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The `/GR` flag has been on by default since MSVC cl 14.0 from VS 2005. Remove it from the default flags to make it easier for projects to pass `/GR-` themselves to turn it off. Projects may be using string processing to replace `/GR` with another flag, so we cannot simply drop it. Add a policy to drop it in a compatible way. Fixes: #21428
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1.9 KiB
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44 lines
1.9 KiB
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CMP0117
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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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This policy was introduced in CMake version 3.20. Use the
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:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
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Unlike many policies, CMake version |release| does *not* warn
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when this policy is not set and simply uses ``OLD`` behavior.
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.. include:: DEPRECATED.txt
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