cmake 2.6.2 now required - changes in handling shared libs

[Alexander Neundorf]

On Tuesday 25 November 2008, Ben Boeckel wrote:
> On Monday 10 November 2008 19:00:50 Alexander Neundorf wrote:
> > 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
> >
> > >> Visit http://mail.kde.org/mailman/listinfo/kde-devel#unsub to
> > >> unsubscribe <<
>
> Hi,
>
> I am developing a project that uses KDE4 and I am trying to get the
> CMakeLists.txt to conform to the changes made upstream. I made the change
> to one of my libraries, but when I try to do it on another library which
> requires it, it errors with:
>
> CMake Error: INSTALL(EXPORT "sigmod_EXPORTS" ...) includes target "sigmod"
> which requires target "sigcore" that is not in the export set.

This means you expüort the target "sigmod" which links to "sigcore", 
but "sigcore" is not exported. 
Is sigcore a shared library ?
Then you should export it too.

Exporting targets is only useful if you install shared libs which should be 
used by other projects. Is that the case for you ?

Alex