[libc++][chrono] Loads tzdata.zi in tzdb.

This implements the loading of the tzdata.zi file and store its contents
in the tzdb struct.

This adds all required members except:
- the leap seconds,
- the locate_zone, and
- current_zone.

The class time_zone is incomplete and only contains the parts needed
for storing the parsed data.

The class time_zone_link is fully implemented including its non-member
functions.

Implements parts of:
- P0355 Extending <chrono> to Calendars and Time Zones
- P1614 The Mothership has Landed

Implements:
- P1982 Rename link to time_zone_link

Author: mordante

libcxx/docs/Status/Cxx20Papers.csv

@@ -180,7 +180,7 @@
 "`P1973R1 <https://wg21.link/P1973R1>`__","LWG","Rename ""_default_init"" Functions, Rev1","Prague","|Complete|","16.0"
 "`P1976R2 <https://wg21.link/P1976R2>`__","LWG","Fixed-size span construction from dynamic range","Prague","|Complete|","11.0","|ranges|"
 "`P1981R0 <https://wg21.link/P1981R0>`__","LWG","Rename leap to leap_second","Prague","* *",""
-"`P1982R0 <https://wg21.link/P1982R0>`__","LWG","Rename link to time_zone_link","Prague","* *",""
+"`P1982R0 <https://wg21.link/P1982R0>`__","LWG","Rename link to time_zone_link","Prague","|Complete|","19.0","|chrono|"
 "`P1983R0 <https://wg21.link/P1983R0>`__","LWG","Wording for GB301, US296, US292, US291, and US283","Prague","|Complete|","15.0","|ranges|"
 "`P1994R1 <https://wg21.link/P1994R1>`__","LWG","elements_view needs its own sentinel","Prague","|Complete|","16.0","|ranges|"
 "`P2002R1 <https://wg21.link/P2002R1>`__","CWG","Defaulted comparison specification cleanups","Prague","* *",""

libcxx/docs/Status/SpaceshipProjects.csv

@@ -171,10 +171,10 @@ Section,Description,Dependencies,Assignee,Complete
 | `month_weekday_last <https://reviews.llvm.org/D152699>`_
 | `year_month_weekday <https://reviews.llvm.org/D152699>`_
 | `year_month_weekday_last <https://reviews.llvm.org/D152699>`_",None,Hristo Hristov,|Complete|
-`[time.zone.nonmembers] <https://wg21.link/time.zone.nonmembers>`_,"`chrono::time_zone`",A ``<chrono>`` implementation,Mark de Wever,|In Progress|
+`[time.zone.nonmembers] <https://wg21.link/time.zone.nonmembers>`_,"`chrono::time_zone`",A ``<chrono>`` implementation,Mark de Wever,|Complete|
 `[time.zone.zonedtime.nonmembers] <https://wg21.link/time.zone.zonedtime.nonmembers>`_,"`chrono::zoned_time`",A ``<chrono>`` implementation,Mark de Wever,|In Progress|
 `[time.zone.leap.nonmembers] <https://wg21.link/time.zone.leap.nonmembers>`_,"`chrono::time_leap_seconds`",A ``<chrono>`` implementation,Mark de Wever,|In Progress|
-`[time.zone.link.nonmembers] <https://wg21.link/time.zone.link.nonmembers>`_,"`chrono::time_zone_link`",A ``<chrono>`` implementation,Mark de Wever,|In Progress|
+`[time.zone.link.nonmembers] <https://wg21.link/time.zone.link.nonmembers>`_,"`chrono::time_zone_link`",A ``<chrono>`` implementation,Mark de Wever,|Complete|
 - `5.13 Clause 28: Localization library <https://wg21.link/p1614r2#clause-28-localization-library>`_,,,,
 "| `[locale] <https://wg21.link/locale>`_
 | `[locale.operators] <https://wg21.link/locale.operators>`_",| remove ops `locale <https://reviews.llvm.org/D152654>`_,None,Hristo Hristov,|Complete|

libcxx/include/CMakeLists.txt

@@ -290,6 +290,8 @@ set(files
   __chrono/steady_clock.h
   __chrono/system_clock.h
   __chrono/time_point.h
+  __chrono/time_zone.h
+  __chrono/time_zone_link.h
   __chrono/tzdb.h
   __chrono/tzdb_list.h
   __chrono/weekday.h

libcxx/include/__chrono/time_zone.h

@@ -0,0 +1,86 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+// For information see https://libcxx.llvm.org/DesignDocs/TimeZone.html
+
+#ifndef _LIBCPP___CHRONO_TIME_ZONE_H
+#define _LIBCPP___CHRONO_TIME_ZONE_H
+
+#include <version>
+// Enable the contents of the header only when libc++ was built with experimental features enabled.
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+
+#  include <__compare/strong_order.h>
+#  include <__config>
+#  include <__memory/unique_ptr.h>
+#  include <string_view>
+
+#  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#    pragma GCC system_header
+#  endif
+
+_LIBCPP_PUSH_MACROS
+#  include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#  if _LIBCPP_STD_VER >= 20 && !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&   \
+      !defined(_LIBCPP_HAS_NO_LOCALIZATION)
+
+namespace chrono {
+
+class _LIBCPP_AVAILABILITY_TZDB time_zone {
+  _LIBCPP_HIDE_FROM_ABI time_zone() = default;
+
+public:
+  class __impl; // public so it can be used by make_unique.
+
+  // The "constructor".
+  //
+  // The default constructor is private to avoid the constructor from being an
+  // ABI interface. Instead use an __ugly_named function as an ABI interface,
+  // since users should not depend on __ugly_names.
+  [[nodiscard]] _LIBCPP_EXPORTED_FROM_ABI static time_zone __create(unique_ptr<__impl>&& __p);
+
+  _LIBCPP_EXPORTED_FROM_ABI ~time_zone();
+
+  _LIBCPP_HIDE_FROM_ABI time_zone(time_zone&&)            = default;
+  _LIBCPP_HIDE_FROM_ABI time_zone& operator=(time_zone&&) = default;
+
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI string_view name() const noexcept { return __name(); }
+
+  [[nodiscard]] _LIBCPP_EXPORTED_FROM_ABI const __impl& __implementation() const noexcept;
+
+  // private:
+  [[nodiscard]] _LIBCPP_EXPORTED_FROM_ABI string_view __name() const noexcept;
+  unique_ptr<__impl> __impl_;
+};
+
+_LIBCPP_NODISCARD_EXT _LIBCPP_AVAILABILITY_TZDB _LIBCPP_HIDE_FROM_ABI inline bool
+operator==(const time_zone& __x, const time_zone& __y) noexcept {
+  return __x.name() == __y.name();
+}
+
+_LIBCPP_NODISCARD_EXT _LIBCPP_AVAILABILITY_TZDB _LIBCPP_HIDE_FROM_ABI inline strong_ordering
+operator<=>(const time_zone& __x, const time_zone& __y) noexcept {
+  return __x.name() <=> __y.name();
+}
+
+} // namespace chrono
+
+#  endif // _LIBCPP_STD_VER >= 20 && !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM)
+         // && !defined(_LIBCPP_HAS_NO_LOCALIZATION)
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+
+#endif // _LIBCPP___CHRONO_TIME_ZONE_H

libcxx/include/__chrono/time_zone_link.h

@@ -0,0 +1,79 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+// For information see https://libcxx.llvm.org/DesignDocs/TimeZone.html
+
+#ifndef _LIBCPP___CHRONO_TIME_ZONE_LINK_H
+#define _LIBCPP___CHRONO_TIME_ZONE_LINK_H
+
+#include <version>
+// Enable the contents of the header only when libc++ was built with experimental features enabled.
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+
+#  include <__compare/strong_order.h>
+#  include <__config>
+#  include <string>
+#  include <string_view>
+
+#  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#    pragma GCC system_header
+#  endif
+
+_LIBCPP_PUSH_MACROS
+#  include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#  if _LIBCPP_STD_VER >= 20 && !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&   \
+      !defined(_LIBCPP_HAS_NO_LOCALIZATION)
+
+namespace chrono {
+
+class time_zone_link {
+public:
+  struct __constructor_tag;
+  _LIBCPP_NODISCARD_EXT
+  _LIBCPP_HIDE_FROM_ABI explicit time_zone_link(string_view __name, string_view __target, __constructor_tag&&)
+      : __name_{__name}, __target_{__target} {}
+
+  _LIBCPP_HIDE_FROM_ABI time_zone_link(time_zone_link&&)            = default;
+  _LIBCPP_HIDE_FROM_ABI time_zone_link& operator=(time_zone_link&&) = default;
+
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI string_view name() const noexcept { return __name_; }
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI string_view target() const noexcept { return __target_; }
+
+private:
+  string __name_;
+  // TODO TZDB instead of the name we can store the pointer to a zone. These
+  // pointers are immutable. This makes it possible to directly return a
+  // pointer in the time_zone in the 'locate_zone' function.
+  string __target_;
+};
+
+_LIBCPP_NODISCARD_EXT _LIBCPP_AVAILABILITY_TZDB _LIBCPP_HIDE_FROM_ABI inline bool
+operator==(const time_zone_link& __x, const time_zone_link& __y) noexcept {
+  return __x.name() == __y.name();
+}
+
+_LIBCPP_NODISCARD_EXT _LIBCPP_AVAILABILITY_TZDB _LIBCPP_HIDE_FROM_ABI inline strong_ordering
+operator<=>(const time_zone_link& __x, const time_zone_link& __y) noexcept {
+  return __x.name() <=> __y.name();
+}
+
+} // namespace chrono
+
+#  endif //_LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+
+#endif // _LIBCPP___CHRONO_TIME_ZONE_LINK_H

libcxx/include/__chrono/tzdb.h

@@ -16,21 +16,30 @@
 // Enable the contents of the header only when libc++ was built with experimental features enabled.
 #if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
 
+#  include <__chrono/time_zone.h>
+#  include <__chrono/time_zone_link.h>
+#  include <__config>
 #  include <string>
+#  include <vector>
 
 #  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #    pragma GCC system_header
 #  endif
 
+_LIBCPP_PUSH_MACROS
+#  include <__undef_macros>
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #  if _LIBCPP_STD_VER >= 20 && !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&   \
       !defined(_LIBCPP_HAS_NO_LOCALIZATION)
 
 namespace chrono {
 
-struct _LIBCPP_AVAILABILITY_TZDB tzdb {
+struct tzdb {
   string version;
+  vector<time_zone> zones;
+  vector<time_zone_link> links;
 };
 
 } // namespace chrono
@@ -40,6 +49,8 @@ struct _LIBCPP_AVAILABILITY_TZDB tzdb {
 
 _LIBCPP_END_NAMESPACE_STD
 
+_LIBCPP_POP_MACROS
+
 #endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
 
 #endif // _LIBCPP___CHRONO_TZDB_H

libcxx/include/__chrono/tzdb_list.h

@@ -19,7 +19,7 @@
 #  include <__availability>
 #  include <__chrono/tzdb.h>
 #  include <forward_list>
-#  include <string_view>
+#  include <string>
 
 #  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #    pragma GCC system_header
@@ -32,9 +32,16 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace chrono {
 
+// TODO TZDB
+// Libc++ recently switched to only export __ugly_names from the dylib.
+// Since the library is still experimental the functions in this header
+// should be adapted to this new style. The other tzdb headers should be
+// evaluated too.
+
 class _LIBCPP_AVAILABILITY_TZDB tzdb_list {
 public:
-  _LIBCPP_EXPORTED_FROM_ABI explicit tzdb_list(tzdb&& __tzdb);
+  class __impl; // public to allow construction in dylib
+  _LIBCPP_EXPORTED_FROM_ABI explicit tzdb_list(__impl* __p);
   _LIBCPP_EXPORTED_FROM_ABI ~tzdb_list();
 
   tzdb_list(const tzdb_list&)            = delete;
@@ -46,16 +53,15 @@ class _LIBCPP_AVAILABILITY_TZDB tzdb_list {
 
   _LIBCPP_EXPORTED_FROM_ABI const_iterator erase_after(const_iterator __p);
 
-  _LIBCPP_EXPORTED_FROM_ABI tzdb& __emplace_front(tzdb&& __tzdb);
-
   _LIBCPP_NODISCARD_EXT _LIBCPP_EXPORTED_FROM_ABI const_iterator begin() const noexcept;
   _LIBCPP_NODISCARD_EXT _LIBCPP_EXPORTED_FROM_ABI const_iterator end() const noexcept;
 
   _LIBCPP_NODISCARD_EXT _LIBCPP_EXPORTED_FROM_ABI const_iterator cbegin() const noexcept;
   _LIBCPP_NODISCARD_EXT _LIBCPP_EXPORTED_FROM_ABI const_iterator cend() const noexcept;
 
+  [[nodiscard]] _LIBCPP_EXPORTED_FROM_ABI __impl& __implementation();
+
 private:
-  class __impl;
   __impl* __impl_;
 };
 

libcxx/include/chrono

@@ -686,6 +686,8 @@ constexpr hours make24(const hours& h, bool is_pm) noexcept;
 // [time.zone.db], time zone database
 struct tzdb {                                                                    // C++20
   string                 version;
+  vector<time_zone>      zones;
+  vector<time_zone_link> links;
 };
 
 class tzdb_list {                                                                // C++20
@@ -716,15 +718,34 @@ tzdb_list& get_tzdb_list();
 const tzdb& reload_tzdb();                                                       // C++20
 string remote_version();                                                         // C++20
 
-// 25.10.5, class time_zone    // C++20
+// 25.10.5, class time_zone                                                      // C++20
 enum class choose {earliest, latest};
-class time_zone;
-bool operator==(const time_zone& x, const time_zone& y) noexcept;
-bool operator!=(const time_zone& x, const time_zone& y) noexcept;
-bool operator<(const time_zone& x, const time_zone& y) noexcept;
-bool operator>(const time_zone& x, const time_zone& y) noexcept;
-bool operator<=(const time_zone& x, const time_zone& y) noexcept;
-bool operator>=(const time_zone& x, const time_zone& y) noexcept;
+class time_zone {
+  time_zone(time_zone&&) = default;
+  time_zone& operator=(time_zone&&) = default;
+
+  // unspecified additional constructors
+
+  string_view name() const noexcept;
+};
+bool operator==(const time_zone& x, const time_zone& y) noexcept;                // C++20
+strong_ordering operator<=>(const time_zone& x, const time_zone& y) noexcept;    // C++20
+
+// [time.zone.link], class time_zone_link
+class time_zone_link {                                                           // C++20
+public:
+  time_zone_link(time_zone_link&&)            = default;
+  time_zone_link& operator=(time_zone_link&&) = default;
+
+  // unspecified additional constructors
+
+  string_view name()   const noexcept;
+  string_view target() const noexcept;
+};
+
+bool operator==(const time_zone_link& x, const time_zone_link& y);               // C++20
+strong_ordering operator<=>(const time_zone_link& x, const time_zone_link& y);   // C++20
+
 }  // chrono
 
 namespace std {
@@ -842,6 +863,8 @@ constexpr chrono::year                                  operator ""y(unsigned lo
 
 #if !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&                              \
     !defined(_LIBCPP_HAS_NO_LOCALIZATION)
+#  include <__chrono/time_zone.h>
+#  include <__chrono/time_zone_link.h>
 #  include <__chrono/tzdb.h>
 #  include <__chrono/tzdb_list.h>
 #endif

libcxx/include/libcxx.imp

@@ -287,6 +287,8 @@
   { include: [ "<__chrono/steady_clock.h>", "private", "<chrono>", "public" ] },
   { include: [ "<__chrono/system_clock.h>", "private", "<chrono>", "public" ] },
   { include: [ "<__chrono/time_point.h>", "private", "<chrono>", "public" ] },
+  { include: [ "<__chrono/time_zone.h>", "private", "<chrono>", "public" ] },
+  { include: [ "<__chrono/time_zone_link.h>", "private", "<chrono>", "public" ] },
   { include: [ "<__chrono/tzdb.h>", "private", "<chrono>", "public" ] },
   { include: [ "<__chrono/tzdb_list.h>", "private", "<chrono>", "public" ] },
   { include: [ "<__chrono/weekday.h>", "private", "<chrono>", "public" ] },

libcxx/include/module.modulemap.in

@@ -1155,6 +1155,12 @@ module std_private_chrono_steady_clock           [system] {
   header "__chrono/steady_clock.h"
   export std_private_chrono_time_point
 }
+module std_private_chrono_time_zone              [system] {
+  header "__chrono/time_zone.h"
+}
+module std_private_chrono_time_zone_link         [system] {
+  header "__chrono/time_zone_link.h"
+}
 module std_private_chrono_system_clock           [system] {
   header "__chrono/system_clock.h"
   export std_private_chrono_time_point