Help/policy/CMP0215.rst

CMP0215
-------

.. versionadded:: 4.4

:ref:`Ninja Generators` emit Swift modules separately from compilation.

In CMake 4.3 and below, Swift targets built by :ref:`Ninja Generators`
emit ``.swiftmodule`` from the Swift compile edge together with object files.
Because Ninja treats a build edge as atomic, downstream Swift targets
must wait for compilation outputs to finish before they can use the module
interface.

CMake 4.4 and above prefer to emit ``.swiftmodule`` from a dedicated
``-emit-module`` build edge so that downstream Swift targets can begin
compiling as soon as the module interface is available.  This policy
provides compatibility with projects that have not been updated.

The ``OLD`` behavior for this policy is to not emit modules separately.
The ``NEW`` behavior for this policy is to emit ``.swiftmodule`` from a
dedicated build edge for importable Swift targets by default.

The :prop_tgt:`Swift_SEPARATE_MODULE_EMISSION` target property and
corresponding :variable:`CMAKE_Swift_SEPARATE_MODULE_EMISSION` variable
may be set to enable or disable the behavior on a per-target basis.

The ``NEW`` behavior requires that policies :policy:`CMP0157` and
:policy:`CMP0195` are also set to ``NEW``.  :policy:`CMP0157` selects the
split Swift build model that provides the dedicated ``.swiftmodule`` edge,
and must be set prior to the first :command:`project` or
:command:`enable_language` command that enables the Swift language.
:policy:`CMP0195` places the module in the Swift module directory structure
that the dedicated edge writes.  If either policy is not ``NEW`` while
``CMP0215`` is ``NEW``, CMake issues a fatal error when the Swift language
is enabled.

.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 4.4
.. |WARNS_OR_DOES_NOT_WARN| replace:: does *not* warn
.. include:: include/STANDARD_ADVICE.rst

.. include:: include/DEPRECATED.rst