esp-idf/examples/build_system/cmake/multi_config/sdkconfig.defaults

# In this example, the default build (obtained with 'idf.py build')
# targets a hypothetical development platform.
CONFIG_EXAMPLE_PRODUCT_NAME="Blinky Development Board"

# This selects 'func_dev.c' file to be compiled and linked, see CMakeLists.txt.
CONFIG_EXAMPLE_FUNC_IMPL_DEV=y