fix(delayWhen): correctly handle synchronous duration observable

spec/operators/delayWhen-spec.ts

@@ -1,5 +1,6 @@
 import * as Rx from '../../dist/cjs/Rx';
 import marbleTestingSignature = require('../helpers/marble-testing'); // tslint:disable-line:no-require-imports
+import { expect } from 'chai';
 
 declare const { asDiagram };
 declare const hot: typeof marbleTestingSignature.hot;
@@ -215,4 +216,16 @@ describe('Observable.prototype.delayWhen', () => {
     expectSubscriptions(selector.subscriptions).toBe([]);
     expectSubscriptions(subDelay.subscriptions).toBe(subDelaySub);
   });
+
+  it('should complete when duration selector returns synchronous observable', () => {
+    let next: boolean = false;
+    let complete: boolean = false;
+
+    Rx.Observable.of(1)
+      .delayWhen(() => Rx.Observable.of(2))
+      .subscribe(() => next = true, null, () => complete = true);
+
+    expect(next).to.be.true;
+    expect(complete).to.be.true;
+  });
 });

src/operator/delayWhen.ts

@@ -56,7 +56,7 @@ export function delayWhen<T>(this: Observable<T>, delayDurationSelector: (value:
                              subscriptionDelay?: Observable<any>): Observable<T> {
   if (subscriptionDelay) {
     return new SubscriptionDelayObservable(this, subscriptionDelay)
-            .lift(new DelayWhenOperator(delayDurationSelector));
+      .lift(new DelayWhenOperator(delayDurationSelector));
   }
   return this.lift(new DelayWhenOperator(delayDurationSelector));
 }
@@ -112,7 +112,7 @@ class DelayWhenSubscriber<T, R> extends OuterSubscriber<T, R> {
         this.tryDelay(delayNotifier, value);
       }
     } catch (err) {
-        this.destination.error(err);
+      this.destination.error(err);
     }
   }
 
@@ -138,9 +138,12 @@ class DelayWhenSubscriber<T, R> extends OuterSubscriber<T, R> {
 
   private tryDelay(delayNotifier: Observable<any>, value: T): void {
     const notifierSubscription = subscribeToResult(this, delayNotifier, value);
-    this.add(notifierSubscription);
 
-    this.delayNotifierSubscriptions.push(notifierSubscription);
+    if (notifierSubscription && !notifierSubscription.closed) {
+      this.add(notifierSubscription);
+      this.delayNotifierSubscriptions.push(notifierSubscription);
+    }
+
     this.values.push(value);
   }