Refactoring two pieces of polymer:

pkg/polymer/lib/src/mirror_loader.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-part of polymer;
+/// Contains logic to initialize polymer apps during development. This
+/// implementation uses dart:mirrors to load each library as they are discovered
+/// through HTML imports. This is only meant to be during development in
+/// dartium, and the polymer transformers replace this implementation with
+/// codege generation in the polymer-build steps.
+library polymer.src.mirror_loader;
 
-/// Annotation used to automatically register polymer elements.
-class CustomTag {
-  final String tagName;
-  const CustomTag(this.tagName);
-}
+import 'dart:async';
+import 'dart:html';
+import 'dart:collection' show LinkedHashMap;
 
-/// Metadata used to label static or top-level methods that are called
-/// automatically when loading the library of a custom element.
-const initMethod = const _InitMethodAnnotation();
+// Technically, we shouldn't need any @MirrorsUsed, since this is for
+// development only, but our test bots don't yet run pub-build. See more details
+// on the comments of the mirrors import in `lib/polymer.dart`.
+@MirrorsUsed(metaTargets:
+    const [CustomTag, InitMethodAnnotation],
+    override: const ['smoke.mirrors', 'polymer.src.mirror_loader'])
+import 'dart:mirrors';
 
-/// Initializes a polymer application as follows:
-///   * set up up polling for observable changes
-///   * initialize Model-Driven Views
-///   * Include some style to prevent flash of unstyled content (FOUC)
-///   * for each library included transitively from HTML and HTML imports,
-///   register custom elements declared there (labeled with [CustomTag]) and
-///   invoke the initialization method on it (top-level functions annotated with
-///   [initMethod]).
-Zone initPolymer() {
-  // We use this pattern, and not the inline lazy initialization pattern, so we
-  // can help dart2js detect that _discoverInitializers can be tree-shaken for
-  // deployment (and hence all uses of dart:mirrors from this loading logic).
-  // TODO(sigmund): fix polymer's transformers so they can replace initPolymer
-  // by initPolymerOptimized.
-  if (_initializers == null) _initializers = _discoverInitializers();
+import 'package:logging/logging.dart' show Logger;
+import 'package:polymer/polymer.dart' show
+    InitMethodAnnotation, CustomTag, initMethod, Polymer;
 
-  // In deployment mode, we rely on change notifiers instead of dirty checking.
-  if (!_deployMode) {
-    return dirtyCheckZone()..run(initPolymerOptimized);
-  }
 
-  return initPolymerOptimized();
-}
-
-/// Same as [initPolymer], but runs the version that is optimized for deployment
-/// to the internet. The biggest difference is it omits the [Zone] that
-/// automatically invokes [Observable.dirtyCheck], and the list of initializers
-/// must be supplied instead of being dynamically searched for at runtime using
-/// mirrors.
-Zone initPolymerOptimized() {
-  // TODO(sigmund): refactor this so we can replace it by codegen.
-  smoke.useMirrors();
-  _hookJsPolymer();
-
-  for (var initializer in _initializers) {
-    initializer();
-  }
-
-  return Zone.current;
-}
-
-/// Configures [initPolymer] making it optimized for deployment to the internet.
-/// With this setup the initializer list is supplied instead of searched for
-/// at runtime. Additionally, after this method is called [initPolymer] omits
-/// the [Zone] that automatically invokes [Observable.dirtyCheck].
-void configureForDeployment(List<Function> initializers) {
-  _initializers = initializers;
-  _deployMode = true;
-}
-
-/// List of initializers that by default will be executed when calling
-/// initPolymer. If null, initPolymer will compute the list of initializers by
-/// crawling HTML imports, searchfing for script tags, and including an
+/// Set of initializers that are invoked by `initPolymer`.  This is computed the
+/// list by crawling HTML imports, searching for script tags, and including an
 /// initializer for each type tagged with a [CustomTag] annotation and for each
-/// top-level method annotated with [initMethod]. The value of this field is
-/// assigned programatically by the code generated from the polymer deploy
-/// scripts.
-List<Function> _initializers;
+/// top-level method annotated with [initMethod].
+List<Function> initializers = _discoverInitializers();
 
 /// True if we're in deployment mode.
-bool _deployMode = false;
+bool deployMode = false;
 
+/// Discovers what script tags are loaded from HTML pages and collects the
+/// initializers of their corresponding libraries.
 List<Function> _discoverInitializers() {
   var initializers = [];
   var librariesToLoad = _discoverScripts(document, window.location.href);
   for (var lib in librariesToLoad) {
     try {
       _loadLibrary(lib, initializers);
     } catch (e, s) {
       // Deliver errors async, so if a single library fails it doesn't prevent
       // other things from loading.
       new Completer().completeError(e, s);
@@ skipping 36 matching lines @@
   return scripts;
 }
 
 /// All libraries in the current isolate.
 final _libs = currentMirrorSystem().libraries;
 
 // TODO(sigmund): explore other (cheaper) ways to resolve URIs relative to the
 // root library (see dartbug.com/12612)
 final _rootUri = currentMirrorSystem().isolate.rootLibrary.uri;
 
-final Logger _loaderLog = new Logger('polymer.loader');
+final Logger _loaderLog = new Logger('polymer.src.mirror_loader');
 
 bool _isHttpStylePackageUrl(Uri uri) {
   var uriPath = uri.path;
   return uri.scheme == _rootUri.scheme &&
       // Don't process cross-domain uris.
       uri.authority == _rootUri.authority &&
       uriPath.endsWith('.dart') &&
       (uriPath.contains('/packages/') || uriPath.startsWith('packages/'));
 }
 
@@ skipping 98 matching lines @@
         " ${method.simpleName} is not.");
     return;
   }
   if (!method.parameters.where((p) => !p.isOptional).isEmpty) {
     print("warning: methods marked with @initMethod should take no "
         "arguments, ${method.simpleName} expects some.");
     return;
   }
   initializers.add(() => obj.invoke(method.simpleName, const []));
 }
-
-class _InitMethodAnnotation {
-  const _InitMethodAnnotation();
-}
-
-/// To ensure Dart can interoperate with polymer-element registered by
-/// polymer.js, we need to be able to execute Dart code if we are registering
-/// a Dart class for that element. We trigger Dart logic by patching
-/// polymer-element's register function and:
-///
-/// * if it has a Dart class, run PolymerDeclaration's register.
-/// * otherwise it is a JS prototype, run polymer-element's normal register.
-void _hookJsPolymer() {
-  var polymerJs = js.context['Polymer'];
-  if (polymerJs == null) {
-    throw new StateError('polymer.js must be loaded before polymer.dart, please'
-        ' add <link rel="import" href="packages/polymer/polymer.html"> to your'
-        ' <head> before any Dart scripts. Alternatively you can get a different'
-        ' version of polymer.js by following the instructions at'
-        ' http://www.polymer-project.org; if you do that be sure to include'
-        ' the platform polyfills.');
-  }
-
-  // TODO(jmesserly): dart:js appears to not callback in the correct zone:
-  // https://code.google.com/p/dart/issues/detail?id=17301
-  var zone = Zone.current;
-
-  polymerJs.callMethod('whenPolymerReady',
-      [zone.bindCallback(() => Polymer._ready.complete())]);
-
-  var jsPolymer = new JsObject.fromBrowserObject(
-      document.createElement('polymer-element'));
-
-  var proto = js.context['Object'].callMethod('getPrototypeOf', [jsPolymer]);
-  if (proto is Node) {
-    proto = new JsObject.fromBrowserObject(proto);
-  }
-
-  JsFunction originalRegister = proto['register'];
-  if (originalRegister == null) {
-    throw new StateError('polymer.js must expose "register" function on '
-        'polymer-element to enable polymer.dart to interoperate.');
-  }
-
-  registerDart(jsElem, String name, String extendee) {
-    // By the time we get here, we'll know for sure if it is a Dart object
-    // or not, because polymer-element will wait for us to notify that
-    // the @CustomTag was found.
-    final type = _getRegisteredType(name);
-    if (type != null) {
-      final extendsDecl = _getDeclaration(extendee);
-      return zone.run(() =>
-          new PolymerDeclaration(jsElem, name, type, extendsDecl).register());
-    }
-    // It's a JavaScript polymer element, fall back to the original register.
-    return originalRegister.apply([name, extendee], thisArg: jsElem);
-  }
-
-  proto['register'] = new JsFunction.withThis(registerDart);
-}