Improve failure analysis with a single bean cycle

See gh-26292

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/diagnostics/analyzer/BeanCurrentlyInCreationFailureAnalyzer.java

@@ -74,7 +74,7 @@ class BeanCurrentlyInCreationFailureAnalyzer extends AbstractFailureAnalyzer<Bea
 		for (int i = 0; i < beansInCycle.size(); i++) {
 			BeanInCycle beanInCycle = beansInCycle.get(i);
 			if (i == cycleStart) {
-				message.append(String.format("┌─────┐%n"));
+				message.append(String.format((beansInCycle.size() == 1) ? "┌──->──┐%n" : "┌─────┐%n"));
 			}
 			else if (i > 0) {
 				String leftSide = (i < cycleStart) ? " " : "↑";
@@ -83,7 +83,7 @@ class BeanCurrentlyInCreationFailureAnalyzer extends AbstractFailureAnalyzer<Bea
 			String leftSide = (i < cycleStart) ? " " : "|";
 			message.append(String.format("%s  %s%n", leftSide, beanInCycle));
 		}
-		message.append(String.format("└─────┘%n"));
+		message.append(String.format((beansInCycle.size() == 1) ? "└──<-──┘%n" : "└─────┘%n"));
 		return message.toString();
 	}
 

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/BeanCurrentlyInCreationFailureAnalyzerTests.java

@@ -109,6 +109,19 @@ class BeanCurrentlyInCreationFailureAnalyzerTests {
 		assertThat(lines.get(11)).isEqualTo("└─────┘");
 	}
 
+	@Test
+	void testSelfReferenceCycle() throws IOException {
+		FailureAnalysis analysis = performAnalysis(SelfReferenceBeanConfiguration.class);
+		List<String> lines = readDescriptionLines(analysis);
+		assertThat(lines).hasSize(5);
+		assertThat(lines.get(0))
+				.isEqualTo("The dependencies of some of the beans in the application context form a cycle:");
+		assertThat(lines.get(1)).isEqualTo("");
+		assertThat(lines.get(2)).isEqualTo("┌──->──┐");
+		assertThat(lines.get(3)).startsWith("|  bean defined in " + SelfReferenceBeanConfiguration.class.getName());
+		assertThat(lines.get(4)).isEqualTo("└──<-──┘");
+	}
+
 	@Test
 	void cycleWithAnUnknownStartIsNotAnalyzed() {
 		assertThat(this.analyzer.analyze(new BeanCurrentlyInCreationException("test"))).isNull();
@@ -137,6 +150,7 @@ class BeanCurrentlyInCreationFailureAnalyzerTests {
 	}
 
 	@org.springframework.context.annotation.Configuration(proxyBeanMethods = false)
+	@SuppressWarnings("unused")
 	static class CyclicBeanMethodsConfiguration {
 
 		@Bean
@@ -167,6 +181,7 @@ class BeanCurrentlyInCreationFailureAnalyzerTests {
 	}
 
 	@Configuration(proxyBeanMethods = false)
+	@SuppressWarnings("unused")
 	static class CycleReferencedViaOtherBeansConfiguration {
 
 		@Bean
@@ -231,6 +246,7 @@ class BeanCurrentlyInCreationFailureAnalyzerTests {
 		@org.springframework.context.annotation.Configuration(proxyBeanMethods = false)
 		static class BeanThreeConfiguration {
 
+			@SuppressWarnings("unused")
 			@Bean
 			BeanThree three(BeanOne one) {
 				return new BeanThree();
@@ -240,6 +256,17 @@ class BeanCurrentlyInCreationFailureAnalyzerTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class SelfReferenceBeanConfiguration {
+
+		@SuppressWarnings("unused")
+		@Bean
+		SelfReferenceBean bean(SelfReferenceBean bean) {
+			return new SelfReferenceBean();
+		}
+
+	}
+
 	static class RefererOne {
 
 		@Autowired
@@ -266,4 +293,11 @@ class BeanCurrentlyInCreationFailureAnalyzerTests {
 
 	}
 
+	static class SelfReferenceBean {
+
+		@Autowired
+		SelfReferenceBean bean;
+
+	}
+
 }