Help/policy/CMP0138.rst

CMP0138
-------

.. versionadded:: 3.24

:module:`CheckIPOSupported` uses flags from calling project.

The :module:`CheckIPOSupported` module :command:`check_ipo_supported`
command compiles a test project to determine whether the toolchain
supports :prop_tgt:`INTERPROCEDURAL_OPTIMIZATION`.  CMake 3.23 and
below run the check with the default values of the
:variable:`CMAKE_<LANG>_FLAGS` and :variable:`CMAKE_<LANG>_FLAGS_<CONFIG>`
variables for the current environment and toolchain settings.
However, some projects may modify these flag variables to add
flags that affect availability of the toolchain's IPO features.
CMake 3.24 and above prefer to honor the calling project's values
for these variables.  This policy provides compatibility for projects
that have not been updated to expect this behavior.

The ``OLD`` behavior for this policy is to ignore the calling
project's values of :variable:`CMAKE_<LANG>_FLAGS` and
:variable:`CMAKE_<LANG>_FLAGS_<CONFIG>`.  The ``NEW`` behavior
for this policy is to use the values of those variables as
compiler flags in the test project.

This policy was introduced in CMake version 3.24. Use the
:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
Unlike many policies, CMake version |release| does *not* warn
when this policy is not set and simply uses ``OLD`` behavior.

.. include:: DEPRECATED.txt