include
-------

The ``include`` stanza allows including the contents of another file in the
current ``dune`` file. Currently, the included file cannot be generated and must
be present in the source tree. This feature is intended for use in conjunction
with promotion, when parts of a ``dune`` file are to be generated.

For instance:

.. code:: dune

    (include dune.inc)

    (rule (with-stdout-to dune.inc.gen (run ./gen-dune.exe)))

    (rule
     (alias  runtest)
     (action (diff dune.inc dune.inc.gen)))

With this ``dune`` file, running Dune as follows will replace the ``dune.inc``
file in the source tree by the generated one:

.. code:: console

    $ dune build @runtest --auto-promote
