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

18 files changed, 450 insertions, 10 deletions

diff --git a/libcxx/test/std/containers/sequences/vector.bool/enabled_hash.pass.cpp b/libcxx/test/std/containers/sequences/vector.bool/enabled_hash.pass.cpp
new file mode 100644
index 00000000000..f8a8dbd8d6d
--- /dev/null
+++ b/libcxx/test/std/containers/sequences/vector.bool/enabled_hash.pass.cpp
@@ -0,0 +1,28 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// <vector>
+
+// Test that <vector> provides all of the arithmetic, enum, and pointer
+// hash specializations.
+
+#include <vector>
+
+#include "poisoned_hash_helper.hpp"
+#include "min_allocator.h"
+
+int main() {
+  test_library_hash_specializations_available();
+  {
+    test_hash_enabled_for_type<std::vector<bool> >();
+    test_hash_enabled_for_type<std::vector<bool, min_allocator<bool>>>();
+  }
+}
diff --git a/libcxx/test/std/diagnostics/syserr/syserr.hash/enabled_hash.pass.cpp b/libcxx/test/std/diagnostics/syserr/syserr.hash/enabled_hash.pass.cpp
new file mode 100644
index 00000000000..f1b46057591
--- /dev/null
+++ b/libcxx/test/std/diagnostics/syserr/syserr.hash/enabled_hash.pass.cpp
@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// <system_error>
+
+// Test that <system_error> provides all of the arithmetic, enum, and pointer
+// hash specializations.
+
+#include <system_error>
+
+#include "poisoned_hash_helper.hpp"
+
+int main() {
+  test_library_hash_specializations_available();
+  {
+    test_hash_enabled_for_type<std::error_code>();
+    test_hash_enabled_for_type<std::error_condition>();
+  }
+}
diff --git a/libcxx/test/std/strings/basic.string.hash/enabled_hashes.pass.cpp b/libcxx/test/std/strings/basic.string.hash/enabled_hashes.pass.cpp
new file mode 100644
index 00000000000..01f01218999
--- /dev/null
+++ b/libcxx/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
+  }
+}
diff --git a/libcxx/test/std/strings/string.view/string.view.hash/enabled_hashes.pass.cpp b/libcxx/test/std/strings/string.view/string.view.hash/enabled_hashes.pass.cpp
new file mode 100644
index 00000000000..2e9ebcb4c03
--- /dev/null
+++ b/libcxx/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
+  }
+}
diff --git a/libcxx/test/std/strings/string.view/string.view.hash/string_view.pass.cpp b/libcxx/test/std/strings/string.view/string.view.hash/string_view.pass.cpp
index 63099e2c886..d0766482551 100644
--- a/libcxx/test/std/strings/string.view/string.view.hash/string_view.pass.cpp
+++ b/libcxx/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()
diff --git a/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/enabled_hashes.pass.cpp b/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/enabled_hashes.pass.cpp
new file mode 100644
index 00000000000..9799467c452
--- /dev/null
+++ b/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/enabled_hashes.pass.cpp
@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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: libcpp-has-no-threads
+// UNSUPPORTED: c++98, c++03
+
+// <thread>
+
+// Test that <thread> provides all of the arithmetic, enum, and pointer
+// hash specializations.
+
+#include <thread>
+
+#include "poisoned_hash_helper.hpp"
+
+int main() {
+  test_library_hash_specializations_available();
+  {
+    test_hash_enabled_for_type<std::thread::id>();
+  }
+}
diff --git a/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/thread_id.pass.cpp b/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/thread_id.pass.cpp
index 106c69e2e4a..f7d4deb8f98 100644
--- a/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/thread_id.pass.cpp
+++ b/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/thread_id.pass.cpp
@@ -9,7 +9,7 @@
 //
 // UNSUPPORTED: libcpp-has-no-threads
 
-// <functional>
+// <thread>
 
 // template <class T>
 // struct hash
diff --git a/libcxx/test/std/utilities/function.objects/unord.hash/enabled_hashes.pass.cpp b/libcxx/test/std/utilities/function.objects/unord.hash/enabled_hashes.pass.cpp
new file mode 100644
index 00000000000..775247fc80b
--- /dev/null
+++ b/libcxx/test/std/utilities/function.objects/unord.hash/enabled_hashes.pass.cpp
@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// <functional>
+
+// Test that <functional> provides all of the arithmetic, enum, and pointer
+// hash specializations.
+
+#include <functional>
+
+#include "poisoned_hash_helper.hpp"
+
+int main() {
+  test_library_hash_specializations_available();
+}
diff --git a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.hash/enabled_hash.pass.cpp b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.hash/enabled_hash.pass.cpp
new file mode 100644
index 00000000000..e9237c534fb
--- /dev/null
+++ b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.hash/enabled_hash.pass.cpp
@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// <memory>
+
+// Test that <memory> provides all of the arithmetic, enum, and pointer
+// hash specializations.
+
+#include <memory>
+
+#include "poisoned_hash_helper.hpp"
+
+int main() {
+  test_library_hash_specializations_available();
+}
diff --git a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.hash/hash_shared_ptr.pass.cpp b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.hash/hash_shared_ptr.pass.cpp
index 990cb58722b..5fba1fc0460 100644
--- a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.hash/hash_shared_ptr.pass.cpp
+++ b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.hash/hash_shared_ptr.pass.cpp
@@ -20,11 +20,25 @@
 #include <memory>
 #include <cassert>
 
+#if TEST_STD_VER >= 11
+#include "poisoned_hash_helper.hpp"
+
+struct A {};
+#endif
+
 int main()
 {
+  {
     int* ptr = new int;
     std::shared_ptr<int> p(ptr);
     std::hash<std::shared_ptr<int> > f;
     std::size_t h = f(p);
     assert(h == std::hash<int*>()(ptr));
+  }
+#if TEST_STD_VER >= 11
+  {
+    test_hash_enabled_for_type<std::shared_ptr<int>>();
+    test_hash_enabled_for_type<std::shared_ptr<A>>();
+  }
+#endif
 }
diff --git a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.hash/hash_unique_ptr.pass.cpp b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.hash/hash_unique_ptr.pass.cpp
index 5cd4ab1f83d..f989a017348 100644
--- a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.hash/hash_unique_ptr.pass.cpp
+++ b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.hash/hash_unique_ptr.pass.cpp
@@ -20,11 +20,76 @@
 #include <memory>
 #include <cassert>
 
+#include "test_macros.h"
+
+#if TEST_STD_VER >= 11
+#include "poisoned_hash_helper.hpp"
+#include "deleter_types.h"
+#include "min_allocator.h"
+
+template <class ValueT, class Del>
+void test_enabled_with_deleter() {
+  using UPtr = std::unique_ptr<ValueT, Del>;
+  using pointer = typename UPtr::pointer;
+  using RawDel = typename std::decay<Del>::type;
+  RawDel d(1);
+  UPtr p(nullptr, std::forward<Del>(d));
+  test_hash_enabled_for_type<UPtr>(p);
+  test_hash_enabled_for_type<pointer>();
+}
+
+template <class ValueT, class Del>
+void test_disabled_with_deleter() {
+  using UPtr = std::unique_ptr<ValueT, Del>;
+  using pointer = typename UPtr::pointer;
+  test_hash_disabled_for_type<UPtr>();
+  test_hash_disabled_for_type<pointer>();
+}
+
+template <class T>
+struct std::hash<min_pointer<T, std::integral_constant<size_t, 1>>> {
+  size_t operator()(min_pointer<T, std::integral_constant<size_t, 1>> p) const {
+    if (!p) return 0;
+    return std::hash<T*>{}(std::addressof(*p));
+  }
+};
+
+struct A {};
+
+#endif // TEST_STD_VER >= 11
+
 int main()
 {
+  {
     int* ptr = new int;
     std::unique_ptr<int> p(ptr);
     std::hash<std::unique_ptr<int> > f;
     std::size_t h = f(p);
     assert(h == std::hash<int*>()(ptr));
+  }
+#if TEST_STD_VER >= 11
+  {
+    test_enabled_with_deleter<int, Deleter<int>>();
+    test_enabled_with_deleter<int[], Deleter<int[]>>();
+    test_enabled_with_deleter<int, CopyDeleter<int>>();
+    test_enabled_with_deleter<int, CopyDeleter<int[]>>();
+    test_enabled_with_deleter<int, NCDeleter<int>&>();
+    test_enabled_with_deleter<int[], NCDeleter<int[]>&>();
+    test_enabled_with_deleter<int, NCConstDeleter<int> const&>();
+    test_enabled_with_deleter<int[], NCConstDeleter<int[]> const&>();
+  }
+  {
+    test_enabled_with_deleter<int, PointerDeleter<int, 1>>();
+    test_enabled_with_deleter<int[], PointerDeleter<int[], 1>>();
+    test_enabled_with_deleter<A, PointerDeleter<A, 1>>();
+    test_enabled_with_deleter<A[], PointerDeleter<A[], 1>>();
+
+#if TEST_STD_VER > 14
+    test_disabled_with_deleter<int, PointerDeleter<int, 0>>();
+    test_disabled_with_deleter<int[], PointerDeleter<int[], 0>>();
+    test_disabled_with_deleter<A, PointerDeleter<A, 0>>();
+    test_disabled_with_deleter<A[], PointerDeleter<A[], 0>>();
+#endif
+  }
+#endif
 }
diff --git a/libcxx/test/std/utilities/optional/optional.hash/enabled_hash.pass.cpp b/libcxx/test/std/utilities/optional/optional.hash/enabled_hash.pass.cpp
new file mode 100644
index 00000000000..e54a4ced841
--- /dev/null
+++ b/libcxx/test/std/utilities/optional/optional.hash/enabled_hash.pass.cpp
@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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, c++11, c++14
+
+// <optional>
+
+// Test that <optional> provides all of the arithmetic, enum, and pointer
+// hash specializations.
+
+#include <optional>
+
+#include "poisoned_hash_helper.hpp"
+
+int main() {
+  test_library_hash_specializations_available();
+  {
+
+  }
+}
diff --git a/libcxx/test/std/utilities/optional/optional.hash/hash.pass.cpp b/libcxx/test/std/utilities/optional/optional.hash/hash.pass.cpp
index dfdd07ddf45..ea89dc3bd92 100644
--- a/libcxx/test/std/utilities/optional/optional.hash/hash.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.hash/hash.pass.cpp
@@ -17,6 +17,15 @@
 #include <memory>
 #include <cassert>
 
+#include "poisoned_hash_helper.hpp"
+
+struct A {};
+struct B {};
+
+template <>
+struct std::hash<B> {
+  size_t operator()(B const&) { return 0; }
+};
 
 int main()
 {
@@ -45,4 +54,16 @@ int main()
         opt = std::unique_ptr<int>(new int(3));
         assert(std::hash<optional<T>>{}(opt) == std::hash<T>{}(*opt));
     }
+    {
+      test_hash_enabled_for_type<std::optional<int> >();
+      test_hash_enabled_for_type<std::optional<int*> >();
+      test_hash_enabled_for_type<std::optional<const int> >();
+      test_hash_enabled_for_type<std::optional<int* const> >();
+
+      test_hash_disabled_for_type<std::optional<A>>();
+      test_hash_disabled_for_type<std::optional<const A>>();
+
+      test_hash_enabled_for_type<std::optional<B>>();
+      test_hash_enabled_for_type<std::optional<const B>>();
+    }
 }
diff --git a/libcxx/test/std/utilities/template.bitset/bitset.hash/enabled_hash.pass.cpp b/libcxx/test/std/utilities/template.bitset/bitset.hash/enabled_hash.pass.cpp
new file mode 100644
index 00000000000..1d8bff41ae5
--- /dev/null
+++ b/libcxx/test/std/utilities/template.bitset/bitset.hash/enabled_hash.pass.cpp
@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// <bitset>
+
+// Test that <bitset> provides all of the arithmetic, enum, and pointer
+// hash specializations.
+
+#include <bitset>
+
+#include "poisoned_hash_helper.hpp"
+
+int main() {
+  test_library_hash_specializations_available();
+  {
+    test_hash_enabled_for_type<std::bitset<0> >();
+    test_hash_enabled_for_type<std::bitset<1> >();
+    test_hash_enabled_for_type<std::bitset<1024> >();
+    test_hash_enabled_for_type<std::bitset<100000> >();
+  }
+}
diff --git a/libcxx/test/std/utilities/type.index/type.index.hash/enabled_hash.pass.cpp b/libcxx/test/std/utilities/type.index/type.index.hash/enabled_hash.pass.cpp
new file mode 100644
index 00000000000..26bada38fdd
--- /dev/null
+++ b/libcxx/test/std/utilities/type.index/type.index.hash/enabled_hash.pass.cpp
@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// <typeindex>
+
+// Test that <typeindex> provides all of the arithmetic, enum, and pointer
+// hash specializations.
+
+#include <typeindex>
+
+#include "poisoned_hash_helper.hpp"
+
+int main() {
+  test_library_hash_specializations_available();
+}
diff --git a/libcxx/test/std/utilities/type.index/type.index.synopsis/hash_type_index.pass.cpp b/libcxx/test/std/utilities/type.index/type.index.synopsis/hash_type_index.pass.cpp
index 6d353f1d305..0fe020bf3d4 100644
--- a/libcxx/test/std/utilities/type.index/type.index.synopsis/hash_type_index.pass.cpp
+++ b/libcxx/test/std/utilities/type.index/type.index.synopsis/hash_type_index.pass.cpp
@@ -18,9 +18,19 @@
 #include <typeindex>
 #include <type_traits>
 
+#include "test_macros.h"
+#if TEST_STD_VER >= 11
+#include "poisoned_hash_helper.hpp"
+#endif
+
 int main()
 {
+  {
     typedef std::hash<std::type_index> H;
     static_assert((std::is_same<typename H::argument_type, std::type_index>::value), "" );
     static_assert((std::is_same<typename H::result_type, std::size_t>::value), "" );
+  }
+  {
+    test_hash_enabled_for_type<std::type_index>(std::type_index(typeid(int)));
+  }
 }
diff --git a/libcxx/test/std/utilities/variant/variant.hash/enabled_hash.pass.cpp b/libcxx/test/std/utilities/variant/variant.hash/enabled_hash.pass.cpp
new file mode 100644
index 00000000000..826dcbae6b9
--- /dev/null
+++ b/libcxx/test/std/utilities/variant/variant.hash/enabled_hash.pass.cpp
@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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, c++11, c++14
+
+// <variant>
+
+// Test that <variant> provides all of the arithmetic, enum, and pointer
+// hash specializations.
+
+#include <variant>
+
+#include "poisoned_hash_helper.hpp"
+
+int main() {
+  test_library_hash_specializations_available();
+}
diff --git a/libcxx/test/std/utilities/variant/variant.hash/hash.pass.cpp b/libcxx/test/std/utilities/variant/variant.hash/hash.pass.cpp
index d807a7c7e2e..96ef967f6c1 100644
--- a/libcxx/test/std/utilities/variant/variant.hash/hash.pass.cpp
+++ b/libcxx/test/std/utilities/variant/variant.hash/hash.pass.cpp
@@ -21,6 +21,7 @@
 
 #include "test_macros.h"
 #include "variant_test_helpers.hpp"
+#include "poisoned_hash_helper.hpp"
 
 #ifndef TEST_HAS_NO_EXCEPTIONS
 namespace std {
@@ -103,6 +104,9 @@ void test_hash_monostate() {
     ASSERT_SAME_TYPE(decltype(h(m1)), std::size_t);
     static_assert(std::is_copy_constructible<H>::value, "");
   }
+  {
+    test_hash_enabled_for_type<std::monostate>();
+  }
 }
 
 void test_hash_variant_duplicate_elements() {
@@ -117,8 +121,34 @@ void test_hash_variant_duplicate_elements() {
     LIBCPP_ASSERT(h(v1) != h(v2));
 }
 
+struct A {};
+struct B {};
+
+template <>
+struct std::hash<B> {
+  size_t operator()(B const&) const {
+    return 0;
+  }
+};
+
+void test_hash_variant_enabled() {
+  {
+    test_hash_enabled_for_type<std::variant<int> >();
+    test_hash_enabled_for_type<std::variant<int*, long, double, const int> >();
+  }
+  {
+    test_hash_disabled_for_type<std::variant<int, A>>();
+    test_hash_disabled_for_type<std::variant<const A, void*>>();
+  }
+  {
+    test_hash_enabled_for_type<std::variant<int, B>>();
+    test_hash_enabled_for_type<std::variant<const B, int>>();
+  }
+}
+
 int main() {
   test_hash_variant();
   test_hash_variant_duplicate_elements();
   test_hash_monostate();
+  test_hash_variant_enabled();
 }