[CMake] Proposal: extra option PRIVATE for target_link_libraries

[Alexander Neundorf]

On Wednesday 23 December 2009, Michael Wild wrote:
> On 23. Dec, 2009, at 15:03 , Alexander Neundorf wrote:
> > On Wednesday 23 December 2009, Michael Wild wrote:
> >> On 23. Dec, 2009, at 14:36 , Alexander Neundorf wrote:
> >>> On Wednesday 23 December 2009, Marcel Loose wrote:
> >>>> Hi all,
> >>>>
> >>>> I suggested this in the quite long thread "third party library
> >>>> dependencies", but it may have been overlooked. Hence, I started a new
> >>>> thread.
> >>>>
> >>>> Upon (re)reading the Mandriva page
> >>>> http://wiki.mandriva.com/en/Overlinking, I was thinking: maybe the
> >>>> issue of overlinking can be solved more or less the same way as
> >>>> pkg-config does: i.e. by defining private dependencies. This could be
> >>>> an extra option to target_link_libraries.
> >>>> Something like:
> >>>>
> >>>> target_link_libraries(mylib public1 public2 PRIVATE private1 private2)
> >>>
> >>> Assuming that public1 and public2 are libraries also built with cmake,
> >>> that can be done already today:
> >>>
> >>> add_library(public1 ...)
> >>> target_link_libraries(public1 private1)
> >>> target_link_libraries(public1 LINK_INTERFACE_LIBRARIES "")
> >>>
> >>> add_library(public2 ...)
> >>> target_link_libraries(public2 private2)
> >>> target_link_libraries(public2 LINK_INTERFACE_LIBRARIES "")
> >>>
> >>> install(TARGETS public1 public2 ... EXPORT MyPublicLibs)
> >>> install(EXPORT ...)
> >>>
> >>>
> >>> Then later on, when loading these exported targets, you will get what
> >>> you want. If public1/2 are shared libs, their "link interface" will be
> >>> empty. If they are static, you will link against everything they have
> >>> been "linked" against, independent of the LINK_INTERFACE_LIBRARIES
> >>> (which is used only for shared libs).
> >>>
> >>> Alex
> >>
> >> So, the last step in doing
> >>
> >> add_library(public1 ...)
> >> add_library(public2 ...)
> >> target_link_libraries(public2 public1 private1)
> >> target_link_libraries(public2 LINK_INTERFACE_LIBRARIES public1)
> >>
> >> is equivalent to
> >>
> >> set_target_properties(public2 PROPERTIES LINK_INTERFACE_LIBRARIES
> >> "public1")
> >>
> >> Am I right?
> >
> > Yes, but if you use
> > target_link_libraries(public2 LINK_INTERFACE_LIBRARIES public1)
> > it can handle the "optimized" and "debug" keywords, which may be
> > contained in some of the _LIBRARY/_LIBRARIES variables.
> >
> >> So, this should definitely go somewhere on the Wiki, that when one
> >> creates a project that does an install(EXPORT ...) and provides a
> >> XXX-config.cmake file, that one should carefully use
> >> target_link_libraries(...
> >> LINK_INTERFACE_LIBRARIES ...) to make things play nicely.
> >>
> >> This doesn't solve the problem for non-cmake built libraries which are
> >> discovered through FindXXX.cmake modules, though.
> >
> > Well, partly. The FindXXX.cmake module can also set up the library as an
> > imported target and set the respective properties manually.
> > But I'm not aware of any Findxxx.cmake module which does that currently.
> >
> > Alex
>
> That's what I've been referring to earlier in this thread... The only catch
> with IMPORTED targets I can make out is that if the author of the
> FindXXX.cmake module uses a common name for the target, that it might clash
> with a target name in the client project. Perhaps the FindXXX.cmake module
> could do (here the case for zlib)
>
> find_library(ZLIB_LIBRARY z)
> # TODO detect whether it is static or shared
> add_library(ZLIB_z SHARED IMPORTED)
> set_target_properties(ZLIB_z PROPERTIES IMPORTED_LOCATION "${ZLIB_LIBRARY})
> # TODO set up IMPORTED_LINK_INTERFACE_LIBRARIES
> set(ZLIB_LIBRARIES "ZLIB_z")
>
>
> What do you think? 

Yes, it should do exactly that.
When exporting libraries, you can have the same effect by specifying a 
NAMESPACE option with install(EXPORT ... )

About shared or static... I think this is currently hard to do in cmake, AFAIK 
since it is hard to figure out whether a lib file on Windows is for a shared 
are static library.

Alex