New in version 3.20.
LANGUAGE source file property explicitly compiles as specified
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
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.
OLD behavior for this policy is to interpret the
property using its undocumented meaning to "use the
NEW behavior for this policy is to interpret the
property using its documented meaning to "compile as a
This policy was introduced in CMake version 3.20. Use the
cmake_policy() command to set it to
Unlike many policies, CMake version 3.21.7 does not warn
when this policy is not set and simply uses
OLD behavior of a policy is
deprecated by definition
and may be removed in a future version of CMake.