[CMake] Using find_package() portably?

[Carsten Fuchs]

Hello Johannes,

Am 2017-11-22 um 12:03 schrieb Johannes Zarl-Zierl:
> The problem in this specific case is that CMake ships with a FindJPEG module
> that does not define modern import libs, but uses the old way of defining
> <PACKAGE>_LIBRARIES and <PACKAGE>_INCLUDE_DIRS.
> IMO this highlights one of the main problems with find modules: nobody really
> maintains them.
> 
> If JPEG had proper imported targets, your code could look like this:
> [...]
> You just have to make sure that your shipped libjpeg creates the proper
> namespaced target:
> add_library(JPEG ...)
> add_library(JPEG::JPEG ALIAS JPEG)

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 ???>)

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,

   - or write my `../ExtLibs/libjpeg/CMakeLists.txt` so that it globally 
defines JPEG_LIBRARIES and JPEG_INCLUDE_DIRS

Is that right?

Best regards,
Carsten