2.x: reintroduce OnErrorNotImplementedException for 0-1 arg subscribe…

…() (#5036)

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

@@ -1702,6 +1702,10 @@ public final Disposable subscribe(final Action onComplete, final Consumer<? supe
      * Subscribes to this Completable and calls the given Action when this Completable
      * completes normally.
      * <p>
+     * If the Completable emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
+     * <p>
      * If this Completable emits an error, it is sent to RxJavaPlugins.onError and gets swallowed.
      * <dl>
      *  <dt><b>Scheduler:</b></dt>

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

@@ -5559,6 +5559,11 @@ public final void blockingSubscribe() {
 
     /**
      * Subscribes to the source and calls the given callbacks <strong>on the current thread</strong>.
+     * <p>
+     * If the Flowable emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
+     * <p>
      * <dl>
      *  <dt><b>Backpressure:</b></dt>
      *  <dd>The operator consumes the source {@code Flowable} in an unbounded manner
@@ -5572,7 +5577,7 @@ public final void blockingSubscribe() {
     @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final void blockingSubscribe(Consumer<? super T> onNext) {
-        FlowableBlockingSubscribe.subscribe(this, onNext, Functions.ERROR_CONSUMER, Functions.EMPTY_ACTION);
+        FlowableBlockingSubscribe.subscribe(this, onNext, Functions.ON_ERROR_MISSING, Functions.EMPTY_ACTION);
     }
 
     /**
@@ -8983,6 +8988,10 @@ public final Disposable forEach(Consumer<? super T> onNext) {
     /**
      * Subscribes to the {@link Publisher} and receives notifications for each element until the
      * onNext Predicate returns false.
+     * <p>
+     * If the Flowable emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
      * <dl>
      *  <dt><b>Backpressure:</b><dt>
      *  <dd>The operator consumes the source {@code Publisher} in an unbounded manner (i.e., no
@@ -9003,7 +9012,7 @@ public final Disposable forEach(Consumer<? super T> onNext) {
     @BackpressureSupport(BackpressureKind.NONE)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Disposable forEachWhile(Predicate<? super T> onNext) {
-        return forEachWhile(onNext, Functions.ERROR_CONSUMER, Functions.EMPTY_ACTION);
+        return forEachWhile(onNext, Functions.ON_ERROR_MISSING, Functions.EMPTY_ACTION);
     }
 
     /**
@@ -12713,7 +12722,9 @@ public final Flowable<T> strict() {
     /**
      * Subscribes to a Publisher and ignores {@code onNext} and {@code onComplete} emissions.
      * <p>
-     * If the Flowable emits an error, it is routed to the RxJavaPlugins.onError handler.
+     * If the Flowable emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
      * <dl>
      *  <dt><b>Backpressure:</b><dt>
      *  <dd>The operator consumes the source {@code Publisher} in an unbounded manner (i.e., no
@@ -12729,14 +12740,16 @@ public final Flowable<T> strict() {
     @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Disposable subscribe() {
-        return subscribe(Functions.emptyConsumer(), Functions.ERROR_CONSUMER,
+        return subscribe(Functions.emptyConsumer(), Functions.ON_ERROR_MISSING,
                 Functions.EMPTY_ACTION, FlowableInternalHelper.RequestMax.INSTANCE);
     }
 
     /**
      * Subscribes to a Publisher and provides a callback to handle the items it emits.
      * <p>
-     * If the Flowable emits an error, it is routed to the RxJavaPlugins.onError handler.
+     * If the Flowable emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
      * <dl>
      *  <dt><b>Backpressure:</b><dt>
      *  <dd>The operator consumes the source {@code Publisher} in an unbounded manner (i.e., no
@@ -12757,7 +12770,7 @@ public final Disposable subscribe() {
     @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Disposable subscribe(Consumer<? super T> onNext) {
-        return subscribe(onNext, Functions.ERROR_CONSUMER,
+        return subscribe(onNext, Functions.ON_ERROR_MISSING,
                 Functions.EMPTY_ACTION, FlowableInternalHelper.RequestMax.INSTANCE);
     }
 

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

@@ -3592,7 +3592,9 @@ public final Maybe<T> retryWhen(
     /**
      * Subscribes to a Maybe and ignores {@code onSuccess} and {@code onComplete} emissions.
      * <p>
-     * If the Maybe emits an error, it is routed to the RxJavaPlugins.onError handler.
+     * If the Maybe emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
      * <dl>
      *  <dt><b>Scheduler:</b></dt>
      *  <dd>{@code subscribe} does not operate by default on a particular {@link Scheduler}.</dd>
@@ -3604,13 +3606,15 @@ public final Maybe<T> retryWhen(
      */
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Disposable subscribe() {
-        return subscribe(Functions.emptyConsumer(), Functions.ERROR_CONSUMER, Functions.EMPTY_ACTION);
+        return subscribe(Functions.emptyConsumer(), Functions.ON_ERROR_MISSING, Functions.EMPTY_ACTION);
     }
 
     /**
      * Subscribes to a Maybe and provides a callback to handle the items it emits.
      * <p>
-     * If the Maybe emits an error, it is routed to the RxJavaPlugins.onError handler.
+     * If the Maybe emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
      * <dl>
      *  <dt><b>Scheduler:</b></dt>
      *  <dd>{@code subscribe} does not operate by default on a particular {@link Scheduler}.</dd>
@@ -3627,7 +3631,7 @@ public final Disposable subscribe() {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Disposable subscribe(Consumer<? super T> onSuccess) {
-        return subscribe(onSuccess, Functions.ERROR_CONSUMER, Functions.EMPTY_ACTION);
+        return subscribe(onSuccess, Functions.ON_ERROR_MISSING, Functions.EMPTY_ACTION);
     }
 
     /**

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

@@ -4917,6 +4917,10 @@ public final void blockingSubscribe() {
 
     /**
      * Subscribes to the source and calls the given callbacks <strong>on the current thread</strong>.
+     * <p>
+     * If the Observable emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
      * <dl>
      *  <dt><b>Scheduler:</b></dt>
      *  <dd>{@code blockingSubscribe} does not operate by default on a particular {@link Scheduler}.</dd>
@@ -4926,7 +4930,7 @@ public final void blockingSubscribe() {
      */
     @SchedulerSupport(SchedulerSupport.NONE)
     public final void blockingSubscribe(Consumer<? super T> onNext) {
-        ObservableBlockingSubscribe.subscribe(this, onNext, Functions.ERROR_CONSUMER, Functions.EMPTY_ACTION);
+        ObservableBlockingSubscribe.subscribe(this, onNext, Functions.ON_ERROR_MISSING, Functions.EMPTY_ACTION);
     }
 
     /**
@@ -6761,7 +6765,7 @@ public final Observable<T> doFinally(Action onFinally) {
      * The action is shared between subscriptions and thus may be called concurrently from multiple
      * threads; the action must be thread safe.
      * <p>
-     * If the action throws a runtime exception, that exception is rethrown by the {@code unsubscribe()} call,
+     * If the action throws a runtime exception, that exception is rethrown by the {@code dispose()} call,
      * sometimes as a {@code CompositeException} if there were multiple exceptions along the way.
      * <p>
      * Note that terminal events trigger the action unless the {@code ObservableSource} is subscribed to via {@code unsafeSubscribe()}.
@@ -7785,6 +7789,10 @@ public final Disposable forEach(Consumer<? super T> onNext) {
     /**
      * Subscribes to the {@link ObservableSource} and receives notifications for each element until the
      * onNext Predicate returns false.
+     * <p>
+     * If the Observable emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
      * <dl>
      *  <dt><b>Scheduler:</b></dt>
      *  <dd>{@code forEachWhile} does not operate by default on a particular {@link Scheduler}.</dd>
@@ -7801,7 +7809,7 @@ public final Disposable forEach(Consumer<? super T> onNext) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Disposable forEachWhile(Predicate<? super T> onNext) {
-        return forEachWhile(onNext, Functions.ERROR_CONSUMER, Functions.EMPTY_ACTION);
+        return forEachWhile(onNext, Functions.ON_ERROR_MISSING, Functions.EMPTY_ACTION);
     }
 
     /**
@@ -10536,7 +10544,9 @@ public final Observable<T> startWithArray(T... items) {
     /**
      * Subscribes to an ObservableSource and ignores {@code onNext} and {@code onComplete} emissions.
      * <p>
-     * If the Observable emits an error, it is routed to the RxJavaPlugins.onError handler.
+     * If the Observable emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
      * <dl>
      *  <dt><b>Scheduler:</b></dt>
      *  <dd>{@code subscribe} does not operate by default on a particular {@link Scheduler}.</dd>
@@ -10548,13 +10558,15 @@ public final Observable<T> startWithArray(T... items) {
      */
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Disposable subscribe() {
-        return subscribe(Functions.emptyConsumer(), Functions.ERROR_CONSUMER, Functions.EMPTY_ACTION, Functions.emptyConsumer());
+        return subscribe(Functions.emptyConsumer(), Functions.ON_ERROR_MISSING, Functions.EMPTY_ACTION, Functions.emptyConsumer());
     }
 
     /**
      * Subscribes to an ObservableSource and provides a callback to handle the items it emits.
      * <p>
-     * If the Observable emits an error, it is routed to the RxJavaPlugins.onError handler.
+     * If the Observable emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
      * <dl>
      *  <dt><b>Scheduler:</b></dt>
      *  <dd>{@code subscribe} does not operate by default on a particular {@link Scheduler}.</dd>
@@ -10571,7 +10583,7 @@ public final Disposable subscribe() {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Disposable subscribe(Consumer<? super T> onNext) {
-        return subscribe(onNext, Functions.ERROR_CONSUMER, Functions.EMPTY_ACTION, Functions.emptyConsumer());
+        return subscribe(onNext, Functions.ON_ERROR_MISSING, Functions.EMPTY_ACTION, Functions.emptyConsumer());
     }
 
     /**

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

@@ -2553,6 +2553,10 @@ public final Single<T> retryWhen(Function<? super Flowable<Throwable>, ? extends
 
     /**
      * Subscribes to a Single but ignore its emission or notification.
+     * <p>
+     * If the Single emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
      * <dl>
      * <dt><b>Scheduler:</b></dt>
      * <dd>{@code subscribe} does not operate by default on a particular {@link Scheduler}.</dd>
@@ -2563,7 +2567,7 @@ public final Single<T> retryWhen(Function<? super Flowable<Throwable>, ? extends
      */
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Disposable subscribe() {
-        return subscribe(Functions.emptyConsumer(), Functions.ERROR_CONSUMER);
+        return subscribe(Functions.emptyConsumer(), Functions.ON_ERROR_MISSING);
     }
 
     /**
@@ -2594,6 +2598,10 @@ public final Disposable subscribe(final BiConsumer<? super T, ? super Throwable>
 
     /**
      * Subscribes to a Single and provides a callback to handle the item it emits.
+     * <p>
+     * If the Single emits an error, it is wrapped into an
+     * {@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
+     * and routed to the RxJavaPlugins.onError handler.
      * <dl>
      * <dt><b>Scheduler:</b></dt>
      * <dd>{@code subscribe} does not operate by default on a particular {@link Scheduler}.</dd>
@@ -2609,7 +2617,7 @@ public final Disposable subscribe(final BiConsumer<? super T, ? super Throwable>
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Disposable subscribe(Consumer<? super T> onSuccess) {
-        return subscribe(onSuccess, Functions.ERROR_CONSUMER);
+        return subscribe(onSuccess, Functions.ON_ERROR_MISSING);
     }
 
     /**

src/main/java/io/reactivex/exceptions/OnErrorNotImplementedException.java

@@ -0,0 +1,53 @@
+/**
+ * Copyright (c) 2016-present, RxJava Contributors.
+ *
+ * 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.exceptions;
+
+import io.reactivex.annotations.Experimental;
+
+/**
+ * Represents an exception used to signal to the {@code RxJavaPlugins.onError()} that a
+ * callback-based subscribe() method on a base reactive type didn't specify
+ * an onError handler.
+ * @since 2.0.6 - experimental
+ */
+@Experimental
+public final class OnErrorNotImplementedException extends RuntimeException {
+
+    private static final long serialVersionUID = -6298857009889503852L;
+
+    /**
+     * Customizes the {@code Throwable} with a custom message and wraps it before it
+     * is signalled to the {@code RxJavaPlugins.onError()} handler as {@code OnErrorNotImplementedException}.
+     *
+     * @param message
+     *          the message to assign to the {@code Throwable} to signal
+     * @param e
+     *          the {@code Throwable} to signal; if null, a NullPointerException is constructed
+     */
+    public OnErrorNotImplementedException(String message, Throwable e) {
+        super(message, e != null ? e : new NullPointerException());
+    }
+
+    /**
+     * Wraps the {@code Throwable} before it
+     * is signalled to the {@code RxJavaPlugins.onError()}
+     * handler as {@code OnErrorNotImplementedException}.
+     *
+     * @param e
+     *          the {@code Throwable} to signal; if null, a NullPointerException is constructed
+     */
+    public OnErrorNotImplementedException(Throwable e) {
+        super(e != null ? e.getMessage() : null, e != null ? e : new NullPointerException());
+    }
+}

src/main/java/io/reactivex/internal/functions/Functions.java

@@ -18,6 +18,7 @@
 import org.reactivestreams.Subscription;
 
 import io.reactivex.*;
+import io.reactivex.exceptions.OnErrorNotImplementedException;
 import io.reactivex.functions.*;
 import io.reactivex.plugins.RxJavaPlugins;
 import io.reactivex.schedulers.Timed;
@@ -218,6 +219,17 @@ public void accept(Throwable error) {
         }
     };
 
+    /**
+     * Wraps the consumed Throwable into an OnErrorNotImplementedException and
+     * signals it to the plugin error handler.
+     */
+    public static final Consumer<Throwable> ON_ERROR_MISSING = new Consumer<Throwable>() {
+        @Override
+        public void accept(Throwable error) {
+            RxJavaPlugins.onError(new OnErrorNotImplementedException(error));
+        }
+    };
+
     public static final LongConsumer EMPTY_LONG_CONSUMER = new LongConsumer() {
         @Override
         public void accept(long v) { }

src/main/java/io/reactivex/internal/observers/CallbackCompletableObserver.java

@@ -17,9 +17,9 @@
 
 import io.reactivex.CompletableObserver;
 import io.reactivex.disposables.Disposable;
-import io.reactivex.exceptions.Exceptions;
+import io.reactivex.exceptions.*;
 import io.reactivex.functions.*;
-import io.reactivex.internal.disposables.*;
+import io.reactivex.internal.disposables.DisposableHelper;
 import io.reactivex.plugins.RxJavaPlugins;
 
 public final class CallbackCompletableObserver
@@ -43,7 +43,7 @@ public CallbackCompletableObserver(Consumer<? super Throwable> onError, Action o
 
     @Override
     public void accept(Throwable e) {
-        RxJavaPlugins.onError(e);
+        RxJavaPlugins.onError(new OnErrorNotImplementedException(e));
     }
 
     @Override

src/main/java/io/reactivex/internal/observers/EmptyCompletableObserver.java

@@ -17,7 +17,8 @@
 
 import io.reactivex.CompletableObserver;
 import io.reactivex.disposables.Disposable;
-import io.reactivex.internal.disposables.*;
+import io.reactivex.exceptions.OnErrorNotImplementedException;
+import io.reactivex.internal.disposables.DisposableHelper;
 import io.reactivex.plugins.RxJavaPlugins;
 
 public final class EmptyCompletableObserver
@@ -46,7 +47,7 @@ public void onComplete() {
     @Override
     public void onError(Throwable e) {
         lazySet(DisposableHelper.DISPOSED);
-        RxJavaPlugins.onError(e);
+        RxJavaPlugins.onError(new OnErrorNotImplementedException(e));
     }
 
     @Override