HHH-18819 Add test for issue

hibernate-core/src/test/java/org/hibernate/orm/test/metamodel/EmbeddableMetaModelTest.java

@@ -26,6 +26,8 @@
 		Person.class,
 		Measurement.class,
 		Height.class,
+		WeightClass.class,
+		Weight.class,
 } )
 public class EmbeddableMetaModelTest {
 	@Test
@@ -60,4 +62,18 @@ public void test(EntityManagerFactoryScope scope) {
 			assertNotNull( Measurement_.unit );
 		} );
 	}
+
+	@Test
+	@Jira( "https://hibernate.atlassian.net/browse/HHH-18819" )
+	public void testIdClass(EntityManagerFactoryScope scope) {
+		scope.inTransaction( entityManager -> {
+			final EmbeddableDomainType<Weight> embeddable = (EmbeddableDomainType<Weight>) entityManager.getMetamodel()
+					.embeddable( Weight.class );
+			assertNotNull( embeddable.getSuperType() );
+			assertEquals( MAPPED_SUPERCLASS, embeddable.getSuperType().getPersistenceType() );
+			assertEquals( Measurement.class, embeddable.getSuperType().getJavaType() );
+			assertNotNull( Weight_.weight );
+			assertNotNull( Measurement_.unit );
+		} );
+	}
 }

hibernate-core/src/test/java/org/hibernate/orm/test/metamodel/Weight.java

@@ -0,0 +1,15 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.orm.test.metamodel;
+
+import jakarta.persistence.Embeddable;
+
+/**
+ * @author Marco Belladelli
+ */
+@Embeddable
+public class Weight extends Measurement {
+	private float weight;
+}

hibernate-core/src/test/java/org/hibernate/orm/test/metamodel/WeightClass.java

@@ -0,0 +1,24 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.orm.test.metamodel;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.IdClass;
+
+/**
+ * @author Marco Belladelli
+ */
+@Entity
+@IdClass(Weight.class)
+public class WeightClass {
+	@Id
+	private String unit;
+
+	@Id
+	private float weight;
+
+	private String description;
+}