Enables codegen support in polymer

pkg/polymer/lib/src/build/script_compactor.dart

Index: pkg/polymer/lib/src/build/script_compactor.dart
diff --git a/pkg/polymer/lib/src/build/script_compactor.dart b/pkg/polymer/lib/src/build/script_compactor.dart
index 61a6b7199e5a41ac3ffd1a06f5e70a21d9a4b527..6a9fc420eb6e9258a69428a3f90f5960068a2f4d 100644
--- a/pkg/polymer/lib/src/build/script_compactor.dart
+++ b/pkg/polymer/lib/src/build/script_compactor.dart
@@ -8,12 +8,24 @@ library polymer.src.build.script_compactor;
 import 'dart:async';
 import 'dart:convert';
 
-import 'package:html5lib/dom.dart' show Document, Element;
+import 'package:html5lib/dom.dart' show Document, Element, Text;
+import 'package:html5lib/dom_parsing.dart';
 import 'package:analyzer/src/generated/ast.dart';
+import 'package:analyzer/src/generated/element.dart' hide Element;
+import 'package:analyzer/src/generated/element.dart' as analyzer show Element;
 import 'package:barback/barback.dart';
 import 'package:code_transformers/assets.dart';
 import 'package:path/path.dart' as path;
 import 'package:source_maps/span.dart' show SourceFile;
+import 'package:smoke/codegen/generator.dart';
+import 'package:smoke/codegen/recorder.dart';
+import 'package:code_transformers/resolver.dart';
+import 'package:code_transformers/src/dart_sdk.dart';
+import 'package:template_binding/src/mustache_tokens.dart' show MustacheTokens;
+
+import 'package:polymer_expressions/expression.dart' as pe;
+import 'package:polymer_expressions/parser.dart' as pe;
+import 'package:polymer_expressions/visitor.dart' as pe;
 
 import 'import_inliner.dart' show ImportInliner; // just for docs.
 import 'common.dart';
@@ -29,16 +41,18 @@ import 'common.dart';
 /// statement to a library, and then uses `initPolymer` (see polymer.dart)  to
 /// process `@initMethod` and `@CustomTag` annotations in those libraries.
 class ScriptCompactor extends Transformer {
+  final Resolvers resolvers;
   final TransformOptions options;
 
-  ScriptCompactor(this.options);
+  ScriptCompactor(this.options, {String sdkDir})
+      : resolvers = new Resolvers(sdkDir != null ? sdkDir : dartSdkDirectory);
 
   /// Only run on entry point .html files.
   Future<bool> isPrimary(Asset input) =>
       new Future.value(options.isHtmlEntryPoint(input.id));
 
   Future apply(Transform transform) =>
-      new _ScriptCompactor(transform, options).apply();
+      new _ScriptCompactor(transform, options, resolvers).apply();
 }
 
 /// Helper class mainly use to flatten the async code.
@@ -49,13 +63,39 @@ class _ScriptCompactor extends PolymerTransformer {
   final AssetId docId;
   final AssetId bootstrapId;
 
+  /// HTML document parsed from [docId].
   Document document;
+
+  /// List of ids for each Dart entry script tag (the main tag and any tag
+  /// included on each custom element definition).
   List<AssetId> entryLibraries;
+
+  /// The id of the main Dart program.
   AssetId mainLibraryId;
+
+  /// Script tag that loads the Dart entry point.
   Element mainScriptTag;
-  final Map<AssetId, List<_Initializer>> initializers = {};
 
-  _ScriptCompactor(Transform transform, this.options)
+  /// Initializers that will register custom tags or invoke `initMethod`s.
+  final List<_Initializer> initializers = [];
+
+  /// Attributes published on a custom-tag. We make these available via
+  /// reflection even if @published was not used.
+  final Map<String, List<String>> publishedAttributes = {};
+
+  /// Hook needed to access the analyzer within barback transformers.
+  final Resolvers resolvers;
+
+  /// Resolved types used for analyzing the user's sources and generating code.
+  _ResolvedTypes types;
+
+  /// The resolver instance associated with a single run of this transformer.
+  Resolver resolver;
+
+  /// Code generator used to create the static initialization for smoke.
+  final generator = new SmokeCodeGenerator();
+
+  _ScriptCompactor(Transform transform, this.options, this.resolvers)
       : transform = transform,
         logger = transform.logger,
         docId = transform.primaryInput.id,
@@ -120,171 +160,246 @@ class _ScriptCompactor extends PolymerTransformer {
     // Emit the bootstrap .dart file
     mainScriptTag.attributes['src'] = path.url.basename(bootstrapId.path);
     entryLibraries.add(mainLibraryId);
-    return _computeInitializers().then(_createBootstrapCode).then((code) {
-      transform.addOutput(new Asset.fromString(bootstrapId, code));
-      transform.addOutput(new Asset.fromString(docId, document.outerHtml));
-    });
-  }
 
-  /// Emits the actual bootstrap code.
-  String _createBootstrapCode(_) {
-    StringBuffer code = new StringBuffer()..writeln(MAIN_HEADER);
-    for (int i = 0; i < entryLibraries.length; i++) {
-      var url = assetUrlFor(entryLibraries[i], bootstrapId, logger);
-      if (url != null) code.writeln("import '$url' as i$i;");
-    }
+    return _initResolver()
+        .then(_extractUsesOfMirrors)
+        .then(_emitFiles)
+        .then((_) => resolver.release());
+  }
 
-    code..write('\n')
-        ..writeln('void main() {')
-        ..writeln('  configureForDeployment([');
+  /// Load a resolver that computes information for every library in
+  /// [entryLibraries], then use it to initialize the [recorder] (for import
+  /// resolution) and to resolve specific elements (for analyzing the user's
+  /// code).
+  Future _initResolver() => resolvers.get(transform, entryLibraries).then((r) {
+    resolver = r;
+    types = new _ResolvedTypes(resolver);
+  });
+
+  /// Inspects the entire program to find out anything that polymer accesses
+  /// using mirrors and produces static information that can be used to replace
+  /// the mirror-based loader and the uses of mirrors through the `smoke`
+  /// package. This includes:
+  ///
+  ///   * visiting entry-libraries to extract initializers,
+  ///   * visiting polymer-expressions to extract getters and setters,
+  ///   * looking for published fields of custom elements, and
+  ///   * looking for event handlers and callbacks of change notifications.
+  ///
+  void _extractUsesOfMirrors(_) {
+    // Generate getters and setters needed to evaluate polymer expressions, and
+    // extract information about published attributes.
+    new _HtmlExtractor(generator, publishedAttributes).visit(document);
+
+    // Create a recorder that uses analyzer data to feed data to [generator].
+    var recorder = new Recorder(generator,
+        (lib) => resolver.getImportUri(lib, from: bootstrapId).toString());
+
+    // Process all classes and top-level functions to include initializers,
+    // register custom elements, and include special fields and methods in
+    // custom element classes.
+    for (var id in entryLibraries) {
+      var lib = resolver.getLibrary(id);
+      for (var fun in _visibleTopLevelMethodsOf(lib)) {
+        _processFunction(fun, id);
+      }
 
-    // Inject @CustomTag and @initMethod initializations for each library
-    // that is sourced in a script tag.
-    for (int i = 0; i < entryLibraries.length; i++) {
-      for (var init in initializers[entryLibraries[i]]) {
-        var initCode = init.asCode('i$i');
-        code.write("      $initCode,\n");
+      for (var cls in _visibleClassesOf(lib)) {
+        _processClass(cls, id, recorder);
       }
     }
-    code..writeln('    ]);')
-        ..writeln('  i${entryLibraries.length - 1}.main();')
-        ..writeln('}');
-    return code.toString();
   }
 
-  /// Computes initializers needed for each library in [entryLibraries]. Results
-  /// are available afterwards in [initializers].
-  Future _computeInitializers() => Future.forEach(entryLibraries, (lib) {
-      return _initializersOf(lib).then((res) {
-        initializers[lib] = res;
-      });
-    });
+  /// Process a class ([cls]). If it contains an appropriate [CustomTag]
+  /// annotation, we include an initializer to register this class, and make
+  /// sure to include everything that might be accessed or queried from them
+  /// using the smoke package. In particular, polymer uses smoke for the
+  /// following:
+  ///    * invoke #registerCallback on custom elements classes, if present.
+  ///    * query for methods ending in `*Changed`.
+  ///    * query for methods with the `@ObserveProperty` annotation.
+  ///    * query for non-final properties labeled with `@published`.
+  ///    * read declarations of properties named in the `attributes` attribute.
+  ///    * read/write the value of published properties .
+  ///    * invoke methods in event handlers.
+  _processClass(ClassElement cls, AssetId id, Recorder recorder) {
+    if (!_hasPolymerMixin(cls)) return;
+
+    // Check whether the class has a @CustomTag annotation. Typically we expect
+    // a single @CustomTag, but it's possible to have several.
+    var tagNames = [];
+    for (var meta in cls.node.metadata) {
+      var tagName = _extractTagName(meta, cls);
+      if (tagName != null) tagNames.add(tagName);
+    }
 
-  /// Computes the initializers of [dartLibrary]. That is, a closure that calls
-  /// Polymer.register for each @CustomTag, and any public top-level methods
-  /// labeled with @initMethod.
-  Future<List<_Initializer>> _initializersOf(AssetId dartLibrary) {
-    var result = [];
-    return transform.readInputAsString(dartLibrary).then((code) {
-      var file = new SourceFile.text(_simpleUriForSource(dartLibrary), code);
-      var unit = parseCompilationUnit(code);
-
-      return Future.forEach(unit.directives, (directive) {
-        // Include anything from parts.
-        if (directive is PartDirective) {
-          var targetId = uriToAssetId(dartLibrary, directive.uri.stringValue,
-              logger, _getSpan(file, directive));
-          return _initializersOf(targetId).then(result.addAll);
-        }
-
-        // Similarly, include anything from exports except what's filtered by
-        // the show/hide combinators.
-        if (directive is ExportDirective) {
-          var targetId = uriToAssetId(dartLibrary, directive.uri.stringValue,
-              logger, _getSpan(file, directive));
-          return _initializersOf(targetId).then(
-            (r) => _processExportDirective(directive, r, result));
-        }
-      }).then((_) {
-        // Scan the code for classes and top-level functions.
-        for (var node in unit.declarations) {
-          if (node is ClassDeclaration) {
-            _processClassDeclaration(node, result, file, logger);
-          } else if (node is FunctionDeclaration &&
-              node.metadata.any(_isInitMethodAnnotation)) {
-            _processFunctionDeclaration(node, result, file, logger);
-          }
-        }
-        return result;
-      });
-    });
-  }
+    if (cls.isPrivate && tagNames.isNotEmpty) {
+      var name = tagNames.first;
+      logger.error('@CustomTag is not currently supported on private classes:'
+          ' $name. Consider making this class public, or create a '
+          'public initialization method marked with `@initMethod` that calls '
+          '`Polymer.register($name, ${cls.name})`.',
+          span: _spanForNode(cls, cls.node.name));
+      return;
+    }
 
-  static String _simpleUriForSource(AssetId source) =>
-      source.path.startsWith('lib/')
-      ? 'package:${source.package}/${source.path.substring(4)}' : source.path;
-
-  /// Filter [exportedInitializers] according to [directive]'s show/hide
-  /// combinators and add the result to [result].
-  // TODO(sigmund): call the analyzer's resolver instead?
-  static _processExportDirective(ExportDirective directive,
-      List<_Initializer> exportedInitializers,
-      List<_Initializer> result) {
-    for (var combinator in directive.combinators) {
-      if (combinator is ShowCombinator) {
-        var show = combinator.shownNames.map((n) => n.name).toSet();
-        exportedInitializers.retainWhere((e) => show.contains(e.symbolName));
-      } else if (combinator is HideCombinator) {
-        var hide = combinator.hiddenNames.map((n) => n.name).toSet();
-        exportedInitializers.removeWhere((e) => hide.contains(e.symbolName));
+    // Include #registerCallback if it exists. Note that by default lookupMember
+    // and query will also add the corresponding getters and setters.
+    recorder.lookupMember(cls, 'registerCallback');
+
+    // Include methods that end with *Changed.
+    recorder.runQuery(cls, new QueryOptions(
+          includeFields: false, includeProperties: false,
+          includeInherited: true, includeMethods: true,
+          includeUpTo: types.htmlElementElement,
+          matches: (n) => n.endsWith('Changed') && n != 'attributeChanged'));
+
+    // Include methods marked with @ObserveProperty.
+    recorder.runQuery(cls, new QueryOptions(
+          includeFields: false, includeProperties: false,
+          includeInherited: true, includeMethods: true,
+          includeUpTo: types.htmlElementElement,
+          withAnnotations: [types.observePropertyElement]));
+
+    // Include @published and @observable properties.
+    // Symbols in @published are used when resolving bindings on published
+    // attributes, symbols for @observable are used via path observers when
+    // implementing *Changed an @ObserveProperty.
+    // TODO(sigmund): consider including only those symbols mentioned in
+    // *Changed and @ObserveProperty instead.
+    recorder.runQuery(cls, new QueryOptions(
+          includeUpTo: types.htmlElementElement,
+          withAnnotations: [types.publishedElement, types.observableElement]));
+
+    for (var tagName in tagNames) {
+      // Include an initializer that will call Polymer.register
+      initializers.add(new _CustomTagInitializer(id, tagName, cls.displayName));
+
+      // Include also properties published via the `attributes` attribute.
+      var attrs = publishedAttributes[tagName];
+      if (attrs == null) continue;
+      for (var attr in attrs) {
+        recorder.lookupMember(cls, attr, recursive: true);
       }
     }
-    result.addAll(exportedInitializers);
   }
 
-  /// Add an initializer to register [node] as a polymer element if it contains
-  /// an appropriate [CustomTag] annotation.
-  static _processClassDeclaration(ClassDeclaration node,
-      List<_Initializer> result, SourceFile file,
-      TransformLogger logger) {
-    for (var meta in node.metadata) {
-      if (!_isCustomTagAnnotation(meta)) continue;
-      var args = meta.arguments.arguments;
-      if (args == null || args.length == 0) {
-        logger.error('Missing argument in @CustomTag annotation',
-            span: _getSpan(file, meta));
-        continue;
+  /// Determines if [cls] or a supertype has a mixin of the Polymer class.
+  bool _hasPolymerMixin(ClassElement cls) {
+    while (cls != types.htmlElementElement) {
+      for (var m in cls.mixins) {
+        if (m.element == types.polymerClassElement) return true;
       }
+      if (cls.supertype == null) return false;
+      cls = cls.supertype.element;
+    }
+    return false;
+  }
 
-      var tagName = args[0].stringValue;
-      var typeName = node.name.name;
-      if (typeName.startsWith('_')) {
-        logger.error('@CustomTag is no longer supported on private '
-          'classes: $tagName', span: _getSpan(file, node.name));
-        continue;
-      }
-      result.add(new _CustomTagInitializer(tagName, typeName));
+  /// If [meta] is [CustomTag], extract the name associated with the tag.
+  String _extractTagName(Annotation meta, ClassElement cls) {
+    if (meta.element != types.customTagConstructor) return null;
+
+    // Read argument from the AST
+    var args = meta.arguments.arguments;
+    if (args == null || args.length == 0) {
+      logger.warning('Missing argument in @CustomTag annotation',
+          span: _spanForNode(cls, meta));
+      return null;
+    }
+
+    var res = resolver.evaluateConstant(
+        cls.enclosingElement.enclosingElement, args[0]);
+    if (!res.isValid || res.value.type != types.stringType) {
+      logger.warning('The parameter to @CustomTag seems to be invalid.',
+          span: _spanForNode(cls, args[0]));
+      return null;
     }
+    return res.value.stringValue;
   }
 
-  /// Add a method initializer for [function].
-  static _processFunctionDeclaration(FunctionDeclaration function,
-      List<_Initializer> result, SourceFile file,
-      TransformLogger logger) {
-    var name = function.name.name;
-    if (name.startsWith('_')) {
+  /// Adds the top-level [function] as an initalizer if it's marked with
+  /// `@initMethod`.
+  _processFunction(FunctionElement function, AssetId id) {
+    bool initMethodFound = false;
+    for (var meta in function.metadata) {
+      var e = meta.element;
+      if (e is PropertyAccessorElement &&
+          e.variable == types.initMethodElement) {
+        initMethodFound = true;
+        break;
+      }
+    }
+    if (!initMethodFound) return;
+    if (function.isPrivate) {
       logger.error('@initMethod is no longer supported on private '
-        'functions: $name', span: _getSpan(file, function.name));
+          'functions: ${function.displayName}',
+          span: _spanForNode(function, function.node.name));
       return;
     }
-    result.add(new _InitMethodInitializer(name));
+    initializers.add(new _InitMethodInitializer(id, function.displayName));
+  }
+
+  /// Writes the final output for the bootstrap Dart file and entrypoint HTML
+  /// file.
+  void _emitFiles(_) {
+    StringBuffer code = new StringBuffer()..writeln(MAIN_HEADER);
+    Map<AssetId, String> prefixes = {};
+    int i = 0;
+    for (var id in entryLibraries) {
+      var url = assetUrlFor(id, bootstrapId, logger);
+      if (url == null) continue;
+      code.writeln("import '$url' as i$i;");
+      prefixes[id] = 'i$i';
+      i++;
+    }
+
+    // Include smoke initialization.
+    generator.writeImports(code);
+    generator.writeTopLevelDeclarations(code);
+    code.writeln('\nvoid main() {');
+    generator.writeInitCall(code);
+    code.writeln('  configureForDeployment([');
+
+    // Include initializers to switch from mirrors_loader to static_loader.
+    for (var init in initializers) {
+      var initCode = init.asCode(prefixes[init.assetId]);
+      code.write("      $initCode,\n");
+    }
+    code..writeln('    ]);')
+        ..writeln('  i${entryLibraries.length - 1}.main();')
+        ..writeln('}');
+    transform.addOutput(new Asset.fromString(bootstrapId, code.toString()));
+    transform.addOutput(new Asset.fromString(docId, document.outerHtml));
   }
-}
 
-// TODO(sigmund): consider support for importing annotations with prefixes.
-bool _isInitMethodAnnotation(Annotation node) =>
-    node.name.name == 'initMethod' && node.constructorName == null &&
-    node.arguments == null;
-bool _isCustomTagAnnotation(Annotation node) => node.name.name == 'CustomTag';
+  _spanForNode(analyzer.Element context, AstNode node) {
+    var file = resolver.getSourceFile(context);
+    return file.span(node.offset, node.end);
+  }
+}
 
 abstract class _Initializer {
+  AssetId get assetId;
   String get symbolName;
   String asCode(String prefix);
 }
 
 class _InitMethodInitializer implements _Initializer {
-  String methodName;
+  final AssetId assetId;
+  final String methodName;
   String get symbolName => methodName;
-  _InitMethodInitializer(this.methodName);
+  _InitMethodInitializer(this.assetId, this.methodName);
 
   String asCode(String prefix) => "$prefix.$methodName";
 }
 
 class _CustomTagInitializer implements _Initializer {
-  String tagName;
-  String typeName;
+  final AssetId assetId;
+  final String tagName;
+  final String typeName;
   String get symbolName => typeName;
-  _CustomTagInitializer(this.tagName, this.typeName);
+  _CustomTagInitializer(this.assetId, this.tagName, this.typeName);
 
   String asCode(String prefix) =>
       "() => Polymer.register('$tagName', $prefix.$typeName)";
@@ -296,5 +411,294 @@ const MAIN_HEADER = """
 library app_bootstrap;
 
 import 'package:polymer/polymer.dart';
-import 'package:smoke/static.dart' as smoke;
 """;
+
+/// An html visitor that:
+///   * finds all polymer expressions and records the getters and setters that
+///     will be needed to evaluate them at runtime.
+///   * extracts all attributes declared in the `attribute` attributes of
+///     polymer elements.
+class _HtmlExtractor extends TreeVisitor {
+  final Map<String, List<String>> publishedAttributes;
+  final SmokeCodeGenerator generator;
+  final _SubExpressionVisitor visitor;
+  bool _inTemplate = false;
+
+  _HtmlExtractor(SmokeCodeGenerator generator, this.publishedAttributes)
+      : generator = generator,
+        visitor = new _SubExpressionVisitor(generator);
+
+  void visitElement(Element node) {
+    if (_inTemplate) _processNormalElement(node);
+    if (node.localName == 'polymer-element') {
+      _processPolymerElement(node);
+      _processNormalElement(node);
+    }
+
+    if (node.localName == 'template') {
+      var last = _inTemplate;
+      _inTemplate = true;
+      super.visitElement(node);
+      _inTemplate = last;
+    } else {
+      super.visitElement(node);
+    }
+  }
+
+  void visitText(Text node) {
+    if (!_inTemplate) return;
+    var bindings = _Mustaches.parse(node.data);
+    if (bindings == null) return;
+    for (var e in bindings.expressions) {
+      _addExpression(e, false, false);
+    }
+  }
+
+  /// Registers getters and setters for all published attributes.
+  void _processPolymerElement(Element node) {
+    var tagName = node.attributes['name'];
+    var value = node.attributes['attributes'];
+    if (value != null) {
+      publishedAttributes[tagName] =
+          value.split(ATTRIBUTES_REGEX).map((a) => a.trim()).toList();
+    }
+  }
+
+  /// Produces warnings for misuses of on-foo event handlers, and for instanting
+  /// custom tags incorrectly.
+  void _processNormalElement(Element node) {
+    var tag = node.localName;
+    var isCustomTag = isCustomTagName(tag) || node.attributes['is'] != null;
+
+    // Event handlers only allowed inside polymer-elements
+    node.attributes.forEach((name, value) {
+      var bindings = _Mustaches.parse(value);
+      if (bindings == null) return;
+      var isEvent = false;
+      var isTwoWay = false;
+      if (name is String) {
+        name = name.toLowerCase();
+        isEvent = name.startsWith('on-');
+        isTwoWay = !isEvent && bindings.isWhole && (isCustomTag ||
+            tag == 'input' && (name == 'value' || name =='checked') ||
+            tag == 'select' && (name == 'selectedindex' || name == 'value') ||
+            tag == 'textarea' && name == 'value');
+      }
+      for (var exp in bindings.expressions) {
+        _addExpression(exp, isEvent, isTwoWay);
+      }
+    });
+  }
+
+  void _addExpression(String stringExpression, bool inEvent, bool isTwoWay) {
+    if (inEvent) {
+      if (!stringExpression.startsWith("@")) {
+        generator.addGetter(stringExpression);
+        generator.addSymbol(stringExpression);
+        return;
+      }
+      stringExpression = stringExpression.substring(1);
+    }
+    visitor.run(pe.parse(stringExpression), isTwoWay);
+  }
+}
+
+/// A polymer-expression visitor that records every getter and setter that will
+/// be needed to evaluate a single expression at runtime.
+class _SubExpressionVisitor extends pe.RecursiveVisitor {
+  final SmokeCodeGenerator generator;
+  bool _includeSetter;
+
+  _SubExpressionVisitor(this.generator);
+
+  /// Visit [exp], and record getters and setters that are needed in order to
+  /// evaluate it at runtime. [includeSetter] is only true if this expression
+  /// occured in a context where it could be updated, for example in two-way
+  /// bindings such as `<input value={{exp}}>`.
+  void run(pe.Expression exp, bool includeSetter) {
+    _includeSetter = includeSetter;
+    visit(exp);
+  }
+
+  /// Adds a getter and symbol for [name], and optionally a setter.
+  _add(String name) {
+    generator.addGetter(name);
+    generator.addSymbol(name);
+    if (_includeSetter) generator.addSetter(name);
+  }
+
+  void preVisitExpression(e) {
+    // For two-way bindings the outermost expression may be updated, so we need
+    // both the getter and the setter, but subexpressions only need the getter.
+    // So we exclude setters as soon as we go deeper in the tree.
+    _includeSetter = false;
+  }
+
+  visitIdentifier(pe.Identifier e) {
+    if (e.value != 'this') _add(e.value);
+    super.visitIdentifier(e);
+  }
+
+  visitGetter(pe.Getter e) {
+    _add(e.name);
+    super.visitGetter(e);
+  }
+
+  visitInvoke(pe.Invoke e) {
+    _includeSetter = false; // Invoke is only valid as an r-value.
+    _add(e.method);
+    super.visitInvoke(e);
+  }
+}
+
+/// Parses and collects information about bindings found in polymer templates.
+class _Mustaches {
+  /// Each expression that appears within `{{...}}` and `[[...]]`.
+  final List<String> expressions;
+
+  /// Whether the whole text returned by [parse] was a single expression.
+  final bool isWhole;
+
+  _Mustaches(this.isWhole, this.expressions);
+
+  static _Mustaches parse(String text) {
+    if (text == null || text.isEmpty) return null;
+    // Use template-binding's parser, but provide a delegate function factory to
+    // save the expressions without parsing them as [PropertyPath]s.
+    var tokens = MustacheTokens.parse(text, (s) => () => s);
+    if (tokens == null) return null;
+    var length = tokens.length;
+    bool isWhole = length == 1 && tokens.getText(length) == '' &&
+        tokens.getText(0) == '';
+    var expressions = new List(length);
+    for (int i = 0; i < length; i++) {
+      expressions[i] = tokens.getPrepareBinding(i)();
+    }
+    return new _Mustaches(isWhole, expressions);
+  }
+}
+
+/// Holds types that are used in queries 
+class _ResolvedTypes {
+  /// Element representing `HtmlElement`.
+  final ClassElement htmlElementElement;
+
+  /// Element representing `String`.
+  final InterfaceType stringType;
+
+  /// Element representing `Polymer`.
+  final ClassElement polymerClassElement;
+
+  /// Element representing the constructor of `@CustomTag`.
+  final ConstructorElement customTagConstructor;
+
+  /// Element representing the type of `@published`.
+  final ClassElement publishedElement;
+
+  /// Element representing the type of `@observable`.
+  final ClassElement observableElement;
+
+  /// Element representing the type of `@ObserveProperty`.
+  final ClassElement observePropertyElement;
+
+  /// Element representing the `@initMethod` annotation.
+  final TopLevelVariableElement initMethodElement;
+
+
+  factory _ResolvedTypes(Resolver resolver) {
+    // Load class elements that are used in queries for codegen.
+    var polymerLib = resolver.getLibrary(
+        new AssetId('polymer', 'lib/polymer.dart'));
+    if (polymerLib == null) _definitionError('the polymer library');
+
+    var htmlLib = resolver.getLibraryByUri(Uri.parse('dart:html'));
+    if (htmlLib == null) _definitionError('the "dart:html" library');
+
+    var coreLib = resolver.getLibraryByUri(Uri.parse('dart:core'));
+    if (coreLib == null) _definitionError('the "dart:core" library');
+
+    var observeLib = resolver.getLibrary(
+        new AssetId('observe', 'lib/src/metadata.dart'));
+    if (observeLib == null) _definitionError('the observe library');
+
+    var initMethodElement = null;
+    for (var unit in polymerLib.parts) {
+      if (unit.uri == 'src/loader.dart') {
+        initMethodElement = unit.topLevelVariables.firstWhere(
+            (t) => t.displayName == 'initMethod');
+        break;
+      }
+    }
+    var customTagConstructor =
+        _lookupType(polymerLib, 'CustomTag').constructors.first;
+    var publishedElement = _lookupType(polymerLib, 'PublishedProperty');
+    var observableElement = _lookupType(observeLib, 'ObservableProperty');
+    var observePropertyElement = _lookupType(polymerLib, 'ObserveProperty');
+    var polymerClassElement = _lookupType(polymerLib, 'Polymer');
+    var htmlElementElement = _lookupType(htmlLib, 'HtmlElement');
+    var stringType = _lookupType(coreLib, 'String').type;
+    if (initMethodElement == null) _definitionError('@initMethod');
+
+    return new _ResolvedTypes.internal(htmlElementElement, stringType,
+      polymerClassElement, customTagConstructor, publishedElement,
+      observableElement, observePropertyElement, initMethodElement);
+  }
+
+  _ResolvedTypes.internal(this.htmlElementElement, this.stringType,
+      this.polymerClassElement, this.customTagConstructor,
+      this.publishedElement, this.observableElement,
+      this.observePropertyElement, this.initMethodElement);
+
+  static _lookupType(LibraryElement lib, String typeName) {
+    var result = lib.getType(typeName);
+    if (result == null) _definitionError(typeName);
+    return result;
+  }
+
+  static _definitionError(name) {
+    throw new StateError("Internal error in polymer-builder: couldn't find "
+        "definition of $name.");
+  }
+}
+
+/// Retrieves all classses that are visible if you were to import [lib]. This
+/// includes exported classes from other libraries.
+List<ClassElement> _visibleClassesOf(LibraryElement lib) {
+  var result = [];
+  result.addAll(lib.units.expand((u) => u.types));
+  for (var e in lib.exports) {
+    var exported = e.exportedLibrary.units.expand((u) => u.types).toList();
+    _filter(exported, e.combinators);
+    result.addAll(exported);
+  }
+  return result;
+}
+
+/// Retrieves all top-level methods that are visible if you were to import
+/// [lib]. This includes exported methods from other libraries too.
+List<ClassElement> _visibleTopLevelMethodsOf(LibraryElement lib) {
+  var result = [];
+  result.addAll(lib.units.expand((u) => u.functions));
+  for (var e in lib.exports) {
+    var exported = e.exportedLibrary.units
+        .expand((u) => u.functions).toList();
+    _filter(exported, e.combinators);
+    result.addAll(exported);
+  }
+  return result;
+}
+
+/// Filters [elements] that come from an export, according to its show/hide
+/// combinators. This modifies [elements] in place.
+void _filter(List<analyzer.Element> elements,
+    List<NamespaceCombinator> combinators) {
+  for (var c in combinators) {
+    if (c is ShowElementCombinator) {
+      var show = c.shownNames.toSet();
+      elements.retainWhere((e) => show.contains(e.displayName));
+    } else if (c is HideElementCombinator) {
+      var hide = c.hiddenNames.toSet();
+      elements.removeWhere((e) => hide.contains(e.displayName));
+    }
+  }
+}