Implement LWG 2842, in_place_t check for optional::optional(U&&) should decay U.

Implement LWG 2842, in_place_t check for optional::optional(U&&)
should decay U.
* include/std/optional (_Optional_base(in_place_t, _Args&&...)):
Constrain.
(_Optional_base(in_place_t, initializer_list<_Up>, _Args&&...)):
Turn the int-pack constraint hack into a saner bool.
(_Optional_base<_Tp, false>::_Optional_base(in_place_t, _Args&&...)):
Constrain.
(_Optional_base<_Tp, false>::_Optional_base(in_place_t,
initializer_list<_Up>, _Args&&...)):
Turn the int-pack constraint hack into a saner bool.
(optional(_Up&&)): Constrain against in_place_t.
(optional(in_place_t, _Args&&...)): Constrain.
(constexpr optional(in_place_t, initializer_list<_Up>, _Args&&...)):
Turn the int-pack constraint hack into a saner bool.
* testsuite/20_util/optional/cons/value_neg.cc: Add a test for
a type that is constructible from in_place.

From-SVN: r243966

3 files changed, 42 insertions, 15 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 32b81e8..34ca95a 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,23 @@
+2016-12-29  Ville Voutilainen  <ville.voutilainen@gmail.com>
+
+	Implement LWG 2842, in_place_t check for optional::optional(U&&)
+	should decay U.
+	* include/std/optional (_Optional_base(in_place_t, _Args&&...)):
+	Constrain.
+	(_Optional_base(in_place_t, initializer_list<_Up>, _Args&&...)):
+	Turn the int-pack constraint hack into a saner bool.
+	(_Optional_base<_Tp, false>::_Optional_base(in_place_t, _Args&&...)):
+	Constrain.
+	(_Optional_base<_Tp, false>::_Optional_base(in_place_t,
+	initializer_list<_Up>, _Args&&...)):
+	Turn the int-pack constraint hack into a saner bool.
+	(optional(_Up&&)): Constrain against in_place_t.
+	(optional(in_place_t, _Args&&...)): Constrain.
+	(constexpr optional(in_place_t, initializer_list<_Up>, _Args&&...)):
+	Turn the int-pack constraint hack into a saner bool.
+	* testsuite/20_util/optional/cons/value_neg.cc: Add a test for
+	a type that is constructible from in_place.
+
 2016-12-24  François Dumont  <fdumont@gcc.gnu.org>
 
 	* include/ext/random.tcc: Fix usage of _OutputIteratorConcept.
diff --git a/libstdc++-v3/include/std/optional b/libstdc++-v3/include/std/optional
index 3d69e10..73bc2b4 100644
--- a/libstdc++-v3/include/std/optional
+++ b/libstdc++-v3/include/std/optional
@@ -128,15 +128,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       : _Optional_base{} { }
 
       // Constructors for engaged optionals.
-      template<typename... _Args>
+      template<typename... _Args,
+	       enable_if_t<is_constructible_v<_Tp, _Args&&...>, bool> = false>
         constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
         : _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { }
 
       template<typename _Up, typename... _Args,
-               enable_if_t<is_constructible<_Tp,
-                                            initializer_list<_Up>&,
-                                            _Args&&...>::value,
-                           int>...>
+               enable_if_t<is_constructible_v<_Tp,
+					      initializer_list<_Up>&,
+					      _Args&&...>, bool> = false>
         constexpr explicit _Optional_base(in_place_t,
                                           initializer_list<_Up> __il,
                                           _Args&&... __args)
@@ -264,15 +264,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       constexpr _Optional_base(nullopt_t) noexcept
       : _Optional_base{} { }
 
-      template<typename... _Args>
+      template<typename... _Args,
+	       enable_if_t<is_constructible_v<_Tp, _Args&&...>, bool> = false>
         constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
         : _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { }
 
       template<typename _Up, typename... _Args,
-               enable_if_t<is_constructible<_Tp,
-                                            initializer_list<_Up>&,
-                                            _Args&&...>::value,
-			   int>...>
+               enable_if_t<is_constructible_v<_Tp,
+					      initializer_list<_Up>&,
+					      _Args&&...>, bool> = false>
         constexpr explicit _Optional_base(in_place_t,
                                           initializer_list<_Up> __il,
                                           _Args&&... __args)
@@ -432,6 +432,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template <typename _Up = _Tp,
                 enable_if_t<__and_<
 			      __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
+			      __not_<is_same<in_place_t, decay_t<_Up>>>,
 			      is_constructible<_Tp, _Up&&>,
 			      is_convertible<_Up&&, _Tp>
 			      >::value, bool> = true>
@@ -441,6 +442,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template <typename _Up = _Tp,
                 enable_if_t<__and_<
 			      __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
+			      __not_<is_same<in_place_t, decay_t<_Up>>>,
 			      is_constructible<_Tp, _Up&&>,
 			      __not_<is_convertible<_Up&&, _Tp>>
 			      >::value, bool> = false>
@@ -499,15 +501,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  emplace(std::move(*__t));
       }
 
-      template<typename... _Args>
+      template<typename... _Args,
+	       enable_if_t<is_constructible_v<_Tp, _Args&&...>, bool> = false>
       explicit constexpr optional(in_place_t, _Args&&... __args)
         : _Base(std::in_place, std::forward<_Args>(__args)...) { }
 
       template<typename _Up, typename... _Args,
-               enable_if_t<is_constructible<_Tp,
-                                            initializer_list<_Up>&,
-                                            _Args&&...>::value,
-                           int>...>
+               enable_if_t<is_constructible_v<_Tp,
+					      initializer_list<_Up>&,
+					      _Args&&...>, bool> = false>
       explicit constexpr optional(in_place_t,
 				  initializer_list<_Up> __il,
 				  _Args&&... __args)
diff --git a/libstdc++-v3/testsuite/20_util/optional/cons/value_neg.cc b/libstdc++-v3/testsuite/20_util/optional/cons/value_neg.cc
index 21e86c5..6a2827e 100644
--- a/libstdc++-v3/testsuite/20_util/optional/cons/value_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/optional/cons/value_neg.cc
@@ -35,5 +35,10 @@ int main()
     std::optional<X> ox2 = 42; // { dg-error "conversion" }
     std::optional<std::unique_ptr<int>> oup{new int};
     std::optional<std::unique_ptr<int>> oup2 = new int;  // { dg-error "conversion" }
+    struct U { explicit U(std::in_place_t); };
+    std::optional<U> ou(std::in_place); // { dg-error "no matching" }
+    // { dg-error "no type" "" { target { *-*-* } } 438 }
+    // { dg-error "no type" "" { target { *-*-* } } 448 }
+    // { dg-error "no type" "" { target { *-*-* } } 505 }
   }
 }