Register Hibernate `@EmbeddableInstantiator` reflection hints

This commit updates PersistenceManagedTypesBeanRegistrationAotProcessor
to register reflection hints for `@EmbeddableInstantiator` annotations
available as of Hibernate 6.0 when needed.

Related tests will be added in
https://github.com/spring-projects/spring-aot-smoke-tests.

Closes gh-31534

spring-orm/src/main/java/org/springframework/orm/jpa/persistenceunit/PersistenceManagedTypesBeanRegistrationAotProcessor.java

@@ -23,6 +23,7 @@ import javax.lang.model.element.Modifier;
 
 import jakarta.persistence.Convert;
 import jakarta.persistence.Converter;
+import jakarta.persistence.Embedded;
 import jakarta.persistence.EntityListeners;
 import jakarta.persistence.IdClass;
 import jakarta.persistence.PostLoad;
@@ -64,11 +65,26 @@ import org.springframework.util.ReflectionUtils;
  * @author Sebastien Deleuze
  * @since 6.0
  */
+@SuppressWarnings("unchecked")
 class PersistenceManagedTypesBeanRegistrationAotProcessor implements BeanRegistrationAotProcessor {
 
 	private static final List<Class<? extends Annotation>> CALLBACK_TYPES = List.of(PreUpdate.class,
 			PostUpdate.class, PrePersist.class, PostPersist.class, PreRemove.class, PostRemove.class, PostLoad.class);
 
+	@Nullable
+	private static Class<? extends Annotation> embeddableInstantiatorClass;
+
+	static {
+		try {
+			embeddableInstantiatorClass = (Class<? extends Annotation>) ClassUtils.forName("org.hibernate.annotations.EmbeddableInstantiator",
+					PersistenceManagedTypesBeanRegistrationAotProcessor.class.getClassLoader());
+		}
+		catch (ClassNotFoundException ex) {
+			embeddableInstantiatorClass = null;
+		}
+	}
+
+
 	@Nullable
 	@Override
 	public BeanRegistrationAotContribution processAheadOfTime(RegisteredBean registeredBean) {
@@ -129,6 +145,7 @@ class PersistenceManagedTypesBeanRegistrationAotProcessor implements BeanRegistr
 					contributeIdClassHints(hints, managedClass);
 					contributeConverterHints(hints, managedClass);
 					contributeCallbackHints(hints, managedClass);
+					contributeHibernateHints(hints, managedClass);
 				}
 				catch (ClassNotFoundException ex) {
 					throw new IllegalArgumentException("Failed to instantiate the managed class: " + managedClassName, ex);
@@ -176,5 +193,23 @@ class PersistenceManagedTypesBeanRegistrationAotProcessor implements BeanRegistr
 					reflection.registerMethod(method, ExecutableMode.INVOKE),
 					method -> CALLBACK_TYPES.stream().anyMatch(method::isAnnotationPresent));
 		}
+
+		@SuppressWarnings("unchecked")
+		private void contributeHibernateHints(RuntimeHints hints, Class<?> managedClass) {
+			if (embeddableInstantiatorClass == null) {
+				return;
+			}
+			ReflectionHints reflection = hints.reflection();
+			ReflectionUtils.doWithFields(managedClass, field -> {
+				Embedded embeddedAnnotation = AnnotationUtils.findAnnotation(field, Embedded.class);
+				if (embeddedAnnotation != null && field.getAnnotatedType().getType() instanceof Class<?> embeddedClass) {
+						Annotation embeddableInstantiatorAnnotation = AnnotationUtils.findAnnotation(embeddedClass, embeddableInstantiatorClass);
+						if (embeddableInstantiatorAnnotation != null) {
+							Class<?> embeddableInstantiatorClass = (Class<?>) AnnotationUtils.getAnnotationAttributes(embeddableInstantiatorAnnotation).get("value");
+							reflection.registerType(embeddableInstantiatorClass, MemberCategory.INVOKE_DECLARED_CONSTRUCTORS);
+						}
+				}
+			});
+		}
 	}
 }