[oe] [meta-qt5] Problems with Qt5 and CMake

[Manuel Nickschas]

On Monday 10 June 2013 20:32:27 Stefan Herbrechtsmeier wrote:
> Am 10.06.2013 16:09, schrieb Manuel Nickschas:
> > On Friday 24 May 2013 16:56:41 Stefan Herbrechtsmeier wrote:
> >> All paths in the target sysroot represents the path on the target. They
> >> should be
> >> adapted via an variable or automatically detected during runtime.
> > 
> > What would be the proper way of doing this in the CMake files shipped 
by
> > Qt5?
> > 
> > /usr/bin/qt5/moc is hard-coded. We could prepend that with
> > ${STAGING_DIR_NATIVE} maybe, which could be exported (via
> > EXTRA_OECMAKE) by recipes so it's picked up by CMake, and it would
> > resolve to nothing if it's not set (so the CMake file would still work
> > outside of Bitbake).
> 
> You can try to import the executable from a file passed via -P parameter
> to cmake. I'm not sure if this works.

It does not; -P is for processing a cmake script (see -E), but you can't use it 
to prepend a normal cmake file, unfortunately. I didn't find any other option 
that would allow to do that, either.

> add_executable(Qt5::rcc IMPORTED)
> set_target_properties(Qt5::rcc PROPERTIES IMPORTED_LOCATION
> "${STAGING_BINDIR_NATIVE}/rcc4")

This gave me the idea for an ugly workaround at least; I can overwrite the 
location in my project's CMakeLists.txt after processing 
find_package(Qt5Core). Or I could check if something like qtpaths.cmake 
exists in the source dir and include that conditionally at this point.

To avoid Yocto-specific hacks ending up in the upstream repo, I think the 
best workaround for now would be to have my recipe patch the 
CMakeLists.txt to include a generated file that overwrites the locations.

But this really should be properly fixed in meta-qt5, by modifying the 
relevant *Config.cmake files in such a way that the native tools are used 
when something is built by Bitbake (e.g. by setting some variable), and the 
target tools in case someone compiles manually on the target. We 
shouldn't force developers to have to include hackish workarounds in their 
own recipes, or worse, their upstream code. With the proliferation of Qt5 in 
the embedded space, and the fact that CMake is the de-facto build system 
for Qt-based things these days, it's a problem that will come up quite often 
in the future and deserves a global solution.

Cheers,
~ Sput
-- 
Manuel "Sput" Nickschas * Development Specialist, Team GENIVI
BMW Car IT GmbH * http://www.bmw-carit.de
Embedded Software House Ulm * Lise-Meitner-Str. 14 * 89081 Ulm
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