esp-idf/tools/cmake/targets.cmake

#
# Set the target used for the standard project build.
#
macro(__target_init)
    # Input is IDF_TARGET environement variable
    set(env_idf_target $ENV{IDF_TARGET})

    if(NOT env_idf_target)
        # IDF_TARGET not set in environment, see if it is set in cache
        if(IDF_TARGET)
            set(env_idf_target ${IDF_TARGET})
        else()
            set(env_idf_target esp32)
            message(STATUS "IDF_TARGET not set, using default target: ${env_idf_target}")
        endif()
    else()
        # IDF_TARGET set both in environment and in cache, must be the same
        if(NOT ${IDF_TARGET} STREQUAL ${env_idf_target})
            message(FATAL_ERROR "IDF_TARGET in CMake cache does not match "
                            "IDF_TARGET environment variable. To change the target, clear "
                            "the build directory and sdkconfig file, and build the project again")
        endif()
    endif()

    # IDF_TARGET will be used by Kconfig, make sure it is set
    set(ENV{IDF_TARGET} ${env_idf_target})

    # Finally, set IDF_TARGET in cache
    set(IDF_TARGET ${env_idf_target} CACHE STRING "IDF Build Target")
endmacro()

#
# Check that the set build target and the config target matches.
#
function(__target_check)
    # Should be called after sdkconfig CMake file has been included.
    idf_build_get_property(idf_target IDF_TARGET)
    if(NOT ${idf_target} STREQUAL ${CONFIG_IDF_TARGET})
        message(FATAL_ERROR "CONFIG_IDF_TARGET in sdkconfig does not match "
            "IDF_TARGET environment variable. To change the target, delete "
            "sdkconfig file and build the project again.")
    endif()
endfunction()

#
# Used by the project CMake file to set the toolchain before project() call.
#
macro(__target_set_toolchain)
    idf_build_get_property(idf_path IDF_PATH)

    # See if Clang toolchain should be used
    set(env_idf_toolchain $ENV{IDF_TOOLCHAIN})
    if(NOT env_idf_toolchain)
        # IDF_TOOLCHAIN not set in environment, see if it is set in cache
        if(IDF_TOOLCHAIN)
            set(env_idf_toolchain ${IDF_TOOLCHAIN})
        else()
            set(env_idf_toolchain gcc)
        endif()
    else()
        # IDF_TOOLCHAIN set both in environment and in cache, must be the same
        if(NOT ${IDF_TOOLCHAIN} STREQUAL ${env_idf_toolchain})
            message(FATAL_ERROR "IDF_TOOLCHAIN in CMake cache does not match "
                    "IDF_TOOLCHAIN environment variable. To change the toolchain, clear "
                    "the build directory and sdkconfig file, and build the project again")
        endif()
    endif()

    # Finally, set IDF_TOOLCHAIN in cache
    set(IDF_TOOLCHAIN ${env_idf_toolchain} CACHE STRING "IDF Build Toolchain Type")

    if(${env_idf_toolchain} STREQUAL "clang")
        set(toolchain_type "clang-")
    endif()

    # First try to load the toolchain file from the tools/cmake/directory of IDF
    set(toolchain_file_global ${idf_path}/tools/cmake/toolchain-${toolchain_type}${IDF_TARGET}.cmake)
    if(EXISTS ${toolchain_file_global})
        set(CMAKE_TOOLCHAIN_FILE ${toolchain_file_global})
    else()
        message(FATAL_ERROR "Toolchain file ${toolchain_file_global} not found")
    endif()
endmacro()