Fix Posix::time_zone for southern hemisphere

* The get_info functions were not prepared for the case where the start
  and end times of a rule are chronologically reversed for a year.  I.e.
  the daylight saving start comes later in the year than the daylight
  saving end.  When save is positive, this happens in the southern
  hemisphere (e.g. "Australia/Sydney" -> "AEST-10AEDT,M10.1.0,M4.1.0/3").
  It also happens in the nothern hemisphere when the save is negative
  (e.g. "Europe/Dublin" -> "IST-1GMT0,M10.5.0,M3.5.0/1").

* Added tests for Posix::time_zone.

include/date/ptz.h

@@ -269,8 +269,76 @@ public:
     std::string name() const;
 
     friend bool operator==(const time_zone& x, const time_zone& y);
+
+private:
+    date::sys_seconds get_start(date::year y) const;
+    date::sys_seconds get_prev_start(date::year y) const;
+    date::sys_seconds get_next_start(date::year y) const;
+    date::sys_seconds get_end(date::year y) const;
+    date::sys_seconds get_prev_end(date::year y) const;
+    date::sys_seconds get_next_end(date::year y) const;
+    date::sys_info contant_offset() const;
 };
 
+inline
+date::sys_seconds
+time_zone::get_start(date::year y) const
+{
+    return date::sys_seconds{(start_rule_(y) - offset_).time_since_epoch()};
+}
+
+inline
+date::sys_seconds
+time_zone::get_prev_start(date::year y) const
+{
+    return date::sys_seconds{(start_rule_(--y) - offset_).time_since_epoch()};
+}
+
+inline
+date::sys_seconds
+time_zone::get_next_start(date::year y) const
+{
+    return date::sys_seconds{(start_rule_(++y) - offset_).time_since_epoch()};
+}
+
+inline
+date::sys_seconds
+time_zone::get_end(date::year y) const
+{
+    return date::sys_seconds{(end_rule_(y) - (offset_ + save_)).time_since_epoch()};
+}
+
+inline
+date::sys_seconds
+time_zone::get_prev_end(date::year y) const
+{
+    return date::sys_seconds{(end_rule_(--y) - (offset_ + save_)).time_since_epoch()};
+}
+
+inline
+date::sys_seconds
+time_zone::get_next_end(date::year y) const
+{
+    return date::sys_seconds{(end_rule_(++y) - (offset_ + save_)).time_since_epoch()};
+}
+
+date::sys_info
+time_zone::contant_offset() const
+{
+    using date::year;
+    using date::sys_info;
+    using date::sys_days;
+    using date::January;
+    using date::December;
+    using date::last;
+    sys_info r;
+    r.begin = sys_days{year::min()/January/1};
+    r.end   = sys_days{year::max()/December/last};
+    r.abbrev = std_abbrev_;
+    r.offset = offset_;
+    return r;
+}
+
 inline
 time_zone::time_zone(const detail::string_t& s)
 {
@@ -313,12 +381,10 @@ time_zone::get_info(date::sys_time<Duration> st) const
 {
     using date::sys_info;
     using date::year_month_day;
-    using date::sys_seconds;
     using date::sys_days;
     using date::floor;
     using date::ceil;
     using date::days;
-    using date::years;
     using date::year;
     using date::January;
     using date::December;
@@ -329,36 +395,59 @@ time_zone::get_info(date::sys_time<Duration> st) const
     if (start_rule_.ok())
     {
         auto y = year_month_day{floor<days>(st)}.year();
-        auto start = sys_seconds{(start_rule_(y) - offset_).time_since_epoch()};
-        auto end   = sys_seconds{(end_rule_(y) - (offset_ + save_)).time_since_epoch()};
-        if (start <= st && st < end)
+        auto start = get_start(y);
+        auto end   = get_end(y);
+        if (start <= end)  // (northern hemisphere)
         {
-            r.begin = start;
-            r.end = end;
-            r.offset += save_;
-            r.save = ceil<minutes>(save_);
-            r.abbrev = dst_abbrev_;
+            if (start <= st && st < end)
+            {
+                r.begin = start;
+                r.end = end;
+                r.offset += save_;
+                r.save = ceil<minutes>(save_);
+                r.abbrev = dst_abbrev_;
+            }
+            else if (st < start)
+            {
+                r.begin = get_prev_end(y);
+                r.end = start;
+                r.abbrev = std_abbrev_;
+            }
+            else  // st >= end
+            {
+                r.begin = end;
+                r.end = get_next_start(y);
+                r.abbrev = std_abbrev_;
+            }
         }
-        else if (st < start)
+        else  // end < start (southern hemisphere)
         {
-            r.begin = sys_seconds{(end_rule_(y-years{1}) -
-                                   (offset_ + save_)).time_since_epoch()};
-            r.end = start;
-            r.abbrev = std_abbrev_;
-        }
-        else  // st >= end
-        {
-            r.begin = end;
-            r.end = sys_seconds{(start_rule_(y+years{1}) - offset_).time_since_epoch()};
-            r.abbrev = std_abbrev_;
+            if (end <= st && st < start)
+            {
+                r.begin = end;
+                r.end = start;
+                r.abbrev = std_abbrev_;
+            }
+            else if (st < end)
+            {
+                r.begin = get_prev_start(y);
+                r.end = end;
+                r.offset += save_;
+                r.save = ceil<minutes>(save_);
+                r.abbrev = dst_abbrev_;
+            }
+            else  // st >= start
+            {
+                r.begin = start;
+                r.end = get_next_end(y);
+                r.offset += save_;
+                r.save = ceil<minutes>(save_);
+                r.abbrev = dst_abbrev_;
+            }
         }
     }
-    else  //  constant offset
-    {
-        r.begin = sys_days{year::min()/January/1};
-        r.end   = sys_days{year::max()/December/last};
-        r.abbrev = std_abbrev_;
-    }
+    else
+        r = contant_offset();
     return r;
 }
 
@@ -371,7 +460,6 @@ time_zone::get_info(date::local_time<Duration> tp) const
     using date::days;
     using date::sys_days;
     using date::sys_seconds;
-    using date::years;
     using date::year;
     using date::ceil;
     using date::January;
@@ -384,19 +472,25 @@ time_zone::get_info(date::local_time<Duration> tp) const
     if (start_rule_.ok())
     {
         auto y = year_month_day{floor<days>(tp)}.year();
-        auto start = sys_seconds{(start_rule_(y) - offset_).time_since_epoch()};
-        auto end   = sys_seconds{(end_rule_(y) - (offset_ + save_)).time_since_epoch()};
+        auto start = get_start(y);
+        auto end   = get_end(y);
         auto utcs = sys_seconds{floor<seconds>(tp - offset_).time_since_epoch()};
         auto utcd = sys_seconds{floor<seconds>(tp - (offset_ + save_)).time_since_epoch()};
+        auto northern = start <= end;
         if ((utcs < start) != (utcd < start))
         {
-            r.first.begin = sys_seconds{(end_rule_(y-years{1}) -
-                                         (offset_ + save_)).time_since_epoch()};
+            if (northern)
+                r.first.begin = get_prev_end(y);
+            else
+                r.first.begin = end;
             r.first.end = start;
             r.first.offset = offset_;
             r.first.abbrev = std_abbrev_;
             r.second.begin = start;
-            r.second.end = end;
+            if (northern)
+                r.second.end = end;
+            else
+                r.second.end = get_next_end(y);
             r.second.abbrev = dst_abbrev_;
             r.second.offset = offset_ + save_;
             r.second.save = ceil<minutes>(save_);
@@ -405,51 +499,29 @@ time_zone::get_info(date::local_time<Duration> tp) const
         }
         else if ((utcs < end) != (utcd < end))
         {
-            r.first.begin = start;
+            if (northern)
+                r.first.begin = start;
+            else
+                r.first.begin = get_prev_start(y);
             r.first.end = end;
             r.first.offset = offset_ + save_;
             r.first.save = ceil<minutes>(save_);
             r.first.abbrev = dst_abbrev_;
             r.second.begin = end;
-            r.second.end = sys_seconds{(start_rule_(y+years{1}) -
-                                        offset_).time_since_epoch()};
+            if (northern)
+                r.second.end = get_next_start(y);
+            else
+                r.second.end = start;
             r.second.abbrev = std_abbrev_;
             r.second.offset = offset_;
             r.result = save_ > seconds{0} ? local_info::ambiguous
                                           : local_info::nonexistent;
         }
-        else if (utcs < start)
-        {
-            r.first.begin = sys_seconds{(end_rule_(y-years{1}) -
-                                   (offset_ + save_)).time_since_epoch()};
-            r.first.end = start;
-            r.first.offset = offset_;
-            r.first.abbrev = std_abbrev_;
-        }
-        else if (utcs < end)
-        {
-            r.first.begin = start;
-            r.first.end = end;
-            r.first.offset = offset_ + save_;
-            r.first.save = ceil<minutes>(save_);
-            r.first.abbrev = dst_abbrev_;
-        }
         else
-        {
-            r.first.begin = end;
-            r.first.end = sys_seconds{(start_rule_(y+years{1}) -
-                                       offset_).time_since_epoch()};
-            r.first.abbrev = std_abbrev_;
-            r.first.offset = offset_;
-        }
-    }
-    else  //  constant offset
-    {
-        r.first.begin = sys_days{year::min()/January/1};
-        r.first.end   = sys_days{year::max()/December/last};
-        r.first.abbrev = std_abbrev_;
-        r.first.offset = offset_;
+            r.first = get_info(utcs);
     }
+    else
+        r.first = contant_offset();
     return r;
 }
 

test/posix/ptz.pass.cpp

@@ -0,0 +1,108 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2021 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// Test Posix::time_zone
+
+#include "tz.h"
+#include "ptz.h"
+#include <cassert>
+
+bool
+is_equal(date::sys_info const& x, date::sys_info const& y)
+{
+    return x.begin == y.begin &&
+           x.end == y.end &&
+           x.offset == y.offset &&
+           x.save == y.save &&
+           x.abbrev == y.abbrev;
+}
+
+bool
+is_equal(date::local_info const& x, date::local_info const& y)
+{
+    return x.result == y.result && is_equal(x.first, y.first)
+                                && is_equal(x.second, y.second);
+}
+
+int
+main()
+{
+    using namespace date;
+    using namespace std;
+    using namespace std::chrono;
+
+    auto tzi = locate_zone("Australia/Sydney");
+    Posix::time_zone tzp{"AEST-10AEDT,M10.1.0,M4.1.0/3"};
+    auto tp = local_days{2021_y/1/1} + 0s;
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+    
+    tp = local_days{2021_y/10/Sunday[1]} + 2h + 30min;
+    assert(tzp.get_info(tp).result == local_info::nonexistent);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/4/Sunday[1]} + 2h + 30min;
+    assert(tzp.get_info(tp).result == local_info::ambiguous);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/7/1};
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+
+    tzi = locate_zone("America/New_York");
+    tzp = Posix::time_zone{"EST5EDT,M3.2.0,M11.1.0"};
+    tp = local_days{2021_y/1/1};
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/3/Sunday[2]} + 2h + 30min;
+    assert(tzp.get_info(tp).result == local_info::nonexistent);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/11/Sunday[1]} + 1h + 30min;
+    assert(tzp.get_info(tp).result == local_info::ambiguous);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/7/1};
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+
+    tzi = locate_zone("Europe/Dublin");
+    tzp = Posix::time_zone{"IST-1GMT0,M10.5.0,M3.5.0/1"};
+    tp = local_days{2021_y/1/1};
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/3/Sunday[last]} + 1h + 30min;
+    assert(tzp.get_info(tp).result == local_info::nonexistent);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/10/Sunday[last]} + 1h + 30min;
+    assert(tzp.get_info(tp).result == local_info::ambiguous);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/7/1};
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+}