Fix bug in POSIX time zone calculations

zoneinfo/src/posix.rs

@@ -136,41 +136,104 @@ pub enum PosixDate {
 }
 
 impl PosixDate {
-    pub(crate) fn from_rule(rule: &Rule) -> Self {
+    /// Creates a [`PosixDate`] from a provided rule. This method returns both a posix date and an
+    /// integer, representing the days off the target weekday in seconds.
+    pub(crate) fn from_rule(rule: &Rule) -> (Self, i64) {
         match rule.on_date {
-            DayOfMonth::Day(day) if rule.in_month == Month::Jan || rule.in_month == Month::Feb => {
-                PosixDate::JulianNoLeap(month_to_day(rule.in_month as u8, 1) as u16 + day as u16)
-            }
-            DayOfMonth::Day(day) => {
-                PosixDate::JulianLeap(month_to_day(rule.in_month as u8, 1) as u16 + day as u16)
-            }
-            DayOfMonth::Last(wd) => PosixDate::MonthWeekDay(MonthWeekDay(rule.in_month, 5, wd)),
+            DayOfMonth::Day(day) if rule.in_month == Month::Jan || rule.in_month == Month::Feb => (
+                PosixDate::JulianNoLeap(month_to_day(rule.in_month as u8, 1) as u16 + day as u16),
+                0,
+            ),
+            DayOfMonth::Day(day) => (
+                PosixDate::JulianLeap(month_to_day(rule.in_month as u8, 1) as u16 + day as u16),
+                0,
+            ),
+            DayOfMonth::Last(wd) => (
+                PosixDate::MonthWeekDay(MonthWeekDay(rule.in_month, 5, wd)),
+                0,
+            ),
             DayOfMonth::WeekDayGEThanMonthDay(week_day, day_of_month) => {
-                let week = 1 + (day_of_month - 1) / 7;
-                PosixDate::MonthWeekDay(MonthWeekDay(rule.in_month, week, week_day))
+                // Handle week day offset correctly (See America/Santiago; i.e. Sun>=2)
+                //
+                // To do this for the GE case, we work with a zero based day of month,
+                // This ensures that day_of_month being 1 aligns with Sun = 0, for
+                // Sun>=1 purposes.
+                //
+                // The primary purpose for this approach as noted in zic.c is to support
+                // America/Santiago timestamps beyond 2038.
+                //
+                // See the below link for more info.
+                //
+                // https://github.com/eggert/tz/commit/07351e0248b5a42151e49e4506bca0363c846f8c
+
+                // Calculate the difference between the day of month and the week day.
+                let zero_based_day_of_month = day_of_month - 1;
+                let week_day_from_dom = zero_based_day_of_month % 7;
+                // N.B., this could be a negative. If we look at Sun>=2, then this becomes
+                // 0 - 1.
+                let mut adjusted_week_day = week_day as i8 - week_day_from_dom as i8;
+
+                // Calculate what week we are in.
+                //
+                // Since we are operating with a zero based day of month, we add
+                let week = 1 + zero_based_day_of_month / 7;
+
+                // If we have shifted beyond the month, add 7 to shift back into the first
+                // week.
+                if adjusted_week_day < 0 {
+                    adjusted_week_day += 7;
+                }
+                let week_day = WeekDay::from_u8(adjusted_week_day as u8);
+                // N.B. The left of time the target weekday becomes a time overflow added
+                // to the minutes.
+                (
+                    PosixDate::MonthWeekDay(MonthWeekDay(rule.in_month, week, week_day)),
+                    week_day_from_dom as i64 * 86_400,
+                )
             }
             DayOfMonth::WeekDayLEThanMonthDay(week_day, day_of_month) => {
+                // Handle week day offset correctly
+                //
+                // We don't worry about the last day of the month in this scenario, which
+                // is the upper bound as that is handled by DayOfMonth::Last
+                let week_day_from_dom = day_of_month as i8 % 7;
+                let mut adjusted_week_day = week_day as i8 - week_day_from_dom;
                 let week = day_of_month / 7;
-                PosixDate::MonthWeekDay(MonthWeekDay(rule.in_month, week, week_day))
+                if adjusted_week_day < 0 {
+                    adjusted_week_day += 7;
+                }
+                (
+                    PosixDate::MonthWeekDay(MonthWeekDay(
+                        rule.in_month,
+                        week,
+                        WeekDay::from_u8(adjusted_week_day as u8),
+                    )),
+                    week_day_from_dom as i64 * 86_400,
+                )
             }
         }
     }
 }
 
 #[derive(Debug, PartialEq, Clone, Copy)]
 pub struct PosixDateTime {
+    /// The designated [`PosixDate`]
     pub date: PosixDate,
+    /// The local time for a [`PosixDateTime`] at which a transition occurs.
+    ///
+    /// N.B., this can be in the range of -167..=167
     pub time: Time,
 }
 
 impl PosixDateTime {
     pub(crate) fn from_rule_and_transition_info(rule: &Rule, offset: Time, savings: Time) -> Self {
-        let date = PosixDate::from_rule(rule);
+        let (date, time_overflow) = PosixDate::from_rule(rule);
         let time = match rule.at {
             QualifiedTime::Local(time) => time,
             QualifiedTime::Standard(standard_time) => standard_time.add(rule.save),
             QualifiedTime::Universal(universal_time) => universal_time.add(offset).add(savings),
         };
+        let time = time.add(Time::from_seconds(time_overflow));
         Self { date, time }
     }
 }

zoneinfo/src/types.rs

@@ -444,6 +444,21 @@ pub enum WeekDay {
     Sat,
 }
 
+impl WeekDay {
+    pub(crate) fn from_u8(value: u8) -> Self {
+        match value {
+            0 => Self::Sun,
+            1 => Self::Mon,
+            2 => Self::Tues,
+            3 => Self::Wed,
+            4 => Self::Thurs,
+            5 => Self::Fri,
+            6 => Self::Sat,
+            _ => unreachable!("invalid week day value"),
+        }
+    }
+}
+
 impl TryFromStr<LineParseContext> for WeekDay {
     type Error = ZoneInfoParseError;
     fn try_from_str(s: &str, ctx: &mut LineParseContext) -> Result<Self, Self::Error> {

zoneinfo/tests/posix.rs

@@ -40,4 +40,10 @@ fn posix_string_test() {
 
     let moscow_posix = zic.get_posix_time_zone("Europe/Moscow").unwrap();
     assert_eq!(moscow_posix.to_string(), Ok("MSK-3".into()));
+
+    let santiago_posix = zic.get_posix_time_zone("America/Santiago").unwrap();
+    assert_eq!(
+        santiago_posix.to_string(),
+        Ok("<-04>4<-03>,M9.1.6/24,M4.1.6/24".into())
+    )
 }

zoneinfo/tests/zoneinfo

@@ -435,4 +435,61 @@ Zone	Europe/Riga	1:36:34	-	LMT	1880
 			2:00	-	EET	2001 Jan  2
 			2:00	EU	EE%sT
 
+# America/Santiago test case
 
+# Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
+Rule	Chile	1927	1931	-	Sep	 1	0:00	1:00	-
+Rule	Chile	1928	1932	-	Apr	 1	0:00	0	-
+Rule	Chile	1968	only	-	Nov	 3	4:00u	1:00	-
+Rule	Chile	1969	only	-	Mar	30	3:00u	0	-
+Rule	Chile	1969	only	-	Nov	23	4:00u	1:00	-
+Rule	Chile	1970	only	-	Mar	29	3:00u	0	-
+Rule	Chile	1971	only	-	Mar	14	3:00u	0	-
+Rule	Chile	1970	1972	-	Oct	Sun>=9	4:00u	1:00	-
+Rule	Chile	1972	1986	-	Mar	Sun>=9	3:00u	0	-
+Rule	Chile	1973	only	-	Sep	30	4:00u	1:00	-
+Rule	Chile	1974	1987	-	Oct	Sun>=9	4:00u	1:00	-
+Rule	Chile	1987	only	-	Apr	12	3:00u	0	-
+Rule	Chile	1988	1990	-	Mar	Sun>=9	3:00u	0	-
+Rule	Chile	1988	1989	-	Oct	Sun>=9	4:00u	1:00	-
+Rule	Chile	1990	only	-	Sep	16	4:00u	1:00	-
+Rule	Chile	1991	1996	-	Mar	Sun>=9	3:00u	0	-
+Rule	Chile	1991	1997	-	Oct	Sun>=9	4:00u	1:00	-
+Rule	Chile	1997	only	-	Mar	30	3:00u	0	-
+Rule	Chile	1998	only	-	Mar	Sun>=9	3:00u	0	-
+Rule	Chile	1998	only	-	Sep	27	4:00u	1:00	-
+Rule	Chile	1999	only	-	Apr	 4	3:00u	0	-
+Rule	Chile	1999	2010	-	Oct	Sun>=9	4:00u	1:00	-
+Rule	Chile	2000	2007	-	Mar	Sun>=9	3:00u	0	-
+# N.B.: the end of March 29 in Chile is March 30 in Universal time,
+# which is used below in specifying the transition.
+Rule	Chile	2008	only	-	Mar	30	3:00u	0	-
+Rule	Chile	2009	only	-	Mar	Sun>=9	3:00u	0	-
+Rule	Chile	2010	only	-	Apr	Sun>=1	3:00u	0	-
+Rule	Chile	2011	only	-	May	Sun>=2	3:00u	0	-
+Rule	Chile	2011	only	-	Aug	Sun>=16	4:00u	1:00	-
+Rule	Chile	2012	2014	-	Apr	Sun>=23	3:00u	0	-
+Rule	Chile	2012	2014	-	Sep	Sun>=2	4:00u	1:00	-
+Rule	Chile	2016	2018	-	May	Sun>=9	3:00u	0	-
+Rule	Chile	2016	2018	-	Aug	Sun>=9	4:00u	1:00	-
+Rule	Chile	2019	max	-	Apr	Sun>=2	3:00u	0	-
+Rule	Chile	2019	2021	-	Sep	Sun>=2	4:00u	1:00	-
+Rule	Chile	2022	only	-	Sep	Sun>=9	4:00u	1:00	-
+Rule	Chile	2023	max	-	Sep	Sun>=2	4:00u	1:00	-
+# IATA SSIM anomalies: (1992-02) says 1992-03-14;
+# (1996-09) says 1998-03-08.  Ignore these.
+# Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
+Zone America/Santiago	-4:42:45 -	LMT	1890
+			-4:42:45 -	SMT	1910 Jan 10 # Santiago Mean Time
+			-5:00	-	%z	1916 Jul  1
+			-4:42:45 -	SMT	1918 Sep 10
+			-4:00	-	%z	1919 Jul  1
+			-4:42:45 -	SMT	1927 Sep  1
+			-5:00	Chile	%z	1932 Sep  1
+			-4:00	-	%z	1942 Jun  1
+			-5:00	-	%z	1942 Aug  1
+			-4:00	-	%z	1946 Jul 14 24:00
+			-4:00	1:00	%z	1946 Aug 28 24:00 # central CL
+			-5:00	1:00	%z	1947 Mar 31 24:00
+			-5:00	-	%z	1947 May 21 23:00
+			-4:00	Chile	%z