Create CMake XXConfig.cmake let other cmake project invoke - cmake

Question

I download opencl-icd from KhronosGroup and build it fine.
But it doesn't have OpenCLConfig.cmake.
So I decide to create one that my program(CMakeLists.txt) can use find_package(OpenCL) to invoke it.
Following file tree is my OpenCL dir. after I build.
# $PWD is C:/SDKs/ocl-icd
|-- OpenCLConfig.cmake
|-- bin
| `-- OpenCL.dll
|-- include
| `-- CL
... CL Headers
`-- lib
|-- OpenCL.exp
`-- OpenCL.lib
I create OpenCLConfig.cmake which content is:
set(OpenCL_DIR "C:/SDKs/ocl-icd")
set(OpenCL_VERSION 2.2)
set(OpenCL_VERSION_MAJOR 2)
set(OpenCL_VERSION_MINOR 2)
SET(OpenCV_VERSION_PATCH 0)
SET(OpenCV_VERSION_TWEAK 0)
set(OpenCL_INCLUDE_DIR "${OpenCL_DIR}/include")
set(OpenCL_LIBRARIES "OpenCL")
I use find_package(OpenCL) in others CMakeLists.txt:
...
set(OpenCL_DIR "C:/SDKs/ocl-icd" CACHE PATH "OpenCL Root DIR")
find_package(OpenCL 2 REQUIRED)
include_directories (${OpenCL_INCLUDE_DIR})
add_executable (${PROJECT_NAME} test.cc)
target_link_libraries(${OpenCL_LIBRARIES})
...
While I use cmake-gui to configure it, I got error report
CMake Error at C:/Program Files/CMake/share/cmake-3.15/Modules/FindPackageHandleStandardArgs.cmake:137 (message):
Could NOT find OpenCL (missing: OpenCL_INCLUDE_DIR) (Required is at least
version "2")
Call Stack (most recent call first):
C:/Program Files/CMake/share/cmake-3.15/Modules/FindPackageHandleStandardArgs.cmake:378 (_FPHSA_FAILURE_MESSAGE)
C:/Program Files/CMake/share/cmake-3.15/Modules/FindOpenCL.cmake:150 (find_package_handle_standard_args)
CMakeLists.txt:10 (find_package)
I think that it error caused by OpenCLConfig.cmake.
How do I solved it?
update: add OpenCLConfigVersion.cmake
set(OpenCL_VERSION 2.2)
set(OpenCL_VERSION_MAJOR 2)
set(OpenCL_VERSION_MINOR 2)
SET(OpenCV_VERSION_PATCH 0)
SET(OpenCV_VERSION_TWEAK 0)

Answer 1

The error message says, that the error is emitted by the script shipped with CMake:
C:/Program Files/CMake/share/cmake-3.15/Modules/FindOpenCL.cmake
and your script (OpenCLConfig.cmake) is ignored.
The thing is that when find_package() searches the script for process the request, FindXXX.cmake script is searched first. Only if such script is absent, XXXConfig.cmake script is searched.
You may disable searching for FindXXX.cmake script by adding CONFIG or NO_MODULE option to find_package call:
find_package(OpenCL 2 REQUIRED CONFIG)
For some packages (e.g. Boost) their FindXXX.cmake script tries to "leverage" its work to XXXConfig.cmake script, if the latter script exists. But other packages (like OpenCL which you use) do not do that. I know no agreements on this leveraging.