implement more of N4258 - Cleaning up noexcept in the standard library. Specifically add new noexcept stuff to vector and string's move-assignment operations

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@245330 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/basic.string/string.cons/move_assign_noexcept.pass.cpp

@@ -11,14 +11,18 @@
 
 // basic_string& operator=(basic_string&& c)
 //     noexcept(
-//          allocator_type::propagate_on_container_move_assignment::value &&
-//          is_nothrow_move_assignable<allocator_type>::value);
-
-// This tests a conforming extension
+//         allocator_traits<allocator_type>::propagate_on_container_move_assignment::value ||
+//         allocator_traits<allocator_type>::is_always_equal::value); // C++17
+//
+//	before C++17, we use the conforming extension
+//     noexcept(
+//         allocator_type::propagate_on_container_move_assignment::value &&
+//         is_nothrow_move_assignable<allocator_type>::value);
 
 #include <string>
 #include <cassert>
 
+#include "test_macros.h"
 #include "test_allocator.h"
 
 template <class T>
@@ -28,6 +32,32 @@ struct some_alloc
     some_alloc(const some_alloc&);
 };
 
+template <class T>
+struct some_alloc2
+{
+    typedef T value_type;
+    
+    some_alloc2() {}
+    some_alloc2(const some_alloc2&);
+    void deallocate(void*, unsigned) {}
+
+    typedef std::false_type propagate_on_container_move_assignment;
+    typedef std::true_type is_always_equal;
+};
+
+template <class T>
+struct some_alloc3
+{
+    typedef T value_type;
+    
+    some_alloc3() {}
+    some_alloc3(const some_alloc3&);
+    void deallocate(void*, unsigned) {}
+
+    typedef std::false_type propagate_on_container_move_assignment;
+    typedef std::false_type is_always_equal;
+};
+
 int main()
 {
 #if __has_feature(cxx_noexcept)
@@ -41,7 +71,25 @@ int main()
     }
     {
         typedef std::basic_string<char, std::char_traits<char>, some_alloc<char>> C;
+#if TEST_STD_VER > 14
+    //  if the allocators are always equal, then the move assignment can be noexcept
+        static_assert( std::is_nothrow_move_assignable<C>::value, "");
+#else
+        static_assert(!std::is_nothrow_move_assignable<C>::value, "");
+#endif
+    }
+#if TEST_STD_VER > 14
+    {
+    //	POCMA is false, always equal
+        typedef std::basic_string<char, std::char_traits<char>, some_alloc2<char>> C;
+        static_assert( std::is_nothrow_move_assignable<C>::value, "");
+    }
+    {
+    //	POCMA is false, not always equal
+        typedef std::basic_string<char, std::char_traits<char>, some_alloc3<char>> C;
         static_assert(!std::is_nothrow_move_assignable<C>::value, "");
     }
 #endif
+
+#endif
 }