Protect against stack overflow when searching meta annotations

It is legal for an annotation to be annotated with itself. Previously,
when searching for meta annotations this could lead to a stack overflow.
This was likely to occur when using Kotlin as, like Java, its Target
annotation is annotated with itself. A stack overflow doesn’t occur
with Java’s Target annotation due to some short-circuiting logic for
annotations in java.lang.

This commit updates the logic for finding meta-annotations to
short-circuit when an annotation that has already been seen is
encountered.

Closes gh-5902

spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/properties/AnnotationsPropertySource.java

@@ -20,9 +20,11 @@ import java.lang.annotation.Annotation;
 import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -58,13 +60,13 @@ public class AnnotationsPropertySource extends EnumerablePropertySource<Class<?>
 
 	private Map<String, Object> getProperties(Class<?> source) {
 		Map<String, Object> properties = new LinkedHashMap<String, Object>();
-		collectProperties(source, source, properties);
+		collectProperties(source, source, properties, new HashSet<Class<?>>());
 		return Collections.unmodifiableMap(properties);
 	}
 
 	private void collectProperties(Class<?> root, Class<?> source,
-			Map<String, Object> properties) {
-		if (source != null) {
+			Map<String, Object> properties, Set<Class<?>> seen) {
+		if (source != null && seen.add(source)) {
 			for (Annotation annotation : getMergedAnnotations(root, source)) {
 				if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation)) {
 					PropertyMapping typeMapping = annotation.annotationType()
@@ -73,10 +75,11 @@ public class AnnotationsPropertySource extends EnumerablePropertySource<Class<?>
 							.getDeclaredMethods()) {
 						collectProperties(annotation, attribute, typeMapping, properties);
 					}
-					collectProperties(root, annotation.annotationType(), properties);
+					collectProperties(root, annotation.annotationType(), properties,
+							seen);
 				}
 			}
-			collectProperties(root, source.getSuperclass(), properties);
+			collectProperties(root, source.getSuperclass(), properties, seen);
 		}
 	}
 

spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/properties/AnnotationsPropertySourceTests.java

@@ -164,6 +164,11 @@ public class AnnotationsPropertySourceTests {
 		assertThat(source.getProperty("aliasing.value")).isEqualTo("baz");
 	}
 
+	@Test
+	public void selfAnnotatingAnnotationDoesNotCauseStackOverflow() {
+		new AnnotationsPropertySource(PropertyMappedWithSelfAnnotatingAnnotation.class);
+	}
+
 	static class NoAnnotation {
 
 	}
@@ -327,7 +332,9 @@ public class AnnotationsPropertySourceTests {
 	static @interface AttributeWithAliasAnnotation {
 
 		@AliasFor(annotation = AliasedAttributeAnnotation.class, attribute = "value")
-		String value() default "foo";
+		String value()
+
+		default "foo";
 
 		String someOtherAttribute() default "shouldNotBeMapped";
 
@@ -341,4 +348,15 @@ public class AnnotationsPropertySourceTests {
 
 	}
 
+	@Retention(RetentionPolicy.RUNTIME)
+	@SelfAnnotating
+	static @interface SelfAnnotating {
+
+	}
+
+	@SelfAnnotating
+	static class PropertyMappedWithSelfAnnotatingAnnotation {
+
+	}
+
 }