Avoid classes with incomplete hierarchy in Hibernate Validator

As explained in quarkiverse/quarkus-poi#102, some classes cannot be loaded because of an incomplete hierarchy

extensions/hibernate-validator/deployment/src/main/java/io/quarkus/hibernate/validator/deployment/HibernateValidatorProcessor.java

@@ -562,10 +562,7 @@ public void build(
                                 jaxRsMethods,
                                 methodsWithInheritedValidation)));
 
-        Set<Class<?>> classesToBeValidated = new HashSet<>();
-        for (DotName className : classNamesToBeValidated) {
-            classesToBeValidated.add(recorderContext.classProxy(className.toString()));
-        }
+        Set<Class<?>> classesToBeValidated = toClassSet(classNamesToBeValidated);
 
         // Prevent the removal of ValueExtractor beans
         // and collect all classes implementing ValueExtractor (for use in HibernateValidatorRecorder)
@@ -574,10 +571,7 @@ public void build(
             valueExtractorClassNames.add(valueExtractorType.name());
         }
         unremovableBeans.produce(UnremovableBeanBuildItem.beanTypes(valueExtractorClassNames));
-        Set<Class<?>> valueExtractorClassProxies = new HashSet<>();
-        for (DotName className : valueExtractorClassNames) {
-            valueExtractorClassProxies.add(recorderContext.classProxy(className.toString()));
-        }
+        Set<Class<?>> valueExtractorClassProxies = toClassSet(valueExtractorClassNames);
 
         beanContainerListener
                 .produce(new BeanContainerListenerBuildItem(
@@ -590,6 +584,21 @@ public void build(
                                 hibernateValidatorBuildTimeConfig)));
     }
 
+    private static Set<Class<?>> toClassSet(Set<DotName> dotNameSet) {
+        Set<Class<?>> classSet = new HashSet<>(dotNameSet.size());
+        for (DotName className : dotNameSet) {
+            try {
+                Class<?> type = Class.forName(className.toString(), true, Thread.currentThread().getContextClassLoader());
+                // We call getCanonicalName() to make sure the class hierarchy can be loaded
+                LOG.debugf("Loading %s", type.getCanonicalName());
+                classSet.add(type);
+            } catch (NoClassDefFoundError | ClassNotFoundException e) {
+                LOG.debugf(e, "Unable to load class %s", className);
+            }
+        }
+        return classSet;
+    }
+
     @BuildStep
     void indexAdditionalConstrainedClasses(List<AdditionalConstrainedClassBuildItem> additionalConstrainedClasses,
             BuildProducer<AdditionalConstrainedClassesIndexBuildItem> additionalConstrainedClassesIndex) {

extensions/hibernate-validator/deployment/src/test/java/io/quarkus/hibernate/validator/test/ClassHierarchyTest.java

@@ -0,0 +1,65 @@
+package io.quarkus.hibernate.validator.test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.AbstractCollection;
+
+import jakarta.inject.Inject;
+import jakarta.validation.Valid;
+import jakarta.validation.Validator;
+
+import org.jboss.shrinkwrap.api.ShrinkWrap;
+import org.jboss.shrinkwrap.api.asset.ByteArrayAsset;
+import org.jboss.shrinkwrap.api.spec.JavaArchive;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.quarkus.test.QuarkusUnitTest;
+import net.bytebuddy.ByteBuddy;
+import net.bytebuddy.dynamic.DynamicType;
+
+public class ClassHierarchyTest {
+
+    @RegisterExtension
+    static final QuarkusUnitTest test = new QuarkusUnitTest().setArchiveProducer(() -> ShrinkWrap
+            .create(JavaArchive.class)
+            .add(new ByteArrayAsset(createFooClass()), "InnerClass.class")
+            .addClass(Dto.class));
+
+    private static byte[] createFooClass() {
+        // Create the outer class
+        try (DynamicType.Unloaded<?> superClass = new ByteBuddy()
+                .subclass(Object.class)
+                .name("SuperClass")
+                .make();
+                DynamicType.Unloaded<?> outerClass = new ByteBuddy()
+                        .subclass(superClass.getTypeDescription())
+                        .name("OuterClass")
+                        .make();
+                DynamicType.Unloaded<?> innerClass = new ByteBuddy()
+                        .subclass(AbstractCollection.class)
+                        .innerTypeOf(outerClass.getTypeDescription())
+                        .name("InnerClass")
+                        .make();
+                DynamicType.Loaded<?> load = innerClass.load(Thread.currentThread().getContextClassLoader())) {
+            return load.getBytes();
+        }
+    }
+
+    @Inject
+    Validator validator;
+
+    @Test
+    public void doNotFailWhenLoadingIncompleteClassHierarchy() {
+        assertThat(validator).isNotNull();
+    }
+
+    @Valid
+    public static class Dto {
+        String name;
+
+        // XMLBean.ErrorLogger is a subclass with an incomplete hierarchy
+        @Valid
+        AbstractCollection<String> items;
+    }
+}