Cmake: Exporting subproject targets to main project

Question

I currently have a project called LIBS with a structure like this:

├── Lib1
│   ├── CMakeLists.txt
│   ├── lib1-class.cpp
│   └── lib1-class.h
├── lib2
│   └── CMakeLists.txt
│   ├── lib2-class.cpp
│   ├── lib2-class.h
├── cmake
│   └── LIBSConfig.cmake.in
├── CMakeLists.txt

in the main cmake file, I have:

install(
        TARGETS
        lib1
        lib2
        DESTINATION
        ${PROJECT_DIRNAME_lib}
        EXPORT
        ${PROJECT_NAME}Exports
)

install(
        EXPORT
        ${PROJECT_NAME}Exports
        DESTINATION
        ${PROJECT_DIRNAME_lib}
)

as I want to export these in a package that is discoverable by find_package().

My problem is that I generate lib1 and lib2 in their respective directories and when installing them, Cmake tells me that

Error:install TARGETS given target "lib1" which does not exist in this directory.

As suggested here, My understanding is that I should use Export() and in lib1 and lib2, have something of the form:

export(TARGETS lib1 FILE lib1Exports.cmake)

and in the LIBS project, have something like this:

ADD_LIBRARY(lib1 UNKNOWN IMPORTED)
set_property(TARGET lib1 PROPERTY IMPORTED_LOCATION lib1)

However it does not like me using the same name for this library that is being added from the parent project. It tells me:

Error:add_library cannot create imported target "lib1" because another target with the same name already exists.

so the library is available and I can link to it, etc. if I were to create another target in the parent directory, but I can't install it.

I have found the exact same problem in a bug report here but I believe cmake handles things differently now and I am just not doing it correctly. So am I doing it wrong? I would like to avoid using external packages if possible.

Update: the accepted solution works only for cases where there is no dependency between lib1, lib2. In that case one should use the solution provided to this question.

Cmake: Exporting subproject targets to main project

1 Answers