Avoid infinite recursion in BeanValidationBeanRegistrationAotProcessor

Prior to this commit, AOT processing for bean validation failed with a
StackOverflowError for constraints with fields having recursive generic
types.

With this commit, the algorithm tracks visited classes and aborts
preemptively when a cycle is detected.

Closes gh-33950

Co-authored-by: Sam Brannen <sam.brannen@broadcom.com>

spring-context/src/main/java/org/springframework/validation/beanvalidation/BeanValidationBeanRegistrationAotProcessor.java

@@ -18,7 +18,6 @@ package org.springframework.validation.beanvalidation;
 
 import java.util.Collection;
 import java.util.HashSet;
-import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
@@ -104,10 +103,11 @@ class BeanValidationBeanRegistrationAotProcessor implements BeanRegistrationAotP
 			}
 
 			Class<?> beanClass = registeredBean.getBeanClass();
+			Set<Class<?>> visitedClasses = new HashSet<>();
 			Set<Class<?>> validatedClasses = new HashSet<>();
 			Set<Class<? extends ConstraintValidator<?, ?>>> constraintValidatorClasses = new HashSet<>();
 
-			processAheadOfTime(beanClass, validatedClasses, constraintValidatorClasses);
+			processAheadOfTime(beanClass, visitedClasses, validatedClasses, constraintValidatorClasses);
 
 			if (!validatedClasses.isEmpty() || !constraintValidatorClasses.isEmpty()) {
 				return new AotContribution(validatedClasses, constraintValidatorClasses);
@@ -115,9 +115,12 @@ class BeanValidationBeanRegistrationAotProcessor implements BeanRegistrationAotP
 			return null;
 		}
 
-		private static void processAheadOfTime(Class<?> clazz, Collection<Class<?>> validatedClasses,
-				Collection<Class<? extends ConstraintValidator<?, ?>>> constraintValidatorClasses) {
+		private static void processAheadOfTime(Class<?> clazz, Set<Class<?>> visitedClasses, Set<Class<?>> validatedClasses,
+				Set<Class<? extends ConstraintValidator<?, ?>>> constraintValidatorClasses) {
 
+			if (!visitedClasses.add(clazz)) {
+				return;
+			}
 			Assert.notNull(validator, "Validator can't be null");
 
 			BeanDescriptor descriptor;
@@ -149,12 +152,12 @@ class BeanValidationBeanRegistrationAotProcessor implements BeanRegistrationAotP
 
 			ReflectionUtils.doWithFields(clazz, field -> {
 				Class<?> type = field.getType();
-				if (Iterable.class.isAssignableFrom(type) || List.class.isAssignableFrom(type) || Optional.class.isAssignableFrom(type)) {
+				if (Iterable.class.isAssignableFrom(type) || Optional.class.isAssignableFrom(type)) {
 					ResolvableType resolvableType = ResolvableType.forField(field);
 					Class<?> genericType = resolvableType.getGeneric(0).toClass();
 					if (shouldProcess(genericType)) {
 						validatedClasses.add(clazz);
-						processAheadOfTime(genericType, validatedClasses, constraintValidatorClasses);
+						processAheadOfTime(genericType, visitedClasses, validatedClasses, constraintValidatorClasses);
 					}
 				}
 				if (Map.class.isAssignableFrom(type)) {
@@ -163,11 +166,11 @@ class BeanValidationBeanRegistrationAotProcessor implements BeanRegistrationAotP
 					Class<?> valueGenericType = resolvableType.getGeneric(1).toClass();
 					if (shouldProcess(keyGenericType)) {
 						validatedClasses.add(clazz);
-						processAheadOfTime(keyGenericType, validatedClasses, constraintValidatorClasses);
+						processAheadOfTime(keyGenericType, visitedClasses, validatedClasses, constraintValidatorClasses);
 					}
 					if (shouldProcess(valueGenericType)) {
 						validatedClasses.add(clazz);
-						processAheadOfTime(valueGenericType, validatedClasses, constraintValidatorClasses);
+						processAheadOfTime(valueGenericType, visitedClasses, validatedClasses, constraintValidatorClasses);
 					}
 				}
 			});

spring-context/src/test/java/org/springframework/validation/beanvalidation/BeanValidationBeanRegistrationAotProcessorTests.java

@@ -22,6 +22,9 @@ import java.lang.annotation.Retention;
 import java.lang.annotation.Target;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
 
 import jakarta.validation.Constraint;
 import jakarta.validation.ConstraintValidator;
@@ -31,6 +34,8 @@ import jakarta.validation.Valid;
 import jakarta.validation.constraints.Pattern;
 import org.hibernate.validator.internal.constraintvalidators.bv.PatternValidator;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 
 import org.springframework.aot.generate.GenerationContext;
 import org.springframework.aot.hint.MemberCategory;
@@ -121,6 +126,15 @@ class BeanValidationBeanRegistrationAotProcessorTests {
 				.withMemberCategory(MemberCategory.INVOKE_DECLARED_CONSTRUCTORS)).accepts(this.generationContext.getRuntimeHints());
 	}
 
+	@ParameterizedTest  // gh-33936
+	@ValueSource(classes = {BeanWithIterable.class, BeanWithMap.class, BeanWithOptional.class})
+	void shouldProcessRecursiveGenericsWithoutInfiniteRecursion(Class<?> beanClass) {
+		process(beanClass);
+		assertThat(this.generationContext.getRuntimeHints().reflection().typeHints()).hasSize(1);
+		assertThat(RuntimeHintsPredicates.reflection().onType(beanClass)
+				.withMemberCategory(MemberCategory.DECLARED_FIELDS)).accepts(this.generationContext.getRuntimeHints());
+	}
+
 	private void process(Class<?> beanClass) {
 		BeanRegistrationAotContribution contribution = createContribution(beanClass);
 		if (contribution != null) {
@@ -244,4 +258,16 @@ class BeanValidationBeanRegistrationAotProcessorTests {
 		}
 	}
 
+	static class BeanWithIterable {
+		private final Iterable<BeanWithIterable> beans = Set.of();
+	}
+
+	static class BeanWithMap {
+		private final Map<String, BeanWithMap> beans = Map.of();
+	}
+
+	static class BeanWithOptional {
+		private final Optional<BeanWithOptional> beans = Optional.empty();
+	}
+
 }