vendor/libc++/libc++-release_39-r276489

21 files changed, 820 insertions, 68 deletions

diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR22806_constrain_tuple_like_ctor.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR22806_constrain_tuple_like_ctor.pass.cpp
new file mode 100644
index 000000000000..4ddfb463385c
--- /dev/null
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR22806_constrain_tuple_like_ctor.pass.cpp
@@ -0,0 +1,178 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// UNSUPPORTED: c++98, c++03
+
+// <tuple>
+
+// template <class... Types> class tuple;
+
+// template <class TupleLike>
+//   tuple(TupleLike&&);
+// template <class Alloc, class TupleLike>
+//   tuple(std::allocator_arg_t, Alloc const&, TupleLike&&);
+
+// Check that the tuple-like ctors are properly disabled when the UTypes...
+// constructor should be selected. See PR22806.
+
+#include <tuple>
+#include <memory>
+#include <cassert>
+
+template <class Tp>
+using uncvref_t = typename std::remove_cv<typename std::remove_reference<Tp>::type>::type;
+
+template <class Tuple, class = uncvref_t<Tuple>>
+struct IsTuple : std::false_type {};
+
+template <class Tuple, class ...Args>
+struct IsTuple<Tuple, std::tuple<Args...>> : std::true_type {};
+
+struct ConstructibleFromTupleAndInt {
+  enum State { FromTuple, FromInt, Copied, Moved };
+  State state;
+
+  ConstructibleFromTupleAndInt(ConstructibleFromTupleAndInt const&) : state(Copied) {}
+  ConstructibleFromTupleAndInt(ConstructibleFromTupleAndInt &&) : state(Moved) {}
+
+  template <class Tuple, class = typename std::enable_if<IsTuple<Tuple>::value>::type>
+  explicit ConstructibleFromTupleAndInt(Tuple&&) : state(FromTuple) {}
+
+  explicit ConstructibleFromTupleAndInt(int) : state(FromInt) {}
+};
+
+struct ConvertibleFromTupleAndInt {
+  enum State { FromTuple, FromInt, Copied, Moved };
+  State state;
+
+  ConvertibleFromTupleAndInt(ConvertibleFromTupleAndInt const&) : state(Copied) {}
+  ConvertibleFromTupleAndInt(ConvertibleFromTupleAndInt &&) : state(Moved) {}
+
+  template <class Tuple, class = typename std::enable_if<IsTuple<Tuple>::value>::type>
+  ConvertibleFromTupleAndInt(Tuple&&) : state(FromTuple) {}
+
+  ConvertibleFromTupleAndInt(int) : state(FromInt) {}
+};
+
+struct ConstructibleFromInt {
+  enum State { FromInt, Copied, Moved };
+  State state;
+
+  ConstructibleFromInt(ConstructibleFromInt const&) : state(Copied) {}
+  ConstructibleFromInt(ConstructibleFromInt &&) : state(Moved) {}
+
+  explicit ConstructibleFromInt(int) : state(FromInt) {}
+};
+
+struct ConvertibleFromInt {
+  enum State { FromInt, Copied, Moved };
+  State state;
+
+  ConvertibleFromInt(ConvertibleFromInt const&) : state(Copied) {}
+  ConvertibleFromInt(ConvertibleFromInt &&) : state(Moved) {}
+  ConvertibleFromInt(int) : state(FromInt) {}
+};
+
+int main()
+{
+    // Test for the creation of dangling references when a tuple is used to
+    // store a reference to another tuple as its only element.
+    // Ex std::tuple<std::tuple<int>&&>.
+    // In this case the constructors 1) 'tuple(UTypes&&...)'
+    // and 2) 'tuple(TupleLike&&)' need to be manually disambiguated because
+    // when both #1 and #2 participate in partial ordering #2 will always
+    // be chosen over #1.
+    // See PR22806  and LWG issue #2549 for more information.
+    // (https://llvm.org/bugs/show_bug.cgi?id=22806)
+    using T = std::tuple<int>;
+    std::allocator<int> A;
+    { // rvalue reference
+        T t1(42);
+        std::tuple< T&& > t2(std::move(t1));
+        assert(&std::get<0>(t2) == &t1);
+    }
+    { // const lvalue reference
+        T t1(42);
+
+        std::tuple< T const & > t2(t1);
+        assert(&std::get<0>(t2) == &t1);
+
+        std::tuple< T const & > t3(static_cast<T const&>(t1));
+        assert(&std::get<0>(t3) == &t1);
+    }
+    { // lvalue reference
+        T t1(42);
+
+        std::tuple< T & > t2(t1);
+        assert(&std::get<0>(t2) == &t1);
+    }
+    { // const rvalue reference
+        T t1(42);
+
+        std::tuple< T const && > t2(std::move(t1));
+        assert(&std::get<0>(t2) == &t1);
+    }
+    { // rvalue reference via uses-allocator
+        T t1(42);
+        std::tuple< T&& > t2(std::allocator_arg, A, std::move(t1));
+        assert(&std::get<0>(t2) == &t1);
+    }
+    { // const lvalue reference via uses-allocator
+        T t1(42);
+
+        std::tuple< T const & > t2(std::allocator_arg, A, t1);
+        assert(&std::get<0>(t2) == &t1);
+
+        std::tuple< T const & > t3(std::allocator_arg, A, static_cast<T const&>(t1));
+        assert(&std::get<0>(t3) == &t1);
+    }
+    { // lvalue reference via uses-allocator
+        T t1(42);
+
+        std::tuple< T & > t2(std::allocator_arg, A, t1);
+        assert(&std::get<0>(t2) == &t1);
+    }
+    { // const rvalue reference via uses-allocator
+        T const t1(42);
+        std::tuple< T const && > t2(std::allocator_arg, A, std::move(t1));
+        assert(&std::get<0>(t2) == &t1);
+    }
+    // Test constructing a 1-tuple of the form tuple<UDT> from another 1-tuple
+    // 'tuple<T>' where UDT *can* be constructed from 'tuple<T>' In this case
+    // the 'tuple(UTypes...)' ctor should be choosen and 'UDT' constructed frow
+    // 'tuple<T>'.
+    {
+        using VT = ConstructibleFromTupleAndInt;
+        std::tuple<int> t1(42);
+        std::tuple<VT> t2(t1);
+        assert(std::get<0>(t2).state == VT::FromTuple);
+    }
+    {
+        using VT = ConvertibleFromTupleAndInt;
+        std::tuple<int> t1(42);
+        std::tuple<VT> t2 = {t1};
+        assert(std::get<0>(t2).state == VT::FromTuple);
+    }
+    // Test constructing a 1-tuple of the form tuple<UDT> from another 1-tuple
+    // 'tuple<T>' where UDT cannot be constructed from 'tuple<T>' but can
+    // be constructed from 'T'. In this case the tuple-like ctor should be
+    // chosen and 'UDT' constructed from 'T'
+    {
+        using VT = ConstructibleFromInt;
+        std::tuple<int> t1(42);
+        std::tuple<VT> t2(t1);
+        assert(std::get<0>(t2).state == VT::FromInt);
+    }
+    {
+        using VT = ConvertibleFromInt;
+        std::tuple<int> t1(42);
+        std::tuple<VT> t2 = {t1};
+        assert(std::get<0>(t2).state == VT::FromInt);
+    }
+}
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR23256_constrain_UTypes_ctor.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR23256_constrain_UTypes_ctor.pass.cpp
new file mode 100644
index 000000000000..ed3cafadbf08
--- /dev/null
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR23256_constrain_UTypes_ctor.pass.cpp
@@ -0,0 +1,96 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// UNSUPPORTED: c++98, c++03
+
+// <tuple>
+
+// template <class... Types> class tuple;
+
+// template <class ...UTypes>
+//    EXPLICIT(...) tuple(UTypes&&...)
+
+// Check that the UTypes... ctor is properly disabled before evaluating any
+// SFINAE when the tuple-like copy/move ctor should *clearly* be selected
+// instead. This happens 'sizeof...(UTypes) == 1' and the first element of
+// 'UTypes...' is an instance of the tuple itself. See PR23256.
+
+#include <tuple>
+#include <memory>
+#include <type_traits>
+
+
+struct UnconstrainedCtor {
+  int value_;
+
+  UnconstrainedCtor() : value_(0) {}
+
+  // Blows up when instantiated for any type other than int. Because the ctor
+  // is constexpr it is instantiated by 'is_constructible' and 'is_convertible'
+  // for Clang based compilers. GCC does not instantiate the ctor body
+  // but it does instantiate the noexcept specifier and it will blow up there.
+  template <typename T>
+  constexpr UnconstrainedCtor(T value) noexcept(noexcept(value_ = value))
+      : value_(static_cast<int>(value))
+  {
+      static_assert(std::is_same<int, T>::value, "");
+  }
+};
+
+struct ExplicitUnconstrainedCtor {
+  int value_;
+
+  ExplicitUnconstrainedCtor() : value_(0) {}
+
+  template <typename T>
+  constexpr explicit ExplicitUnconstrainedCtor(T value)
+    noexcept(noexcept(value_ = value))
+      : value_(static_cast<int>(value))
+  {
+      static_assert(std::is_same<int, T>::value, "");
+  }
+
+};
+
+int main() {
+    typedef UnconstrainedCtor A;
+    typedef ExplicitUnconstrainedCtor ExplicitA;
+    {
+        static_assert(std::is_copy_constructible<std::tuple<A>>::value, "");
+        static_assert(std::is_move_constructible<std::tuple<A>>::value, "");
+        static_assert(std::is_copy_constructible<std::tuple<ExplicitA>>::value, "");
+        static_assert(std::is_move_constructible<std::tuple<ExplicitA>>::value, "");
+    }
+    {
+        static_assert(std::is_constructible<
+            std::tuple<A>,
+            std::allocator_arg_t, std::allocator<void>,
+            std::tuple<A> const&
+        >::value, "");
+        static_assert(std::is_constructible<
+            std::tuple<A>,
+            std::allocator_arg_t, std::allocator<void>,
+            std::tuple<A> &&
+        >::value, "");
+        static_assert(std::is_constructible<
+            std::tuple<ExplicitA>,
+            std::allocator_arg_t, std::allocator<void>,
+            std::tuple<ExplicitA> const&
+        >::value, "");
+        static_assert(std::is_constructible<
+            std::tuple<ExplicitA>,
+            std::allocator_arg_t, std::allocator<void>,
+            std::tuple<ExplicitA> &&
+        >::value, "");
+    }
+    {
+        std::tuple<A&&> t(std::forward_as_tuple(A{}));
+        std::tuple<ExplicitA&&> t2(std::forward_as_tuple(ExplicitA{}));
+    }
+}
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR27684_contains_ref_to_incomplete_type.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR27684_contains_ref_to_incomplete_type.pass.cpp
new file mode 100644
index 000000000000..c8b722f836c1
--- /dev/null
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR27684_contains_ref_to_incomplete_type.pass.cpp
@@ -0,0 +1,51 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// UNSUPPORTED: c++98, c++03
+
+// <tuple>
+
+// template <class... Types> class tuple;
+
+// template <class Alloc> tuple(allocator_arg_t, Alloc const&)
+
+// Libc++ has to deduce the 'allocator_arg_t' parameter for this constructor
+// as 'AllocArgT'. Previously libc++ has tried to support tags derived from
+// 'allocator_arg_t' by using 'is_base_of<AllocArgT, allocator_arg_t>'.
+// However this breaks whenever a 2-tuple contains a reference to an incomplete
+// type as its first parameter. See PR27684.
+
+#include <tuple>
+#include <cassert>
+
+struct IncompleteType;
+extern IncompleteType inc1;
+extern IncompleteType inc2;
+IncompleteType const& cinc1 = inc1;
+IncompleteType const& cinc2 = inc2;
+
+int main() {
+    using IT = IncompleteType;
+    { // try calling tuple(Tp const&...)
+        using Tup = std::tuple<const IT&, const IT&>;
+        Tup t(cinc1, cinc2);
+        assert(&std::get<0>(t) == &inc1);
+        assert(&std::get<1>(t) == &inc2);
+    }
+    { // try calling tuple(Up&&...)
+        using Tup = std::tuple<const IT&, const IT&>;
+        Tup t(inc1, inc2);
+        assert(&std::get<0>(t) == &inc1);
+        assert(&std::get<1>(t) == &inc2);
+    }
+}
+
+struct IncompleteType {};
+IncompleteType inc1;
+IncompleteType inc2;
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/UTypes.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/UTypes.pass.cpp
index 817cc8f10990..6ab303c735be 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/UTypes.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/UTypes.pass.cpp
@@ -82,6 +82,8 @@ void test_default_constructible_extension_sfinae()
             MoveOnly, Tuple, MoveOnly, MoveOnly
         >::value, "");
     }
+    // testing extensions
+#ifdef _LIBCPP_VERSION
     {
         typedef std::tuple<MoveOnly, int> Tuple;
         typedef std::tuple<MoveOnly, Tuple, MoveOnly, MoveOnly> NestedTuple;
@@ -96,6 +98,7 @@ void test_default_constructible_extension_sfinae()
             MoveOnly, Tuple, MoveOnly, MoveOnly
         >::value, "");
     }
+#endif
 }
 
 int main()
@@ -118,6 +121,7 @@ int main()
         assert(std::get<2>(t) == 2);
     }
     // extensions
+#ifdef _LIBCPP_VERSION
     {
         std::tuple<MoveOnly, MoveOnly, MoveOnly> t(MoveOnly(0),
                                                    MoveOnly(1));
@@ -131,7 +135,8 @@ int main()
         assert(std::get<1>(t) == MoveOnly());
         assert(std::get<2>(t) == MoveOnly());
     }
-#if _LIBCPP_STD_VER > 11
+#endif
+#if TEST_STD_VER > 11
     {
         constexpr std::tuple<Empty> t0{Empty()};
     }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc.pass.cpp
index 39776822cbda..4da5fc7f8397 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc.pass.cpp
@@ -7,6 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: c++98, c++03
+
 // <tuple>
 
 // template <class... Types> class tuple;
@@ -14,7 +16,9 @@
 // template <class Alloc>
 //   tuple(allocator_arg_t, const Alloc& a);
 
-// UNSUPPORTED: c++98, c++03
+// NOTE: this constructor does not currently support tags derived from
+// allocator_arg_t because libc++ has to deduce the parameter as a template
+// argument. See PR27684 (https://llvm.org/bugs/show_bug.cgi?id=27684)
 
 #include <tuple>
 #include <cassert>
@@ -24,6 +28,18 @@
 #include "../alloc_first.h"
 #include "../alloc_last.h"
 
+template <class T = void>
+struct NonDefaultConstructible {
+  constexpr NonDefaultConstructible() {
+      static_assert(!std::is_same<T, T>::value, "Default Ctor instantiated");
+  }
+
+  explicit constexpr NonDefaultConstructible(int) {}
+};
+
+
+struct DerivedFromAllocArgT : std::allocator_arg_t {};
+
 int main()
 {
     {
@@ -78,4 +94,14 @@ int main()
         assert(!alloc_last::allocator_constructed);
         assert(std::get<2>(t) == alloc_last());
     }
+    {
+        // Test that the uses-allocator default constructor does not evaluate
+        // it's SFINAE when it otherwise shouldn't be selected. Do this by
+        // using 'NonDefaultConstructible' which will cause a compile error
+        // if std::is_default_constructible is evaluated on it.
+        using T = NonDefaultConstructible<>;
+        T v(42);
+        std::tuple<T, T> t(v, v);
+        std::tuple<T, T> t2(42, 42);
+    }
 }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_UTypes.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_UTypes.pass.cpp
index 3929965cd273..e174e9b321b8 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_UTypes.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_UTypes.pass.cpp
@@ -24,16 +24,29 @@
 #include "../alloc_first.h"
 #include "../alloc_last.h"
 
-struct NoDefault { NoDefault() = delete; };
+template <class T = void>
+struct DefaultCtorBlowsUp {
+  constexpr DefaultCtorBlowsUp() {
+      static_assert(!std::is_same<T, T>::value, "Default Ctor instantiated");
+  }
 
-// Make sure the _Up... constructor SFINAEs out when the types that
-// are not explicitly initialized are not all default constructible.
-// Otherwise, std::is_constructible would return true but instantiating
-// the constructor would fail.
-void test_default_constructible_extension_sfinae()
+  explicit constexpr DefaultCtorBlowsUp(int x) : value(x) {}
+
+  int value;
+};
+
+
+struct DerivedFromAllocArgT : std::allocator_arg_t {};
+
+
+// Make sure the _Up... constructor SFINAEs out when the number of initializers
+// is less that the number of elements in the tuple. Previously libc++ would
+// offer these constructers as an extension but they broke conforming code.
+void test_uses_allocator_sfinae_evaluation()
 {
+     using BadDefault = DefaultCtorBlowsUp<>;
     {
-        typedef std::tuple<MoveOnly, NoDefault> Tuple;
+        typedef std::tuple<MoveOnly, MoveOnly, BadDefault> Tuple;
 
         static_assert(!std::is_constructible<
             Tuple,
@@ -42,11 +55,11 @@ void test_default_constructible_extension_sfinae()
 
         static_assert(std::is_constructible<
             Tuple,
-            std::allocator_arg_t, A1<int>, MoveOnly, NoDefault
+            std::allocator_arg_t, A1<int>, MoveOnly, MoveOnly, BadDefault
         >::value, "");
     }
     {
-        typedef std::tuple<MoveOnly, MoveOnly, NoDefault> Tuple;
+        typedef std::tuple<MoveOnly, MoveOnly, BadDefault, BadDefault> Tuple;
 
         static_assert(!std::is_constructible<
             Tuple,
@@ -55,53 +68,44 @@ void test_default_constructible_extension_sfinae()
 
         static_assert(std::is_constructible<
             Tuple,
-            std::allocator_arg_t, A1<int>, MoveOnly, MoveOnly, NoDefault
-        >::value, "");
-    }
-    {
-        // Same idea as above but with a nested tuple
-        typedef std::tuple<MoveOnly, NoDefault> Tuple;
-        typedef std::tuple<MoveOnly, Tuple, MoveOnly, MoveOnly> NestedTuple;
-
-        static_assert(!std::is_constructible<
-            NestedTuple,
-            std::allocator_arg_t, A1<int>, MoveOnly, MoveOnly, MoveOnly, MoveOnly
-        >::value, "");
-
-        static_assert(std::is_constructible<
-            NestedTuple,
-            std::allocator_arg_t, A1<int>, MoveOnly, Tuple, MoveOnly, MoveOnly
-        >::value, "");
-    }
-    {
-        typedef std::tuple<MoveOnly, int> Tuple;
-        typedef std::tuple<MoveOnly, Tuple, MoveOnly, MoveOnly> NestedTuple;
-
-        static_assert(std::is_constructible<
-            NestedTuple,
-            std::allocator_arg_t, A1<int>, MoveOnly, MoveOnly, MoveOnly, MoveOnly
-        >::value, "");
-
-        static_assert(std::is_constructible<
-            NestedTuple,
-            std::allocator_arg_t, A1<int>, MoveOnly, Tuple, MoveOnly, MoveOnly
+            std::allocator_arg_t, A1<int>, MoveOnly, MoveOnly, BadDefault, BadDefault
         >::value, "");
     }
 }
 
+struct Explicit {
+  int value;
+  explicit Explicit(int x) : value(x) {}
+};
+
 int main()
 {
     {
+        std::tuple<Explicit> t{std::allocator_arg, std::allocator<void>{}, 42};
+        assert(std::get<0>(t).value == 42);
+    }
+    {
         std::tuple<MoveOnly> t(std::allocator_arg, A1<int>(), MoveOnly(0));
         assert(std::get<0>(t) == 0);
     }
     {
+        using T = DefaultCtorBlowsUp<>;
+        std::tuple<T> t(std::allocator_arg, A1<int>(), T(42));
+        assert(std::get<0>(t).value == 42);
+    }
+    {
         std::tuple<MoveOnly, MoveOnly> t(std::allocator_arg, A1<int>(),
                                          MoveOnly(0), MoveOnly(1));
         assert(std::get<0>(t) == 0);
         assert(std::get<1>(t) == 1);
     }
     {
+        using T = DefaultCtorBlowsUp<>;
+        std::tuple<T, T> t(std::allocator_arg, A1<int>(), T(42), T(43));
+        assert(std::get<0>(t).value == 42);
+        assert(std::get<1>(t).value == 43);
+    }
+    {
         std::tuple<MoveOnly, MoveOnly, MoveOnly> t(std::allocator_arg, A1<int>(),
                                                    MoveOnly(0),
                                                    1, 2);
@@ -110,6 +114,13 @@ int main()
         assert(std::get<2>(t) == 2);
     }
     {
+        using T = DefaultCtorBlowsUp<>;
+        std::tuple<T, T, T> t(std::allocator_arg, A1<int>(), T(1), T(2), T(3));
+        assert(std::get<0>(t).value == 1);
+        assert(std::get<1>(t).value == 2);
+        assert(std::get<2>(t).value == 3);
+    }
+    {
         alloc_first::allocator_constructed = false;
         alloc_last::allocator_constructed = false;
         std::tuple<int, alloc_first, alloc_last> t(std::allocator_arg,
@@ -120,22 +131,22 @@ int main()
         assert(alloc_last::allocator_constructed);
         assert(std::get<2>(t) == alloc_last(3));
     }
-    // extensions
-    {
-        std::tuple<MoveOnly, MoveOnly, MoveOnly> t(std::allocator_arg, A1<int>(),
-                                                   0, 1);
-        assert(std::get<0>(t) == 0);
-        assert(std::get<1>(t) == 1);
-        assert(std::get<2>(t) == MoveOnly());
-    }
     {
-        std::tuple<MoveOnly, MoveOnly, MoveOnly> t(std::allocator_arg, A1<int>(),
-                                                   0);
-        assert(std::get<0>(t) == 0);
-        assert(std::get<1>(t) == MoveOnly());
-        assert(std::get<2>(t) == MoveOnly());
+        // Check that uses-allocator construction is still selected when
+        // given a tag type that derives from allocator_arg_t.
+        DerivedFromAllocArgT tag;
+        alloc_first::allocator_constructed = false;
+        alloc_last::allocator_constructed = false;
+        std::tuple<int, alloc_first, alloc_last> t(tag,
+                                                   A1<int>(5), 1, 2, 3);
+        assert(std::get<0>(t) == 1);
+        assert(alloc_first::allocator_constructed);
+        assert(std::get<1>(t) == alloc_first(2));
+        assert(alloc_last::allocator_constructed);
+        assert(std::get<2>(t) == alloc_last(3));
     }
-    // Check that SFINAE is properly applied with the default reduced arity
-    // constructor extensions.
-    test_default_constructible_extension_sfinae();
+    // Stress test the SFINAE on the uses-allocator constructors and
+    // ensure that the "reduced-arity-initialization" extension is not offered
+    // for these constructors.
+    test_uses_allocator_sfinae_evaluation();
 }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_const_Types.fail.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_const_Types.fail.cpp
new file mode 100644
index 000000000000..b28ad6dab5ab
--- /dev/null
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_const_Types.fail.cpp
@@ -0,0 +1,43 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <tuple>
+
+// template <class... Types> class tuple;
+
+// template <class Alloc>
+//   EXPLICIT tuple(allocator_arg_t, const Alloc& a, const Types&...);
+
+// UNSUPPORTED: c++98, c++03
+
+#include <tuple>
+#include <memory>
+#include <cassert>
+
+struct ExplicitCopy {
+  explicit ExplicitCopy(ExplicitCopy const&) {}
+  explicit ExplicitCopy(int) {}
+};
+
+std::tuple<ExplicitCopy> const_explicit_copy_test() {
+    const ExplicitCopy e(42);
+    return {std::allocator_arg, std::allocator<void>{}, e};
+    // expected-error@-1 {{chosen constructor is explicit in copy-initialization}}
+}
+
+std::tuple<ExplicitCopy> non_const_explicity_copy_test() {
+    ExplicitCopy e(42);
+    return {std::allocator_arg, std::allocator<void>{}, e};
+    // expected-error@-1 {{chosen constructor is explicit in copy-initialization}}
+}
+int main()
+{
+    const_explicit_copy_test();
+    non_const_explicity_copy_test();
+}
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_const_Types.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_const_Types.pass.cpp
index 0f68926376f2..73d53a4c0e26 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_const_Types.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_const_Types.pass.cpp
@@ -17,15 +17,37 @@
 // UNSUPPORTED: c++98, c++03
 
 #include <tuple>
+#include <memory>
 #include <cassert>
 
 #include "allocators.h"
 #include "../alloc_first.h"
 #include "../alloc_last.h"
 
+struct ImplicitCopy {
+  explicit ImplicitCopy(int) {}
+  ImplicitCopy(ImplicitCopy const&) {}
+};
+
+// Test that tuple(std::allocator_arg, Alloc, Types const&...) allows implicit
+// copy conversions in return value expressions.
+std::tuple<ImplicitCopy> testImplicitCopy1() {
+    ImplicitCopy i(42);
+    return {std::allocator_arg, std::allocator<void>{}, i};
+}
+
+std::tuple<ImplicitCopy> testImplicitCopy2() {
+    const ImplicitCopy i(42);
+    return {std::allocator_arg, std::allocator<void>{}, i};
+}
+
 int main()
 {
     {
+        // check that the literal '0' can implicitly initialize a stored pointer.
+        std::tuple<int*> t = {std::allocator_arg, std::allocator<void>{}, 0};
+    }
+    {
         std::tuple<int> t(std::allocator_arg, A1<int>(), 3);
         assert(std::get<0>(t) == 3);
     }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_copy.fail.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_copy.fail.cpp
new file mode 100644
index 000000000000..ccf08833b537
--- /dev/null
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_copy.fail.cpp
@@ -0,0 +1,43 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <tuple>
+
+// template <class... Types> class tuple;
+
+// template <class Alloc, class ...UTypes>
+//   tuple(allocator_arg_t, const Alloc& a, tuple<UTypes...> const&);
+
+// UNSUPPORTED: c++98, c++03
+
+#include <tuple>
+#include <memory>
+
+struct ExplicitCopy {
+  explicit ExplicitCopy(int) {}
+  explicit ExplicitCopy(ExplicitCopy const&) {}
+
+};
+
+std::tuple<ExplicitCopy> const_explicit_copy_test() {
+    const std::tuple<int> t1(42);
+    return {std::allocator_arg, std::allocator<void>{}, t1};
+    // expected-error@-1 {{chosen constructor is explicit in copy-initialization}}
+}
+
+std::tuple<ExplicitCopy> non_const_explicit_copy_test() {
+    std::tuple<int> t1(42);
+    return {std::allocator_arg, std::allocator<void>{}, t1};
+    // expected-error@-1 {{chosen constructor is explicit in copy-initialization}}
+}
+
+int main()
+{
+
+}
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_copy.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_copy.pass.cpp
index 8acfde7a98eb..36d9f32879cb 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_copy.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_copy.pass.cpp
@@ -17,12 +17,23 @@
 // UNSUPPORTED: c++98, c++03
 
 #include <tuple>
+#include <memory>
 #include <cassert>
 
 #include "allocators.h"
 #include "../alloc_first.h"
 #include "../alloc_last.h"
 
+struct Explicit {
+  int value;
+  explicit Explicit(int x) : value(x) {}
+};
+
+struct Implicit {
+  int value;
+  Implicit(int x) : value(x) {}
+};
+
 int main()
 {
     {
@@ -66,4 +77,14 @@ int main()
         assert(std::get<1>(t1) == 2);
         assert(std::get<2>(t1) == 3);
     }
+    {
+        const std::tuple<int> t1(42);
+        std::tuple<Explicit> t2{std::allocator_arg, std::allocator<void>{},  t1};
+        assert(std::get<0>(t2).value == 42);
+    }
+    {
+        const std::tuple<int> t1(42);
+        std::tuple<Implicit> t2 = {std::allocator_arg, std::allocator<void>{}, t1};
+        assert(std::get<0>(t2).value == 42);
+    }
 }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_move.fail.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_move.fail.cpp
new file mode 100644
index 000000000000..d3539cebf950
--- /dev/null
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_move.fail.cpp
@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <tuple>
+
+// template <class... Types> class tuple;
+
+// template <class Alloc, class ...UTypes>
+//   tuple(allocator_arg_t, const Alloc& a, tuple<UTypes...>&&);
+
+// UNSUPPORTED: c++98, c++03
+
+#include <tuple>
+#include <memory>
+
+struct ExplicitCopy {
+  explicit ExplicitCopy(int) {}
+  explicit ExplicitCopy(ExplicitCopy const&) {}
+};
+
+std::tuple<ExplicitCopy> explicit_move_test() {
+    std::tuple<int> t1(42);
+    return {std::allocator_arg, std::allocator<void>{}, std::move(t1)};
+    // expected-error@-1 {{chosen constructor is explicit in copy-initialization}}
+}
+
+int main()
+{
+
+}
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_move.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_move.pass.cpp
index c862d3b64d56..d3a6add5da6a 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_move.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_convert_move.pass.cpp
@@ -40,6 +40,16 @@ struct D
     explicit D(int i) : B(i) {}
 };
 
+struct Explicit {
+  int value;
+  explicit Explicit(int x) : value(x) {}
+};
+
+struct Implicit {
+  int value;
+  Implicit(int x) : value(x) {}
+};
+
 int main()
 {
     {
@@ -81,4 +91,14 @@ int main()
         assert(std::get<1>(t1) == 2);
         assert(std::get<2>(t1)->id_ == 3);
     }
+    {
+        std::tuple<int> t1(42);
+        std::tuple<Explicit> t2{std::allocator_arg, std::allocator<void>{}, std::move(t1)};
+        assert(std::get<0>(t2).value == 42);
+    }
+    {
+        std::tuple<int> t1(42);
+        std::tuple<Implicit> t2 = {std::allocator_arg, std::allocator<void>{}, std::move(t1)};
+        assert(std::get<0>(t2).value == 42);
+    }
 }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_copy.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_copy.pass.cpp
index 14e127e59ba9..7c9f60cbf901 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_copy.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_copy.pass.cpp
@@ -52,6 +52,8 @@ int main()
         assert(alloc_last::allocator_constructed);
         assert(std::get<0>(t) == 2);
     }
+// testing extensions
+#ifdef _LIBCPP_VERSION
     {
         typedef std::tuple<alloc_first, alloc_last> T;
         T t0(2, 3);
@@ -75,4 +77,5 @@ int main()
         assert(std::get<1>(t) == 2);
         assert(std::get<2>(t) == 3);
     }
+#endif
 }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_move.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_move.pass.cpp
index 54d3f7ee0c07..a3e1a9de6195 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_move.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_move.pass.cpp
@@ -53,6 +53,8 @@ int main()
         assert(alloc_last::allocator_constructed);
         assert(std::get<0>(t) == 1);
     }
+// testing extensions
+#ifdef _LIBCPP_VERSION
     {
         typedef std::tuple<MoveOnly, alloc_first> T;
         T t0(0 ,1);
@@ -74,4 +76,5 @@ int main()
         assert(std::get<1>(t) == 2);
         assert(std::get<2>(t) == 3);
     }
+#endif
 }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_Types.fail.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_Types.fail.cpp
index 00e2af265b36..b72f0fc2efec 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_Types.fail.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_Types.fail.cpp
@@ -19,9 +19,30 @@
 #include <string>
 #include <cassert>
 
+struct ExplicitCopy {
+  ExplicitCopy(int) {}
+  explicit ExplicitCopy(ExplicitCopy const&) {}
+};
+
+std::tuple<ExplicitCopy> const_explicit_copy() {
+    const ExplicitCopy e(42);
+    return {e};
+    // expected-error@-1 {{chosen constructor is explicit in copy-initialization}}
+}
+
+
+std::tuple<ExplicitCopy> non_const_explicit_copy() {
+    ExplicitCopy e(42);
+    return {e};
+    // expected-error@-1 {{chosen constructor is explicit in copy-initialization}}
+}
+
+std::tuple<ExplicitCopy> const_explicit_copy_no_brace() {
+    const ExplicitCopy e(42);
+    return e;
+    // expected-error@-1 {{no viable conversion}}
+}
+
 int main()
 {
-    {
-        std::tuple<int*> t = 0;
-    }
 }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_Types.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_Types.pass.cpp
index bbadf8de1600..367f19e5d8dd 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_Types.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_Types.pass.cpp
@@ -53,13 +53,40 @@ struct NoValueCtorEmpty
     { static_assert(never<T>::value, "This should not be instantiated"); }
 };
 
+
+struct ImplicitCopy {
+  explicit ImplicitCopy(int) {}
+  ImplicitCopy(ImplicitCopy const&) {}
+};
+
+// Test that tuple(std::allocator_arg, Alloc, Types const&...) allows implicit
+// copy conversions in return value expressions.
+std::tuple<ImplicitCopy> testImplicitCopy1() {
+    ImplicitCopy i(42);
+    return {i};
+}
+
+std::tuple<ImplicitCopy> testImplicitCopy2() {
+    const ImplicitCopy i(42);
+    return {i};
+}
+
+std::tuple<ImplicitCopy> testImplicitCopy3() {
+    const ImplicitCopy i(42);
+    return i;
+}
+
 int main()
 {
     {
+        // check that the literal '0' can implicitly initialize a stored pointer.
+        std::tuple<int*> t = 0;
+    }
+    {
         std::tuple<int> t(2);
         assert(std::get<0>(t) == 2);
     }
-#if _LIBCPP_STD_VER > 11 
+#if _LIBCPP_STD_VER > 11
     {
         constexpr std::tuple<int> t(2);
         static_assert(std::get<0>(t) == 2, "");
@@ -74,7 +101,7 @@ int main()
         assert(std::get<0>(t) == 2);
         assert(std::get<1>(t) == nullptr);
     }
-#if _LIBCPP_STD_VER > 11 
+#if _LIBCPP_STD_VER > 11
     {
         constexpr std::tuple<int, char*> t(2, nullptr);
         static_assert(std::get<0>(t) == 2, "");
@@ -109,7 +136,8 @@ int main()
         assert(std::get<2>(t) == 2);
         assert(std::get<3>(t) == 3);
     }
-    // extensions
+// extensions
+#ifdef _LIBCPP_VERSION
     {
         std::tuple<int, char*, std::string> t(2);
         assert(std::get<0>(t) == 2);
@@ -129,4 +157,5 @@ int main()
         assert(std::get<2>(t) == "text");
         assert(std::get<3>(t) == 0.0);
     }
+#endif
 }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_pair.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_pair.pass.cpp
index 740b6589e511..d6d489fd0ea4 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_pair.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_pair.pass.cpp
@@ -29,7 +29,7 @@ int main()
         assert(std::get<0>(t1) == 2);
         assert(std::get<1>(t1) == short('a'));
     }
-#if _LIBCPP_STD_VER > 11 
+#if _LIBCPP_STD_VER > 11
     {
         typedef std::pair<double, char> P0;
         typedef std::tuple<int, short> T1;
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/convert_copy.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/convert_copy.pass.cpp
index 5ad4f9227f48..b7fa2e3a03cc 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/convert_copy.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/convert_copy.pass.cpp
@@ -20,6 +20,16 @@
 #include <string>
 #include <cassert>
 
+struct Explicit {
+  int value;
+  explicit Explicit(int x) : value(x) {}
+};
+
+struct Implicit {
+  int value;
+  Implicit(int x) : value(x) {}
+};
+
 struct B
 {
     int id_;
@@ -33,7 +43,7 @@ struct D
     explicit D(int i) : B(i) {}
 };
 
-#if _LIBCPP_STD_VER > 11 
+#if _LIBCPP_STD_VER > 11
 
 struct A
 {
@@ -62,7 +72,7 @@ int main()
         T1 t1 = t0;
         assert(std::get<0>(t1) == 2);
     }
-#if _LIBCPP_STD_VER > 11 
+#if _LIBCPP_STD_VER > 11
     {
         typedef std::tuple<double> T0;
         typedef std::tuple<A> T1;
@@ -115,4 +125,14 @@ int main()
         assert(std::get<1>(t1) == int('a'));
         assert(std::get<2>(t1).id_ == 3);
     }
+    {
+        const std::tuple<int> t1(42);
+        std::tuple<Explicit> t2(t1);
+        assert(std::get<0>(t2).value == 42);
+    }
+    {
+        const std::tuple<int> t1(42);
+        std::tuple<Implicit> t2 = t1;
+        assert(std::get<0>(t2).value == 42);
+    }
 }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/convert_move.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/convert_move.pass.cpp
index 3a6abd3a95af..8423f5d0145f 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/convert_move.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/convert_move.pass.cpp
@@ -20,6 +20,16 @@
 #include <memory>
 #include <cassert>
 
+struct Explicit {
+  int value;
+  explicit Explicit(int x) : value(x) {}
+};
+
+struct Implicit {
+  int value;
+  Implicit(int x) : value(x) {}
+};
+
 struct B
 {
     int id_;
@@ -81,4 +91,14 @@ int main()
         assert(std::get<1>(t1) == int('a'));
         assert(std::get<2>(t1)->id_ == 3);
     }
+    {
+        std::tuple<int> t1(42);
+        std::tuple<Explicit> t2(std::move(t1));
+        assert(std::get<0>(t2).value == 42);
+    }
+    {
+        std::tuple<int> t1(42);
+        std::tuple<Implicit> t2 = std::move(t1);
+        assert(std::get<0>(t2).value == 42);
+    }
 }
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/move.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/move.pass.cpp
index 0cda96846f71..1bd7d6d4e8a8 100644
--- a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/move.pass.cpp
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/move.pass.cpp
@@ -29,8 +29,10 @@ struct ConstructsWithTupleLeaf
     ConstructsWithTupleLeaf(ConstructsWithTupleLeaf &&) {}
 
     template <class T>
-    ConstructsWithTupleLeaf(T t)
-    { assert(false); }
+    ConstructsWithTupleLeaf(T t) {
+        static_assert(!std::is_same<T, T>::value,
+                      "Constructor instantiated for type other than int");
+    }
 };
 
 int main()
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/test_lazy_sfinae.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/test_lazy_sfinae.pass.cpp
new file mode 100644
index 000000000000..76f7e794a8e8
--- /dev/null
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/test_lazy_sfinae.pass.cpp
@@ -0,0 +1,102 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <tuple>
+
+// template <class... Types> class tuple;
+
+// UNSUPPORTED: c++98, c++03
+
+#include <tuple>
+#include <utility>
+#include <cassert>
+
+template <class ConstructFrom>
+struct ConstructibleFromT {
+  ConstructibleFromT() = default;
+  ConstructibleFromT(ConstructFrom v) : value(v) {}
+  ConstructFrom value;
+};
+
+template <class AssertOn>
+struct CtorAssertsT {
+  bool defaulted;
+  CtorAssertsT() : defaulted(true) {}
+  template <class T>
+  constexpr CtorAssertsT(T) : defaulted(false) {
+      static_assert(!std::is_same<T, AssertOn>::value, "");
+  }
+};
+
+template <class AllowT, class AssertT>
+struct AllowAssertT {
+  AllowAssertT() = default;
+  AllowAssertT(AllowT) {}
+  template <class U>
+  constexpr AllowAssertT(U) {
+      static_assert(!std::is_same<U, AssertT>::value, "");
+  }
+};
+
+// Construct a tuple<T1, T2> from pair<int, int> where T1 and T2
+// are not constructible from ints but T1 is constructible from std::pair.
+// This considers the following constructors:
+// (1) tuple(TupleLike) -> checks is_constructible<Tn, int>
+// (2) tuple(UTypes...) -> checks is_constructible<T1, pair<int, int>>
+//                            and is_default_constructible<T2>
+// The point of this test is to ensure that the consideration of (1)
+// short circuits before evaluating is_constructible<T2, int>, which
+// will cause a static assertion.
+void test_tuple_like_lazy_sfinae() {
+#if defined(_LIBCPP_VERSION)
+    // This test requires libc++'s reduced arity initialization.
+    using T1 = ConstructibleFromT<std::pair<int, int>>;
+    using T2 = CtorAssertsT<int>;
+    std::pair<int, int> p(42, 100);
+    std::tuple<T1, T2> t(p);
+    assert(std::get<0>(t).value == p);
+    assert(std::get<1>(t).defaulted);
+#endif
+}
+
+
+struct NonConstCopyable {
+  NonConstCopyable() = default;
+  explicit NonConstCopyable(int v) : value(v) {}
+  NonConstCopyable(NonConstCopyable&) = default;
+  NonConstCopyable(NonConstCopyable const&) = delete;
+  int value;
+};
+
+template <class T>
+struct BlowsUpOnConstCopy {
+  BlowsUpOnConstCopy() = default;
+  constexpr BlowsUpOnConstCopy(BlowsUpOnConstCopy const&) {
+      static_assert(!std::is_same<T, T>::value, "");
+  }
+  BlowsUpOnConstCopy(BlowsUpOnConstCopy&) = default;
+};
+
+// Test the following constructors:
+// (1) tuple(Types const&...)
+// (2) tuple(UTypes&&...)
+// Test that (1) short circuits before evaluating the copy constructor of the
+// second argument. Constructor (2) should be selected.
+void test_const_Types_lazy_sfinae()
+{
+    NonConstCopyable v(42);
+    BlowsUpOnConstCopy<int> b;
+    std::tuple<NonConstCopyable, BlowsUpOnConstCopy<int>> t(v, b);
+    assert(std::get<0>(t).value == 42);
+}
+
+int main() {
+    test_tuple_like_lazy_sfinae();
+    test_const_Types_lazy_sfinae();
+}