HHH-17661 add test for issue

tooling/metamodel-generator/src/test/java/org/hibernate/jpamodelgen/test/hhh17661/Entity.java

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+package org.hibernate.jpamodelgen.test.hhh17661;
+
+import jakarta.persistence.Id;
+import jakarta.persistence.MappedSuperclass;
+
+import java.io.Serializable;
+
+@MappedSuperclass
+public abstract class Entity implements Serializable {
+
+    @Id
+    private Long id;
+
+}

tooling/metamodel-generator/src/test/java/org/hibernate/jpamodelgen/test/hhh17661/HHH17661Test.java

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+package org.hibernate.jpamodelgen.test.hhh17661;
+
+import org.hibernate.jpamodelgen.test.util.CompilationTest;
+import org.hibernate.jpamodelgen.test.util.TestForIssue;
+import org.hibernate.jpamodelgen.test.util.TestUtil;
+import org.hibernate.jpamodelgen.test.util.WithClasses;
+import org.junit.Test;
+
+@TestForIssue(jiraKey = " HHH-17661")
+public class HHH17661Test extends CompilationTest {
+
+	@Test
+	@WithClasses({ Entity.class, Tree.class, TreeRelation.class })
+	@TestForIssue(jiraKey = " HHH-17661")
+	public void test() {
+		System.out.println( TestUtil.getMetaModelSourceAsString( Entity.class ) );
+		System.out.println( TestUtil.getMetaModelSourceAsString( Tree.class ) );
+		System.out.println( TestUtil.getMetaModelSourceAsString( TreeRelation.class ) );
+	}
+}

tooling/metamodel-generator/src/test/java/org/hibernate/jpamodelgen/test/hhh17661/Tree.java

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+package org.hibernate.jpamodelgen.test.hhh17661;
+
+import jakarta.persistence.CascadeType;
+import jakarta.persistence.FetchType;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.MappedSuperclass;
+import jakarta.persistence.OneToMany;
+
+import java.util.HashSet;
+import java.util.Set;
+
+@MappedSuperclass
+public abstract class Tree<T extends Tree<T, TR>, TR extends TreeRelation<T>> extends Entity {
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    private T parent;
+
+    @OneToMany(mappedBy = "parent")
+    private Set<TR> childRelation = new HashSet<>();
+
+    @OneToMany(mappedBy = "child", cascade = {CascadeType.ALL}, orphanRemoval = true)
+    private Set<TR> parentRelation = new HashSet<>();
+}

tooling/metamodel-generator/src/test/java/org/hibernate/jpamodelgen/test/hhh17661/TreeRelation.java

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+package org.hibernate.jpamodelgen.test.hhh17661;
+
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.MappedSuperclass;
+
+@MappedSuperclass
+public abstract class TreeRelation<T extends Tree<T, ? extends TreeRelation<T>>> extends Entity {
+
+    @ManyToOne(optional = false)
+    private T parent;
+
+    @ManyToOne(optional = false)
+    private T child;
+}