[libc++] check that std::atomic is only instantiated for cv-unqualified types

Author: dalg24

libcxx/include/__atomic/support.h

@@ -10,7 +10,9 @@
 #define _LIBCPP___ATOMIC_SUPPORT_H
 
 #include <__config>
+#include <__type_traits/is_same.h>
 #include <__type_traits/is_trivially_copyable.h>
+#include <__type_traits/remove_cv.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -114,6 +116,8 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 template <typename _Tp, typename _Base = __cxx_atomic_base_impl<_Tp> >
 struct __cxx_atomic_impl : public _Base {
   static_assert(is_trivially_copyable<_Tp>::value, "std::atomic<T> requires that 'T' be a trivially copyable type");
+  static_assert(is_same<_Tp, typename remove_cv<_Tp>::type>::value,
+                "std::atomic<T> requires that 'T' be a cv-unqualified type");
 
   _LIBCPP_HIDE_FROM_ABI __cxx_atomic_impl() _NOEXCEPT = default;
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __cxx_atomic_impl(_Tp __value) _NOEXCEPT : _Base(__value) {}

libcxx/include/__cxx03/__atomic/cxx_atomic_impl.h

@@ -14,8 +14,10 @@
 #include <__cxx03/__config>
 #include <__cxx03/__memory/addressof.h>
 #include <__cxx03/__type_traits/is_assignable.h>
+#include <__cxx03/__type_traits/is_same.h>
 #include <__cxx03/__type_traits/is_trivially_copyable.h>
 #include <__cxx03/__type_traits/remove_const.h>
+#include <__cxx03/__type_traits/remove_cv.h>
 #include <__cxx03/cstddef>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -500,6 +502,8 @@ __cxx_atomic_fetch_xor(__cxx_atomic_base_impl<_Tp>* __a, _Tp __pattern, memory_o
 template <typename _Tp, typename _Base = __cxx_atomic_base_impl<_Tp> >
 struct __cxx_atomic_impl : public _Base {
   static_assert(is_trivially_copyable<_Tp>::value, "std::atomic<T> requires that 'T' be a trivially copyable type");
+  static_assert(is_same<_Tp, typename remove_cv<_Tp>::type>::value,
+                "std::atomic<T> requires that 'T' be a cv-unqualified type");
 
   _LIBCPP_HIDE_FROM_ABI __cxx_atomic_impl() _NOEXCEPT = default;
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __cxx_atomic_impl(_Tp __value) _NOEXCEPT : _Base(__value) {}

libcxx/test/std/atomics/atomics.types.generic/cv_unqualified.verify.cpp

@@ -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
+//
+//===----------------------------------------------------------------------===//
+
+// <atomic>
+
+// template <class T>
+// struct atomic;
+
+// This test checks that we static_assert inside std::atomic<T> when T
+// is cv-qualified, however Clang will sometimes emit additional
+// errors while trying to instantiate the rest of std::atomic<T>.
+// We silence those to make the test more robust.
+// ADDITIONAL_COMPILE_FLAGS: -Xclang -verify-ignore-unexpected=error
+
+#include <atomic>
+
+void f() {
+  std::atomic<const int> a; // expected-error@*:* {{std::atomic<T> requires that 'T' be a cv-unqualified type}}
+}
+