# CMP0049

Do not expand variables in target source entries.

CMake 2.8.12 and lower performed an extra layer of variable expansion when evaluating source file names:

    set(a_source foo.c)
    add_executable(foo \${a_source})

This was undocumented behavior.

The `OLD` behavior for this policy is to expand such variables when processing the target sources. The `NEW` behavior for this policy is to issue an error if such variables need to be expanded.

This policy was introduced in CMake version 3.0. CMake version 3.19.4 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.