Implement LWG-3767 codecvt<charN_t, char8_t, mbstate_t> incorrectly added to locale

stl/inc/xlocale

@@ -1397,7 +1397,7 @@ struct _NODISCARD _Codecvt_guard {
 };
 
 extern "C++" template <>
-class codecvt<char16_t, char8_t, mbstate_t> : public codecvt_base {
+class _CXX20_DEPRECATE_CODECVT_CHAR8_T_FACETS codecvt<char16_t, char8_t, mbstate_t> : public codecvt_base {
     // facet for converting between UTF-16 and UTF-8 sequences
 public:
     using intern_type = char16_t;
@@ -1678,7 +1678,7 @@ protected:
 };
 
 extern "C++" template <>
-class codecvt<char32_t, char8_t, mbstate_t> : public codecvt_base {
+class _CXX20_DEPRECATE_CODECVT_CHAR8_T_FACETS codecvt<char32_t, char8_t, mbstate_t> : public codecvt_base {
     // facet for converting between UTF-32 and UTF-8 sequences
 public:
     using intern_type = char32_t;
@@ -2321,26 +2321,85 @@ private:
 #endif // defined(_NATIVE_WCHAR_T_DEFINED) && !_ENFORCE_FACET_SPECIALIZATIONS
 
 _EXPORT_STD template <class _Elem, class _Byte, class _Statype>
-class codecvt_byname : public codecvt<_Elem, _Byte, _Statype> { // codecvt for named locale
+class codecvt_byname : public codecvt<_Elem, _Byte, _Statype> {
 public:
     static_assert(!_ENFORCE_FACET_SPECIALIZATIONS
-                      || _Is_any_of_v<codecvt_byname,
-#ifdef __cpp_char8_t
-                          codecvt_byname<char16_t, char8_t, mbstate_t>, codecvt_byname<char32_t, char8_t, mbstate_t>,
-#endif // defined(__cpp_char8_t)
-                          codecvt_byname<char, char, mbstate_t>, codecvt_byname<wchar_t, char, mbstate_t>>,
+                      || _Is_any_of_v<codecvt_byname, codecvt_byname<char, char, mbstate_t>,
+                          codecvt_byname<wchar_t, char, mbstate_t>>,
         _FACET_SPECIALIZATION_MESSAGE);
 
     explicit __CLR_OR_THIS_CALL codecvt_byname(const char* _Locname, size_t _Refs = 0)
-        : codecvt<_Elem, _Byte, _Statype>(_Locinfo(_Locname), _Refs) {} // construct for named locale
+        : codecvt<_Elem, _Byte, _Statype>(_Locinfo(_Locname), _Refs) {}
+
+    explicit __CLR_OR_THIS_CALL codecvt_byname(const string& _Str, size_t _Refs = 0)
+        : codecvt<_Elem, _Byte, _Statype>(_Locinfo(_Str.c_str()), _Refs) {}
+
+protected:
+    __CLR_OR_THIS_CALL ~codecvt_byname() noexcept override {}
+};
+
+_STL_DISABLE_DEPRECATED_WARNING
+
+template <>
+class _CXX20_DEPRECATE_CODECVT_FACETS codecvt_byname<char16_t, char, mbstate_t>
+    : public codecvt<char16_t, char, mbstate_t> {
+public:
+    explicit __CLR_OR_THIS_CALL codecvt_byname(const char* _Locname, size_t _Refs = 0)
+        : codecvt(_Locinfo(_Locname), _Refs) {}
+
+    explicit __CLR_OR_THIS_CALL codecvt_byname(const string& _Str, size_t _Refs = 0)
+        : codecvt(_Locinfo(_Str.c_str()), _Refs) {}
+
+protected:
+    __CLR_OR_THIS_CALL ~codecvt_byname() noexcept override {}
+};
+
+template <>
+class _CXX20_DEPRECATE_CODECVT_FACETS codecvt_byname<char32_t, char, mbstate_t>
+    : public codecvt<char32_t, char, mbstate_t> {
+public:
+    explicit __CLR_OR_THIS_CALL codecvt_byname(const char* _Locname, size_t _Refs = 0)
+        : codecvt(_Locinfo(_Locname), _Refs) {}
+
+    explicit __CLR_OR_THIS_CALL codecvt_byname(const string& _Str, size_t _Refs = 0)
+        : codecvt(_Locinfo(_Str.c_str()), _Refs) {}
+
+protected:
+    __CLR_OR_THIS_CALL ~codecvt_byname() noexcept override {}
+};
+
+#ifdef __cpp_char8_t
+template <>
+class _CXX20_DEPRECATE_CODECVT_CHAR8_T_FACETS codecvt_byname<char16_t, char8_t, mbstate_t>
+    : public codecvt<char16_t, char8_t, mbstate_t> {
+public:
+    explicit __CLR_OR_THIS_CALL codecvt_byname(const char* _Locname, size_t _Refs = 0)
+        : codecvt(_Locinfo(_Locname), _Refs) {}
 
     explicit __CLR_OR_THIS_CALL codecvt_byname(const string& _Str, size_t _Refs = 0)
-        : codecvt<_Elem, _Byte, _Statype>(_Locinfo(_Str.c_str()), _Refs) {} // construct for named locale
+        : codecvt(_Locinfo(_Str.c_str()), _Refs) {}
 
 protected:
     __CLR_OR_THIS_CALL ~codecvt_byname() noexcept override {}
 };
 
+template <>
+class _CXX20_DEPRECATE_CODECVT_CHAR8_T_FACETS codecvt_byname<char32_t, char8_t, mbstate_t>
+    : public codecvt<char32_t, char8_t, mbstate_t> {
+public:
+    explicit __CLR_OR_THIS_CALL codecvt_byname(const char* _Locname, size_t _Refs = 0)
+        : codecvt(_Locinfo(_Locname), _Refs) {}
+
+    explicit __CLR_OR_THIS_CALL codecvt_byname(const string& _Str, size_t _Refs = 0)
+        : codecvt(_Locinfo(_Str.c_str()), _Refs) {}
+
+protected:
+    __CLR_OR_THIS_CALL ~codecvt_byname() noexcept override {}
+};
+#endif // defined(__cpp_char8_t)
+
+_STL_RESTORE_DEPRECATED_WARNING
+
 #define _XA 0x100 // extra alphabetic
 #define _BB _CONTROL // BEL, BS, etc.
 #define _CN _SPACE // CR, FF, HT, NL, VT

stl/inc/yvals_core.h

@@ -1253,8 +1253,7 @@ _EMIT_STL_ERROR(STL1004, "C++98 unexpected() is incompatible with C++23 unexpect
     [[deprecated("warning STL4020: "                                                                                   \
                  "std::codecvt<char16_t, char, mbstate_t>, std::codecvt<char32_t, char, mbstate_t>, "                  \
                  "std::codecvt_byname<char16_t, char, mbstate_t>, and std::codecvt_byname<char32_t, char, mbstate_t> " \
-                 "are deprecated in C++20 and replaced by specializations with a second argument of type char8_t. "    \
-                 "You can define _SILENCE_CXX20_CODECVT_FACETS_DEPRECATION_WARNING "                                   \
+                 "are deprecated in C++20. You can define _SILENCE_CXX20_CODECVT_FACETS_DEPRECATION_WARNING "          \
                  "or _SILENCE_ALL_CXX20_DEPRECATION_WARNINGS to suppress this warning.")]]
 #else // ^^^ warning enabled / warning disabled vvv
 #define _CXX20_DEPRECATE_CODECVT_FACETS
@@ -1514,7 +1513,19 @@ _EMIT_STL_ERROR(STL1004, "C++98 unexpected() is incompatible with C++23 unexpect
 #define _DEPRECATE_TR1_RANDOM
 #endif // ^^^ warning disabled ^^^
 
-// next warning number: STL4047
+#if _HAS_CXX20 && defined(__cpp_char8_t) && !defined(_SILENCE_CXX20_CODECVT_CHAR8_T_FACETS_DEPRECATION_WARNING) \
+    && !defined(_SILENCE_ALL_CXX20_DEPRECATION_WARNINGS)
+#define _CXX20_DEPRECATE_CODECVT_CHAR8_T_FACETS                                                                     \
+    [[deprecated(                                                                                                   \
+        "warning STL4047: std::codecvt<char16_t, char8_t, mbstate_t>, std::codecvt<char32_t, char8_t, mbstate_t>, " \
+        "std::codecvt_byname<char16_t, char8_t, mbstate_t>, and std::codecvt_byname<char32_t, char8_t, mbstate_t> " \
+        "are deprecated by LWG-3767. You can define _SILENCE_CXX20_CODECVT_CHAR8_T_FACETS_DEPRECATION_WARNING or "  \
+        "_SILENCE_ALL_CXX20_DEPRECATION_WARNINGS to suppress this warning.")]]
+#else // ^^^ warning enabled / warning disabled vvv
+#define _CXX20_DEPRECATE_CODECVT_CHAR8_T_FACETS
+#endif // ^^^ warning disabled ^^^
+
+// next warning number: STL4048
 
 // next error number: STL1006
 

tests/std/tests/Dev09_056375_locale_cleanup/test.cpp

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _SILENCE_CXX20_CODECVT_FACETS_DEPRECATION_WARNING
+#define _SILENCE_CXX20_CODECVT_CHAR8_T_FACETS_DEPRECATION_WARNING
 
 #include <cassert>
 #include <cstdio>

tests/std/tests/VSO_0397980_codecvt_length/test.cpp

@@ -3,6 +3,7 @@
 
 #define _SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING
 #define _SILENCE_CXX20_CODECVT_FACETS_DEPRECATION_WARNING
+#define _SILENCE_CXX20_CODECVT_CHAR8_T_FACETS_DEPRECATION_WARNING
 
 #undef _ENFORCE_FACET_SPECIALIZATIONS
 #define _ENFORCE_FACET_SPECIALIZATIONS 0