CMP0155
-------

.. versionadded:: 3.28

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

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, and need to be scanned.

This policy was introduced in CMake version 3.28.  Use the
:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
Unlike many policies, CMake version |release| does *not* warn
when this policy is not set and simply uses ``OLD`` behavior.

.. include:: DEPRECATED.txt
