Added fix (a hack to be honest!) to account for cases like Asia/Karac…

…hi that rely on UTC seed date when calculating recurrence dates
ical4j · Apr 8, 2021 · fe5752d · fe5752d
1 parent 09e11e8
commit fe5752d
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diff --git a/src/main/java/net/fortuna/ical4j/model/component/Observance.java b/src/main/java/net/fortuna/ical4j/model/component/Observance.java
@@ -224,8 +224,12 @@ public final Date getLatestOnset(final Date date) {
             cal.setTime(date);
             cal.add(Calendar.YEAR, 10);
             onsetLimit = Dates.getInstance(cal.getTime(), Value.DATE_TIME);
-            final DateList recurrenceDates = rrule.getRecur().getDates(initialOnsetUTC,
-                    onsetLimit, Value.DATE_TIME);
+            final DateList recurrenceDates;
+            if (rrule.getRecur().getDayList().isEmpty()) {
+                recurrenceDates = rrule.getRecur().getDates(initialOnset, onsetLimit, Value.DATE_TIME);
+            } else {
+                recurrenceDates = rrule.getRecur().getDates(initialOnsetUTC, onsetLimit, Value.DATE_TIME);
+            }
             for (final Date recurDate : recurrenceDates) {
                 final DateTime rruleOnset = applyOffsetFrom((DateTime) recurDate);
                 if (!rruleOnset.after(date) && rruleOnset.after(onset)) {

diff --git a/src/test/java/net/fortuna/ical4j/model/TimeZoneTest2.java b/src/test/java/net/fortuna/ical4j/model/TimeZoneTest2.java
@@ -0,0 +1,127 @@
+package net.fortuna.ical4j.model;
+
+import net.fortuna.ical4j.model.component.Observance;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class TimeZoneTest2 {
+
+    /* ical4j 3.0.21, but seems to also happen with 4.0.0-alpha8 (couldn't test everything) */
+
+    @Test
+    public void testTzKarachi() throws Exception {
+        TimeZoneRegistry tzReg = TimeZoneRegistryFactory.getInstance().createRegistry();
+
+        TimeZone origKarachi = tzReg.getTimeZone("Asia/Karachi");
+        TimeZone karachi = origKarachi;
+
+        long ts1 = 1609945200000L;       // 20210106T150000Z; 20210106T200000 Asia/Karachi
+        DateTime dt1 = new DateTime(ts1);
+        dt1.setUtc(true);
+
+        System.err.println("Applicable observance: " + karachi.getVTimeZone().getApplicableObservance(dt1));
+        /* prints:
+
+           BEGIN:DAYLIGHT
+           TZNAME:PKST
+           TZOFFSETFROM:+0500
+           TZOFFSETTO:+0600
+           DTSTART:20020407T000000
+           RDATE:20080601T000000
+           RDATE:20090415T000000
+           END:DAYLIGHT
+
+           which is wrong. Should be this one:
+
+           BEGIN:STANDARD
+           TZNAME:PKT
+           TZOFFSETFROM:+0600
+           TZOFFSETTO:+0500
+           DTSTART:20081101T000000
+           RRULE:FREQ=YEARLY;UNTIL=20091031T180000Z
+           END:STANDARD
+        */
+
+        for (Observance obs : karachi.getVTimeZone().getObservances()) {
+            System.err.print("Found observance: " + obs.toString());
+            System.err.println("Latest onset: " + obs.getLatestOnset(dt1));
+            System.err.println();
+        }
+        /* prints:
+
+        Found observance: BEGIN:STANDARD
+        TZNAME:+0530
+        TZOFFSETFROM:+042812
+        TZOFFSETTO:+0530
+        DTSTART:19070101T000000
+        END:STANDARD
+        Latest onset: 19061231T193148Z
+
+        Found observance: BEGIN:DAYLIGHT
+        TZNAME:+0630
+        TZOFFSETFROM:+0530
+        TZOFFSETTO:+0630
+        DTSTART:19420901T000000
+        END:DAYLIGHT
+        Latest onset: 19420831T183000Z
+
+        Found observance: BEGIN:STANDARD
+        TZNAME:+0530
+        TZOFFSETFROM:+0630
+        TZOFFSETTO:+0530
+        DTSTART:19451015T000000
+        END:STANDARD
+        Latest onset: 19451014T173000Z
+
+        Found observance: BEGIN:STANDARD
+        TZNAME:+05
+        TZOFFSETFROM:+0530
+        TZOFFSETTO:+0500
+        DTSTART:19510930T000000
+        END:STANDARD
+        Latest onset: 19510929T183000Z
+
+        Found observance: BEGIN:STANDARD
+        TZNAME:PKT
+        TZOFFSETFROM:+0500
+        TZOFFSETTO:+0500
+        DTSTART:19710326T000000
+        END:STANDARD
+        Latest onset: 19710325T190000Z
+
+        Found observance: BEGIN:DAYLIGHT
+        TZNAME:PKST
+        TZOFFSETFROM:+0500
+        TZOFFSETTO:+0600               // <- this is what is used for 2021
+        DTSTART:20020407T000000
+        RDATE:20080601T000000
+        RDATE:20090415T000000        // <-- newer than 20081031T180000Z so this one is used
+        END:DAYLIGHT
+        Latest onset: 20090414T190000Z
+
+        Found observance: BEGIN:STANDARD
+        TZNAME:PKT
+        TZOFFSETFROM:+0600
+        TZOFFSETTO:+0500
+        DTSTART:20021006T000000
+        END:STANDARD
+        Latest onset: 20021005T180000Z
+
+        Found observance: BEGIN:STANDARD
+        TZNAME:PKT
+        TZOFFSETFROM:+0600
+        TZOFFSETTO:+0500                         // <- this is what should be used for 2021
+        DTSTART:20081101T000000
+        RRULE:FREQ=YEARLY;UNTIL=20091031T180000Z
+        END:STANDARD
+        Latest onset: 20081031T180000Z                // <- this should be 20091031T180000Z
+         */
+
+        assertEquals(5, karachi.getOffset(ts1)/3600000);  // fails!
+
+        DateTime dt2 = new DateTime("20210106T200000", karachi);
+        assertEquals(1609945200000L, dt2.getTime());    // fails!
+    }
+
+}