[libc++] Implement CTAD for std::tuple

Summary:
We were using implicit deduction guides instead of explicit ones,
however the implicit ones don't do work anymore when changing the
constructors.

This commit adds the actual guides specified in the Standard to make
libc++ (1) closer to the Standard and (2) more resistent to changes
in std::tuple's constructors.

Reviewers: Quuxplusone

Subscribers: christof, jkorous, dexonsmith, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D65225

llvm-svn: 368599

2 files changed, 78 insertions, 20 deletions

diff --git a/libcxx/include/tuple b/libcxx/include/tuple
index 65065872991..32bc86913aa 100644
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -69,6 +69,17 @@ public:
     void swap(tuple&) noexcept(AND(swap(declval<T&>(), declval<T&>())...));
 };
 
+template <class ...T>
+tuple(T...) -> tuple<T...>;                                         // since C++17
+template <class T1, class T2>
+tuple(pair<T1, T2>) -> tuple<T1, T2>;                               // since C++17
+template <class Alloc, class ...T>
+tuple(allocator_arg_t, Alloc, T...) -> tuple<T...>;                 // since C++17
+template <class Alloc, class T1, class T2>
+tuple(allocator_arg_t, Alloc, pair<T1, T2>) -> tuple<T1, T2>;       // since C++17
+template <class Alloc, class ...T>
+tuple(allocator_arg_t, Alloc, tuple<T...>) -> tuple<T...>;          // since C++17
+
 inline constexpr unspecified ignore;
 
 template <class... T> tuple<V...>  make_tuple(T&&...); // constexpr in C++14
@@ -943,13 +954,16 @@ public:
 };
 
 #ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
-// NOTE: These are not yet standardized, but are required to simulate the
-// implicit deduction guide that should be generated had libc++ declared the
-// tuple-like constructors "correctly"
-template <class _Alloc, class ..._Args>
-tuple(allocator_arg_t, const _Alloc&, tuple<_Args...> const&) -> tuple<_Args...>;
-template <class _Alloc, class ..._Args>
-tuple(allocator_arg_t, const _Alloc&, tuple<_Args...>&&) -> tuple<_Args...>;
+template <class ..._Tp>
+tuple(_Tp...) -> tuple<_Tp...>;
+template <class _Tp1, class _Tp2>
+tuple(pair<_Tp1, _Tp2>) -> tuple<_Tp1, _Tp2>;
+template <class _Alloc, class ..._Tp>
+tuple(allocator_arg_t, _Alloc, _Tp...) -> tuple<_Tp...>;
+template <class _Alloc, class _Tp1, class _Tp2>
+tuple(allocator_arg_t, _Alloc, pair<_Tp1, _Tp2>) -> tuple<_Tp1, _Tp2>;
+template <class _Alloc, class ..._Tp>
+tuple(allocator_arg_t, _Alloc, tuple<_Tp...>) -> tuple<_Tp...>;
 #endif
 
 template <class ..._Tp>
diff --git a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/implicit_deduction_guides.pass.cpp b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/deduct.pass.cpp
index 3ff089a0b31..e903cd0b476 100644
--- a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/implicit_deduction_guides.pass.cpp
+++ b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/deduct.pass.cpp
@@ -33,13 +33,15 @@
 //  using AT = std::allocator_arg_t
 // ---------------
 // (1)  tuple(const Types&...) -> tuple<Types...>
-// (2)  explicit tuple(const Types&...) -> tuple<Types...>
-// (3)  tuple(AT, A const&, Types const&...) -> tuple<Types...>
-// (4)  explicit tuple(AT, A const&, Types const&...) -> tuple<Types...>
-// (5)  tuple(tuple const& t) -> decltype(t)
-// (6)  tuple(tuple&& t) -> decltype(t)
-// (7)  tuple(AT, A const&, tuple const& t) -> decltype(t)
-// (8)  tuple(AT, A const&, tuple&& t) -> decltype(t)
+// (2)  tuple(pair<T1, T2>) -> tuple<T1, T2>;
+// (3)  explicit tuple(const Types&...) -> tuple<Types...>
+// (4)  tuple(AT, A const&, Types const&...) -> tuple<Types...>
+// (5)  explicit tuple(AT, A const&, Types const&...) -> tuple<Types...>
+// (6)  tuple(AT, A, pair<T1, T2>) -> tuple<T1, T2>
+// (7)  tuple(tuple const& t) -> decltype(t)
+// (8)  tuple(tuple&& t) -> decltype(t)
+// (9)  tuple(AT, A const&, tuple const& t) -> decltype(t)
+// (10) tuple(AT, A const&, tuple&& t) -> decltype(t)
 void test_primary_template()
 {
   const std::allocator<int> A;
@@ -52,6 +54,27 @@ void test_primary_template()
     ASSERT_SAME_TYPE(decltype(t2), std::tuple<int, double, decltype(nullptr)>);
   }
   { // Testing (2)
+    std::pair<int, char> p1(1, 'c');
+    std::tuple t1(p1);
+    ASSERT_SAME_TYPE(decltype(t1), std::tuple<int, char>);
+
+    std::pair<int, std::tuple<char, long, void*>> p2(1, std::tuple<char, long, void*>('c', 3l, nullptr));
+    std::tuple t2(p2);
+    ASSERT_SAME_TYPE(decltype(t2), std::tuple<int, std::tuple<char, long, void*>>);
+
+    int i = 3;
+    std::pair<std::reference_wrapper<int>, char> p3(std::ref(i), 'c');
+    std::tuple t3(p3);
+    ASSERT_SAME_TYPE(decltype(t3), std::tuple<std::reference_wrapper<int>, char>);
+
+    std::pair<int&, char> p4(i, 'c');
+    std::tuple t4(p4);
+    ASSERT_SAME_TYPE(decltype(t4), std::tuple<int&, char>);
+
+    std::tuple t5(std::pair<int, char>(1, 'c'));
+    ASSERT_SAME_TYPE(decltype(t5), std::tuple<int, char>);
+  }
+  { // Testing (3)
     using T = ExplicitTestTypes::TestType;
     static_assert(!std::is_convertible<T const&, T>::value, "");
 
@@ -62,7 +85,7 @@ void test_primary_template()
     std::tuple t2(T{}, 101l, v);
     ASSERT_SAME_TYPE(decltype(t2), std::tuple<T, long, T>);
   }
-  { // Testing (3)
+  { // Testing (4)
     int x = 101;
     std::tuple t1(AT, A, 42);
     ASSERT_SAME_TYPE(decltype(t1), std::tuple<int>);
@@ -70,7 +93,7 @@ void test_primary_template()
     std::tuple t2(AT, A, 42, 0.0, x);
     ASSERT_SAME_TYPE(decltype(t2), std::tuple<int, double, int>);
   }
-  { // Testing (4)
+  { // Testing (5)
     using T = ExplicitTestTypes::TestType;
     static_assert(!std::is_convertible<T const&, T>::value, "");
 
@@ -81,26 +104,47 @@ void test_primary_template()
     std::tuple t2(AT, A, T{}, 101l, v);
     ASSERT_SAME_TYPE(decltype(t2), std::tuple<T, long, T>);
   }
-  { // Testing (5)
+  { // Testing (6)
+    std::pair<int, char> p1(1, 'c');
+    std::tuple t1(AT, A, p1);
+    ASSERT_SAME_TYPE(decltype(t1), std::tuple<int, char>);
+
+    std::pair<int, std::tuple<char, long, void*>> p2(1, std::tuple<char, long, void*>('c', 3l, nullptr));
+    std::tuple t2(AT, A, p2);
+    ASSERT_SAME_TYPE(decltype(t2), std::tuple<int, std::tuple<char, long, void*>>);
+
+    int i = 3;
+    std::pair<std::reference_wrapper<int>, char> p3(std::ref(i), 'c');
+    std::tuple t3(AT, A, p3);
+    ASSERT_SAME_TYPE(decltype(t3), std::tuple<std::reference_wrapper<int>, char>);
+
+    std::pair<int&, char> p4(i, 'c');
+    std::tuple t4(AT, A, p4);
+    ASSERT_SAME_TYPE(decltype(t4), std::tuple<int&, char>);
+
+    std::tuple t5(AT, A, std::pair<int, char>(1, 'c'));
+    ASSERT_SAME_TYPE(decltype(t5), std::tuple<int, char>);
+  }
+  { // Testing (7)
     using Tup = std::tuple<int, decltype(nullptr)>;
     const Tup t(42, nullptr);
 
     std::tuple t1(t);
     ASSERT_SAME_TYPE(decltype(t1), Tup);
   }
-  { // Testing (6)
+  { // Testing (8)
     using Tup = std::tuple<void*, unsigned, char>;
     std::tuple t1(Tup(nullptr, 42, 'a'));
     ASSERT_SAME_TYPE(decltype(t1), Tup);
   }
-  { // Testing (7)
+  { // Testing (9)
     using Tup = std::tuple<int, decltype(nullptr)>;
     const Tup t(42, nullptr);
 
     std::tuple t1(AT, A, t);
     ASSERT_SAME_TYPE(decltype(t1), Tup);
   }
-  { // Testing (8)
+  { // Testing (10)
     using Tup = std::tuple<void*, unsigned, char>;
     std::tuple t1(AT, A, Tup(nullptr, 42, 'a'));
     ASSERT_SAME_TYPE(decltype(t1), Tup);