CMake project shared dependencies

Question

I have:

• a shared library X, which is independent
• a shared library Y, using X
• an executable Z, which uses both X and Y

All of them have their own CMakeLists.txt, and can be configured and built independently.

However, I cannot make the CMakeLists.txt for the executable (Z) to work.

My approach has been this:

foreach(clib ${OWN_LIBS})
   set(LIBS "${LIBS} ${clib}")
   set(CLIB_DIR "${PROJECT_SOURCE_DIR}/../lib${clib}")
   set(CLIB_BUILD_DIR "${CLIB_DIR}/build")

   add_subdirectory("${CLIB_DIR}" "${CLIB_BUILD_DIR}")
   include_directories("${CLIB_DIR}/incl")
   link_directories("${CLIB_BUILD_DIR}")
endforeach(clib)

With OWN_LIBS being just "X" in project Y, and being "X Y" in project Z.

This works for project Y, but in project Z, I get:

CMake Error at ... (add_subdirectory): The binary directory

.../libX/build

is already used to build a source directory. It cannot be used to build source directory

.../libX

Specify a unique binary directory name.

I also tried trying to create a local build directory, so for e.g. there would be libY/build/deps-libX/ containing the configured and built library X (when used from Y), and Z having this for both X and Y. Unfortunately, next I ran into:

add_library cannot create target "X" because another target with the same name already exists. The existing target is a shared library created in source directory "libX". See documentation for policy CMP0002 for more details.

Using ExternalProject is not an option.

Answer 1

An additional answer for others:

I got this error because of a merge "error". In a larger project, after merging, a CMakeLists.txt called "add_subdirectory" twice on the same subdirectory. It causes the same error message.