[cmake-developers] TargetLinkLibraries on OBJECT-libraries

[Patrick Boettcher]

Hi,

I'd like to use target_link_libraries() on an OBJECT-library for the
following reason:

I'm creating an OBJECT-library which has quite some requirement
regarding include-dirs, compile-options and -definitions. Which is why
my CMakeLists.txt currently looks somehow like this: (runtime is an
interface-library)

  add_library(runtime-main OBJECT runtime.cpp)

  target_include_directories(runtime-main
    PRIVATE 
      $<TARGET_PROPERTY:runtime,INTERFACE_INCLUDE_DIRECTORIES>)

  target_compile_features(vsora-runtime-main
    PRIVATE
      $<TARGET_PROPERTY:runtime,INTERFACE_COMPILE_FEATURES>)

  target_compile_options(vsora-runtime-main
    PRIVATE
      $<TARGET_PROPERTY:runtime,INTERFACE_COMPILE_OPTIONS>)

  target_compile_definitions(vsora-runtime-main
    PRIVATE
      $<TARGET_PROPERTY:runtime,INTERFACE_COMPILE_DEFINITIONS>)

I think the last 4 commands could be factored in a simple call to 

  target_link_libraries(runtime-main INTERFACE runtime)

    (INTERFACE would have to be used even when the to be linked
    library is not an INTERFACE library)

or

  target_link_libraries(runtime-main PRIVATE runtime)

or 

  target_link_libraries(runtime-main OBJECT runtime)

I started looking into the code, except removing the check in
cmTargetLinkLibraries.cpp I didn't do much. And this does not make it
work. 

Before continuing I'd like to know whether this is a good idea to work
on or if there are good arguments to never allow "linking" an
object-library to get compile information from other libraries?

best regards,
--
Patrick.