CMake/Help/policy/CMP0126.rst

CMP0126
-------

.. versionadded:: 3.21

When this policy is set to ``NEW``, the :command:`set(CACHE)` command does not
remove any normal variable of the same name from the current scope.
The ``OLD`` behavior removes any normal variable of the same name from the
current scope in the following situations:

* No cache variable of that name existed previously.

* A cache variable of that name existed previously, but it had no type.
  This can occur when the variable was set on the command line using a form
  like ``cmake -DMYVAR=blah`` instead of ``cmake -DMYVAR:STRING=blah``.

* The ``FORCE`` or ``INTERNAL`` keywords were used when setting the cache
  variable.

Note that the ``NEW`` behavior has an important difference to the similar
``NEW`` behavior of policy :policy:`CMP0077`.  The :command:`set(CACHE)`
command always sets the cache variable if it did not exist previously,
regardless of the ``CMP0126`` policy setting.  The :command:`option` command
will *not* set the cache variable if a non-cache variable of the same name
already exists and :policy:`CMP0077` is set to ``NEW``.

Policy ``CMP0126`` was introduced in CMake version 3.21. Use the
:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly
within a project.  Use the :variable:`CMAKE_POLICY_DEFAULT_CMP0126
<CMAKE_POLICY_DEFAULT_CMP\<NNNN\>>` variable to set the policy for
a third-party project in a subdirectory without modifying it.
Unlike many policies, CMake version |release| does *not* warn when the policy
is not set and simply uses ``OLD`` behavior.  See documentation of the
:variable:`CMAKE_POLICY_WARNING_CMP0126 <CMAKE_POLICY_WARNING_CMP<NNNN>>`
variable to control the warning.

.. include:: DEPRECATED.txt