[committed] libstdc++: Implement LWG 1203 for rvalue iostreams

Jonathan Wakely jwakely@redhat.com
Fri Apr 30 13:48:25 GMT 2021


This implements the resolution of LWG 1203 so that the constraints for
rvalue stream insertion/extraction are simpler, and the return type is
the original rvalue stream type not its base class.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/std/istream (operator>>(Istream&&, x&)): Simplify, as
	per LWG 1203.
	* include/std/ostream (operator<<(Ostream&&, const x&)):
	Likewise.
	* testsuite/27_io/basic_istream/extractors_character/char/lwg2499_neg.cc:
	Adjust dg-error pattern.
	* testsuite/27_io/basic_istream/extractors_character/wchar_t/lwg2499_neg.cc:
	Likewise.
	* testsuite/27_io/basic_istream/extractors_other/char/4.cc: Define
	is_extractable trait to replace std::__is_extractable. Make it
	work with rvalue streams as well as lvalues, to replace f() and
	g() helper functions.
	* testsuite/27_io/basic_istream/extractors_other/wchar_t/4.cc:
	Likewise.
	* testsuite/27_io/basic_ostream/inserters_other/char/6.cc:
	Define is_insertable trait to replace std::__is_insertable. Make
	it work with rvalue streams as well as lvalues, to replace f()
	and g() helper functions.
	* testsuite/27_io/basic_ostream/inserters_other/wchar_t/6.cc:
	Likewise.
	* testsuite/27_io/filesystem/path/io/dr2989.cc: Prune additional
	errors from new constraints.
	* testsuite/27_io/rvalue_streams-2.cc: Remove PR 80675 checks,
	which are no longer expected to compile.
	* testsuite/27_io/rvalue_streams.cc: Adjust existing test.
	Verify LWG 1203 changes.

Tested powerpc64le-linux. Committed to trunk.

-------------- next part --------------
commit aa475c4ac80733f85ba47b109fc1900f05e810e2
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Apr 30 14:07:28 2021

    libstdc++: Implement LWG 1203 for rvalue iostreams
    
    This implements the resolution of LWG 1203 so that the constraints for
    rvalue stream insertion/extraction are simpler, and the return type is
    the original rvalue stream type not its base class.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            * include/std/istream (operator>>(Istream&&, x&)): Simplify, as
            per LWG 1203.
            * include/std/ostream (operator<<(Ostream&&, const x&)):
            Likewise.
            * testsuite/27_io/basic_istream/extractors_character/char/lwg2499_neg.cc:
            Adjust dg-error pattern.
            * testsuite/27_io/basic_istream/extractors_character/wchar_t/lwg2499_neg.cc:
            Likewise.
            * testsuite/27_io/basic_istream/extractors_other/char/4.cc: Define
            is_extractable trait to replace std::__is_extractable. Make it
            work with rvalue streams as well as lvalues, to replace f() and
            g() helper functions.
            * testsuite/27_io/basic_istream/extractors_other/wchar_t/4.cc:
            Likewise.
            * testsuite/27_io/basic_ostream/inserters_other/char/6.cc:
            Define is_insertable trait to replace std::__is_insertable. Make
            it work with rvalue streams as well as lvalues, to replace f()
            and g() helper functions.
            * testsuite/27_io/basic_ostream/inserters_other/wchar_t/6.cc:
            Likewise.
            * testsuite/27_io/filesystem/path/io/dr2989.cc: Prune additional
            errors from new constraints.
            * testsuite/27_io/rvalue_streams-2.cc: Remove PR 80675 checks,
            which are no longer expected to compile.
            * testsuite/27_io/rvalue_streams.cc: Adjust existing test.
            Verify LWG 1203 changes.

diff --git a/libstdc++-v3/include/std/istream b/libstdc++-v3/include/std/istream
index 1e5ebe4e88c..ea34cce6298 100644
--- a/libstdc++-v3/include/std/istream
+++ b/libstdc++-v3/include/std/istream
@@ -953,80 +953,34 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     ws(basic_istream<_CharT, _Traits>& __is);
 
 #if __cplusplus >= 201103L
-  template<typename _Ch, typename _Up>
-    basic_istream<_Ch, _Up>&
-    __is_convertible_to_basic_istream_test(basic_istream<_Ch, _Up>*);
-
-  template<typename _Tp, typename = void>
-    struct __is_convertible_to_basic_istream_impl
-    {
-      using __istream_type = void;
-    };
-
-  template<typename _Tp>
-    using __do_is_convertible_to_basic_istream_impl =
-    decltype(__is_convertible_to_basic_istream_test
-	     (declval<typename remove_reference<_Tp>::type*>()));
-
-  template<typename _Tp>
-    struct __is_convertible_to_basic_istream_impl
-    <_Tp,
-     __void_t<__do_is_convertible_to_basic_istream_impl<_Tp>>>
-    {
-      using __istream_type =
-	__do_is_convertible_to_basic_istream_impl<_Tp>;
-    };
-
-  template<typename _Tp>
-    struct __is_convertible_to_basic_istream
-    : __is_convertible_to_basic_istream_impl<_Tp>
-    {
-    public:
-      using type = __not_<is_void<
-        typename __is_convertible_to_basic_istream_impl<_Tp>::__istream_type>>;
-      constexpr static bool value = type::value;
-    };
-
-  template<typename _Istream, typename _Tp, typename = void>
-    struct __is_extractable : false_type {};
-
-  template<typename _Istream, typename _Tp>
-    struct __is_extractable<_Istream, _Tp,
-			    __void_t<decltype(declval<_Istream&>()
-					      >> declval<_Tp>())>>
-    : true_type {};
-
-  template<typename _Istream>
-    using __rvalue_istream_type =
-      typename __is_convertible_to_basic_istream<
-	_Istream>::__istream_type;
-
-  // [27.7.1.6] Rvalue stream extraction
+  // C++11 27.7.2.6 Rvalue stream extraction [istream.rvalue]
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // 2328. Rvalue stream extraction should use perfect forwarding
+  // 1203. More useful rvalue stream insertion
+
+  // SFINAE helper to check constraints for operator>>(Istream&&, T&&).
+  // If the constraints are satisfied, it is an alias for Istream&&.
+  template<typename _Is, typename _Tp,
+	   typename = decltype(std::__rval_streamable<_Is>()
+				 >> std::declval<_Tp>())>
+    using __rvalue_stream_extraction_t = _Is&&;
+
   /**
    *  @brief  Generic extractor for rvalue stream
    *  @param  __is  An input stream.
    *  @param  __x  A reference to the extraction target.
-   *  @return  is
+   *  @return  __is
    *
    *  This is just a forwarding function to allow extraction from
    *  rvalue streams since they won't bind to the extractor functions
    *  that take an lvalue reference.
   */
   template<typename _Istream, typename _Tp>
-    inline
-    typename enable_if<__and_<__not_<is_lvalue_reference<_Istream>>,
-			      __is_convertible_to_basic_istream<_Istream>,
-			      __is_extractable<
-				__rvalue_istream_type<_Istream>,
-				_Tp&&>>::value,
-		       __rvalue_istream_type<_Istream>>::type
+    inline __rvalue_stream_extraction_t<_Istream, _Tp>
     operator>>(_Istream&& __is, _Tp&& __x)
     {
-      __rvalue_istream_type<_Istream> __ret_is = __is;
-      __ret_is >> std::forward<_Tp>(__x);
-      return __ret_is;
+      __is >> std::forward<_Tp>(__x);
+      return std::move(__is);
     }
 #endif // C++11
 
diff --git a/libstdc++-v3/include/std/ostream b/libstdc++-v3/include/std/ostream
index a70221f2513..fdd2a87665c 100644
--- a/libstdc++-v3/include/std/ostream
+++ b/libstdc++-v3/include/std/ostream
@@ -704,77 +704,52 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __os.flush(); }
 
 #if __cplusplus >= 201103L
-  template<typename _Ch, typename _Up>
-    basic_ostream<_Ch, _Up>&
-    __is_convertible_to_basic_ostream_test(basic_ostream<_Ch, _Up>*);
-
-  template<typename _Tp, typename = void>
-    struct __is_convertible_to_basic_ostream_impl
-    {
-      using __ostream_type = void;
-    };
+  // C++11 27.7.3.9 Rvalue stream insertion [ostream.rvalue]
+  // _GLIBCXX_RESOLVE_LIB_DEFECTS
+  // 1203. More useful rvalue stream insertion
 
+  // SFINAE helper to check constraints for operator<<(Ostream&&, const T&).
+  // If Ostream is publicly and unambiguously derived from ios_base, then
+  // __rval_streamable<Ostream>() is equivalent to declval<Ostream&>().
+  // Otherwise, it results in a substitution failure. Specifically, it will
+  // fail if Ostream is an lvalue reference or the same type as ios_base.
+  // Use concepts if possible because they're cheaper to evaluate.
+#if __cpp_lib_concepts
   template<typename _Tp>
-    using __do_is_convertible_to_basic_ostream_impl =
-    decltype(__is_convertible_to_basic_ostream_test
-	     (declval<typename remove_reference<_Tp>::type*>()));
+    requires (!is_same_v<_Tp, ios_base>)
+      && requires (_Tp* __t, ios_base* __b) { __b = __t; }
+    _Tp&
+    __rval_streamable();
+#else
+  template<typename _Tp,
+	   typename = _Require<__not_<__is_one_of<_Tp, _Tp&, ios_base>>>>
+    _Tp&
+    __rval_streamable(ios_base* = (_Tp*)nullptr);
+#endif
 
-  template<typename _Tp>
-    struct __is_convertible_to_basic_ostream_impl
-    <_Tp,
-     __void_t<__do_is_convertible_to_basic_ostream_impl<_Tp>>>
-    {
-      using __ostream_type =
-	__do_is_convertible_to_basic_ostream_impl<_Tp>;
-    };
-
-  template<typename _Tp>
-    struct __is_convertible_to_basic_ostream
-    : __is_convertible_to_basic_ostream_impl<_Tp>
-    {
-    public:
-      using type = __not_<is_void<
-        typename __is_convertible_to_basic_ostream_impl<_Tp>::__ostream_type>>;
-      constexpr static bool value = type::value;
-    };
-
-  template<typename _Ostream, typename _Tp, typename = void>
-    struct __is_insertable : false_type {};
-
-  template<typename _Ostream, typename _Tp>
-    struct __is_insertable<_Ostream, _Tp,
-			   __void_t<decltype(declval<_Ostream&>()
-					     << declval<const _Tp&>())>>
-				    : true_type {};
-
-  template<typename _Ostream>
-    using __rvalue_ostream_type =
-      typename __is_convertible_to_basic_ostream<
-	_Ostream>::__ostream_type;
+  // SFINAE helper to check constraints for operator<<(Ostream&&, const T&).
+  // If the constraints are satisfied, it is an alias for Ostream&&.
+  template<typename _Os, typename _Tp,
+	   typename = decltype(std::__rval_streamable<_Os>()
+				 << std::declval<const _Tp&>())>
+    using __rvalue_stream_insertion_t = _Os&&;
 
   /**
    *  @brief  Generic inserter for rvalue stream
    *  @param  __os  An input stream.
    *  @param  __x  A reference to the object being inserted.
-   *  @return  os
+   *  @return  __os
    *
    *  This is just a forwarding function to allow insertion to
    *  rvalue streams since they won't bind to the inserter functions
    *  that take an lvalue reference.
   */
   template<typename _Ostream, typename _Tp>
-    inline
-    typename enable_if<__and_<__not_<is_lvalue_reference<_Ostream>>,
-			      __is_convertible_to_basic_ostream<_Ostream>,
-			      __is_insertable<
-				__rvalue_ostream_type<_Ostream>,
-				const _Tp&>>::value,
-		       __rvalue_ostream_type<_Ostream>>::type
+    inline __rvalue_stream_insertion_t<_Ostream, _Tp>
     operator<<(_Ostream&& __os, const _Tp& __x)
     {
-      __rvalue_ostream_type<_Ostream> __ret_os = __os;
-      __ret_os << __x;
-      return __ret_os;
+      __os << __x;
+      return std::move(__os);
     }
 
 #if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
diff --git a/libstdc++-v3/testsuite/27_io/basic_istream/extractors_character/char/lwg2499_neg.cc b/libstdc++-v3/testsuite/27_io/basic_istream/extractors_character/char/lwg2499_neg.cc
index 7a39e7c1a3c..abd68af8a9a 100644
--- a/libstdc++-v3/testsuite/27_io/basic_istream/extractors_character/char/lwg2499_neg.cc
+++ b/libstdc++-v3/testsuite/27_io/basic_istream/extractors_character/char/lwg2499_neg.cc
@@ -26,9 +26,9 @@
 void
 test01(std::istream& in, char* pc, signed char* sc, unsigned char* uc)
 {
-  in >> pc; // { dg-error "here" }
-  in >> sc; // { dg-error "here" }
-  in >> uc; // { dg-error "here" }
+  in >> pc; // { dg-error "no match" }
+  in >> sc; // { dg-error "no match" }
+  in >> uc; // { dg-error "no match" }
 }
 
 struct CT : std::char_traits<char> { };
@@ -37,9 +37,9 @@ void
 test02(std::basic_istream<char, CT>& in, char* pc, signed char* sc,
        unsigned char* uc)
 {
-  in >> pc; // { dg-error "here" }
-  in >> sc; // { dg-error "here" }
-  in >> uc; // { dg-error "here" }
+  in >> pc; // { dg-error "no match" }
+  in >> sc; // { dg-error "no match" }
+  in >> uc; // { dg-error "no match" }
 }
 
 // { dg-excess-errors "" }
diff --git a/libstdc++-v3/testsuite/27_io/basic_istream/extractors_character/wchar_t/lwg2499_neg.cc b/libstdc++-v3/testsuite/27_io/basic_istream/extractors_character/wchar_t/lwg2499_neg.cc
index bc8dfacf5f5..214f8d6a931 100644
--- a/libstdc++-v3/testsuite/27_io/basic_istream/extractors_character/wchar_t/lwg2499_neg.cc
+++ b/libstdc++-v3/testsuite/27_io/basic_istream/extractors_character/wchar_t/lwg2499_neg.cc
@@ -26,7 +26,7 @@
 void
 test01(std::wistream& in, wchar_t* wc)
 {
-  in >> wc; // { dg-error "here" }
+  in >> wc; // { dg-error "no match" }
 }
 
 struct WT : std::char_traits<wchar_t> { };
@@ -34,7 +34,7 @@ struct WT : std::char_traits<wchar_t> { };
 void
 test02(std::basic_istream<wchar_t, WT>& in, wchar_t* wc)
 {
-  in >> wc; // { dg-error "here" }
+  in >> wc; // { dg-error "no match" }
 }
 
 // { dg-excess-errors "" }
diff --git a/libstdc++-v3/testsuite/27_io/basic_istream/extractors_other/char/4.cc b/libstdc++-v3/testsuite/27_io/basic_istream/extractors_other/char/4.cc
index 5ad1c1b4e47..9f1e293474f 100644
--- a/libstdc++-v3/testsuite/27_io/basic_istream/extractors_other/char/4.cc
+++ b/libstdc++-v3/testsuite/27_io/basic_istream/extractors_other/char/4.cc
@@ -21,6 +21,21 @@
 
 #include <sstream>
 
+template<typename Istream, typename T, typename = void>
+  struct is_extractable : std::false_type
+  { };
+
+template<typename> using void_t = void;
+
+template<typename Istream, typename T>
+  using extract_result
+    = decltype(std::declval<Istream>() >> std::declval<const T&>());
+
+template<typename Istream, typename T>
+  struct is_extractable<Istream, T, void_t<extract_result<Istream, T>>>
+  : std::true_type
+  { };
+
 struct X {};
 std::istream& operator>>(std::istream&, X&) = delete;
 
@@ -30,20 +45,6 @@ std::istream& operator>>(std::istream& is, Y&&) {return is;}
 
 struct Z{};
 
-template <class T>
-auto f(T&&) -> decltype(void(std::declval<std::istream&>()
-			     >> std::declval<T&&>()),
-			std::true_type());
-
-std::false_type f(...);
-
-template <class T>
-auto g(T&&) -> decltype(void(std::declval<std::istream&&>()
-			     >> std::declval<T&&>()),
-			std::true_type());
-
-std::false_type g(...);
-
 void test01()
 {
   Y y;
@@ -52,42 +53,18 @@ void test01()
   is >> Y();
   std::istringstream() >> y;
   std::istringstream() >> Y();
-  static_assert(!std::__is_extractable<std::istream&, X&>::value, "");
-  static_assert(!std::__is_extractable<std::istream&&, X&>::value, "");
-  static_assert(!std::__is_extractable<std::istream&, X&&>::value, "");
-  static_assert(!std::__is_extractable<std::istream&&, X&&>::value, "");
-  static_assert(std::__is_extractable<std::istream&, Y&>::value, "");
-  static_assert(std::__is_extractable<std::istream&&, Y&>::value, "");
-  static_assert(std::__is_extractable<std::istream&, Y&&>::value, "");
-  static_assert(std::__is_extractable<std::istream&&, Y&&>::value, "");
-  static_assert(!std::__is_extractable<std::istream&, Z&>::value, "");
-  static_assert(!std::__is_extractable<std::istream&&, Z&>::value, "");
-  static_assert(!std::__is_extractable<std::istream&, Z&&>::value, "");
-  static_assert(!std::__is_extractable<std::istream&&, Z&&>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<X&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<X&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Y&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Y&&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Z&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Z&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<X&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<X&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Y&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Y&&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Z&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Z&&>())),
-		std::false_type>::value, "");
+  static_assert(!is_extractable<std::istream&, X&>::value, "");
+  static_assert(!is_extractable<std::istream&&, X&>::value, "");
+  static_assert(!is_extractable<std::istream&, X&&>::value, "");
+  static_assert(!is_extractable<std::istream&&, X&&>::value, "");
+  static_assert(is_extractable<std::istream&, Y&>::value, "");
+  static_assert(is_extractable<std::istream&&, Y&>::value, "");
+  static_assert(is_extractable<std::istream&, Y&&>::value, "");
+  static_assert(is_extractable<std::istream&&, Y&&>::value, "");
+  static_assert(!is_extractable<std::istream&, Z&>::value, "");
+  static_assert(!is_extractable<std::istream&&, Z&>::value, "");
+  static_assert(!is_extractable<std::istream&, Z&&>::value, "");
+  static_assert(!is_extractable<std::istream&&, Z&&>::value, "");
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/27_io/basic_istream/extractors_other/wchar_t/4.cc b/libstdc++-v3/testsuite/27_io/basic_istream/extractors_other/wchar_t/4.cc
index 94f2d9da09d..fc7f5505bf4 100644
--- a/libstdc++-v3/testsuite/27_io/basic_istream/extractors_other/wchar_t/4.cc
+++ b/libstdc++-v3/testsuite/27_io/basic_istream/extractors_other/wchar_t/4.cc
@@ -21,6 +21,21 @@
 
 #include <sstream>
 
+template<typename Istream, typename T, typename = void>
+  struct is_extractable : std::false_type
+  { };
+
+template<typename> using void_t = void;
+
+template<typename Istream, typename T>
+  using extract_result
+    = decltype(std::declval<Istream>() >> std::declval<const T&>());
+
+template<typename Istream, typename T>
+  struct is_extractable<Istream, T, void_t<extract_result<Istream, T>>>
+  : std::true_type
+  { };
+
 struct X {};
 std::wistream& operator>>(std::wistream&, X&) = delete;
 
@@ -30,20 +45,6 @@ std::wistream& operator>>(std::wistream& is, Y&&) {return is;}
 
 struct Z{};
 
-template <class T>
-auto f(T&&) -> decltype(void(std::declval<std::wistream&>()
-			     >> std::declval<T&&>()),
-			std::true_type());
-
-std::false_type f(...);
-
-template <class T>
-auto g(T&&) -> decltype(void(std::declval<std::wistream&&>()
-			     >> std::declval<T&&>()),
-			std::true_type());
-
-std::false_type g(...);
-
 void test01()
 {
   Y y;
@@ -52,42 +53,18 @@ void test01()
   is >> Y();
   std::wistringstream() >> y;
   std::wistringstream() >> Y();
-  static_assert(!std::__is_extractable<std::wistream&, X&>::value, "");
-  static_assert(!std::__is_extractable<std::wistream&&, X&>::value, "");
-  static_assert(!std::__is_extractable<std::wistream&, X&&>::value, "");
-  static_assert(!std::__is_extractable<std::wistream&&, X&&>::value, "");
-  static_assert(std::__is_extractable<std::wistream&, Y&>::value, "");
-  static_assert(std::__is_extractable<std::wistream&&, Y&>::value, "");
-  static_assert(std::__is_extractable<std::wistream&, Y&&>::value, "");
-  static_assert(std::__is_extractable<std::wistream&&, Y&&>::value, "");
-  static_assert(!std::__is_extractable<std::wistream&, Z&>::value, "");
-  static_assert(!std::__is_extractable<std::wistream&&, Z&>::value, "");
-  static_assert(!std::__is_extractable<std::wistream&, Z&&>::value, "");
-  static_assert(!std::__is_extractable<std::wistream&&, Z&&>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<X&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<X&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Y&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Y&&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Z&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Z&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<X&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<X&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Y&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Y&&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Z&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Z&&>())),
-		std::false_type>::value, "");
+  static_assert(!is_extractable<std::wistream&, X&>::value, "");
+  static_assert(!is_extractable<std::wistream&&, X&>::value, "");
+  static_assert(!is_extractable<std::wistream&, X&&>::value, "");
+  static_assert(!is_extractable<std::wistream&&, X&&>::value, "");
+  static_assert(is_extractable<std::wistream&, Y&>::value, "");
+  static_assert(is_extractable<std::wistream&&, Y&>::value, "");
+  static_assert(is_extractable<std::wistream&, Y&&>::value, "");
+  static_assert(is_extractable<std::wistream&&, Y&&>::value, "");
+  static_assert(!is_extractable<std::wistream&, Z&>::value, "");
+  static_assert(!is_extractable<std::wistream&&, Z&>::value, "");
+  static_assert(!is_extractable<std::wistream&, Z&&>::value, "");
+  static_assert(!is_extractable<std::wistream&&, Z&&>::value, "");
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/27_io/basic_ostream/inserters_other/char/6.cc b/libstdc++-v3/testsuite/27_io/basic_ostream/inserters_other/char/6.cc
index b86763c60fd..4801afcba6c 100644
--- a/libstdc++-v3/testsuite/27_io/basic_ostream/inserters_other/char/6.cc
+++ b/libstdc++-v3/testsuite/27_io/basic_ostream/inserters_other/char/6.cc
@@ -21,6 +21,22 @@
 
 #include <sstream>
 
+template<typename Ostream, typename T, typename = void>
+  struct is_insertable
+  : std::false_type
+  { };
+
+template<typename> using void_t = void;
+
+template<typename Ostream, typename T>
+  using insert_result
+    = decltype(std::declval<Ostream>() << std::declval<const T&>());
+
+template<typename Ostream, typename T>
+  struct is_insertable<Ostream, T, void_t<insert_result<Ostream, T>>>
+  : std::true_type
+  { };
+
 struct X {};
 std::ostream& operator<<(std::ostream&, const X&) = delete;
 
@@ -30,20 +46,6 @@ std::ostream& operator<<(std::ostream&& os, const Y&) {return os;}
 
 struct Z{};
 
-template <class T>
-auto f(T&&) -> decltype(void(std::declval<std::ostream&>()
-			     << std::declval<T&&>()),
-			std::true_type());
-
-std::false_type f(...);
-
-template <class T>
-auto g(T&&) -> decltype(void(std::declval<std::ostream&&>()
-			     << std::declval<T&&>()),
-			std::true_type());
-
-std::false_type g(...);
-
 void test01()
 {
   Y y;
@@ -52,42 +54,18 @@ void test01()
   os << Y();
   std::ostringstream() << y;
   std::ostringstream() << Y();
-  static_assert(!std::__is_insertable<std::ostream&, X&>::value, "");
-  static_assert(!std::__is_insertable<std::ostream&&, X&>::value, "");
-  static_assert(!std::__is_insertable<std::ostream&, X&&>::value, "");
-  static_assert(!std::__is_insertable<std::ostream&&, X&&>::value, "");
-  static_assert(std::__is_insertable<std::ostream&, Y&>::value, "");
-  static_assert(std::__is_insertable<std::ostream&&, Y&&>::value, "");
-  static_assert(std::__is_insertable<std::ostream&, Y&>::value, "");
-  static_assert(std::__is_insertable<std::ostream&&, Y&&>::value, "");
-  static_assert(!std::__is_insertable<std::ostream&, Z&>::value, "");
-  static_assert(!std::__is_insertable<std::ostream&&, Z&>::value, "");
-  static_assert(!std::__is_insertable<std::ostream&, Z&&>::value, "");
-  static_assert(!std::__is_insertable<std::ostream&&, Z&&>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<X&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<X&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Y&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Y&&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Z&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Z&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<X&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<X&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Y&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Y&&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Z&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Z&&>())),
-		std::false_type>::value, "");
+  static_assert(!is_insertable<std::ostream&, X&>::value, "");
+  static_assert(!is_insertable<std::ostream&&, X&>::value, "");
+  static_assert(!is_insertable<std::ostream&, X&&>::value, "");
+  static_assert(!is_insertable<std::ostream&&, X&&>::value, "");
+  static_assert(is_insertable<std::ostream&, Y&>::value, "");
+  static_assert(is_insertable<std::ostream&&, Y&&>::value, "");
+  static_assert(is_insertable<std::ostream&, Y&>::value, "");
+  static_assert(is_insertable<std::ostream&&, Y&&>::value, "");
+  static_assert(!is_insertable<std::ostream&, Z&>::value, "");
+  static_assert(!is_insertable<std::ostream&&, Z&>::value, "");
+  static_assert(!is_insertable<std::ostream&, Z&&>::value, "");
+  static_assert(!is_insertable<std::ostream&&, Z&&>::value, "");
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/27_io/basic_ostream/inserters_other/wchar_t/6.cc b/libstdc++-v3/testsuite/27_io/basic_ostream/inserters_other/wchar_t/6.cc
index 0994a949652..3efeb804b00 100644
--- a/libstdc++-v3/testsuite/27_io/basic_ostream/inserters_other/wchar_t/6.cc
+++ b/libstdc++-v3/testsuite/27_io/basic_ostream/inserters_other/wchar_t/6.cc
@@ -21,6 +21,22 @@
 
 #include <sstream>
 
+template<typename Ostream, typename T, typename = void>
+  struct is_insertable
+  : std::false_type
+  { };
+
+template<typename> using void_t = void;
+
+template<typename Ostream, typename T>
+  using insert_result
+    = decltype(std::declval<Ostream>() << std::declval<const T&>());
+
+template<typename Ostream, typename T>
+  struct is_insertable<Ostream, T, void_t<insert_result<Ostream, T>>>
+  : std::true_type
+  { };
+
 struct X {};
 std::wostream& operator<<(std::wostream&, const X&) = delete;
 
@@ -30,20 +46,6 @@ std::wostream& operator<<(std::wostream&& os, const Y&) {return os;}
 
 struct Z{};
 
-template <class T>
-auto f(T&&) -> decltype(void(std::declval<std::wostream&>()
-			     << std::declval<T&&>()),
-			std::true_type());
-
-std::false_type f(...);
-
-template <class T>
-auto g(T&&) -> decltype(void(std::declval<std::wostream&&>()
-			     << std::declval<T&&>()),
-			std::true_type());
-
-std::false_type g(...);
-
 void test01()
 {
   Y y;
@@ -52,42 +54,18 @@ void test01()
   os << Y();
   std::wostringstream() << y;
   std::wostringstream() << Y();
-  static_assert(!std::__is_insertable<std::wostream&, X&>::value, "");
-  static_assert(!std::__is_insertable<std::wostream&&, X&>::value, "");
-  static_assert(!std::__is_insertable<std::wostream&, X&&>::value, "");
-  static_assert(!std::__is_insertable<std::wostream&&, X&&>::value, "");
-  static_assert(std::__is_insertable<std::wostream&, Y&>::value, "");
-  static_assert(std::__is_insertable<std::wostream&&, Y&&>::value, "");
-  static_assert(std::__is_insertable<std::wostream&, Y&>::value, "");
-  static_assert(std::__is_insertable<std::wostream&&, Y&&>::value, "");
-  static_assert(!std::__is_insertable<std::wostream&, Z&>::value, "");
-  static_assert(!std::__is_insertable<std::wostream&&, Z&>::value, "");
-  static_assert(!std::__is_insertable<std::wostream&, Z&&>::value, "");
-  static_assert(!std::__is_insertable<std::wostream&&, Z&&>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<X&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<X&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Y&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Y&&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Z&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(f(std::declval<Z&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<X&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<X&&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Y&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Y&&>())),
-		std::true_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Z&>())),
-		std::false_type>::value, "");
-  static_assert(std::is_same<decltype(g(std::declval<Z&&>())),
-		std::false_type>::value, "");
+  static_assert(!is_insertable<std::wostream&, X&>::value, "");
+  static_assert(!is_insertable<std::wostream&&, X&>::value, "");
+  static_assert(!is_insertable<std::wostream&, X&&>::value, "");
+  static_assert(!is_insertable<std::wostream&&, X&&>::value, "");
+  static_assert(is_insertable<std::wostream&, Y&>::value, "");
+  static_assert(is_insertable<std::wostream&&, Y&&>::value, "");
+  static_assert(is_insertable<std::wostream&, Y&>::value, "");
+  static_assert(is_insertable<std::wostream&&, Y&&>::value, "");
+  static_assert(!is_insertable<std::wostream&, Z&>::value, "");
+  static_assert(!is_insertable<std::wostream&&, Z&>::value, "");
+  static_assert(!is_insertable<std::wostream&, Z&&>::value, "");
+  static_assert(!is_insertable<std::wostream&&, Z&&>::value, "");
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/path/io/dr2989.cc b/libstdc++-v3/testsuite/27_io/filesystem/path/io/dr2989.cc
index c5cda776477..609f1c32a0e 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/path/io/dr2989.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/path/io/dr2989.cc
@@ -33,3 +33,4 @@ void foo(std::iostream& s) {
   s >> p; // { dg-error "no match" }
 }
 // { dg-prune-output "no type .*enable_if" }
+// { dg-prune-output "no matching function for call to '__rval_streamable" }
diff --git a/libstdc++-v3/testsuite/27_io/rvalue_streams-2.cc b/libstdc++-v3/testsuite/27_io/rvalue_streams-2.cc
index 7aa09aef471..d2b6997e4b9 100644
--- a/libstdc++-v3/testsuite/27_io/rvalue_streams-2.cc
+++ b/libstdc++-v3/testsuite/27_io/rvalue_streams-2.cc
@@ -58,16 +58,7 @@ struct X { };
 std::ostream& operator<<(std::ostream& os, const X&) { return os; }
 std::istream& operator>>(std::istream& is, X&&) { return is; }
 
-struct O : std::ostream { };
-
-void operator<<(O&, X) = delete;
-
-struct I : std::istream { };
-
-void operator>>(I&, X) = delete;
-
 // PR libstdc++/65543
-// PR libstdc++/80675
 // PR libstdc++/80940
 int main()
 {
@@ -82,6 +73,4 @@ int main()
   MyStream2 stream2{};
   stream2 << "aaa";
   stream2 >> msi;
-  O{} << X{};
-  I{} >> X{};
 }
diff --git a/libstdc++-v3/testsuite/27_io/rvalue_streams.cc b/libstdc++-v3/testsuite/27_io/rvalue_streams.cc
index def706999a3..3d359091b76 100644
--- a/libstdc++-v3/testsuite/27_io/rvalue_streams.cc
+++ b/libstdc++-v3/testsuite/27_io/rvalue_streams.cc
@@ -25,8 +25,6 @@ void
 test01()
 {
   int i = 1742;
-  // This usage isn't supported by the current draft.
-  // std::string result = (std::ostringstream() << i).str();
   std::ostringstream() << i;
   std::string result ("1742");
   int i2;
@@ -45,10 +43,10 @@ test02()
 {
   X x;
   std::istringstream is;
-  auto& ref1 = (std::move(is) >> x);
+  auto&& ref1 = (std::move(is) >> x);
   VERIFY( &ref1 == &is );
   VERIFY( x.as_rvalue == false );
-  auto& ref2 = (std::move(is) >> std::move(x));
+  auto&& ref2 = (std::move(is) >> std::move(x));
   VERIFY( &ref2 == &is );
   VERIFY( x.as_rvalue == true );
 
@@ -57,6 +55,71 @@ test02()
   std::istringstream("x") >> &arr[0];
 #endif
   std::istringstream("x") >> arr;
+  VERIFY( std::string(arr) == "x" );
+}
+
+// LWG 1203 More useful rvalue stream insertion
+void
+test03()
+{
+  int i = 1203;
+  std::string result = (std::ostringstream() << "i = " << i).str();
+  VERIFY( result == "i = 1203" );
+
+  std::ostringstream os;
+  std::ostringstream&& ros = std::move(os) << result;
+  VERIFY( &ros == &os );
+  VERIFY( ros.str() == result );
+
+  std::stringstream ss;
+  std::stringstream&& rss = std::move(ss) << result;
+  VERIFY( &rss == &ss );
+  VERIFY( rss.str() == result );
+
+  std::istringstream is("first second third");
+  std::istringstream&& ris = std::move(is) >> result;
+  VERIFY( &ris == &is );
+  VERIFY( result == "first" );
+
+  std::stringstream ss2("fourth fifth sixth");
+  std::stringstream&& rss2 = std::move(ss2) >> result;
+  VERIFY( &rss2 == &ss2 );
+  VERIFY( result == "fourth" );
+}
+
+struct A { friend void operator<<(std::ios_base&, A) { } };
+
+struct O : private std::ios_base { friend void operator<<(O&, int) { } };
+
+template<typename Ostream, typename T, typename = void>
+  struct is_insertable
+  : std::false_type
+  { };
+
+template<typename> using void_t = void;
+
+template<typename Ostream, typename T>
+  using insert_result
+    = decltype(std::declval<Ostream>() << std::declval<const T&>());
+
+template<typename Ostream, typename T>
+  struct is_insertable<Ostream, T, void_t<insert_result<Ostream, T>>>
+  : std::true_type
+  { };
+
+// LWG 1203 negative tests
+void
+test04()
+{
+  static_assert( is_insertable<std::ios_base&, A>::value,
+      "valid using the friend operator<<" );
+  static_assert( !is_insertable<std::ios_base&&, A>::value,
+      "ill-formed because ios_base is not derived from ios_base" );
+
+  static_assert( is_insertable<O&, int>::value,
+      "valid using the friend operator<<" );
+  static_assert( !is_insertable<O&&, int>::value,
+      "ill-formed because O is not publicly derived from ios_base" );
 }
 
 int
@@ -64,5 +127,6 @@ main()
 {
   test01();
   test02();
-  return 0;
+  test03();
+  test04();
 }


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