[libc++] Adds a global private constructor tag. (#87920)

This removes the similar tags used in the chrono tzdb implementation.

Fixes: #85432

Author: mordante

libcxx/include/CMakeLists.txt

@@ -863,6 +863,7 @@ set(files
   __utility/pair.h
   __utility/piecewise_construct.h
   __utility/priority_tag.h
+  __utility/private_constructor_tag.h
   __utility/rel_ops.h
   __utility/small_buffer.h
   __utility/swap.h

libcxx/include/__chrono/leap_second.h

@@ -22,6 +22,7 @@
 #  include <__compare/ordering.h>
 #  include <__compare/three_way_comparable.h>
 #  include <__config>
+#  include <__utility/private_constructor_tag.h>
 
 #  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #    pragma GCC system_header
@@ -35,9 +36,8 @@ namespace chrono {
 
 class leap_second {
 public:
-  struct __constructor_tag;
   [[nodiscard]]
-  _LIBCPP_HIDE_FROM_ABI explicit constexpr leap_second(__constructor_tag&&, sys_seconds __date, seconds __value)
+  _LIBCPP_HIDE_FROM_ABI explicit constexpr leap_second(__private_constructor_tag, sys_seconds __date, seconds __value)
       : __date_(__date), __value_(__value) {}
 
   _LIBCPP_HIDE_FROM_ABI leap_second(const leap_second&)            = default;

libcxx/include/__chrono/time_zone_link.h

@@ -18,6 +18,7 @@
 
 #  include <__compare/strong_order.h>
 #  include <__config>
+#  include <__utility/private_constructor_tag.h>
 #  include <string>
 #  include <string_view>
 
@@ -37,9 +38,8 @@ namespace chrono {
 
 class time_zone_link {
 public:
-  struct __constructor_tag;
   _LIBCPP_NODISCARD_EXT
-  _LIBCPP_HIDE_FROM_ABI explicit time_zone_link(__constructor_tag&&, string_view __name, string_view __target)
+  _LIBCPP_HIDE_FROM_ABI explicit time_zone_link(__private_constructor_tag, string_view __name, string_view __target)
       : __name_{__name}, __target_{__target} {}
 
   _LIBCPP_HIDE_FROM_ABI time_zone_link(time_zone_link&&)            = default;

libcxx/include/__locale

@@ -16,6 +16,7 @@
 #include <__mutex/once_flag.h>
 #include <__type_traits/make_unsigned.h>
 #include <__utility/no_destroy.h>
+#include <__utility/private_constructor_tag.h>
 #include <cctype>
 #include <clocale>
 #include <cstdint>
@@ -97,8 +98,7 @@ private:
 
   template <class>
   friend struct __no_destroy;
-  struct __private_tag {};
-  _LIBCPP_HIDE_FROM_ABI explicit locale(__private_tag, __imp* __loc) : __locale_(__loc) {}
+  _LIBCPP_HIDE_FROM_ABI explicit locale(__private_constructor_tag, __imp* __loc) : __locale_(__loc) {}
 
   void __install_ctor(const locale&, facet*, long);
   static locale& __global();
@@ -1248,10 +1248,10 @@ extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char, char
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<wchar_t, char, mbstate_t>;
 #endif
-extern template class _LIBCPP_DEPRECATED_IN_CXX20 _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS
-    codecvt_byname<char16_t, char, mbstate_t>; // deprecated in C++20
-extern template class _LIBCPP_DEPRECATED_IN_CXX20 _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS
-    codecvt_byname<char32_t, char, mbstate_t>; // deprecated in C++20
+extern template class _LIBCPP_DEPRECATED_IN_CXX20
+_LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char16_t, char, mbstate_t>; // deprecated in C++20
+extern template class _LIBCPP_DEPRECATED_IN_CXX20
+_LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char32_t, char, mbstate_t>; // deprecated in C++20
 #ifndef _LIBCPP_HAS_NO_CHAR8_T
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char16_t, char8_t, mbstate_t>; // C++20
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char32_t, char8_t, mbstate_t>; // C++20

libcxx/include/__stop_token/stop_callback.h

@@ -21,6 +21,7 @@
 #include <__type_traits/is_nothrow_constructible.h>
 #include <__utility/forward.h>
 #include <__utility/move.h>
+#include <__utility/private_constructor_tag.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -49,13 +50,13 @@ class _LIBCPP_AVAILABILITY_SYNC stop_callback : private __stop_callback_base {
     requires constructible_from<_Callback, _Cb>
   _LIBCPP_HIDE_FROM_ABI explicit stop_callback(const stop_token& __st,
                                                _Cb&& __cb) noexcept(is_nothrow_constructible_v<_Callback, _Cb>)
-      : stop_callback(__private_tag{}, __st.__state_, std::forward<_Cb>(__cb)) {}
+      : stop_callback(__private_constructor_tag{}, __st.__state_, std::forward<_Cb>(__cb)) {}
 
   template <class _Cb>
     requires constructible_from<_Callback, _Cb>
   _LIBCPP_HIDE_FROM_ABI explicit stop_callback(stop_token&& __st,
                                                _Cb&& __cb) noexcept(is_nothrow_constructible_v<_Callback, _Cb>)
-      : stop_callback(__private_tag{}, std::move(__st.__state_), std::forward<_Cb>(__cb)) {}
+      : stop_callback(__private_constructor_tag{}, std::move(__st.__state_), std::forward<_Cb>(__cb)) {}
 
   _LIBCPP_HIDE_FROM_ABI ~stop_callback() {
     if (__state_) {
@@ -74,10 +75,8 @@ class _LIBCPP_AVAILABILITY_SYNC stop_callback : private __stop_callback_base {
 
   friend __stop_callback_base;
 
-  struct __private_tag {};
-
   template <class _StatePtr, class _Cb>
-  _LIBCPP_HIDE_FROM_ABI explicit stop_callback(__private_tag, _StatePtr&& __state, _Cb&& __cb) noexcept(
+  _LIBCPP_HIDE_FROM_ABI explicit stop_callback(__private_constructor_tag, _StatePtr&& __state, _Cb&& __cb) noexcept(
       is_nothrow_constructible_v<_Callback, _Cb>)
       : __stop_callback_base([](__stop_callback_base* __cb_base) noexcept {
           // stop callback is supposed to only be called once

libcxx/include/__utility/private_constructor_tag.h

@@ -0,0 +1,28 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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_PRIVATE_CONSTRUCTOR_TAG_H
+#define _LIBCPP__UTILITY_PRIVATE_CONSTRUCTOR_TAG_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// This tag allows defining non-standard exposition-only constructors while
+// preventing users from being able to use them, since this reserved-name tag
+// needs to be used.
+struct __private_constructor_tag {};
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP__UTILITY_PRIVATE_CONSTRUCTOR_TAG_H

libcxx/include/module.modulemap

@@ -2090,18 +2090,19 @@ module std_private_utility_pair                   [system] {
   export std_private_type_traits_is_nothrow_move_assignable
   export std_private_utility_pair_fwd
 }
-module std_private_utility_pair_fwd               [system] { header "__fwd/pair.h" }
-module std_private_utility_piecewise_construct    [system] { header "__utility/piecewise_construct.h" }
-module std_private_utility_priority_tag           [system] { header "__utility/priority_tag.h" }
-module std_private_utility_rel_ops                [system] { header "__utility/rel_ops.h" }
-module std_private_utility_small_buffer           [system] { header "__utility/small_buffer.h" }
-module std_private_utility_swap                   [system] {
+module std_private_utility_pair_fwd                [system] { header "__fwd/pair.h" }
+module std_private_utility_piecewise_construct     [system] { header "__utility/piecewise_construct.h" }
+module std_private_utility_priority_tag            [system] { header "__utility/priority_tag.h" }
+module std_private_utility_private_constructor_tag [system] { header "__utility/private_constructor_tag.h" }
+module std_private_utility_rel_ops                 [system] { header "__utility/rel_ops.h" }
+module std_private_utility_small_buffer            [system] { header "__utility/small_buffer.h" }
+module std_private_utility_swap                    [system] {
   header "__utility/swap.h"
   export std_private_type_traits_is_swappable
 }
-module std_private_utility_to_underlying          [system] { header "__utility/to_underlying.h" }
-module std_private_utility_unreachable            [system] { header "__utility/unreachable.h" }
+module std_private_utility_to_underlying           [system] { header "__utility/to_underlying.h" }
+module std_private_utility_unreachable             [system] { header "__utility/unreachable.h" }
 
-module std_private_variant_monostate [system] { header "__variant/monostate.h" }
+module std_private_variant_monostate               [system] { header "__variant/monostate.h" }
 
-module std_private_vector_fwd [system] { header "__fwd/vector.h" }
+module std_private_vector_fwd                      [system] { header "__fwd/vector.h" }

libcxx/src/CMakeLists.txt

@@ -334,8 +334,6 @@ endif()
 
 if (LIBCXX_ENABLE_LOCALIZATION AND LIBCXX_ENABLE_FILESYSTEM AND LIBCXX_ENABLE_TIME_ZONE_DATABASE)
   list(APPEND LIBCXX_EXPERIMENTAL_SOURCES
-    include/tzdb/leap_second_private.h
-    include/tzdb/time_zone_link_private.h
     include/tzdb/time_zone_private.h
     include/tzdb/types_private.h
     include/tzdb/tzdb_list_private.h

libcxx/src/include/tzdb/leap_second_private.h

@@ -497,7 +497,7 @@ constinit __no_destroy<locale::__imp>
     locale::__imp::classic_locale_imp_(__uninitialized_tag{}); // initialized below in classic()
 
 const locale& locale::classic() {
-  static const __no_destroy<locale> classic_locale(__private_tag{}, [] {
+  static const __no_destroy<locale> classic_locale(__private_constructor_tag{}, [] {
     // executed exactly once on first initialization of `classic_locale`
     locale::__imp::classic_locale_imp_.__emplace(1u);
     return &locale::__imp::classic_locale_imp_.__get();

libcxx/src/include/tzdb/time_zone_link_private.h

@@ -15,8 +15,6 @@
 #include <stdexcept>
 #include <string>
 
-#include "include/tzdb/leap_second_private.h"
-#include "include/tzdb/time_zone_link_private.h"
 #include "include/tzdb/time_zone_private.h"
 #include "include/tzdb/types_private.h"
 #include "include/tzdb/tzdb_list_private.h"
@@ -582,7 +580,7 @@ static void __parse_link(tzdb& __tzdb, istream& __input) {
   string __name = chrono::__parse_string(__input);
   chrono::__skip_line(__input);
 
-  __tzdb.links.emplace_back(time_zone_link::__constructor_tag{}, std::move(__name), std::move(__target));
+  __tzdb.links.emplace_back(std::__private_constructor_tag{}, std::move(__name), std::move(__target));
 }
 
 static void __parse_tzdata(tzdb& __db, __tz::__rules_storage_type& __rules, istream& __input) {
@@ -649,7 +647,7 @@ static void __parse_leap_seconds(vector<leap_second>& __leap_seconds, istream&&
     seconds __value{chrono::__parse_integral(__input, false)};
     chrono::__skip_line(__input);
 
-    __leap_seconds.emplace_back(leap_second::__constructor_tag{}, __date, __value);
+    __leap_seconds.emplace_back(std::__private_constructor_tag{}, __date, __value);
   }
 }
 

libcxx/src/locale.cpp

@@ -0,0 +1,19 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// struct __private_constructor_tag{};
+
+// The private constructor tag is intended to be a trivial type that can easily
+// be used to mark a constructor exposition-only.
+//
+// Tests whether the type is trivial.
+
+#include <__utility/private_constructor_tag.h>
+#include <type_traits>
+
+static_assert(std::is_trivial<std::__private_constructor_tag>::value, "");

libcxx/src/tzdb.cpp

@@ -27,8 +27,6 @@
 #include <type_traits>
 #include <cassert>
 
-// Add the include path required by test_chrono_leap_second.h when using libc++.
-// ADDITIONAL_COMPILE_FLAGS(stdlib=libc++): -I %{libcxx-dir}/src/include
 #include "test_chrono_leap_second.h"
 
 constexpr bool test() {

libcxx/test/libcxx/utilities/utility/private_constructor_tag.compile.pass.cpp

@@ -25,8 +25,6 @@
 #include <concepts>
 #include <cassert>
 
-// Add the include path required by test_chrono_leap_second.h when using libc++.
-// ADDITIONAL_COMPILE_FLAGS(stdlib=libc++): -I %{libcxx-dir}/src/include
 #include "test_chrono_leap_second.h"
 
 constexpr bool test() {

libcxx/test/std/time/time.zone/time.zone.leap/assign.copy.pass.cpp

@@ -23,8 +23,6 @@
 
 #include "test_macros.h"
 
-// Add the include path required by test_chrono_leap_second.h when using libc++.
-// ADDITIONAL_COMPILE_FLAGS(stdlib=libc++): -I %{libcxx-dir}/src/include
 #include "test_chrono_leap_second.h"
 
 constexpr void test(const std::chrono::leap_second leap_second, std::chrono::sys_seconds expected) {

libcxx/test/std/time/time.zone/time.zone.leap/cons.copy.pass.cpp

@@ -23,8 +23,6 @@
 
 #include "test_macros.h"
 
-// Add the include path required by test_chrono_leap_second.h when using libc++.
-// ADDITIONAL_COMPILE_FLAGS(stdlib=libc++): -I %{libcxx-dir}/src/include
 #include "test_chrono_leap_second.h"
 
 constexpr void test(const std::chrono::leap_second leap_second, std::chrono::seconds expected) {

libcxx/test/std/time/time.zone/time.zone.leap/members/date.pass.cpp

@@ -50,8 +50,6 @@
 #include "test_macros.h"
 #include "test_comparisons.h"
 
-// Add the include path required by test_chrono_leap_second.h when using libc++.
-// ADDITIONAL_COMPILE_FLAGS(stdlib=libc++): -I %{libcxx-dir}/src/include
 #include "test_chrono_leap_second.h"
 
 constexpr void test_comparison(const std::chrono::leap_second lhs, const std::chrono::leap_second rhs) {

libcxx/test/std/time/time.zone/time.zone.leap/members/value.pass.cpp

@@ -32,16 +32,11 @@
 
 #ifdef _LIBCPP_VERSION
 
-// In order to find this include the calling test needs to provide this path in
-// the search path. Typically this looks like:
-//   ADDITIONAL_COMPILE_FLAGS(stdlib=libc++): -I %{libcxx-dir}/src/include
-// where the number of `../` sequences depends on the subdirectory level of the
-// test.
-#  include "tzdb/leap_second_private.h" // Header in the dylib
+#  include <__utility/private_constructor_tag.h>
 
 inline constexpr std::chrono::leap_second
 test_leap_second_create(const std::chrono::sys_seconds& date, const std::chrono::seconds& value) {
-  return std::chrono::leap_second{std::chrono::leap_second::__constructor_tag{}, date, value};
+  return std::chrono::leap_second{std::__private_constructor_tag{}, date, value};
 }
 
 #else // _LIBCPP_VERSION

libcxx/test/std/time/time.zone/time.zone.leap/nonmembers/comparison.pass.cpp

@@ -11,6 +11,7 @@ def IWYU_mapping(header: str) -> typing.Optional[typing.List[str]]:
         "__debug_utils/.+",
         "__fwd/get[.]h",
         "__support/.+",
+        "__utility/private_constructor_tag.h",
     ]
     if any(re.match(pattern, header) for pattern in ignore):
         return None