Add annotation for hidden members used by apps.

/*

 * Copyright (C) 2018 The Android Open Source Project

 *

 * 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

 *

 *      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 android.annotation;

import static java.lang.annotation.ElementType.CONSTRUCTOR;

import static java.lang.annotation.ElementType.FIELD;

import static java.lang.annotation.ElementType.METHOD;

import static java.lang.annotation.RetentionPolicy.CLASS;

import java.lang.annotation.Retention;

import java.lang.annotation.Target;

/**

 * Indicates that a class member, that is not part of the SDK, is used by apps.

 * Since the member is not part of the SDK, such use is not supported.

 *

 * This annotation acts as a heads up that changing a given method or field

 * may affect apps, potentially breaking them when the next Android version is

 * released. In some cases, for members that are heavily used, this annotation

 * may imply restrictions on changes to the member.

 *

 * This annotation also results in access to the member being permitted by the

 * runtime, with a warning being generated in debug builds.

 *

 * For more details, see go/UnsupportedAppUsage.

 *

 * {@hide}

 */

@Retention(CLASS)

@Target({CONSTRUCTOR, METHOD, FIELD})

public @interface UnsupportedAppUsage {

    /**

     * Associates a bug tracking the work to add a public alternative to this API. Optional.

     *

     * @return ID of the associated tracking bug

     */

    long trackingBug() default 0;

    /**

     * For debug use only. The expected dex signature to be generated for this API, used to verify

     * parts of the build process.

     *

     * @return A dex API signature.

     */

    String expectedSignature() default "";

}