use bounded wildcards for errorHandler (fixes ReactiveX#5045) (ReactiveX#5049)

* use bounded wildcards for errorHandler (fixes ReactiveX#5045)

* add test to ensure signature

Author: jschneider

src/main/java/io/reactivex/plugins/RxJavaPlugins.java

@@ -49,7 +49,7 @@
  */
 public final class RxJavaPlugins {
     @Nullable
-    static volatile Consumer<Throwable> errorHandler;
+    static volatile Consumer<? super Throwable> errorHandler;
 
     @Nullable
     static volatile Function<Runnable, Runnable> onScheduleHandler;
@@ -197,7 +197,7 @@ public static Function<Scheduler, Scheduler> getComputationSchedulerHandler() {
      * @return the hook consumer, may be null
      */
     @Nullable
-    public static Consumer<Throwable> getErrorHandler() {
+    public static Consumer<? super Throwable> getErrorHandler() {
         return errorHandler;
     }
 
@@ -356,7 +356,7 @@ public static Scheduler onComputationScheduler(@NonNull Scheduler defaultSchedul
      * @param error the error to report
      */
     public static void onError(@NonNull Throwable error) {
-        Consumer<Throwable> f = errorHandler;
+        Consumer<? super Throwable> f = errorHandler;
 
         if (error == null) {
             error = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
@@ -497,7 +497,7 @@ public static void setComputationSchedulerHandler(@Nullable Function<Scheduler,
      * Sets the specific hook function.
      * @param handler the hook function to set, null allowed
      */
-    public static void setErrorHandler(@Nullable Consumer<Throwable> handler) {
+    public static void setErrorHandler(@Nullable Consumer<? super Throwable> handler) {
         if (lockdown) {
             throw new IllegalStateException("Plugins can't be changed anymore");
         }

src/test/java/io/reactivex/plugins/RxJavaPluginsTest.java

@@ -1168,7 +1168,28 @@ public void uncaughtException(Thread t, Throwable e) {
         }
     }
 
-    @SuppressWarnings({ "rawtypes", "unchecked" })
+    /**
+     * Ensure setErrorHandler() accepts a consumer with "? super Throwable"
+     */
+    @Test
+    public void onErrorWithSuper() throws Exception {
+        try {
+            Consumer<? super Throwable> errorHandler = new Consumer<Throwable>() {
+                @Override
+                public void accept(Throwable t) {
+                    throw new TestException("Forced failure 2");
+                }
+            };
+            RxJavaPlugins.setErrorHandler(errorHandler);
+
+            Consumer<? super Throwable> errorHandler1 = RxJavaPlugins.getErrorHandler();
+            assertSame(errorHandler, errorHandler1);
+        } finally {
+            RxJavaPlugins.reset();
+        }
+    }
+
+    @SuppressWarnings({"rawtypes", "unchecked" })
     @Test
     public void clearIsPassthrough() {
         try {