pkg/polymer/lib/src/build/linter.dart - sdk.git - Git at Google

 // 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;

 import 'dart:async';

 import 'package:barback/barback.dart';
 import 'package:code_transformers/assets.dart';
 import 'package:html5lib/dom.dart';
 import 'package:html5lib/dom_parsing.dart';
 import 'package:source_maps/span.dart';

 import 'common.dart';
 import 'utils.dart';

 /// A linter that checks for common Polymer errors and produces warnings to
 /// show on the editor or the command line. Leaves sources unchanged, but
 /// creates a new asset containing all the warnings.
 class Linter extends Transformer with PolymerTransformer {
   final TransformOptions options;

   /// Only run on .html files.
   final String allowedExtensions = '.html';

   Linter(this.options);

   Future apply(Transform transform) {
     var seen = new Set<AssetId>();
     var primary = transform.primaryInput;
     var id = primary.id;
     transform.addOutput(primary); // this phase is analysis only
     seen.add(id);
     return readPrimaryAsHtml(transform).then((document) {
       return _collectElements(document, id, transform, seen).then((elements) {
         bool isEntrypoint = options.isHtmlEntryPoint(id);
         new _LinterVisitor(id, transform.logger, elements, isEntrypoint)
             .run(document);
       });
     });
   }

   /// Collect into [elements] any data about each polymer-element defined in
   /// [document] or any of it's imports, unless they have already been [seen].
   /// Elements are added in the order they appear, transitive imports are added
   /// first.
   Future<Map<String, _ElementSummary>> _collectElements(
       Document document, AssetId sourceId, Transform transform,
       Set<AssetId> seen, [Map<String, _ElementSummary> elements]) {
     if (elements == null) elements = <String, _ElementSummary>{};
     return _getImportedIds(document, sourceId, transform)
         // Note: the import order is relevant, so we visit in that order.
         .then((ids) => Future.forEach(ids,
               (id) => _readAndCollectElements(id, transform, seen, elements)))
         .then((_) {
           if (sourceId.package == 'polymer' &&
               sourceId.path == 'lib/src/js/polymer/polymer.html' &&
               elements['polymer-element'] == null) {
             elements['polymer-element'] =
                 new _ElementSummary('polymer-element', null, null);
           }
           return _addElements(document, transform.logger, elements);
         })
         .then((_) => elements);
   }

   Future _readAndCollectElements(AssetId id, Transform transform,
       Set<AssetId> seen, Map<String, _ElementSummary> elements) {
     if (id == null || seen.contains(id)) return new Future.value(null);
     seen.add(id);
     return readAsHtml(id, transform, showWarnings: false).then(
         (doc) => _collectElements(doc, id, transform, seen, elements));
   }

   Future<List<AssetId>> _getImportedIds(
       Document document, AssetId sourceId, Transform transform) {
     var importIds = [];
     var logger = transform.logger;
     for (var tag in document.querySelectorAll('link')) {
       if (tag.attributes['rel'] != 'import') continue;
       var href = tag.attributes['href'];
       var span = tag.sourceSpan;
       var id = uriToAssetId(sourceId, href, logger, span);
       if (id == null) continue;
       importIds.add(assetExists(id, transform).then((exists) {
         if (exists) return id;
         if (sourceId == transform.primaryInput.id) {
           logger.warning('couldn\'t find imported asset "${id.path}" in package'
               ' "${id.package}".', span: span);
         }
       }));
     }
     return Future.wait(importIds);
   }

   void _addElements(Document document, TransformLogger logger,
       Map<String, _ElementSummary> elements) {
     for (var tag in document.querySelectorAll('polymer-element')) {
       var name = tag.attributes['name'];
       if (name == null) continue;
       var extendsTag = tag.attributes['extends'];
       var span = tag.sourceSpan;
       var existing = elements[name];
       if (existing != null) {

         // Report warning only once.
         if (existing.hasConflict) continue;
         existing.hasConflict = true;
         logger.warning('duplicate definition for custom tag "$name".',
             span: existing.span);
         logger.warning('duplicate definition for custom tag "$name" '
             ' (second definition).', span: span);
         continue;
       }

       elements[name] = new _ElementSummary(name, extendsTag, tag.sourceSpan);
     }
   }
 }


 /// Information needed about other polymer-element tags in order to validate
 /// how they are used and extended.
 ///
 /// Note: these are only created for polymer-element, because pure custom
 /// elements don't have a declarative form.
 class _ElementSummary {
   final String tagName;
   final String extendsTag;
   final Span span;

   _ElementSummary extendsType;
   bool hasConflict = false;

   String get baseExtendsTag {
     if (extendsType != null) return extendsType.baseExtendsTag;
     if (extendsTag != null && !extendsTag.contains('-')) return extendsTag;
     return null;
   }

   _ElementSummary(this.tagName, this.extendsTag, this.span);

   String toString() => "($tagName <: $extendsTag)";
 }

 class _LinterVisitor extends TreeVisitor {
   TransformLogger _logger;
   AssetId _sourceId;
   bool _inPolymerElement = false;
   bool _dartTagSeen = false;
   bool _polymerHtmlSeen = false;
   bool _polymerExperimentalHtmlSeen = false;
   bool _isEntrypoint;
   Map<String, _ElementSummary> _elements;

   _LinterVisitor(
       this._sourceId, 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.localName) {
       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 && !_dartTagSeen && !_polymerExperimentalHtmlSeen) {
       _logger.warning(USE_INIT_DART, 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' && _dartTagSeen) {
       _logger.warning("Move HTML imports above your Dart script tag.",
           span: node.sourceSpan);
     }

     var href = node.attributes['href'];
     if (href == null || href == '') {
       _logger.warning('link rel="$rel" missing href.', span: node.sourceSpan);
       return;
     }

     if (rel != 'import') return;

     if (_inPolymerElement) {
       _logger.error(NO_IMPORT_WITHIN_ELEMENT, span: node.sourceSpan);
       return;
     }

     if (href == POLYMER_EXPERIMENTAL_HTML) {
       _polymerExperimentalHtmlSeen = true;
     }
     // TODO(sigmund): warn also if href can't be resolved.
   }

   /// Produce warnings if using `<element>` instead of `<polymer-element>`.
   void _validateElementElement(Element node) {
     _logger.warning('<element> elements are not supported, use'
         ' <polymer-element> instead', span: node.sourceSpan);
   }

   /// Produce warnings if using `<polymer-element>` in the wrong place or if the
   /// definition is not complete.
   void _validatePolymerElement(Element node) {
     if (!_elements.containsKey('polymer-element')) {
       _logger.warning(usePolymerHtmlMessageFrom(_sourceId),
           span: node.sourceSpan);
     }

     if (_inPolymerElement) {
       _logger.error('Nested polymer element definitions are not allowed.',
           span: node.sourceSpan);
       return;
     }

     var tagName = node.attributes['name'];
     var extendsTag = node.attributes['extends'];

     if (tagName == null) {
       _logger.error('Missing tag name of the custom element. Please include an '
           'attribute like \'name="your-tag-name"\'.',
           span: node.sourceSpan);
     } else if (!isCustomTagName(tagName)) {
       _logger.error('Invalid name "$tagName". Custom element names must have '
           'at least one dash and can\'t be any of the following names: '
           '${invalidTagNames.keys.join(", ")}.',
           span: node.sourceSpan);
     }

     if (_elements[extendsTag] == null && isCustomTagName(extendsTag)) {
       _logger.warning('custom element with name "$extendsTag" not found.',
           span: node.sourceSpan);
     }

     var attrs = node.attributes['attributes'];
     if (attrs != null) {
       var attrsSpan = node.attributeSpans['attributes'];

       // names='a b c' or names='a,b,c'
       // record each name for publishing
       for (var attr in attrs.split(ATTRIBUTES_REGEX)) {
         if (!_validateCustomAttributeName(attr.trim(), attrsSpan)) break;
       }
     }

     var oldValue = _inPolymerElement;
     _inPolymerElement = true;
     super.visitElement(node);
     _inPolymerElement = oldValue;
   }

   /// Checks for multiple Dart script tags in the same page, which is invalid.
   void _validateScriptElement(Element node) {
     var scriptType = node.attributes['type'];
     var isDart = scriptType == 'application/dart';
     var src = node.attributes['src'];

     if (isDart) {
       if (_dartTagSeen) _logger.warning(ONLY_ONE_TAG, span: node.sourceSpan);
       if (_isEntrypoint && _polymerExperimentalHtmlSeen) {
         _logger.warning(NO_DART_SCRIPT_AND_EXPERIMENTAL, span: node.sourceSpan);
       }
       _dartTagSeen = true;
     }

     if (src == null) return;

     if (src.endsWith('.dart') && !isDart) {
       _logger.warning('Wrong script type, expected type="application/dart".',
           span: node.sourceSpan);
       return;
     }

     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
   /// custom tags incorrectly.
   void _validateNormalElement(Element node) {
     // Event handlers only allowed inside polymer-elements
     node.attributes.forEach((name, value) {
       if (name is String && name.startsWith('on')) {
         _validateEventHandler(node, name, value);
       }
     });

     // Validate uses of custom-tags
     var nodeTag = node.localName;
     var hasIsAttribute;
     var customTagName;
     if (isCustomTagName(nodeTag)) {
       // <fancy-button>
       customTagName = nodeTag;
       hasIsAttribute = false;
     } else {
       // <button is="fancy-button">
       customTagName = node.attributes['is'];
       hasIsAttribute = true;
     }

     if (customTagName == null || customTagName == 'polymer-element') return;

     var info = _elements[customTagName];
     if (info == null) {
       // TODO(jmesserly): this warning is wrong if someone is using raw custom
       // elements. Is there another way we can handle this warning that won't
       // generate false positives?
       _logger.warning('definition for Polymer element with tag name '
           '"$customTagName" not found.', span: node.sourceSpan);
       return;
     }

     var baseTag = info.baseExtendsTag;
     if (baseTag != null && !hasIsAttribute) {
       _logger.warning(
           'custom element "$customTagName" extends from "$baseTag", but '
           'this tag will not include the default properties of "$baseTag". '
           'To fix this, either write this tag as <$baseTag '
           'is="$customTagName"> or remove the "extends" attribute from '
           'the custom element declaration.', span: node.sourceSpan);
       return;
     }

     if (hasIsAttribute && baseTag == null) {
       _logger.warning(
           'custom element "$customTagName" doesn\'t declare any type '
           'extensions. To fix this, either rewrite this tag as '
           '<$customTagName> or add \'extends="$nodeTag"\' to '
           'the custom element declaration.', span: node.sourceSpan);
       return;
     }

     if (hasIsAttribute && baseTag != nodeTag) {
       _logger.warning(
           'custom element "$customTagName" extends from "$baseTag". '
           'Did you mean to write <$baseTag is="$customTagName">?',
           span: node.sourceSpan);
     }
   }

   /// Validate an attribute on a custom-element. Returns true if valid.
   bool _validateCustomAttributeName(String name, FileSpan span) {
     if (name.contains('-')) {
       var newName = toCamelCase(name);
       _logger.warning('PolymerElement no longer recognizes attribute names with '
           'dashes such as "$name". Use "$newName" or "${newName.toLowerCase()}" '
           'instead (both forms are equivalent in HTML).', span: span);
       return false;
     }
     return true;
   }

   /// Validate event handlers are used correctly.
   void _validateEventHandler(Element node, String name, String value) {
     if (!name.startsWith('on-')) return;

     if (!_inPolymerElement) {
       _logger.warning('Inline event handlers are only supported inside '
           'declarations of <polymer-element>.',
           span: node.attributeSpans[name]);
       return;
     }


     // Valid bindings have {{ }}, don't look like method calls foo(bar), and are
     // non empty.
     if (!value.startsWith("{{") || !value.endsWith("}}") || value.contains('(')
         || value.substring(2, value.length - 2).trim() == '') {
       _logger.warning('Invalid event handler body "$value". Declare a method '
           'in your custom element "void handlerName(event, detail, target)" '
           'and use the form $name="{{handlerName}}".',
           span: node.attributeSpans[name]);
     }
   }
 }

 const String ONLY_ONE_TAG =
     'Only one "application/dart" script tag per document is allowed.';

 String usePolymerHtmlMessageFrom(AssetId id) {
   var segments = id.path.split('/');
   var upDirCount = 0;
   if (segments[0] == 'lib') {
     // lib/foo.html => ../../packages/
     upDirCount = segments.length;
   } else if (segments.length > 2) {
     // web/a/foo.html => ../packages/
     upDirCount = segments.length - 2;
   }
   return usePolymerHtmlMessage(upDirCount);
 }

 String usePolymerHtmlMessage(int upDirCount) {
   var reachOutPrefix = '../' * upDirCount;
   return 'Missing definition for <polymer-element>, please add the following '
     'HTML import at the top of this file: <link rel="import" '
     'href="${reachOutPrefix}packages/polymer/polymer.html">.';
 }

 const String NO_IMPORT_WITHIN_ELEMENT = 'Polymer.dart\'s implementation of '
     'HTML imports are not supported within polymer element definitions, yet. '
     'Please move the import out of this <polymer-element>.';

 const String USE_INIT_DART =
     'To run a polymer application, you need to call "initPolymer". You can '
     'either include a generic script tag that does this for you:'
     '\'<script type="application/dart">export "package:polymer/init.dart";'
     '</script>\' or add your own script tag and call that function. '
     'Make sure the script tag is placed after all HTML imports.';

 const String NO_DART_SCRIPT_AND_EXPERIMENTAL =
     'The experimental bootstrap feature doesn\'t support script tags on '
     'the main document (for now).';
	// 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;

	import 'dart:async';

	import 'package:barback/barback.dart';
	import 'package:code_transformers/assets.dart';
	import 'package:html5lib/dom.dart';
	import 'package:html5lib/dom_parsing.dart';
	import 'package:source_maps/span.dart';

	import 'common.dart';
	import 'utils.dart';

	/// A linter that checks for common Polymer errors and produces warnings to
	/// show on the editor or the command line. Leaves sources unchanged, but
	/// creates a new asset containing all the warnings.
	class Linter extends Transformer with PolymerTransformer {
	final TransformOptions options;

	/// Only run on .html files.
	final String allowedExtensions = '.html';

	Linter(this.options);

	Future apply(Transform transform) {
	var seen = new Set<AssetId>();
	var primary = transform.primaryInput;
	var id = primary.id;
	transform.addOutput(primary); // this phase is analysis only
	seen.add(id);
	return readPrimaryAsHtml(transform).then((document) {
	return _collectElements(document, id, transform, seen).then((elements) {
	bool isEntrypoint = options.isHtmlEntryPoint(id);
	new _LinterVisitor(id, transform.logger, elements, isEntrypoint)
	.run(document);
	});
	});
	}

	/// Collect into [elements] any data about each polymer-element defined in
	/// [document] or any of it's imports, unless they have already been [seen].
	/// Elements are added in the order they appear, transitive imports are added
	/// first.
	Future<Map<String, _ElementSummary>> _collectElements(
	Document document, AssetId sourceId, Transform transform,
	Set<AssetId> seen, [Map<String, _ElementSummary> elements]) {
	if (elements == null) elements = <String, _ElementSummary>{};
	return _getImportedIds(document, sourceId, transform)
	// Note: the import order is relevant, so we visit in that order.
	.then((ids) => Future.forEach(ids,
	(id) => _readAndCollectElements(id, transform, seen, elements)))
	.then((_) {
	if (sourceId.package == 'polymer' &&
	sourceId.path == 'lib/src/js/polymer/polymer.html' &&
	elements['polymer-element'] == null) {
	elements['polymer-element'] =
	new _ElementSummary('polymer-element', null, null);
	}
	return _addElements(document, transform.logger, elements);
	})
	.then((_) => elements);
	}

	Future _readAndCollectElements(AssetId id, Transform transform,
	Set<AssetId> seen, Map<String, _ElementSummary> elements) {
	if (id == null \|\| seen.contains(id)) return new Future.value(null);
	seen.add(id);
	return readAsHtml(id, transform, showWarnings: false).then(
	(doc) => _collectElements(doc, id, transform, seen, elements));
	}

	Future<List<AssetId>> _getImportedIds(
	Document document, AssetId sourceId, Transform transform) {
	var importIds = [];
	var logger = transform.logger;
	for (var tag in document.querySelectorAll('link')) {
	if (tag.attributes['rel'] != 'import') continue;
	var href = tag.attributes['href'];
	var span = tag.sourceSpan;
	var id = uriToAssetId(sourceId, href, logger, span);
	if (id == null) continue;
	importIds.add(assetExists(id, transform).then((exists) {
	if (exists) return id;
	if (sourceId == transform.primaryInput.id) {
	logger.warning('couldn\'t find imported asset "${id.path}" in package'
	' "${id.package}".', span: span);
	}
	}));
	}
	return Future.wait(importIds);
	}

	void _addElements(Document document, TransformLogger logger,
	Map<String, _ElementSummary> elements) {
	for (var tag in document.querySelectorAll('polymer-element')) {
	var name = tag.attributes['name'];
	if (name == null) continue;
	var extendsTag = tag.attributes['extends'];
	var span = tag.sourceSpan;
	var existing = elements[name];
	if (existing != null) {

	// Report warning only once.
	if (existing.hasConflict) continue;
	existing.hasConflict = true;
	logger.warning('duplicate definition for custom tag "$name".',
	span: existing.span);
	logger.warning('duplicate definition for custom tag "$name" '
	' (second definition).', span: span);
	continue;
	}

	elements[name] = new _ElementSummary(name, extendsTag, tag.sourceSpan);
	}
	}
	}


	/// Information needed about other polymer-element tags in order to validate
	/// how they are used and extended.
	///
	/// Note: these are only created for polymer-element, because pure custom
	/// elements don't have a declarative form.
	class _ElementSummary {
	final String tagName;
	final String extendsTag;
	final Span span;

	_ElementSummary extendsType;
	bool hasConflict = false;

	String get baseExtendsTag {
	if (extendsType != null) return extendsType.baseExtendsTag;
	if (extendsTag != null && !extendsTag.contains('-')) return extendsTag;
	return null;
	}

	_ElementSummary(this.tagName, this.extendsTag, this.span);

	String toString() => "($tagName <: $extendsTag)";
	}

	class _LinterVisitor extends TreeVisitor {
	TransformLogger _logger;
	AssetId _sourceId;
	bool _inPolymerElement = false;
	bool _dartTagSeen = false;
	bool _polymerHtmlSeen = false;
	bool _polymerExperimentalHtmlSeen = false;
	bool _isEntrypoint;
	Map<String, _ElementSummary> _elements;

	_LinterVisitor(
	this._sourceId, 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.localName) {
	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 && !_dartTagSeen && !_polymerExperimentalHtmlSeen) {
	_logger.warning(USE_INIT_DART, 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' && _dartTagSeen) {
	_logger.warning("Move HTML imports above your Dart script tag.",
	span: node.sourceSpan);
	}

	var href = node.attributes['href'];
	if (href == null \|\| href == '') {
	_logger.warning('link rel="$rel" missing href.', span: node.sourceSpan);
	return;
	}

	if (rel != 'import') return;

	if (_inPolymerElement) {
	_logger.error(NO_IMPORT_WITHIN_ELEMENT, span: node.sourceSpan);
	return;
	}

	if (href == POLYMER_EXPERIMENTAL_HTML) {
	_polymerExperimentalHtmlSeen = true;
	}
	// TODO(sigmund): warn also if href can't be resolved.
	}

	/// Produce warnings if using `<element>` instead of `<polymer-element>`.
	void _validateElementElement(Element node) {
	_logger.warning('<element> elements are not supported, use'
	' <polymer-element> instead', span: node.sourceSpan);
	}

	/// Produce warnings if using `<polymer-element>` in the wrong place or if the
	/// definition is not complete.
	void _validatePolymerElement(Element node) {
	if (!_elements.containsKey('polymer-element')) {
	_logger.warning(usePolymerHtmlMessageFrom(_sourceId),
	span: node.sourceSpan);
	}

	if (_inPolymerElement) {
	_logger.error('Nested polymer element definitions are not allowed.',
	span: node.sourceSpan);
	return;
	}

	var tagName = node.attributes['name'];
	var extendsTag = node.attributes['extends'];

	if (tagName == null) {
	_logger.error('Missing tag name of the custom element. Please include an '
	'attribute like \'name="your-tag-name"\'.',
	span: node.sourceSpan);
	} else if (!isCustomTagName(tagName)) {
	_logger.error('Invalid name "$tagName". Custom element names must have '
	'at least one dash and can\'t be any of the following names: '
	'${invalidTagNames.keys.join(", ")}.',
	span: node.sourceSpan);
	}

	if (_elements[extendsTag] == null && isCustomTagName(extendsTag)) {
	_logger.warning('custom element with name "$extendsTag" not found.',
	span: node.sourceSpan);
	}

	var attrs = node.attributes['attributes'];
	if (attrs != null) {
	var attrsSpan = node.attributeSpans['attributes'];

	// names='a b c' or names='a,b,c'
	// record each name for publishing
	for (var attr in attrs.split(ATTRIBUTES_REGEX)) {
	if (!_validateCustomAttributeName(attr.trim(), attrsSpan)) break;
	}
	}

	var oldValue = _inPolymerElement;
	_inPolymerElement = true;
	super.visitElement(node);
	_inPolymerElement = oldValue;
	}

	/// Checks for multiple Dart script tags in the same page, which is invalid.
	void _validateScriptElement(Element node) {
	var scriptType = node.attributes['type'];
	var isDart = scriptType == 'application/dart';
	var src = node.attributes['src'];

	if (isDart) {
	if (_dartTagSeen) _logger.warning(ONLY_ONE_TAG, span: node.sourceSpan);
	if (_isEntrypoint && _polymerExperimentalHtmlSeen) {
	_logger.warning(NO_DART_SCRIPT_AND_EXPERIMENTAL, span: node.sourceSpan);
	}
	_dartTagSeen = true;
	}

	if (src == null) return;

	if (src.endsWith('.dart') && !isDart) {
	_logger.warning('Wrong script type, expected type="application/dart".',
	span: node.sourceSpan);
	return;
	}

	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
	/// custom tags incorrectly.
	void _validateNormalElement(Element node) {
	// Event handlers only allowed inside polymer-elements
	node.attributes.forEach((name, value) {
	if (name is String && name.startsWith('on')) {
	_validateEventHandler(node, name, value);
	}
	});

	// Validate uses of custom-tags
	var nodeTag = node.localName;
	var hasIsAttribute;
	var customTagName;
	if (isCustomTagName(nodeTag)) {
	// <fancy-button>
	customTagName = nodeTag;
	hasIsAttribute = false;
	} else {
	// <button is="fancy-button">
	customTagName = node.attributes['is'];
	hasIsAttribute = true;
	}

	if (customTagName == null \|\| customTagName == 'polymer-element') return;

	var info = _elements[customTagName];
	if (info == null) {
	// TODO(jmesserly): this warning is wrong if someone is using raw custom
	// elements. Is there another way we can handle this warning that won't
	// generate false positives?
	_logger.warning('definition for Polymer element with tag name '
	'"$customTagName" not found.', span: node.sourceSpan);
	return;
	}

	var baseTag = info.baseExtendsTag;
	if (baseTag != null && !hasIsAttribute) {
	_logger.warning(
	'custom element "$customTagName" extends from "$baseTag", but '
	'this tag will not include the default properties of "$baseTag". '
	'To fix this, either write this tag as <$baseTag '
	'is="$customTagName"> or remove the "extends" attribute from '
	'the custom element declaration.', span: node.sourceSpan);
	return;
	}

	if (hasIsAttribute && baseTag == null) {
	_logger.warning(
	'custom element "$customTagName" doesn\'t declare any type '
	'extensions. To fix this, either rewrite this tag as '
	'<$customTagName> or add \'extends="$nodeTag"\' to '
	'the custom element declaration.', span: node.sourceSpan);
	return;
	}

	if (hasIsAttribute && baseTag != nodeTag) {
	_logger.warning(
	'custom element "$customTagName" extends from "$baseTag". '
	'Did you mean to write <$baseTag is="$customTagName">?',
	span: node.sourceSpan);
	}
	}

	/// Validate an attribute on a custom-element. Returns true if valid.
	bool _validateCustomAttributeName(String name, FileSpan span) {
	if (name.contains('-')) {
	var newName = toCamelCase(name);
	_logger.warning('PolymerElement no longer recognizes attribute names with '
	'dashes such as "$name". Use "$newName" or "${newName.toLowerCase()}" '
	'instead (both forms are equivalent in HTML).', span: span);
	return false;
	}
	return true;
	}

	/// Validate event handlers are used correctly.
	void _validateEventHandler(Element node, String name, String value) {
	if (!name.startsWith('on-')) return;

	if (!_inPolymerElement) {
	_logger.warning('Inline event handlers are only supported inside '
	'declarations of <polymer-element>.',
	span: node.attributeSpans[name]);
	return;
	}


	// Valid bindings have {{ }}, don't look like method calls foo(bar), and are
	// non empty.
	if (!value.startsWith("{{") \|\| !value.endsWith("}}") \|\| value.contains('(')
	\|\| value.substring(2, value.length - 2).trim() == '') {
	_logger.warning('Invalid event handler body "$value". Declare a method '
	'in your custom element "void handlerName(event, detail, target)" '
	'and use the form $name="{{handlerName}}".',
	span: node.attributeSpans[name]);
	}
	}
	}

	const String ONLY_ONE_TAG =
	'Only one "application/dart" script tag per document is allowed.';

	String usePolymerHtmlMessageFrom(AssetId id) {
	var segments = id.path.split('/');
	var upDirCount = 0;
	if (segments[0] == 'lib') {
	// lib/foo.html => ../../packages/
	upDirCount = segments.length;
	} else if (segments.length > 2) {
	// web/a/foo.html => ../packages/
	upDirCount = segments.length - 2;
	}
	return usePolymerHtmlMessage(upDirCount);
	}

	String usePolymerHtmlMessage(int upDirCount) {
	var reachOutPrefix = '../' * upDirCount;
	return 'Missing definition for <polymer-element>, please add the following '
	'HTML import at the top of this file: <link rel="import" '
	'href="${reachOutPrefix}packages/polymer/polymer.html">.';
	}

	const String NO_IMPORT_WITHIN_ELEMENT = 'Polymer.dart\'s implementation of '
	'HTML imports are not supported within polymer element definitions, yet. '
	'Please move the import out of this <polymer-element>.';

	const String USE_INIT_DART =
	'To run a polymer application, you need to call "initPolymer". You can '
	'either include a generic script tag that does this for you:'
	'\'<script type="application/dart">export "package:polymer/init.dart";'
	'</script>\' or add your own script tag and call that function. '
	'Make sure the script tag is placed after all HTML imports.';

	const String NO_DART_SCRIPT_AND_EXPERIMENTAL =
	'The experimental bootstrap feature doesn\'t support script tags on '
	'the main document (for now).';