[CMake] Using find_package() portably?

[Florent Castelli]

On 29/11/2017 12:02, Johannes Zarl-Zierl wrote:
> Hello Carsten,
>
> On Samstag, 25. November 2017 11:46:44 CET Carsten Fuchs wrote:
>> Thanks for your reply, but how can I proceed from here?
>>
>> In order to be able to write in the parent script something that works
>> in either case, that is,
>>
>> target_link_libraries(main_program <either JPEG::JPEG or ${JPEG...} or ???>)
> Well, that's one way, but that doesn't really provide any benefit above the
> original solution (i.e. just define the JPEG_INCLUDES and JPEG_LIBRARIES
> variables accordingly).
>
>> it seems that I either
>>
>>     - have to make a copy of FindJPEG.cmake, customize it to define
>> target JPEG::JEPG and ship it along with my project,
> Either that or you define it yourself:
> find_package(JPEG)
> if (JPEG_FOUND)

I'd say "if(JPEG_FOUND AND NOT TARGET JPEG::JPEG)"
If someone improves FindJPEG.cmake, you won't break your build.

>   add_library(JPEG::JPEG UNKNOWN IMPORTED)
>   set_property(
>    TARGET JPEG::JPEG
>    PROPERTY IMPORTED_LOCATION ${JPEG_LIBRARIES}
>    )
>   set_property(
>    TARGET JPEG::JPEG PROPERTY
>    INTERFACE_INCLUDE_DIRECTORIES ${JPEG_INCLUDES}
>   )
> endif()
>
> I admit it's not a huge benefit over just using the variables. The advantages:
> - you get slightly better error handling
> - your target_link_libraries commands are slightly more readable.
>
>>     - or write my `../ExtLibs/libjpeg/CMakeLists.txt` so that it globally
>> defines JPEG_LIBRARIES and JPEG_INCLUDE_DIRS
> That will work, too.
>
>
> Cheers,
>    Johannes
>