Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/polymer/src/build/script_compactor.dart

+// Copyright (c) 2013, 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.
+
+/// Transfomer that combines multiple dart script tags into a single one.
+library polymer.src.build.script_compactor;
+
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:html5lib/dom.dart' show Document, Element, Text;
+import 'package:html5lib/dom_parsing.dart';
+import 'package:html5lib/parser.dart' show parseFragment;
+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/messages/build_logger.dart';
+import 'package:path/path.dart' as path;
+import 'package:source_span/source_span.dart';
+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 'common.dart';
+import 'import_inliner.dart' show ImportInliner; // just for docs.
+import 'messages.dart';
+
+/// Combines Dart script tags into a single script tag, and creates a new Dart
+/// file that calls the main function of each of the original script tags.
+///
+/// This transformer assumes that all script tags point to external files. To
+/// support script tags with inlined code, use this transformer after running
+/// [ImportInliner] on an earlier phase.
+///
+/// Internally, this transformer will convert each script tag into an import
+/// 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, {String sdkDir})
+      // TODO(sigmund): consider restoring here a resolver that uses the real
+      // SDK once the analyzer is lazy and only an resolves what it needs:
+      //: resolvers = new Resolvers(sdkDir != null ? sdkDir : dartSdkDirectory);
+      : resolvers = new Resolvers.fromMock({
+        // The list of types below is derived from:
+        //   * types we use via our smoke queries, including HtmlElement and
+        //     types from `_typeHandlers` (deserialize.dart)
+        //   * types that are used internally by the resolver (see
+        //   _initializeFrom in resolver.dart).
+        'dart:core': '''
+            library dart.core;
+            class Object {}
+            class Function {}
+            class StackTrace {}
+            class Symbol {}
+            class Type {}
+
+            class String extends Object {}
+            class bool extends Object {}
+            class num extends Object {}
+            class int extends num {}
+            class double extends num {}
+            class DateTime extends Object {}
+            class Null extends Object {}
+
+            class Deprecated extends Object {
+              final String expires;
+              const Deprecated(this.expires);
+            }
+            const Object deprecated = const Deprecated("next release");
+            class _Override { const _Override(); }
+            const Object override = const _Override();
+            class _Proxy { const _Proxy(); }
+            const Object proxy = const _Proxy();
+
+            class List<V> extends Object {}
+            class Map<K, V> extends Object {}
+            ''',
+        'dart:html': '''
+            library dart.html;
+            class HtmlElement {}
+            ''',
+      });
+
+
+
+  /// Only run on entry point .html files.
+  // TODO(nweiz): This should just take an AssetId when barback <0.13.0 support
+  // is dropped.
+  Future<bool> isPrimary(idOrAsset) {
+    var id = idOrAsset is AssetId ? idOrAsset : idOrAsset.id;
+    return new Future.value(options.isHtmlEntryPoint(id));
+  }
+
+  Future apply(Transform transform) =>
+      new _ScriptCompactor(transform, options, resolvers).apply();
+}
+
+/// Helper class mainly use to flatten the async code.
+class _ScriptCompactor extends PolymerTransformer {
+  final TransformOptions options;
+  final Transform transform;
+  final BuildLogger logger;
+  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;
+
+  /// Whether we are using the experimental bootstrap logic.
+  bool experimentalBootstrap;
+
+  /// 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();
+
+  _SubExpressionVisitor expressionVisitor;
+
+  _ScriptCompactor(Transform transform, options, this.resolvers)
+      : transform = transform,
+        options = options,
+        logger = new BuildLogger(
+            transform, convertErrorsToWarnings: !options.releaseMode,
+            detailsUri: 'http://goo.gl/5HPeuP'),
+        docId = transform.primaryInput.id,
+        bootstrapId = transform.primaryInput.id.addExtension('_bootstrap.dart');
+
+  Future apply() =>
+      _loadDocument()
+      .then(_loadEntryLibraries)
+      .then(_processHtml)
+      .then(_emitNewEntrypoint)
+      .then((_) {
+        // Write out the logs collected by our [BuildLogger].
+        if (options.injectBuildLogsInOutput) return logger.writeOutput();
+      });
+
+  /// Loads the primary input as an html document.
+  Future _loadDocument() =>
+      readPrimaryAsHtml(transform, logger).then((doc) { document = doc; });
+
+  /// Populates [entryLibraries] as a list containing the asset ids of each
+  /// library loaded on a script tag. The actual work of computing this is done
+  /// in an earlier phase and emited in the `entrypoint._data` asset.
+  Future _loadEntryLibraries(_) =>
+      transform.readInputAsString(docId.addExtension('._data')).then((data) {
+        var map = JSON.decode(data);
+        experimentalBootstrap = map['experimental_bootstrap'];
+        entryLibraries = map['script_ids']
+              .map((id) => new AssetId.deserialize(id))
+              .toList();
+        return Future.forEach(entryLibraries, logger.addLogFilesFromAsset);
+      });
+
+  /// Removes unnecessary script tags, and identifies the main entry point Dart
+  /// script tag (if any).
+  void _processHtml(_) {
+    for (var tag in document.querySelectorAll('script')) {
+      var src = tag.attributes['src'];
+      if (src == 'packages/polymer/boot.js') {
+        tag.remove();
+        continue;
+      }
+      if (tag.attributes['type'] == 'application/dart') {
+        logger.warning(INTERNAL_ERROR_UNEXPECTED_SCRIPT, span: tag.sourceSpan);
+      }
+    }
+  }
+
+  /// Emits the main HTML and Dart bootstrap code for the application. If there
+  /// were not Dart entry point files, then this simply emits the original HTML.
+  Future _emitNewEntrypoint(_) {
+    // If we don't find code, there is nothing to do.
+    if (entryLibraries.isEmpty) return null;
+    return _initResolver()
+        .then(_extractUsesOfMirrors)
+        .then(_emitFiles)
+        .whenComplete(() {
+          if (resolver != null) resolver.release();
+        });
+  }
+
+  /// 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() {
+    // We include 'polymer.dart' to simplify how we do resolution below. This
+    // way we can assume polymer is there, even if the user didn't include an
+    // import to it. If not, the polymer build will fail with an error when
+    // trying to create _ResolvedTypes below.
+    var libsToLoad = [new AssetId('polymer', 'lib/polymer.dart')]
+        ..addAll(entryLibraries);
+    return resolvers.get(transform, libsToLoad).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.
+    expressionVisitor = new _SubExpressionVisitor(generator, logger);
+    new _HtmlExtractor(logger, generator, publishedAttributes,
+        expressionVisitor).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.
+    var functionsSeen = new Set<FunctionElement>();
+    var classesSeen = new Set<ClassElement>();
+    for (var id in entryLibraries) {
+      var lib = resolver.getLibrary(id);
+      for (var fun in _visibleTopLevelMethodsOf(lib)) {
+        if (functionsSeen.contains(fun)) continue;
+        functionsSeen.add(fun);
+        _processFunction(fun, id);
+      }
+
+      for (var cls in _visibleClassesOf(lib)) {
+        if (classesSeen.contains(cls)) continue;
+        classesSeen.add(cls);
+        _processClass(cls, id, recorder);
+      }
+    }
+  }
+
+  /// 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);
+    }
+
+    if (cls.isPrivate && tagNames.isNotEmpty) {
+      var name = tagNames.first;
+      logger.error(PRIVATE_CUSTOM_TAG.create(
+              {'name': name, 'class': cls.name}),
+          span: _spanForNode(cls, cls.node.name));
+      return;
+    }
+
+    // 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,
+          types.computedPropertyElement]));
+
+    // Include @ComputedProperty and process their expressions
+    var computed = [];
+    recorder.runQuery(cls, new QueryOptions(
+          includeUpTo: types.htmlElementElement,
+          withAnnotations: [types.computedPropertyElement]),
+          results: computed);
+    _processComputedExpressions(computed);
+
+    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,
+            includeUpTo: types.htmlElementElement);
+      }
+    }
+  }
+
+  /// 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;
+  }
+
+  /// If [meta] is [CustomTag], extract the name associated with the tag.
+  String _extractTagName(Annotation meta, ClassElement cls) {
+    if (meta.element != types.customTagConstructor) return null;
+    return _extractFirstAnnotationArgument(meta, 'CustomTag', cls);
+  }
+
+  /// Extract the first argument of an annotation and validate that it's type is
+  /// String. For instance, return "bar" from `@Foo("bar")`.
+  String _extractFirstAnnotationArgument(Annotation meta, String name,
+      analyzer.Element context) {
+
+    // Read argument from the AST
+    var args = meta.arguments.arguments;
+    if (args == null || args.length == 0) {
+      logger.warning(MISSING_ANNOTATION_ARGUMENT.create({'name': name}),
+          span: _spanForNode(context, meta));
+      return null;
+    }
+
+    var lib = context;
+    while (lib is! LibraryElement) lib = lib.enclosingElement;
+    var res = resolver.evaluateConstant(lib, args[0]);
+    if (!res.isValid || res.value.type != types.stringType) {
+      logger.warning(INVALID_ANNOTATION_ARGUMENT.create({'name': name}),
+          span: _spanForNode(context, args[0]));
+      return null;
+    }
+    return res.value.stringValue;
+  }
+
+  /// 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(PRIVATE_INIT_METHOD.create({'name': function.displayName}),
+          span: _spanForNode(function, function.node.name));
+      return;
+    }
+    initializers.add(new _InitMethodInitializer(id, function.displayName));
+  }
+
+  /// Process members that are annotated with `@ComputedProperty` and records
+  /// the accessors of their expressions.
+  _processComputedExpressions(List<analyzer.Element> computed) {
+    var constructor = types.computedPropertyElement.constructors.first;
+    for (var member in computed) {
+      for (var meta in member.node.metadata) {
+        if (meta.element != constructor) continue;
+        var expr = _extractFirstAnnotationArgument(
+            meta, 'ComputedProperty', member);
+        if (expr == null) continue;
+        expressionVisitor.run(pe.parse(expr), true,
+            _spanForNode(member.enclosingElement, meta.arguments.arguments[0]));
+      }
+    }
+  }
+
+  /// 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;");
+      if (options.injectBuildLogsInOutput) {
+        code.writeln("import 'package:polymer/src/build/log_injector.dart';");
+      }
+      prefixes[id] = 'i$i';
+      i++;
+    }
+
+    // Include smoke initialization.
+    generator.writeImports(code);
+    generator.writeTopLevelDeclarations(code);
+    code.writeln('\nvoid main() {');
+    code.write('  useGeneratedCode(');
+    generator.writeStaticConfiguration(code);
+    code.writeln(');');
+
+    if (options.injectBuildLogsInOutput) {
+      var buildUrl = "${path.basename(docId.path)}$LOG_EXTENSION";
+      code.writeln("  new LogInjector().injectLogsFromUrl('$buildUrl');");
+    }
+
+    if (experimentalBootstrap) {
+      code.write('  startPolymer([');
+    } else {
+      code.write('  configureForDeployment([');
+    }
+
+    // Include initializers to switch from mirrors_loader to static_loader.
+    if (!initializers.isEmpty) {
+      code.writeln();
+      for (var init in initializers) {
+        var initCode = init.asCode(prefixes[init.assetId]);
+        code.write("      $initCode,\n");
+      }
+      code.writeln('    ]);');
+    } else {
+      if (experimentalBootstrap) logger.warning(NO_INITIALIZATION);
+      code.writeln(']);');
+    }
+    if (!experimentalBootstrap) {
+      code.writeln('  i${entryLibraries.length - 1}.main();');
+    }
+
+    // End of main().
+    code.writeln('}');
+    transform.addOutput(new Asset.fromString(bootstrapId, code.toString()));
+
+
+    // Emit the bootstrap .dart file
+    var srcUrl = path.url.basename(bootstrapId.path);
+    document.body.nodes.add(parseFragment(
+        '<script type="application/dart" src="$srcUrl"></script>'));
+
+    // Add the styles for the logger widget.
+    if (options.injectBuildLogsInOutput) {
+      document.head.append(parseFragment(
+          '<link rel="stylesheet" type="text/css"'
+          ' href="packages/polymer/src/build/log_injector.css">'));
+    }
+
+    transform.addOutput(new Asset.fromString(docId, document.outerHtml));
+  }
+
+  _spanForNode(analyzer.Element context, AstNode node) {
+    var file = resolver.getSourceFile(context);
+    return file.span(node.offset, node.end);
+  }
+}
+
+abstract class _Initializer {
+  AssetId get assetId;
+  String get symbolName;
+  String asCode(String prefix);
+}
+
+class _InitMethodInitializer implements _Initializer {
+  final AssetId assetId;
+  final String methodName;
+  String get symbolName => methodName;
+  _InitMethodInitializer(this.assetId, this.methodName);
+
+  String asCode(String prefix) => "$prefix.$methodName";
+}
+
+class _CustomTagInitializer implements _Initializer {
+  final AssetId assetId;
+  final String tagName;
+  final String typeName;
+  String get symbolName => typeName;
+  _CustomTagInitializer(this.assetId, this.tagName, this.typeName);
+
+  String asCode(String prefix) =>
+      "() => Polymer.register('$tagName', $prefix.$typeName)";
+}
+
+const MAIN_HEADER = """
+library app_bootstrap;
+
+import 'package:polymer/polymer.dart';
+""";
+
+
+/// 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 expressionVisitor;
+  final BuildLogger logger;
+  bool _inTemplate = false;
+  bool _inPolymerJs = false;
+
+  _HtmlExtractor(this.logger, this.generator, this.publishedAttributes,
+      this.expressionVisitor);
+
+  void visitElement(Element node) {
+    var lastInPolymerJs = _inPolymerJs;
+    if (node.localName == 'template'
+        && node.attributes['is'] == 'auto-binding') {
+      _inPolymerJs = true;
+    }
+
+    if (_inTemplate) _processNormalElement(node);
+
+    if (node.localName == 'polymer-element') {
+      // Detect Polymer JS elements, the current logic is any element with only
+      // non-dart script tags.
+      var scripts = node.querySelectorAll('script');
+      _inPolymerJs = scripts.isNotEmpty &&
+          scripts.every((s) => s.attributes['type'] != 'application/dart');
+      _processPolymerElement(node);
+      _processNormalElement(node);
+    }
+
+    if (node.localName == 'template') {
+      var last = _inTemplate;
+      _inTemplate = true;
+      super.visitElement(node);
+      _inTemplate = last;
+    } else {
+      super.visitElement(node);
+    }
+    _inPolymerJs = lastInPolymerJs;
+  }
+
+  void visitText(Text node) {
+    // Nothing here applies if inside a polymer js element
+    if (!_inTemplate || _inPolymerJs) return;
+    var bindings = _Mustaches.parse(node.data);
+    if (bindings == null) return;
+    for (var e in bindings.expressions) {
+      _addExpression(e, false, false, node.sourceSpan);
+    }
+  }
+
+  /// Registers getters and setters for all published attributes.
+  void _processPolymerElement(Element node) {
+    // Nothing here applies if inside a polymer js element
+    if (_inPolymerJs) return;
+
+    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) {
+    // Nothing here applies if inside a polymer js element
+    if (_inPolymerJs) return;
+
+    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, node.sourceSpan);
+      }
+    });
+  }
+
+  void _addExpression(String stringExpression, bool inEvent, bool isTwoWay,
+      SourceSpan span) {
+
+    if (inEvent) {
+      if (stringExpression.startsWith('@')) {
+        logger.warning(AT_EXPRESSION_REMOVED, span: span);
+        return;
+      }
+
+      if (stringExpression == '') return;
+      if (stringExpression.startsWith('_')) {
+        logger.warning(NO_PRIVATE_EVENT_HANDLERS, span: span);
+        return;
+      }
+      generator.addGetter(stringExpression);
+      generator.addSymbol(stringExpression);
+    }
+    expressionVisitor.run(pe.parse(stringExpression), isTwoWay, span);
+  }
+}
+
+/// 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;
+  final BuildLogger logger;
+  bool _includeSetter;
+  SourceSpan _currentSpan;
+
+  _SubExpressionVisitor(this.generator, this.logger);
+
+  /// 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, span) {
+    _currentSpan = span;
+    _includeSetter = includeSetter;
+    visit(exp);
+  }
+
+  /// Adds a getter and symbol for [name], and optionally a setter.
+  _add(String name) {
+    if (name.startsWith('_')) {
+      logger.warning(NO_PRIVATE_SYMBOLS_IN_BINDINGS, span: _currentSpan);
+      return;
+    }
+    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 we only need the getter for
+    // subexpressions. We exclude setters as soon as we go deeper in the tree,
+    // except when we see a filter (that can potentially be a two-way
+    // transformer).
+    if (e is pe.BinaryOperator && e.operator == '|') return;
+    _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.
+    if (e.method != null) _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 type of `@ComputedProperty`.
+  final ClassElement computedPropertyElement;
+
+  /// 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 computedPropertyElement = _lookupType(polymerLib, 'ComputedProperty');
+    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, computedPropertyElement,
+      initMethodElement);
+  }
+
+  _ResolvedTypes.internal(this.htmlElementElement, this.stringType,
+      this.polymerClassElement, this.customTagConstructor,
+      this.publishedElement, this.observableElement,
+      this.observePropertyElement, this.computedPropertyElement,
+      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<FunctionElement> _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));
+    }
+  }
+}