commit c4ecb11e4f7ea15f636e463248c8b14083bef05d
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Oct 19 11:38:26 2021

    libstdc++: Fix std::stack deduction guide
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/stl_stack.h (stack(Iterator, Iterator)): Remove
            non-deducible template parameter from deduction guide.
            * testsuite/23_containers/stack/deduction.cc: Check new C++23
            deduction guides.

diff --git a/libstdc++-v3/include/bits/stl_stack.h b/libstdc++-v3/include/bits/stl_stack.h
index 429743f5514..76b2e242c37 100644
--- a/libstdc++-v3/include/bits/stl_stack.h
+++ b/libstdc++-v3/include/bits/stl_stack.h
@@ -322,7 +322,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     -> stack<typename _Container::value_type, _Container>;
 
 #ifdef __cpp_lib_adaptor_iterator_pair_constructor
-  template<typename _InputIterator, typename _Allocator,
+  template<typename _InputIterator,
 	   typename _ValT
 	     = typename iterator_traits<_InputIterator>::value_type,
 	   typename = _RequireInputIter<_InputIterator>>
diff --git a/libstdc++-v3/testsuite/23_containers/stack/deduction.cc b/libstdc++-v3/testsuite/23_containers/stack/deduction.cc
index 169a063687b..dea7ba060d9 100644
--- a/libstdc++-v3/testsuite/23_containers/stack/deduction.cc
+++ b/libstdc++-v3/testsuite/23_containers/stack/deduction.cc
@@ -87,3 +87,17 @@ test02()
   std::stack s8(std::move(l), l.get_allocator());
   check_type<std::stack<long, std::list<long>>>(s8);
 }
+
+#if __cpp_lib_adaptor_iterator_pair_constructor
+void
+test03()
+{
+  std::list<long> l;
+
+  std::stack s1(l.begin(), l.end());
+  check_type<std::stack<long>>(s1);
+
+  std::stack s2(l.begin(), l.end(), std::allocator<long>());
+  check_type<std::stack<long>>(s1);
+}
+#endif