How to include external (shared) library with several dlls/dylibs - c++

Question

I need to integrate an externally built (shared) library as a logical
build target into my CMake configuration which consists of several
shared library files (dlls/dylibs).
Usually I'd do the following:
find_path(MyLib_INCLUDE_DIR mylib.h HINTS ${MyLib_PATH}/include)
find_library(MyLib_LIBRARY NAMES MyLib HINTS ${MyLib_PATH}/bin)
find_library(MyLib_LIBRARY_DEBUG NAMES MyLib_d ${MyLib_PATH}/bin)
include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(MyLib DEFAULT_MSG
MyLib_LIBRARY MyLib_LIBRARY_DEBUG MyLib_INCLUDE_DIR)
if(MyLib_FOUND AND NOT TARGET MyLib::MyLib)
set(MyLib_LIBRARIES ${MyLib_LIBRARY})
set(MyLib_INCLUDE_DIRS ${MyLib_INCLUDE_DIR})
add_library(MyLib::MyLib UNKNOWN IMPORTED)
set_target_properties(MyLib::MyLib PROPERTIES
INTERFACE_INCLUDE_DIRECTORIES ${MyLib_INCLUDE_DIR}
IMPORTED_LOCATION ${MyLib_LIBRARY}
IMPORTED_LOCATION_DEBUG ${MyLib_LIBRARY_DEBUG})
mark_as_advanced(MyLib_INCLUDE_DIR MyLib_LIBRARY MyLib_LIBRARY_DEBUG)
endif()
My understanding is that add_library(... UNKOWN IMPORTED) will CMake
figure out shared/static libraries by itself (and based on the option
BUILD_SHARED_LIBS probably, but this shouldn't be necessary). However,
CMake doesn't allow to add a list of libraries to the property
IMPORTED_LOCATION. For Instance, in case I want to import MyLib,
MyLibFoo and MyLibBar both as debug and release builds, this is not
possible using the listed approach.
I'm aware of add_library(MyLib::MyLib INTERFACE IMPORTED) and set a
list of libraries to the property INTERFACE_LINK_LIBRARIES, but this
is problematic in the case of creating relocatable packages (as
mentioned in the CMake documentation). Furthermore, there's no such
property as INTERFACE_LINK_LIBRARIES_DEBUG, thus it would only be
possible to refer to either the release or debug builds of my
externally imported library.
So, how am I supposed to import my externally built library as an
relocatable-ready logical CMake target which actually includes several
either debug or release build shared library files?
Disclaimer: I've already asked this on the CMake mailing list, but haven't received any answer so far.

Answer 1

However, CMake doesn't allow to add a list of libraries to the property IMPORTED_LOCATION.
This is logical, because a single library (even IMPORTED) should have a single file.
Just create a library IMPORTED target per actual library:
add_library(MyLib::MyLibFoo UNKNOWN IMPORTED)
set_target_properties(MyLib::MyLibFoo PROPERTIES
INTERFACE_INCLUDE_DIRECTORIES ${MyLibFoo_INCLUDE_DIR}
IMPORTED_LOCATION ${MyLibFoo_LIBRARY}
IMPORTED_LOCATION_DEBUG ${MyLibFoo_LIBRARY_DEBUG})
add_library(MyLib::MyLibBar UNKNOWN IMPORTED)
set_target_properties(MyLib::MyLibBar PROPERTIES
INTERFACE_INCLUDE_DIRECTORIES ${MyLibBar_INCLUDE_DIR}
IMPORTED_LOCATION ${MyLibBar_LIBRARY}
IMPORTED_LOCATION_DEBUG ${MyLibBar_LIBRARY_DEBUG})
And create a single INTERFACE IMPORTED library target, which links above targets:
add_library(MyLib::MyLib INTERFACE IMPORTED)
set_property(TARGET MyLib::MyLib PROPERTY
INTERFACE_LINK_LIBRARIES MyLib::MyLibFoo MyLib::MyLibBar)
So, when user links MyLib::MyLib, he actually links all of your libraries.