[libcxx-commits] [libcxx] [libcxx][P1831R1] Deprecating volatile: library (PR #101439)

[Josh Karns via libcxx-commits]

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@@ -741,6 +741,15 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_DEPRECATED_WITH_CHAR8_T
 #  endif
 
+// P1831R1 deprecated many uses of volatile, but the way attributes work with template specializations require this
+// work-around to always raise warnings in cases where templates are specialized for volatile variants of STL types.
+template <class _Tp, bool __cxx20 = _LIBCPP_STD_VER >= 20>
+_LIBCPP_HIDE_FROM_ABI constexpr bool __volatile_deprecated_since_cxx20_warning = true;
+template <class _Tp>
+_LIBCPP_DEPRECATED_IN_CXX20 _LIBCPP_HIDE_FROM_ABI constexpr bool __volatile_deprecated_since_cxx20_warning<_Tp, true> = true;
+#  define _LIBCPP_VOLATILE_DEPRECATED_WARNING static_assert(__volatile_deprecated_since_cxx20_warning<volatile _Tp>)
+#  define _LIBCPP_CONST_VOLATILE_DEPRECATED_WARNING static_assert(__volatile_deprecated_since_cxx20_warning<const volatile _Tp>)
+
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jkarns275 wrote:

Hmm I do think differentiating between `volatile` and `const volatile` may be confusing.

I'm not sure what a better name would be since there isn't a specific condition to refer to like `!is_always_lock_free`. 

https://github.com/llvm/llvm-project/pull/101439