fix(switchMap): stop listening to a synchronous inner-obervable when …

…unsubscribed

spec/operators/switchMap-spec.ts

@@ -1,7 +1,7 @@
 import { expect } from 'chai';
 import { hot, cold, expectObservable, expectSubscriptions } from '../helpers/marble-testing';
-import { switchMap, mergeMap, map } from 'rxjs/operators';
-import { of, Observable } from 'rxjs';
+import { switchMap, mergeMap, map, takeWhile } from 'rxjs/operators';
+import { concat, defer, of, Observable } from 'rxjs';
 
 declare function asDiagram(arg: string): Function;
 
@@ -169,6 +169,31 @@ describe('switchMap', () => {
     expectSubscriptions(e1.subscriptions).toBe(e1subs);
   });
 
+  it('should stop listening to a synchronous observable when unsubscribed', () => {
+    const sideEffects: number[] = [];
+    const synchronousObservable = concat(
+      defer(() => {
+        sideEffects.push(1);
+        return of(1);
+      }),
+      defer(() => {
+        sideEffects.push(2);
+        return of(2);
+      }),
+      defer(() => {
+        sideEffects.push(3);
+        return of(3);
+      })
+    );
+
+    of(null).pipe(
+      switchMap(() => synchronousObservable),
+      takeWhile((x) => x != 2) // unsubscribe at the second side-effect
+    ).subscribe(() => { /* noop */ });
+
+    expect(sideEffects).to.deep.equal([1, 2]);
+  });
+
   it('should switch inner cold observables, inner never completes', () => {
     const x =   cold(         '--a--b--c--d--e--|          ');
     const xsubs =    '         ^         !                 ';

src/internal/operators/switchMap.ts

@@ -113,7 +113,9 @@ class SwitchMapSubscriber<T, R> extends OuterSubscriber<T, R> {
     if (innerSubscription) {
       innerSubscription.unsubscribe();
     }
-    this.add(this.innerSubscription = subscribeToResult(this, result, value, index));
+    const innerSubscriber = new InnerSubscriber(this, undefined, undefined);
+    this.add(innerSubscriber);
+    this.innerSubscription = subscribeToResult(this, result, value, index, innerSubscriber);
   }
 
   protected _complete(): void {