From 2d26d4ce69d8510e32a5a4b9653de9dee0109f04 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Thu, 14 Jun 2018 20:02:40 +0100
Subject: [PATCH] Partially revert move of std::tuple_element_t to <tuple>

Defining std::tuple_element_t in <utility> makes it available wherever
std::tuple_element is available.

	* include/std/tuple (__cpp_lib_tuple_element_t, tuple_element_t):
	Move back to <utility>.
	* include/std/utility (__cpp_lib_tuple_element_t. tuple_element_t):
	Restore to here.

From-SVN: r261604
---
 libstdc++-v3/ChangeLog           |  5 +++++
 libstdc++-v3/include/std/tuple   |  7 -------
 libstdc++-v3/include/std/utility | 10 ++++++++++
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 94541d1a68d..2bfda083ee3 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,10 @@
 2018-06-14  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/std/tuple (__cpp_lib_tuple_element_t, tuple_element_t):
+	Move back to <utility>.
+	* include/std/utility (__cpp_lib_tuple_element_t. tuple_element_t):
+	Restore to here.
+
 	P0935R0 Eradicating unnecessarily explicit default constructors
 	* include/backward/strstream (strstreambuf): Add non-explicit default
 	constructor.
diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
index 0f890504889..dd7daf7f1cf 100644
--- a/libstdc++-v3/include/std/tuple
+++ b/libstdc++-v3/include/std/tuple
@@ -1298,13 +1298,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  "tuple index is in range");
     };
 
-#if __cplusplus >= 201402L
-#define __cpp_lib_tuple_element_t 201402L
-
-  template<size_t __i, typename _Tp>
-    using tuple_element_t = typename tuple_element<__i, _Tp>::type;
-#endif
-
   template<std::size_t __i, typename _Head, typename... _Tail>
     constexpr _Head&
     __get_helper(_Tuple_impl<__i, _Head, _Tail...>& __t) noexcept
diff --git a/libstdc++-v3/include/std/utility b/libstdc++-v3/include/std/utility
index 7bf80de3745..17e7d4cbe7a 100644
--- a/libstdc++-v3/include/std/utility
+++ b/libstdc++-v3/include/std/utility
@@ -135,6 +135,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       typedef typename add_cv<__tuple_element_t<__i, _Tp>>::type type;
     };
 
+#if __cplusplus >= 201402L
+// The standard says this macro and alias template should be in <tuple>
+// but we define them here, to be available when the partial specializations
+// of tuple_element<pair<T,U>> and tuple_element<array<T,N>> are defined.
+#define __cpp_lib_tuple_element_t 201402L
+
+  template<std::size_t __i, typename _Tp>
+    using tuple_element_t = typename tuple_element<__i, _Tp>::type;
+#endif
+
   // Various functions which give std::pair a tuple-like interface.
 
   /// Partial specialization for std::pair
-- 
2.30.2