2.x: fix takeUntil() other triggering twice (#4962)

Author: akarnokd

src/main/java/io/reactivex/internal/operators/single/SingleTakeUntil.java

@@ -147,7 +147,7 @@ public void onSubscribe(Subscription s) {
         @Override
         public void onNext(Object t) {
             if (SubscriptionHelper.cancel(this)) {
-                onComplete();
+                parent.otherError(new CancellationException());
             }
         }
 
@@ -158,7 +158,10 @@ public void onError(Throwable t) {
 
         @Override
         public void onComplete() {
-            parent.otherError(new CancellationException());
+            if (get() != SubscriptionHelper.CANCELLED) {
+                lazySet(SubscriptionHelper.CANCELLED);
+                parent.otherError(new CancellationException());
+            }
         }
 
         public void dispose() {

src/test/java/io/reactivex/internal/operators/maybe/MaybeTakeUntilPublisherTest.java

@@ -184,4 +184,18 @@ public void run() {
             to.assertResult();
         }
     }
+
+    @Test
+    public void otherSignalsAndCompletes() {
+        List<Throwable> errors = TestHelper.trackPluginErrors();
+        try {
+            Maybe.just(1).takeUntil(Flowable.just(1).take(1))
+            .test()
+            .assertResult();
+
+            assertTrue(errors.toString(), errors.isEmpty());
+        } finally {
+            RxJavaPlugins.reset();
+        }
+    }
 }

src/test/java/io/reactivex/internal/operators/single/SingleTakeUntilTest.java

@@ -16,6 +16,7 @@
 import java.util.List;
 import java.util.concurrent.CancellationException;
 
+import static org.junit.Assert.*;
 import org.junit.Test;
 
 import io.reactivex.*;
@@ -259,4 +260,18 @@ public void run() {
             }
         }
     }
+
+    @Test
+    public void otherSignalsAndCompletes() {
+        List<Throwable> errors = TestHelper.trackPluginErrors();
+        try {
+            Single.just(1).takeUntil(Flowable.just(1).take(1))
+            .test()
+            .assertFailure(CancellationException.class);
+
+            assertTrue(errors.toString(), errors.isEmpty());
+        } finally {
+            RxJavaPlugins.reset();
+        }
+    }
 }