Issue building opencv using FetchContent cmake command - c++

Question

I really need your help because I really don't understand what I am doing wrong.
Using the very simple attached CMakeLists.txt, I got the following error (a lot of times):
CMake Error in build/_deps/opencv-src/modules/core/CMakeLists.txt:
Target "opencv_core" INTERFACE_INCLUDE_DIRECTORIES property contains path:
"/home/myuser/tmp/build"
which is prefixed in the build directory.
Can you help me fix it ?
Thank you for the help.
The CMakeLists.txt I am using:
cmake_minimum_required(VERSION 3.8 FATAL_ERROR)
project(TEST_PROJECT)
set(CMAKE_CXX_STANDARD 14)
if (CMAKE_VERSION VERSION_GREATER_EQUAL "3.24.0")
cmake_policy(SET CMP0135 NEW)
endif ()
include(FetchContent)
FetchContent_Declare(
opencv
GIT_REPOSITORY https://github.com/opencv/opencv.git
GIT_TAG 4.6.0
GIT_SHALLOW TRUE
GIT_PROGRESS TRUE
)
FetchContent_MakeAvailable(opencv)
set(OpenCV_DIR ${CMAKE_CURRENT_BINARY_DIR})
find_package(OpenCV REQUIRED)

Answer 1

Tried the same on a Windows system - with no success either.
In the end, I installed OpenCV outside of the build and source tree. Then used only find_package in the CMakeList.txt.
I had problems passing varibales to the OpenCV build when using FetchContent too. E.g. for using TBB or CUDA.

Answer 2

As #sweenish guessed, the problem was the OpenCV_DIR variable definition. So I remove this line and add the OVERRIDE_FIND_PACKAGE in the FetchContent_Declare call. And now it works fine on both systems, Linux and Windows.
My CMakeLists.txt now looks like:
cmake_minimum_required(VERSION 3.8 FATAL_ERROR)
project(TEST_PROJECT)
set(CMAKE_CXX_STANDARD 14)
if (CMAKE_VERSION VERSION_GREATER_EQUAL "3.24.0")
cmake_policy(SET CMP0135 NEW)
endif ()
include(FetchContent)
FetchContent_Declare(
opencv
GIT_REPOSITORY https://github.com/opencv/opencv.git
GIT_TAG 4.6.0
GIT_SHALLOW TRUE
GIT_PROGRESS TRUE
OVERRIDE_FIND_PACKAGE
)
FetchContent_MakeAvailable(opencv)
find_package(OpenCV REQUIRED)