[libc++] Adds __utility/to_underlying.h.

[Mordante]

Summary

During the review of D97115 it was mentioned adding the <utility>
header for __to_underlying was a bit unfortunate. Nowadays we tend to
implement smaller headers, so a good reason to move std::to_underlying
to its own header and adjust <charconv> to use the new header.

[• Quuxplusone]

Looks good to me. Please wait for at least one more reviewer, if not @ldionne himself, to OK it, though — I don't think it should be just me and yourself looking at this.

libcxx/include/__utility/to_underlying.h

2

This filename (on line 2, that is) doesn't seem quite right; is this libc++ style? I haven't checked.

[curdeius]

LGTM. Please update the filename in the comment as indicated by Arthur before landing.

[Mordante]

Thanks for the reviews.

libcxx/include/__utility/to_underlying.h

2

It's indeed wrong. I've adjusted it.

libcxx/include/CMakeLists.txt

set(files
   __split_buffer
   __sso_allocator
   __std_stream
   __string
   __threading_support
   __tree
   __tuple
   __undef_macros
+  __utility/to_underlying.h
   algorithm
   any
   array
   atomic
   barrier
   bit
   bitset
   cassert

libcxx/include/__utility/to_underlying.h

+// -*- C++ -*-
+//===----------------- __utility_to_underlying.h --------------------------===//
+//
+// 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___UTILITY_TO_UNDERLYING_H
+#define _LIBCPP___UTILITY_TO_UNDERLYING_H
+
+#include <__config>
+#include <type_traits>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#ifndef _LIBCPP_CXX03_LANG
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr typename underlying_type<_Tp>::type
+__to_underlying(_Tp __val) noexcept {
+  return static_cast<typename underlying_type<_Tp>::type>(__val);
+}
+#endif // !_LIBCPP_CXX03_LANG
+
+#if _LIBCPP_STD_VER > 20
+template <class _Tp>
+_LIBCPP_NODISCARD_EXT _LIBCPP_INLINE_VISIBILITY constexpr underlying_type_t<_Tp>
+to_underlying(_Tp __val) noexcept {
+  return _VSTD::__to_underlying(__val);
+}
+#endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___UTILITY_TO_UNDERLYING_H

libcxx/include/charconv

 
 } // namespace std
 
 */
 
 #include <__config>
 #include <__availability>
 #include <__errc>
+#include <__utility/to_underlying.h>
 #include <cmath> // for log2f
 #include <cstdint>
 #include <cstring>
 #include <limits>
 #include <type_traits>
-#include <utility>
 
 #include <__debug>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 
 _LIBCPP_PUSH_MACROS

libcxx/include/utility

template <class T>
     constexpr underlying_type_t<T> to_underlying( T value ) noexcept; // C++2b
 
 }  // std
 
 */
 
 #include <__config>
 #include <__tuple>
+#include <__utility/to_underlying.h>
 #include <compare>
 #include <type_traits>
 #include <initializer_list>
 #include <cstddef>
 #include <cstring>
 #include <cstdint>
 #include <limits>
 #include <version>

 using __enable_hash_helper _LIBCPP_NODEBUG_TYPE  = __enable_hash_helper_imp<_Type,
   typename enable_if<__all<__has_enabled_hash<_Keys>::value...>::value>::type
 >;
 #else
 template <class _Type, class ...>
 using __enable_hash_helper _LIBCPP_NODEBUG_TYPE = _Type;
 #endif
 
-template <class _Tp>
-_LIBCPP_INLINE_VISIBILITY constexpr typename underlying_type<_Tp>::type
-__to_underlying(_Tp __val) noexcept {
-  return static_cast<typename underlying_type<_Tp>::type>(__val);
-}
 #endif // !_LIBCPP_CXX03_LANG
 
-#if _LIBCPP_STD_VER > 20
-template <class _Tp>
-_LIBCPP_NODISCARD_EXT _LIBCPP_INLINE_VISIBILITY constexpr underlying_type_t<_Tp>
-to_underlying(_Tp __val) noexcept {
-  return _VSTD::__to_underlying(__val);
-}
-#endif
-
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP_UTILITY