Tolerate unidirectional alias declaration for annotation attribute pair

Closes spring-projectsgh-23834

Author: jhoeller

spring-core/src/main/java/org/springframework/core/annotation/AnnotationTypeMapping.java

@@ -27,7 +27,6 @@
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
-import java.util.Objects;
 import java.util.Set;
 import java.util.function.BiFunction;
 
@@ -179,30 +178,25 @@ private Method resolveAliasTarget(Method attribute, AliasFor aliasFor, boolean c
 		}
 		if (isAliasPair(target) && checkAliasPair) {
 			AliasFor targetAliasFor = target.getAnnotation(AliasFor.class);
-			if (targetAliasFor == null) {
-				throw new AnnotationConfigurationException(String.format(
-						"%s must be declared as an @AliasFor '%s'.",
-						StringUtils.capitalize(AttributeMethods.describe(target)),
-						attribute.getName()));
-			}
-			Method mirror = resolveAliasTarget(target, targetAliasFor, false);
-			if (!mirror.equals(attribute)) {
-				throw new AnnotationConfigurationException(String.format(
-						"%s must be declared as an @AliasFor '%s', not '%s'.",
-						StringUtils.capitalize(AttributeMethods.describe(target)),
-						attribute.getName(), mirror.getName()));
+			if (targetAliasFor != null) {
+				Method mirror = resolveAliasTarget(target, targetAliasFor, false);
+				if (!mirror.equals(attribute)) {
+					throw new AnnotationConfigurationException(String.format(
+							"%s must be declared as an @AliasFor '%s', not '%s'.",
+							StringUtils.capitalize(AttributeMethods.describe(target)),
+							attribute.getName(), mirror.getName()));
+				}
 			}
 		}
 		return target;
 	}
 
 	private boolean isAliasPair(Method target) {
-		return target.getDeclaringClass().equals(this.annotationType);
+		return (this.annotationType == target.getDeclaringClass());
 	}
 
 	private boolean isCompatibleReturnType(Class<?> attributeType, Class<?> targetType) {
-		return Objects.equals(attributeType, targetType) ||
-				Objects.equals(attributeType, targetType.getComponentType());
+		return (attributeType == targetType || attributeType == targetType.getComponentType());
 	}
 
 	private void processAliases() {

spring-core/src/test/java/org/springframework/core/annotation/AnnotatedElementUtilsTests.java

@@ -1200,7 +1200,7 @@ static class MetaCycleAnnotatedClass {
 		@AliasFor("basePackages")
 		String[] value() default {};
 
-		@AliasFor("value")
+		// Intentionally no alias declaration for "value"
 		String[] basePackages() default {};
 
 		Filter[] excludeFilters() default {};
@@ -1485,15 +1485,15 @@ class ForAnnotationsClass {
 	}
 
 	@Retention(RetentionPolicy.RUNTIME)
-	static @interface ValueAttribute {
+	@interface ValueAttribute {
 
 		String[] value();
 
 	}
 
 	@Retention(RetentionPolicy.RUNTIME)
 	@ValueAttribute("FromValueAttributeMeta")
-	static @interface ValueAttributeMeta {
+	@interface ValueAttributeMeta {
 
 		@AliasFor("alias")
 		String[] value() default {};
@@ -1505,7 +1505,7 @@ class ForAnnotationsClass {
 
 	@Retention(RetentionPolicy.RUNTIME)
 	@ValueAttributeMeta("FromValueAttributeMetaMeta")
-	static @interface ValueAttributeMetaMeta {
+	@interface ValueAttributeMetaMeta {
 	}
 
 	@ValueAttributeMetaMeta