Licensing in Qt's modules

This page provides an overview of how we document copyright and license within the Qt modules and how this information is used.

Where is licensing documented?

In-file using, SPDX tags

When possible, the copyright and license are documented using a license header.

There must be at least one line for copyright and one line for the license. It is possible to have multiple copyright lines but there can only be one license line.

The license must be documented using a SPDX tag and License ID. If the license is not part of the SPDX license list, it can be documented using LicenseRef- followed by a chosen ID.

The license IDs must be linked together with one of the following separators: WITH, AND, OR.

Example of a license header:

# Copyright (C) 2022 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0

In three types of external files

REUSE.toml

REUSE.toml files document copyright and licensing information when it cannot be included in-file due to file format constraints or when the in-file license corresponds to another file (e.g., for generation or documentation purpose).

The REUSE.toml files, along with the in-file licensing information are processed by the reuse tool to check for reuse compliance and generate the source SBOM.

Refer to the REUSE.toml full documentation. Below is an example of a REUSE.toml file:

version = 1

[[annotations]]
path = ["<path1>",
        "<folder1/**>",
        "<folder2/*>"]
precedence = "override"
comment = "test"
SPDX-FileCopyrightText = "Copyright (C) 2024 The Qt Company Ltd."
SPDX-License-Identifier = "LicenseRef-Qt-Commercial OR GPL-3.0-only"

[[annotations]]
path = "<path2>"
precedence = "closest"
comment = "test"
SPDX-FileCopyrightText = ["Copyright (C) 2024 The Qt Company Ltd.",
                          "Copyright (C) 2023 someone else"]
SPDX-License-Identifier = "LicenseRef-Qt-Commercial OR GPL-3.0-only"

[[annotations]]
path = "<path3>"
precedence = "aggregate"
comment = "test"
SPDX-FileCopyrightText = "Copyright (C) 2024 The Qt Company Ltd."
SPDX-License-Identifier = "LicenseRef-Qt-Commercial OR GPL-3.0-only"

A REUSE.toml file always starts with version. Each annotation represents a license and copyright assignment.

About the path field:

• It specifies where the annotation applies.
• It can be a list.
• I does not support exceptions.
• * matches everything in a folder.
• ** matches everything in and down a folder.

Licensing information for a given file can be present in-file and in multiple REUSE.toml files. Precedence rules are set using precedence field:

• closest - Uses in-file licensing if available, otherwise, the annotation from the REUSE.toml file closest to the file is used.
• aggregate - Collects all available licensing information for a given file ( from in-file and REUSE.toml files).
• override - Uses only the licensing information in the REUSE.toml file closest to the module's base, ignoring in-file and downstream REUSE.toml files.

SPDX-FileCopyrightText and SPDX-License-Identifier are self-explanatory and can contain lists.

Other fields, such as ''comment'', may be added for documentation purposes.

licenseRule.json

Each Qt module has a single licenseRule.json file. This file lists the licensing rule for this module. It enforces the QUIP18 rule set and offers the possibility to add exceptions. The file format is presented in the patch introducing it, for example for qtbase.

This file is read by qtqa license test tst_license.pl to check the in-file licensing and the source SBOM.

qt_attribution.json

qt_attribution.json files document information related to the third-party components within a module (see QUIP4).

Licensing information from these files is processed by the qattributionscanner tool to generate the third party licensing information in the Qt documentation.

License files

License files corresponding to an SPDX license tag or referenced within a used REUSE.toml annotation must be found in the LICENSES directory at the base of the module. The license file name must follow the format: <Id>.txt.

Any unused license file present in the LICENSES directory breaks reuse compliance.

A license file corresponding to a license ID documented only in a qt_attribution.json file should be placed next to the qt_attribution.json file and be named LICENSE.Id.json

License files must either be located in a LICENSES directory or have a LICENSE. prefix to be ignored by the reuse tool.

Where is license used?

reuse tool

The reuse tool reads in-file SPDX license tags and copyright information as well as REUSE.toml files for reuse compliance and source SBOM generation.

To be reuse-compliant a module must provide licensing information for all files present in this module with few exceptions, typically .gitignore, files within LICENSES directory and LICENCE. prefixed files.

The source SBOM is a SPDX document providing copyright and licensing information for all files in the module, with the same exceptions as for reuse compliance.

qtqa license test: tst_licenses.pl

License check mode

In license check mode, tst_licenses.pl reads copyright and SPDX tag in the file's license header and checks what has been found against our rule set in licenseRule.json. In this test the checking was not made compulsory for every file.

To run a license check on a module, run:

QT_MODULE_TO_TEST=<path_to_module> perl <path_to_qtqa>/tests/prebuild/license/tst_licenses.pl

Source SBOM check mode

In source SBOM check mode, tst_licenses.pl reads the source SBOM generated by the reuse tool. It checks the license ID against our rule set in licenseRule.json.

To create a source SBOM run:

reuse spdx -o <module_source_SBOM>

from the base of the module.

To check the generated source SBOM, run:

QT_MODULE_TO_TEST=<path_to_module> perl <path_to_qtqa>/tests/prebuild/license/tst_licenses.pl -sbom <module_source_SBOM> -sbomonly

Currently, the check skips files located down the 3rdparty directories.

qattributionscanner

This reads the qt_attribution.json files to provide the licensing for Qt documentation pages.

qattributionscanner is looking for the license files documented in the qt_attribution.json. It searches for the <LicenseID>.txt files withing the LICENSES directory or for LICENSE.<LicenseID>.txt next to the qt_attribution.json file. The use of LicenseFile within qt_attribution.json is discouraged and will soon be deprecated.

Useful links

QUIP18: The licensing specification in Qt's modules.

QUIP04: Third-party components.

SBOM: Qt Software Bill of Materials (build SBOM).

SPDX Id: The official SPDX license Id.

source SBOM: The other type of Qt Software Bill of Materials.

reuse tool: Everything you need to know about the reuse tool.

REUSE.toml: The other way to document licensing.