GH-652 - Allow to configure the ApplicationModuleDetectionStrategy via a configuration property.

We now expose a configuration property spring.modulith.detection-strategy that can take either of the two prepared values "direct-sub-packages" (default) or "explicitly-annotated", or a fully qualified class name of the strategy to use.

Removed ApplicationModuleStrategies enum to avoid exposing the enum values as additional implementations. Those are now held as inline lambda expression in the factory methods on ApplicationModuleStrategy. Extracted the lookup of the strategy to use into ApplicationModuleDetectionStrategyLookup for easier testability.

spring-modulith-core/src/test/java/org/springframework/modulith/core/ApplicationModuleDetectionStrategyLookupTests.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 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.
+ * 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.modulith.core;
+
+import static org.assertj.core.api.Assertions.*;
+
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for {@link ApplicationModuleDetectionStrategy}.
+ *
+ * @author Oliver Drotbohm
+ */
+class ApplicationModuleDetectionStrategyLookupTests {
+
+	@Test // GH-652
+	void usesExplicitlyAnnotatedStrategyIfConfigured() {
+
+		System.setProperty("spring.config.additional-location", "classpath:detection/explicitly-annotated.properties");
+
+		assertThat(ApplicationModuleDetectionStrategyLookup.getStrategy())
+				.isEqualTo(ApplicationModuleDetectionStrategy.explictlyAnnotated());
+	}
+
+	@Test // GH-652
+	void usesDirectSubPackagesStrategyIfConfigured() {
+
+		System.setProperty("spring.config.additional-location", "classpath:detection/direct-sub-packages.properties");
+
+		assertThat(ApplicationModuleDetectionStrategyLookup.getStrategy())
+				.isEqualTo(ApplicationModuleDetectionStrategy.directSubPackage());
+	}
+
+	@Test // GH-652
+	void usesCustomStrategyIfConfigured() {
+
+		System.setProperty("spring.config.additional-location", "classpath:detection/custom-type.properties");
+
+		assertThat(ApplicationModuleDetectionStrategyLookup.getStrategy())
+				.isInstanceOf(TestStrategy.class);
+	}
+
+	static class TestStrategy implements ApplicationModuleDetectionStrategy {
+
+		@Override
+		public Stream<JavaPackage> getModuleBasePackages(JavaPackage basePackage) {
+			return null;
+		}
+	}
+}

spring-modulith-core/src/test/java/org/springframework/modulith/core/ModuleDetectionStrategyUnitTest.java

@@ -29,20 +29,6 @@ import com.tngtech.archunit.core.importer.ImportOption;
  */
 class ModuleDetectionStrategyUnitTest {
 
-	@Test
-	void usesExplicitlyAnnotatedConstant() {
-
-		assertThat(ApplicationModuleDetectionStrategy.explictlyAnnotated())
-				.isEqualTo(ApplicationModuleDetectionStrategies.EXPLICITLY_ANNOTATED);
-	}
-
-	@Test
-	void usesDirectSubPackages() {
-
-		assertThat(ApplicationModuleDetectionStrategy.directSubPackage())
-				.isEqualTo(ApplicationModuleDetectionStrategies.DIRECT_SUB_PACKAGES);
-	}
-
 	@Test
 	void detectsJMoleculesAnnotatedModule() {