Merge pull request #12715 from Wenwei Liao

* gh-12715:
  Polish "Use modifiable set for @ServletComponentScan with no packages"
  Use modifiable set for @ServletComponentScan with no packages

spring-boot/src/main/java/org/springframework/boot/web/servlet/ServletComponentScanRegistrar.java

 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -17,7 +17,6 @@
 package org.springframework.boot.web.servlet;
 
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
@@ -84,8 +83,7 @@ class ServletComponentScanRegistrar implements ImportBeanDefinitionRegistrar {
 			packagesToScan.add(ClassUtils.getPackageName(basePackageClass));
 		}
 		if (packagesToScan.isEmpty()) {
-			return Collections
-					.singleton(ClassUtils.getPackageName(metadata.getClassName()));
+			packagesToScan.add(ClassUtils.getPackageName(metadata.getClassName()));
 		}
 		return packagesToScan;
 	}

spring-boot/src/test/java/org/springframework/boot/web/servlet/ServletComponentScanRegistrarTests.java

 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -107,6 +107,37 @@ public class ServletComponentScanRegistrarTests {
 				"com.example.bar", "com.example.baz");
 	}
 
+	@Test
+	public void withNoBasePackagesScanningUsesBasePackageOfAnnotatedClass() {
+		this.context = new AnnotationConfigApplicationContext(NoBasePackages.class);
+		ServletComponentRegisteringPostProcessor postProcessor = this.context
+				.getBean(ServletComponentRegisteringPostProcessor.class);
+		assertThat(postProcessor.getPackagesToScan())
+				.containsExactly("org.springframework.boot.web.servlet");
+	}
+
+	@Test
+	public void noBasePackageAndBasePackageAreCombinedCorrectly() {
+		this.context = new AnnotationConfigApplicationContext(NoBasePackages.class,
+				BasePackages.class);
+		ServletComponentRegisteringPostProcessor postProcessor = this.context
+				.getBean(ServletComponentRegisteringPostProcessor.class);
+		assertThat(postProcessor.getPackagesToScan()).containsExactlyInAnyOrder(
+				"org.springframework.boot.web.servlet", "com.example.foo",
+				"com.example.bar");
+	}
+
+	@Test
+	public void basePackageAndNoBasePackageAreCombinedCorrectly() {
+		this.context = new AnnotationConfigApplicationContext(BasePackages.class,
+				NoBasePackages.class);
+		ServletComponentRegisteringPostProcessor postProcessor = this.context
+				.getBean(ServletComponentRegisteringPostProcessor.class);
+		assertThat(postProcessor.getPackagesToScan()).containsExactlyInAnyOrder(
+				"org.springframework.boot.web.servlet", "com.example.foo",
+				"com.example.bar");
+	}
+
 	@Configuration
 	@ServletComponentScan({ "com.example.foo", "com.example.bar" })
 	static class ValuePackages {
@@ -137,4 +168,10 @@ public class ServletComponentScanRegistrarTests {
 
 	}
 
+	@Configuration
+	@ServletComponentScan
+	static class NoBasePackages {
+
+	}
+
 }