Add @IntegrationComponentScan auto-configuration

Update Spring Integration auto-configuration so that
`@IntegrationComponentScan` from `AutoConfigurationPackages` is
implicitly applied. Prior to this commit `@MessagingGateway` interfaces
would only get picked up if `@IntegrationComponentScan` was added
alongside with the `@SpringBootApplication`.

Fixes gh-2037
Closes gh-7718

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/integration/IntegrationAutoConfigurationTests.java

@@ -30,6 +30,9 @@ import org.springframework.context.annotation.AnnotationConfigApplicationContext
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Primary;
+import org.springframework.integration.annotation.IntegrationComponentScan;
+import org.springframework.integration.annotation.MessagingGateway;
+import org.springframework.integration.gateway.RequestReplyExchanger;
 import org.springframework.integration.support.channel.HeaderChannelRegistry;
 import org.springframework.integration.support.management.IntegrationManagementConfigurer;
 import org.springframework.jmx.export.MBeanExporter;
@@ -61,24 +64,34 @@ public class IntegrationAutoConfigurationTests {
 	@Test
 	public void integrationIsAvailable() {
 		load();
-		assertThat(this.context.getBean(HeaderChannelRegistry.class)).isNotNull();
+		assertThat(this.context.getBean(TestGateway.class)).isNotNull();
+		assertThat(this.context.getBean(IntegrationAutoConfiguration.IntegrationComponentScanAutoConfiguration.class))
+				.isNotNull();
+	}
+
+	@Test
+	public void explicitIntegrationComponentScan() {
+		this.context = new AnnotationConfigApplicationContext();
+		this.context.register(IntegrationComponentScanConfiguration.class,
+				JmxAutoConfiguration.class,
+				IntegrationAutoConfiguration.class);
+		this.context.refresh();
+		assertThat(this.context.getBean(TestGateway.class)).isNotNull();
+		assertThat(this.context.getBeansOfType(IntegrationAutoConfiguration.IntegrationComponentScanAutoConfiguration.class))
+				.isEmpty();
 	}
 
 	@Test
 	public void parentContext() {
-		this.context = new AnnotationConfigApplicationContext();
-		this.context.register(JmxAutoConfiguration.class,
-				IntegrationAutoConfiguration.class);
-		this.context.refresh();
+		load();
 		AnnotationConfigApplicationContext parent = this.context;
 		this.context = new AnnotationConfigApplicationContext();
 		this.context.setParent(parent);
 		this.context.register(JmxAutoConfiguration.class,
 				IntegrationAutoConfiguration.class);
+		TestPropertySourceUtils.addInlinedPropertiesToEnvironment(this.context, "SPRING_JMX_DEFAULT_DOMAIN=org.foo");
 		this.context.refresh();
 		assertThat(this.context.getBean(HeaderChannelRegistry.class)).isNotNull();
-		((ConfigurableApplicationContext) this.context.getParent()).close();
-		this.context.close();
 	}
 
 	@Test
@@ -151,4 +164,15 @@ public class IntegrationAutoConfigurationTests {
 
 	}
 
+	@Configuration
+	@IntegrationComponentScan
+	static class IntegrationComponentScanConfiguration {
+
+	}
+
+	@MessagingGateway
+	public interface TestGateway extends RequestReplyExchanger {
+
+	}
+
 }