Build a project depending on the Swiften XMPP library with CMake - c++

Question

I am currently trying to setup my C++ project using CMake, I successfully included dependencies like OpenMPI, but when going to Swiften, this became complex. This is not delivered in the form a package, but as shown in the git repository linked up there. Building that wasn't an issue, but I searched quite a lot of time, without finding any way to include libraries that don't provide a .so, and no main headers.
Here's my current CMakeLists.txt, made for testing only.
cmake_minimum_required (VERSION 3.0.0)
#set the executable
project (mtest)
set(EXECUTABLE_OUTPUT_PATH .)
add_executable (mtest main.cpp)
#defines libs
find_package(MPI REQUIRED)
set(CMAKE_CXX_COMPILE_FLAGS ${CMAKE_CXX_COMPILE_FLAGS} ${MPI_COMPILE_FLAGS})
set(CMAKE_CXX_LINK_FLAGS ${CMAKE_CXX_LINK_FLAGS} ${MPI_LINK_FLAGS})
include_directories(SYSTEM ${MPI_INCLUDE_PATH})
include_directories(SYSTEM Swiften)
target_link_libraries(mtest ${MPI_LIBRARIES})
add_library(swiften SHARED IMPORTED)
set_target_properties(swiften PROPERTIES
IMPORTED_LOCATION "${CMAKE_SOURCE_DIR}/Swiften/libSwiften.a"
INTERFACE_INCLUDE_DIRECTORIES "${CMAKE_SOURCE_DIR}/Swiften"
)
target_link_libraries(mtest swiften)
And when trying to run make, here's the error :
-- Configuring done
-- Generating done
-- Build files have been written to: /home/user/Documents/CTests/build
[ 50%] Building CXX object CMakeFiles/mtest.dir/main.cpp.o
/home/user/Documents/CTests/main.cpp:12:10: fatal error: Swiften/Client/Client.h: No such file or directory
#include <Swiften/Client/Client.h>
^~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
CMakeFiles/mtest.dir/build.make:62: recipe for target 'CMakeFiles/mtest.dir/main.cpp.o' failed
make[2]: *** [CMakeFiles/mtest.dir/main.cpp.o] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/mtest.dir/all' failed
make[1]: *** [CMakeFiles/mtest.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2
By the way, if the directory structure may help you, here's a tree output : https://pastebin.com/giPb9229