CMakeLists.txt

if (NOT TARGET fmt)
    cmake_minimum_required(VERSION 3.8)

    # Download and unpack fmt at configure time
    configure_file(CMakeLists.txt.in fmt-download/CMakeLists.txt)

    execute_process(COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}" .
            RESULT_VARIABLE result
            WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/fmt-download)

    if (result)
        message(FATAL_ERROR "CMake step for fmt failed: ${result}")
    endif ()

    execute_process(COMMAND ${CMAKE_COMMAND} --build .
            RESULT_VARIABLE result
            WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/fmt-download)

    if (result)
        message(FATAL_ERROR "Build step for fmt failed: ${result}")
    endif ()

    # Add fmt directly to our build. This defines the fmt target.
    add_subdirectory(${CMAKE_CURRENT_BINARY_DIR}/fmt-src
            ${CMAKE_CURRENT_BINARY_DIR}/fmt-build
            EXCLUDE_FROM_ALL
            )
endif ()