Improves how to initialize polymer apps and fixes polymer build and linter to

pkg/polymer/lib/src/build/linter.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.
 
 /**
  * Logic to validate that developers are correctly using Polymer constructs.
  * This is mainly used to produce warnings for feedback in the editor.
  */
 library polymer.src.build.linter;
 
@@ skipping 203 matching lines @@
 
   _ElementSummary(this.tagName, this.extendsTag, this.span);
 
   String toString() => "($tagName <: $extendsTag)";
 }
 
 class _LinterVisitor extends TreeVisitor {
   TransformLogger _logger;
   bool _inPolymerElement = false;
   bool _dartJSSeen = false;
-  bool _initSeen = false;
+  bool _dartTagSeen = false;
   bool _isEntrypoint;
   Map<String, _ElementSummary> _elements;
 
   _LinterVisitor(this._logger, this._elements, this._isEntrypoint) {
     // We normalize the map, so each element has a direct reference to any
     // element it extends from.
     for (var tag in _elements.values) {
       var extendsTag = tag.extendsTag;
       if (extendsTag == null) continue;
       tag.extendsType = _elements[extendsTag];
     }
   }
 
   void visitElement(Element node) {
     switch (node.tagName) {
       case 'link': _validateLinkElement(node); break;
       case 'element': _validateElementElement(node); break;
       case 'polymer-element': _validatePolymerElement(node); break;
       case 'script': _validateScriptElement(node); break;
       default:
          _validateNormalElement(node);
          super.visitElement(node);
          break;
     }
   }
 
   void run(Document doc) {
     visit(doc);
 
-    if (_isEntrypoint && !_initSeen) {
+    if (_isEntrypoint && !_dartTagSeen) {
       _logger.error(USE_INIT_DART, span: doc.body.sourceSpan);
     } 
 
     if (_isEntrypoint && !_dartJSSeen) {
       // TODO(sigmund): remove this when webkitStartDart is gone.
       _logger.error(USE_DART_JS, span: doc.body.sourceSpan);
     }
   }
 
   /** Produce warnings for invalid link-rel tags. */
   void _validateLinkElement(Element node) {
     var rel = node.attributes['rel'];
     if (rel != 'import' && rel != 'stylesheet') return;
 
-    if (rel == 'import' && _initSeen) {
+    if (rel == 'import' && _dartTagSeen) {
       _logger.warning(
-          "Move HTML imports above the 'polymer/init.dart' script tag",
+          "Move HTML imports above your Dart script tag.",
           span: node.sourceSpan);
     }
 
     var href = node.attributes['href'];
     if (href != null && href != '') return;
 
     // TODO(sigmund): warn also if href can't be resolved.
     _logger.warning('link rel="$rel" missing href.', span: node.sourceSpan);
   }
 
@@ skipping 58 matching lines @@
    * error, we warn about it when  src file ends in .dart, but the type is
    * incorrect, or when users write code in an inline script tag of a custom
    * element.
    *
    * The hope is that these cases shouldn't break existing valid code, but that
    * they'll help Polymer authors avoid having their Dart code accidentally
    * interpreted as JavaScript by the browser.
    */
   void _validateScriptElement(Element node) {
     var scriptType = node.attributes['type'];
+    var isDart = scriptType == 'application/dart';
     var src = node.attributes['src'];
 
     if (scriptType == null) {
       if (src == null && _inPolymerElement) {
         // TODO(sigmund): revisit this check once we start interop with polymer
         // elements written in JS. Maybe we need to inspect the contents of the
         // script to find whether there is an import or something that indicates
         // that the code is indeed using Dart.
         _logger.warning('script tag in polymer element with no type will '
             'be treated as JavaScript. Did you forget type="application/dart"?',
             span: node.sourceSpan);
       }
-      if (src != null && src.endsWith('.dart')) {
-        _logger.warning('script tag with .dart source file but no type will '
-            'be treated as JavaScript. Did you forget type="application/dart"?',
-            span: node.sourceSpan);
+    } else if (isDart) {
+      if (_dartTagSeen) {
+        _logger.warning('Only one "application/dart" script tag per document '
+            'is allowed.', span: node.sourceSpan);
       }
+      _dartTagSeen = true;
     }
 
     if (src == null) return;
 
     if (src == 'packages/polymer/boot.js') {
       _logger.warning(BOOT_JS_DEPRECATED, span: node.sourceSpan);
       return;
     }
     if (src == 'packages/browser/dart.js' ||
         src == 'packages/unittest/test_controller.js') {
       _dartJSSeen = true;
       return;
     }
 
-    if (src == 'packages/polymer/init.dart') {
-      _initSeen = true;
-      if (scriptType != 'application/dart') {
-        _logger.warning('wrong script type, expected type="application/dart".',
-            span: node.sourceSpan);
-      }
+    if (src.endsWith('.dart') && !isDart) {
+      _logger.warning('Wrong script type, expected type="application/dart".',
+          span: node.sourceSpan);
       return;
     }
 
-    if (scriptType != 'application/dart') return;
-
-    if (!src.endsWith('.dart')) {
+    if (!src.endsWith('.dart') && isDart) {
       _logger.warning('"application/dart" scripts should '
           'use the .dart file extension.',
           span: node.sourceSpan);
+      return;
     }
 
     if (node.innerHtml.trim() != '') {
       _logger.warning('script tag has "src" attribute and also has script '
           'text.', span: node.sourceSpan);
     }
   }
 
   /**
    * Produces warnings for misuses of on-foo event handlers, and for instanting
@@ skipping 131 matching lines @@
 bool _isCustomTag(String name) {
   if (name == null || !name.contains('-')) return false;
   return !_invalidTagNames.containsKey(name);
 }
 
 const String _RED_COLOR = '\u001b[31m';
 const String _MAGENTA_COLOR = '\u001b[35m';
 const String _NO_COLOR = '\u001b[0m';
 
 const String USE_INIT_DART = 
-    'To run a polymer applications, make sure to include '
+    'To run a polymer applications, you need to call "initPolymer". You can '
+    'either include a generic script tag that does this for you:'
     '\'<script type="application/dart" src="packages/polymer/init.dart">'
-    '</script>\' in your page, after all HTML imports.';
+    '</script>\' or add your own script tag and call that function. '
+    'Make sure the script tag is placed after all HTML imports.';
 
 const String USE_DART_JS =
     'To run a polymer applications in Dartium, make sure to include'
     '\'<script src="packages/browser/dart.js"></script>\' in your page';
 
 const String BOOT_JS_DEPRECATED = 
     '"boot.js" is now deprecated. Instead, you can initialize your polymer '
     'application by calling "initPolymer()" in your main. If you don\'t have a '
     'main, then you can include our generic main by adding the following '
     'script tag to your page: \'<script type="application/dart" '
     'src="packages/polymer/init.dart"> </script>\'. Additionally you need to '
     'include: \'<script src="packages/browser/dart.js"></script>\' in the page '
     'too. Make sure these script tags come after all HTML imports.';