[CMake] find_package REQUIRED ignores OPTIONAL_COMPONENTS

[Alexander Stein]

On Tuesday 08 March 2016, 10:00:00 wrote Nicholas Braden:
> Jakob, I don't think there is any confusion about what REQUIRED means.
> Whether or not REQUIRED is provided, the list of OPTIONAL_COMPONENTS
> should not be required under any circumstances. The example error
> message seems pretty clear to me that the expected behavior and actual
> behavior are different. I went and looked at the source code of the
> find module:
> 
> https://github.com/Kitware/CMake/blob/master/Modules/FindQt4.cmake
> 
> It seems that there is no check whatsoever for
> Qt4_FIND_REQUIRED_<component>, so the find module just blindly assumes
> that all components are required.
> 
> More info: https://cmake.org/cmake/help/latest/manual/cmake-developer.7.html#find-modules
> 
> To me this seems like a bug in the find module.

Yep, FindQt4.cmake doesn't support OPTIONAL_COMPONENTS which seems only to work if FIND_PACKAGE_HANDLE_STANDARD_ARGS is called with HANDLE_COMPONENTS passed. This is not the case and does not work. I guess due to different naming scheme used for components. AFAICS they have to be e.g. Qt4_QtCore_FOUND, but not QT_QTCORE_FOUND.

Best regards,
Alexander