recur_expansion: EXDATE can be DATE and DTSTART can be DATE-TIME

When EXDATE is in DATE format and DTSTART is DATE-TIME, then
to determine whether an occurrence shall be excluded, the
occurrence shall be converted to DATE and then compared to EXDATE.

This applies also for the very first EXDATE, when it coincides with
DTSTART.

lib/ical/recur_expansion.js

@@ -198,6 +198,21 @@ class RecurExpansion {
     }
   }
 
+  /**
+   * Compare two ICAL.Time objects.  When the second parameter is a timeless date
+   * and the first parameter is date-with-time, strip the time and compare only
+   * the days.
+   *
+   * @private
+   * @param {ICAL.Time} a   The one object to compare
+   * @param {ICAL.Time} b   The other object to compare
+   */
+  _compare_special(a, b) {
+    if (!a.isDate && b.isDate)
+      return new Time({ year: a.year, month: a.month, day: a.day }).compare(b);
+    return a.compare(b);
+  }
+
   /**
    * Retrieve the next occurrence in the series.
    * @return {ICAL.Time}
@@ -248,9 +263,10 @@ class RecurExpansion {
 
       // check the negative rules
       if (this.exDate) {
-        compare = this.exDate.compare(this.last);
+        //EXDATE can be in DATE format, but DTSTART is in DATE-TIME format
+        compare = this._compare_special(this.last, this.exDate);
 
-        if (compare < 0) {
+        if (compare > 0) {
           this._nextExDay();
         }
 
@@ -397,10 +413,12 @@ class RecurExpansion {
     if (component.hasProperty('exdate')) {
       this.exDates = this._extractDates(component, 'exdate');
       // if we have a .last day we increment the index to beyond it.
+      // When DTSTART is in DATE-TIME format, EXDATE is in DATE format and EXDATE is
+      // the date of DTSTART, _compare_special finds this out and compareTime fails.
       this.exDateInc = binsearchInsert(
         this.exDates,
         this.last,
-        (a, b) => a.compare(b)
+        this._compare_special
       );
 
       this.exDate = this.exDates[this.exDateInc];

samples/rdate_exdate.ics

@@ -0,0 +1,8 @@
+BEGIN:VCALENDAR
+BEGIN:VEVENT
+UID:123
+DTSTART:20240609T030000Z
+RRULE:FREQ=DAILY;INTERVAL=1;COUNT=4
+EXDATE;VALUE=DATE:20240611
+END:VEVENT
+END:VCALENDAR

test/recur_expansion_test.js

@@ -329,4 +329,17 @@ suite('recur_expansion', function() {
 
   });
 
+  suite('EXDATE and DTSTART have different value type', function() {
+    createSubject('rdate_exdate.ics');
+    test('Compare EXDATE;VALUE=DATE and DTSTART;VALUE=DATE-TIME', function() {
+      let dates = [], next;
+      while ((next = subject.next()))
+        dates.push(next.toJSDate());
+      assert.deepEqual(dates, [
+        new Date('2024-06-09T03:00:00.000Z'),
+        new Date('2024-06-10T03:00:00.000Z'),
+        new Date('2024-06-12T03:00:00.000Z')
+      ]);
+    });
+  });
 });