Message Title

Trying to upgrade a project from Hibernate 5 to 6 I run into the following issue:

class ….MyEmbeddable cannot be cast to class org.hibernate.usertype.CompositeUserType (….MyEmbeddable and org.hibernate.usertype.CompositeUserType are in unnamed module of loader 'app')
	at org.hibernate.type.ComponentType.<init>(ComponentType.java:113) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]
	at org.hibernate.mapping.Component.getType(Component.java:255) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]
	at org.hibernate.metamodel.internal.AttributeFactory.determineAttributeMetadata(AttributeFactory.java:375) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]
	at org.hibernate.metamodel.internal.AttributeFactory.buildAttribute(AttributeFactory.java:111) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]
	at org.hibernate.metamodel.internal.AttributeFactory.buildAttribute(AttributeFactory.java:96) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]
	at org.hibernate.metamodel.internal.MetadataContext.wrapUp(MetadataContext.java:331) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]
	at org.hibernate.metamodel.model.domain.internal.JpaMetamodelImpl.processJpa(JpaMetamodelImpl.java:504) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]
	at org.hibernate.metamodel.model.domain.internal.MappingMetamodelImpl.finishInitialization(MappingMetamodelImpl.java:244) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]
	at org.hibernate.metamodel.internal.RuntimeMetamodelsImpl.finishInitialization(RuntimeMetamodelsImpl.java:60) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]
	at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:308) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]
	at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:415) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]
	at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:1425) ~[hibernate-core-6.1.3.Final.jar:6.1.3.Final]

@Embeddable
class MyEmbeddable { }

@MappedSuperclass
class SuperType<T> {
  MyEmbeddable embeddable;
}

@Entity
class ConcreteType<T> extends SuperType<T> { }

org.hibernate.cfg.ClassPropertyHolder.addPropertyToMappedSuperclass(Property, XClass) runs into a special branch of the code if the mapped superclass has generic parameters. In that case, it ultimately ends up calling setTypeName(…) with the type name of the embeddable as parameter. ComponentType later inspects that type name and tries to resolve it in its constructor, unconditionally casting it to CompositeUserType.