[Hackathon] Create SdkExtensionMethod annotation

core/annotations/src/main/java/software/amazon/awssdk/annotations/SdkExtensionMethod.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file 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 software.amazon.awssdk.annotations;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Target;
+
+/**
+ * {@link SdkExtensionMethod} indicates a method that has been explicitly added to a service client interface on behalf of the
+ * SDK. While most service clients are automatically and fully generated based upon the corresponding service's API model, the SDK
+ * may sometimes choose to extend a service's logical API in order to provide improved abstractions or convenience functions. As
+ * such, {@link SdkExtensionMethod} implementations may invoke one or more service requests to fulfil their behavior.
+ */
+@Target(ElementType.METHOD)
+@SdkProtectedApi
+public @interface SdkExtensionMethod {
+}

services/s3/src/main/java/software/amazon/awssdk/services/s3/extensions/S3ClientExtensionMethods.java

@@ -15,6 +15,7 @@
 
 package software.amazon.awssdk.services.s3.extensions;
 
+import software.amazon.awssdk.annotations.SdkExtensionMethod;
 import software.amazon.awssdk.annotations.SdkPublicApi;
 import software.amazon.awssdk.services.s3.S3Client;
 import software.amazon.awssdk.services.s3.model.NoSuchBucketException;
@@ -36,6 +37,7 @@ public interface S3ClientExtensionMethods {
      * @return true if the bucket exists and you have permission to access it; false if the bucket does not exist
      * @throws S3Exception if the bucket exists but is not accessible
      */
+    @SdkExtensionMethod
     default boolean doesBucketExist(String bucketName) {
         Validate.notNull(bucketName, "bucketName");
         S3Client s3Client = (S3Client) this;