Implement P0163r0. Add shared_ptr::weak_type.

This patch adds the weak_type typedef in shared_ptr. It is available in
C++17 and newer.

This patch also updates the _LIBCPP_STD_VER and TEST_STD_VER macros to
have the value of 16, since 2016 is the current year.

llvm-svn: 273839

libcxx/include/__config

@@ -756,7 +756,7 @@ template <unsigned> struct __static_assert_check {};
 #  elif __cplusplus <= 201402L
 #    define _LIBCPP_STD_VER 14
 #  else
-#    define _LIBCPP_STD_VER 15  // current year, or date of c++17 ratification
+#    define _LIBCPP_STD_VER 16  // current year, or date of c++17 ratification
 #  endif
 #endif  // _LIBCPP_STD_VER
 

libcxx/include/memory

@@ -361,6 +361,7 @@ class shared_ptr
 {
 public:
     typedef T element_type;
+    typedef weak_ptr<T> weak_type; // C++17
 
     // constructors:
     constexpr shared_ptr() noexcept;
@@ -3863,6 +3864,9 @@ class _LIBCPP_TYPE_VIS_ONLY shared_ptr
 {
 public:
     typedef _Tp element_type;
+#if _LIBCPP_STD_VER > 14
+    typedef weak_ptr<_Tp> weak_type;
+#endif
 private:
     element_type*      __ptr_;
     __shared_weak_count* __cntrl_;

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/types.pass.cpp

@@ -13,14 +13,20 @@
 // {
 // public:
 //     typedef T element_type;
+//     typedef weak_ptr<T> weak_type; // C++17
 //     ...
 // };
 
 #include <memory>
 
+#include "test_macros.h"
+
 struct A;  // purposefully incomplete
 
 int main()
 {
     static_assert((std::is_same<std::shared_ptr<A>::element_type, A>::value), "");
+#if TEST_STD_VER > 14
+    static_assert((std::is_same<std::shared_ptr<A>::weak_type, std::weak_ptr<A>>::value), "");
+#endif
 }

libcxx/test/support/test_macros.h

@@ -43,7 +43,7 @@
 #elif __cplusplus <= 201402L
 # define TEST_STD_VER 14
 #else
-# define TEST_STD_VER 99    // greater than current standard
+# define TEST_STD_VER 16    // current year; greater than current standard
 #endif
 #endif