LWG-3515: [stacktrace.basic.nonmem]: operator<< should be less templatized

stl/inc/stacktrace

@@ -339,13 +339,12 @@ _NODISCARD string to_string(const basic_stacktrace<_Alloc>& _St) {
     return _Result;
 }
 
-_EXPORT_STD template <class _CharT, class _Traits>
-basic_ostream<_CharT, _Traits>& operator<<(basic_ostream<_CharT, _Traits>& _Os, const stacktrace_entry& _Fx) {
+_EXPORT_STD ostream& operator<<(ostream& _Os, const stacktrace_entry& _Fx) {
     return _Os << _STD to_string(_Fx);
 }
 
-_EXPORT_STD template <class _CharT, class _Traits, class _Alloc>
-basic_ostream<_CharT, _Traits>& operator<<(basic_ostream<_CharT, _Traits>& _Os, const basic_stacktrace<_Alloc>& _St) {
+_EXPORT_STD template <class _Alloc>
+ostream& operator<<(ostream& _Os, const basic_stacktrace<_Alloc>& _St) {
     return _Os << _STD to_string(_St);
 }
 

tests/std/test.lst

@@ -224,6 +224,7 @@ tests\LWG3146_excessive_unwrapping_ref_cref
 tests\LWG3234_math_special_overloads
 tests\LWG3422_seed_seq_ctors
 tests\LWG3480_directory_iterator_range
+tests\LWG3515_stacktrace_ostream_operator_should_be_less_templatized
 tests\LWG3610_iota_view_size_and_integer_class
 tests\P0019R8_atomic_ref
 tests\P0024R2_parallel_algorithms_adjacent_difference

tests/std/tests/LWG3515_stacktrace_ostream_operator_should_be_less_templatized/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/LWG3515_stacktrace_ostream_operator_should_be_less_templatized/test.compile.pass.cpp

@@ -0,0 +1,39 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <concepts>
+#include <memory>
+#include <memory_resource>
+#include <ostream>
+#include <sstream>
+#include <stacktrace>
+#include <string>
+
+using namespace std;
+
+template <class Ostream, class Alloc = allocator<stacktrace_entry>>
+concept CanPrintStacktrace = requires(Ostream& os, const stacktrace_entry& f, const basic_stacktrace<Alloc>& st) {
+                                 os << f;
+                                 os << st;
+                             };
+
+template <class CharT>
+struct FancyCharTraits : char_traits<CharT> {};
+
+static_assert(CanPrintStacktrace<ostream>);
+static_assert(CanPrintStacktrace<ostringstream>);
+static_assert(CanPrintStacktrace<ostream, pmr::polymorphic_allocator<stacktrace_entry>>);
+
+static_assert(!CanPrintStacktrace<wostream>);
+static_assert(!CanPrintStacktrace<wostringstream>);
+static_assert(!CanPrintStacktrace<wostream, pmr::polymorphic_allocator<stacktrace_entry>>);
+
+using FancyCharStream = basic_ostream<char, FancyCharTraits<char>>;
+static_assert(!CanPrintStacktrace<FancyCharStream>);
+static_assert(!CanPrintStacktrace<FancyCharStream, pmr::polymorphic_allocator<stacktrace_entry>>);
+
+using FancyWcharStream = basic_ostream<wchar_t, FancyCharTraits<wchar_t>>;
+static_assert(!CanPrintStacktrace<FancyWcharStream>);
+static_assert(!CanPrintStacktrace<FancyWcharStream, pmr::polymorphic_allocator<stacktrace_entry>>);
+
+int main() {} // COMPILE-ONLY