Implement P0513R0 - "Poisoning the Hash"

Summary:
Exactly what the title says.

This patch also adds a `std::hash<nullptr_t>` specialization in C++17, but it was not added by this paper and I can't find the actual paper that adds it.

See http://wg21.link/P0513R0 for more info.

If there are no comments in the next couple of days I'll commit this

Reviewers: mclow.lists, K-ballo, EricWF

Reviewed By: EricWF

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D28938

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@292684 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/basic.string.hash/enabled_hashes.pass.cpp

@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// <string>
+
+// Test that <string> provides all of the arithmetic, enum, and pointer
+// hash specializations.
+
+#include <string>
+
+#include "poisoned_hash_helper.hpp"
+
+int main() {
+  test_library_hash_specializations_available();
+  {
+    test_hash_enabled_for_type<std::string>();
+    test_hash_enabled_for_type<std::wstring>();
+#ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
+    test_hash_enabled_for_type<std::u16string>();
+    test_hash_enabled_for_type<std::u32string>();
+#endif
+  }
+}

test/std/strings/string.view/string.view.hash/enabled_hashes.pass.cpp

@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// <string_view>
+
+// Test that <string_view> provides all of the arithmetic, enum, and pointer
+// hash specializations.
+
+#include <string_view>
+
+#include "poisoned_hash_helper.hpp"
+
+int main() {
+  test_library_hash_specializations_available();
+  {
+    test_hash_enabled_for_type<std::string_view>();
+    test_hash_enabled_for_type<std::wstring_view>();
+#ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
+    test_hash_enabled_for_type<std::u16string_view>();
+    test_hash_enabled_for_type<std::u32string_view>();
+#endif
+  }
+}

test/std/strings/string.view/string.view.hash/string_view.pass.cpp

@@ -19,29 +19,38 @@
 // Not very portable
 
 #include <string_view>
+#include <string>
 #include <cassert>
 #include <type_traits>
 
 using std::string_view;
 
-template <class T>
+template <class SV>
 void
 test()
 {
-    typedef std::hash<T> H;
-    static_assert((std::is_same<typename H::argument_type, T>::value), "" );
+    typedef std::hash<SV> H;
+    static_assert((std::is_same<typename H::argument_type, SV>::value), "" );
     static_assert((std::is_same<typename H::result_type, std::size_t>::value), "" );
-    H h;
-//     std::string g1 = "1234567890";
-//     std::string g2 = "1234567891";
-    typedef typename T::value_type char_type;
+
+    typedef typename SV::value_type char_type;
+    typedef std::basic_string<char_type> String;
+    typedef std::hash<String> SH;
+
     char_type g1 [ 10 ];
     char_type g2 [ 10 ];
     for ( int i = 0; i < 10; ++i )
         g1[i] = g2[9-i] = static_cast<char_type>('0' + i);
-    T s1(g1, 10);
-    T s2(g2, 10);
+    H h;
+    SH sh;
+    SV s1(g1, 10);
+    String ss1(s1);
+    SV s2(g2, 10);
+    String ss2(s2);
+    assert(h(s1) == h(s1));
     assert(h(s1) != h(s2));
+    assert(sh(ss1) == h(s1));
+    assert(sh(ss2) == h(s2));
 }
 
 int main()