Handling of frameworks using Qt-based translations

[Aurélien Gâteau]

Hi,

I started working on how to handle Qt based translations, and make it as
simple as possible to work with for framework maintainers as well as
framework users.

I picked KBookmarks as my guinea pig and got to the point where
kbookmarkdialogtest shows a translated dialog.

Here is how it currently works. All of this is liberally inspired from
the way Trojita works:

# String extraction

I created a src/Messages.sh which contains the following:

lupdate -silent -recursive . -ts $podir/tmp.ts
lconvert $podir/tmp.ts --sort-contexts --output-format pot -o
$podir/kbookmarks5.pot
rm $podir/tmp.ts

# String compilation

I modified the toplevel CMakeLists.txt, adding these lines:

if (EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/po)                               
    include(${CMAKE_CURRENT_SOURCE_DIR}/QmSupport.cmake)                 
    qm_setup(kbookmarks5 po)                                             
endif() 

I created a QmSupport.cmake file, which exposes a qm_setup() function.
This function does three things:
1. Create a "qm" target which turns all .po into .qm files.

2. Call install(FILES...) on the generated qm files, installing them in
share/${name}/locale, where ${name} is the firt argument of qm_setup().

3. Generate a "${name}_translation.h" which contain two inline functions
to make it easy to load the translations.
Using the translation is then just a matter of including
${name}_translation.h and calling ${name}_installTranslator(). If more
control is needed, ${name}_installTranslator() also accepts an optional
argument: the language. For even finer control, the .h also contains a
${name}_createTranslator() function, which returns a QTranslator loaded
with strings for the right language.

# Questions

Does this approach sounds sane to you?

I think QmSupport.cmake should go to extra-cmake-modules. Any
objections?

Right now qm_setup() is very inflexible: it installs files and creates
the _translation.h file based on the name argument, meaning in my
example it creates share/kbookmarks5/locale/kbookmarks5_*.qm and
include/kbookmarks5_translation.h, which contains the functions
kbookmarks5_createTranslator and kbookmarks5_installTranslator.

I think we want to be able to customize the install dir of the
_translation.h file because some frameworks install header files in a
subdir, others do not.

Should we also be able to customize the install data dir for qm files,
as well as the prefix of the function names from _translation.h? I am
tempted to default to ${PROJECT_NAME} for the prefix of the function
names, its lowercase version for the install data dir and add an
optional PROJECT_NAME argument to qm_setup(). Opinions?

I am attaching the diff of the current state. I do not intend to commit
it as is since po files are not supposed to be in the framework
repository, but it should make it easy for you to try it if you are
interested.

Aurélien
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