====== CMakeLists.txt ======

===== source =====

<code cmake>
add_subdirectory(src)
add_subdirectory(lib)
zephyr_include_directories(include)
</code>

===== library =====

==== add common code as part of zephyr library  ====

<code cmake>
zephyr_library()

add_subdirectory(src_dir_for_common_parts)
add_subdirectory_ifdef(CONFIG_LIB_FEAT1 src_dir_for_feat1)
add_subdirectory_ifdef(CONFIG_LIB_FEAT2 src_dir_for_feat2)

zephyr_library_sources_ifdef(CONFIG_LIB_FEAT1 feat1.c)
zephyr_library_sources_ifdef(CONFIG_LIB_FEAT2 feat2.c)

zephyr_library_link_libraries_ifdef(CONFIG_LIB_SOME_OTHER_LIB otherlib)
</code>