esp-idf/docs/en/cmake-warning.rst

.. note::
   This is documentation for the CMake-based build system which is currently in preview release. If you encounter any gaps or bugs, please report them in the `Issues <https://github.com/espressif/esp-idf/issues>`_ section of the ESP-IDF repository.

   The CMake-based build system will become the default build system in ESP-IDF V4.0. The existing GNU Make based build system will be deprecated in ESP-IDF V5.0.