build_external_proj.cmake

# --------------------------------------------------
# Builds a external project at configuration time instead of build time
# See: https://gist.github.com/amir-saniyan/4339e6f3ef109c75eda8018f7d5192a7
function (build_external_git_project target git_url)

    set(CMAKELIST_CONTENT "
        cmake_minimum_required(VERSION ${CMAKE_MINIMUM_REQUIRED_VERSION})
        project(build_external_git_project)
        include(ExternalProject)
        ExternalProject_add(${target}
            GIT_REPOSITORY \"${git_url}\" 
            CMAKE_GENERATOR \"${CMAKE_GENERATOR}\"
            CMAKE_GENERATOR_PLATFORM \"${CMAKE_GENERATOR_PLATFORM}\"
            CMAKE_GENERATOR_TOOLSET \"${CMAKE_GENERATOR_TOOLSET}\"
            CMAKE_GENERATOR_INSTANCE \"${CMAKE_GENERATOR_INSTANCE}\"
            CMAKE_ARGS ${ARGN}
            LOG_DOWNLOAD 1 LOG_UPDATE 1 LOG_CONFIGURE 1 LOG_BUILD 1 LOG_INSTALL 1)
        add_custom_target(build_external_project)
        add_dependencies(build_external_project ${target})
    ")

    set(TARGET_DIR "${CMAKE_CURRENT_BINARY_DIR}/ExternalProjects/${target}")

    file(WRITE "${TARGET_DIR}/CMakeLists.txt" "${CMAKELIST_CONTENT}")

    file(MAKE_DIRECTORY "${TARGET_DIR}" "${TARGET_DIR}/build")

    execute_process(COMMAND ${CMAKE_COMMAND}
        -G "${CMAKE_GENERATOR}"
        -A "${CMAKE_GENERATOR_PLATFORM}"
        -T "${CMAKE_GENERATOR_TOOLSET}"
        ..
        WORKING_DIRECTORY "${TARGET_DIR}/build")

    execute_process(COMMAND ${CMAKE_COMMAND}
        --build .
        WORKING_DIRECTORY "${TARGET_DIR}/build")

endfunction()