[CMake] Qt translation handling

[angroyer]

Bonjour Francis,

thank you for sharing this snippet.

I have read thoroughly your example and tried it but it seems to me that
this snippet is similar to the qt5_create_translation() function.

First of all, with cmake >= 3.0.0 and AUTORCC set to ON, adding
${CMAKE_CURRENT_BINARY_DIR}/translations.qrc in add_executable() make the
executable depends on the translations.qrc and make also translations.qrc
depends on the files listed in the translations.qrc. So everytime a .qm
listed in translations.qrc changes, the qrc_translations.cpp is created and
compiled. So, it is not necessary to add ${QM_FILES} in the add_executable()
statement.

So, with your piece of code:
 * ${CMAKE_CURRENT_BINARY_DIR}/translations.qrc in add_executable make App
depend on the qrc_translations.qrc and qrc_translations.qrc depend on files
listed in qrc_translations.qrc
 * each .qm file is dependent on a .ts file: statement qt5_add_translation()
 * each .ts file is dependent on ${TS_SOURCES}: statement
add_custom_command()

So everytime a file listed in ${TS_SOURCES} changes, the .ts is rebuilt, the
.qm is rebuilt and the qrc_translations.cpp is compiled. You could have
obtained the same thing with:

set(TS_FILES
    ${CMAKE_CURRENT_SOURCE_DIR}/translations/app_fr.ts
)
file(GLOB_RECURSE TS_SOURCES "*.cpp" "*.h" "*.ui")
qt5_create_translation(QM_FILES ${TS_FILES} ${TS_SOURCES})

configure_file(translations.qrc ${CMAKE_CURRENT_BINARY_DIR} COPYONLY)
add_executable(App
    ${CMAKE_CURRENT_BINARY_DIR}/translations.qrc
)

and translations.qrc containing:
<RCC>
    <qresource prefix="/">
        <file>gui_fr.qm</file>
    </qresource>
</RCC>

I have tested with cmake 3.16.1.

It is worth mentioning that the Qt documentation:
https://doc.qt.io/qt-5/qtlinguist-cmake-qt5-create-translation.html
indicates:
qt5_create_translation(QM_FILES ${CMAKE_SOURCE_DIR} helloworld_en.ts
helloworld_de.ts)
without passing the list of source/headers files. So the .ts files are
reconstructed when the date of the source folder changes but not for the
date of the subdirectories. The date of the source folder changes when some
files are created/removed/modified in the directory but not for the files in
subdirectories.

This could leads to errors since the .ts files would not be rebuilt when a
file in a subdirectory change. So changing from branch to branch might
change the date of the source folder and regenerates the .ts files.

What do you think ?

In case you want to keep the .qm files in your source folder, you could
indicate to the cmake rule where to generate the .qm file with the
OUTPUT_LOCATION:
set_source_files_properties(${TS_FILES} PROPERTIES OUTPUT_LOCATION
${CMAKE_SOURCE_DIR}/translations)
See https://doc.qt.io/qt-5/qtlinguist-cmake-qt5-add-translation.html
It works also for qt5_create_translation() that calls in turn the
qt5_add_translation().

And so you do not need to copy the translations.qrc to the build folder. The
code becomes:

set(TS_FILES
    ${CMAKE_CURRENT_SOURCE_DIR}/translations/app_fr.ts
)
set_source_files_properties(${TS_FILES} PROPERTIES OUTPUT_LOCATION
${CMAKE_CURRENT_SOURCE_DIR}/translations)
file(GLOB_RECURSE TS_SOURCES "*.cpp" "*.h" "*.ui")
qt5_create_translation(QM_FILES ${TS_FILES} ${TS_SOURCES})

add_executable(App
    translations/translations.qrc
)

and translations/translations.qrc containing:
<RCC>
    <qresource prefix="/">
        <file>gui_fr.qm</file>
    </qresource>
</RCC>

Cordialement,
Anthony




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