HHH-7686 Clarify and test initialization code in the writeReplace() method in proxies

If we copy the behavior of "traditional" (non-map) proxies to the
"dynamic-map" proxies, we'd better know what this behavior is and be
sure it works correctly.

hibernate-core/src/main/java/org/hibernate/proxy/AbstractLazyInitializer.java

@@ -233,6 +233,26 @@ public abstract class AbstractLazyInitializer implements LazyInitializer {
 		}
 	}
 
+	/**
+	 * Attempt to initialize the proxy without loading anything from the database.
+	 *
+	 * This will only have any effect if the proxy is still attached to a session,
+	 * and the entity being proxied has been loaded and added to the persistence context
+	 * of that session since the proxy was created.
+	 */
+	protected final void initializeWithoutLoadIfPossible() {
+		if ( !initialized && session != null && session.isOpen() ) {
+			final EntityKey key = session.generateEntityKey(
+					getIdentifier(),
+					session.getFactory().getMetamodel().entityPersister( getEntityName() )
+			);
+			final Object entity = session.getPersistenceContext().getEntity( key );
+			if ( entity != null ) {
+				setImplementation( entity );
+			}
+		}
+	}
+
 	/**
 	 * Initialize internal state based on the currently attached session,
 	 * in order to be ready to load data even after the proxy is detached from the session.

hibernate-core/src/main/java/org/hibernate/proxy/pojo/BasicLazyInitializer.java

@@ -9,7 +9,6 @@ package org.hibernate.proxy.pojo;
 import java.io.Serializable;
 import java.lang.reflect.Method;
 
-import org.hibernate.engine.spi.EntityKey;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.internal.util.MarkerObject;
 import org.hibernate.proxy.AbstractLazyInitializer;
@@ -91,17 +90,11 @@ public abstract class BasicLazyInitializer extends AbstractLazyInitializer {
 	}
 
 	private Object getReplacement() {
-		final SharedSessionContractImplementor session = getSession();
-		if ( isUninitialized() && session != null && session.isOpen() ) {
-			final EntityKey key = session.generateEntityKey(
-					getIdentifier(),
-					session.getFactory().getMetamodel().entityPersister( getEntityName() )
-			);
-			final Object entity = session.getPersistenceContext().getEntity( key );
-			if ( entity != null ) {
-				setImplementation( entity );
-			}
-		}
+		/*
+		 * If the target has already been loaded somewhere, just not set on the proxy,
+		 * then use it to initialize the proxy so that we will serialize that instead of the proxy.
+		 */
+		initializeWithoutLoadIfPossible();
 
 		if ( isUninitialized() ) {
 			if ( replacement == null ) {

hibernate-core/src/test/java/org/hibernate/serialization/EntityProxySerializationTest.java

@@ -8,6 +8,7 @@ package org.hibernate.serialization;
 
 import java.io.Serializable;
 import java.util.HashSet;
+import java.util.Map;
 import java.util.Set;
 import javax.persistence.Entity;
 import javax.persistence.FetchType;
@@ -94,6 +95,86 @@ public class EntityProxySerializationTest extends BaseCoreFunctionalTestCase {
 		}
 	}
 
+	/**
+	 * Tests that serializing an initialized proxy will serialize the target instead.
+	 */
+	@SuppressWarnings("unchecked")
+	@Test
+	public void testInitializedProxySerializationIfTargetInPersistenceContext() {
+		final Session s = openSession();
+
+		final Transaction t = s.beginTransaction();
+		try {
+			final ChildEntity child = s.find( ChildEntity.class, 1L );
+
+			final SimpleEntity parent = child.getParent();
+
+			// assert we have an uninitialized proxy
+			assertTrue( parent instanceof HibernateProxy );
+			assertFalse( Hibernate.isInitialized( parent ) );
+
+			// Initialize the proxy
+			parent.getName();
+			assertTrue( Hibernate.isInitialized( parent ) );
+
+			// serialize/deserialize the proxy
+			final SimpleEntity deserializedParent = (SimpleEntity) SerializationHelper.clone( parent );
+
+			// assert the deserialized object is no longer a proxy, but the target of the proxy
+			assertFalse( deserializedParent instanceof HibernateProxy );
+			assertEquals( "TheParent", deserializedParent.getName() );
+		}
+		finally {
+			if ( t.isActive() ) {
+				t.rollback();
+			}
+			s.close();
+		}
+	}
+
+	/**
+	 * Tests that serializing a proxy which is not initialized
+	 * but whose target has been (separately) added to the persistence context
+	 * will serialize the target instead.
+	 */
+	@SuppressWarnings("unchecked")
+	@Test
+	public void testUninitializedProxySerializationIfTargetInPersistenceContext() {
+		final Session s = openSession();
+
+		final Transaction t = s.beginTransaction();
+		try {
+			final ChildEntity child = s.find( ChildEntity.class, 1L );
+
+			final SimpleEntity parent = child.getParent();
+
+			// assert we have an uninitialized proxy
+			assertTrue( parent instanceof HibernateProxy );
+			assertFalse( Hibernate.isInitialized( parent ) );
+
+			// Load the target of the proxy without the proxy being made aware of it
+			s.detach( parent );
+			s.find( SimpleEntity.class, 1L );
+			s.update( parent );
+
+			// assert we still have an uninitialized proxy
+			assertFalse( Hibernate.isInitialized( parent ) );
+
+			// serialize/deserialize the proxy
+			final SimpleEntity deserializedParent = (SimpleEntity) SerializationHelper.clone( parent );
+
+			// assert the deserialized object is no longer a proxy, but the target of the proxy
+			assertFalse( deserializedParent instanceof HibernateProxy );
+			assertEquals( "TheParent", deserializedParent.getName() );
+		}
+		finally {
+			if ( t.isActive() ) {
+				t.rollback();
+			}
+			s.close();
+		}
+	}
+
 	/**
 	 * Tests that lazy loading without transaction nor open session is generally
 	 * working. The magic is done by {@link AbstractLazyInitializer} who opens a