function(z_kmpkg_setup_pkgconfig_path)
    cmake_parse_arguments(PARSE_ARGV 0 "arg" "" "CONFIG" "")

    if("${arg_CONFIG}" STREQUAL "")
        message(FATAL_ERROR "CONFIG is required.")
    endif()
    if(DEFINED arg_UNPARSED_ARGUMENTS)
        message(FATAL_ERROR "${CMAKE_CURRENT_FUNCTION} was passed extra arguments: ${arg_UNPARSED_ARGUMENTS}")
    endif()

    foreach(envvar IN ITEMS PKG_CONFIG PKG_CONFIG_PATH)
        if(DEFINED ENV{${envvar}})
            set("z_kmpkg_env_backup_${envvar}" "$ENV{${envvar}}" PARENT_SCOPE)
        else()
            unset("z_kmpkg_env_backup_${envvar}" PARENT_SCOPE)
        endif()
    endforeach()

    kmpkg_find_acquire_program(PKGCONFIG)
    get_filename_component(pkgconfig_path "${PKGCONFIG}" DIRECTORY)
    cmake_path(CONVERT "$ENV{PATH}" TO_CMAKE_PATH_LIST path_list NORMALIZE)
    cmake_path(CONVERT "${pkgconfig_path}" TO_CMAKE_PATH_LIST pkgconfig_path NORMALIZE)
    if(NOT "${pkgconfig_path}" IN_LIST path_list)
      kmpkg_add_to_path("${pkgconfig_path}")
    endif()
    unset(path_list)
    unset(pkgconfig_path)

    set(ENV{PKG_CONFIG} "${PKGCONFIG}")

    foreach(prefix IN ITEMS "${CURRENT_INSTALLED_DIR}" "${CURRENT_PACKAGES_DIR}")
        kmpkg_host_path_list(PREPEND ENV{PKG_CONFIG_PATH} "${prefix}/share/pkgconfig")
        if(arg_CONFIG STREQUAL "RELEASE")
            kmpkg_host_path_list(PREPEND ENV{PKG_CONFIG_PATH} "${prefix}/lib/pkgconfig")
            # search order is lib, share, external
        elseif(arg_CONFIG STREQUAL "DEBUG")
            kmpkg_host_path_list(PREPEND ENV{PKG_CONFIG_PATH} "${prefix}/debug/lib/pkgconfig")
            # search order is debug/lib, share, external
        else()
            message(FATAL_ERROR "CONFIG must be either RELEASE or DEBUG.")
        endif()
    endforeach()
    # total search order is current packages dir, current installed dir, external
endfunction()

function(z_kmpkg_restore_pkgconfig_path)
    cmake_parse_arguments(PARSE_ARGV 0 "arg" "" "" "")
    if(DEFINED arg_UNPARSED_ARGUMENTS)
        message(FATAL_ERROR "${CMAKE_CURRENT_FUNCTION} was passed extra arguments: ${arg_UNPARSED_ARGUMENTS}")
    endif()

    foreach(envvar IN ITEMS PKG_CONFIG PKG_CONFIG_PATH)
        if(DEFINED z_kmpkg_env_backup_${envvar})
            set("ENV{${envvar}}" "${z_kmpkg_env_backup_${envvar}}")
        else()
            unset("ENV{${envvar}}")
        endif()
    endforeach()
endfunction()