feat(pipes): add support for pure pipes

By default, pipes are pure. This means that an instance of a pipe will be reused and the pipe will be called only when its arguments change.

BREAKING CHANGE

Before:

@Pipe({name: 'date'}) class DatePipe {} defines an impure pipe.

After:

@Pipe({name: 'date'}) class DatePipe {} defines a pure pipe.
@Pipe({name: 'date', pure: false}) class DatePipe {} defines an impure pipe.

Closes #3966

modules/angular2/src/core/change_detection/change_detection_jit_generator.ts

@@ -236,13 +236,18 @@ export class ChangeDetectorJITGenerator {
     var newValue = this._names.getLocalName(r.selfIndex);
 
     var pipe = this._names.getPipeName(r.selfIndex);
-    var pipeType = r.name;
+    var pipeName = r.name;
-    var read = `
+
+    var init = `
       if (${pipe} === ${UTIL}.uninitialized) {
-        ${pipe} = ${this._names.getPipesAccessorName()}.get('${pipeType}');
+        ${pipe} = ${this._names.getPipesAccessorName()}.get('${pipeName}');
       }
-      ${newValue} = ${pipe}.transform(${context}, [${argString}]);
     `;
+    var read = `${newValue} = ${pipe}.pipe.transform(${context}, [${argString}]);`;
+
+    var contexOrArgCheck = r.args.map((a) => this._names.getChangeName(a));
+    contexOrArgCheck.push(this._names.getChangeName(r.contextIndex));
+    var condition = `!${pipe}.pure || (${contexOrArgCheck.join(" || ")})`;
 
     var check = `
       if (${oldValue} !== ${newValue}) {
@@ -254,7 +259,13 @@ export class ChangeDetectorJITGenerator {
       }
     `;
 
-    return r.shouldBeChecked() ? `${read}${check}` : read;
+    var genCode = r.shouldBeChecked() ? `${read}${check}` : read;
+
+    if (r.isUsedByOtherRecord()) {
+      return `${init} if (${condition}) { ${genCode} } else { ${newValue} = ${oldValue}; }`;
+    } else {
+      return `${init} if (${condition}) { ${genCode} }`;
+    }
   }
 
   _genReferenceCheck(r: ProtoRecord): string {

modules/angular2/src/core/change_detection/change_detection_util.ts

@@ -12,6 +12,7 @@ import {ChangeDetectionStrategy, isDefaultChangeDetectionStrategy} from './const
 import {implementsOnDestroy} from './pipe_lifecycle_reflector';
 import {BindingTarget} from './binding_record';
 import {DirectiveIndex} from './directive_record';
+import {SelectedPipe} from './pipes';
 
 
 /**
@@ -193,9 +194,9 @@ export class ChangeDetectionUtil {
                protos[selfIndex - 1];  // self index is shifted by one because of context
   }
 
-  static callPipeOnDestroy(pipe: any): void {
+  static callPipeOnDestroy(selectedPipe: SelectedPipe): void {
-    if (implementsOnDestroy(pipe)) {
+    if (implementsOnDestroy(selectedPipe.pipe)) {
-      pipe.onDestroy();
+      (<any>selectedPipe.pipe).onDestroy();
     }
   }
 

modules/angular2/src/core/change_detection/dynamic_change_detector.ts

@@ -333,10 +333,10 @@ export class DynamicChangeDetector extends AbstractChangeDetector<any> {
 
   _pipeCheck(proto: ProtoRecord, throwOnChange: boolean, values: any[]) {
     var context = this._readContext(proto, values);
+    var selectedPipe = this._pipeFor(proto, context);
+    if (!selectedPipe.pure || this._argsOrContextChanged(proto)) {
       var args = this._readArgs(proto, values);
-
+      var currValue = selectedPipe.pipe.transform(context, args);
-    var pipe = this._pipeFor(proto, context);
-    var currValue = pipe.transform(context, args);
 
       if (proto.shouldBeChecked()) {
         var prevValue = this._readSelf(proto, values);
@@ -367,6 +367,7 @@ export class DynamicChangeDetector extends AbstractChangeDetector<any> {
         return null;
       }
     }
+  }
 
   _pipeFor(proto: ProtoRecord, context) {
     var storedPipe = this._readPipe(proto);
@@ -413,6 +414,10 @@ export class DynamicChangeDetector extends AbstractChangeDetector<any> {
     return false;
   }
 
+  _argsOrContextChanged(proto: ProtoRecord): boolean {
+    return this._argsChanged(proto) || this.changes[proto.contextIndex];
+  }
+
   _readArgs(proto: ProtoRecord, values: any[]) {
     var res = ListWrapper.createFixedSize(proto.args.length);
     var args = proto.args;

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

@@ -1,3 +1,7 @@
 import {PipeTransform} from './pipe_transform';
 
-export interface Pipes { get(name: string): PipeTransform; }
+export interface Pipes { get(name: string): SelectedPipe; }
+
+export class SelectedPipe {
+  constructor(public pipe: PipeTransform, public pure: boolean) {}
+}

modules/angular2/src/core/change_detection/proto_change_detector.ts

@@ -102,6 +102,11 @@ export class ProtoRecordBuilder {
         rec.args.forEach(recordIndex => this.records[recordIndex - 1].argumentToPureFunction =
                              true);
       }
+      if (rec.mode === RecordType.Pipe) {
+        rec.args.forEach(recordIndex => this.records[recordIndex - 1].argumentToPureFunction =
+                             true);
+        this.records[rec.contextIndex - 1].argumentToPureFunction = true;
+      }
     }
   }
 

modules/angular2/src/core/change_detection/proto_record.ts

@@ -36,7 +36,8 @@ export class ProtoRecord {
   isUsedByOtherRecord(): boolean { return !this.lastInBinding || this.referencedBySelf; }
 
   shouldBeChecked(): boolean {
-    return this.argumentToPureFunction || this.lastInBinding || this.isPureFunction();
+    return this.argumentToPureFunction || this.lastInBinding || this.isPureFunction() ||
+           this.isPipeRecord();
   }
 
   isPipeRecord(): boolean { return this.mode === RecordType.Pipe; }

modules/angular2/src/core/metadata.dart

@@ -69,7 +69,7 @@ class View extends ViewMetadata {
  * See: [PipeMetadata] for docs.
  */
 class Pipe extends PipeMetadata {
-  const Pipe({name}) : super(name: name);
+  const Pipe({name, pure}) : super(name: name, pure: pure);
 }
 
 /**

modules/angular2/src/core/metadata.ts

@@ -398,10 +398,8 @@ export interface QueryFactory {
  * ```
  */
 export interface PipeFactory {
-  (obj: {name: string}): any;
+  (obj: {name: string, pure?: boolean}): any;
-  new (obj: {
+  new (obj: {name: string, pure?: boolean}): any;
-    name: string,
-  }): any;
 }
 
 /**

modules/angular2/src/core/metadata/directives.ts

@@ -1,6 +1,6 @@
-import {CONST, CONST_EXPR} from 'angular2/src/core/facade/lang';
+import {isPresent, CONST, CONST_EXPR} from 'angular2/src/core/facade/lang';
-import {ChangeDetectionStrategy} from 'angular2/src/core/change_detection';
 import {InjectableMetadata} from 'angular2/src/core/di/metadata';
+import {ChangeDetectionStrategy} from 'angular2/src/core/change_detection';
 
 /**
  * Directives allow you to attach behavior to elements in the DOM.
@@ -861,11 +861,15 @@ export class ComponentMetadata extends DirectiveMetadata {
 @CONST()
 export class PipeMetadata extends InjectableMetadata {
   name: string;
+  _pure: boolean;
 
-  constructor({name}: {name: string}) {
+  constructor({name, pure}: {name: string, pure: boolean}) {
     super();
     this.name = name;
+    this._pure = pure;
   }
+
+  get pure(): boolean { return isPresent(this._pure) ? this._pure : true; }
 }
 
 /**

modules/angular2/src/core/pipes/async_pipe.ts

@@ -59,7 +59,7 @@ var _observableStrategy = new ObservableStrategy();
  *
  * ```
  */
-@Pipe({name: 'async'})
+@Pipe({name: 'async', pure: false})
 @Injectable()
 export class AsyncPipe implements PipeTransform, PipeOnDestroy {
   _latestValue: Object = null;

modules/angular2/src/core/pipes/pipe_binding.ts

@@ -4,14 +4,15 @@ import {Key, ResolvedBinding, Binding} from 'angular2/src/core/di';
 import {PipeMetadata} from '../metadata/directives';
 
 export class PipeBinding extends ResolvedBinding {
-  constructor(public name: string, key: Key, resolvedFactories: ResolvedFactory[],
+  constructor(public name: string, public pure: boolean, key: Key,
-              multiBinding: boolean) {
+              resolvedFactories: ResolvedFactory[], multiBinding: boolean) {
     super(key, resolvedFactories, multiBinding);
   }
 
   static createFromType(type: Type, metadata: PipeMetadata): PipeBinding {
     var binding = new Binding(type, {toClass: type});
     var rb = resolveBinding(binding);
-    return new PipeBinding(metadata.name, rb.key, rb.resolvedFactories, rb.multiBinding);
+    return new PipeBinding(metadata.name, metadata.pure, rb.key, rb.resolvedFactories,
+                           rb.multiBinding);
   }
 }

modules/angular2/src/core/pipes/pipes.ts

@@ -1,4 +1,5 @@
 import {isBlank, isPresent, BaseException, CONST, Type} from 'angular2/src/core/facade/lang';
+import {StringMapWrapper} from 'angular2/src/core/facade/collection';
 import {
   Injectable,
   OptionalMetadata,
@@ -25,11 +26,25 @@ export class ProtoPipes {
   }
 }
 
+
+
 export class Pipes implements cd.Pipes {
+  _config: StringMap<string, cd.SelectedPipe> = {};
+
   constructor(public proto: ProtoPipes, public injector: Injector) {}
 
-  get(name: string): any {
+  get(name: string): cd.SelectedPipe {
-    var b = this.proto.get(name);
+    var cached = StringMapWrapper.get(this._config, name);
-    return this.injector.instantiateResolved(b);
+    if (isPresent(cached)) return cached;
+
+    var p = this.proto.get(name);
+    var transform = this.injector.instantiateResolved(p);
+    var res = new cd.SelectedPipe(transform, p.pure);
+
+    if (p.pure) {
+      StringMapWrapper.set(this._config, name, res);
+    }
+
+    return res;
   }
 }

modules/angular2/test/core/change_detection/change_detector_spec.ts

@@ -17,7 +17,8 @@ import {
   isBlank,
   isJsObject,
   BaseException,
-  FunctionWrapper
+  FunctionWrapper,
+  normalizeBool
 } from 'angular2/src/core/facade/lang';
 import {ListWrapper, MapWrapper, StringMapWrapper} from 'angular2/src/core/facade/collection';
 
@@ -41,7 +42,7 @@ import {
   ProtoChangeDetector
 } from 'angular2/src/core/change_detection/change_detection';
 
-import {Pipes} from 'angular2/src/core/change_detection/pipes';
+import {SelectedPipe, Pipes} from 'angular2/src/core/change_detection/pipes';
 import {JitProtoChangeDetector} from 'angular2/src/core/change_detection/jit_proto_change_detector';
 
 import {getDefinition} from './change_detector_config';
@@ -351,6 +352,36 @@ export function main() {
             expect(val.dispatcher.loggedValues).toEqual(['value one two default']);
           });
 
+          it('should not reevaluate pure pipes unless its context or arg changes', () => {
+            var pipe = new CountingPipe();
+            var registry = new FakePipes('pipe', () => pipe, {pure: true});
+            var person = new Person('bob');
+            var val = _createChangeDetector('name | pipe', person, registry);
+
+            val.changeDetector.detectChanges();
+            expect(pipe.state).toEqual(1);
+
+            val.changeDetector.detectChanges();
+            expect(pipe.state).toEqual(1);
+
+            person.name = 'jim';
+            val.changeDetector.detectChanges();
+            expect(pipe.state).toEqual(2);
+          });
+
+          it('should reevaluate impure pipes neither context nor arg changes', () => {
+            var pipe = new CountingPipe();
+            var registry = new FakePipes('pipe', () => pipe, {pure: false});
+            var person = new Person('bob');
+            var val = _createChangeDetector('name | pipe', person, registry);
+
+            val.changeDetector.detectChanges();
+            expect(pipe.state).toEqual(1);
+
+            val.changeDetector.detectChanges();
+            expect(pipe.state).toEqual(2);
+          });
+
           it('should support pipes as arguments to pure functions', () => {
             var registry = new FakePipes('pipe', () => new IdentityPipe());
             var person = new Person('bob');
@@ -1116,24 +1147,6 @@ export function main() {
         });
       });
 
-      describe('pipes', () => {
-        it('should support pipes', () => {
-          var registry = new FakePipes('pipe', () => new CountingPipe());
-          var ctx = new Person('Megatron');
-
-          var val = _createChangeDetector('name | pipe', ctx, registry);
-
-          val.changeDetector.detectChanges();
-
-          expect(val.dispatcher.log).toEqual(['propName=Megatron state:0']);
-
-          val.dispatcher.clear();
-          val.changeDetector.detectChanges();
-
-          expect(val.dispatcher.log).toEqual(['propName=Megatron state:1']);
-        });
-      });
-
       it('should do nothing when no change', () => {
         var registry = new FakePipes('pipe', () => new IdentityPipe());
         var ctx = new Person('Megatron');
@@ -1256,13 +1269,16 @@ class MultiArgPipe implements PipeTransform {
 
 class FakePipes implements Pipes {
   numberOfLookups = 0;
+  pure: boolean;
 
-  constructor(public pipeType: string, public factory: Function) {}
+  constructor(public pipeType: string, public factory: Function, {pure}: {pure?: boolean} = {}) {
+    this.pure = normalizeBool(pure);
+  }
 
   get(type: string) {
     if (type != this.pipeType) return null;
     this.numberOfLookups++;
-    return this.factory();
+    return new SelectedPipe(this.factory(), this.pure);
   }
 }
 

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

@@ -36,7 +36,8 @@ export function main() {
     it('should instantiate a pipe', () => {
       var proto = new ProtoPipes([PipeBinding.createFromType(PipeA, new Pipe({name: 'a'}))]);
       var pipes = new Pipes(proto, injector);
-      expect(pipes.get("a")).toBeAnInstanceOf(PipeA);
+
+      expect(pipes.get("a").pipe).toBeAnInstanceOf(PipeA);
     });
 
     it('should throw when no pipe found', () => {
@@ -48,7 +49,25 @@ export function main() {
     it('should inject dependencies from the provided injector', () => {
       var proto = new ProtoPipes([PipeBinding.createFromType(PipeB, new Pipe({name: 'b'}))]);
       var pipes = new Pipes(proto, injector);
-      expect(pipes.get("b").dep).toEqual("dependency");
+      expect((<any>pipes.get("b").pipe).dep).toEqual("dependency");
+    });
+
+    it('should cache pure pipes', () => {
+      var proto =
+          new ProtoPipes([PipeBinding.createFromType(PipeA, new Pipe({name: 'a', pure: true}))]);
+      var pipes = new Pipes(proto, injector);
+
+      expect(pipes.get("a").pure).toEqual(true);
+      expect(pipes.get("a")).toBe(pipes.get("a"));
+    });
+
+    it('should NOT cache impure pipes', () => {
+      var proto =
+          new ProtoPipes([PipeBinding.createFromType(PipeA, new Pipe({name: 'a', pure: false}))]);
+      var pipes = new Pipes(proto, injector);
+
+      expect(pipes.get("a").pure).toEqual(false);
+      expect(pipes.get("a")).not.toBe(pipes.get("a"));
     });
   });
 }

modules_dart/transform/lib/src/transform/template_compiler/change_detector_codegen.dart

@@ -335,13 +335,20 @@ class _CodegenState {
     var pipe = _names.getPipeName(r.selfIndex);
     var pipeType = r.name;
 
-    var read = '''
+    var init = '''
       if ($_IDENTICAL_CHECK_FN($pipe, $_UTIL.uninitialized)) {
         $pipe = ${_names.getPipesAccessorName()}.get('$pipeType');
       }
-      $newValue = $pipe.transform($context, [$argString]);
     ''';
 
+    var read = '''
+      $newValue = $pipe.pipe.transform($context, [$argString]);
+    ''';
+
+    var contexOrArgCheck = r.args.map((a) => _names.getChangeName(a)).toList();
+    contexOrArgCheck.add(_names.getChangeName(r.contextIndex));
+    var condition = '''!${pipe}.pure || (${contexOrArgCheck.join(" || ")})''';
+
     var check = '''
       if ($_NOT_IDENTICAL_CHECK_FN($oldValue, $newValue)) {
         $newValue = $_UTIL.unwrapValue($newValue);
@@ -352,7 +359,13 @@ class _CodegenState {
       }
     ''';
 
-    return r.shouldBeChecked() ? "${read}${check}" : read;
+    var genCode = r.shouldBeChecked() ? '''${read}${check}''' : read;
+
+    if (r.isUsedByOtherRecord()) {
+      return '''${init} if (${condition}) { ${genCode} } else { ${newValue} = ${oldValue}; }''';
+    } else {
+      return '''${init} if (${condition}) { ${genCode} }''';
+    }
   }
 
   String _genReferenceCheck(ProtoRecord r) {