# CMP0054

Only interpret `if()` arguments as variables or keywords when unquoted.

CMake 3.1 and above no longer implicitly dereference variables or interpret keywords in an `if()` command argument when it is a Quoted Argument or a Bracket Argument.

The `OLD` behavior for this policy is to dereference variables and interpret keywords even if they are quoted or bracketed. The `NEW` behavior is to not dereference variables or interpret keywords that have been quoted or bracketed.

Given the following partial example:

    set(A E)
    set(E "")

    if("${A}" STREQUAL "")
      message("Result is TRUE before CMake 3.1 or when CMP0054 is OLD")
    else()
      message("Result is FALSE in CMake 3.1 and above if CMP0054 is NEW")
    endif()

After explicit expansion of variables this gives:

    if("E" STREQUAL "")

With the policy set to `OLD` implicit expansion reduces this semantically to:

    if("" STREQUAL "")

With the policy set to `NEW` the quoted arguments will not be further dereferenced:

    if("E" STREQUAL "")

This policy was introduced in CMake version 3.1. CMake version 3.16.3 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.