fix(takeWhile): force unsubscribe when it completes or errors (#2470)

Force unsubscribe on `takeWhile` when it completes or errors,
even when used with operator that does not unsubscribe reliably,
so that source Observable is never subscribed longer than it
needs to.

spec/helpers/doNotUnsubscribe.ts

@@ -0,0 +1,16 @@
+///<reference path='../../typings/index.d.ts'/>
+import * as Rx from '../../dist/cjs/Rx';
+
+export function doNotUnsubscribe<T>(ob: Rx.Observable<T>): Rx.Observable<T> {
+ return ob.lift(new DoNotUnsubscribeOperator());
+}
+
+class DoNotUnsubscribeOperator<T, R> implements Rx.Operator<T, R> {
+ call(subscriber: Rx.Subscriber<R>, source: any): any {
+ return source.subscribe(new DoNotUnsubscribeSubscriber(subscriber));
+ }
+}
+
+class DoNotUnsubscribeSubscriber<T> extends Rx.Subscriber<T> {
+ unsubscribe() {} // tslint:disable-line no-empty
+}

spec/operators/takeWhile-spec.ts

@@ -1,6 +1,7 @@
 import {expect} from 'chai';
 import * as Rx from '../../dist/cjs/Rx';
 import marbleTestingSignature = require('../helpers/marble-testing'); // tslint:disable-line:no-require-imports
+import { doNotUnsubscribe } from '../helpers/doNotUnsubscribe';
 
 declare const { asDiagram };
 declare const hot: typeof marbleTestingSignature.hot;
@@ -205,4 +206,37 @@ describe('Observable.prototype.takeWhile', () => {
  expectObservable(result, unsub).toBe(expected);
  expectSubscriptions(e1.subscriptions).toBe(e1subs);
  });
+
+ it('should unsubscribe from source Observable after complete,' +
+ ' even if destination does not unsubscribe', () => {
+ const e1 = hot('--a-^-b--c--d--e--|');
+ const e1subs = '^-------! ';
+ const expected = '--b--c--|';
+
+ function predicate(value) {
+ return value !== 'd';
+ }
+
+ const result = e1.takeWhile(predicate).let(doNotUnsubscribe);
+
+ expectObservable(result).toBe(expected);
+ expectSubscriptions(e1.subscriptions).toBe(e1subs);
+ });
+
+ it('should unsubscribe from source Observable after error,' +
+ ' even if destination does not unsubscribe', () => {
+ const e1 = hot('--a-^-b--c--d--e--|');
+ const e1subs = '^----! ';
+ const expected = '--b--#';
+
+ function predicate(value) {
+ if (value === 'c') { throw 'error'; }
+ return value !== 'd';
+ }
+
+ const result = e1.takeWhile(predicate).let(doNotUnsubscribe);
+
+ expectObservable(result).toBe(expected);
+ expectSubscriptions(e1.subscriptions).toBe(e1subs);
+ });
 });

src/operator/takeWhile.ts

@@ -72,6 +72,7 @@ class TakeWhileSubscriber<T> extends Subscriber<T> {
  result = this.predicate(value, this.index++);
  } catch (err) {
  destination.error(err);
+ this.unsubscribe();
  return;
  }
  this.nextOrComplete(value, result);
@@ -83,6 +84,7 @@ class TakeWhileSubscriber<T> extends Subscriber<T> {
  destination.next(value);
  } else {
  destination.complete();
+ this.unsubscribe();
  }
  }
 }