Avoid proxy replacement for generic return type signatures

Issue: SPR-15010

spring-aop/src/main/java/org/springframework/aop/framework/CglibAopProxy.java

@@ -351,7 +351,8 @@ class CglibAopProxy implements AopProxy, Serializable {
 	 */
 	private static Object processReturnType(Object proxy, Object target, Method method, Object retVal) {
 		// Massage return value if necessary
-		if (retVal != null && retVal == target && !RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
+		if (retVal != null && retVal == target &&
+				!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
 			// Special case: it returned "this". Note that we can't help
 			// if the target sets a reference to itself in another returned object.
 			retVal = proxy;

spring-aop/src/main/java/org/springframework/aop/framework/JdkDynamicAopProxy.java

@@ -215,7 +215,8 @@ final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializa
 
 			// Massage return value if necessary.
 			Class<?> returnType = method.getReturnType();
-			if (retVal != null && retVal == target && returnType.isInstance(proxy) &&
+			if (retVal != null && retVal == target &&
+					returnType != Object.class && returnType.isInstance(proxy) &&
 					!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
 				// Special case: it returned "this" and the return type of the method
 				// is type-compatible. Note that we can't help if the target sets

spring-orm/src/test/java/org/springframework/orm/jpa/hibernate/HibernateEntityManagerFactoryIntegrationTests.java

@@ -16,10 +16,16 @@
 
 package org.springframework.orm.jpa.hibernate;
 
+import javax.persistence.EntityManager;
+
 import org.hibernate.Session;
 import org.hibernate.SessionFactory;
+import org.hibernate.jpa.HibernateEntityManager;
+import org.hibernate.jpa.HibernateEntityManagerFactory;
 import org.junit.Test;
 
+import org.springframework.aop.framework.ProxyFactory;
+import org.springframework.aop.target.SingletonTargetSource;
 import org.springframework.orm.jpa.AbstractContainerEntityManagerFactoryIntegrationTests;
 import org.springframework.orm.jpa.EntityManagerFactoryInfo;
 import org.springframework.orm.jpa.EntityManagerProxy;
@@ -32,6 +38,7 @@ import static org.junit.Assert.*;
  * @author Juergen Hoeller
  * @author Rod Johnson
  */
+@SuppressWarnings("deprecation")
 public class HibernateEntityManagerFactoryIntegrationTests extends AbstractContainerEntityManagerFactoryIntegrationTests {
 
 	@Override
@@ -43,12 +50,25 @@ public class HibernateEntityManagerFactoryIntegrationTests extends AbstractConta
 	@Test
 	public void testCanCastNativeEntityManagerFactoryToHibernateEntityManagerFactoryImpl() {
 		EntityManagerFactoryInfo emfi = (EntityManagerFactoryInfo) entityManagerFactory;
+		assertTrue(emfi.getNativeEntityManagerFactory() instanceof HibernateEntityManagerFactory);
 		assertTrue(emfi.getNativeEntityManagerFactory() instanceof SessionFactory);  // as of Hibernate 5.2
 	}
 
 	@Test
 	public void testCanCastSharedEntityManagerProxyToHibernateEntityManager() {
+		assertTrue(sharedEntityManager instanceof HibernateEntityManager);
 		assertTrue(((EntityManagerProxy) sharedEntityManager).getTargetEntityManager() instanceof Session);  // as of Hibernate 5.2
 	}
 
+	@Test
+	public void testCanUnwrapAopProxy() {
+		EntityManager em = entityManagerFactory.createEntityManager();
+		EntityManager proxy = ProxyFactory.getProxy(EntityManager.class, new SingletonTargetSource(em));
+		assertTrue(em instanceof HibernateEntityManager);
+		assertFalse(proxy instanceof HibernateEntityManager);
+		assertTrue(proxy.unwrap(HibernateEntityManager.class) instanceof HibernateEntityManager);
+		assertSame(em, proxy.unwrap(HibernateEntityManager.class));
+		assertSame(em.getDelegate(), proxy.getDelegate());
+	}
+
 }