[Development] Licensing of qtbase

[Florian Bruhin]

Hi,

(The usual "I am not a lawyer" disclaimer applies.)

On Wed, Jul 13, 2022 at 12:14:27PM +0200, Felix Crazzolara wrote:
> I would like to use Qt for a personal project. In my project, I use a
> relatively small part of Qt and I think that the components of QtBase here
> https://github.com/qt/qtbase suffice for my application.

If you don't redistribute your project, you don't need to care much
about licenses.

If you do redistribute it, do so under a license compatible with the
GPLv3, and you will be fine.

> I read about the Qt licensing model on the official website. What surprised
> me now to see, is that there are quite a few licenses in the LICENSES
> folder in the repository referred to above. Among them is for example an
> MIT license.
> 
> How can I understand this? Is the QtBase component of Qt itself licensed
> with an MIT license? Can I choose which license in the LICENSES folder to
> use if I restrict myself to QtBase?

The Licenses folder contains *all* licenses used in the project,
including those of third-party components.

The license which actually applies is specified on a per-file level,
e.g. here: https://github.com/qt/qtbase/blob/dev/src/corelib/io/qurl.cpp#L3

https://www.qt.io/product/features?hsLang=en#js-6-3 lets you see the
individual components of Qt and what license they are available as.

Most of Qt is available under the LGPL (or commercial), some of it under
the GPL (or commercial). For qtbase, I *think* it should all be LGPL
even, but don't quote me on that.

For a quick overview, here is what I found in the Qt 6.4 qtbase repo, by
running this and then some manual editing:

$ git grep -ho "SPDX-License-Identifier: .*" | sort | uniq -c | sort -nr
   3478 SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
   1797 SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
   1591 SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
        (those seem to be code snippets in the documentation)
    359 SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
        (example code apparently?)
     46 SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
      3 SPDX-License-Identifier: MIT
      1 SPDX-License-Identifier: LicenseRef-Qt-Commercial OR
      1 SPDX-License-Identifier: BSL-1.0
      1 SPDX-License-Identifier: BSD-3-Clause
      1 SPDX-License-Identifier: Apache-2.0 OR MIT
      1 SPDX-License-Identifier: Apache-2.0

For an opensource project, even more so for a small personal one, I'd
recommend licensing it under the GPLv3 and you should be all set.

Florian

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