Update filesystem library to use GetTempPath2 on Windows 11 (#2302)

Co-authored-by: Nicole Mazzuca <mazzucan@outlook.com>
Co-authored-by: Stephan T. Lavavej <stl@microsoft.com>

stl/src/filesys.cpp

@@ -15,6 +15,13 @@
 
 #include <Windows.h>
 
+#ifdef _M_CEE_PURE
+#define __crtGetTempPath2W(BufferLength, Buffer) GetTempPathW(BufferLength, Buffer)
+#else // vvv !defined(_M_CEE_PURE) vvv
+extern "C" _Success_(return > 0 && return < BufferLength) DWORD
+    __stdcall __crtGetTempPath2W(_In_ DWORD BufferLength, _Out_writes_to_opt_(BufferLength, return +1) LPWSTR Buffer);
+#endif // ^^^ !defined(_M_CEE_PURE) ^^^
+
 _FS_BEGIN
 static file_type _Map_mode(int _Mode) { // map Windows file attributes to file_status
     constexpr int _File_attribute_regular =
@@ -162,7 +169,7 @@ _FS_DLL wchar_t* __CLRCALL_PURE_OR_CDECL _Symlink_get(wchar_t (&_Dest)[_MAX_FILE
 _FS_DLL wchar_t* __CLRCALL_PURE_OR_CDECL _Temp_get(wchar_t (&_Dest)[_MAX_FILESYS_NAME]) {
     // get temp directory
     wchar_t _Dentry[MAX_PATH];
-    return _Strcpy(_Dest, GetTempPathW(MAX_PATH, _Dentry) != 0 ? _Dentry : L".");
+    return _Strcpy(_Dest, __crtGetTempPath2W(MAX_PATH, _Dentry) != 0 ? _Dentry : L".");
 }
 
 

stl/src/filesystem.cpp

@@ -9,6 +9,7 @@
 // Do not include or define anything else here.
 // In particular, basic_string must not be included here.
 
+#include <atomic>
 #include <clocale>
 #include <corecrt_terminate.h>
 #include <cstdlib>
@@ -761,13 +762,38 @@ _Success_(return == __std_win_error::_Success) __std_win_error
     return __std_win_error{GetLastError()};
 }
 
+namespace {
+    _Success_(return > 0 && return < nBufferLength) DWORD WINAPI
+        _Stl_GetTempPath2W(_In_ DWORD nBufferLength, _Out_writes_to_opt_(nBufferLength, return +1) LPWSTR lpBuffer) {
+        using _Fun_ptr = decltype(&::GetTempPath2W);
+
+        _Fun_ptr _PfGetTempPath2W;
+        {
+            static _STD atomic<_Fun_ptr> _Static{nullptr};
+
+            _PfGetTempPath2W = _Static.load(_STD memory_order_relaxed);
+            if (!_PfGetTempPath2W) {
+                const auto _Kernel32 = ::GetModuleHandleW(L"kernel32.dll");
+                _Analysis_assume_(_Kernel32);
+                _PfGetTempPath2W = reinterpret_cast<_Fun_ptr>(::GetProcAddress(_Kernel32, "GetTempPath2W"));
+                if (!_PfGetTempPath2W) {
+                    _PfGetTempPath2W = &::GetTempPathW;
+                }
+                _Static.store(_PfGetTempPath2W, _STD memory_order_relaxed); // overwriting with the same value is okay
+            }
+        }
+
+        return _PfGetTempPath2W(nBufferLength, lpBuffer);
+    }
+} // unnamed namespace
+
 [[nodiscard]] _Success_(return._Error == __std_win_error::_Success) __std_ulong_and_error
     __stdcall __std_fs_get_temp_path(_Out_writes_z_(__std_fs_temp_path_max) wchar_t* const _Target) noexcept {
-    // calls GetTempPathW
+    // calls GetTempPath2W if available (Win11+), else calls GetTempPathW
     // If getting the path failed, returns 0 size; otherwise, returns the size of the
     // expected directory. If the path could be resolved to an existing directory,
     // returns __std_win_error::_Success; otherwise, returns __std_win_error::_Max.
-    const auto _Size = GetTempPathW(__std_fs_temp_path_max, _Target);
+    const auto _Size = _Stl_GetTempPath2W(__std_fs_temp_path_max, _Target);
     if (_Size == 0) {
         return {0, __std_win_error{GetLastError()}};
     }

stl/src/winapisupp.cpp

@@ -27,10 +27,12 @@ namespace {
         eGetSystemTimePreciseAsFileTime,
 #endif // _STL_WIN32_WINNT < _WIN32_WINNT_WIN8
 
+        eGetTempPath2W,
+
         eMaxKernel32Function
     };
 
-    PVOID __KERNEL32Functions[eMaxKernel32Function > 0 ? eMaxKernel32Function : 1]{};
+    PVOID __KERNEL32Functions[eMaxKernel32Function]{};
 
 // Use this macro for caching a function pointer from a DLL
 #define STOREFUNCTIONPOINTER(instance, function_name) \
@@ -384,6 +386,19 @@ extern "C" void __cdecl __crtGetSystemTimePreciseAsFileTime(_Out_ LPFILETIME lpS
 
 #endif // _STL_WIN32_WINNT < _WIN32_WINNT_WIN8
 
+extern "C" _Success_(return > 0 && return < BufferLength) DWORD
+    __stdcall __crtGetTempPath2W(_In_ DWORD BufferLength, _Out_writes_to_opt_(BufferLength, return +1) LPWSTR Buffer) {
+#if !defined(_ONECORE)
+    // use GetTempPath2W if it is available (only on Windows 11+)...
+    IFDYNAMICGETCACHEDFUNCTION(GetTempPath2W) {
+        return pfGetTempPath2W(BufferLength, Buffer);
+    }
+#endif // ^^^ !defined(_ONECORE) ^^^
+
+    // ...otherwise use GetTempPathW.
+    return GetTempPathW(BufferLength, Buffer);
+}
+
 
 // Helper to load all necessary Win32 API function pointers
 
@@ -405,6 +420,10 @@ static int __cdecl initialize_pointers() {
     STOREFUNCTIONPOINTER(hKernel32, GetSystemTimePreciseAsFileTime);
 #endif // _STL_WIN32_WINNT < _WIN32_WINNT_WIN8
 
+    // Note that GetTempPath2W is defined as of Windows 10 Build 20348 (a server release) or Windows 11,
+    // but there is no "_WIN32_WINNT_WIN11" constant, so we will always dynamically load it
+    STOREFUNCTIONPOINTER(hKernel32, GetTempPath2W);
+
     return 0;
 }