Support @componentscan as a repeatable composed annotation

This is a "proof of concept".

See spring-projectsgh-30941

spring-context/src/main/java/org/springframework/context/annotation/AnnotationConfigUtils.java

@@ -51,6 +51,7 @@
  * @author Chris Beams
  * @author Phillip Webb
  * @author Stephane Nicoll
+ * @author Sam Brannen
  * @since 2.5
  * @see ContextAnnotationAutowireCandidateResolver
  * @see ConfigurationClassPostProcessor
@@ -288,7 +289,7 @@ static Set<AnnotationAttributes> attributesForRepeatable(AnnotationMetadata meta
 		Set<AnnotationAttributes> result = new LinkedHashSet<>();
 
 		// Direct annotation present or meta-present?
-		addAttributesIfNotNull(result, metadata.getAnnotationAttributes(annotationType.getName()));
+		addAttributes(result, metadata.getAllMergedAnnotationAttributes(annotationType.getName()));
 
 		// Container annotation present or meta-present?
 		Map<String, Object> container = metadata.getAnnotationAttributes(containerType.getName());
@@ -302,6 +303,14 @@ static Set<AnnotationAttributes> attributesForRepeatable(AnnotationMetadata meta
 		return Collections.unmodifiableSet(result);
 	}
 
+	private static void addAttributes(
+			Set<AnnotationAttributes> result, Set<? extends Map<String, Object>> attributesList) {
+
+			for (Map<String, Object> attributes : attributesList) {
+				result.add(AnnotationAttributes.fromMap(attributes));
+			}
+	}
+
 	private static void addAttributesIfNotNull(
 			Set<AnnotationAttributes> result, @Nullable Map<String, Object> attributes) {
 

spring-core/src/main/java/org/springframework/core/type/AnnotatedTypeMetadata.java

@@ -17,7 +17,10 @@
 package org.springframework.core.type;
 
 import java.lang.annotation.Annotation;
+import java.util.LinkedHashSet;
 import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
 
 import org.springframework.core.annotation.MergedAnnotation;
 import org.springframework.core.annotation.MergedAnnotation.Adapt;
@@ -151,4 +154,47 @@ default MultiValueMap<String, Object> getAllAnnotationAttributes(
 						map -> (map.isEmpty() ? null : map), adaptations));
 	}
 
+	/**
+	 * Retrieve all attributes of all annotations of the given type, if any (i.e. if
+	 * defined on the underlying element, as direct annotation or meta-annotation).
+	 * <p>Note: in contrast to {@link #getAllAnnotationAttributes(String)},
+	 * this method <em>does</em> take attribute overrides on composed annotations
+	 * into account.
+	 * @param annotationName the fully qualified class name of the annotation
+	 * type to look for
+	 * @return a list of maps of attributes, with the attribute name as map key
+	 * (e.g. "key") and the attribute value as map value; never {@code null} but
+	 * potentially empty if no such annotations are found
+	 * @since 6.1
+	 * @see #getAllMergedAnnotationAttributes(String, boolean)
+	 */
+	default Set<? extends Map<String, Object>> getAllMergedAnnotationAttributes(String annotationName) {
+		return getAllMergedAnnotationAttributes(annotationName, false);
+	}
+
+	/**
+	 * Retrieve all attributes of all annotations of the given type, if any (i.e. if
+	 * defined on the underlying element, as direct annotation or meta-annotation).
+	 * <p>Note: in contrast to {@link #getAllAnnotationAttributes(String, boolean)},
+	 * this method <em>does</em> take attribute overrides on composed annotations
+	 * into account.
+	 * @param annotationName the fully qualified class name of the annotation
+	 * type to look for
+	 * @param classValuesAsString whether to convert class references to String
+	 * @return a list of maps of attributes, with the attribute name as map key
+	 * (e.g. "key") and the attribute value as map value; never {@code null} but
+	 * potentially empty if no such annotations are found
+	 * @since 6.1
+	 * @see #getAllMergedAnnotationAttributes(String)
+	 */
+	default Set<? extends Map<String, Object>> getAllMergedAnnotationAttributes(
+			String annotationName, boolean classValuesAsString) {
+
+		Adapt[] adaptations = Adapt.values(classValuesAsString, true);
+		return getAnnotations().stream(annotationName)
+				.filter(MergedAnnotationPredicates.unique(MergedAnnotation::getMetaTypes))
+				.map(annotation -> annotation.asAnnotationAttributes(adaptations))
+				.collect(Collectors.toCollection(LinkedHashSet::new));
+	}
+
 }

spring-test/src/test/java/org/springframework/test/gh30941/AppConfig.java

@@ -0,0 +1,25 @@
+/*
+ * 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.test.gh30941;
+
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+@ConnectedToModuleA
+@ConnectedToModuleB
+class AppConfig {
+}

spring-test/src/test/java/org/springframework/test/gh30941/ComponentScanTests.java

@@ -0,0 +1,43 @@
+/*
+ * 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.test.gh30941;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
+import org.springframework.test.gh30941.a.ModuleAClient;
+import org.springframework.test.gh30941.b.ModuleBClient;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@SpringJUnitConfig(AppConfig.class)
+class ComponentScanTests {
+
+	@Autowired
+	ModuleAClient clientA;
+
+	@Autowired
+	ModuleBClient clientB;
+
+	@Test
+	void test() {
+		assertThat(clientA).isNotNull();
+		assertThat(clientB).isNotNull();
+	}
+
+}

spring-test/src/test/java/org/springframework/test/gh30941/ConnectedToModuleA.java

@@ -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.test.gh30941;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.test.gh30941.a.ModuleAClient;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+@ComponentScan(basePackageClasses = ModuleAClient.class)
+@interface ConnectedToModuleA {
+}

spring-test/src/test/java/org/springframework/test/gh30941/ConnectedToModuleB.java

@@ -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.test.gh30941;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.test.gh30941.b.ModuleBClient;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+@ComponentScan(basePackageClasses = ModuleBClient.class)
+@interface ConnectedToModuleB {
+}

spring-test/src/test/java/org/springframework/test/gh30941/a/ModuleAClient.java

@@ -0,0 +1,23 @@
+/*
+ * 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.test.gh30941.a;
+
+import org.springframework.stereotype.Component;
+
+@Component
+public class ModuleAClient {
+}

spring-test/src/test/java/org/springframework/test/gh30941/b/ModuleBClient.java

@@ -0,0 +1,23 @@
+/*
+ * 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.test.gh30941.b;
+
+import org.springframework.stereotype.Component;
+
+@Component
+public class ModuleBClient {
+}