From 174d0e4576b1bbd8c8bdb9cee3bf6cf844715e5d Mon Sep 17 00:00:00 2001
From: Brian Clozel <brian.clozel@broadcom.com>
Date: Thu, 6 Feb 2025 18:27:07 +0100
Subject: [PATCH] Fix "Nth day of week" Quartz-style cron expressions

Prior to this commit, `CronExpression` would support Quartz-style
expressions with "Nth occurence of a  dayOfWeek" semantics by using the
`TemporalAdjusters.dayOfWeekInMonth` JDK support. This method will
return the Nth occurence starting with the month of the given temporal,
but in some cases will overflow to the next or previous month.
This behavior is not expected for our cron expression support.

This commit ensures that when an overflow happens (meaning, the
resulting date is not in the same month as the input temporal), we
should instead have another attempt at finding a valid month for this
expression.

Fixes gh-34360
---
 .../scheduling/support/QuartzCronField.java     | 14 +++++++++++---
 .../scheduling/support/CronExpressionTests.java | 17 ++++++++++++++++-
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/spring-context/src/main/java/org/springframework/scheduling/support/QuartzCronField.java b/spring-context/src/main/java/org/springframework/scheduling/support/QuartzCronField.java
index 8c0873d151..b49b49357c 100644
--- a/spring-context/src/main/java/org/springframework/scheduling/support/QuartzCronField.java
+++ b/spring-context/src/main/java/org/springframework/scheduling/support/QuartzCronField.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -317,8 +317,16 @@ final class QuartzCronField extends CronField {
 	private static TemporalAdjuster dayOfWeekInMonth(int ordinal, DayOfWeek dayOfWeek) {
 		TemporalAdjuster adjuster = TemporalAdjusters.dayOfWeekInMonth(ordinal, dayOfWeek);
 		return temporal -> {
-			Temporal result = adjuster.adjustInto(temporal);
-			return rollbackToMidnight(temporal, result);
+			// TemporalAdjusters can overflow to a different month
+			// in this case, attempt the same adjustment with the next/previous month
+			for (int i = 0; i < 12; i++) {
+				Temporal result = adjuster.adjustInto(temporal);
+				if (result.get(ChronoField.MONTH_OF_YEAR) == temporal.get(ChronoField.MONTH_OF_YEAR)) {
+					return rollbackToMidnight(temporal, result);
+				}
+				temporal = result;
+			}
+			return null;
 		};
 	}
 
diff --git a/spring-context/src/test/java/org/springframework/scheduling/support/CronExpressionTests.java b/spring-context/src/test/java/org/springframework/scheduling/support/CronExpressionTests.java
index 57372204cb..3c74291dc2 100644
--- a/spring-context/src/test/java/org/springframework/scheduling/support/CronExpressionTests.java
+++ b/spring-context/src/test/java/org/springframework/scheduling/support/CronExpressionTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -39,6 +39,7 @@ import static java.time.temporal.TemporalAdjusters.next;
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
+ * Tests for {@link CronExpression}.
  * @author Arjen Poutsma
  */
 class CronExpressionTests {
@@ -1092,6 +1093,20 @@ class CronExpressionTests {
 		assertThat(actual.getDayOfWeek()).isEqualTo(FRIDAY);
 	}
 
+	@Test
+	void quartz5thMondayOfTheMonthDayName() {
+		CronExpression expression = CronExpression.parse("0 0 0 ? * MON#5");
+
+		LocalDateTime last = LocalDateTime.of(2025, 1, 1, 0, 0, 0);
+
+		// first occurrence of 5 mondays in a month from last
+		LocalDateTime expected = LocalDateTime.of(2025, 3, 31, 0, 0, 0);
+		LocalDateTime actual = expression.next(last);
+		assertThat(actual).isNotNull();
+		assertThat(actual).isEqualTo(expected);
+		assertThat(actual.getDayOfWeek()).isEqualTo(MONDAY);
+	}
+
 	@Test
 	void quartzFifthWednesdayOfTheMonth() {
 		CronExpression expression = CronExpression.parse("0 0 0 ? * 3#5");