New in version 3.15.
MSVC runtime library flags are selected by an abstraction.
Compilers targeting the MSVC ABI have flags to select the MSVC runtime library. Runtime library selection typically varies with build configuration because there is a separate runtime library for Debug builds.
In CMake 3.14 and below, MSVC runtime library selection flags are added to
CMAKE_<LANG>_FLAGS_<CONFIG> cache entries by CMake
automatically. This allows users to edit their cache entries to adjust the
flags. However, the presence of such default flags is problematic for
projects that want to choose a different runtime library programmatically.
In particular, it requires string editing of the
CMAKE_<LANG>_FLAGS_<CONFIG> variables with knowledge of the
CMake builtin defaults so they can be replaced.
CMake 3.15 and above prefer to leave the MSVC runtime library selection flags
out of the default
CMAKE_<LANG>_FLAGS_<CONFIG> values and instead
offer a first-class abstraction. The
MSVC_RUNTIME_LIBRARY target property may be set to
select the MSVC runtime library. If they are not set then CMake uses the
MultiThreaded$<$<CONFIG:Debug>:Debug>DLL which is
equivalent to the original flags.
This policy provides compatibility with projects that have not been updated
to be aware of the abstraction. The policy setting takes effect as of the
enable_language() command that enables
a language whose compiler targets the MSVC ABI.
Once the policy has taken effect at the top of a project, that choice must be used throughout the tree. In projects that have nested projects in subdirectories, be sure to convert everything together.
OLD behavior for this policy is to place MSVC runtime library
flags in the default
entries and ignore the
NEW behavior for this policy is to not place MSVC runtime
library flags in the default cache entries and use the abstraction instead.
This policy was introduced in CMake version 3.15. Use the
cmake_policy() command to set it to
Unlike many policies, CMake version 3.21.20210928-g3dc0ab7 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.