CMP0089
-------

Compiler id for IBM Clang-based XL compilers is now ``XLClang``.

CMake 3.15 and above recognize that IBM's Clang-based XL compilers
that define ``__ibmxl__`` are a new front-end distinct from ``xlc``
with a different command line and set of capabilities.
CMake now prefers to present this to projects by setting the
:variable:`CMAKE_<LANG>_COMPILER_ID` variable to ``XLClang`` instead
of ``XL``.  However, existing projects may assume the compiler id for
Clang-based XL is just ``XL`` as it was in CMake versions prior to 3.15.
Therefore this policy determines for Clang-based XL compilers which
compiler id to report in the :variable:`CMAKE_<LANG>_COMPILER_ID`
variable after language ``<LANG>`` is enabled by the :command:`project`
or :command:`enable_language` command.  The policy must be set prior
to the invocation of either command.

The OLD behavior for this policy is to use compiler id ``XL``.  The
NEW behavior for this policy is to use compiler id ``XLClang``.

This policy was introduced in CMake version 3.15.  Use the
:command:`cmake_policy` command to set this policy to OLD or NEW explicitly.
Unlike most policies, CMake version |release| does *not* warn
by default when this policy is not set and simply uses OLD behavior.
See documentation of the
:variable:`CMAKE_POLICY_WARNING_CMP0089 <CMAKE_POLICY_WARNING_CMP<NNNN>>`
variable to control the warning.

.. include:: DEPRECATED.txt
