Reduce warnings in polymer:

pkg/polymer/lib/src/build/common.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.
 
 /// Common methods used by transfomers.
 library polymer.src.build.common;
 
 import 'dart:async';
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/parser.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:barback/barback.dart';
 import 'package:html5lib/dom.dart' show Document;
 import 'package:html5lib/parser.dart' show HtmlParser;
 import 'package:path/path.dart' as path;
 import 'package:observe/transformer.dart' show ObservableTransformer;
 import 'package:source_maps/span.dart' show Span;
 
+const _ignoredErrors = const [
+  'unexpected-dash-after-double-dash-in-comment',
+  'unexpected-char-in-comment',
+];
+
 /// Parses an HTML file [contents] and returns a DOM-like tree. Adds emitted
 /// error/warning to [logger].
 Document _parseHtml(String contents, String sourcePath, TransformLogger logger,
-    {bool checkDocType: true}) {
+    {bool checkDocType: true, bool showWarnings: true}) {
   // TODO(jmesserly): make HTTP encoding configurable
-  var parser = new HtmlParser(contents, encoding: 'utf8', generateSpans: true,
-      sourceUrl: sourcePath);
+  var parser = new HtmlParser(contents, encoding: 'utf8',
+      generateSpans: showWarnings, 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) {
-    if (checkDocType || e.errorCode != 'expected-doctype-but-got-start-tag') {
-      logger.warning(e.message, span: e.span);
+  if (showWarnings) {
+    for (var e in parser.errors) {
+      if (_ignoredErrors.contains(e.errorCode)) continue;
+      if (checkDocType || e.errorCode != 'expected-doctype-but-got-start-tag') {
+        logger.warning(e.message, span: e.span);
+      }
     }
   }
   return document;
 }
 
 /// Additional options used by polymer transformers
 class TransformOptions {
   /// List of entrypoints paths. The paths are relative to the package root and
   /// are represented using posix style, which matches the representation used
   /// in asset ids in barback. If null, anything under 'web/' or 'test/' is
@@ skipping 47 matching lines @@
 
   Future<Document> readPrimaryAsHtml(Transform transform) {
     var asset = transform.primaryInput;
     var id = asset.id;
     return asset.readAsString().then((content) {
       return _parseHtml(content, id.path, transform.logger,
         checkDocType: options.isHtmlEntryPoint(id));
     });
   }
 
-  Future<Document> readAsHtml(AssetId id, Transform transform) {
+  Future<Document> readAsHtml(AssetId id, Transform transform,
+      {bool showWarnings: true}) {
     var primaryId = transform.primaryInput.id;
     bool samePackage = id.package == primaryId.package;
     var url = spanUrlFor(id, transform);
     return transform.readInputAsString(id).then((content) {
       return _parseHtml(content, url, transform.logger,
-        checkDocType: samePackage && options.isHtmlEntryPoint(id));
+        checkDocType: samePackage && options.isHtmlEntryPoint(id),
+        showWarnings: showWarnings);
     });
   }
 
   Future<bool> assetExists(AssetId id, Transform transform) =>
       transform.getInput(id).then((_) => true).catchError((_) => false);
 
   String toString() => 'polymer ($runtimeType)';
 }
 
 /// Gets the appropriate URL to use in a [Span] to produce messages
@@ skipping 71 matching lines @@
 bool isCustomTagName(String name) {
   if (name == null || !name.contains('-')) return false;
   return !invalidTagNames.containsKey(name);
 }
 
 /// Regex to split names in the 'attributes' attribute, which supports 'a b c',
 /// 'a,b,c', or even 'a b,c'. This is the same as in `lib/src/declaration.dart`.
 final ATTRIBUTES_REGEX = new RegExp(r'\s|,');
 
 const POLYMER_EXPERIMENTAL_HTML = 'packages/polymer/polymer_experimental.html';