CMP0155
-------

.. versionadded:: 3.28

C++ sources in targets with at least C++20 are scanned for imports
when supported.

CMake 3.27 and below assume that C++ sources do not ``import`` modules.
CMake 3.28 and above prefer to assume that C++ sources in targets using C++20
or higher might ``import`` modules, and must be scanned before compiling,
unless explicitly disabled.  This policy provides compatibility for projects
that use C++20 or higher, without modules, that have not been updated to turn
off scanning, e.g., via the :variable:`CMAKE_CXX_SCAN_FOR_MODULES` variable.
See the :manual:`cmake-cxxmodules(7)` manual for more details on C++ module
support.

The ``OLD`` behavior for this policy is to assume that C++ 20 and newer
sources do not import modules.  The ``NEW`` behavior for this policy is to
assume that C++ 20 and newer files may import modules if the compiler
understands how to scan for their dependencies, and need to be scanned.

.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 3.28
.. |WARNS_OR_DOES_NOT_WARN| replace:: does *not* warn
.. include:: include/STANDARD_ADVICE.rst

.. include:: include/DEPRECATED.rst
