feat(change_detection): add static append method to Pipes

This change allows creation of a new Pipes object with new pipes appended
to pipes of an inherited Pipes.

Closes angular#2901

modules/angular2/src/change_detection/pipes/pipes.ts

@@ -1,4 +1,4 @@
-import {List, ListWrapper} from 'angular2/src/facade/collection';
+import {ListWrapper, isListLikeIterable, StringMapWrapper} from 'angular2/src/facade/collection';
 import {isBlank, isPresent, BaseException, CONST} from 'angular2/src/facade/lang';
 import {Pipe, PipeFactory} from './pipe';
 import {Injectable} from 'angular2/src/di/decorators';
@@ -20,6 +20,30 @@ export class Pipes {
     return factory.create(cdRef);
   }
 
+  static append (config) {
+    return (pipes:Pipes):Pipes => {
+      var mergedConfig:StringMap<string,PipeFactory[]> = <StringMap<string,PipeFactory[]>>{};
+
+      // Manual deep copy of existing Pipes config,
+      // so that lists of PipeFactories don't get mutated.
+      StringMapWrapper.forEach(pipes.config, (v:PipeFactory[], k:string) => {
+        mergedConfig[k] = [];
+        v.forEach((p:PipeFactory) => {
+          (<PipeFactory[]>mergedConfig[k]).push(p);
+        });
+      });
+
+      StringMapWrapper.forEach(config, (v:PipeFactory[], k:string) => {
+        if (isListLikeIterable(mergedConfig[k])) {
+          mergedConfig[k] = ListWrapper.concat(mergedConfig[k], config[k]);
+        } else {
+          mergedConfig[k] = config[k];
+        }
+      });
+      return new Pipes(mergedConfig);
+    };
+  }
+
   private _getListOfFactories(type: string, obj: any): PipeFactory[] {
     var listOfFactories = this.config[type];
     if (isBlank(listOfFactories)) {

modules/angular2/test/change_detection/pipes/pipes_spec.ts

@@ -12,6 +12,7 @@ import {
 } from 'angular2/test_lib';
 
 import {Pipes} from 'angular2/src/change_detection/pipes/pipes';
+import {PipeFactory} from 'angular2/src/change_detection/pipes/pipe';
 
 export function main() {
   describe("pipe registry", () => {
@@ -73,5 +74,24 @@ export function main() {
       expect(() => r.get("type", "some object"))
           .toThrowError(`Cannot find 'type' pipe supporting object 'some object'`);
     });
+
+    describe('.append()', () => {
+      it('should create a factory that appends new pipes to old', () => {
+        firstPipeFactory.spy("supports").andReturn(false);
+        secondPipeFactory.spy("supports").andReturn(true);
+        secondPipeFactory.spy("create").andReturn(secondPipe);
+        var originalPipes:Pipes = new Pipes({
+          'async': [firstPipeFactory]
+        });
+        var factory = Pipes.append({
+          'async': <PipeFactory[]>[secondPipeFactory] 
+        });
+        var pipes = factory(originalPipes);
+
+        expect(pipes.config['async'].length).toBe(2);
+        expect(originalPipes.config['async'].length).toBe(1);
+        expect(pipes.get('async', 'second plz')).toBe(secondPipe);
+      });
+    });
   });
 }