Re-introduce support for annotation declarations with self references

Closes gh-31400

Author: jhoeller

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

@@ -45,6 +45,7 @@
  *
  * @author Phillip Webb
  * @author Sam Brannen
+ * @author Juergen Hoeller
  * @since 5.2
  * @see AnnotationTypeMappings
  */
@@ -402,9 +403,11 @@ private boolean computeSynthesizableFlag() {
 				if (type.isAnnotation() || (type.isArray() && type.getComponentType().isAnnotation())) {
 					Class<? extends Annotation> annotationType =
 							(Class<? extends Annotation>) (type.isAnnotation() ? type : type.getComponentType());
-					AnnotationTypeMapping mapping = AnnotationTypeMappings.forAnnotationType(annotationType).get(0);
-					if (mapping.isSynthesizable()) {
-						return true;
+					if (annotationType != this.annotationType) {
+						AnnotationTypeMapping mapping = AnnotationTypeMappings.forAnnotationType(annotationType).get(0);
+						if (mapping.isSynthesizable()) {
+							return true;
+						}
 					}
 				}
 			}

spring-core/src/test/kotlin/org/springframework/core/annotation/KotlinMergedAnnotationsTests.kt

@@ -0,0 +1,86 @@
+/*
+ * Copyright 2002-2023 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.annotation
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+
+/**
+ * Tests for {@link MergedAnnotations} and {@link MergedAnnotation} in Kotlin.
+ *
+ * @author Sam Brannen
+ * @author Juergen Hoeller
+ * @since 5.3.16
+ */
+class KotlinMergedAnnotationsTests {
+
+	@Test  // gh-28012
+	fun recursiveAnnotationWithAlias() {
+		val method = javaClass.getMethod("personWithAliasMethod")
+
+		// MergedAnnotations
+		val mergedAnnotations = MergedAnnotations.from(method)
+		assertThat(mergedAnnotations.isPresent(PersonWithAlias::class.java)).isTrue();
+
+		// MergedAnnotation
+		val mergedAnnotation = MergedAnnotation.from(method.getAnnotation(PersonWithAlias::class.java))
+		assertThat(mergedAnnotation).isNotNull();
+
+		// Synthesized Annotations
+		val jane = mergedAnnotation.synthesize()
+		assertThat(jane.value).isEqualTo("jane")
+		assertThat(jane.name).isEqualTo("jane")
+		val synthesizedFriends = jane.friends
+		assertThat(synthesizedFriends).hasSize(2)
+
+		val john = synthesizedFriends[0]
+		assertThat(john.value).isEqualTo("john")
+		assertThat(john.name).isEqualTo("john")
+
+		val sally = synthesizedFriends[1]
+		assertThat(sally.value).isEqualTo("sally")
+		assertThat(sally.name).isEqualTo("sally")
+	}
+
+	@Test  // gh-31400
+	fun recursiveAnnotationWithoutAlias() {
+		val method = javaClass.getMethod("personWithoutAliasMethod")
+
+		// MergedAnnotations
+		val mergedAnnotations = MergedAnnotations.from(method)
+		assertThat(mergedAnnotations.isPresent(PersonWithoutAlias::class.java)).isTrue();
+
+		// MergedAnnotation
+		val mergedAnnotation = MergedAnnotation.from(method.getAnnotation(PersonWithoutAlias::class.java))
+		assertThat(mergedAnnotation).isNotNull();
+
+		// Synthesized Annotations
+		val jane = mergedAnnotation.synthesize()
+		val synthesizedFriends = jane.friends
+		assertThat(synthesizedFriends).hasSize(2)
+	}
+
+
+	@PersonWithAlias("jane", friends = [PersonWithAlias("john"), PersonWithAlias("sally")])
+	fun personWithAliasMethod() {
+	}
+
+	@PersonWithoutAlias("jane", friends = [PersonWithoutAlias("john"), PersonWithoutAlias("sally")])
+	fun personWithoutAliasMethod() {
+	}
+
+}

spring-core/src/test/kotlin/org/springframework/core/annotation/PersonWithAlias.kt

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2002-2023 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.annotation
+
+@Target(AnnotationTarget.FUNCTION)
+@Retention(AnnotationRetention.RUNTIME)
+annotation class PersonWithAlias(
+
+	@get:AliasFor("name")
+	val value: String = "",
+
+	@get:AliasFor("value")
+	val name: String = "",
+
+	vararg val friends: PersonWithAlias = []
+
+)

spring-core/src/test/kotlin/org/springframework/core/annotation/PersonWithoutAlias.kt

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2002-2023 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.annotation
+
+@Target(AnnotationTarget.FUNCTION)
+@Retention(AnnotationRetention.RUNTIME)
+annotation class PersonWithoutAlias(
+
+	val value: String = "",
+
+	val name: String = "",
+
+	vararg val friends: PersonWithoutAlias = []
+
+)