style(dart/transform): Do not format generated code by default

Formatting code requires time and memory during the build -- do not do
it unless explicitly requested via a parameter to the transformer.

Add an entry to the
[wiki](https://github.com/angular/angular/wiki/Angular-2-Dart-Transformer)
describing the added parameter.

modules/angular2/src/transform/common/formatter.dart

@@ -2,18 +2,31 @@ library angular2.transform.common.formatter;
 
 import 'package:dart_style/dart_style.dart';
 
-import 'logging.dart';
-
-DartFormatter _formatter = null;
+AngularDartFormatter _formatter = null;
 
 void init(DartFormatter formatter) {
-  _formatter = formatter;
+  _formatter = new _RealFormatter(formatter);
 }
 
-DartFormatter get formatter {
+AngularDartFormatter get formatter {
   if (_formatter == null) {
-    logger.info('Formatter never initialized, using default formatter.');
-    _formatter = new DartFormatter();
+    _formatter = new _PassThroughFormatter();
   }
   return _formatter;
 }
+
+abstract class AngularDartFormatter {
+  String format(String source, {uri});
+}
+
+class _PassThroughFormatter implements AngularDartFormatter {
+  String format(String source, {uri}) => source;
+}
+
+class _RealFormatter implements AngularDartFormatter {
+  final DartFormatter _formatter;
+
+  _RealFormatter(this._formatter);
+
+  String format(source, {uri}) => _formatter.format(source, uri: uri);
+}

modules/angular2/src/transform/common/options.dart

@@ -8,6 +8,7 @@ const DEFAULT_OPTIMIZATION_PHASES = 5;
 
 const CUSTOM_ANNOTATIONS_PARAM = 'custom_annotations';
 const ENTRY_POINT_PARAM = 'entry_points';
+const FORMAT_CODE_PARAM = 'format_code';
 const GENERATE_CHANGE_DETECTORS_PARAM = 'generate_change_detectors';
 const INIT_REFLECTOR_PARAM = 'init_reflector';
 const INLINE_VIEWS_PARAM = 'inline_views';
@@ -51,6 +52,11 @@ class TransformerOptions {
   /// The "correct" number of phases varies with the structure of the app.
   final int optimizationPhases;
 
+  /// Whether to format generated code.
+  /// Code that is only modified will never be formatted because doing so may
+  /// invalidate the source maps generated by `dart2js` and/or other tools.
+  final bool formatCode;
+
   TransformerOptions._internal(
       this.entryPoints,
       this.reflectionEntryPoints,
@@ -59,8 +65,9 @@ class TransformerOptions {
       this.initReflector,
       this.annotationMatcher,
       this.optimizationPhases,
-      this.generateChangeDetectors,
-      this.inlineViews);
+      {this.generateChangeDetectors,
+      this.inlineViews,
+      this.formatCode});
 
   factory TransformerOptions(List<String> entryPoints,
       {List<String> reflectionEntryPoints,
@@ -70,7 +77,8 @@ class TransformerOptions {
       List<ClassDescriptor> customAnnotationDescriptors: const [],
       int optimizationPhases: DEFAULT_OPTIMIZATION_PHASES,
       bool inlineViews: true,
-      bool generateChangeDetectors: true}) {
+      bool generateChangeDetectors: true,
+      bool formatCode: false}) {
     if (reflectionEntryPoints == null || reflectionEntryPoints.isEmpty) {
       reflectionEntryPoints = entryPoints;
     }
@@ -85,7 +93,8 @@ class TransformerOptions {
         initReflector,
         annotationMatcher,
         optimizationPhases,
-        generateChangeDetectors,
-        inlineViews);
+        generateChangeDetectors: generateChangeDetectors,
+        inlineViews: inlineViews,
+        formatCode: formatCode);
   }
 }

modules/angular2/src/transform/common/options_reader.dart

@@ -15,6 +15,7 @@ TransformerOptions parseBarbackSettings(BarbackSettings settings) {
   var inlineViews = _readBool(config, INLINE_VIEWS_PARAM, defaultValue: true);
   var generateChangeDetectors =
       _readBool(config, GENERATE_CHANGE_DETECTORS_PARAM, defaultValue: true);
+  var formatCode = _readBool(config, FORMAT_CODE_PARAM, defaultValue: false);
   String mirrorModeVal =
       config.containsKey(MIRROR_MODE_PARAM) ? config[MIRROR_MODE_PARAM] : '';
   var mirrorMode = MirrorMode.none;
@@ -39,7 +40,8 @@ TransformerOptions parseBarbackSettings(BarbackSettings settings) {
       inlineViews: inlineViews,
       customAnnotationDescriptors: _readCustomAnnotations(config),
       optimizationPhases: optimizationPhases,
-      generateChangeDetectors: generateChangeDetectors);
+      generateChangeDetectors: generateChangeDetectors,
+      formatCode: formatCode);
 }
 
 bool _readBool(Map config, String paramName, {bool defaultValue}) {

modules/angular2/src/transform/transformer.dart

@@ -18,8 +18,10 @@ export 'common/options.dart';
 
 /// Replaces Angular 2 mirror use with generated code.
 class AngularTransformerGroup extends TransformerGroup {
-  AngularTransformerGroup._(phases) : super(phases) {
-    formatter.init(new DartFormatter());
+  AngularTransformerGroup._(phases, {bool formatCode: false}) : super(phases) {
+    if (formatCode) {
+      formatter.init(new DartFormatter());
+    }
   }
 
   factory AngularTransformerGroup(TransformerOptions options) {
@@ -38,7 +40,8 @@ class AngularTransformerGroup extends TransformerGroup {
       [new BindGenerator(options)],
       [new TemplateCompiler(options)]
     ]);
-    return new AngularTransformerGroup._(phases);
+    return new AngularTransformerGroup._(phases,
+        formatCode: options.formatCode);
   }
 
   factory AngularTransformerGroup.asPlugin(BarbackSettings settings) {

modules/angular2/test/transform/integration/all_tests.dart

@@ -14,7 +14,8 @@ main() {
 var formatter = new DartFormatter();
 var transform = new AngularTransformerGroup(new TransformerOptions(
     ['web/index.dart'],
-    reflectionEntryPoints: ['web/index.dart']));
+    reflectionEntryPoints: ['web/index.dart'],
+    formatCode: true));
 
 class IntegrationTestConfig {
   final String name;