Support cross-parameter validation

Closes gh-33271

Author: rstoyanchev

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

@@ -18,6 +18,7 @@
 
 import java.lang.reflect.Method;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Comparator;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
@@ -301,6 +302,7 @@ private MethodValidationResult adaptViolations(
 
 		Map<Path.Node, ParamValidationResultBuilder> paramViolations = new LinkedHashMap<>();
 		Map<Path.Node, ParamErrorsBuilder> nestedViolations = new LinkedHashMap<>();
+		List<MessageSourceResolvable> crossParamErrors = null;
 
 		for (ConstraintViolation<Object> violation : violations) {
 			Iterator<Path.Node> nodes = violation.getPropertyPath().iterator();
@@ -315,6 +317,11 @@ private MethodValidationResult adaptViolations(
 				else if (node.getKind().equals(ElementKind.RETURN_VALUE)) {
 					parameter = parameterFunction.apply(-1);
 				}
+				else if (node.getKind().equals(ElementKind.CROSS_PARAMETER)) {
+					crossParamErrors = (crossParamErrors != null ? crossParamErrors : new ArrayList<>());
+					crossParamErrors.add(createCrossParamError(target, method, violation));
+					break;
+				}
 				else {
 					continue;
 				}
@@ -382,7 +389,8 @@ else if (arg instanceof Optional<?> optional) {
 		nestedViolations.forEach((key, builder) -> resultList.add(builder.build()));
 		resultList.sort(resultComparator);
 
-		return MethodValidationResult.create(target, method, resultList);
+		return MethodValidationResult.create(target, method, resultList,
+				(crossParamErrors != null ? crossParamErrors : Collections.emptyList()));
 	}
 
 	private MethodParameter initMethodParameter(Method method, int index) {
@@ -413,6 +421,19 @@ private BindingResult createBindingResult(MethodParameter parameter, @Nullable O
 		return result;
 	}
 
+	private MessageSourceResolvable createCrossParamError(
+			Object target, Method method, ConstraintViolation<Object> violation) {
+
+		String objectName = Conventions.getVariableName(target) + "#" + method.getName();
+
+		ConstraintDescriptor<?> descriptor = violation.getConstraintDescriptor();
+		String code = descriptor.getAnnotation().annotationType().getSimpleName();
+		String[] codes = this.messageCodesResolver.resolveMessageCodes(code, objectName);
+		Object[] arguments = this.validatorAdapter.get().getArgumentsForConstraint(objectName, "", descriptor);
+
+		return new ViolationMessageSourceResolvable(codes, arguments, violation.getMessage(), violation);
+	}
+
 
 	/**
 	 * Strategy to resolve the name of an {@code @Valid} method parameter to

spring-context/src/main/java/org/springframework/validation/method/DefaultMethodValidationResult.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@
 import java.lang.reflect.Method;
 import java.util.List;
 
+import org.springframework.context.MessageSourceResolvable;
 import org.springframework.util.Assert;
 
 /**
@@ -33,19 +34,26 @@ final class DefaultMethodValidationResult implements MethodValidationResult {
 
 	private final Method method;
 
-	private final List<ParameterValidationResult> allValidationResults;
+	private final List<ParameterValidationResult> parameterValidationResults;
+
+	private final List<MessageSourceResolvable> crossParamResults;
 
 	private final boolean forReturnValue;
 
 
-	DefaultMethodValidationResult(Object target, Method method, List<ParameterValidationResult> results) {
-		Assert.notEmpty(results, "'results' is required and must not be empty");
+	DefaultMethodValidationResult(
+			Object target, Method method, List<ParameterValidationResult> results,
+			List<MessageSourceResolvable> crossParamResults) {
+
+		Assert.isTrue(!results.isEmpty() || !crossParamResults.isEmpty(), "Expected validation results");
 		Assert.notNull(target, "'target' is required");
 		Assert.notNull(method, "Method is required");
+
 		this.target = target;
 		this.method = method;
-		this.allValidationResults = results;
-		this.forReturnValue = (results.get(0).getMethodParameter().getParameterIndex() == -1);
+		this.parameterValidationResults = results;
+		this.crossParamResults = crossParamResults;
+		this.forReturnValue = (!results.isEmpty() && results.get(0).getMethodParameter().getParameterIndex() == -1);
 	}
 
 
@@ -65,10 +73,14 @@ public boolean isForReturnValue() {
 	}
 
 	@Override
-	public List<ParameterValidationResult> getAllValidationResults() {
-		return this.allValidationResults;
+	public List<ParameterValidationResult> getParameterValidationResults() {
+		return this.parameterValidationResults;
 	}
 
+	@Override
+	public List<MessageSourceResolvable> getCrossParameterValidationResults() {
+		return this.crossParamResults;
+	}
 
 	@Override
 	public String toString() {

spring-context/src/main/java/org/springframework/validation/method/EmptyMethodValidationResult.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,8 @@
 import java.util.Collections;
 import java.util.List;
 
+import org.springframework.context.MessageSourceResolvable;
+
 /**
  * {@link MethodValidationResult} with an empty list of results.
  *
@@ -44,7 +46,12 @@ public boolean isForReturnValue() {
 	}
 
 	@Override
-	public List<ParameterValidationResult> getAllValidationResults() {
+	public List<ParameterValidationResult> getParameterValidationResults() {
+		return Collections.emptyList();
+	}
+
+	@Override
+	public List<MessageSourceResolvable> getCrossParameterValidationResults() {
 		return Collections.emptyList();
 	}
 

spring-context/src/main/java/org/springframework/validation/method/MethodValidationException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@
 import java.lang.reflect.Method;
 import java.util.List;
 
+import org.springframework.context.MessageSourceResolvable;
 import org.springframework.util.Assert;
 
 /**
@@ -57,8 +58,13 @@ public boolean isForReturnValue() {
 	}
 
 	@Override
-	public List<ParameterValidationResult> getAllValidationResults() {
-		return this.validationResult.getAllValidationResults();
+	public List<ParameterValidationResult> getParameterValidationResults() {
+		return this.validationResult.getParameterValidationResults();
+	}
+
+	@Override
+	public List<MessageSourceResolvable> getCrossParameterValidationResults() {
+		return this.validationResult.getCrossParameterValidationResults();
 	}
 
 }

spring-context/src/main/java/org/springframework/validation/method/MethodValidationResult.java

@@ -17,6 +17,7 @@
 package org.springframework.validation.method;
 
 import java.lang.reflect.Method;
+import java.util.Collections;
 import java.util.List;
 
 import org.springframework.context.MessageSourceResolvable;
@@ -55,54 +56,75 @@ public interface MethodValidationResult {
 	 * Whether the result contains any validation errors.
 	 */
 	default boolean hasErrors() {
-		return !getAllValidationResults().isEmpty();
+		return !getParameterValidationResults().isEmpty();
 	}
 
 	/**
 	 * Return a single list with all errors from all validation results.
-	 * @see #getAllValidationResults()
+	 * @see #getParameterValidationResults()
 	 * @see ParameterValidationResult#getResolvableErrors()
 	 */
 	default List<? extends MessageSourceResolvable> getAllErrors() {
-		return getAllValidationResults().stream()
+		return getParameterValidationResults().stream()
 				.flatMap(result -> result.getResolvableErrors().stream())
 				.toList();
 	}
 
+	/**
+	 * Return all validation results per method parameter, including both
+	 * {@link #getValueResults()} and {@link #getBeanResults()}.
+	 * <p>Use {@link #getCrossParameterValidationResults()} for access to errors
+	 * from cross-parameter validation.
+	 * @since 6.2
+	 * @see #getValueResults()
+	 * @see #getBeanResults()
+	 */
+	List<ParameterValidationResult> getParameterValidationResults();
+
 	/**
 	 * Return all validation results. This includes both method parameters with
 	 * errors directly on them, and Object method parameters with nested errors
 	 * on their fields and properties.
 	 * @see #getValueResults()
 	 * @see #getBeanResults()
+	 * @deprecated deprecated in favor of {@link #getParameterValidationResults()}
 	 */
-	List<ParameterValidationResult> getAllValidationResults();
+	@Deprecated(since = "6.2", forRemoval = true)
+	default List<ParameterValidationResult> getAllValidationResults() {
+		return getParameterValidationResults();
+	}
 
 	/**
-	 * Return the subset of {@link #getAllValidationResults() allValidationResults}
+	 * Return the subset of {@link #getParameterValidationResults() allValidationResults}
 	 * that includes method parameters with validation errors directly on method
 	 * argument values. This excludes {@link #getBeanResults() beanResults} with
 	 * nested errors on their fields and properties.
 	 */
 	default List<ParameterValidationResult> getValueResults() {
-		return getAllValidationResults().stream()
+		return getParameterValidationResults().stream()
 				.filter(result -> !(result instanceof ParameterErrors))
 				.toList();
 	}
 
 	/**
-	 * Return the subset of {@link #getAllValidationResults() allValidationResults}
+	 * Return the subset of {@link #getParameterValidationResults() allValidationResults}
 	 * that includes Object method parameters with nested errors on their fields
 	 * and properties. This excludes {@link #getValueResults() valueResults} with
 	 * validation errors directly on method arguments.
 	 */
 	default List<ParameterErrors> getBeanResults() {
-		return getAllValidationResults().stream()
+		return getParameterValidationResults().stream()
 				.filter(ParameterErrors.class::isInstance)
 				.map(result -> (ParameterErrors) result)
 				.toList();
 	}
 
+	/**
+	 * Return errors from cross-parameter validation.
+	 * @since 6.2
+	 */
+	List<MessageSourceResolvable> getCrossParameterValidationResults();
+
 
 	/**
 	 * Factory method to create a {@link MethodValidationResult} instance.
@@ -112,7 +134,23 @@ default List<ParameterErrors> getBeanResults() {
 	 * @return the created instance
 	 */
 	static MethodValidationResult create(Object target, Method method, List<ParameterValidationResult> results) {
-		return new DefaultMethodValidationResult(target, method, results);
+		return create(target, method, results, Collections.emptyList());
+	}
+
+	/**
+	 * Factory method to create a {@link MethodValidationResult} instance.
+	 * @param target the target Object
+	 * @param method the target method
+	 * @param results method validation results, expected to be non-empty
+	 * @param crossParameterErrors cross-parameter validation errors
+	 * @return the created instance
+	 * @since 6.2
+	 */
+	static MethodValidationResult create(
+			Object target, Method method, List<ParameterValidationResult> results,
+			List<MessageSourceResolvable> crossParameterErrors) {
+
+		return new DefaultMethodValidationResult(target, method, results, crossParameterErrors);
 	}
 
 	/**