ninja-require-byproducts
------------------------

* The :generator:`Ninja` generator now requires that calls to the
  :command:`add_custom_command` and :command:`add_custom_target`
  commands use the ``BYPRODUCTS`` option to explicitly specify any
  files generated by the custom commands that are not listed as
  outputs (perhaps because their timestamps are allowed to be older
  than the inputs).  See policy :policy:`CMP0058`.