Allow @Aspect classes to extend concrete @Aspect classes

Closes gh-29830

spring-aop/src/main/java/org/springframework/aop/aspectj/annotation/AbstractAspectJAdvisorFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -20,7 +20,6 @@ import java.lang.annotation.Annotation;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
-import java.lang.reflect.Modifier;
 import java.util.Map;
 import java.util.StringTokenizer;
 
@@ -52,6 +51,7 @@ import org.springframework.lang.Nullable;
  * @author Rod Johnson
  * @author Adrian Colyer
  * @author Juergen Hoeller
+ * @author Sam Brannen
  * @since 2.0
  */
 public abstract class AbstractAspectJAdvisorFactory implements AspectJAdvisorFactory {
@@ -101,14 +101,6 @@ public abstract class AbstractAspectJAdvisorFactory implements AspectJAdvisorFac
 
 	@Override
 	public void validate(Class<?> aspectClass) throws AopConfigException {
-		// If the parent has the annotation and isn't abstract it's an error
-		Class<?> superclass = aspectClass.getSuperclass();
-		if (superclass.getAnnotation(Aspect.class) != null &&
-				!Modifier.isAbstract(superclass.getModifiers())) {
-			throw new AopConfigException("[" + aspectClass.getName() + "] cannot extend concrete aspect [" +
-					superclass.getName() + "]");
-		}
-
 		AjType<?> ajType = AjTypeSystem.getAjType(aspectClass);
 		if (!ajType.isAspect()) {
 			throw new NotAnAtAspectException(aspectClass);

spring-aop/src/test/java/org/springframework/aop/aspectj/annotation/AbstractAspectJAdvisorFactoryTests.java

@@ -482,6 +482,19 @@ abstract class AbstractAspectJAdvisorFactoryTests {
 		assertThat(aspect.invocations).containsExactly("around - start", "before", "after throwing", "after", "around - end");
 	}
 
+	@Test
+	void nonAbstractParentAspect() throws Exception {
+		IncrementingAspect aspect = new IncrementingAspect();
+
+		// Precondition:
+		assertThat(Modifier.isAbstract(aspect.getClass().getSuperclass().getModifiers())).isFalse();
+
+		List<Advisor> advisors = getAdvisorFactory().getAdvisors(aspectInstanceFactory(aspect, "incrementingAspect"));
+
+		ITestBean proxy = createProxy(new TestBean("Jane", 42), ITestBean.class, advisors);
+		assertThat(proxy.getAge()).isEqualTo(86); // (42 + 1) * 2
+	}
+
 	@Test
 	void failureWithoutExplicitDeclarePrecedence() {
 		TestBean target = new TestBean();
@@ -748,6 +761,26 @@ abstract class AbstractAspectJAdvisorFactoryTests {
 	}
 
 
+	@Aspect
+	class DoublingAspect {
+
+		@Around("execution(* getAge())")
+		public Object doubleAge(ProceedingJoinPoint pjp) throws Throwable {
+			return ((int) pjp.proceed()) * 2;
+		}
+	}
+
+	@Aspect
+	class IncrementingAspect extends DoublingAspect {
+
+		@Around("execution(* getAge())")
+		public int incrementAge(ProceedingJoinPoint pjp) throws Throwable {
+			return ((int) pjp.proceed()) + 1;
+		}
+	}
+
+
+
 	@Aspect
 	private static class InvocationTrackingAspect {