move polymer.dart into dart svn

pkg/polymer/lib/src/compiler.dart

+// Copyright (c) 2012, 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.
+
+library compiler;
+
+import 'dart:async';
+import 'dart:collection' show SplayTreeMap;
+import 'dart:json' as json;
+
+import 'package:analyzer_experimental/src/generated/ast.dart' show Directive, UriBasedDirective;
+import 'package:csslib/visitor.dart' show StyleSheet, treeToDebugString;
+import 'package:html5lib/dom.dart';
+import 'package:html5lib/parser.dart';
+import 'package:observe/transform.dart' show transformObservables;
+import 'package:source_maps/span.dart' show Span;
+import 'package:source_maps/refactor.dart' show TextEditTransaction;
+import 'package:source_maps/printer.dart';
+
+import 'analyzer.dart';
+import 'css_analyzer.dart' show analyzeCss, findUrlsImported,
+       findImportsInStyleSheet, parseCss;
+import 'css_emitters.dart' show rewriteCssUris,
+       emitComponentStyleSheet, emitOriginalCss, emitStyleSheet;
+import 'dart_parser.dart';
+import 'emitters.dart';
+import 'file_system.dart';
+import 'files.dart';
+import 'info.dart';
+import 'messages.dart';
+import 'compiler_options.dart';
+import 'paths.dart';
+import 'utils.dart';
+
+/**
+ * Parses an HTML file [contents] and returns a DOM-like tree.
+ * Note that [contents] will be a [String] if coming from a browser-based
+ * [FileSystem], or it will be a [List<int>] if running on the command line.
+ *
+ * Adds emitted error/warning to [messages], if [messages] is supplied.
+ */
+Document parseHtml(contents, String sourcePath, Messages messages) {
+  var parser = new HtmlParser(contents, generateSpans: true,
+      sourceUrl: sourcePath);
+  var document = parser.parse();
+
+  // Note: errors aren't fatal in HTML (unless strict mode is on).
+  // So just print them as warnings.
+  for (var e in parser.errors) {
+    messages.warning(e.message, e.span);
+  }
+  return document;
+}
+
+/** Compiles an application written with Dart web components. */
+class Compiler {
+  final FileSystem fileSystem;
+  final CompilerOptions options;
+  final List<SourceFile> files = <SourceFile>[];
+  final List<OutputFile> output = <OutputFile>[];
+
+  String _mainPath;
+  String _resetCssFile;
+  StyleSheet _cssResetStyleSheet;
+  PathMapper _pathMapper;
+  Messages _messages;
+
+  FutureGroup _tasks;
+  Set _processed;
+
+  /** Information about source [files] given their href. */
+  final Map<String, FileInfo> info = new SplayTreeMap<String, FileInfo>();
+  final _edits = new Map<DartCodeInfo, TextEditTransaction>();
+
+  final GlobalInfo global = new GlobalInfo();
+
+  /** Creates a compiler with [options] using [fileSystem]. */
+  Compiler(this.fileSystem, this.options, this._messages) {
+    _mainPath = options.inputFile;
+    var mainDir = path.dirname(_mainPath);
+    var baseDir = options.baseDir != null ? options.baseDir : mainDir;
+    var outputDir = options.outputDir != null ? options.outputDir : mainDir;
+    var packageRoot = options.packageRoot != null ? options.packageRoot
+        : path.join(path.dirname(_mainPath), 'packages');
+
+    if (options.resetCssFile != null) {
+      _resetCssFile = options.resetCssFile;
+      if (path.isRelative(_resetCssFile)) {
+        // If CSS reset file path is relative from our current path.
+        _resetCssFile = path.resolve(_resetCssFile);
+      }
+    }
+
+    // Normalize paths - all should be relative or absolute paths.
+    if (path.isAbsolute(_mainPath) || path.isAbsolute(baseDir) ||
+        path.isAbsolute(outputDir) || path.isAbsolute(packageRoot)) {
+      if (path.isRelative(_mainPath)) _mainPath = path.resolve(_mainPath);
+      if (path.isRelative(baseDir)) baseDir = path.resolve(baseDir);
+      if (path.isRelative(outputDir)) outputDir = path.resolve(outputDir);
+      if (path.isRelative(packageRoot)) {
+        packageRoot = path.resolve(packageRoot);
+      }
+    }
+    _pathMapper = new PathMapper(
+        baseDir, outputDir, packageRoot, options.forceMangle,
+        options.rewriteUrls);
+  }
+
+  /** Compile the application starting from the given input file. */
+  Future run() {
+    if (path.basename(_mainPath).endsWith('.dart')) {
+      _messages.error("Please provide an HTML file as your entry point.",
+          null);
+      return new Future.value(null);
+    }
+    return _parseAndDiscover(_mainPath).then((_) {
+      _analyze();
+
+      // Analyze all CSS files.
+      _time('Analyzed Style Sheets', '', () =>
+          analyzeCss(_pathMapper.packageRoot, files, info,
+              global.pseudoElements, _messages,
+              warningsAsErrors: options.warningsAsErrors));
+
+      // TODO(jmesserly): need to go through our errors, and figure out if some
+      // of them should be warnings instead.
+      if (_messages.hasErrors || options.analysisOnly) return;
+      _transformDart();
+      _emit();
+    });
+  }
+
+  /**
+   * Asynchronously parse [inputFile] and transitively discover web components
+   * to load and parse. Returns a future that completes when all files are
+   * processed.
+   */
+  Future _parseAndDiscover(String inputFile) {
+    _tasks = new FutureGroup();
+    _processed = new Set();
+    _processed.add(inputFile);
+    _tasks.add(_parseHtmlFile(new UrlInfo(inputFile, inputFile, null)));
+    return _tasks.future;
+  }
+
+  void _processHtmlFile(UrlInfo inputUrl, SourceFile file) {
+    if (file == null) return;
+
+    bool isEntryPoint = _processed.length == 1;
+
+    files.add(file);
+
+    var fileInfo = _time('Analyzed definitions', inputUrl.url, () {
+      return analyzeDefinitions(global, inputUrl, file.document,
+        _pathMapper.packageRoot, _messages, isEntryPoint: isEntryPoint);
+    });
+    info[inputUrl.resolvedPath] = fileInfo;
+
+    if (isEntryPoint && _resetCssFile != null) {
+      _processed.add(_resetCssFile);
+      _tasks.add(_parseCssFile(new UrlInfo(_resetCssFile, _resetCssFile,
+          null)));
+    }
+
+    _setOutputFilenames(fileInfo);
+    _processImports(fileInfo);
+
+    // Load component files referenced by [file].
+    for (var link in fileInfo.componentLinks) {
+      _loadFile(link, _parseHtmlFile);
+    }
+
+    // Load stylesheet files referenced by [file].
+    for (var link in fileInfo.styleSheetHrefs) {
+      _loadFile(link, _parseCssFile);
+    }
+
+    // Load .dart files being referenced in the page.
+    _loadFile(fileInfo.externalFile, _parseDartFile);
+
+    // Process any @imports inside of a <style> tag.
+    var urlInfos = findUrlsImported(fileInfo, fileInfo.inputUrl,
+        _pathMapper.packageRoot, file.document, _messages, options);
+    for (var urlInfo in urlInfos) {
+      _loadFile(urlInfo, _parseCssFile);
+    }
+
+    // Load .dart files being referenced in components.
+    for (var component in fileInfo.declaredComponents) {
+      if (component.externalFile != null) {
+        _loadFile(component.externalFile, _parseDartFile);
+      } else if (component.userCode != null) {
+        _processImports(component);
+      }
+
+      // Process any @imports inside of the <style> tag in a component.
+      var urlInfos = findUrlsImported(component,
+          component.declaringFile.inputUrl, _pathMapper.packageRoot,
+          component.element, _messages, options);
+      for (var urlInfo in urlInfos) {
+        _loadFile(urlInfo, _parseCssFile);
+      }
+    }
+  }
+
+  /**
+   * Helper function to load [urlInfo] and parse it using [loadAndParse] if it
+   * hasn't been loaded before.
+   */
+  void _loadFile(UrlInfo urlInfo, Future loadAndParse(UrlInfo inputUrl)) {
+    if (urlInfo == null) return;
+    var resolvedPath = urlInfo.resolvedPath;
+    if (!_processed.contains(resolvedPath)) {
+      _processed.add(resolvedPath);
+      _tasks.add(loadAndParse(urlInfo));
+    }
+  }
+
+  void _setOutputFilenames(FileInfo fileInfo) {
+    var filePath = fileInfo.dartCodeUrl.resolvedPath;
+    fileInfo.outputFilename = _pathMapper.mangle(path.basename(filePath),
+        '.dart', path.extension(filePath) == '.html');
+    for (var component in fileInfo.declaredComponents) {
+      var externalFile = component.externalFile;
+      var name = null;
+      if (externalFile != null) {
+        name = _pathMapper.mangle(
+            path.basename(externalFile.resolvedPath), '.dart');
+      } else {
+        var declaringFile = component.declaringFile;
+        var prefix = path.basename(declaringFile.inputUrl.resolvedPath);
+        if (declaringFile.declaredComponents.length == 1
+            && !declaringFile.codeAttached && !declaringFile.isEntryPoint) {
+          name = _pathMapper.mangle(prefix, '.dart', true);
+        } else {
+          var componentName = component.tagName.replaceAll('-', '_');
+          name = _pathMapper.mangle('${prefix}_$componentName', '.dart', true);
+        }
+      }
+      component.outputFilename = name;
+    }
+  }
+
+  /** Parse an HTML file. */
+  Future _parseHtmlFile(UrlInfo inputUrl) {
+    if (!_pathMapper.checkInputPath(inputUrl, _messages)) {
+      return new Future<SourceFile>.value(null);
+    }
+    var filePath = inputUrl.resolvedPath;
+    return fileSystem.readTextOrBytes(filePath)
+        .catchError((e) => _readError(e, inputUrl))
+        .then((source) {
+          if (source == null) return;
+          var file = new SourceFile(filePath);
+          file.document = _time('Parsed', filePath,
+              () => parseHtml(source, filePath, _messages));
+          _processHtmlFile(inputUrl, file);
+        });
+  }
+
+  /** Parse a Dart file. */
+  Future _parseDartFile(UrlInfo inputUrl) {
+    if (!_pathMapper.checkInputPath(inputUrl, _messages)) {
+      return new Future<SourceFile>.value(null);
+    }
+    var filePath = inputUrl.resolvedPath;
+    return fileSystem.readText(filePath)
+        .catchError((e) => _readError(e, inputUrl))
+        .then((code) {
+          if (code == null) return;
+          var file = new SourceFile(filePath, type: SourceFile.DART);
+          file.code = code;
+          _processDartFile(inputUrl, file);
+        });
+  }
+
+  /** Parse a stylesheet file. */
+  Future _parseCssFile(UrlInfo inputUrl) {
+    if (!options.emulateScopedCss ||
+        !_pathMapper.checkInputPath(inputUrl, _messages)) {
+      return new Future<SourceFile>.value(null);
+    }
+    var filePath = inputUrl.resolvedPath;
+    return fileSystem.readText(filePath)
+        .catchError((e) => _readError(e, inputUrl, isWarning: true))
+        .then((code) {
+          if (code == null) return;
+          var file = new SourceFile(filePath, type: SourceFile.STYLESHEET);
+          file.code = code;
+          _processCssFile(inputUrl, file);
+        });
+  }
+
+
+  SourceFile _readError(error, UrlInfo inputUrl, {isWarning: false}) {
+    var message = 'unable to open file "${inputUrl.resolvedPath}"';
+    if (options.verbose) {
+      message = '$message. original message:\n $error';
+    }
+    if (isWarning) {
+      _messages.warning(message, inputUrl.sourceSpan);
+    } else {
+      _messages.error(message, inputUrl.sourceSpan);
+    }
+    return null;
+  }
+
+  void _processDartFile(UrlInfo inputUrl, SourceFile dartFile) {
+    if (dartFile == null) return;
+
+    files.add(dartFile);
+
+    var resolvedPath = inputUrl.resolvedPath;
+    var fileInfo = new FileInfo(inputUrl);
+    info[resolvedPath] = fileInfo;
+    fileInfo.inlinedCode = parseDartCode(resolvedPath, dartFile.code);
+    fileInfo.outputFilename =
+        _pathMapper.mangle(path.basename(resolvedPath), '.dart', false);
+
+    _processImports(fileInfo);
+  }
+
+  void _processImports(LibraryInfo library) {
+    if (library.userCode == null) return;
+
+    for (var directive in library.userCode.directives) {
+      _loadFile(_getDirectiveUrlInfo(library, directive), _parseDartFile);
+    }
+  }
+
+  void _processCssFile(UrlInfo inputUrl, SourceFile cssFile) {
+    if (cssFile == null) return;
+
+    files.add(cssFile);
+
+    var fileInfo = new FileInfo(inputUrl);
+    info[inputUrl.resolvedPath] = fileInfo;
+
+    var styleSheet = parseCss(cssFile.code, _messages, options);
+    if (inputUrl.url == _resetCssFile) {
+      _cssResetStyleSheet = styleSheet;
+    } else if (styleSheet != null) {
+      _resolveStyleSheetImports(inputUrl, cssFile.path, styleSheet);
+      fileInfo.styleSheets.add(styleSheet);
+    }
+  }
+
+  /** Load and parse all style sheets referenced with an @imports. */
+  void _resolveStyleSheetImports(UrlInfo inputUrl, String processingFile,
+      StyleSheet styleSheet) {
+    var urlInfos = _time('CSS imports', processingFile, () =>
+        findImportsInStyleSheet(styleSheet, _pathMapper.packageRoot, inputUrl,
+            _messages));
+
+    for (var urlInfo in urlInfos) {
+      if (urlInfo == null) break;
+      // Load any @imported stylesheet files referenced in this style sheet.
+      _loadFile(urlInfo, _parseCssFile);
+    }
+  }
+
+  String _directiveUri(Directive directive) {
+    var uriDirective = (directive as UriBasedDirective).uri;
+    return (uriDirective as dynamic).value;
+  }
+
+  UrlInfo _getDirectiveUrlInfo(LibraryInfo library, Directive directive) {
+    var uri = _directiveUri(directive);
+    if (uri.startsWith('dart:')) return null;
+    if (uri.startsWith('package:') && uri.startsWith('package:polymer/')) {
+      // Don't process our own package -- we'll implement @observable manually.
+      return null;
+    }
+
+    var span = library.userCode.sourceFile.span(
+        directive.offset, directive.end);
+    return UrlInfo.resolve(uri, library.dartCodeUrl, span,
+        _pathMapper.packageRoot, _messages);
+  }
+
+  /**
+   * Transform Dart source code.
+   * Currently, the only transformation is [transformObservables].
+   * Calls _emitModifiedDartFiles to write the transformed files.
+   */
+  void _transformDart() {
+    var libraries = _findAllDartLibraries();
+
+    var transformed = [];
+    for (var lib in libraries) {
+      var userCode = lib.userCode;
+      var transaction = transformObservables(userCode.compilationUnit,
+          userCode.sourceFile, userCode.code, _messages);
+      if (transaction != null) {
+        _edits[lib.userCode] = transaction;
+        if (transaction.hasEdits) {
+          transformed.add(lib);
+        } else if (lib.htmlFile != null) {
+          // All web components will be transformed too. Track that.
+          transformed.add(lib);
+        }
+      }
+    }
+
+    _findModifiedDartFiles(libraries, transformed);
+
+    libraries.forEach(_fixImports);
+
+    _emitModifiedDartFiles(libraries);
+  }
+
+  /**
+   * Finds all Dart code libraries.
+   * Each library will have [LibraryInfo.inlinedCode] that is non-null.
+   * Also each inlinedCode will be unique.
+   */
+  List<LibraryInfo> _findAllDartLibraries() {
+    var libs = <LibraryInfo>[];
+    void _addLibrary(LibraryInfo lib) {
+      if (lib.inlinedCode != null) libs.add(lib);
+    }
+
+    for (var sourceFile in files) {
+      var file = info[sourceFile.path];
+      _addLibrary(file);
+      file.declaredComponents.forEach(_addLibrary);
+    }
+
+    // Assert that each file path is unique.
+    assert(_uniquePaths(libs));
+    return libs;
+  }
+
+  bool _uniquePaths(List<LibraryInfo> libs) {
+    var seen = new Set();
+    for (var lib in libs) {
+      if (seen.contains(lib.inlinedCode)) {
+        throw new StateError('internal error: '
+            'duplicate user code for ${lib.dartCodeUrl.resolvedPath}.'
+            ' Files were: $files');
+      }
+      seen.add(lib.inlinedCode);
+    }
+    return true;
+  }
+
+  /**
+   * Queue modified Dart files to be written.
+   * This will not write files that are handled by [WebComponentEmitter] and
+   * [EntryPointEmitter].
+   */
+  void _emitModifiedDartFiles(List<LibraryInfo> libraries) {
+    for (var lib in libraries) {
+      // Components will get emitted by WebComponentEmitter, and the
+      // entry point will get emitted by MainPageEmitter.
+      // So we only need to worry about other .dart files.
+      if (lib.modified && lib is FileInfo &&
+          lib.htmlFile == null && !lib.isEntryPoint) {
+        var transaction = _edits[lib.userCode];
+
+        // Save imports that were modified by _fixImports.
+        for (var d in lib.userCode.directives) {
+          transaction.edit(d.offset, d.end, d.toString());
+        }
+
+        if (!lib.userCode.isPart) {
+          var pos = lib.userCode.firstPartOffset;
+          // Note: we use a different prefix than "autogenerated" to make
+          // ChangeRecord unambiguous. Otherwise it would be imported by this
+          // and polymer, resulting in a collision.
+          // TODO(jmesserly): only generate this for libraries that need it.
+          transaction.edit(pos, pos, "\nimport "
+              "'package:observe/observe.dart' as __observe;\n");
+        }
+        _emitFileAndSourceMaps(lib, transaction.commit(), lib.dartCodeUrl);
+      }
+    }
+  }
+
+  /**
+   * This method computes which Dart files have been modified, starting
+   * from [transformed] and marking recursively through all files that import
+   * the modified files.
+   */
+  void _findModifiedDartFiles(List<LibraryInfo> libraries,
+      List<FileInfo> transformed) {
+
+    if (transformed.length == 0) return;
+
+    // Compute files that reference each file, then use this information to
+    // flip the modified bit transitively. This is a lot simpler than trying
+    // to compute it the other way because of circular references.
+    for (var lib in libraries) {
+      for (var directive in lib.userCode.directives) {
+        var importPath = _getDirectiveUrlInfo(lib, directive);
+        if (importPath == null) continue;
+
+        var importInfo = info[importPath.resolvedPath];
+        if (importInfo != null) {
+          importInfo.referencedBy.add(lib);
+        }
+      }
+    }
+
+    // Propegate the modified bit to anything that references a modified file.
+    void setModified(LibraryInfo library) {
+      if (library.modified) return;
+      library.modified = true;
+      library.referencedBy.forEach(setModified);
+    }
+    transformed.forEach(setModified);
+
+    for (var lib in libraries) {
+      // We don't need this anymore, so free it.
+      lib.referencedBy = null;
+    }
+  }
+
+  void _fixImports(LibraryInfo library) {
+    // Fix imports. Modified files must use the generated path, otherwise
+    // we need to make the path relative to the input.
+    for (var directive in library.userCode.directives) {
+      var importPath = _getDirectiveUrlInfo(library, directive);
+      if (importPath == null) continue;
+      var importInfo = info[importPath.resolvedPath];
+      if (importInfo == null) continue;
+
+      String newUri = null;
+      if (importInfo.modified) {
+        // Use the generated URI for this file.
+        newUri = _pathMapper.importUrlFor(library, importInfo);
+      } else if (options.rewriteUrls) {
+        // Get the relative path to the input file.
+        newUri = _pathMapper.transformUrl(
+            library.dartCodeUrl.resolvedPath, directive.uri.value);
+      }
+      if (newUri != null) {
+        directive.uri = createStringLiteral(newUri);
+      }
+    }
+  }
+
+  /** Run the analyzer on every input html file. */
+  void _analyze() {
+    var uniqueIds = new IntIterator();
+    for (var file in files) {
+      if (file.isHtml) {
+        _time('Analyzed contents', file.path, () =>
+            analyzeFile(file, info, uniqueIds, global, _messages,
+              options.emulateScopedCss));
+      }
+    }
+  }
+
+  /** Emit the generated code corresponding to each input file. */
+  void _emit() {
+    for (var file in files) {
+      if (file.isDart || file.isStyleSheet) continue;
+      _time('Codegen', file.path, () {
+        var fileInfo = info[file.path];
+        _emitComponents(fileInfo);
+      });
+    }
+
+    var entryPoint = files[0];
+    assert(info[entryPoint.path].isEntryPoint);
+    _emitMainDart(entryPoint);
+    _emitMainHtml(entryPoint);
+
+    assert(_unqiueOutputs());
+  }
+
+  bool _unqiueOutputs() {
+    var seen = new Set();
+    for (var file in output) {
+      if (seen.contains(file.path)) {
+        throw new StateError('internal error: '
+            'duplicate output file ${file.path}. Files were: $output');
+      }
+      seen.add(file.path);
+    }
+    return true;
+  }
+
+  /** Emit the main .dart file. */
+  void _emitMainDart(SourceFile file) {
+    var fileInfo = info[file.path];
+
+    var codeInfo = fileInfo.userCode;
+    if (codeInfo != null) {
+      var printer = new NestedPrinter(0);
+      if (codeInfo.libraryName == null) {
+        printer.addLine('library ${fileInfo.libraryName};');
+      }
+      printer.add(codeInfo.code);
+      _emitFileAndSourceMaps(fileInfo, printer, fileInfo.dartCodeUrl);
+    }
+  }
+
+  // TODO(jmesserly): refactor this out of Compiler.
+  /** Generate an html file with the (trimmed down) main html page. */
+  void _emitMainHtml(SourceFile file) {
+    var fileInfo = info[file.path];
+
+    var bootstrapName = '${path.basename(file.path)}_bootstrap.dart';
+    var bootstrapPath = path.join(path.dirname(file.path), bootstrapName);
+    var bootstrapOutPath = _pathMapper.outputPath(bootstrapPath, '');
+    var bootstrapOutName = path.basename(bootstrapOutPath);
+    var bootstrapInfo = new FileInfo(new UrlInfo('', bootstrapPath, null));
+    var printer = generateBootstrapCode(bootstrapInfo, fileInfo, global,
+        _pathMapper, options);
+    printer.build(bootstrapOutPath);
+    output.add(new OutputFile(
+          bootstrapOutPath, printer.text, source: file.path));
+
+    var document = file.document;
+    var hasCss = _emitAllCss();
+    transformMainHtml(document, fileInfo, _pathMapper, hasCss,
+        options.rewriteUrls, _messages, global, bootstrapOutName);
+    output.add(new OutputFile(_pathMapper.outputPath(file.path, '.html'),
+        document.outerHtml, source: file.path));
+  }
+
+  // TODO(jmesserly): refactor this and other CSS related transforms out of
+  // Compiler.
+  /**
+   * Generate an CSS file for all style sheets (main and components).
+   * Returns true if a file was generated, otherwise false.
+   */
+  bool _emitAllCss() {
+    if (!options.emulateScopedCss) return false;
+
+    var buff = new StringBuffer();
+
+    // Emit all linked style sheet files first.
+    for (var file in files) {
+      var css = new StringBuffer();
+      var fileInfo = info[file.path];
+      if (file.isStyleSheet) {
+        for (var styleSheet in fileInfo.styleSheets) {
+          // Translate any URIs in CSS.
+          rewriteCssUris(_pathMapper, fileInfo.inputUrl.resolvedPath,
+              options.rewriteUrls, styleSheet);
+          css.write(
+              '/* Auto-generated from style sheet href = ${file.path} */\n'
+              '/* DO NOT EDIT. */\n\n');
+          css.write(emitStyleSheet(styleSheet, fileInfo));
+          css.write('\n\n');
+        }
+
+        // Emit the linked style sheet in the output directory.
+        if (fileInfo.inputUrl.url != _resetCssFile) {
+          var outCss = _pathMapper.outputPath(fileInfo.inputUrl.resolvedPath,
+              '');
+          output.add(new OutputFile(outCss, css.toString()));
+        }
+      }
+    }
+
+    // Emit all CSS for each component (style scoped).
+    for (var file in files) {
+      if (file.isHtml) {
+        var fileInfo = info[file.path];
+        for (var component in fileInfo.declaredComponents) {
+          for (var styleSheet in component.styleSheets) {
+            // Translate any URIs in CSS.
+            rewriteCssUris(_pathMapper, fileInfo.inputUrl.resolvedPath,
+                options.rewriteUrls, styleSheet);
+
+            if (buff.isEmpty) {
+              buff.write(
+                  '/* Auto-generated from components style tags. */\n'
+                  '/* DO NOT EDIT. */\n\n');
+            }
+            buff.write(
+                '/* ==================================================== \n'
+                '   Component ${component.tagName} stylesheet \n'
+                '   ==================================================== */\n');
+
+            var tagName = component.tagName;
+            if (!component.hasAuthorStyles) {
+              if (_cssResetStyleSheet != null) {
+                // If component doesn't have apply-author-styles then we need to
+                // reset the CSS the styles for the component (if css-reset file
+                // option was passed).
+                buff.write('\n/* Start CSS Reset */\n');
+                var style;
+                if (options.emulateScopedCss) {
+                  style = emitComponentStyleSheet(_cssResetStyleSheet, tagName);
+                } else {
+                  style = emitOriginalCss(_cssResetStyleSheet);
+                }
+                buff.write(style);
+                buff.write('/* End CSS Reset */\n\n');
+              }
+            }
+            if (options.emulateScopedCss) {
+              buff.write(emitComponentStyleSheet(styleSheet, tagName));
+            } else {
+              buff.write(emitOriginalCss(styleSheet));
+            }
+            buff.write('\n\n');
+          }
+        }
+      }
+    }
+
+    if (buff.isEmpty) return false;
+
+    var cssPath = _pathMapper.outputPath(_mainPath, '.css', true);
+    output.add(new OutputFile(cssPath, buff.toString()));
+    return true;
+  }
+
+  /** Emits the Dart code for all components in [fileInfo]. */
+  void _emitComponents(FileInfo fileInfo) {
+    for (var component in fileInfo.declaredComponents) {
+      // TODO(terry): Handle more than one stylesheet per component
+      if (component.styleSheets.length > 1 && options.emulateScopedCss) {
+        var span = component.externalFile != null
+            ? component.externalFile.sourceSpan : null;
+        _messages.warning(
+            'Component has more than one stylesheet - first stylesheet used.',
+            span);
+      }
+      var printer = emitPolymerElement(
+          component, _pathMapper, _edits[component.userCode], options);
+      _emitFileAndSourceMaps(component, printer, component.externalFile);
+    }
+  }
+
+  /**
+   * Emits a file that was created using [NestedPrinter] and it's corresponding
+   * source map file.
+   */
+  void _emitFileAndSourceMaps(
+      LibraryInfo lib, NestedPrinter printer, UrlInfo dartCodeUrl) {
+    // Bail if we had an error generating the code for the file.
+    if (printer == null) return;
+
+    var libPath = _pathMapper.outputLibraryPath(lib);
+    var dir = path.dirname(libPath);
+    var filename = path.basename(libPath);
+    printer.add('\n//# sourceMappingURL=$filename.map');
+    printer.build(libPath);
+    var sourcePath = dartCodeUrl != null ? dartCodeUrl.resolvedPath : null;
+    output.add(new OutputFile(libPath, printer.text, source: sourcePath));
+    // Fix-up the paths in the source map file
+    var sourceMap = json.parse(printer.map);
+    var urls = sourceMap['sources'];
+    for (int i = 0; i < urls.length; i++) {
+      urls[i] = path.relative(urls[i], from: dir);
+    }
+    output.add(new OutputFile(path.join(dir, '$filename.map'),
+          json.stringify(sourceMap)));
+  }
+
+  _time(String logMessage, String filePath, callback(),
+      {bool printTime: false}) {
+    var message = new StringBuffer();
+    message.write(logMessage);
+    var filename = path.basename(filePath);
+    for (int i = (60 - logMessage.length - filename.length); i > 0 ; i--) {
+      message.write(' ');
+    }
+    message.write(filename);
+    return time(message.toString(), callback,
+        printTime: options.verbose || printTime);
+  }
+}