QUIP 18: License specification in Qt's modules

This QUIP specifies the licenses that are used in different parts of a
typical Qt module repository. Note that repositories may deviate from
this guideline. Check with the authors and copyright holders of the
repository in question.

Task-number: QTBUG-104704
Change-Id: I1487cd3a16be4a6dc4e36252a17ce894c09676a2
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 167 insertions, 0 deletions

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+QUIP: 18
+Title: License specification in Qt's modules
+Author: Lucie Gerard,
+        Jörg Bornemann
+Status: Active
+Type: Informational
+Created: 2022-09-26
+Post-History: https://lists.qt-project.org/pipermail/development/2023-February/043648.html
+
+Overview
+========
+
+This QUIP specifies the licenses that are used in different parts of a
+typical Qt module repository and also provides helpful guidance about
+how to express which license source code is under.
+
+License header format
+=====================
+
+The license header follows the SPDX standard [0]_.
+
+There is at least one copyright line and exactly one license
+expression line::
+
+  Copyright (C) 2023 The Qt Company Ltd.
+  SPDX-License-Identifier: <spdx-license-expression>
+
+A copyright line for code written by a contributor outside the Qt
+Company can include that contributor's name (or a legal entity they
+represent) in the Copyright header.
+
+The copyright line should include the year the file was created, or -
+in the case of additional copyright lines - the year the additional
+copyright notice was added. Updating the copyright year when changes
+are made to the file is possible.
+
+The copyright line may be prefixed with `SPDX-FileCopyrightText:`.
+
+The `<spdx-license-expression>` must be a valid expression, according
+to the SPDX standard as defined in [1]_.
+
+The license identifiers used in a license expression are either from
+the list of known licenses [2]_ or prefixed with `LicenseRef-`.
+
+The license files are placed into a `LICENSES` directory below the Qt
+module repository's root. The license files are named after the SPDX
+license identifier followed by ``.txt`` [3]_.
+
+Classification of files
+=======================
+
+There are various kinds of files in a Qt module repository that should
+include license headers. Here, we classify these files in order to
+identify which files should be under which licenses.
+
+Files that do not support inline comments do not have to contain
+licensing information. If licensing information for such files is
+still desirable, it should be placed into an adjacent ``.license``
+text file. For example, ``blob.bin`` may be accompanied by
+``blob.bin.license`` in the same directory.
+
+Licensing information may be omitted for files with trivial content.
+
+The documentation landing page of a Qt module contains a "Licenses and
+Attributions" section that defines the licenses under which the module
+and plugin implementation is available. See the list of Qt modules
+[6]_.
+
+Module and plugin implementation
+--------------------------------
+
+Files that belong to the implementation of Qt modules and plugins. The
+usual locations for module source code are the subdirectories ``src/``
+and ``plugins/``.
+
+There are two licensing models for module and plugin implementations:
+GPL-only and one that is additionally licensed under LPGL.
+
+The license expression permitting the LPGL is
+``LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR
+GPL-3.0-only``.
+
+The GPL-only license expression is ``LicenseRef-Qt-Commercial OR
+GPL-3.0-only``.
+
+Examples
+--------
+
+Files that belong to the implementation of Qt examples. The usual
+locations for examples is the ``examples/`` subdirectory.
+
+The license expression for examples is ``LicenseRef-Qt-Commercial OR
+BSD-3-Clause``.
+
+Tests
+-----
+
+Files that belong to the implementation of Qt tests. The usual
+location is the ``tests/`` subdirectory.
+
+The license expression for tests is ``LicenseRef-Qt-Commercial OR
+GPL-3.0-only``.
+
+Tools
+-----
+
+Files that belong to the implementation of Qt tools that are for use
+by Qt users. The usual location is the ``src/tools/`` subdirectory.
+
+The license expression for tools is ``LicenseRef-Qt-Commercial OR
+GPL-3.0-only WITH Qt-GPL-exception-1.0``.
+
+Documentation
+-------------
+
+All ``.qdoc``, ``.qdocinc`` and ``.qdocconf`` files that are needed to
+generate the documentation.
+
+The license expression for documentation is ``LicenseRef-Qt-Commercial
+OR GFDL-1.3-no-invariants-only``.
+
+Documentation snippets
+----------------------
+
+Any source code that appears in the documentation. The usual locations are
+``doc/snippets/`` directories throughout the Qt module repository's directory
+tree.
+
+The license expression for documentation snippets is
+``LicenseRef-Qt-Commercial OR BSD-3-Clause``.
+
+Build System Files
+------------------
+
+All files that contribute to Qt's build system. That includes the following file
+name patterns:
+
+- ``CMakeLists.txt``
+- ``*.cmake``
+- ``*.pro``
+- ``*.pri``
+- ``*.prf``
+
+The license expression for build system files is ``BSD-3-Clause``.
+
+Related Work
+============
+
+The "Software License Agreement between The KDE Free Qt Foundation and
+The Qt Company Oy" [4]_ poses restrictions for the licenses of the Qt
+Free Edition modules.
+
+To a certain extent, Qt follows REUSE [5]_. REUSE is a guideline on
+how to specify the licenses in a project. We don't aim for full
+compliance at this point, due to small/binary files and 3rd party
+content.
+
+References
+==========
+
+.. [0] https://spdx.github.io/spdx-spec/v2.3/
+.. [1] https://spdx.github.io/spdx-spec/v2.3/SPDX-license-expressions/
+.. [2] https://spdx.org/licenses/
+.. [3] https://reuse.software/tutorial/#step-1
+.. [4] https://kde.org/community/whatiskde/Software_License_Agreement_2015_Text.pdf
+.. [5] https://reuse.software/spec/
+.. [6] https://doc.qt.io/qt-6/qtmodules.html