[CMake] providing library information, what's the cmake way

[Alexander Neundorf]

On Tuesday 23 November 2010, Johannes Zarl wrote:
> Sorry for hijacking this thread, but I'm wondering about this for some
> time, too. (And the information in the doc/wiki is somewhat dated and/or
> ambiguous [1,2,3,4]). I will just go on and write my thoughts and what I
> (think I) know, in the hope that somebody corrects those things I got
> wrong.
>
> So summarizing the previous mesage in the thread, one can say:
>  + cmake aware packages should provide LibraryConfig.cmake scripts
>    (and optionally LibraryVersion.cmake scrips), just like they would
>    provide pkg-config files.
>  + developers should create FindLibrary.cmake scripts for packages
>    they are using that are not cmake aware.

Yes.

> I think that information should be transported more clearly, because
> in practice most cmake based software provides a FindLibrary.cmake
> file for itself.

If that's the case, that's wrong.

> Also, I could not find a definitive answer on where these packages
> should put the LibraryConfig.cmake script. If I read the search paths in
> [1] correctly, the preferred paths are:
>  + <prefix>/ on windows
>  + <prefix>/(share|lib)/cmake/<name>*/ on linux, and
>  + <prefix>/<name>.framework/Resources/ on Apple

Yes.

> We have have every library and library-version in its own prefix and use
> shell modules[5] to provide the correct environment that a user wants.
> Is there any way to let cmake know about specific prefix directories it
> should be aware of? Unfortunately, the CMAKE_MODULE_PATH variable has
> to be manually set, and not influenced by the environment.

CMAKE_MODULE_PATH is only for finding Find-modules, not for finding the actual 
packages or Config-files.
For that you can set CMAKE_PREFIX_PATH. CMake uses each directory contained in 
CMAKE_PREFIX_PATH for all its find_program/file/path/library/package() calls 
to search in the respective subdirectories for the 
executables/files/libraries/Config-files.

> Something like the PKG_CONFIG_PATH environment variable for pkg-config
> would be really nice to have in cmake.
>
> Another somehow related topic seems to be import/export of targets. Should
> a LibraryConfig.cmake or FindLibrary.cmake file create imported targets
> for the library?

Yes.

> And is there any documentation on how to create a LibraryConfig.cmake file
> with support for components?

In KDE we have a macro MACRO_WRITE_BASIC_CMAKE_VERSION_FILE() which helps with 
creating a basic version-info file which should be installed along with the 
Config-file.
It consists of MacroWriteBasicCMakeVersionFile.cmake and 
BasicFindPackageVersion.cmake.in which you can find in 
http://websvn.kde.org/trunk/KDE/kdelibs/cmake/modules/ .

Alex