CMake/Help/policy/CMP0054.rst

CMP0054
-------

Only interpret :command:`if` arguments as variables or keywords when unquoted.

CMake 3.1 and above no longer implicitly dereference variables or
interpret keywords in an :command:`if` command argument when
it is a :ref:`Quoted Argument` or a :ref:`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(MONKEY 1)
  set(ANIMAL MONKEY)

  if("${ANIMAL}" STREQUAL "MONKEY")

After explicit expansion of variables this gives:

::

  if("MONKEY" STREQUAL "MONKEY")

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

::

  if("1" STREQUAL "1")

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

::

  if("MONKEY" STREQUAL "MONKEY")

This policy was introduced in CMake version 3.1.
CMake version |release| warns when the policy is not set and uses
``OLD`` behavior.  Use the :command:`cmake_policy` command to set
it to ``OLD`` or ``NEW`` explicitly.