libstdc++: Use std::construct_at in std::common_iterator [PR103992]

This should have been done as part of the LWG 3574 changes.

libstdc++-v3/ChangeLog:

	PR libstdc++/103992
	* include/bits/stl_iterator.h (common_iterator): Use
	std::construct_at instead of placement new.
	* testsuite/24_iterators/common_iterator/1.cc: Check copy
	construction is usable in constant expressions.

2 files changed, 20 insertions, 4 deletions

diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 24a71ea..24c106e 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1907,14 +1907,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    if constexpr (is_trivially_default_constructible_v<_It>)
 	      _M_it = std::move(__x._M_it);
 	    else
-	      ::new((void*)std::__addressof(_M_it)) _It(__x._M_it);
+	      std::construct_at(std::__addressof(_M_it), __x._M_it);
 	  }
 	else if (_M_index == 1)
 	  {
 	    if constexpr (is_trivially_default_constructible_v<_Sent>)
 	      _M_sent = std::move(__x._M_sent);
 	    else
-	      ::new((void*)std::__addressof(_M_sent)) _Sent(__x._M_sent);
+	      std::construct_at(std::__addressof(_M_sent), __x._M_sent);
 	  }
       }
 
@@ -1928,14 +1928,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  if constexpr (is_trivially_default_constructible_v<_It>)
 	    _M_it = std::move(__x._M_it);
 	  else
-	    ::new((void*)std::__addressof(_M_it)) _It(__x._M_it);
+	    std::construct_at(std::__addressof(_M_it), __x._M_it);
 	}
       else if (_M_index == 1)
 	{
 	  if constexpr (is_trivially_default_constructible_v<_Sent>)
 	    _M_sent = std::move(__x._M_sent);
 	  else
-	    ::new((void*)std::__addressof(_M_sent)) _Sent(__x._M_sent);
+	    std::construct_at(std::__addressof(_M_sent), __x._M_sent);
 	}
     }
 
diff --git a/libstdc++-v3/testsuite/24_iterators/common_iterator/1.cc b/libstdc++-v3/testsuite/24_iterators/common_iterator/1.cc
index 484d0cc..365ee89 100644
--- a/libstdc++-v3/testsuite/24_iterators/common_iterator/1.cc
+++ b/libstdc++-v3/testsuite/24_iterators/common_iterator/1.cc
@@ -157,6 +157,22 @@ test04()
   VERIFY( x.i == 2 );
 }
 
+constexpr bool
+test_pr103992()
+{
+  using C1 = std::common_iterator<std::reverse_iterator<int*>,
+				  std::unreachable_sentinel_t>;
+  using C2 = std::common_iterator<std::reverse_iterator<const int*>,
+				  std::unreachable_sentinel_t>;
+  C1 c1;
+  C2 c2 = c1;
+  C1 c3 = c1;
+
+  return true;
+}
+
+static_assert( test_pr103992() );
+
 int
 main()
 {