CMP0051
-------

List TARGET_OBJECTS in SOURCES target property.

CMake 3.0 and lower did not include the ``TARGET_OBJECTS``
:manual:`generator expression <cmake-generator-expressions(7)>` when
returning the :prop_tgt:`SOURCES` target property.

Configure-time CMake code is not able to handle generator expressions.  If
using the :prop_tgt:`SOURCES` target property at configure time, it may be
necessary to first remove generator expressions using the
:command:`string(GENEX_STRIP)` command.  Generate-time CMake code such as
:command:`file(GENERATE)` can handle the content without stripping.

The ``OLD`` behavior for this policy is to omit ``TARGET_OBJECTS``
expressions from the :prop_tgt:`SOURCES` target property.  The ``NEW``
behavior for this policy is to include ``TARGET_OBJECTS`` expressions
in the output.

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.