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/src/main/java/org/springframework/boot/test/context/ImportsContextCustomizer.java

@@ -49,6 +49,7 @@ import org.springframework.test.context.MergedContextConfiguration;
  * test classes.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  * @see ImportsContextCustomizerFactory
  */
 class ImportsContextCustomizer implements ContextCustomizer {
@@ -217,27 +218,31 @@ class ImportsContextCustomizer implements ContextCustomizer {
 
 		ContextCustomizerKey(Class<?> testClass) {
 			Set<Annotation> annotations = new HashSet<Annotation>();
-			collectClassAnnotations(testClass, annotations);
+			Set<Class<?>> seen = new HashSet<Class<?>>();
+			collectClassAnnotations(testClass, annotations, seen);
 			this.annotations = Collections.unmodifiableSet(annotations);
 		}
 
 		private void collectClassAnnotations(Class<?> classType,
-				Set<Annotation> annotations) {
-			collectElementAnnotations(classType, annotations);
-			for (Class<?> interfaceType : classType.getInterfaces()) {
-				collectClassAnnotations(interfaceType, annotations);
-			}
-			if (classType.getSuperclass() != null) {
-				collectClassAnnotations(classType.getSuperclass(), annotations);
+				Set<Annotation> annotations, Set<Class<?>> seen) {
+			if (seen.add(classType)) {
+				collectElementAnnotations(classType, annotations, seen);
+				for (Class<?> interfaceType : classType.getInterfaces()) {
+					collectClassAnnotations(interfaceType, annotations, seen);
+				}
+				if (classType.getSuperclass() != null) {
+					collectClassAnnotations(classType.getSuperclass(), annotations, seen);
+				}
 			}
 		}
 
 		private void collectElementAnnotations(AnnotatedElement element,
-				Set<Annotation> annotations) {
+				Set<Annotation> annotations, Set<Class<?>> seen) {
 			for (Annotation annotation : element.getDeclaredAnnotations()) {
 				if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation)) {
 					annotations.add(annotation);
-					collectClassAnnotations(annotation.annotationType(), annotations);
+					collectClassAnnotations(annotation.annotationType(), annotations,
+							seen);
 				}
 			}
 		}

spring-boot-test/src/test/java/org/springframework/boot/test/context/ImportsContextCustomizerFactoryTests.java

@@ -37,6 +37,7 @@ import static org.mockito.Mockito.mock;
  * Tests for {@link ImportsContextCustomizerFactory} and {@link ImportsContextCustomizer}.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  */
 public class ImportsContextCustomizerFactoryTests {
 
@@ -101,6 +102,12 @@ public class ImportsContextCustomizerFactoryTests {
 		assertThat(context.getBean(ImportedBean.class)).isNotNull();
 	}
 
+	@Test
+	public void selfAnnotatingAnnotationDoesNotCauseStackOverflow() {
+		assertThat(this.factory.createContextCustomizer(
+				TestWithImportAndSelfAnnotatingAnnotation.class, null)).isNotNull();
+	}
+
 	static class TestWithNoImport {
 
 	}
@@ -137,6 +144,12 @@ public class ImportsContextCustomizerFactoryTests {
 
 	}
 
+	@SelfAnnotating
+	@Import(ImportedBean.class)
+	static class TestWithImportAndSelfAnnotatingAnnotation {
+
+	}
+
 	@Retention(RetentionPolicy.RUNTIME)
 	@Import(ImportedBean.class)
 	@interface MetaImport {
@@ -153,4 +166,10 @@ public class ImportsContextCustomizerFactoryTests {
 
 	}
 
+	@Retention(RetentionPolicy.RUNTIME)
+	@SelfAnnotating
+	static @interface SelfAnnotating {
+
+	}
+
 }