Export VCRuntime entities properly

stl/inc/exception

@@ -35,8 +35,8 @@ _STD_END
 
 _STD_BEGIN
 
-_EXPORT_STD class exception;
-_EXPORT_STD class bad_exception;
+_EXPORT_STD using exception     = exception;
+_EXPORT_STD using bad_exception = bad_exception;
 
 _EXPORT_STD using ::terminate;
 

stl/inc/new

@@ -23,11 +23,6 @@ _STL_DISABLE_CLANG_WARNINGS
 
 // Mirroring <vcruntime_new.h> declarations:
 
-_STD_BEGIN
-_EXPORT_STD extern "C++" struct nothrow_t;
-_EXPORT_STD extern "C++" const nothrow_t nothrow;
-_STD_END
-
 _EXPORT_STD extern "C++" _NODISCARD _VCRT_ALLOCATOR void* __CRTDECL operator new(size_t);
 _EXPORT_STD extern "C++" _NODISCARD _VCRT_ALLOCATOR void* __CRTDECL operator new(
     size_t, const _STD nothrow_t&) noexcept;
@@ -43,13 +38,7 @@ _EXPORT_STD extern "C++" void __CRTDECL operator delete[](void*, const _STD noth
 
 #ifdef __cpp_aligned_new
 _STD_BEGIN
-#ifdef __EDG__ // TRANSITION, VSO-1618988
-extern "C++" {
-_EXPORT_STD enum class align_val_t : size_t;
-}
-#else // ^^^ workaround / no workaround vvv
-_EXPORT_STD extern "C++" enum class align_val_t : size_t;
-#endif // ^^^ no workaround ^^^
+_EXPORT_STD using align_val_t = align_val_t;
 _STD_END
 
 _EXPORT_STD extern "C++" _NODISCARD _VCRT_ALLOCATOR void* __CRTDECL operator new(size_t, _STD align_val_t);
@@ -76,8 +65,8 @@ _EXPORT_STD extern "C++" void __CRTDECL operator delete[](void*, void*) noexcept
 
 _STD_BEGIN
 #if _HAS_EXCEPTIONS
-_EXPORT_STD class bad_alloc;
-_EXPORT_STD class bad_array_new_length;
+_EXPORT_STD using bad_alloc            = bad_alloc;
+_EXPORT_STD using bad_array_new_length = bad_array_new_length;
 #else // ^^^ _HAS_EXCEPTIONS / !_HAS_EXCEPTIONS vvv
 // <exception> exports bad_alloc and bad_array_new_length.
 #endif // ^^^ !_HAS_EXCEPTIONS ^^^

stl/inc/typeinfo

@@ -23,7 +23,7 @@ _STL_DISABLE_CLANG_WARNINGS
 #include <vcruntime_typeinfo.h>
 #pragma pop_macro("raw_name")
 
-_EXPORT_STD extern "C++" class type_info; // for typeid, MSVC looks for type_info in the global namespace
+_EXPORT_STD using type_info = type_info; // for typeid, MSVC looks for type_info in the global namespace
 
 _STD_BEGIN
 
@@ -33,8 +33,8 @@ _INLINE_VAR constexpr int _Small_object_num_ptrs = 6 + 16 / sizeof(void*);
 _EXPORT_STD using ::type_info;
 
 #if _HAS_EXCEPTIONS
-_EXPORT_STD class bad_cast;
-_EXPORT_STD class bad_typeid;
+_EXPORT_STD using bad_cast   = bad_cast;
+_EXPORT_STD using bad_typeid = bad_typeid;
 #else // ^^^ _HAS_EXCEPTIONS / !_HAS_EXCEPTIONS vvv
 _EXPORT_STD class bad_cast : public exception { // base of all bad cast exceptions
 public:

stl/modules/std.ixx

@@ -7,6 +7,12 @@ module;
 // This named module expects to be built with classic headers, not header units.
 #define _BUILD_STD_MODULE
 
+// N4971 [module.interface]/6: "A redeclaration of an entity X is implicitly exported
+// if X was introduced by an exported declaration; otherwise it shall not be exported."
+// Therefore, we'll need to introduce the `nothrow` object with an exported declaration,
+// instead of allowing <vcruntime_new.h> to declare it.
+#define __NOTHROW_T_DEFINED
+
 // The subset of "C headers" [tab:c.headers] corresponding to
 // the "C++ headers for C library facilities" [tab:headers.cpp.c]
 #include <assert.h>
@@ -36,6 +42,16 @@ export module std;
 #pragma warning(push)
 #pragma warning(disable : 5244) // '#include <meow>' in the purview of module 'std' appears erroneous.
 
+#include <yvals_core.h>
+#pragma pack(push, _CRT_PACKING)
+_STD_BEGIN
+_EXPORT_STD extern "C++" struct nothrow_t {
+    explicit nothrow_t() = default;
+};
+_EXPORT_STD extern "C++" const nothrow_t nothrow;
+_STD_END
+#pragma pack(pop)
+
 // "C++ library headers" [tab:headers.cpp]
 #include <algorithm>
 #if _HAS_STATIC_RTTI

tests/std/include/test_header_units_and_modules.hpp

@@ -204,6 +204,10 @@ void test_deque() {
 void test_exception() {
     using namespace std;
     puts("Testing <exception>.");
+
+    static_assert(is_class_v<exception>);
+    static_assert(is_class_v<bad_exception>);
+
     assert(uncaught_exceptions() == 0);
     const exception_ptr ep = current_exception();
     assert(!ep);
@@ -471,6 +475,12 @@ void test_mutex() {
 void test_new() {
     using namespace std;
     puts("Testing <new>.");
+
+    static_assert(is_class_v<bad_alloc>);
+    static_assert(is_class_v<bad_array_new_length>);
+    static_assert(is_same_v<underlying_type_t<align_val_t>, size_t>);
+    static_assert(is_class_v<nothrow_t>);
+
     bool caught_bad_alloc = false;
 
     try {
@@ -988,6 +998,11 @@ void test_typeindex() {
 void test_typeinfo() {
     using namespace std;
     puts("Testing <typeinfo>.");
+
+    static_assert(is_class_v<type_info>);
+    static_assert(is_class_v<bad_cast>);
+    static_assert(is_class_v<bad_typeid>);
+
     const type_info& t1 = typeid(int);
     const type_info& t2 = typeid(const int&);
     const type_info& t3 = typeid(double);