Implement P1147R1 "Printing volatile Pointers" (#2262)

Co-authored-by: Casey Carter <Casey@Carter.net>
Co-authored-by: Stephan T. Lavavej <stl@nuwen.net>

stl/inc/ostream

@@ -454,7 +454,14 @@ public:
         return *this;
     }
 
-#if _HAS_CXX17 // LWG-2221 "No formatted output operator for nullptr"
+#if _HAS_CXX23
+    template <class = void> // TRANSITION, ABI
+    basic_ostream& operator<<(const volatile void* _Val) {
+        return *this << const_cast<const void*>(_Val);
+    }
+#endif // _HAS_CXX23
+
+#if _HAS_CXX17
     template <class = void> // TRANSITION, ABI
     basic_ostream& operator<<(nullptr_t) { // insert a null pointer
         return *this << "nullptr";

stl/inc/yvals_core.h

@@ -276,6 +276,7 @@
 // P0943R6 Supporting C Atomics In C++
 // P1048R1 is_scoped_enum
 // P1132R7 out_ptr(), inout_ptr()
+// P1147R1 Printing volatile Pointers
 // P1272R4 byteswap()
 // P1425R4 Iterator Pair Constructors For stack And queue
 // P1659R3 ranges::starts_with, ranges::ends_with

tests/std/test.lst

@@ -434,6 +434,7 @@ tests\P1135R6_atomic_wait_vista
 tests\P1135R6_barrier
 tests\P1135R6_latch
 tests\P1135R6_semaphore
+tests\P1147R1_printing_volatile_pointers
 tests\P1165R1_consistently_propagating_stateful_allocators
 tests\P1208R6_source_location
 tests\P1272R4_byteswap

tests/std/tests/P1147R1_printing_volatile_pointers/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/P1147R1_printing_volatile_pointers/test.cpp

@@ -0,0 +1,29 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <cassert>
+#include <sstream>
+#include <string>
+
+using namespace std;
+
+template <typename T>
+string getTextValue(T* ptr) {
+    ostringstream out;
+    out << ptr;
+    return out.str();
+}
+
+void test(int value) {
+    int* p0          = &value;
+    volatile int* p1 = p0;
+
+    const string expected = getTextValue(p0);
+    const string actual   = getTextValue(p1);
+
+    assert(expected == actual);
+}
+
+int main() {
+    test(42);
+}