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CMP0120
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-------
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.. versionadded:: 3.20
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The :module:`WriteCompilerDetectionHeader` module is removed.
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CMake versions 3.1 through 3.19 provide this module to generate a
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C++ compatibility layer by re-using information from CMake's table of
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preprocessor checks for :manual:`cmake-compile-features(7)`. However:
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* Those granular features have been superseded by meta-features for
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:ref:`Requiring Language Standards` such as ``cxx_std_11``. Therefore
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no new granular feature checks will be added and projects will need to
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use other means to conditionally use new C++ features.
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* The module exposes some of CMake's implementation details directly
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to C++ translation units.
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* The module's approach effectively provides a header file with CMake,
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thus tying the version of the header to the version of CMake.
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Many projects found that the :module:`WriteCompilerDetectionHeader` was
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best used by manually generating its header locally with a recent version
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of CMake and then bundling it with the project source so that it could
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be used with older CMake versions.
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For reasons including the above, CMake 3.20 and above prefer to not
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provide the :module:`WriteCompilerDetectionHeader` module. This policy
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provides compatibility for projects that have not been ported away from
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it. Projects using the module should be updated to stop using it.
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Alternatives include:
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* Bundle a copy of the generated header in the project's source.
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* Use a third-party alternative, such as the CC0-licensed `Hedley`_.
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* Drop support for compilers too old to provide the features natively.
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The ``OLD`` behavior of this policy is for inclusion of the deprecated
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:module:`WriteCompilerDetectionHeader` module to work. The ``NEW``
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behavior is for inclusion of the module to fail as if it does not exist.
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.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 3.20
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.. |WARNS_OR_DOES_NOT_WARN| replace:: warns
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.. include:: STANDARD_ADVICE.txt
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.. include:: DEPRECATED.txt
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.. _`Hedley`: https://nemequ.github.io/hedley/
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