Add @AutoConfiguration annotation

This annotation can be used to mark auto-configurations with a dedicated
annotation. Under the hood, it's a standard @Configuration with
proxyBeanMethods set to false.

Closes gh-29870

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

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2012-2022 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.boot.autoconfigure;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Inherited;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.context.annotation.Conditional;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * Auto-configuration classes are regular Spring {@link Configuration @Configuration}
+ * beans. Generally auto-configuration beans are {@link Conditional @Conditional} beans
+ * (most often using {@link ConditionalOnClass @ConditionalOnClass} and
+ * {@link ConditionalOnMissingBean @ConditionalOnMissingBean} annotations).
+ *
+ * @author Moritz Halbritter
+ * @see EnableAutoConfiguration
+ * @see Conditional
+ * @see ConditionalOnClass
+ * @see ConditionalOnMissingBean
+ * @since 2.7.0
+ */
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+@Inherited
+@Configuration(proxyBeanMethods = false)
+public @interface AutoConfiguration {
+
+}

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/developing-auto-configuration.adoc

@@ -12,7 +12,8 @@ TIP: A https://github.com/snicoll-demos/spring-boot-master-auto-configuration[de
 
 [[features.developing-auto-configuration.understanding-auto-configured-beans]]
 === Understanding Auto-configured Beans
-Under the hood, auto-configuration is implemented with standard `@Configuration` classes.
+Under the hood, auto-configuration is implemented with the `@AutoConfiguration` annotation.
+This annotation itself is meta-annotated with `@Configuration`, making auto-configurations standard `@Configuration` classes.
 Additional `@Conditional` annotations are used to constrain when the auto-configuration should apply.
 Usually, auto-configuration classes use `@ConditionalOnClass` and `@ConditionalOnMissingBean` annotations.
 This ensures that auto-configuration applies only when relevant classes are found and when you have not declared your own `@Configuration`.