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

llvm-svn: 292684

1 files changed, 30 insertions, 0 deletions

diff --git a/libcxx/test/support/test.support/test_poisoned_hash_helper.pass.cpp b/libcxx/test/support/test.support/test_poisoned_hash_helper.pass.cpp
new file mode 100644
index 00000000000..4dffae6dbdf
--- /dev/null
+++ b/libcxx/test/support/test.support/test_poisoned_hash_helper.pass.cpp
@@ -0,0 +1,30 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// Test that the header `poisoned_hash_helper.hpp` doesn't include any
+// headers that provide hash<T> specializations. This is required so that the
+// 'test_library_hash_specializations_available()' function returns false
+// by default, unless a STL header providing hash has already been included.
+
+#include "poisoned_hash_helper.hpp"
+
+template <class T, size_t = sizeof(T)>
+constexpr bool is_complete_imp(int) { return true; }
+template <class> constexpr bool is_complete_imp(long) { return false; }
+template <class T> constexpr bool is_complete() { return is_complete_imp<T>(0); }
+
+template <class T> struct has_complete_hash {
+  enum { value = is_complete<std::hash<T> >() };
+};
+
+int main() {
+  static_assert(LibraryHashTypes::assertTrait<has_complete_hash, false>(), "");
+}