How to make ExternalProject_Add acting like ADD_SUBDIRECTORY command with cmake? - c++

Question

I'm creating a native library under Android Studio, and I'm hurting the following problem.
In my AndroidStudio project CMakeLists.txt, I have this:
cmake_minimum_required(VERSION 3.7.0)
add_library(native-lib
SHARED
src/main/cpp/native-lib.cpp )
IF(USE_EXTERNAL)
include(ExternalProject)
ExternalProject_Add(
project_mylib
DOWNLOAD_COMMAND ""
SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/src/main/cpp/mylib/"
CMAKE_ARGS
-DCMAKE_INSTALL_PREFIX=${PROJECT_BINARY_DIR}
)
add_dependencies(native-lib project_mylib)
ELSE()
add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/src/main/cpp/mylib/)
ENDIF()
find_library( # Sets the name of the path variable.
log-lib
# Specifies the name of the NDK library that
# you want CMake to locate.
log )
target_link_libraries(native-lib
${log-lib}
mylib
)
A self-made library is located in src/main/cpp/mylib/, with a CMakeLists.txt:
cmake_minimum_required(VERSION 3.7.0)
project(lib)
add_library(mylib SHARED lib.cpp)
INSTALL(TARGETS mylib
RUNTIME DESTINATION ${CMAKE_INSTALL_PREFIX}/bin
LIBRARY DESTINATION ${CMAKE_INSTALL_PREFIX}/lib
)
When I use the "traditional" add_subdirectory(...) everything goes well. But, if I use the ExternalProject_Add(...) version, linker is skipping the compiled libmylib.so library and so cannot link mylib to native-lib.
I have the following message: skipping incompatible /home/.../app/.externalNativeBuild/cmake/debug/arm64-v8a/lib/libmylib.so when searching for -lmylib
My guess is that all the flags set by AndroidStudio for the root CMakeLists.txt are not set when the ExternalProject is compile leading to an incompatible shared library.
So, I wonder if there is a way to compile a cmake ExternalProject like it was part of the root project (sharing the same compile flags etc) ?
Thanks for any advice