GH-613 - Add SPI to support external ApplicationModuleSource contributions.

We now expose ApplicationModuleSourceFactory as Spring Factories-based SPI interface to further contribute ApplicationModuleSource instances either from a provided root package subject for module detection through a (potentially customized) ApplicationModuleDetectionStrategy or by explicitly listing particular module base packages.

spring-modulith-integration-test/src/test/java/org/springframework/modulith/core/ApplicationModulesIntegrationTest.java

@@ -242,6 +242,25 @@ class ApplicationModulesIntegrationTest {
 		assertThatIllegalArgumentException().isThrownBy(() -> ApplicationModules.of("non.existant"));
 	}
 
+	@Test // GH-613
+	void detectsContributedApplicationModules() {
+
+		var location = ApplicationModuleSourceContributions.LOCATION;
+
+		ApplicationModuleSourceContributions.LOCATION = "META-INF/spring-test.factories";
+
+		try {
+
+			var modules = org.springframework.modulith.test.TestUtils.createApplicationModules(Application.class);
+
+			assertThat(modules.getModuleByName("detected")).isNotEmpty();
+			assertThat(modules.getModuleByName("enumerated")).isNotEmpty();
+
+		} finally {
+			ApplicationModuleSourceContributions.LOCATION = location;
+		}
+	}
+
 	private static void verifyNamedInterfaces(NamedInterfaces interfaces, String name, Class<?>... types) {
 
 		Stream.of(types).forEach(type -> {

spring-modulith-integration-test/src/test/java/org/springframework/modulith/test/TestUtils.java

@@ -23,6 +23,7 @@ import org.springframework.boot.test.context.SpringBootContextLoader;
 import org.springframework.boot.test.context.SpringBootTestContextBootstrapper;
 import org.springframework.boot.test.context.assertj.AssertableApplicationContext;
 import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.modulith.core.ApplicationModules;
 import org.springframework.test.context.BootstrapContext;
 import org.springframework.test.context.CacheAwareContextLoaderDelegate;
 import org.springframework.test.context.ContextLoadException;
@@ -30,11 +31,25 @@ import org.springframework.test.context.MergedContextConfiguration;
 import org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate;
 import org.springframework.test.context.support.DefaultBootstrapContext;
 
+import com.tngtech.archunit.base.DescribedPredicate;
+import com.tngtech.archunit.core.domain.JavaClass;
+
 /**
  * @author Oliver Drotbohm
  */
 public class TestUtils {
 
+	/**
+	 * Creates a fresh {@link ApplicationModules} instance no matter the caching state.
+	 *
+	 * @param type must not be {@literal null}.
+	 * @return will never be {@literal null}.
+	 * @since 1.3
+	 */
+	public static ApplicationModules createApplicationModules(Class<?> type) {
+		return ApplicationModules.of(type, cacheInvalidator());
+	}
+
 	public static void assertDependencyMissing(Class<?> testClass, Class<?> expectedMissingDependency) {
 
 		CacheAwareContextLoaderDelegate delegate = new DefaultCacheAwareContextLoaderDelegate();
@@ -72,4 +87,15 @@ public class TestUtils {
 	private static RuntimeException asRuntimeException(Throwable o_O) {
 		return o_O instanceof RuntimeException ? (RuntimeException) o_O : new RuntimeException(o_O);
 	}
+
+	private static DescribedPredicate<JavaClass> cacheInvalidator() {
+
+		return new DescribedPredicate<JavaClass>("invalidator") {
+
+			@Override
+			public boolean test(JavaClass t) {
+				return false;
+			}
+		};
+	}
 }