# CMP0001

`CMAKE_BACKWARDS_COMPATIBILITY` should no longer be used.

The behavior is to check `CMAKE_BACKWARDS_COMPATIBILITY` and present it to the user. The `NEW` behavior is to ignore CMAKE_BACKWARDS_COMPATIBILITY completely.

In CMake 2.4 and below the variable `CMAKE_BACKWARDS_COMPATIBILITY` was used to request compatibility with earlier versions of CMake. In CMake 2.6 and above all compatibility issues are handled by policies and the `cmake_policy()` command. However, CMake must still check `CMAKE_BACKWARDS_COMPATIBILITY` for projects written for CMake 2.4 and below.

This policy was introduced in CMake version 2.6.0. CMake version 3.19.3 warns when the policy is not set and uses `OLD` behavior. Use the `cmake_policy()` command to set it to `OLD` or `NEW` explicitly.

Note

The `OLD` behavior of a policy is `deprecated by definition` and may be removed in a future version of CMake.