Do I have to pay money?

sierdzio

@SimonSchroeder
Why would someone choosing Qt Open Source elect GPL over LGPL? Obviously, assuming not using those few Qt components which require GPL not LGPL.

Some people like & want GPL. For example if they want to make it hard or impossible to be used in commercial apps. Or they want to make sure all contributions will also be open.

kshegunov

@sierdzio said in Do I have to pay money?:

No. LGPL clearly states a few requirements: your need to ship a copy of the license, you need to inform your users that LGPL Qt is used etc.
For OSS software this is very easy to fulfill, of course - but still has to be done.

Fair enough!

@sierdzio said in Do I have to pay money?:

Or they want to make sure all contributions will also be open.

I'm pretty sure this also applies to the LGPL.

SGaist

@kshegunov said in Do I have to pay money?:

I'm pretty sure this also applies to the LGPL.

You have to provide the modifications you did to the LGPL dependencies you are using but you are not required to upstream them.

JKSH

@sierdzio said in Do I have to pay money?:

@JonB said in Do I have to pay money?:

@SimonSchroeder
Why would someone choosing Qt Open Source elect GPL over LGPL? Obviously, assuming not using those few Qt components which require GPL not LGPL.

Some people like & want GPL. For example if they want to make it hard or impossible to be used in commercial apps.

To add another perspective: We're used to thinking in terms of pricing and obligations for the developers, but the free software movement thinks in terms of freedoms for the end-user. Specifically, freedom to run, study, share, and modify software.

From that perspective, the GPL guarantees greater freedoms for the end-user compared to the LGPL (L = "Lesser"). If I release my library under the GPL, I'm guaranteeing that all apps that use my library can be studied & modified by the end-user. However, if I release my library under the LGPL, an app that uses my library might be proprietary and can't be studied & modified by the end user.

kshegunov

@SGaist said in Do I have to pay money?:

You have to provide the modifications you did to the LGPL dependencies you are using but you are not required to upstream them.

Hm, okay. I was wrong then.

SGaist

@kshegunov said in Do I have to pay money?:

@SGaist said in Do I have to pay money?:

You have to provide the modifications you did to the LGPL dependencies you are using but you are not required to upstream them.

Hm, okay. I was wrong then.

Not completely, upstreaming is the nice thing to do so everybody can benefit from your changes. However, it can happen that some features might not align with a project goal hence they might not be suitable for inclusion.
You might also be using a library which is working fine but is currently not maintained, etc.

kshegunov

@SGaist, sure, but I was under the false impression that you're obligated to upstream the changes. Perhaps I was mixing it up with Qt's CLA.

Trigve

Reading this thread I was thinking about the situation like this:

For whatever reason I want to use GPL version of Qt (for instance because WebAssembly isn't available under LGPL) in my application (which in a sense is "proprietary"). Now, I also use proprietary library which is optional dependency (if not used the program would be usable but could have some usability issues in some specific areas). AFAIK my application needs to be also GPL (or could I use another license???). But from what I've read in the FAQ GPL application must not link to the proprietary library.

So what are my options?

JKSH

@Trigve said in Do I have to pay money?:

AFAIK my application needs to be also GPL

Correct. If your application links to a GPL library, then your application must also be released under the GPL license.

from what I've read in the FAQ GPL application must not link to the proprietary library.

Correct. A GPL application can link to libraries whose licenses that are compatible with GPL (see https://www.gnu.org/licenses/license-list.html#GPLCompatibleLicenses for a list of compatible licenses). However, proprietary licenses are not compatible with GPL, so proprietary libraries cannot be used in a GPL application.

Now, I also use proprietary library which is optional dependency (if not used the program would be usable but could have some usability issues in some specific areas)

If removing the library creates some usability issues, then I'm not convinced that it's truly optional... See @Chris-Kawa's link below about plugins.

So what are my options?

Some options include:

Get a commercial license for all the libraries you want to use. This way, you obtain the rights for your application to link to all of those libraries. Note: Using this option, you cannot release your application under a free software license.
Convince the owners of the proprietary library to release their library under a GPL-compatible license too. This way, your GPL application can link to it.
Replace the proprietary library with a different one which is GPL-compatible. This way, your GPL application can link to it.

JonB

@JKSH
Programs can "interact" with each other in a myriad of ways. For example, they might use sockets or files to exchange information. You can mix GPL with commercial/proprietary in this way, because everyone does it.

So... why can't I/the OP provide a non-linked, on-demand dynamic library for his optional dependency features, which he does LoadLibrary/GetProcAddress-type interface to allow that kind of "interaction"?

Chris Kawa

@JonB said in Do I have to pay money?:

So... why can't I/the OP provide a non-linked, on-demand dynamic library for his optional dependency features,

Because dynamic linking is still linking. FSF considers it "cheating" and treats plugins, shared memory etc. to fall under a single combined program definition and thus also require such plugins to be GPL compatible. See source.

Keep in mind that GPL is aggressively viral and intentionally so and thus trying to "workaround" it in any way is strictly against its idea.

JKSH

@JonB said in Do I have to pay money?:

@JKSH
Programs can "interact" with each other in a myriad of ways. For example, they might use sockets or files to exchange information. You can mix GPL with commercial/proprietary in this way

If the 2 components are truly independent, then sure you can "mix" them this way.

However, @Trigve's description does not sound like independent components so @Chris-Kawa's point applies.

Trigve

@JKSH said in Do I have to pay money?:

If the 2 components are truly independent, then sure you can "mix" them this way.

However, @Trigve's description does not sound like independent components so @Chris-Kawa's point applies.

In my case the optional dependency is library used for viewing some documents, which isn't necessary altogether, because I could render the document as .pdf and use system viewer (in my case the "proprietary dependency" contains also an executable which encapsulate the library so in this case I could use the .exe instead of library and should be OK, AFAIK).

JonB

@Trigve said in Do I have to pay money?:

because I could render the document as .pdf and use system viewer

Indeed! The sort of thing I had in mind. So perhaps you should indeed do that!

JKSH

@Trigve said in Do I have to pay money?:

In my case the optional dependency is library used for viewing some documents, which isn't necessary altogether, because I could render the document as .pdf and use system viewer

Does this mean you've found a way to resolve the "usability issues" you mentioned before, without depending on the proprietary library/application? If so, then I don't see a problem -- You can certainly distribute a GPL app which produces PDF files and launches the system viewer (via the Qt PDF module and QDesktopServices class, I presume?)

Trigve

@JKSH said in Do I have to pay money?:

Does this mean you've found a way to resolve the "usability issues" you mentioned before, without depending on the proprietary library/application?

Usability issue is that you either use proprietary viewer with more functionality or else convert to .pdf and use system viewer. What I had in mind was that application could either use or not proprietary library (if one has a license), which should be resolved at build time. But in this case the application cannot be GPL.

nickmillers

This post is deleted!