GH-522 - Support for package info types.

Introduce @PackageInfo annotation to allow marking a types as alternative to Java's native package-info.java so that annotation lookups on a JavaPackage will also find annotations placed on that type. Useful to declare package scoped metadata like @ApplicationModule and @NamedInterface for languages that do not support packages well enough (read: Kotlin).

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

@@ -0,0 +1,45 @@
+/*
+ * 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 org.junit.jupiter.api.Test;
+
+import com.tngtech.archunit.core.domain.JavaClasses;
+import com.tngtech.archunit.core.importer.ClassFileImporter;
+import com.tngtech.archunit.core.importer.ImportOption;
+
+/**
+ * Unit tests for {@link ApplicationModuleInformation}.
+ *
+ * @author Oliver Drotbohm
+ */
+class ApplicationModuleInformationUnitTests {
+
+	static final JavaClasses PKG_CLASSES = new ClassFileImporter() //
+			.withImportOption(ImportOption.Predefined.DO_NOT_INCLUDE_TESTS) //
+			.importPackages("pkg");
+
+	@Test // GH-522
+	void detectsApplicationInformationOnType() {
+
+		var pkg = JavaPackage.of(Classes.of(PKG_CLASSES), "pkg.ontype");
+		var information = ApplicationModuleInformation.of(pkg);
+
+		assertThat(information.getDisplayName()).hasValue("onType");
+	}
+}

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

@@ -18,6 +18,7 @@ package org.springframework.modulith.core;
 import static org.assertj.core.api.Assertions.*;
 
 import org.junit.jupiter.api.Test;
+import org.springframework.modulith.ApplicationModule;
 
 import com.tngtech.archunit.core.domain.JavaClasses;
 import com.tngtech.archunit.core.importer.ClassFileImporter;
@@ -29,11 +30,15 @@ import com.tngtech.archunit.core.importer.ImportOption;
 class JavaPackageUnitTests {
 
 	static final JavaClasses ALL_CLASSES = new ClassFileImporter() //
-			.withImportOption(ImportOption.Predefined.DO_NOT_INCLUDE_TESTS)
+			.withImportOption(ImportOption.Predefined.DO_NOT_INCLUDE_TESTS) //
 			.importPackages("com.acme.myproject");
 
+	static final JavaClasses PKG_CLASSES = new ClassFileImporter() //
+			.withImportOption(ImportOption.Predefined.DO_NOT_INCLUDE_TESTS) //
+			.importPackages("pkg");
+
 	@Test
-	void testName() throws Exception {
+	void detectsDirectSubPackages() throws Exception {
 
 		Classes classes = Classes.of(ALL_CLASSES);
 		JavaPackage pkg = JavaPackage.of(classes, "com.acme.myproject.complex");
@@ -43,4 +48,35 @@ class JavaPackageUnitTests {
 				.extracting(JavaPackage::getLocalName) //
 				.contains("api", "internal", "spi");
 	}
+
+	@Test // GH-522
+	void findsAnnotationOnPackageInfo() {
+
+		var annotation = JavaPackage.of(Classes.of(PKG_CLASSES), "pkg.onpackage") //
+				.getAnnotation(ApplicationModule.class);
+
+		assertThat(annotation).hasValueSatisfying(it -> {
+			assertThat(it.displayName()).isEqualTo("onPackage");
+		});
+	}
+
+	@Test // GH-522
+	void findsAnnotationOnPackageType() {
+
+		var annotation = JavaPackage.of(Classes.of(PKG_CLASSES), "pkg.ontype") //
+				.findAnnotation(ApplicationModule.class);
+
+		assertThat(annotation).hasValueSatisfying(it -> {
+			assertThat(it.displayName()).isEqualTo("onType");
+		});
+	}
+
+	@Test // GH-522
+	void rejectsMultipleAnnotationsOnType() {
+
+		assertThatIllegalStateException().isThrownBy(() -> {
+			JavaPackage.of(Classes.of(PKG_CLASSES), "pkg.multipleontype") //
+					.findAnnotation(ApplicationModule.class);
+		});
+	}
 }