finding software with cmake

[Alexander Neundorf]

Hi,

I just committed a change to FindKDE4Internal.cmake so that more directories 
are searched by default by the FIND_XXX() commands.
Now also always the directories in the current install prefix and in the 
install location of the currently running cmake will be searched. This will 
be also the case starting with the next major cmake release, maybe already 
starting with 2.4.8.

Additionally the kde4 install directories are now also searched by default.

So e.g. if you install cmake and e.g. kdesupport stuff (like strigi) to 
$HOME/bin, lib and include and kde4 to $HOME/kde4/bin, lib and include, 
everything in these directories will now be found automatically, e.g.

find_library(STRIGI_STREAMANALYZER_LIBRARY NAMES streamanalyzer)

would in this case work because it would be in $HOME/lib and cmake would be in 
$HOME/bin.

Regarding pkgconfig:
it is useful, but it has issues.
-it doesn't exist on all platforms
-it doesn't work correctly if PKGCONFIG_PATH isn't set up correctly
-the information for the libraries can be used only as additional hint, 
because cmake should get only libraries with the full path, e.g. libs which 
were found using FIND_LIBRARY(). If e.g. the link flags from pkgconfig are 
simply given to cmake using TARGET_LINK_LIBRARIES() cmake can't check for 
conflicting libraries and so can't sort the link directories correctly.

It is a good thing to use pkgconfig as additional source of information, but 
not more.

Instead, if even with the changes above some stuff isn't found by the 
FIND_XXX() commands, you can set the CMAKE_INCLUDE_PATH, CMAKE_PROGRAM_PATH 
and  CMAKE_LIBRARY_PATH environment variables to tell cmake about additional 
directories where FIND_XXX() should search.

About searching software which has been built with cmake:
kdelibs install a file KDELibsDependencies.cmake to share/apps/cmake/modules/, 
this will stop one of the next mondays, then the file will be installed only 
as "KDE4Config.cmake" to lib/kde4/cmake/.
Any software built with cmake can install such a file which contains 
information about itself, e.g. lib dependencies, include dirs, the version, 
compile flags, etc.
Since these are machine dependent, they should be installed under lib/. 
Software which wants to use that software can then simply include() this file 
in its own cmake files to get all the information (of course the file has to 
be found first...)

In one of the future cmake releases the FIND_PACKAGE() command will support 
these files, if you look at the current documentation for FIND_PACKAGE() you 
will notice that FooConfig.cmake is mentioned, but only under special 
circumstances. This will be extended so it becomes much easier to use 
software built with cmake with other cmake projects.

Bye
Alex

P.S. did you know about the "edit_cache" and "rebuild_cache" make targets ?
The first one starts ccmake on the current project, the second one reruns 
cmake on the current project -> easier than typing these commands manually