Standard Library Modules: Fix time_put<wchar_t> linker errors

stl/inc/xlocale

@@ -843,7 +843,7 @@ _NODISCARD int _Codecvt_do_length(
 
 enum _Codecvt_mode { _Consume_header = 4, _Generate_header = 2 };
 
-template <>
+extern "C++" template <>
 class _CRTIMP2_PURE_IMPORT_UNLESS_CODECVT_ID_SATELLITE _CXX20_DEPRECATE_CODECVT_FACETS
     codecvt<char16_t, char, mbstate_t> : public codecvt_base {
     // facet for converting between char16_t and UTF-8 byte sequences
@@ -1141,7 +1141,7 @@ private:
     _Codecvt_mode _Mode; // default: _Consume_header
 };
 
-template <>
+extern "C++" template <>
 class _CRTIMP2_PURE_IMPORT_UNLESS_CODECVT_ID_SATELLITE _CXX20_DEPRECATE_CODECVT_FACETS
     codecvt<char32_t, char, mbstate_t> : public codecvt_base {
     // facet for converting between char32_t and UTF-8 byte sequences
@@ -1395,7 +1395,7 @@ struct _NODISCARD _Codecvt_guard {
     }
 };
 
-template <>
+extern "C++" template <>
 class codecvt<char16_t, char8_t, mbstate_t> : public codecvt_base {
     // facet for converting between UTF-16 and UTF-8 sequences
 public:
@@ -1676,7 +1676,7 @@ protected:
     }
 };
 
-template <>
+extern "C++" template <>
 class codecvt<char32_t, char8_t, mbstate_t> : public codecvt_base {
     // facet for converting between UTF-32 and UTF-8 sequences
 public:
@@ -1919,7 +1919,7 @@ protected:
 };
 #endif // defined(__cpp_char8_t) && !defined(_M_CEE_PURE)
 
-template <>
+extern "C++" template <>
 class _CRTIMP2_PURE_IMPORT codecvt<wchar_t, char, mbstate_t> : public codecvt_base {
     // facet for converting between wchar_t and char (_Byte) sequences
 public:
@@ -2118,7 +2118,7 @@ private:
 };
 
 #if defined(_NATIVE_WCHAR_T_DEFINED) && !_ENFORCE_FACET_SPECIALIZATIONS
-template <>
+extern "C++" template <>
 class _CRTIMP2_PURE_IMPORT codecvt<unsigned short, char, mbstate_t> : public codecvt_base {
     // facet for converting between unsigned short and char sequences
 public:
@@ -2615,7 +2615,7 @@ locale::id ctype<_Elem>::id;
 #pragma clang diagnostic pop
 #endif // __clang__
 
-template <>
+extern "C++" template <>
 class _CRTIMP2_PURE_IMPORT ctype<char> : public ctype_base { // facet for classifying char elements, converting cases
 public:
     using _Elem     = char;
@@ -2805,7 +2805,7 @@ private:
     _Locinfo::_Ctypevec _Ctype; // information
 };
 
-template <>
+extern "C++" template <>
 class _CRTIMP2_PURE_IMPORT ctype<wchar_t>
     : public ctype_base { // facet for classifying wchar_t elements, converting cases
 public:
@@ -3006,7 +3006,7 @@ private:
 };
 
 #if defined(_NATIVE_WCHAR_T_DEFINED) && !_ENFORCE_FACET_SPECIALIZATIONS
-template <>
+extern "C++" template <>
 class _CRTIMP2_PURE_IMPORT ctype<unsigned short>
     : public ctype_base { // facet for classifying unsigned short elements, converting cases
 public:

stl/inc/xloctime

@@ -772,9 +772,8 @@ __PURE_APPDOMAIN_GLOBAL locale::id time_put<_Elem, _OutIt>::id;
 #pragma clang diagnostic pop
 #endif // __clang__
 
-template <class _OutIt>
-class _CRTIMP2_PURE_IMPORT time_put<wchar_t, _OutIt>
-    : public locale::facet { // facet for converting encoded times to wchar_t text
+extern "C++" template <class _OutIt>
+class time_put<wchar_t, _OutIt> : public locale::facet { // facet for converting encoded times to wchar_t text
 public:
     using _Elem     = wchar_t;
     using char_type = _Elem;
@@ -905,8 +904,8 @@ __PURE_APPDOMAIN_GLOBAL locale::id time_put<wchar_t, _OutIt>::id;
 
 #if defined(_CRTBLD)
 
-template <class _OutIt>
-class _CRTIMP2_PURE_IMPORT time_put<unsigned short, _OutIt>
+extern "C++" template <class _OutIt>
+class time_put<unsigned short, _OutIt>
     : public locale::facet { // facet for converting encoded times to unsigned short text
 public:
     using _Elem     = unsigned short;

tests/std/include/test_header_units_and_modules.hpp

@@ -1004,6 +1004,41 @@ void test_version() {
 #endif // ^^^ named modules ^^^
 }
 
+// VSO-1593165 "Standard Library Modules: time_put<wchar_t> emits bogus error LNK2019: unresolved external symbol"
+void test_VSO_1593165() {
+    using namespace std;
+    puts("Testing VSO-1593165.");
+
+    // Originally from the Dev11_0494593_time_put_wchar_t test:
+    using Facet = time_put<wchar_t, wstring::iterator>;
+
+    const tm t = [] {
+        tm ret{};
+
+        ret.tm_sec   = 57;
+        ret.tm_min   = 42;
+        ret.tm_hour  = 20;
+        ret.tm_mday  = 28;
+        ret.tm_mon   = 3;
+        ret.tm_year  = 108;
+        ret.tm_wday  = 1;
+        ret.tm_yday  = 118;
+        ret.tm_isdst = 0;
+
+        return ret;
+    }();
+
+    const locale l;
+    wstring s(15, L'x');
+    wstringstream stream;
+    const wchar_t fill          = L' ';
+    const wchar_t pattern[]     = L"%Y.%m.%d";
+    const wstring::iterator ret = use_facet<Facet>(l).put(s.begin(), stream, fill, &t, begin(pattern), end(pattern));
+    assert(ret == s.begin() + 11);
+    const wstring correct(L"2008.04.28\0xxxx", 15);
+    assert(s == correct);
+}
+
 void all_cpp_header_tests() {
     test_algorithm();
     test_any();
@@ -1085,4 +1120,6 @@ void all_cpp_header_tests() {
     test_variant();
     test_vector();
     test_version();
+
+    test_VSO_1593165();
 }