GH-332 - Avoid proxying configuration classes for observability purposes.

We now skip configuration classes for observability-related proxying as it's hard to detect those during the ProxyFactory setup to configure target class proxying. Also, configuration classes are usually no targets of inter-module communication and thus don't need to be observed at all.

Author: odrotbohm

spring-modulith-observability/src/main/java/org/springframework/modulith/observability/DefaultObservedModule.java

@@ -140,7 +140,7 @@ public ObservedModuleType getObservedModuleType(Class<?> type, ApplicationModule
 				.map(SpringBean::toArchitecturallyEvidentType)
 				.findFirst()
 				.map(it -> new ObservedModuleType(modules, this, it))
-				.filter(ObservedModuleType::shouldBeTraced)
+				.filter(ObservedModuleType::shouldBeObserved)
 				.orElse(null);
 	}
 

spring-modulith-observability/src/main/java/org/springframework/modulith/observability/ObservedModuleType.java

@@ -23,6 +23,7 @@
 
 import org.springframework.aop.TargetClassAware;
 import org.springframework.aop.framework.Advised;
+import org.springframework.context.annotation.Configuration;
 import org.springframework.modulith.core.ApplicationModules;
 import org.springframework.modulith.core.ArchitecturallyEvidentType;
 import org.springframework.modulith.core.ArchitecturallyEvidentType.ReferenceMethod;
@@ -34,7 +35,7 @@
  *
  * @author Oliver Drotbohm
  */
-public class ObservedModuleType {
+class ObservedModuleType {
 
 	private static Collection<Class<?>> IGNORED_TYPES = List.of(Advised.class, TargetClassAware.class);
 
@@ -62,16 +63,20 @@ public class ObservedModuleType {
 	}
 
 	/**
-	 * Returns whether the type should be traced at all. Can be skipped for types not exposed by the module unless they
+	 * Returns whether the type should be observed at all. Can be skipped for types not exposed by the module unless they
 	 * listen to events of other modules.
 	 *
 	 * @return
 	 */
-	public boolean shouldBeTraced() {
+	public boolean shouldBeObserved() {
 
-		boolean isApiType = module.exposes(type.getType());
+		if (type.getType().isMetaAnnotatedWith(Configuration.class)) {
+			return false;
+		}
 
-		return type.isController() || listensToOtherModulesEvents() || isApiType;
+		return type.isController()
+				|| listensToOtherModulesEvents()
+				|| module.exposes(type.getType());
 	}
 
 	/**

spring-modulith-observability/src/test/java/example/sample/SampleConfiguration.java

@@ -0,0 +1,24 @@
+/*
+ * Copyright 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 example.sample;
+
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * @author Oliver Drotbohm
+ */
+@Configuration
+public class SampleConfiguration {}

spring-modulith-observability/src/test/java/org/springframework/modulith/observability/ObservedModuleTypeUnitTests.java

@@ -18,6 +18,7 @@
 import static org.assertj.core.api.Assertions.*;
 
 import example.sample.SampleComponent;
+import example.sample.SampleConfiguration;
 
 import org.junit.jupiter.api.Test;
 import org.springframework.aop.framework.Advised;
@@ -55,6 +56,15 @@ void onlyExposesUserMethodsAsToBeIntercepted() {
 
 	@Test // GH-106
 	void considersExposedTypeAsToBeIntercepted() {
-		assertThat(observedType.shouldBeTraced()).isTrue();
+		assertThat(observedType.shouldBeObserved()).isTrue();
+	}
+
+	@Test // GH-332
+	void doesNotObserveConfigurationClasses() {
+
+		var type = module.getArchitecturallyEvidentType(SampleConfiguration.class);
+		var observedType = new ObservedModuleType(modules, new DefaultObservedModule(module), type);
+
+		assertThat(observedType.shouldBeObserved()).isFalse();
 	}
 }