From c4f1888e42d596296b0319cd65d5e8dbf26b758d Mon Sep 17 00:00:00 2001
From: Markus Minichmayr <markus@tapkey.com>
Date: Sun, 20 Oct 2024 22:38:28 +0200
Subject: [PATCH] RRULE Evaluation: Apply `BYYEARDAY=366` only in leap years.

---
 Ical.Net/Evaluation/RecurrencePatternEvaluator.cs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Ical.Net/Evaluation/RecurrencePatternEvaluator.cs b/Ical.Net/Evaluation/RecurrencePatternEvaluator.cs
index 937c9455..dc466fe0 100644
--- a/Ical.Net/Evaluation/RecurrencePatternEvaluator.cs
+++ b/Ical.Net/Evaluation/RecurrencePatternEvaluator.cs
@@ -467,7 +467,9 @@ private List<DateTime> GetYearDayVariants(List<DateTime> dates, RecurrencePatter
                     var date1 = date;
                     yearDayDates.AddRange(pattern.ByYearDay.Select(yearDay => yearDay > 0
                         ? date1.AddDays(-date1.DayOfYear + yearDay)
-                        : date1.AddDays(-date1.DayOfYear + 1).AddYears(1).AddDays(yearDay)));
+                        : date1.AddDays(-date1.DayOfYear + 1).AddYears(1).AddDays(yearDay))
+                        // Ignore the BY values that don't fit into the current year (i.e. +-366 in non-leap-years).
+                        .Where(d => d.Year == date1.Year));
                 }
                 return yearDayDates;
             }
@@ -483,7 +485,7 @@ private List<DateTime> GetYearDayVariants(List<DateTime> dates, RecurrencePatter
                         ? date.AddDays(-date.DayOfYear + yearDay)
                         : date.AddDays(-date.DayOfYear + 1).AddYears(1).AddDays(yearDay);
 
-                    if (newDate.DayOfYear == date.DayOfYear)
+                    if (newDate.Date == date.Date)
                     {
                         goto Next;
                     }