Add CheckReturnValue annotation

src/main/java/io/reactivex/Completable.java

@@ -1555,6 +1555,7 @@ public final void subscribe(CompletableObserver s) {
      * @throws NullPointerException if {@code observer} is null
      * @since 2.0
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <E extends CompletableObserver> E subscribeWith(E observer) {
         subscribe(observer);
@@ -1871,6 +1872,7 @@ public final Completable unsubscribeOn(final Scheduler scheduler) {
      * @return the new TestObserver instance
      * @since 2.0
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final TestObserver<Void> test() {
         TestObserver<Void> ts = new TestObserver<Void>();
@@ -1889,6 +1891,7 @@ public final TestObserver<Void> test() {
      * @return the new TestObserver instance
      * @since 2.0
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final TestObserver<Void> test(boolean cancelled) {
         TestObserver<Void> ts = new TestObserver<Void>();

src/main/java/io/reactivex/Flowable.java

@@ -12266,6 +12266,7 @@ public final void subscribe(Subscriber<? super T> s) {
      * @throws NullPointerException if {@code subscriber} is null
      * @since 2.0
      */
+    @CheckReturnValue
     @BackpressureSupport(BackpressureKind.SPECIAL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <E extends Subscriber<? super T>> E subscribeWith(E subscriber) {
@@ -15303,6 +15304,7 @@ public final <U, R> Flowable<R> zipWith(Publisher<? extends U> other,
      * @return the new TestSubscriber instance
      * @since 2.0
      */
+    @CheckReturnValue
     @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final TestSubscriber<T> test() { // NoPMD
@@ -15324,6 +15326,7 @@ public final TestSubscriber<T> test() { // NoPMD
      * @return the new TestSubscriber instance
      * @since 2.0
      */
+    @CheckReturnValue
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final TestSubscriber<T> test(long initialRequest) { // NoPMD
@@ -15347,6 +15350,7 @@ public final TestSubscriber<T> test(long initialRequest) { // NoPMD
      * @return the new TestSubscriber instance
      * @since 2.0
      */
+    @CheckReturnValue
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final TestSubscriber<T> test(long initialRequest, boolean cancel) { // NoPMD

src/main/java/io/reactivex/Maybe.java

@@ -3625,6 +3625,7 @@ public final Maybe<T> subscribeOn(Scheduler scheduler) {
      * @return the input {@code subscriber}
      * @throws NullPointerException if {@code subscriber} is null
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <E extends MaybeObserver<? super T>> E subscribeWith(E observer) {
         subscribe(observer);
@@ -3954,6 +3955,7 @@ public final <U, R> Maybe<R> zipWith(MaybeSource<? extends U> other, BiFunction<
      * </dl>
      * @return the new TestObserver instance
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final TestObserver<T> test() {
         TestObserver<T> ts = new TestObserver<T>();
@@ -3971,6 +3973,7 @@ public final TestObserver<T> test() {
      * Maybe.
      * @return the new TestObserver instance
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final TestObserver<T> test(boolean cancelled) {
         TestObserver<T> ts = new TestObserver<T>();

src/main/java/io/reactivex/Observable.java

@@ -10224,6 +10224,7 @@ public final void subscribe(Observer<? super T> observer) {
      * @throws NullPointerException if {@code observer} is null
      * @since 2.0
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <E extends Observer<? super T>> E subscribeWith(E observer) {
         subscribe(observer);
@@ -12872,6 +12873,7 @@ public final <U, R> Observable<R> zipWith(ObservableSource<? extends U> other,
      * @return the new TestObserver instance
      * @since 2.0
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final TestObserver<T> test() { // NoPMD
         TestObserver<T> ts = new TestObserver<T>();
@@ -12891,6 +12893,7 @@ public final TestObserver<T> test() { // NoPMD
      * @return the new TestObserver instance
      * @since 2.0
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final TestObserver<T> test(boolean dispose) { // NoPMD
         TestObserver<T> ts = new TestObserver<T>();

src/main/java/io/reactivex/Single.java

@@ -2596,6 +2596,7 @@ public final void subscribe(SingleObserver<? super T> subscriber) {
      * @throws NullPointerException if {@code observer} is null
      * @since 2.0
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <E extends SingleObserver<? super T>> E subscribeWith(E observer) {
         subscribe(observer);
@@ -2946,6 +2947,7 @@ public final <U, R> Single<R> zipWith(SingleSource<U> other, BiFunction<? super
      * @return the new TestObserver instance
      * @since 2.0
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final TestObserver<T> test() {
         TestObserver<T> ts = new TestObserver<T>();
@@ -2964,6 +2966,7 @@ public final TestObserver<T> test() {
      * @return the new TestObserver instance
      * @since 2.0
      */
+    @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final TestObserver<T> test(boolean cancelled) {
         TestObserver<T> ts = new TestObserver<T>();

src/main/java/io/reactivex/annotations/CheckReturnValue.java

@@ -0,0 +1,33 @@
+/**
+ * Copyright 2016 Netflix, Inc.
+ *
+ * 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 io.reactivex.annotations;
+
+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;
+
+/**
+ * Marks methods whose return values should be checked.
+ * 
+ * @since 2.0.2 - experimental
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+@Target(ElementType.METHOD)
+@Experimental
+public @interface CheckReturnValue {
+
+}