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/main/java/example/declared/first/First.java

@@ -0,0 +1,29 @@
+/*
+ * 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.declared.first;
+
+import example.declared.second.Second;
+
+import org.springframework.stereotype.Component;
+
+/**
+ * @author Oliver Drotbohm
+ */
+@Component
+public class First {
+
+	First(Second second) {}
+}

spring-modulith-integration-test/src/main/java/example/declared/first/package-info.java

@@ -0,0 +1,3 @@
+// No dependencies allowed
+@org.springframework.modulith.ApplicationModule(allowedDependencies = {})
+package example.declared.first;

spring-modulith-integration-test/src/main/java/example/declared/fourth/Fourth.java

@@ -0,0 +1,26 @@
+/*
+ * 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.declared.fourth;
+
+import org.springframework.stereotype.Component;
+
+/**
+ * @author Oliver Drotbohm
+ */
+@Component
+public class Fourth {
+
+}

spring-modulith-integration-test/src/main/java/example/declared/second/Second.java

@@ -0,0 +1,28 @@
+/*
+ * 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.declared.second;
+
+import example.declared.third.Third;
+
+import org.springframework.stereotype.Component;
+
+/**
+ * @author Oliver Drotbohm
+ */
+@Component
+public class Second {
+	Second(Third third) {}
+}

spring-modulith-integration-test/src/main/java/example/declared/second/package-info.java

@@ -0,0 +1,3 @@
+// No explicit allowed dependencies -> all allowed
+@org.springframework.modulith.ApplicationModule(displayName = "Second")
+package example.declared.second;

spring-modulith-integration-test/src/main/java/example/declared/third/Third.java

@@ -0,0 +1,28 @@
+/*
+ * 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.declared.third;
+
+import example.declared.fourth.Fourth;
+
+import org.springframework.stereotype.Component;
+
+/**
+ * @author Oliver Drotbohm
+ */
+@Component
+public class Third {
+	Third(Fourth fourth) {}
+}

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 -> {