GH-348 - Avoid eager reference to runtime artifact from core starter.

Removed the inclusion of the spring-modulith-runtime artifact from the …-starter-core one to avoid issues in native images in a Spring Modulith default setup. As the artifact is still needed to support ApplicationModuleInitializer implementations, we now explicitly check for the presence of those and verify the artifact is actually available and hint the user at explicitly adding it if missing.

spring-modulith-core/src/test/java/org/springframework/modulith/core/config/ApplicationModuleInitializerRuntimeVerificationTests.java

@@ -0,0 +1,61 @@
+/*
+ * 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 org.springframework.modulith.core.config;
+
+import static org.assertj.core.api.Assertions.*;
+import static org.mockito.Mockito.*;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.modulith.ApplicationModuleInitializer;
+
+/**
+ * Tests for {@link ApplicationModuleInitializerRuntimeVerification}.
+ *
+ * @author Oliver Drotbohm
+ * @since 1.1
+ */
+class ApplicationModuleInitializerRuntimeVerificationTests {
+
+	@Test // GH-348
+	void startsWithoutApplicationModuleInititalizersPresent() {
+
+		new ApplicationContextRunner()
+				.withConfiguration(AutoConfigurations.of(ApplicationModuleInitializerRuntimeVerification.class))
+				.run(ctx -> {
+					assertThat(ctx).hasNotFailed();
+				});
+	}
+
+	@Test // GH-348
+	void rejectsPresenceOfAppliactionModuleInitializerBeanIfRuntimeArtifactIsMissing() {
+
+		new ApplicationContextRunner()
+				.withConfiguration(AutoConfigurations.of(ApplicationModuleInitializerRuntimeVerification.class))
+				.withBean(ApplicationModuleInitializer.class, () -> mock(ApplicationModuleInitializer.class))
+				.run(ctx -> {
+
+					assertThat(ctx)
+							.hasFailed()
+							.getFailure()
+							.isInstanceOf(IllegalStateException.class)
+							.hasMessageContaining("ApplicationModuleInitializer") // Type
+							.hasMessageContaining("applicationModuleInitializer") // Bean name
+							.hasMessageContaining("spring-modulith-runtime"); // Missing artifact
+				});
+	}
+}