[libcxx-commits] [libcxx] [libc++] Disable cv-qualified arithmetic hash specializations (PR #155786)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 updated https://github.com/llvm/llvm-project/pull/155786

>From 565cf2a974aac2ca007181f92a0fafc206867774 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Thu, 28 Aug 2025 10:37:06 +0200
Subject: [PATCH] [libc++] Disabled cv-qualified arithmetic hash
 specializations

---
 libcxx/include/CMakeLists.txt                 |  1 +
 libcxx/include/__functional/hash.h            | 14 ++++++++---
 libcxx/include/__type_traits/is_unqualified.h | 25 +++++++++++++++++++
 libcxx/include/module.modulemap.in            |  1 +
 .../function.objects/unord.hash/enum.pass.cpp | 10 ++++++++
 .../unord.hash/floating.pass.cpp              | 10 ++++++++
 .../unord.hash/integral.pass.cpp              | 10 ++++++++
 7 files changed, 67 insertions(+), 4 deletions(-)
 create mode 100644 libcxx/include/__type_traits/is_unqualified.h

diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index 6fd16419f0c49..1f91b4828d4d3 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -872,6 +872,7 @@ set(files
   __type_traits/is_trivially_relocatable.h
   __type_traits/is_unbounded_array.h
   __type_traits/is_union.h
+  __type_traits/is_unqualified.h
   __type_traits/is_unsigned.h
   __type_traits/is_valid_expansion.h
   __type_traits/is_void.h
diff --git a/libcxx/include/__functional/hash.h b/libcxx/include/__functional/hash.h
index 489a6f00b8a3d..83bbf1b5e26c3 100644
--- a/libcxx/include/__functional/hash.h
+++ b/libcxx/include/__functional/hash.h
@@ -21,6 +21,7 @@
 #include <__type_traits/is_enum.h>
 #include <__type_traits/is_floating_point.h>
 #include <__type_traits/is_integral.h>
+#include <__type_traits/is_unqualified.h>
 #include <__type_traits/underlying_type.h>
 #include <__utility/pair.h>
 #include <__utility/swap.h>
@@ -355,7 +356,8 @@ struct __hash_impl {
 };
 
 template <class _Tp>
-struct __hash_impl<_Tp, __enable_if_t<is_enum<_Tp>::value> > : __unary_function<_Tp, size_t> {
+struct __hash_impl<_Tp, __enable_if_t<is_enum<_Tp>::value && __is_unqualified_v<_Tp> > >
+    : __unary_function<_Tp, size_t> {
   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
     using type = __underlying_type_t<_Tp>;
     return hash<type>()(static_cast<type>(__v));
@@ -363,17 +365,21 @@ struct __hash_impl<_Tp, __enable_if_t<is_enum<_Tp>::value> > : __unary_function<
 };
 
 template <class _Tp>
-struct __hash_impl<_Tp, __enable_if_t<is_integral<_Tp>::value && (sizeof(_Tp) <= sizeof(size_t))> >
+struct __hash_impl<
+    _Tp,
+    __enable_if_t<is_integral<_Tp>::value && __is_unqualified_v<_Tp> && (sizeof(_Tp) <= sizeof(size_t))> >
     : __unary_function<_Tp, size_t> {
   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 };
 
 template <class _Tp>
-struct __hash_impl<_Tp, __enable_if_t<is_integral<_Tp>::value && (sizeof(_Tp) > sizeof(size_t))> >
+struct __hash_impl<_Tp,
+                   __enable_if_t<is_integral<_Tp>::value && __is_unqualified_v<_Tp> && (sizeof(_Tp) > sizeof(size_t))> >
     : __scalar_hash<_Tp> {};
 
 template <class _Tp>
-struct __hash_impl<_Tp, __enable_if_t<is_floating_point<_Tp>::value> > : __scalar_hash<_Tp> {
+struct __hash_impl<_Tp, __enable_if_t<is_floating_point<_Tp>::value && __is_unqualified_v<_Tp> > >
+    : __scalar_hash<_Tp> {
   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
     // -0.0 and 0.0 should return same hash
     if (__v == 0.0f)
diff --git a/libcxx/include/__type_traits/is_unqualified.h b/libcxx/include/__type_traits/is_unqualified.h
new file mode 100644
index 0000000000000..7970b3611601f
--- /dev/null
+++ b/libcxx/include/__type_traits/is_unqualified.h
@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___TYPE_TRAITS_IS_UNQUALIFIED_H
+#define _LIBCPP___TYPE_TRAITS_IS_UNQUALIFIED_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Tp>
+inline const bool __is_unqualified_v = __is_same(_Tp, __remove_cvref(_Tp));
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___TYPE_TRAITS_IS_UNQUALIFIED_H
diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
index ee18d04c78d0e..c50c4dd73d4bb 100644
--- a/libcxx/include/module.modulemap.in
+++ b/libcxx/include/module.modulemap.in
@@ -335,6 +335,7 @@ module std_core [system] {
       header "__type_traits/is_union.h"
       export std_core.type_traits.integral_constant
     }
+    module is_unqualified { header "__type_traits/is_unqualified.h" }
     module is_unsigned {
       header "__type_traits/is_unsigned.h"
       export std_core.type_traits.integral_constant
diff --git a/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp b/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp
index fd1fbe5f113ba..05a19329f909a 100644
--- a/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp
+++ b/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp
@@ -21,6 +21,10 @@
 
 #include "test_macros.h"
 
+#if TEST_STD_VER >= 11
+#  include "poisoned_hash_helper.h"
+#endif
+
 enum class Colors { red, orange, yellow, green, blue, indigo, violet };
 enum class Cardinals { zero, one, two, three, five=5 };
 enum class LongColors : short { red, orange, yellow, green, blue, indigo, violet };
@@ -33,6 +37,12 @@ template <class T>
 void
 test()
 {
+#if TEST_STD_VER >= 11
+    test_hash_disabled<const T>();
+    test_hash_disabled<volatile T>();
+    test_hash_disabled<const volatile T>();
+#endif
+
     typedef std::hash<T> H;
 #if TEST_STD_VER <= 17
     static_assert((std::is_same<typename H::argument_type, T>::value), "");
diff --git a/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp b/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp
index b8f85e193dc8f..f6c31d068b231 100644
--- a/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp
+++ b/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp
@@ -27,10 +27,20 @@
 
 #include "test_macros.h"
 
+#if TEST_STD_VER >= 11
+#  include "poisoned_hash_helper.h"
+#endif
+
 template <class T>
 void
 test()
 {
+#if TEST_STD_VER >= 11
+    test_hash_disabled<const T>();
+    test_hash_disabled<volatile T>();
+    test_hash_disabled<const volatile T>();
+#endif
+
     typedef std::hash<T> H;
 #if TEST_STD_VER <= 17
     static_assert((std::is_same<typename H::argument_type, T>::value), "");
diff --git a/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp b/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp
index 14af7093c1e36..c798b3aa77ea5 100644
--- a/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp
+++ b/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp
@@ -26,10 +26,20 @@
 
 #include "test_macros.h"
 
+#if TEST_STD_VER >= 11
+#  include "poisoned_hash_helper.h"
+#endif
+
 template <class T>
 void
 test()
 {
+#if TEST_STD_VER >= 11
+    test_hash_disabled<const T>();
+    test_hash_disabled<volatile T>();
+    test_hash_disabled<const volatile T>();
+#endif
+
     typedef std::hash<T> H;
 #if TEST_STD_VER <= 17
     static_assert((std::is_same<typename H::argument_type, T>::value), "");