CMake/Help/policy/CMP0047.rst
Brad King a41c0a9dcb Do not warn by default when policy CMP0025 or CMP0047 is not set
These policies are triggered by the use of a particular compiler rather
than outdated CMake code in a project.  Avoid warning in every project
that enables a language by not displaying the policy warning by default.
Add variable CMAKE_POLICY_WARNING_CMP<NNNN> to control the warning
explicitly; otherwise enable the warning with --debug-output or --trace.

This breaks with strict policy convention because it does not provide
developers with any warning about the behavior change by default.
Existing projects will continue to build without a warning or change in
behavior.  When a developer changes the minimum required version of
CMake in a project to a sufficiently high value (3.0), the project will
suddenly get the new compiler id and may break, but at least the
breakage comes with a change to the project rather than the version of
CMake used to build it.

Breaking strict policy convention is worthwhile in this case because
very few projects will be affected by the behavior change but every
project would have to see the warning if it were enabled by default.
2014-04-02 14:43:54 -04:00

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CMP0047
-------
Use ``QCC`` compiler id for the qcc drivers on QNX.
CMake 3.0 and above recognize that the QNX qcc compiler driver is
different from the GNU compiler.
CMake now prefers to present this to projects by setting the
:variable:`CMAKE_<LANG>_COMPILER_ID` variable to ``QCC`` instead
of ``GNU``. However, existing projects may assume the compiler id for
QNX qcc is just ``GNU`` as it was in CMake versions prior to 3.0.
Therefore this policy determines for QNX qcc 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 the ``GNU`` compiler id
for the qcc and QCC compiler drivers. The NEW behavior for this policy
is to use the ``QCC`` compiler id for those drivers.
This policy was introduced in CMake version 3.0. 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_CMP0047 <CMAKE_POLICY_WARNING_CMP<NNNN>>`
variable to control the warning.