path: root/src/linguist/linguist/doc/cmake-macros.qdoc

// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
\group cmake-commands-qtlinguisttools
\title CMake Commands in Qt6 LinguistTools

The following CMake commands are defined when Qt6::LinguistTools is loaded, for instance
with

\code
find_package(Qt6 REQUIRED COMPONENTS LinguistTools)
\endcode

\sa{CMake Command Reference}
*/

/*!
\page qtlinguist-cmake-qt-add-translation.html
\ingroup cmake-commands-qtlinguisttools

\title qt_add_translation
\target qt6_add_translation

\summary {Compiles Qt Linguist .ts files into .qm files.}

\include cmake-find-package-linguisttools.qdocinc

\warning This function is deprecated. Consider using the target-based
functions \l{qt6_add_lrelease} or \l{qt6_add_translations} instead.

\section1 Synopsis

\badcode
qt_add_translation(<VAR> file1.ts [file2.ts ...]
                    [OPTIONS ...])
\endcode

\versionlessCMakeCommandsNote qt6_add_translation

\section1 Description

Calls \c{lrelease} on each \c{.ts} file passed as an argument, generating
\c{.qm} files. The paths of the generated files are added to \c{<VAR>}.

\section1 Options

You can set additional \c{OPTIONS} that should be passed when \c{lrelease} is
invoked. You can find possible options in the \l{lrelease}{lrelease documentation}.

By default, the \c{qm} files will be placed in the current build directory
(\c{CMAKE_CURRENT_BINARY_DIR}). To change this, you can set \c{OUTPUT_LOCATION}
as a property of the source \c{.ts} file.

For example, with the following code, the \c{.qm} files are generated
in a \c{translations} directory below the current build directory.

\snippet cmake-macros/examples.cmake set_output_location_on_ts_file

\section1 Examples

Generating \c{helloworld_en.qm}, \c{helloworld_de.qm} in the build
directory:

\snippet cmake-macros/examples.cmake qt_add_translation

Generating \c{helloworld_en.qm}, \c{helloworld_de.qm} in a \c{l10n}
sub-directory:

\snippet cmake-macros/examples.cmake qt_add_translation_output_location
*/

/*!
\page qtlinguist-cmake-qt-create-translation.html
\ingroup cmake-commands-qtlinguisttools

\title qt_create_translation
\target qt6_create_translation

\summary {Sets up the Qt Linguist translation toolchain.}

\include cmake-find-package-linguisttools.qdocinc

\warning This function is deprecated. Consider using the target-based
functions \l{qt6_add_lupdate} or \l{qt6_add_translations} instead.

\section1 Synopsis

\badcode
qt_create_translation(<VAR> ts-file-or-sources [ts-file-or-sources2 ...]
                      [OPTIONS ...])
\endcode

\versionlessCMakeCommandsNote qt6_create_translation

\section1 Description

Processes given sources (directories or individual files) to generate
Qt Linguist \c{.ts} files. The \c{.ts} files are in turn compiled into \c{.qm}
files of the same base name that are stored in the build
directory. Paths to the generated \c{.qm} files are added to \c{<VAR>}.

The translation files to create or update need to have a \c{.ts} suffix. If
the given file path is not absolute it is resolved relative to the current
source directory. If no \c{.ts} file is passed as an argument, the macro
does nothing.

Any arguments that do not have a \c{.ts} suffix are passed as input to the
\c{lupdate}. \c{lupdate} accepts directories and source files as input.
See also the \l{lupdate}{lupdate documentation} on further details.

\section1 Options

You can set additional \c{OPTIONS} that should be passed when \c{lupdate} is
invoked. You can find possible options in the \l{lupdate}{lupdate documentation}.

\section1 Examples

Recursively look up Qt translations from source files in current directory and
generate or update \c{helloworld_en.ts} and \c{helloworld_de.ts} file using
\c{lupdate}. Compile said files into \c{helloworld_en.qm} and \c{helloworld.de.qm}
files in the build directory:

\snippet cmake-macros/examples.cmake qt_create_translation
*/

/*!
\page qtlinguist-cmake-qt-add-lupdate.html
\ingroup cmake-commands-qtlinguisttools

\title qt_add_lupdate
\target qt6_add_lupdate

\summary {Add targets to generate or update Qt Linguist .ts files.}

\include cmake-find-package-linguisttools.qdocinc

\cmakecommandsince 6.2

\section1 Synopsis

Since 6.7:
\badcode
qt_add_lupdate(TS_FILES file1.ts [file2.ts ...]
               [PLURALS_TS_FILE file.ts]
               [SOURCE_TARGETS target1 [target2 ...]]
               [SOURCES source1.cpp [sources2.cpp ...]]
               [INCLUDE_DIRECTORIES directory1 [directory2 ...]]
               [LUPDATE_TARGET target-name]
               [NO_GLOBAL_TARGET]
               [OPTIONS ...])
\endcode

Since 6.2 (deprecated):
\badcode
qt_add_lupdate(target TS_FILES file1.ts [file2.ts ...]
               [SOURCES source1.cpp [sources2.cpp ...]]
               [INCLUDE_DIRECTORIES directory1 [directory2 ...]]
               [NO_GLOBAL_TARGET]
               [OPTIONS ...])
\endcode

\versionlessCMakeCommandsNote qt6_add_lupdate()

\section1 Description

Creates a custom target to generate or update Qt Linguist \c{.ts}
files with \l{lupdate}.

The name of that custom target defaults to \c{${PROJECT_NAME}_lupdate}. Further
calls of \c qt_add_lupdate will create target names with an increasing number
appended. The custom target name can be specified with the \c LUPDATE_TARGET
option.

With the \c{SOURCE_TARGETS} argument you can specify a list of targets that
contain sources with translatable strings. If \c{SOURCE_TARGETS} is not
specified, you can specify \c{SOURCES}, which is described below. If neither
\c{SOURCE_TARGETS} nor \c{SOURCES} is given, the command
\l{qt6_collect_translation_source_targets}{qt_collect_translation_source_targets}
is called to retrieve the list of targets.

The \c{.ts} files must be specified with the argument \c{TS_FILES}.

This function is designed to be used in conjunction with
\l{qt6_add_lrelease}{qt_add_lrelease}.  See also the convenience wrapper
\l{qt6_add_translations}{qt_add_translations}.

//! [sources-and-include-dirs]
\section1 Sources and Include Directories

With \c{SOURCES} you can explicitly specify additional source files that contain
translatable strings.

You can use \c{INCLUDE_DIRECTORIES} to explicitly specify include directories
for those source files.
//! [sources-and-include-dirs]

\section1 Options

You can set additional \c{OPTIONS} that should be passed when \c{lupdate} is
invoked. You can find possible options in the \l{lupdate}{lupdate
documentation}.

\section1 Umbrella Target

In addition to the target \c{${target}_lupdate}, an umbrella target
\c{update_translations} is created. This target will build all
\c{${target}_lupdate} targets that were created with \c{qt_add_lupdate}.

Pass \c{NO_GLOBAL_TARGET} to \c{qt_add_lupdate} to prevent this behavior.

The name of this target can be overridden by setting the variable
\c{QT_GLOBAL_LUPDATE_TARGET} before calling \c{qt_add_lupdate}.

//! [plurals-ts-file]
\section1 Plural Forms

\l QT_I18N_SOURCE_LANGUAGE specifies the language in which the source code
strings are written. For handling plural forms correctly, create an additional
\c{.ts} file for that language that only contains translatable strings for
plural forms. See \l{Handle Plural Forms} for details.

With \c PLURALS_TS_FILE you can specify the \c{.ts} file for the source
language. This file will only contain plural forms.
//! [plurals-ts-file]

\section1 Deprecated Command Signature

Older versions of \c qt_add_lupdate took a target as the first argument. This is
deprecated. Use the \c SOURCE_TARGETS argument instead.

\section1 Examples

Add the targets \c{myapp_lupdate} and \c{update_translations} for updating the
\c{.ts} file of an application \c{myapp}.

\snippet cmake-macros/examples.cmake qt_add_lupdate

You can specify the name of the created target by passing the \c LUPDATE_TARGET
argument:

\badcode
qt_add_lupdate(
    LUPDATE_TARGET update_application_translations
    TS_FILES myapp_de.ts
    PLURALS_TS_FILE myapp_en.ts
)
\endcode
*/

/*!
\page qtlinguist-cmake-qt-add-lrelease.html
\ingroup cmake-commands-qtlinguisttools

\title qt_add_lrelease
\target qt6_add_lrelease

\summary {Add targets to transform Qt Linguist .ts files into .qm files.}

\include cmake-find-package-linguisttools.qdocinc

\cmakecommandsince 6.2

\section1 Synopsis

Since 6.7:
\badcode
qt_add_lrelease(TS_FILES file1.ts [file2.ts ...]
                [LRELEASE_TARGET target-name]
                [EXCLUDE_FROM_ALL]
                [NO_GLOBAL_TARGET]
                [QM_FILES_OUTPUT_VARIABLE variable-name]
                [OPTIONS ...])
\endcode

Since 6.2 (deprecated):
\badcode
qt_add_lrelease(target TS_FILES file1.ts [file2.ts ...]
                [NO_TARGET_DEPENDENCY]
                [NO_GLOBAL_TARGET]
                [QM_FILES_OUTPUT_VARIABLE variable-name]
                [OPTIONS ...])
\endcode

\versionlessCMakeCommandsNote qt6_add_lrelease()

\warning Calling \c qt_add_lrelease in a directory scope different than the
target directory scope requires at least CMake version 3.18.

\section1 Description

Creates a custom command to transform \c{.ts} files into \c{.qm} files with
\l{lrelease}.

The execution of the custom command is driven by a custom target that is built
by default. The name of that custom target defaults to
\c{${PROJECT_NAME}_lrelease}. Further calls of \c qt_add_lrelease will create
target names with an increasing number appended. The custom target name can be
specified with the \c LRELEASE_TARGET option.

The \c{.ts} files must be specified with the argument \c{TS_FILES}.

This function is designed to be used in conjunction with
\l{qt6_add_lupdate}{qt_add_lupdate}.  See also the convenience wrapper
\l{qt6_add_translations}{qt_add_translations}.

\section1 Options

You can set additional \c{OPTIONS} that should be passed when \c{lrelease} is
invoked. You can find possible options in the \l{lrelease}{lrelease
documentation}.

By default, the \c{.qm} files will be placed in the current build directory
(\c{CMAKE_CURRENT_BINARY_DIR}). To change this, you can set \c{OUTPUT_LOCATION}
as a property of the source \c{.ts} file.

For example, with the following code, the \c{.qm} files are generated
in a \c{translations} directory below the current build directory.

\snippet cmake-macros/examples.cmake set_output_location_on_ts_file

\section1 Processing Generated .qm Files

To further process the generated \c{.qm} files, for example to create install
rules, \c{qt_add_lrelease} can store the paths of the \c{.qm} files in a
variable. Pass \c{QM_FILES_OUTPUT_VARIABLE <variable-name>} to the function for
that.

\section1 Build by Default

By default, the command creates a custom target that is added to the default
build target. This ensures that the \c{.qm} files are always up-to-date when the
project is built. This behavior can be turned off with the \c{EXCLUDE_FROM_ALL}
argument. In this case, the user must build the \c{${PROJECT_NAME}_lrelease}
target manually.

\section1 Umbrella Target

In addition to the target \c{${target}_lrelease}, an umbrella target
\c{release_translations} is created. This target will build all
\c{${target}_lrelease} targets that were created with \c{qt_add_lrelease}.

Pass \c{NO_GLOBAL_TARGET} to \c{qt_add_lrelease} to prevent this behavior.

The name of this target can be overridden by setting the variable
\c{QT_GLOBAL_LRELEASE_TARGET} before calling \c{qt_add_lrelease}.

\section1 Deprecated Command Signature

Older versions of \c qt_add_lrelease took a target as the first argument. This
is still possible but deprecated.

\section1 Examples

Add the targets \c{myapp_lrelease} and \c{release_translations} for transforming
the given \c{.ts} files into \c{.qm} files. Also, install the generated \c{.qm}
files. The target \c{myapp_lrelease} is built by default.

\badcode
project(myapp)
...
qt_add_lrelease(
    TS_FILES myapp_de.ts myapp_fr.ts
    QM_FILES_OUTPUT_VARIABLE qm_files
)
install(FILES ${qm_files} DESTINATION "translations")
\endcode

You can specify the name of the created target by passing the \c LRELEASE_TARGET
argument:

\badcode
qt_add_lrelease(
    LRELEASE_TARGET create_myapp_qm_files
    TS_FILES myapp_de.ts myapp_fr.ts
    QM_FILES_OUTPUT_VARIABLE qm_files
)
\endcode
*/

/*!
\page qtlinguist-cmake-qt-add-translations.html
\ingroup cmake-commands-qtlinguisttools

\title qt_add_translations
\target qt6_add_translations

\summary {Add targets to update and transform Qt Linguist .ts files into .qm files.}

\include cmake-find-package-linguisttools.qdocinc

\cmakecommandsince 6.2

\section1 Synopsis

Since Qt 6.7:
\badcode
qt_add_translations([target]
                    [TARGETS target1 [target2...]]
                    [SOURCE_TARGETS target1 [target2...]]
                    [TS_FILE_BASE name]
                    [TS_FILE_DIR directory]
                    [TS_FILES file1.ts [file2.ts ...]]
                    [PLURALS_TS_FILE file.ts]
                    [NO_GENERATE_PLURALS_TS_FILE]
                    [RESOURCE_PREFIX prefix]
                    [OUTPUT_TARGETS variable-name]
                    [QM_FILES_OUTPUT_VARIABLE variable-name]
                    [SOURCES source1.cpp [sources2.cpp ...]]
                    [INCLUDE_DIRECTORIES directory1 [directory2 ...]]
                    [LUPDATE_TARGET target-name]
                    [LUPDATE_OPTIONS ...]
                    [LRELEASE_TARGET target-name]
                    [LRELEASE_OPTIONS ...]
                    [IMMEDIATE_CALL])
\endcode

Since Qt 6.2 (deprecated):
\badcode
qt_add_translations(target TS_FILES file1.ts [file2.ts ...]
                    [RESOURCE_PREFIX prefix]
                    [OUTPUT_TARGETS variable-name]
                    [QM_FILES_OUTPUT_VARIABLE variable-name]
                    [SOURCES source1.cpp [sources2.cpp ...]]
                    [INCLUDE_DIRECTORIES directory1 [directory2 ...]]
                    [LUPDATE_OPTIONS ...]
                    [LRELEASE_OPTIONS ...])
\endcode

\versionlessCMakeCommandsNote qt6_add_translations()

\warning Calling \c qt_add_translations in a directory scope different than the
target directory scope requires at least CMake version 3.18.

\section1 Description

Creates targets for updating Qt Linguist \c{.ts} files and for transforming them
into \c{.qm} files. This function is a convenience wrapper around
\l{qt6_add_lupdate}{qt_add_lupdate} and \l{qt6_add_lrelease}{qt_add_lrelease}
and aims to offer the most common usage of both functions with one call.

The parameter \c TARGETS specifies a list of targets that intend to load the
generated \c{.qm} files at run time. If there's only one such target, you may
directly pass the target's name as the first argument.

The parameter \c SOURCE_TARGETS specifies a list of executable or library
targets that contain sources with translatable strings. From the sources of
these targets, \c{.ts} files will be created.

If \c SOURCE_TARGETS is not given, targets are automatically gathered by calling
\l{qt6_collect_translation_source_targets}{qt_collect_translation_source_targets}
at the end of the directory scope of \c{PROJECT_SOURCE_DIR}. This functionality
requires CMake 3.19 or newer. This functionality can be turned off with the
argument \c{IMMEDIATE_CALL}.

This function will create the target \c{update_translations} that scans all
source files with \c lupdate and creates and updates the \c{.ts} files.

This function will create the target \c{release_translations} that generates the
\c{.qm} files from the \c{.ts} files. This target is built by default.

The \c{.ts} files may be specified with the argument \c{TS_FILES}, but it's more
convenient to let \c qt_add_translations figure out the file paths
automatically. See \l{Automatic Determination of .ts File Paths} for
details.

\include cmake-macros.qdoc sources-and-include-dirs

\section1 Automatic Determination of .ts File Paths

The paths of the \c{.ts} files that are used as input for \c qt_add_translations
can be automatically determined if \l{QT_I18N_TRANSLATED_LANGUAGES} has been
set. This variable can be conveniently set with \l qt_standard_project_setup.

The following project setup is usually enough:

\snippet cmake-macros/examples.cmake auto_determine_ts_file_paths

This will create the files \c{myproject_de.ts} and \c{myproject_fr.ts} in the
project's source directory.

By default, the \c{.ts} files are created in \c{CMAKE_CURRENT_SOURCE_DIR}. You
can change the location by passing a different directory with the \c TS_FILE_DIR
argument.

By default, the \c{.ts} file names are constructed from \c{PROJECT_NAME}. You
can specify a different base name with the \c{TS_FILE_BASE} argument.

\include cmake-macros.qdoc plurals-ts-file

A plurals-only \c{.ts} is automatically generated unless the option \c
NO_GENERATE_PLURALS_TS_FILE is specified.

For example,
\badcode
project(myapp)
qt_standard_project_setup(
    I18N_SOURCE_LANGUAGE en         # optional - this is the default
    I18N_TRANSLATED_LANGUAGES de
)
qt_add_executable(myapp ...)
...
qt_add_translations(myapp)
\endcode
creates the full translation file \c{myapp_de.ts} and the plurals-only file
\c{myapp_en.ts}.

If you need a full translation of the source language, add it to
\l{QT_I18N_TRANSLATED_LANGUAGES}

For example,
\badcode
project(myapp)
qt_standard_project_setup(I18N_TRANSLATED_LANGUAGES en de)
qt_add_executable(myapp ...)
...
qt_add_translations(myapp)
\endcode
creates the full translation files
\list
\li \c{myapp_en.ts}
\li \c{myapp_de.ts}
\endlist

\section1 Options

You can specify the name of the custom target that calls lupdate with the \c
LUPDATE_TARGET option. Likewise, \c LRELEASE_TARGET controls the name of the
custom target that drives the call to \c lrelease.

You can set additional options for \l{lupdate} and \l{lrelease} with
\c{LUPDATE_OPTIONS} and \c{LRELEASE_OPTIONS}. You can find possible options in
the \l{lupdate options} and \l{lrelease options}.

For example, to use \l{Text ID based translations}{ID based translations}, you
need to pass \c{LRELEASE_OPTIONS -idbased} to \c qt_add_translations.

By default, the \c{.qm} files will be placed in the current build directory
(\c{CMAKE_CURRENT_BINARY_DIR}). To change this, you can set \c{OUTPUT_LOCATION}
as a property of the source \c{.ts} file.

For example, with the following code, the \c{.qm} files are generated
in a \c{translations} directory below the current build directory.

\snippet cmake-macros/examples.cmake set_output_location_on_ts_file

\section1 Embedding Generated .qm Files in Resources

By default, the generated \c{.qm} files are embedded in a Qt resource that will
be linked into the targets passed with \c{TARGETS}. The files in the resource
are accessible under the resource prefix \c{"/i18n"}.

You can set the resource prefix with \c{RESOURCE_PREFIX}.

In a static Qt build, when a resource target is created, additional targets can
be created. You can instruct \c{qt_add_translations} to store these targets in a
variable, by passing \c{OUTPUT_TARGETS <variable-name>}.

If \c OUTPUT_TARGETS is used, either \c IMMEDIATE_CALL or \c SOURCE_TARGETS must
be specified.

The automatic resource embedding can be turned off by giving the
\c{QM_FILES_OUTPUT_VARIABLE} option, followed by the name of a variable in which
the command should store the list of generated \c{.qm} files.

\section1 \c{qt_add_translations} before Qt 6.7

Before Qt 6.7, this command accepted only one target as the first argument. This
target was used for both, extracting translatable sources and embedding \c{.qm}
files.

Since Qt 6.7, the target in the first argument is not used for source extraction
anymore.

\section1 Examples

Add a German and a French translation to the target \c{frogger} using
\c{qt_add_translations}:

\snippet cmake-macros/examples.cmake qt_add_translations_default

This will create the \c{.ts} files \c{frogger_de.ts} and \c{frogger_fr.ts} in
the source directory. \l lupdate sees the source files of all targets that are
eligible for translation, according to the rules of \l
qt_collect_translation_source_targets.

The \c{.qm} files that are created from the \c{.ts} files
are embedded in the \c frogger_game target under the resource prefix \c{"i18n"}.

The \c qt_add_translations call in the above example is roughly equivalent to
the following:

\snippet cmake-macros/examples.cmake qt_lupdate_lrelease

\section2 Excluding directories, targets, and sources

You can exclude targets and directories from the automatic collection of source
targets. The following excludes the target \c helper_lib and everything under
the \c tests directory. See the \l{directory property
QT_EXCLUDE_FROM_TRANSLATION} and the \l{target property
QT_EXCLUDE_FROM_TRANSLATION}.

\badcode
# <project_root>/CMakeLists.txt
qt_add_translations(frogger_game)
\endcode

\badcode
# <project_root>/src/helper_lib/CMakeLists.txt
qt_add_library(helper_lib STATIC helpers.cpp)
set_property(TARGET helper_lib PROPERTY QT_EXCLUDE_FROM_TRANSLATION ON)
\endcode

\badcode
# <project_root>/tests/CMakeLists.txt
add_subdirectory(behavior_tests)
add_subdirectory(physics_tests)
set_directory_properties(PROPERTIES QT_EXCLUDE_FROM_TRANSLATION ON)
\endcode

In the following example, we exclude source files that are part of the \c
frogger_game target using the \l QT_EXCLUDE_SOURCES_FROM_TRANSLATION target
property:

\badcode
qt_add_executable(frogger_game
    main.cpp
    3rdparty/jumpsim.cpp
    3rdparty/frogmath.cpp
)
set_property(TARGET frogger_game
    PROPERTY QT_EXCLUDE_SOURCES_FROM_TRANSLATION "3rdparty/*"
)
\endcode

\section2 Explicit specification of source targets

If you don't want to use the automatic collection of source targets you can
specify the source targets explicitly:

\snippet cmake-macros/examples.cmake qt_add_translations_explicit_source_targets

\section2 Custom resource prefix

Now, let's embed the \c{.qm} files in \c frogger_game and \c
frogger_level_editor and set a custom resource prefix.

\snippet cmake-macros/examples.cmake qt_add_translations_resource_prefix

\section2 Installing .qm files

Instead of embedding the \c{.qm} files we can install them as regular files:

\snippet cmake-macros/examples.cmake qt_add_translations_install

\section2 Influencing the names of the .ts files

Place the \c{.ts} files in a \c translations directory and change the base name
to \c frogger_i18n:

\badcode
qt_standard_project_setup(I18N_TRANSLATED_LANGUAGES de fr)
...
qt_add_translations(frogger
    TS_FILE_BASE froggo
    TS_FILE_DIR translations
)
\endcode

This creates the following files
\list
\li \c translations/froggo_de.ts
\li \c translations/froggo_fr.ts
\endlist

You can also specify the paths explicitly:
\badcode
qt_add_translations(frogger
    TS_FILES translations/froggo_de.ts translations/froggo_fr.ts
)
\endcode

*/

/*!
\page qtlinguist-cmake-qt-collect-targets-for-translation.html
\ingroup cmake-commands-qtlinguisttools

\title qt_collect_translation_source_targets
\target qt6_collect_translation_source_targets

\summary {Collects targets that are eligible for translation.}

\include cmake-find-package-linguisttools.qdocinc

\cmakecommandsince 6.7

\section1 Synopsis

\badcode
qt_collect_translation_source_targets(out_var [DIRECTORY path])
\endcode

\versionlessCMakeCommandsNote qt6_collect_translation_source_targets()

\section1 Description

Collect targets that are eligible for translation in the given \c DIRECTORY and
all subdirectories. If \c DIRECTORY is not specified, start the target
collection at \c{CMAKE_CURRENT_SOURCE_DIR}.

The command stores the list of targets in the variable that is specified as
first argument.

\section1 Excluding targets from translation

By default, all non-imported executable and library targets are eligible for
translation.

Single targets can be excluded by setting the \l{target property
QT_EXCLUDE_FROM_TRANSLATION}.

Targets below a certain directory can be excluded by setting the \l{directory
property QT_EXCLUDE_FROM_TRANSLATION}.

\section1 When to call this command

The \c qt_collect_translation_source_targets command reads the
\l{https://cmake.org/cmake/help/latest/prop_dir/BUILDSYSTEM_TARGETS.html}{BUILDSYSTEM_TARGETS}
directory properties. As a consequence, it only collects targets that already
have been created. Targets that are created after \c
qt_collect_translation_source_targets has been called are not collected.

To collect all targets of the build system, call \c
qt_collect_translation_source_targets at the end of the top-level \c
CMakeLists.txt or use \c{cmake_language(DEFER CALL)} to set up i18n at the end
of the top-level directory scope.

\section1 Examples

Use the result of \c qt_collect_translation_source_targets as input for \c
qt_add_lupdate.

\snippet cmake-macros/examples.cmake qt_collect_translation_source_targets

With CMake 3.19 and above, you can collect the source targets at the end of the
directory scope. This way, \c qt_collect_translation_source_targets can be
called before all targets have been defined. However, you need to exclude the
tests by setting the directory property \l{directory property
QT_EXCLUDE_FROM_TRANSLATION}{QT_EXCLUDE_FROM_TRANSLATION} to \c{ON}.

\snippet cmake-macros/examples.cmake qt_collect_translation_source_targets_deferred
*/