Keep ABI for _Locinfo

stl/inc/xlocinfo

@@ -134,6 +134,28 @@ private:
     void* _Timeptr; // pointer to time information
 };
 
+template <class _Elem>
+_Elem* _Ntcts_dup_dbg(const _Elem* const _Ptr) noexcept {
+    _STL_INTERNAL_STATIC_ASSERT(_Is_any_of_v<_Elem, char, wchar_t, unsigned short>);
+
+    auto _Iter = _Ptr;
+    while (*_Iter != _Elem{}) {
+        ++_Iter;
+    }
+    const size_t _Count = static_cast<size_t>(_Iter - _Ptr + 1) * sizeof(_Elem);
+
+#ifdef _DEBUG
+    const auto _Result = static_cast<_Elem*>(_CSTD _malloc_dbg(_Count, _CRT_BLOCK, __FILE__, __LINE__));
+#else
+    const auto _Result = static_cast<_Elem*>(_CSTD malloc(_Count));
+#endif
+    if (_Result) {
+        _CSTD memcpy(_Result, _Ptr, _Count);
+    }
+
+    return _Result;
+}
+
 extern "C++" template <class _Elem>
 class _CRTIMP2_PURE_IMPORT _Yarn { // wrap a NTCTS
 public:
@@ -156,26 +178,22 @@ public:
             _Tidy();
 
             if (_Right) { // new is not empty, copy it
-                const _Elem* _Ptr = _Right;
-                while (*_Ptr != _Elem{}) {
-                    ++_Ptr;
-                }
+                _Myptr = _STD _Ntcts_dup_dbg(_Right);
+            }
+        }
 
-                const auto _Count = (++_Ptr - _Right) * sizeof(_Elem);
+        return *this;
+    }
 
-#ifdef _DEBUG
-                _Myptr = static_cast<_Elem*>(_malloc_dbg(_Count, _CRT_BLOCK, __FILE__, __LINE__));
-#else
-                _Myptr = static_cast<_Elem*>(_CSTD malloc(_Count));
-#endif
+    template <class _Elem2 = _Elem, enable_if_t<is_same_v<_Elem2, char>, int> = 0>
+    void _From_wide(const wchar_t* const _Right) noexcept {
+        if (reinterpret_cast<wchar_t*>(_Myptr) != _Right) { // new value, discard old and copy new
+            _Tidy();
 
-                if (_Myptr) {
-                    _CSTD memcpy(_Myptr, _Right, _Count);
-                }
+            if (_Right) { // new is not empty, copy it
+                _Myptr = reinterpret_cast<char*>(_STD _Ntcts_dup_dbg(_Right));
             }
         }
-
-        return *this;
     }
 
     __CLR_OR_THIS_CALL ~_Yarn() noexcept {
@@ -382,7 +400,8 @@ private:
     _Yarn<char> _Months; // month names
     _Yarn<wchar_t> _W_Days; // wide weekday names
     _Yarn<wchar_t> _W_Months; // wide month names
-    _Yarn<wchar_t> _Oldlocname; // old locale name to revert to on destruction
+    // TRANSITION, ABI, `_Oldlocname._Myptr` is reinterpreted as `wchar_t*`. `wchar` should be wrapped instead.
+    _Yarn<char> _Oldlocname; // old locale name to revert to on destruction
     _Yarn<char> _Newlocname; // new locale name for this object
 };
 _STD_END

stl/src/locale.cpp

@@ -137,7 +137,7 @@ void __CLRCALL_PURE_OR_CDECL locale::_Locimp::_Locimp_Addfac(
 
 void __CLRCALL_PURE_OR_CDECL _Locinfo::_Locinfo_ctor(
     _Locinfo* pLocinfo, int cat, const char* locname) { // capture a named locale
-    pLocinfo->_Oldlocname = _wsetlocale(LC_ALL, nullptr);
+    pLocinfo->_Oldlocname._From_wide(_wsetlocale(LC_ALL, nullptr));
     _Locinfo_Addcats(pLocinfo, cat, locname);
 }
 

stl/src/locale0.cpp

@@ -222,7 +222,7 @@ void __CLRCALL_PURE_OR_CDECL locale::_Locimp::_Locimp_dtor(_Locimp* _This) { //
 
 void __CLRCALL_PURE_OR_CDECL _Locinfo::_Locinfo_ctor(
     _Locinfo* pLocinfo, const char* locname) { // switch to a named locale
-    pLocinfo->_Oldlocname = _wsetlocale(LC_ALL, nullptr);
+    pLocinfo->_Oldlocname._From_wide(_wsetlocale(LC_ALL, nullptr));
 
     if (locname != nullptr) {
         locname = setlocale(LC_ALL, locname);
@@ -232,7 +232,13 @@ void __CLRCALL_PURE_OR_CDECL _Locinfo::_Locinfo_ctor(
 }
 
 void __CLRCALL_PURE_OR_CDECL _Locinfo::_Locinfo_dtor(_Locinfo* pLocinfo) { // destroy a _Locinfo object, revert locale
-    _wsetlocale(LC_ALL, pLocinfo->_Oldlocname._C_str());
+    if (pLocinfo->_Oldlocname._Empty()) {
+        // `pLocinfo->_Oldlocname._C_str()` points to a single `char` of value 0 in this case,
+        // so reinterpret_cast is not reliable.
+        _wsetlocale(LC_ALL, L"");
+    } else {
+        _wsetlocale(LC_ALL, reinterpret_cast<const wchar_t*>(pLocinfo->_Oldlocname._C_str()));
+    }
 }
 _STD_END