cmake 2.6.2 now required - changes in handling shared libs

[Alexander Neundorf]

Hi,

as of now cmake 2.6.2 is required to build KDE4 trunk.

This brings some bugfixes, some nice features and one relatively big change, 
which concerns shared library handling.

Warning: if you get linker errors or errors related to different build 
types/configurations (i.e. debug vs. release etc.) please let me know .


Now straight on to the big change(TM).

Short version:
In kdelibs, when creating a shared lib, now also add the arguments
"EXPORT kdelibsLibraryTargets" to the install(TARGETS ...) command, like this:

install(TARGETS threadweaver EXPORT kdelibsLibraryTargets
                             ${INSTALL_TARGETS_DEFAULT_ARGS})

And to define a minimal link interface, do this:

target_link_libraries(threadweaver
                              LINK_INTERFACE_LIBRARIES ${QT_QTCORE_LIBRARY} )


Now the long version (you should read it):

The correct way to create and install a shared library is now:

kde4_add_library(kfoo SHARED ${kfooSources} ) 
target_link_libraries(kfoo kdecore ${QT_QTCORE_LIBRARY} ${ZLIB_LIBRARY})

# No changes so far, but the next line is new.
# It specifies to which libraries other targets will be linked which 
# link to libkfoo. By default these are all libraries kfoo links against,
# which can lead to some unnecessary dependencies, slower startup, etc.
# So we now specifiy which "link interface" the library kfoo has, ZLIB
# is used only internally, so users of kfoo don't have to link against it:

target_link_libraries(kfoo LINK_INTERFACE_LIBRARIES 
                           kdecore ${QT_QTCORE_LIBRARY})

# Next change: shared libraries are now exported as targets, i.e. for every
# library target a snippet of cmake code is created which can be included by 
# other cmake-using projects, and there this code will create "imported"
# library targets. E.g. here we have the target kfoo, which can be referenced
# within this project simply by its name "kfoo". With the exported (and then
# imported) targets this is now also possible in external projects. 
# In order to have a target "exported", it must be installed and be marked as 
# belonging to an "export set", which can be assigned arbitrary names, here I
# decided to name it "MyKFooExports":

install(TARGETS kfoo EXPORT MyKFooExports ${INSTALL_TARGETS_DEFAULT_ARGS})

# The command above basically tells cmake to create the mentioned script
# snippets. Now these must actually be installed themselves, so the following
# command does that for all targets which have been marked as belonging to 
# "MyKFooExports":
install(EXPORT MyKFooExports DESTINATION ${DATA_INSTALL_DIR}/cmake/modules
                             FILE MyKFooExportedLibraryTargets.cmake )


Alex