fix(change detection): preserve memoized results from pure functions

Author: yjbanov

modules/angular2/src/change_detection/change_detection_jit_generator.ts

@@ -291,7 +291,7 @@ export class ChangeDetectorJITGenerator {
 
     if (r.isPureFunction()) {
       var condition = r.args.map((a) => this._changeNames[a]).join(" || ");
-      return `if (${condition}) { ${check} }`;
+      return `if (${condition}) { ${check} } else { ${newValue} = ${oldValue}; }`;
     } else {
       return check;
     }

modules/angular2/src/core/application.ts

@@ -69,12 +69,11 @@ var _rootBindings = [bind(Reflector).toValue(reflector), TestabilityRegistry];
 
 function _injectorBindings(appComponentType): List<Type | Binding | List<any>> {
   var bestChangeDetection: Type = DynamicChangeDetection;
-  // Re-enable once all e2e tests pass
-  // if (PreGeneratedChangeDetection.isSupported()) {
-  //  bestChangeDetection = PreGeneratedChangeDetection;
-  //} else if (JitChangeDetection.isSupported()) {
-  //  bestChangeDetection = JitChangeDetection;
-  //}
+  if (PreGeneratedChangeDetection.isSupported()) {
+    bestChangeDetection = PreGeneratedChangeDetection;
+  } else if (JitChangeDetection.isSupported()) {
+    bestChangeDetection = JitChangeDetection;
+  }
   return [
     bind(DOCUMENT_TOKEN)
         .toValue(DOM.defaultDoc()),

modules/angular2/src/transform/template_compiler/change_detector_codegen.dart

@@ -352,7 +352,7 @@ class _CodegenState {
     if (r.isPureFunction()) {
       // Add an "if changed guard"
       var condition = r.args.map((a) => _changeNames[a]).join(' || ');
-      return 'if ($condition) { $check }';
+      return 'if ($condition) { $check } else { $newValue = $oldValue; }';
     } else {
       return check;
     }

modules/angular2/test/change_detection/change_detector_config.ts

@@ -303,5 +303,6 @@ var _availableDefinitions = [
   'address?.toString()',
   'sayHi("Jim")',
   'a()(99)',
-  'a.sayHi("Jim")'
+  'a.sayHi("Jim")',
+  'passThrough([12])'
 ];

modules/angular2/test/change_detection/change_detector_spec.ts

@@ -54,8 +54,8 @@ const _DEFAULT_CONTEXT = CONST_EXPR(new Object());
 /**
  * Tests in this spec run against three different implementations of `AbstractChangeDetector`,
  * `dynamic` (which use reflection to inspect objects), `JIT` (which are generated only for
- * Javascript at runtime using `eval` to avoid the need for reflection) and `Pregen` (which are
- * generated only for Dart prior to app deploy to avoid the need for reflection).
+ * Javascript at runtime using `eval`) and `Pregen` (which are generated only for Dart prior
+ * to app deploy to avoid the need for reflection).
  *
  * Pre-generated classes require knowledge of the shape of the change detector at the time of Dart
  * transformation, so in these tests we abstract a `ChangeDetectorDefinition` out into the
@@ -304,6 +304,16 @@ export function main() {
         expect(val.dispatcher.log).toEqual(['propName=BvalueA']);
       });
 
+      describe('pure functions', () => {
+        it('should preserve memoized result', () => {
+          var person = new Person('bob');
+          var val = _createChangeDetector('passThrough([12])', person);
+          val.changeDetector.detectChanges();
+          val.changeDetector.detectChanges();
+          expect(val.dispatcher.loggedValues).toEqual([[12]]);
+        });
+      });
+
       describe('change notification', () => {
         describe('simple checks', () => {
           it('should pass a change record to the dispatcher', () => {
@@ -948,6 +958,8 @@ class Person {
 
   sayHi(m) { return `Hi, ${m}`; }
 
+  passThrough(val) { return val; }
+
   toString(): string {
     var address = this.address == null ? '' : ' address=' + this.address.toString();