Implement P2467R1 ios_base::noreplace: Exclusive Mode For fstreams (#2932)

stl/inc/xiosbase

@@ -73,6 +73,9 @@ public:
     static constexpr _Openmode _Nocreate  = static_cast<_Openmode>(0x40);
     static constexpr _Openmode _Noreplace = static_cast<_Openmode>(0x80);
     static constexpr _Openmode binary     = static_cast<_Openmode>(0x20);
+#if _HAS_CXX23
+    static constexpr _Openmode noreplace = _Noreplace;
+#endif
 
     enum _Seekdir { // constants for file positioning options
         _Seekbeg,

stl/inc/yvals_core.h

@@ -341,6 +341,7 @@
 // P2445R1 forward_like()
 // P2446R2 views::as_rvalue
 // P2465R3 Standard Library Modules std And std.compat
+// P2467R1 ios_base::noreplace: Exclusive Mode For fstreams
 // P2494R2 Relaxing Range Adaptors To Allow Move-Only Types
 // P2499R0 string_view Range Constructor Should Be explicit
 // P2549R1 unexpected<E>::error()
@@ -1661,6 +1662,7 @@ _EMIT_STL_ERROR(STL1004, "C++98 unexpected() is incompatible with C++23 unexpect
 
 #define __cpp_lib_forward_like   202207L
 #define __cpp_lib_invoke_r       202106L
+#define __cpp_lib_ios_noreplace  202207L
 #define __cpp_lib_is_scoped_enum 202011L
 
 #if !defined(__clang__) && !defined(__EDG__) // TRANSITION, Clang and EDG support for modules

stl/src/fiopen.cpp

@@ -10,14 +10,16 @@ namespace {
 
     FILE* _Xfsopen(_In_z_ const char* filename, _In_ int mode, _In_ int prot) {
         static const char* const mods[] = {// fopen mode strings corresponding to valid[i]
-            "r", "w", "w", "a", "rb", "wb", "wb", "ab", "r+", "w+", "a+", "r+b", "w+b", "a+b", nullptr};
+            "r", "w", "w", "a", "rb", "wb", "wb", "ab", "r+", "w+", "a+", "r+b", "w+b", "a+b", "wx", "wx", "w+x", "wbx",
+            "wbx", "w+bx", nullptr};
 
         return _fsopen(filename, mods[mode], prot);
     }
 
     FILE* _Xfsopen(_In_z_ const wchar_t* filename, _In_ int mode, _In_ int prot) {
         static const wchar_t* const mods[] = {// fopen mode strings corresponding to valid[i]
-            L"r", L"w", L"w", L"a", L"rb", L"wb", L"wb", L"ab", L"r+", L"w+", L"a+", L"r+b", L"w+b", L"a+b", nullptr};
+            L"r", L"w", L"w", L"a", L"rb", L"wb", L"wb", L"ab", L"r+", L"w+", L"a+", L"r+b", L"w+b", L"a+b", L"wx",
+            L"wx", L"w+x", L"wbx", L"wbx", L"w+bx", nullptr};
 
         return _wfsopen(filename, mods[mode], prot);
     }
@@ -40,11 +42,16 @@ namespace {
             ios_base::in | ios_base::out | ios_base::binary,
             ios_base::in | ios_base::out | ios_base::trunc | ios_base::binary,
             ios_base::in | ios_base::out | ios_base::app | ios_base::binary,
+            ios_base::out | ios_base::_Noreplace,
+            ios_base::out | ios_base::trunc | ios_base::_Noreplace,
+            ios_base::out | ios_base::in | ios_base::trunc | ios_base::_Noreplace,
+            ios_base::out | ios_base::binary | ios_base::_Noreplace,
+            ios_base::out | ios_base::binary | ios_base::trunc | ios_base::_Noreplace,
+            ios_base::out | ios_base::in | ios_base::trunc | ios_base::binary | ios_base::_Noreplace,
         };
 
         FILE* fp                     = nullptr;
         ios_base::openmode atendflag = mode & ios_base::ate;
-        ios_base::openmode norepflag = mode & ios_base::_Noreplace;
 
         if (mode & ios_base::_Nocreate) {
             mode |= ios_base::in; // file must exist
@@ -54,7 +61,7 @@ namespace {
             mode |= ios_base::out; // extension -- app implies out
         }
 
-        mode &= ~(ios_base::ate | ios_base::_Nocreate | ios_base::_Noreplace);
+        mode &= ~(ios_base::ate | ios_base::_Nocreate);
 
         // look for a valid mode
         int n = 0;
@@ -64,16 +71,6 @@ namespace {
             }
         }
 
-        if (norepflag && (mode & (ios_base::out | ios_base::app))
-            && (fp = _Xfsopen(filename, 0, prot)) != nullptr) { // file must not exist, close and fail
-            fclose(fp);
-            return nullptr;
-        }
-
-        if (fp != nullptr && fclose(fp) != 0) {
-            return nullptr; // can't close after test open
-        }
-
         if ((fp = _Xfsopen(filename, n, prot)) == nullptr) {
             return nullptr; // open failed
         }

tests/std/test.lst

@@ -574,6 +574,7 @@ tests\P2443R1_views_chunk_by_death
 tests\P2445R1_forward_like
 tests\P2446R2_views_as_rvalue
 tests\P2465R3_standard_library_modules
+tests\P2467R1_exclusive_mode_fstreams
 tests\P2494R2_move_only_range_adaptors
 tests\P2517R1_apply_conditional_noexcept
 tests\VSO_0000000_allocator_propagation

tests/std/tests/P2467R1_exclusive_mode_fstreams/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\usual_latest_matrix.lst

tests/std/tests/P2467R1_exclusive_mode_fstreams/test.cpp

@@ -0,0 +1,68 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <cassert>
+#include <filesystem>
+#include <fstream>
+#include <ios>
+
+namespace fs = std::filesystem;
+
+const fs::path test_file{L"test.dat"};
+
+struct CreateTempFile {
+    fs::path m_path;
+    CreateTempFile(const fs::path& path) : m_path(path) {
+        std::ofstream{path};
+    }
+
+    ~CreateTempFile() {
+        fs::remove(m_path);
+    }
+};
+
+void test_file_create(const std::ios_base::openmode mode) {
+    {
+        std::fstream file{test_file, mode};
+        assert(!file.fail());
+    }
+    assert(fs::exists(test_file));
+    fs::remove(test_file);
+}
+
+void test_file_already_exists(const std::ios_base::openmode mode) {
+    CreateTempFile tmp{test_file};
+    std::fstream file{test_file, mode};
+    assert(file.fail());
+}
+
+void test_file_create_fail(const std::ios_base::openmode bad_mode) {
+    {
+        std::fstream file{test_file, bad_mode};
+        assert(file.fail());
+    }
+    assert(!fs::exists(test_file));
+}
+
+int main() {
+    using IB = std::ios_base;
+
+    test_file_create(IB::out | IB::noreplace);
+    test_file_create(IB::out | IB::trunc | IB::noreplace);
+    test_file_create(IB::out | IB::in | IB::trunc | IB::noreplace);
+    test_file_create(IB::out | IB::binary | IB::noreplace);
+    test_file_create(IB::out | IB::binary | IB::trunc | IB::noreplace);
+    test_file_create(IB::out | IB::in | IB::trunc | IB::binary | IB::noreplace);
+
+    test_file_already_exists(IB::out | IB::noreplace);
+    test_file_already_exists(IB::out | IB::trunc | IB::noreplace);
+    test_file_already_exists(IB::out | IB::in | IB::trunc | IB::noreplace);
+    test_file_already_exists(IB::out | IB::binary | IB::noreplace);
+    test_file_already_exists(IB::out | IB::binary | IB::trunc | IB::noreplace);
+    test_file_already_exists(IB::out | IB::in | IB::trunc | IB::binary | IB::noreplace);
+
+    test_file_create_fail(IB::in | IB::noreplace);
+    test_file_create_fail(IB::in | IB::trunc | IB::noreplace);
+    test_file_create_fail(IB::in | IB::binary | IB::noreplace);
+    test_file_create_fail(IB::in | IB::binary | IB::trunc | IB::noreplace);
+}

tests/std/tests/VSO_0157762_feature_test_macros/test.compile.pass.cpp

@@ -1036,6 +1036,20 @@ STATIC_ASSERT(__cpp_lib_invoke_r == 202106L);
 #endif
 #endif
 
+#if _HAS_CXX23
+#ifndef __cpp_lib_ios_noreplace
+#error __cpp_lib_ios_noreplace is not defined
+#elif __cpp_lib_ios_noreplace != 202207L
+#error __cpp_lib_ios_noreplace is not 202207L
+#else
+STATIC_ASSERT(__cpp_lib_ios_noreplace == 202207L);
+#endif
+#else
+#ifdef __cpp_lib_ios_noreplace
+#error __cpp_lib_ios_noreplace is defined
+#endif
+#endif
+
 #if _HAS_CXX17
 #ifndef __cpp_lib_is_aggregate
 #error __cpp_lib_is_aggregate is not defined