[CMake] Cmake Boost::boost target PRIVATE link, forcing dependency on client

[rmawatson rmawatson]

I am having a problem with make 3.12 (windows) and cmake version 3.13.0-rc2 (linux). I am attempting to link boost headers privately to a static library, which is then linked by a client executable, that I do not want to depend on boost.

According to the docs, the find_package(Boost) provides a target for the header only portion of the boost library, Boost::boost. this is the target I am using, and I am linking the target privately, ie

target_link_libraries(testlib PRIVATE Boost::boost)

However a the client testexe which uses testlib from the install dir with find_package(testlib)and links it with target_link_libraries(testexe testlib::testlib) is causing cmake to search for a Boost dependency for the testexe. As this is linked privately, it shouldn't as far as I can see.

Interestingly adding an INTERFACE IMPORTED target in testlib and using this to link, and the client no longer needs boost.

find_package(Boost REQUIRED)

add_library(boost INTERFACE IMPORTED)

set_property(TARGET boost PROPERTY
    INTERFACE_INCLUDE_DIRECTORIES ${Boost_INCLUDE_DIR})
target_link_libraries(testlib
    PRIVATE
        #using the imported target instead
        boost
        #Boost::boost)

this is almost identical to the lines in the Find boost source here<https://github.com/Kitware/CMake/blob/master/Modules/FindBoost.cmake#L2026-L2030>. The only difference being the target the properties are set on.

I have a workaround but I would like to know what is going on.

The complete source for the two test projects are availabe here<https://github.com/rmawatson/share/tree/master/cmake_boost>.

This is the output from cmake with using the Boost::boost target and the INTERFACE IMPORTEDtarget, which works

###using to the provided Boost::boost target

C:\Temp\cmake_boost\testlib\build>cmake ../ -DBOOST_ROOT=d:\sdk\boost\boost_1_68_0
-- Boost version: 1.68.0-- Configuring done
-- Generating done
-- Build files have been written to: C:/Temp/cmake_boost/testlib/build

C:\Temp\cmake_boost\testexe\build>cmake ../ -DCMAKE_PREFIX_PATH="C:\Temp\cmake_boost\testlib\build"-- Configuring done
CMake Error at CMakeLists.txt:6 (add_executable):
  Target "test" links to target "Boost::boost" but the target was not found.
  Perhaps a find_package() call is missing for an IMPORTED target, or an
  ALIAS target is missing?............-- Generating done
-- Build files have been written to: C:/Temp/cmake_boost/testexe/build



#When using the imported library target.

C:\Temp\cmake_boost\testlib\build>cmake ../ -DBOOST_ROOT=d:\sdk\boost\boost_1_68_0
-- Boost version: 1.68.0-- Configuring done
-- Generating done
-- Build files have been written to: C:/Temp/cmake_boost/testlib/build


C:\Temp\cmake_boost\testexe\build>cmake ../ -DCMAKE_PREFIX_PATH="C:\Temp\cmake_boost\testlib\build"-- Configuring done
-- Generating done
-- Build files have been written to: C:/Temp/cmake_boost/testexe/build

Thanks!
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