In my CMake script I append the path to a folder containing <PackageName>Config.cmake to <PackageName>_ROOT and then call find_package(<PackageName> REQUIRED) but it can't find my package.
When I use CMAKE_FIND_DEBUG_MODE I see my folder listed in <PackageName>_ROOT CMake variable [CMAKE_FIND_USE_PACKAGE_ROOT_PATH] (it is actually the only folder there), but it is not listed after find_package considered the following locations for the Config module:.
Why am I getting such behaviour? I use CMake 3.18.1 from Android Studio. The package I'm trying to find is OpenCV.
Relatively to my CMakeLists.txt file OpenCV is installed in ../../build/opencv-build<custom suffix>, so my code for finding it is:
get_filename_component(OPENCV_BUILD_DIRS_ROOT ../../build REALPATH)
file(GLOB OPENCV_BUILD_DIRS ${OPENCV_BUILD_DIRS_ROOT}/opencv-build*)
list(APPEND OpenCV_ROOT ${OPENCV_BUILD_DIRS})
find_package(OpenCV ${OPENCV_VERSION} REQUIRED ${OPENCV_PUBLIC_LIBRARIES} ${OPENCV_PRIVATE_LIBRARIES})
When I run it on Linux (WSL actually), everything works fine and CMake finds OpenCV succesfully in ../../build/opencv-build (or <project path>/build/opencv-build in the form of absolute path).
But when I try to build the project from Android Studio it doesn't, and I get this output from CMAKE_FIND_DEBUG_MODE:
CMake Debug Log at external/opencv/CMakeLists.txt:12 (find_package):
find_package considered the following paths for OpenCV.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/cmake/3.18.1/share/cmake-3.18/Modules/FindOpenCV.cmake
The file was not found.
<PackageName>_ROOT CMake variable [CMAKE_FIND_USE_PACKAGE_ROOT_PATH].
<project path>/build/opencv-build
CMAKE_PREFIX_PATH variable [CMAKE_FIND_USE_CMAKE_PATH].
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/windows-x86_64
CMAKE_FRAMEWORK_PATH and CMAKE_APPBUNDLE_PATH variables
[CMAKE_FIND_USE_CMAKE_PATH].
Env variable OpenCV_DIR [CMAKE_FIND_USE_CMAKE_ENVIRONMENT_PATH].
none
CMAKE_PREFIX_PATH env variable [CMAKE_FIND_USE_CMAKE_ENVIRONMENT_PATH].
none
CMAKE_FRAMEWORK_PATH and CMAKE_APPBUNDLE_PATH env variables
[CMAKE_FIND_USE_CMAKE_ENVIRONMENT_PATH].
none
Paths specified by the find_package HINTS option.
none
Standard system environment variables
[CMAKE_FIND_USE_SYSTEM_ENVIRONMENT_PATH].
<a lot of unrelated directories>
CMake User Package Registry [CMAKE_FIND_USE_PACKAGE_REGISTRY].
none
CMake variables defined in the Platform file
[CMAKE_FIND_USE_CMAKE_SYSTEM_PATH].
C:/Users/<username>/AppData/Local/Android/Sdk/cmake/3.18.1
<other unrelated directories>
CMake System Package Registry
[CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY].
none
Paths specified by the find_package PATHS option.
none
find_package considered the following locations for the Config module:
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/windows-x86_64/OpenCVConfig.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/windows-x86_64/opencv-config.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/OpenCVConfig.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/opencv-config.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/windows-x86_64/sysroot/usr/lib/i686-linux-android/21/OpenCVConfig.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/windows-x86_64/sysroot/usr/lib/i686-linux-android/21/opencv-config.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/windows-x86_64/sysroot/usr/local/OpenCVConfig.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/windows-x86_64/sysroot/usr/local/opencv-config.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/windows-x86_64/sysroot/usr/OpenCVConfig.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/windows-x86_64/sysroot/usr/opencv-config.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/windows-x86_64/sysroot/OpenCVConfig.cmake
C:/Users/<username>/AppData/Local/Android/Sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/windows-x86_64/sysroot/opencv-config.cmake
The file was not found.
So, the problem actually was that for Android (and, probably, iOS) CMake sets CMAKE_FIND_ROOT_PATH_MODE_PACKAGE variable (and other CMAKE_FIND_ROOT_PATH_MODE_* variables) to ONLY which makes find_package (and other find_* functions) prefix paths with what is in CMAKE_FIND_ROOT_PATH list.
To override this, one can do some of the following:
CMAKE_FIND_ROOT_PATH_MODE_* to BOTH or NEVERCMAKE_FIND_ROOT_PATH_BOTH or NO_CMAKE_FIND_ROOT_PATH for each find_* callIt should also fix the issues when CMake ignores paths from HINTS, PATHS and other prefix construction steps.