Backport UnstableApi from 9229ed98e2eb3159abe3195459e0ffc78200d358

common/src/main/java/io/netty/util/internal/UnstableApi.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2016 The Netty Project
+ *
+ * The Netty Project licenses this file to you 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:
+ *
+ *   http://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 io.netty.util.internal;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Indicates a public API that can change at any time (even in minor/bugfix releases).
+ *
+ * Usage guidelines:
+ *
+ * <ol>
+ *     <li>Is not needed for things located in *.internal.* packages</li>
+ *     <li>Only public acessible classes/interfaces must be annotated</li>
+ *     <li>If this annotation is not present the API is considered stable and so no backward compatibility can be
+ *         broken in a non-major release!</li>
+ * </ol>
+ */
+@Retention(RetentionPolicy.SOURCE)
+@Target({
+        ElementType.ANNOTATION_TYPE,
+        ElementType.CONSTRUCTOR,
+        ElementType.FIELD,
+        ElementType.METHOD,
+        ElementType.PACKAGE,
+        ElementType.TYPE
+})
+@Documented
+public @interface UnstableApi {
+}