GH-267 - Explicitly declared empty allowed dependencies now forbids any dependency.

The default for @ApplicationModule(allowedDependencies) is now a single element list with a dedicated token we recognize as "all dependencies allowed". This allows users to declare an empty array explicitly to disallow any outgoing dependencies for an application module. Previously, such a declaration would have allowed any dependency.

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

@@ -17,6 +17,11 @@ package org.springframework.modulith.core;
 
 import static org.assertj.core.api.Assertions.*;
 
+import example.declared.first.First;
+import example.declared.fourth.Fourth;
+import example.declared.second.Second;
+import example.declared.third.Third;
+
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
@@ -164,6 +169,22 @@ class ApplicationModulesIntegrationTest {
 		assertThat(source).containsExactly(ServiceComponentA.class, ServiceComponentB.class, String.class);
 	}
 
+	@Test // GH-267
+	void explicitEmptyAllowedModulesResultsInAllDependenciesRejected() {
+
+		var modules = ApplicationModules.of("example.declared");
+		var first = modules.getModuleByType(First.class).orElseThrow();
+		var second = modules.getModuleByType(Second.class).orElseThrow();
+		var third = modules.getModuleByType(Third.class).orElseThrow();
+
+		// Disallowed due to allowedDependencies = {}
+		assertThat(first.getDeclaredDependencies(modules).isAllowedDependency(Second.class)).isFalse();
+
+		// Allowed as allowedDependencies not set
+		assertThat(second.getDeclaredDependencies(modules).isAllowedDependency(Third.class)).isTrue();
+		assertThat(third.getDeclaredDependencies(modules).isAllowedDependency(Fourth.class)).isTrue();
+	}
+
 	private static void verifyNamedInterfaces(NamedInterfaces interfaces, String name, Class<?>... types) {
 
 		Stream.of(types).forEach(type -> {