CMP0149

Visual Studio Generators select latest Windows SDK by default.

Visual Studio Generators select a Windows SDK version to put in the WindowsTargetPlatformVersion setting in .vcxproj files. CMake sets the CMAKE_VS_WINDOWS_TARGET_PLATFORM_VERSION variable to the selected SDK version.

Prior to CMake 3.27, the SDK version was always selected by the value of the CMAKE_SYSTEM_VERSION variable. Users or toolchain files could set that variable to one of the exact Windows SDK versions available on the host system. Since CMAKE_SYSTEM_VERSION defaults to CMAKE_HOST_SYSTEM_VERSION, and it is not guaranteed that a matching Windows SDK version is available, CMake had to fall back to using the latest Windows SDK version if no exact match was available. This approach was problematic:

• The latest Windows SDK might or might not be selected based on whether the host version of Windows happens to match an available SDK version.
• An old Windows SDK version might be selected that has not been updated for newer language standards such as C11.

CMake 3.27 and higher prefer to ignore the exact value of CMAKE_SYSTEM_VERSION and by default select the latest SDK version available. An exact SDK version may be specified explicitly using a version= field in the CMAKE_GENERATOR_PLATFORM variable. See Visual Studio Platform Selection.

This policy provides compatibility for projects, toolchain files, and build scripts that have not been ported away from using CMAKE_SYSTEM_VERSION to specify an exact SDK version.

The OLD behavior for this policy is to use the exact value of CMAKE_SYSTEM_VERSION if possible. The NEW behavior for this policy is to ignore it.

This policy was introduced in CMake version 3.27. It may be set by cmake_policy() or cmake_minimum_required(). If it is not set, CMake does not warn, and uses OLD behavior.