions.
Incompatibility occur when the rules and conditions of two or more licenses demand something impossible, like the case where one condition require an action and the other forbid said action. Both conditions can not be met at the same time and thus the licenses are incompatible.
If neither aspects is an issue then the additional work needed to add GPL code to an MIT licensed project is practically zero.
There are however naturally implication for downstream which in combination of additionally third licenses (such as proprietary licenses) can cause real issues, and the relationship between such downstream and the MIT project could as a result lead to reasons why the MIT project feel like they can not include GPL into their code. There might even be contractional reasons involved which mean not only do you now have three different copyright licenses to follow but you also have contract law involved in order to follow the law and have a legal right to distribute the combined work. I can see how the permissive licenses in those kind of situation feel simpler since they do not interact much with the other legal stake holders.
Previously, someone could use your MIT code in a closed source product and distribute the resulting executables to their customers without including the source. In the future, that someone would have to start following the GPL rules or stop using your not-MIT-anymore project.
Under MIT, Microsoft can take code from A and put it into the source code of Visual Studio, provided that they keep the copyright and license with the code they've copied. Visual Studio can then be licensed however they want.
Let's say that project A takes code from project B. Now because they have GPLed code, A has to be distributed with terms at least as open as the GPL3's terms, due to copyleft.[1]
This might not matter to the maintainers of project A, but it certainly matters to Microsoft, because now if they use code from project A, they also have to distribute it with terms at least as open as the GPL3's terms. So if they use code from project A in Visual Studio, they've effectively licensed Visual Studio under the GPL3.
The GPL3 is "infectious" in this way--once you use GPL3 code in your project, your project is effectively licensed under the GPL3.
[1] https://en.wikipedia.org/wiki/GNU_General_Public_License#Cop...
Doesn't it have to be licensed as GPL3?
I'm no lawyer, but if I'm understanding correctly, yes, it does have to be licensed under the GPL3, but it doesn't have to be licensed only under the GPL3. With a license like MIT, the could apply a second license which would, for example, amend the MIT license to require you to pay for the software.
However, the "No Further Restrictions" paragraph in the GPL I think puts a much stronger set of requirements:
> You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License. For example, you may not impose a license fee, royalty, or other charge for exercise of rights granted under this License, and you may not initiate litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using, selling, offering for sale, or importing the Program or any portion of it.
This is why I think Stallman often uses the language "licensed with terms at least as open as the GPL" instead of saying "licensed under the GPL"--yes, it has to be licensed under the GPL3 but that doesn't quite capture the whole story. Someone can apply another license (i.e. Apache 2, to explicitly grant patents) so their licensing might not be just the GPL3, but further licenses can only expand freedoms, not restrict them.
I would encourage anyone who is interested in this sort of thing to read the license for themselves. Don't get intimidated and assume it's all in legalese: while I'm hesitant to think I understand it since the law is not my area of expertise, the GPL is written in what seems like fairly straightforward English.
In that case we have three licenses. We have the MIT licenses, the GPL license, and the license of Visual Studio owned by microsoft.
If the MIT licensed project have a relation with Microsoft which they value higher than the code from the GPL project then the GPL code will be incompatible with the goals of the MIT project.
The incompatibility depend on the relationship and can only be answered based on defining said relationship.
If you're working on something that you hope to (eventually?) make money from, but you also want to benefit from the collegial atmosphere of open source, then choose the GPL. This simple decision instantly eliminates a whole subset of would-be competitors, who you now don't have to worry about undermining your business or otherwise threatening your source of income while they rely on being able to use your own work against you, since the GPL automatically places your work in their do-not-touch category.
This is true, and yet your conversation partner still has the winning answer. The point is that, notwithstanding these restrictions on developers—some of whom have the desire to be able to take without reciprocation—the freedom guaranteed by the GPL to users more than makes up for it. We're essentially talking about local versus global maxima here.
> It's almost impossible for a commercial product to use GPL 3 licensed software at all.
On the contrary—GPL is very beneficial, for the reasons I just laid out in another comment[1]. GPL-licensed code is not ipso facto any harder to commercialize than if you were to make the end result available under MIT. It's arguably even easier, since your competitors will have a more difficult time competing with you than if you'd chosen MIT. As Eben Moglen once put it, if you're trying to decide on a license, then by all means you should go with a permissive one—if you're what you're looking for is "a really good license for your competitor to use"[2].
You need only look to history then compare and contrast it with the industry's current preoccupation with funding the development of free and open source software. Red Hat/Cygnus were largely built on top of GPL code. Meanwhile, today's developers entrenched in the GitHub culture, with its permissive-first obsession with licenses like the MIT, have been bamboozled into working against their own interests by giving away their strongest bargaining chip when they decide to go with the flow instead of choosing the GPL.
And super permissive licenses like MIT hurt developers too, because it means I oftentimes can't see the source code that someone else has modified, even though it would help me a lot to be able to do so. With GPL-licensed software, I am always guaranteed this freedom.