From 27cdf401eaa84e0d4ae82d174ddba6453e882856 Mon Sep 17 00:00:00 2001
From: Eric Fiselier <eric@efcs.ca>
Date: Sat, 2 Jul 2016 01:25:46 +0000
Subject: [PATCH] Cleanup SFINAE in tuple, and add tests for reference
 assignment

llvm-svn: 274414
---
 libcxx/include/__tuple                        | 45 +++++++------------
 .../tuple.assign/convert_copy.pass.cpp        | 12 +++++
 .../tuple.assign/convert_move.pass.cpp        | 19 ++++++++
 3 files changed, 47 insertions(+), 29 deletions(-)

diff --git a/libcxx/include/__tuple b/libcxx/include/__tuple
index 0d180c701593..cc9fbbebc096 100644
--- a/libcxx/include/__tuple
+++ b/libcxx/include/__tuple
@@ -335,11 +335,11 @@ struct __make_tuple_types_flat<_Tuple<_Types...>, __tuple_indices<_Idx...>> {
 
 template <class _Vt, size_t _Np, size_t ..._Idx>
 struct __make_tuple_types_flat<array<_Vt, _Np>, __tuple_indices<_Idx...>> {
-  using _Array = array<_Vt, _Np>;
-
+  template <size_t>
+  using __value_type = _Vt;
   template <class _Tp, class _ApplyFn = __apply_cv_t<_Tp>>
   using __apply_quals = __tuple_types<
-      typename _ApplyFn::template __apply<typename tuple_element<_Idx, _Array>::type>...
+      typename _ApplyFn::template __apply<__value_type<_Idx>>...
     >;
 };
 
@@ -371,32 +371,19 @@ template <bool ..._Pred>
 using __all = is_same<__all_dummy<_Pred...>, __all_dummy<(_Pred, true)...>>;
 
 struct __tuple_sfinae_base {
-  template <class ..._FromArgs, class ..._ToArgs>
-  static auto __test_constructible(__tuple_types<_FromArgs...>, __tuple_types<_ToArgs...>)
-    -> __all<typename enable_if<
-        is_constructible<_ToArgs, _FromArgs>::value
-      , bool>::type{true}...>;
-  static auto __test_constructible(...) -> false_type;
-  template <class _Types1, class _Types2>
-  using __constructible = decltype(__test_constructible(_Types1{}, _Types2{}));
+  template <template <class, class...> class _Trait,
+            class ..._LArgs, class ..._RArgs>
+  static auto __do_test(__tuple_types<_LArgs...>, __tuple_types<_RArgs...>)
+    -> __all<typename enable_if<_Trait<_LArgs, _RArgs>::value, bool>::type{true}...>;
+  template <template <class...> class>
+  static auto __do_test(...) -> false_type;
 
-  template <class ..._FromArgs, class ..._ToArgs>
-  static auto __test_convertible(__tuple_types<_FromArgs...>, __tuple_types<_ToArgs...>)
-    -> __all<typename enable_if<
-          is_convertible<_FromArgs, _ToArgs>::value
-      , bool>::type{true}...>;
-  static auto __test_convertible(...) -> false_type;
-  template <class _Types1, class _Types2>
-  using __convertible = decltype(__test_convertible(_Types1{}, _Types2{}));
-
-  template <class ..._FromArgs, class ..._ToArgs>
-  static auto __test_assignable(__tuple_types<_FromArgs...>, __tuple_types<_ToArgs...>)
-    -> __all<typename enable_if<
-          is_assignable<_ToArgs&, _FromArgs>::value
-      , bool>::type{true}...>;
-  static auto __test_assignable(...) -> false_type;
-  template <class _Types1, class _Types2>
-  using __assignable = decltype(__test_assignable(_Types1{}, _Types2{}));
+  template <class _FromArgs, class _ToArgs>
+  using __constructible = decltype(__do_test<is_constructible>(_ToArgs{}, _FromArgs{}));
+  template <class _FromArgs, class _ToArgs>
+  using __convertible = decltype(__do_test<is_convertible>(_FromArgs{}, _ToArgs{}));
+  template <class _FromArgs, class _ToArgs>
+  using __assignable = decltype(__do_test<is_assignable>(_ToArgs{}, _FromArgs{}));
 };
 
 // __tuple_convertible
@@ -440,7 +427,7 @@ template <class _Tp, class _Up>
 struct __tuple_assignable<_Tp, _Up, true, true>
     : public __tuple_sfinae_base::__assignable<
       typename __make_tuple_types<_Tp>::type
-    , typename __make_tuple_types<_Up>::type
+    , typename __make_tuple_types<_Up&>::type
     >
 {};
 
diff --git a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/convert_copy.pass.cpp b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/convert_copy.pass.cpp
index 2dde6b5521f2..91892efaf139 100644
--- a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/convert_copy.pass.cpp
+++ b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/convert_copy.pass.cpp
@@ -74,4 +74,16 @@ int main()
         assert(std::get<1>(t1) == int('a'));
         assert(std::get<2>(t1).id_ == 2);
     }
+    {
+        // Test that tuple evaluates correctly applies an lvalue reference
+        // before evaluating is_assignable (ie 'is_assignable<int&, int&>')
+        // instead of evaluating 'is_assignable<int&&, int&>' which is false.
+        int x = 42;
+        int y = 43;
+        std::tuple<int&&> t(std::move(x));
+        std::tuple<int&> t2(y);
+        t = t2;
+        assert(std::get<0>(t) == 43);
+        assert(&std::get<0>(t) == &x);
+    }
 }
diff --git a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/convert_move.pass.cpp b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/convert_move.pass.cpp
index 11bfdd0c94a9..afd3e0fdb8e3 100644
--- a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/convert_move.pass.cpp
+++ b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/convert_move.pass.cpp
@@ -37,6 +37,13 @@ struct D
     explicit D(int i) : B(i) {}
 };
 
+struct E {
+  E() = default;
+  E& operator=(int val) {
+      return *this;
+  }
+};
+
 int main()
 {
     {
@@ -88,4 +95,16 @@ int main()
         assert(std::get<1>(t1) == int('a'));
         assert(std::get<2>(t1)->id_ == 3);
     }
+    {
+        // Test that tuple evaluates correctly applies an lvalue reference
+        // before evaluating is_assignable (ie 'is_assignable<int&, int&&>')
+        // instead of evaluating 'is_assignable<int&&, int&&>' which is false.
+        int x = 42;
+        int y = 43;
+        std::tuple<int&&, E> t(std::move(x), E{});
+        std::tuple<int&&, int> t2(std::move(y), 44);
+        t = std::move(t2);
+        assert(std::get<0>(t) == 43);
+        assert(&std::get<0>(t) == &x);
+    }
 }