CMake/Help/policy/CMP0119.rst

CMP0119
-------

.. versionadded:: 3.20

:prop_sf:`LANGUAGE` source file property explicitly compiles as specified
language.

The :prop_sf:`LANGUAGE` source file property is documented to mean that the
source file is written in the specified language.  In CMake 3.19 and below,
setting this property causes CMake to compile the source file using the
compiler for the specified language.  However, it only passes an explicit
flag to tell the compiler to treat the source as the specified language
for MSVC-like, XL, and Embarcadero compilers for the ``CXX`` language.
CMake 3.20 and above prefer to also explicitly tell the compiler to use
the specified language using a flag such as ``-x c`` on all compilers
for which such flags are known.

This policy provides compatibility for projects that have not been updated
to expect this behavior.  For example, some projects were setting the
``LANGUAGE`` property to ``C`` on assembly-language ``.S`` source files
in order to compile them using the C compiler.  Such projects should be
updated to use ``enable_language(ASM)``, for which CMake will often choose
the C compiler as the assembler on relevant platforms anyway.

The ``OLD`` behavior for this policy is to interpret the ``LANGUAGE <LANG>``
property using its undocumented meaning to "use the ``<LANG>`` compiler".
The ``NEW`` behavior for this policy is to interpret the ``LANGUAGE <LANG>``
property using its documented meaning to "compile as a ``<LANG>`` source".

This policy was introduced in CMake version 3.20.  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