PR72792 PR72793 relax requirements on rebind members

	PR libstdc++/72792
	PR libstdc++/72793
	* include/bits/alloc_traits.h (__allocator_traits_base::__rebind):
	Replace with class template using void_t.
	(__alloc_rebind): Define in terms of
	__allocator_traits_base::__rebind.
	(allocator_traits): Remove unconditional static_assert for
	rebind_alloc.
	* include/bits/ptr_traits.h (__replace_first_arg): Remove type member.
	(pointer_traits::__rebind): Replace with class template using void_t.
	(pointer_traits::rebind): Define in terms of __rebind.
	(pointer_traits): Remove unconditional static_assert for rebind.
	* testsuite/20_util/allocator_traits/members/rebind_alloc.cc: New test.
	* testsuite/20_util/pointer_traits/rebind.cc: New test.

From-SVN: r244680

libstdc++-v3/ChangeLog

 2017-01-20  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/72792
+	PR libstdc++/72793
+	* include/bits/alloc_traits.h (__allocator_traits_base::__rebind):
+	Replace with class template using void_t.
+	(__alloc_rebind): Define in terms of
+	__allocator_traits_base::__rebind.
+	(allocator_traits): Remove unconditional static_assert for
+	rebind_alloc.
+	* include/bits/ptr_traits.h (__replace_first_arg): Remove type member.
+	(pointer_traits::__rebind): Replace with class template using void_t.
+	(pointer_traits::rebind): Define in terms of __rebind.
+	(pointer_traits): Remove unconditional static_assert for rebind.
+	* testsuite/20_util/allocator_traits/members/rebind_alloc.cc: New test.
+	* testsuite/20_util/pointer_traits/rebind.cc: New test.
+
 	PR libstdc++/69321
 	* include/experimental/any (__any_caster): Avoid instantiating
 	manager function for types that can't be stored in any.

libstdc++-v3/include/bits/alloc_traits.h

@@ -44,8 +44,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   struct __allocator_traits_base
   {
-    template<typename _Alloc, typename _Up>
-      using __rebind = typename _Alloc::template rebind<_Up>::other;
+    template<typename _Tp, typename _Up, typename = void>
+      struct __rebind : __replace_first_arg<_Tp, _Up> { };
+
+    template<typename _Tp, typename _Up>
+      struct __rebind<_Tp, _Up,
+		      __void_t<typename _Tp::template rebind<_Up>::other>>
+      { using type = typename _Tp::template rebind<_Up>::other; };
 
   protected:
     template<typename _Tp>
@@ -71,9 +76,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   };
 
   template<typename _Alloc, typename _Up>
-    using __alloc_rebind = __detected_or_t_<__replace_first_arg_t,
-					    __allocator_traits_base::__rebind,
-					    _Alloc, _Up>;
+    using __alloc_rebind
+      = typename __allocator_traits_base::template __rebind<_Alloc, _Up>::type;
 
   /**
    * @brief  Uniform interface to all allocator types.
@@ -184,9 +188,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template<typename _Tp>
 	using rebind_traits = allocator_traits<rebind_alloc<_Tp>>;
 
-      static_assert(!is_same<rebind_alloc<value_type>, __undefined>::value,
-	  "allocator defines rebind or is like Alloc<T, Args>");
-
     private:
       template<typename _Alloc2>
 	static auto

libstdc++-v3/include/bits/ptr_traits.h

@@ -56,7 +56,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // Given Template<T, ...> and U return Template<U, ...>, otherwise invalid.
   template<typename _Tp, typename _Up>
     struct __replace_first_arg
-    { using type = __undefined; };
+    { };
 
   template<template<typename, typename...> class _Template, typename _Up,
            typename _Tp, typename... _Types>
@@ -84,8 +84,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template<typename _Tp>
 	using __difference_type = typename _Tp::difference_type;
 
+      template<typename _Tp, typename _Up, typename = void>
+	struct __rebind : __replace_first_arg<_Tp, _Up> { };
+
       template<typename _Tp, typename _Up>
-	using __rebind = typename _Tp::template rebind<_Up>;
+	struct __rebind<_Tp, _Up, __void_t<typename _Tp::template rebind<_Up>>>
+	{ using type = typename _Tp::template rebind<_Up>; };
 
     public:
       /// The pointer type.
@@ -101,8 +105,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       /// A pointer to a different type.
       template<typename _Up>
-        using rebind
-	  = __detected_or_t_<__replace_first_arg_t, __rebind, _Ptr, _Up>;
+        using rebind = typename __rebind<_Ptr, _Up>::type;
 
       static _Ptr
       pointer_to(__make_not_void<element_type>& __e)
@@ -110,8 +113,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       static_assert(!is_same<element_type, __undefined>::value,
 	  "pointer type defines element_type or is like SomePointer<T, Args>");
-      static_assert(!is_same<rebind<element_type>, __undefined>::value,
-	  "pointer type defines rebind<U> or is like SomePointer<T, Args>");
     };
 
   /**

libstdc++-v3/testsuite/20_util/allocator_traits/members/rebind_alloc.cc

+// Copyright (C) 2017 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do compile { target c++11 } }
+
+#include <memory>
+
+using std::is_same;
+
+template<typename T, typename U>
+  using Rebind = typename std::allocator_traits<T>::template rebind_alloc<U>;
+
+template<typename T>
+  struct HasRebind {
+    using value_type = T;
+    template<typename U> struct rebind { using other = std::allocator<U>; };
+  };
+
+static_assert(is_same<Rebind<HasRebind<int>, long>,
+		      std::allocator<long>>::value,
+	      "nested alias template is used");
+
+template<typename T>
+  struct NoRebind0 {
+    using value_type = T;
+  };
+
+static_assert(is_same<Rebind<NoRebind0<int>, long>,
+		      NoRebind0<long>>::value,
+	      "first template argument is replaced");
+
+template<typename T, typename>
+  struct NoRebind1 {
+    using value_type = T;
+  };
+
+static_assert(is_same<Rebind<NoRebind1<int, void>, long>,
+		      NoRebind1<long, void>>::value,
+	      "first template argument is replaced");
+
+template<typename T, typename, typename>
+  struct NoRebind2 {
+    using value_type = T;
+  };
+
+static_assert(is_same<Rebind<NoRebind2<int, void, void>, long>,
+		      NoRebind2<long, void, void>>::value,
+	      "first template argument is replaced");
+
+template<typename T, typename...>
+  struct NoRebindN {
+    using value_type = T;
+  };
+
+static_assert(is_same<Rebind<NoRebindN<int>, long>,
+		      NoRebindN<long>>::value,
+	      "first template argument is replaced");
+static_assert(is_same<Rebind<NoRebindN<int, void>, long>,
+		      NoRebindN<long, void>>::value,
+	      "first template argument is replaced");
+
+template<typename T, int = 0>
+  struct CannotRebind {
+    using value_type = T;
+  };
+// PR libstdc++/72792 specialization of allocator_traits is still well-formed:
+std::allocator_traits<CannotRebind<int>>::value_type v;

libstdc++-v3/testsuite/20_util/pointer_traits/rebind.cc

+// Copyright (C) 2017 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do compile { target c++11 } }
+
+#include <memory>
+
+using std::is_same;
+
+template<typename T, typename U>
+  using Rebind = typename std::pointer_traits<T>::template rebind<U>;
+
+template<typename T>
+  struct HasRebind {
+    template<typename U> using rebind = U*;
+  };
+
+static_assert(is_same<Rebind<HasRebind<int>, long>,
+		      long*>::value,
+	      "nested alias template is used");
+
+template<typename T> struct NoRebind0 { };
+
+static_assert(is_same<Rebind<NoRebind0<int>, long>,
+		      NoRebind0<long>>::value,
+	      "first template argument is replaced");
+
+template<typename T, typename> struct NoRebind1 { };
+
+static_assert(is_same<Rebind<NoRebind1<int, void>, long>,
+		      NoRebind1<long, void>>::value,
+	      "first template argument is replaced");
+
+template<typename T, typename, typename> struct NoRebind2 { };
+
+static_assert(is_same<Rebind<NoRebind2<int, void, void>, long>,
+		      NoRebind2<long, void, void>>::value,
+	      "first template argument is replaced");
+
+template<typename T, typename...> struct NoRebindN { };
+
+static_assert(is_same<Rebind<NoRebindN<int>, long>,
+		      NoRebindN<long>>::value,
+	      "first template argument is replaced");
+static_assert(is_same<Rebind<NoRebindN<int, void>, long>,
+		      NoRebindN<long, void>>::value,
+	      "first template argument is replaced");
+
+template<typename T, int = 0>
+  struct CannotRebind {
+    using element_type = T;
+  };
+// PR libstdc++/72793 specialization of pointer_traits is still well-formed:
+std::pointer_traits<CannotRebind<int>>::element_type e;