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Let's say I made an application using Qt's QML language and I didn't have a commercial license, am I required to disclose the whole source code for said application or just the modules I modified (if I even modified them to begin with)?

Basically, if I just use the QML language and the LGPL modules without modifying their source code, am I required to disclose my source anyway?

As am example, I wrote ApplicationX using Qt Quick/QML/etc but I didn't modify the source of the modules I used. I just used it to write an application, am I then required to disclose ApplicationX's source code if I release the binary to the public? Or can I just release the source code of the (unmodified) modules I used?

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If you write an application in the QML language, there's a strong argument to be made that your application is not derived from Qt so that the Qt license has no effect over your code. You can freely decide what you do with your source code and whether you want to disclose it at all.

This changes if you combine your application with Qt software into a single program, and give someone else a copy of that combined program. Since that combined program contains Qt software, you will need to comply with that license.

For the LGPL, this involves providing the corresponding source code of the LGPL-covered parts, even if you did not modify them. You must also make it possible for recipients to modify the LGPL-covered parts. One way to satisfy that requirement is to provide source code for the entire program. But in general, the LGPL does not require you to publish source code for the entire program.

So this depends mostly on how you will distribute your QML application.

  • Thanks for the answer! Can you clarify what "This changes if you combine your application with Qt software into a single program" means? How else could I distribute the application if the Qt libraries aren't included with it? – user9564371 Sep 28 at 21:23
  • I added an example in my question too – user9564371 Sep 28 at 21:38
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No Free or Open Source licence compels you to publish, even if you make changes to the original. They only set rules about how to publish.

Read the Open Source and Free Software definitions.

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