[libc++][NFC] Make __desugars_to a variable template and rename the header to desugars_to.h

libcxx/include/CMakeLists.txt

@@ -737,6 +737,7 @@ set(files
   __type_traits/datasizeof.h
   __type_traits/decay.h
   __type_traits/dependent_type.h
+  __type_traits/desugars_to.h
   __type_traits/disjunction.h
   __type_traits/enable_if.h
   __type_traits/extent.h
@@ -821,7 +822,6 @@ set(files
   __type_traits/nat.h
   __type_traits/negation.h
   __type_traits/noexcept_move_assign_container.h
-  __type_traits/operation_traits.h
   __type_traits/promote.h
   __type_traits/rank.h
   __type_traits/remove_all_extents.h

libcxx/include/__algorithm/comp.h

@@ -10,8 +10,7 @@
 #define _LIBCPP___ALGORITHM_COMP_H
 
 #include <__config>
-#include <__type_traits/integral_constant.h>
-#include <__type_traits/operation_traits.h>
+#include <__type_traits/desugars_to.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -27,7 +26,7 @@ struct __equal_to {
 };
 
 template <class _Tp, class _Up>
-struct __desugars_to<__equal_tag, __equal_to, _Tp, _Up> : true_type {};
+inline const bool __desugars_to_v<__equal_tag, __equal_to, _Tp, _Up> = true;
 
 // The definition is required because __less is part of the ABI, but it's empty
 // because all comparisons should be transparent.

libcxx/include/__algorithm/equal.h

@@ -18,12 +18,11 @@
 #include <__iterator/distance.h>
 #include <__iterator/iterator_traits.h>
 #include <__string/constexpr_c_functions.h>
+#include <__type_traits/desugars_to.h>
 #include <__type_traits/enable_if.h>
-#include <__type_traits/integral_constant.h>
 #include <__type_traits/is_constant_evaluated.h>
 #include <__type_traits/is_equality_comparable.h>
 #include <__type_traits/is_volatile.h>
-#include <__type_traits/operation_traits.h>
 #include <__utility/move.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -47,7 +46,7 @@ _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 boo
 template <class _Tp,
           class _Up,
           class _BinaryPredicate,
-          __enable_if_t<__desugars_to<__equal_tag, _BinaryPredicate, _Tp, _Up>::value && !is_volatile<_Tp>::value &&
+          __enable_if_t<__desugars_to_v<__equal_tag, _BinaryPredicate, _Tp, _Up> && !is_volatile<_Tp>::value &&
                             !is_volatile<_Up>::value && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
                         int> = 0>
 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
@@ -87,7 +86,7 @@ template <class _Tp,
           class _Pred,
           class _Proj1,
           class _Proj2,
-          __enable_if_t<__desugars_to<__equal_tag, _Pred, _Tp, _Up>::value && __is_identity<_Proj1>::value &&
+          __enable_if_t<__desugars_to_v<__equal_tag, _Pred, _Tp, _Up> && __is_identity<_Proj1>::value &&
                             __is_identity<_Proj2>::value && !is_volatile<_Tp>::value && !is_volatile<_Up>::value &&
                             __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
                         int> = 0>

libcxx/include/__algorithm/mismatch.h

@@ -16,11 +16,11 @@
 #include <__algorithm/unwrap_iter.h>
 #include <__config>
 #include <__functional/identity.h>
+#include <__type_traits/desugars_to.h>
 #include <__type_traits/invoke.h>
 #include <__type_traits/is_constant_evaluated.h>
 #include <__type_traits/is_equality_comparable.h>
 #include <__type_traits/is_integral.h>
-#include <__type_traits/operation_traits.h>
 #include <__utility/move.h>
 #include <__utility/pair.h>
 #include <__utility/unreachable.h>
@@ -59,7 +59,7 @@ template <class _Tp,
           class _Pred,
           class _Proj1,
           class _Proj2,
-          __enable_if_t<is_integral<_Tp>::value && __desugars_to<__equal_tag, _Pred, _Tp, _Tp>::value &&
+          __enable_if_t<is_integral<_Tp>::value && __desugars_to_v<__equal_tag, _Pred, _Tp, _Tp> &&
                             __is_identity<_Proj1>::value && __is_identity<_Proj2>::value,
                         int> = 0>
 _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Tp*, _Tp*>

libcxx/include/__algorithm/pstl_backends/cpu_backends/transform_reduce.h

@@ -14,9 +14,9 @@
 #include <__iterator/concepts.h>
 #include <__iterator/iterator_traits.h>
 #include <__numeric/transform_reduce.h>
+#include <__type_traits/desugars_to.h>
 #include <__type_traits/is_arithmetic.h>
 #include <__type_traits/is_execution_policy.h>
-#include <__type_traits/operation_traits.h>
 #include <__utility/move.h>
 #include <new>
 #include <optional>
@@ -37,7 +37,7 @@ template <typename _DifferenceType,
           typename _BinaryOperation,
           typename _UnaryOperation,
           typename _UnaryResult = invoke_result_t<_UnaryOperation, _DifferenceType>,
-          __enable_if_t<__desugars_to<__plus_tag, _BinaryOperation, _Tp, _UnaryResult>::value && is_arithmetic_v<_Tp> &&
+          __enable_if_t<__desugars_to_v<__plus_tag, _BinaryOperation, _Tp, _UnaryResult> && is_arithmetic_v<_Tp> &&
                             is_arithmetic_v<_UnaryResult>,
                         int>    = 0>
 _LIBCPP_HIDE_FROM_ABI _Tp
@@ -53,8 +53,8 @@ template <typename _Size,
           typename _BinaryOperation,
           typename _UnaryOperation,
           typename _UnaryResult = invoke_result_t<_UnaryOperation, _Size>,
-          __enable_if_t<!(__desugars_to<__plus_tag, _BinaryOperation, _Tp, _UnaryResult>::value &&
-                          is_arithmetic_v<_Tp> && is_arithmetic_v<_UnaryResult>),
+          __enable_if_t<!(__desugars_to_v<__plus_tag, _BinaryOperation, _Tp, _UnaryResult> && is_arithmetic_v<_Tp> &&
+                          is_arithmetic_v<_UnaryResult>),
                         int>    = 0>
 _LIBCPP_HIDE_FROM_ABI _Tp
 __simd_transform_reduce(_Size __n, _Tp __init, _BinaryOperation __binary_op, _UnaryOperation __f) noexcept {

libcxx/include/__functional/operations.h

@@ -13,8 +13,7 @@
 #include <__config>
 #include <__functional/binary_function.h>
 #include <__functional/unary_function.h>
-#include <__type_traits/integral_constant.h>
-#include <__type_traits/operation_traits.h>
+#include <__type_traits/desugars_to.h>
 #include <__utility/forward.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -41,10 +40,10 @@ _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(plus);
 // The non-transparent std::plus specialization is only equivalent to a raw plus
 // operator when we don't perform an implicit conversion when calling it.
 template <class _Tp>
-struct __desugars_to<__plus_tag, plus<_Tp>, _Tp, _Tp> : true_type {};
+inline const bool __desugars_to_v<__plus_tag, plus<_Tp>, _Tp, _Tp> = true;
 
 template <class _Tp, class _Up>
-struct __desugars_to<__plus_tag, plus<void>, _Tp, _Up> : true_type {};
+inline const bool __desugars_to_v<__plus_tag, plus<void>, _Tp, _Up> = true;
 
 #if _LIBCPP_STD_VER >= 14
 template <>
@@ -315,11 +314,11 @@ struct _LIBCPP_TEMPLATE_VIS equal_to<void> {
 // The non-transparent std::equal_to specialization is only equivalent to a raw equality
 // comparison when we don't perform an implicit conversion when calling it.
 template <class _Tp>
-struct __desugars_to<__equal_tag, equal_to<_Tp>, _Tp, _Tp> : true_type {};
+inline const bool __desugars_to_v<__equal_tag, equal_to<_Tp>, _Tp, _Tp> = true;
 
 // In the transparent case, we do not enforce that
 template <class _Tp, class _Up>
-struct __desugars_to<__equal_tag, equal_to<void>, _Tp, _Up> : true_type {};
+inline const bool __desugars_to_v<__equal_tag, equal_to<void>, _Tp, _Up> = true;
 
 #if _LIBCPP_STD_VER >= 14
 template <class _Tp = void>

libcxx/include/__functional/ranges_operations.h

@@ -13,8 +13,7 @@
 #include <__concepts/equality_comparable.h>
 #include <__concepts/totally_ordered.h>
 #include <__config>
-#include <__type_traits/integral_constant.h>
-#include <__type_traits/operation_traits.h>
+#include <__type_traits/desugars_to.h>
 #include <__utility/forward.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -98,7 +97,7 @@ struct greater_equal {
 // For ranges we do not require that the types on each side of the equality
 // operator are of the same type
 template <class _Tp, class _Up>
-struct __desugars_to<__equal_tag, ranges::equal_to, _Tp, _Up> : true_type {};
+inline const bool __desugars_to_v<__equal_tag, ranges::equal_to, _Tp, _Up> = true;
 
 #endif // _LIBCPP_STD_VER >= 20
 

libcxx/include/__numeric/pstl_transform_reduce.h

@@ -87,7 +87,7 @@ _LIBCPP_HIDE_FROM_ABI _Tp transform_reduce(
 }
 
 // This overload doesn't get a customization point because it's trivial to detect (through e.g.
-// __desugars_to) when specializing the more general variant, which should always be preferred
+// __desugars_to_v) when specializing the more general variant, which should always be preferred
 template <class _ExecutionPolicy,
           class _ForwardIterator1,
           class _ForwardIterator2,

libcxx/include/__type_traits/operation_traits.h → libcxx/include/__type_traits/desugars_to.h

@@ -6,11 +6,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___TYPE_TRAITS_OPERATION_TRAITS_H
-#define _LIBCPP___TYPE_TRAITS_OPERATION_TRAITS_H
+#ifndef _LIBCPP___TYPE_TRAITS_DESUGARS_TO_H
+#define _LIBCPP___TYPE_TRAITS_DESUGARS_TO_H
 
 #include <__config>
-#include <__type_traits/integral_constant.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -33,8 +32,8 @@ struct __plus_tag {};
 // predicate being passed is actually going to call a builtin operator, or has
 // some specific semantics.
 template <class _CanonicalTag, class _Operation, class... _Args>
-struct __desugars_to : false_type {};
+inline const bool __desugars_to_v = false;
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP___TYPE_TRAITS_OPERATION_TRAITS_H
+#endif // _LIBCPP___TYPE_TRAITS_DESUGARS_TO_H

libcxx/include/libcxx.imp

@@ -733,6 +733,7 @@
   { include: [ "<__type_traits/datasizeof.h>", "private", "<type_traits>", "public" ] },
   { include: [ "<__type_traits/decay.h>", "private", "<type_traits>", "public" ] },
   { include: [ "<__type_traits/dependent_type.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/desugars_to.h>", "private", "<type_traits>", "public" ] },
   { include: [ "<__type_traits/disjunction.h>", "private", "<type_traits>", "public" ] },
   { include: [ "<__type_traits/enable_if.h>", "private", "<type_traits>", "public" ] },
   { include: [ "<__type_traits/extent.h>", "private", "<type_traits>", "public" ] },
@@ -817,7 +818,6 @@
   { include: [ "<__type_traits/nat.h>", "private", "<type_traits>", "public" ] },
   { include: [ "<__type_traits/negation.h>", "private", "<type_traits>", "public" ] },
   { include: [ "<__type_traits/noexcept_move_assign_container.h>", "private", "<type_traits>", "public" ] },
-  { include: [ "<__type_traits/operation_traits.h>", "private", "<type_traits>", "public" ] },
   { include: [ "<__type_traits/promote.h>", "private", "<type_traits>", "public" ] },
   { include: [ "<__type_traits/rank.h>", "private", "<type_traits>", "public" ] },
   { include: [ "<__type_traits/remove_all_extents.h>", "private", "<type_traits>", "public" ] },

libcxx/include/module.modulemap

@@ -1863,6 +1863,7 @@ module std_private_type_traits_decay                                     [system
   export std_private_type_traits_add_pointer
 }
 module std_private_type_traits_dependent_type                            [system] { header "__type_traits/dependent_type.h" }
+module std_private_type_traits_desugars_to                               [system] { header "__type_traits/desugars_to.h" }
 module std_private_type_traits_disjunction                               [system] { header "__type_traits/disjunction.h" }
 module std_private_type_traits_enable_if                                 [system] { header "__type_traits/enable_if.h" }
 module std_private_type_traits_extent                                    [system] { header "__type_traits/extent.h" }
@@ -2013,7 +2014,6 @@ module std_private_type_traits_maybe_const                               [system
 module std_private_type_traits_nat                                       [system] { header "__type_traits/nat.h" }
 module std_private_type_traits_negation                                  [system] { header "__type_traits/negation.h" }
 module std_private_type_traits_noexcept_move_assign_container            [system] { header "__type_traits/noexcept_move_assign_container.h" }
-module std_private_type_traits_operation_traits                          [system] { header "__type_traits/operation_traits.h" }
 module std_private_type_traits_promote                                   [system] { header "__type_traits/promote.h" }
 module std_private_type_traits_rank                                      [system] { header "__type_traits/rank.h" }
 module std_private_type_traits_remove_all_extents                        [system] { header "__type_traits/remove_all_extents.h" }