Do not enable @ConfigurationPropertiesScan be default

In 2.2.0, @ConfigurationPropertiesScan was enabled by default.
Unfortunately, this had the unexpected side-effect of breaking
conditional enablement of a @ConfigurationProperties class via
@EnableConfigurationProperties if the @ConfigurationProperties class
was in a package covered by scanning.

This commit remove @ConfigurationPropertiesScan from
@SpringBootApplication so that it is no longer enabled by default.
2.1.x users who rely upon such conditional enablement of
@ConfigurationProperties classes can now upgrade to 2.2.x without
having to make any changes. Users who do not have such a need and are
in a position to use configuration properties scanning can now opt-in
by adding @ConfigurationPropertiesScan to their main application class
alongside @SpringBootApplication.

Closes gh-18674

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/SpringBootApplication.java

@@ -40,8 +40,7 @@ import org.springframework.data.repository.Repository;
  * auto-configuration}, {@link ComponentScan component scanning}, and
  * {@link ConfigurationPropertiesScan configuration properties scanning}. This is a
  * convenience annotation that is equivalent to declaring {@code @Configuration},
- * {@code @EnableAutoConfiguration}, {@code @ComponentScan}, and
- * {@code @ConfigurationPropertiesScan}.
+ * {@code @EnableAutoConfiguration}, {@code @ComponentScan}.
  *
  * @author Phillip Webb
  * @author Stephane Nicoll
@@ -56,7 +55,6 @@ import org.springframework.data.repository.Repository;
 @EnableAutoConfiguration
 @ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
 		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
-@ConfigurationPropertiesScan
 public @interface SpringBootApplication {
 
 	/**

spring-boot-project/spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -917,21 +917,12 @@ TIP: If you have more than one constructor for your class you can also use `@Con
 
 [[boot-features-external-config-enabling]]
 ==== Enabling `@ConfigurationProperties`-annotated types
-Spring Boot provides an infrastructure to bind such types and register them as beans automatically.
-If your application uses `@SpringBootApplication`, classes annotated with `@ConfigurationProperties` will automatically be scanned and registered as beans.
-By default, scanning will occur from the package of the class that declares this annotation.
-If you want to define specific packages to scan, you can do so using an explicit `@ConfigurationPropertiesScan` directive on your `@SpringBootApplication`-annotated class as shown in the following example:
+Spring Boot provides infrastructure to bind `@ConfigurationProperties` types and register them as beans.
+You can either enable configuration properties on a class-by-class basis or enable configuration property scanning that works in a similar manner to component scanning.
 
-[source,java,indent=0]
-----
-	@SpringBootApplication
-	@ConfigurationPropertiesScan({ "com.example.app", "org.acme.another" })
-	public class MyApplication {
-	}
-----
-
-Sometimes, classes annotated with `@ConfigurationProperties` might not be suitable for scanning, for example, if you're developing your own auto-configuration.
-In these cases, you can specify the list of types to process on any `@Configuration` class as shown in the following example:
+Sometimes, classes annotated with `@ConfigurationProperties` might not be suitable for scanning, for example, if you're developing your own auto-configuration or you want to enable them conditionally.
+In these cases, specify the list of types to process using the `@EnableConfigurationProperties` annotation.
+This can be done on any `@Configuration` class, as shown in the following example:
 
 [source,java,indent=0]
 ----
@@ -941,6 +932,19 @@ In these cases, you can specify the list of types to process on any `@Configurat
 	}
 ----
 
+To use configuration property scanning, add the `@ConfigurationPropertiesScan` annotation to your application.
+Typically, it is added to the main application class that is annotated with `@SpringBootApplication` but it can be added to any `@Configuration` class.
+By default, scanning will occur from the package of the class that declares the annotation.
+If you want to define specific packages to scan, you can do so as shown in the following example:
+
+[source,java,indent=0]
+----
+	@SpringBootApplication
+	@ConfigurationPropertiesScan({ "com.example.app", "org.acme.another" })
+	public class MyApplication {
+	}
+----
+
 [NOTE]
 ====
 When the `@ConfigurationProperties` bean is registered using configuration property scanning or via `@EnableConfigurationProperties`, the bean has a conventional name: `<prefix>-<fqn>`, where `<prefix>` is the environment key prefix specified in the `@ConfigurationProperties` annotation and `<fqn>` is the fully qualified name of the bean.

spring-boot-project/spring-boot-docs/src/main/asciidoc/using-spring-boot.adoc

@@ -298,7 +298,7 @@ The <<using-boot-using-springbootapplication-annotation, `@SpringBootApplication
 For example, if you are writing a JPA application, the package of the `@SpringBootApplication` annotated class is used to search for `@Entity` items.
 Using a root package also allows component scan to apply only on your project.
 
-TIP: If you don't want to use `@SpringBootApplication`, the `@EnableAutoConfiguration` `@ComponentScan`, and `@ConfigurationPropertiesScan` annotations that it imports defines that behaviour so you can also use those instead.
+TIP: If you don't want to use `@SpringBootApplication`, the `@EnableAutoConfiguration` and `@ComponentScan` annotations that it imports defines that behaviour so you can also use those instead.
 
 The following listing shows a typical layout:
 
@@ -480,7 +480,6 @@ A single `@SpringBootApplication` annotation can be used to enable those three f
 
 * `@EnableAutoConfiguration`: enable <<using-boot-auto-configuration,Spring Boot's auto-configuration mechanism>>
 * `@ComponentScan`: enable `@Component` scan on the package where the application is located (see <<using-boot-structuring-your-code,the best practices>>)
-* `@ConfigurationPropertiesScan`: enable `@ConfigurationProperties` scan on the package where the application is located (see <<using-boot-structuring-your-code,the best practices>>)
 * `@Configuration`: allow to register extra beans in the context or import additional configuration classes
 
 [source,java,indent=0]
@@ -490,7 +489,7 @@ A single `@SpringBootApplication` annotation can be used to enable those three f
 	import org.springframework.boot.SpringApplication;
 	import org.springframework.boot.autoconfigure.SpringBootApplication;
 
-	@SpringBootApplication // same as @Configuration @EnableAutoConfiguration @ComponentScan @ConfigurationPropertiesScan
+	@SpringBootApplication // same as @Configuration @EnableAutoConfiguration @ComponentScan
 	public class Application {
 
 		public static void main(String[] args) {

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/ExampleWebClientApplication.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.test.autoconfigure.web.client;
 
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.context.properties.ConfigurationPropertiesScan;
 
 /**
  * Example {@link SpringBootApplication @SpringBootApplication} used with
@@ -25,6 +26,7 @@ import org.springframework.boot.autoconfigure.SpringBootApplication;
  * @author Phillip Webb
  */
 @SpringBootApplication
+@ConfigurationPropertiesScan
 public class ExampleWebClientApplication {
 
 }