Support nested annotations in ASM-based processing again

Spring Framework 5.0 introduced a regression in ASM-based annotation
processing. Specifically, nested annotations were no longer supported,
and component scanning resulted in an exception if a candidate
component was annotated with an annotation that contained nested
annotations.

This commit fixes this regression by introducing special handling in
AnnotationTypeMapping that supports extracting values from objects of
type TypeMappedAnnotation when necessary.

Closes gh-24375

spring-context/src/test/java/example/gh24375/AnnotatedComponent.java

@@ -19,6 +19,6 @@ package example.gh24375;
 import org.springframework.stereotype.Component;
 
 @Component
-@A(other = @B)
-public class MyComponent {
+@EnclosingAnnotation(nested2 = @NestedAnnotation)
+public class AnnotatedComponent {
 }

spring-context/src/test/java/example/gh24375/EnclosingAnnotation.java

@@ -25,11 +25,12 @@ import org.springframework.core.annotation.AliasFor;
 
 @Target(ElementType.TYPE)
 @Retention(RetentionPolicy.RUNTIME)
-public @interface A {
+public @interface EnclosingAnnotation {
 
-	@AliasFor("value")
-	B other() default @B;
+	@AliasFor("nested2")
+	NestedAnnotation nested1() default @NestedAnnotation;
+
+	@AliasFor("nested1")
+	NestedAnnotation nested2() default @NestedAnnotation;
 
-	@AliasFor("other")
-	B value() default @B;
 }

spring-context/src/test/java/example/gh24375/NestedAnnotation.java

@@ -23,7 +23,8 @@ import java.lang.annotation.Target;
 
 @Target(ElementType.ANNOTATION_TYPE)
 @Retention(RetentionPolicy.RUNTIME)
-public @interface B {
+public @interface NestedAnnotation {
 
 	String name() default "";
+
 }

spring-context/src/test/java/org/springframework/context/annotation/ClassPathScanningCandidateComponentProviderTests.java

@@ -21,7 +21,7 @@ import java.lang.annotation.RetentionPolicy;
 import java.util.Set;
 import java.util.regex.Pattern;
 
-import example.gh24375.MyComponent;
+import example.gh24375.AnnotatedComponent;
 import example.profilescan.DevComponent;
 import example.profilescan.ProfileAnnotatedComponent;
 import example.profilescan.ProfileMetaAnnotatedComponent;
@@ -39,7 +39,6 @@ import example.scannable.ServiceInvocationCounter;
 import example.scannable.StubFooDao;
 import example.scannable.sub.BarComponent;
 import org.aspectj.lang.annotation.Aspect;
-import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.annotation.AnnotatedGenericBeanDefinition;
@@ -503,12 +502,11 @@ public class ClassPathScanningCandidateComponentProviderTests {
 	}
 
 	@Test
-	@Disabled("Disabled until gh-24375 is resolved")
-	public void gh24375() {
+	public void componentScanningFindsComponentsAnnotatedWithAnnotationsContainingNestedAnnotations() {
 		ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(true);
-		Set<BeanDefinition> components = provider.findCandidateComponents(MyComponent.class.getPackage().getName());
+		Set<BeanDefinition> components = provider.findCandidateComponents(AnnotatedComponent.class.getPackage().getName());
 		assertThat(components).hasSize(1);
-		assertThat(components.iterator().next().getBeanClassName()).isEqualTo(MyComponent.class.getName());
+		assertThat(components.iterator().next().getBeanClassName()).isEqualTo(AnnotatedComponent.class.getName());
 	}