Add TYPE_HIERARCHY_AND_ENCLOSING_CLASSES strategy

Add a `TYPE_HIERARCHY_AND_ENCLOSING_CLASSES` annotation search strategy
that can be used to search the full type hierarchy as well as any
enclosing classes.

Closes gh-23378

spring-core/src/main/java/org/springframework/core/annotation/AnnotationsScanner.java

@@ -123,10 +123,12 @@ abstract class AnnotationsScanner {
 			case INHERITED_ANNOTATIONS:
 				return processClassInheritedAnnotations(context, source, processor, classFilter);
 			case SUPERCLASS:
-				return processClassHierarchy(context, new int[] {0}, source, processor, classFilter, false);
+				return processClassHierarchy(context, source, processor, classFilter, false, false);
 			case EXHAUSTIVE:
 			case TYPE_HIERARCHY:
-				return processClassHierarchy(context, new int[] {0}, source, processor, classFilter, true);
+				return processClassHierarchy(context, source, processor, classFilter, true, false);
+			case TYPE_HIERARCHY_AND_ENCLOSING_CLASSES:
+				return processClassHierarchy(context, source, processor, classFilter, true, true);
 		}
 		throw new IllegalStateException("Unsupported search strategy " + searchStrategy);
 	}
@@ -184,10 +186,22 @@ abstract class AnnotationsScanner {
 		return null;
 	}
 
+	@Nullable
+	private static <C, R> R processClassHierarchy(C context, Class<?> source,
+			AnnotationsProcessor<C, R> processor,
+			@Nullable BiPredicate<C, Class<?>> classFilter, boolean includeInterfaces,
+			boolean includeEnclosing) {
+
+		int[] aggregateIndex = new int[] { 0 };
+		return processClassHierarchy(context, aggregateIndex, source, processor,
+				classFilter, includeInterfaces, includeEnclosing);
+	}
+
 	@Nullable
 	private static <C, R> R processClassHierarchy(C context, int[] aggregateIndex,
 			Class<?> source, AnnotationsProcessor<C, R> processor,
-			@Nullable BiPredicate<C, Class<?>> classFilter, boolean includeInterfaces) {
+			@Nullable BiPredicate<C, Class<?>> classFilter, boolean includeInterfaces,
+			boolean includeEnclosing) {
 
 		R result = processor.doWithAggregate(context, aggregateIndex[0]);
 		if (result != null) {
@@ -205,7 +219,7 @@ abstract class AnnotationsScanner {
 		if (includeInterfaces) {
 			for (Class<?> interfaceType : source.getInterfaces()) {
 				R interfacesResult = processClassHierarchy(context, aggregateIndex,
-						interfaceType, processor, classFilter, true);
+						interfaceType, processor, classFilter, true, includeEnclosing);
 				if (interfacesResult != null) {
 					return interfacesResult;
 				}
@@ -214,11 +228,21 @@ abstract class AnnotationsScanner {
 		Class<?> superclass = source.getSuperclass();
 		if (superclass != Object.class && superclass != null) {
 			R superclassResult = processClassHierarchy(context, aggregateIndex,
-					superclass, processor, classFilter, includeInterfaces);
+					superclass, processor, classFilter, includeInterfaces,
+					includeEnclosing);
 			if (superclassResult != null) {
 				return superclassResult;
 			}
 		}
+		Class<?> enclosingClass = source.getEnclosingClass();
+		if (includeEnclosing && enclosingClass != null) {
+			R enclosingResult = processClassHierarchy(context, aggregateIndex,
+					enclosingClass, processor, classFilter, includeInterfaces,
+					includeEnclosing);
+			if (enclosingResult != null) {
+				return enclosingResult;
+			}
+		}
 		return null;
 	}
 
@@ -237,6 +261,7 @@ abstract class AnnotationsScanner {
 						processor, classFilter, source, false);
 			case EXHAUSTIVE:
 			case TYPE_HIERARCHY:
+			case TYPE_HIERARCHY_AND_ENCLOSING_CLASSES:
 				return processMethodHierarchy(context, new int[] {0}, source.getDeclaringClass(),
 						processor, classFilter, source, true);
 		}

spring-core/src/main/java/org/springframework/core/annotation/MergedAnnotations.java

@@ -434,12 +434,22 @@ public interface MergedAnnotations extends Iterable<MergedAnnotation<Annotation>
 		EXHAUSTIVE,
 
 		/**
-		 * Perform a full search of the entire type hierarchy , including
+		 * Perform a full search of the entire type hierarchy, including
 		 * superclasses and implemented interfaces. Superclass annotations do
 		 * not need to be meta-annotated with {@link Inherited @Inherited}.
 		 */
-		TYPE_HIERARCHY
+		TYPE_HIERARCHY,
 
+		/**
+		 * Perform a full search of the entire type hierarchy on the source
+		 * <em>and</em> any enclosing classes. This strategy is similar to
+		 * {@link #TYPE_HIERARCHY} except that {@link Class#getEnclosingClass()
+		 * enclosing classes} are also searched. Superclass annotations do not
+		 * need to be meta-annotated with {@link Inherited @Inherited}. When
+		 * searching a {@link Method} source, this strategy is identical to
+		 * {@link #TYPE_HIERARCHY}.
+		 */
+		TYPE_HIERARCHY_AND_ENCLOSING_CLASSES
 	}
 
 }

spring-core/src/test/java/org/springframework/core/annotation/AnnotationEnclosingClassSample.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2002-2019 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.annotation;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * Example class used to test {@link AnnotationsScanner} with enclosing classes.
+ *
+ * @author Phillip Webb
+ * @since 5.2
+ */
+@AnnotationEnclosingClassSample.EnclosedOne
+public class AnnotationEnclosingClassSample {
+
+	@EnclosedTwo
+	public static class EnclosedStatic {
+
+		@EnclosedThree
+		public static class EnclosedStaticStatic {
+
+		}
+
+	}
+
+	@EnclosedTwo
+	public class EnclosedInner {
+
+		@EnclosedThree
+		public class EnclosedInnerInner {
+
+		}
+
+	}
+
+	@Retention(RetentionPolicy.RUNTIME)
+	public static @interface EnclosedOne {
+
+	}
+
+	@Retention(RetentionPolicy.RUNTIME)
+	public static @interface EnclosedTwo {
+
+	}
+
+	@Retention(RetentionPolicy.RUNTIME)
+	public static @interface EnclosedThree {
+
+	}
+
+}

spring-core/src/test/java/org/springframework/core/annotation/AnnotationsScannerTests.java

@@ -454,6 +454,29 @@ public class AnnotationsScannerTests {
 				"0:TestAnnotation1");
 	}
 
+	@Test
+	public void typeHierarchyWithEnclosedStrategyOnEnclosedStaticClassScansAnnotations() {
+		Class<?> source = AnnotationEnclosingClassSample.EnclosedStatic.EnclosedStaticStatic.class;
+		assertThat(scan(source, SearchStrategy.TYPE_HIERARCHY_AND_ENCLOSING_CLASSES))
+				.containsExactly("0:EnclosedThree", "1:EnclosedTwo", "2:EnclosedOne");
+	}
+
+	@Test
+	public void typeHierarchyWithEnclosedStrategyOnEnclosedInnerClassScansAnnotations() {
+		Class<?> source = AnnotationEnclosingClassSample.EnclosedInner.EnclosedInnerInner.class;
+		assertThat(scan(source, SearchStrategy.TYPE_HIERARCHY_AND_ENCLOSING_CLASSES))
+				.containsExactly("0:EnclosedThree", "1:EnclosedTwo", "2:EnclosedOne");
+	}
+
+	@Test
+	public void typeHierarchyWithEnclosedStrategyOnMethodHierarchyUsesTypeHierarchyScan() {
+		Method source = methodFrom(WithHierarchy.class);
+		assertThat(scan(source, SearchStrategy.TYPE_HIERARCHY_AND_ENCLOSING_CLASSES)).containsExactly(
+				"0:TestAnnotation1", "1:TestAnnotation5", "1:TestInheritedAnnotation5",
+				"2:TestAnnotation6", "3:TestAnnotation2", "3:TestInheritedAnnotation2",
+				"4:TestAnnotation3", "5:TestAnnotation4");
+	}
+
 	@Test
 	public void scanWhenProcessorReturnsFromDoWithAggregateExitsEarly() {
 		String result = AnnotationsScanner.scan(this, WithSingleSuperclass.class,