[libcxx-commits] [libcxx] [libc++][chrono] Loads tzdata.zi in tzdb. (PR #74928)

[Louis Dionne via libcxx-commits]

================
@@ -0,0 +1,106 @@
+// -*- 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_SRC_INCLUDE_TZDB_TYPES_H
+#define __LIBCPP_SRC_INCLUDE_TZDB_TYPES_H
+
+#include <chrono>
+#include <string>
+#include <utility>
+#include <variant>
+#include <vector>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// TODO TZDB
+// The helper classes in this header have no constructor but are loaded with
+// dedicated parse functions. In the original design this header was public and
+// the parsing is done in the dylib. In that design having constructors would
+// expand the ABI interface. Since this header is now in the dylib that design
+// should be reconsidered. (For now the design is kept as is, in case this
+// header needs to be public for unforseen reasons.)
+
+namespace chrono::__tz {
+
+// Sun>=8   first Sunday on or after the eighth
+// Sun<=25  last Sunday on or before the 25th
+struct __constrained_weekday {
+  /*  year_month_day operator()(year __year, month __month);*/ // needed but not implemented
+
+  weekday __weekday;
+  enum __comparison_t { __le, __ge } __comparison;
+  day __day;
+};
+
+// The on field has a few alternative presentations
+//  5        the fifth of the month
+//  lastSun  the last Sunday in the month
+//  lastMon  the last Monday in the month
+//  Sun>=8   first Sunday on or after the eighth
+//  Sun<=25  last Sunday on or before the 25th
+using __on = variant<day, weekday_last, __constrained_weekday>;
+
+enum class __clock { __local, __standard, __universal };
+
+struct __at {
+  seconds __time{0};
+  __tz::__clock __clock{__tz::__clock::__local};
+};
+
+struct __save {
+  seconds __time;
+  bool __is_dst;
+};
+
+// The names of the fields match the fields of a Rule.
+struct __rule {
+  year __from;
+  year __to;
+  month __in;
+  __tz::__on __on;
+  __tz::__at __at;
+  __tz::__save __save;
+  string __letters;
+};
+
+using __rules_storage_type = std::vector<std::pair<string, vector<__tz::__rule>>>; // TODO TZDB use flat_map;
+
+struct __continuation {
+  // Non-owning link to the RULE entries.
+  __tz::__rules_storage_type* __rule_database_;
+
+  seconds __stdoff;
+
+  // The RULES is either a SAVE or a NAME.
+  // The size_t is used as cache. After loading the rules they are
+  // sorted and remain stable, then an index in the vector can be
+  // used.
+  // If this field contains - then standard time always
+  // applies. This is indicated by the monostate.
+  using __rules_t = variant<monostate, __tz::__save, string, size_t>;
+
+  __rules_t __rules;
+
+  string __format;
+  // TODO TZDB until can be contain more than just a year.
----------------
ldionne wrote:

```suggestion
  // TODO TZDB The `until` field can contain more than just a year.
```

https://github.com/llvm/llvm-project/pull/74928