CMAKE_PREFIX_PATH doesn't help CMake in finding Qt5

I installed the following missing packages:

sudo apt-get install qtbase5-dev
sudo apt-get install qtdeclarative5-dev

Attaching any kind of prefix is not required now:

CMakeList:

    :~/junk/qtquick_hello_cmake$ cat CMakeLists.txt
    cmake_minimum_required(VERSION 2.8.12)
    
    project(qtquick_hello_cmake)
    
    set(CMAKE_INCLUDE_CURRENT_DIR ON)
    set(CMAKE_AUTOMOC ON)
    set(CMAKE_AUTORCC ON)
    
    find_package(Qt5 COMPONENTS Quick Core REQUIRED)
    
    qt5_add_resources(RESOURCES qml.qrc)
    
    add_executable(${PROJECT_NAME} "main.cpp" "qml.qrc")
    
    qt5_use_modules(${PROJECT_NAME} Quick Core)
    
    target_link_libraries(${PROJECT_NAME} Qt5::Core Qt5::Quick)

New output:

:~/junk/qtquick_hello_cmake$ ls
build  CMakeLists.txt  main.cpp  main.qml  qml.qrc

:~/junk/qtquick_hello_cmake$ cd build/
:~/junk/qtquick_hello_cmake/build$ rm -rf *

:~/junk/qtquick_hello_cmake/build$ cmake ../
-- The C compiler identification is GNU 4.8.4
-- The CXX compiler identification is GNU 4.8.4
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/.../junk/qtquick_hello_cmake/build

Errors are gone now.

Thanks to:
https://answers.ros.org/question/236324/could-not-find-a-package-configuration-file-provided-by-qt5widgets/
https://askubuntu.com/questions/508503/whats-the-development-package-for-qt5-in-14-04

For macOS export the following variable in the terminal.

export CMAKE_PREFIX_PATH=/usr/local/Cellar/qt5/5.15.1/  

There may be another version, check which one you have and change the last path component accordingly.

Issue the build reconfiguration

cmake ../

CMake error message about failed find_package and setting CMAKE_PREFIX_PATH variable

Add the installation prefix of "Qt5" to CMAKE_PREFIX_PATH

is somehow misleading. It talks only about "installation prefix", but this installation still require to contain Qt5Config.cmake or qt5-config.cmake files inside for being discoverable by find_package.

But the message

If "Qt5" provides a separate development package or SDK, be sure it has been installed.

is clear:

One need to install a development package which contains required config files.

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Everything above is applicable only to CONFIG mode of find_package, when "Find" script is provided neither by CMake nor by CMake project which uses this command.