ad3c2c0b03
Every policy's documentation has a paragraph on what version of CMake introduced it, how to set the policy, and whether CMake warns if the policy is not set. The wording of this paragraph has diverged across policies over time. Factor the paragraph out into a standard advice document included by every policy.
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CMP0117
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-------
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.. versionadded:: 3.20
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MSVC RTTI flag ``/GR`` is not added to
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:variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>` by default.
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When using MSVC-like compilers in CMake 3.19 and below, the RTTI flag
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``/GR`` is added to :variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>` by
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default. This behavior is left from support for MSVC versions from Visual
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Studio 2003 and below that did not enable RTTI by default. It is no longer
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necessary. Furthermore, it is problematic for projects that want to change
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to ``/GR-`` programmatically. In particular, it requires string editing of
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the :variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>` variable with knowledge
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of the CMake builtin default so it can be replaced.
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CMake 3.20 and above prefer to leave out ``/GR`` from the value of
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:variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>` by default.
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This policy provides compatibility with projects that have not been updated
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to expect the lack of the ``/GR`` flag. The policy setting takes effect as
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of the first :command:`project` or :command:`enable_language` command that
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initializes :variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>`.
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.. note::
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Once the policy has taken effect at the top of a project for a given
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language, that choice must be used throughout the tree for that language.
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In projects that have nested projects in subdirectories, be sure to
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convert everything together.
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The ``OLD`` behavior for this policy is to place the MSVC ``/GR`` flag in the
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default :variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>` cache entry. The
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``NEW`` behavior for this policy is to *not* place the MSVC ``/GR`` flag in
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the default cache entry.
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.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 3.20
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.. |WARNS_OR_DOES_NOT_WARN| replace:: does *not* warn
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.. include:: STANDARD_ADVICE.txt
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.. include:: DEPRECATED.txt
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