packages/polymer/lib/src/build/linter.dart - observatory_pub_packages - 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 'dart:convert';

 import 'package:barback/barback.dart';
 import 'package:code_transformers/assets.dart';
 import 'package:code_transformers/messages/build_logger.dart';
 import 'package:code_transformers/messages/messages.dart' show Message;
 import 'package:html/dom.dart';
 import 'package:html/dom_parsing.dart';
 import 'package:path/path.dart' as path;
 import 'package:source_span/source_span.dart';

 import 'common.dart';
 import 'utils.dart';
 import 'messages.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;
   final bool skipMissingElementWarning;

   Linter(this.options, {this.skipMissingElementWarning: false});

   isPrimary(AssetId id) =>
       id.extension == '.html' && options.lint.shouldLint(id.path);

   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);
     bool isEntryPoint = options.isHtmlEntryPoint(id);

     var logger = new BuildLogger(transform,
         convertErrorsToWarnings: !options.releaseMode,
         detailsUri: 'http://goo.gl/5HPeuP');

     return readPrimaryAsHtml(transform, logger).then((document) {
       return _collectElements(document, id, transform, logger, seen)
           .then((elements) {
         new _LinterVisitor(id, logger, elements, isEntryPoint,
             skipMissingElementWarning || !isEntryPoint).run(document);

         // Write out the logs collected by our [BuildLogger].
         if (options.injectBuildLogsInOutput && logger is BuildLogger) {
           return (logger as BuildLogger).writeOutput();
         }
       });
     });
   }

   /// 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, BuildLogger logger,
       Set<AssetId> seen, [Map<String, _ElementSummary> elements]) {
     if (elements == null) elements = <String, _ElementSummary>{};
     return _getImportedIds(document, sourceId, transform, logger)
         // Note: the import order is relevant, so we visit in that order.
         .then((ids) => Future.forEach(ids, (id) =>
             _readAndCollectElements(id, transform, logger, seen, elements)))
         .then((_) {
       if (sourceId.package == 'polymer_interop' &&
           sourceId.path == 'lib/src/js/polymer.html' &&
           elements['polymer-element'] == null) {
         elements['polymer-element'] =
             new _ElementSummary('polymer-element', null, null);
       }
       return _addElements(document, logger, elements);
     }).then((_) => elements);
   }

   Future _readAndCollectElements(AssetId id, Transform transform,
       BuildLogger logger, 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, logger, showWarnings: false).then(
         (doc) => _collectElements(doc, id, transform, logger, seen, elements));
   }

   Future<List<AssetId>> _getImportedIds(Document document, AssetId sourceId,
       Transform transform, BuildLogger logger) {
     var importIds = [];
     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(
               IMPORT_NOT_FOUND.create({'path': id.path, 'package': id.package}),
               span: span);
         }
       }));
     }
     return Future.wait(importIds);
   }

   void _addElements(Document document, BuildLogger 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.create({'name': name, 'second': ''}),
             span: existing.span);
         logger.warning(DUPLICATE_DEFINITION
                 .create({'name': name, 'second': ' (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 SourceSpan 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 {
   BuildLogger _logger;
   AssetId _sourceId;
   bool _inPolymerElement = false;
   bool _inAutoBindingElement = false;
   bool _dartTagSeen = false;
   bool _polymerHtmlSeen = false;
   bool _polymerExperimentalHtmlSeen = false;
   bool _isEntryPoint;
   Map<String, _ElementSummary> _elements;
   bool _skipMissingElementWarning;

   _LinterVisitor(this._sourceId, this._logger, this._elements,
       this._isEntryPoint, this._skipMissingElementWarning) {
     // 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;
       case 'template':
         var isTag = node.attributes['is'];
         var oldInAutoBindingElement = _inAutoBindingElement;
         if (isTag != null && AUTO_BINDING_ELEMENTS.contains(isTag)) {
           _inAutoBindingElement = true;
         }
         _validateNormalElement(node);
         super.visitElement(node);
         _inAutoBindingElement = oldInAutoBindingElement;
         break;
       default:
         _validateNormalElement(node);
         super.visitElement(node);
         break;
     }
   }

   void run(Document doc) {
     visit(doc);

     if (_isEntryPoint && !_dartTagSeen && !_polymerExperimentalHtmlSeen) {
       _logger.warning(MISSING_INIT_POLYMER, 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_IMPORTS_UP, span: node.sourceSpan);
     }

     var href = node.attributes['href'];
     if (href == null || href == '') {
       _logger.warning(MISSING_HREF.create({'rel': rel}), 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_DEPRECATED_EONS_AGO, 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 (!_skipMissingElementWarning &&
         !_elements.containsKey('polymer-element')) {
       _logger.warning(usePolymerHtmlMessageFrom(_sourceId),
           span: node.sourceSpan);
     }

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

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

     if (tagName == null) {
       _logger.error(MISSING_TAG_NAME, span: node.sourceSpan);
     } else if (!isCustomTagName(tagName)) {
       _logger.error(INVALID_TAG_NAME.create({'name': tagName}),
           span: node.sourceSpan);
     }

     if (!_skipMissingElementWarning &&
         _elements[extendsTag] == null &&
         isCustomTagName(extendsTag)) {
       _logger.warning(CUSTOM_ELEMENT_NOT_FOUND.create({'tag': extendsTag}),
           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 && src.endsWith('web_components/dart_support.js')) {
       _logger.warning(DART_SUPPORT_NO_LONGER_REQUIRED, span: node.sourceSpan);
     }

     if (src != null && src.contains('web_components/webcomponents.')) {
       _logger.warning(WEB_COMPONENTS_NO_LONGER_REQUIRED, span: node.sourceSpan);
     }

     if (src != null && src.contains('web_components/platform.')) {
       _logger.warning(PLATFORM_JS_RENAMED, span: node.sourceSpan);
     }

     var isEmpty = node.innerHtml.trim() == '';

     if (src == null) {
       if (isDart && isEmpty) {
         _logger.warning(SCRIPT_TAG_SEEMS_EMPTY, span: node.sourceSpan);
       }
       return;
     }

     if (src.endsWith('.dart') && !isDart) {
       _logger.warning(EXPECTED_DART_MIME_TYPE, span: node.sourceSpan);
       return;
     }

     if (!src.endsWith('.dart') && isDart) {
       _logger.warning(EXPECTED_DART_EXTENSION, span: node.sourceSpan);
       return;
     }

     if (!isEmpty) {
       _logger.warning(FOUND_BOTH_SCRIPT_SRC_AND_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 ||
         INTERNALLY_DEFINED_ELEMENTS.contains(customTagName)) {
       return;
     }

     var info = _elements[customTagName];
     if (info == null) {
       if (!_skipMissingElementWarning && _isEntryPoint) {
         _logger.warning(CUSTOM_ELEMENT_NOT_FOUND.create({'tag': customTagName}),
             span: node.sourceSpan);
       }
       return;
     }

     var baseTag = info.baseExtendsTag;
     if (baseTag != null && !hasIsAttribute) {
       _logger.warning(BAD_INSTANTIATION_MISSING_BASE_TAG
               .create({'tag': customTagName, 'base': baseTag}),
           span: node.sourceSpan);
       return;
     }

     if (hasIsAttribute && baseTag == null) {
       _logger.warning(BAD_INSTANTIATION_BOGUS_BASE_TAG
               .create({'tag': customTagName, 'base': nodeTag}),
           span: node.sourceSpan);
       return;
     }

     if (hasIsAttribute && baseTag != nodeTag) {
       _logger.warning(BAD_INSTANTIATION_WRONG_BASE_TAG
               .create({'tag': customTagName, 'base': baseTag}),
           span: node.sourceSpan);
     }

     // FOUC check, if content is supplied
     if (_isEntryPoint && !node.innerHtml.isEmpty) {
       var parent = node;
       var hasFoucFix = false;
       while (parent != null && !hasFoucFix) {
         if (parent.localName == 'polymer-element' ||
             parent.attributes['unresolved'] != null) {
           hasFoucFix = true;
         }
         if (parent.localName == 'body') break;
         parent = parent.parent;
       }
       if (!hasFoucFix) _logger.warning(POSSIBLE_FUOC, 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);
       var alternative = '"$newName" or "${newName.toLowerCase()}"';
       _logger.warning(NO_DASHES_IN_CUSTOM_ATTRIBUTES
           .create({'name': name, 'alternative': alternative}), 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 && !_inAutoBindingElement) {
       _logger.warning(EVENT_HANDLERS_ONLY_WITHIN_POLYMER,
           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.create({'value': value, 'name': name}),
           span: node.attributeSpans[name]);
     }
   }
 }

 Message usePolymerHtmlMessageFrom(AssetId id) {
   var segments = path.url.split(id.path);
   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;
   }
   var reachOutPrefix = '../' * upDirCount;
   return USE_POLYMER_HTML.create({'reachOutPrefix': reachOutPrefix});
 }

 const List<String> INTERNALLY_DEFINED_ELEMENTS = const [
   'auto-binding-dart',
   'polymer-element'
 ];
 const List<String> AUTO_BINDING_ELEMENTS = const [
   'auto-binding-dart',
   'auto-binding'
 ];
	// 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 'dart:convert';

	import 'package:barback/barback.dart';
	import 'package:code_transformers/assets.dart';
	import 'package:code_transformers/messages/build_logger.dart';
	import 'package:code_transformers/messages/messages.dart' show Message;
	import 'package:html/dom.dart';
	import 'package:html/dom_parsing.dart';
	import 'package:path/path.dart' as path;
	import 'package:source_span/source_span.dart';

	import 'common.dart';
	import 'utils.dart';
	import 'messages.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;
	final bool skipMissingElementWarning;

	Linter(this.options, {this.skipMissingElementWarning: false});

	isPrimary(AssetId id) =>
	id.extension == '.html' && options.lint.shouldLint(id.path);

	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);
	bool isEntryPoint = options.isHtmlEntryPoint(id);

	var logger = new BuildLogger(transform,
	convertErrorsToWarnings: !options.releaseMode,
	detailsUri: 'http://goo.gl/5HPeuP');

	return readPrimaryAsHtml(transform, logger).then((document) {
	return _collectElements(document, id, transform, logger, seen)
	.then((elements) {
	new _LinterVisitor(id, logger, elements, isEntryPoint,
	skipMissingElementWarning \|\| !isEntryPoint).run(document);

	// Write out the logs collected by our [BuildLogger].
	if (options.injectBuildLogsInOutput && logger is BuildLogger) {
	return (logger as BuildLogger).writeOutput();
	}
	});
	});
	}

	/// 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, BuildLogger logger,
	Set<AssetId> seen, [Map<String, _ElementSummary> elements]) {
	if (elements == null) elements = <String, _ElementSummary>{};
	return _getImportedIds(document, sourceId, transform, logger)
	// Note: the import order is relevant, so we visit in that order.
	.then((ids) => Future.forEach(ids, (id) =>
	_readAndCollectElements(id, transform, logger, seen, elements)))
	.then((_) {
	if (sourceId.package == 'polymer_interop' &&
	sourceId.path == 'lib/src/js/polymer.html' &&
	elements['polymer-element'] == null) {
	elements['polymer-element'] =
	new _ElementSummary('polymer-element', null, null);
	}
	return _addElements(document, logger, elements);
	}).then((_) => elements);
	}

	Future _readAndCollectElements(AssetId id, Transform transform,
	BuildLogger logger, 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, logger, showWarnings: false).then(
	(doc) => _collectElements(doc, id, transform, logger, seen, elements));
	}

	Future<List<AssetId>> _getImportedIds(Document document, AssetId sourceId,
	Transform transform, BuildLogger logger) {
	var importIds = [];
	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(
	IMPORT_NOT_FOUND.create({'path': id.path, 'package': id.package}),
	span: span);
	}
	}));
	}
	return Future.wait(importIds);
	}

	void _addElements(Document document, BuildLogger 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.create({'name': name, 'second': ''}),
	span: existing.span);
	logger.warning(DUPLICATE_DEFINITION
	.create({'name': name, 'second': ' (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 SourceSpan 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 {
	BuildLogger _logger;
	AssetId _sourceId;
	bool _inPolymerElement = false;
	bool _inAutoBindingElement = false;
	bool _dartTagSeen = false;
	bool _polymerHtmlSeen = false;
	bool _polymerExperimentalHtmlSeen = false;
	bool _isEntryPoint;
	Map<String, _ElementSummary> _elements;
	bool _skipMissingElementWarning;

	_LinterVisitor(this._sourceId, this._logger, this._elements,
	this._isEntryPoint, this._skipMissingElementWarning) {
	// 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;
	case 'template':
	var isTag = node.attributes['is'];
	var oldInAutoBindingElement = _inAutoBindingElement;
	if (isTag != null && AUTO_BINDING_ELEMENTS.contains(isTag)) {
	_inAutoBindingElement = true;
	}
	_validateNormalElement(node);
	super.visitElement(node);
	_inAutoBindingElement = oldInAutoBindingElement;
	break;
	default:
	_validateNormalElement(node);
	super.visitElement(node);
	break;
	}
	}

	void run(Document doc) {
	visit(doc);

	if (_isEntryPoint && !_dartTagSeen && !_polymerExperimentalHtmlSeen) {
	_logger.warning(MISSING_INIT_POLYMER, 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_IMPORTS_UP, span: node.sourceSpan);
	}

	var href = node.attributes['href'];
	if (href == null \|\| href == '') {
	_logger.warning(MISSING_HREF.create({'rel': rel}), 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_DEPRECATED_EONS_AGO, 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 (!_skipMissingElementWarning &&
	!_elements.containsKey('polymer-element')) {
	_logger.warning(usePolymerHtmlMessageFrom(_sourceId),
	span: node.sourceSpan);
	}

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

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

	if (tagName == null) {
	_logger.error(MISSING_TAG_NAME, span: node.sourceSpan);
	} else if (!isCustomTagName(tagName)) {
	_logger.error(INVALID_TAG_NAME.create({'name': tagName}),
	span: node.sourceSpan);
	}

	if (!_skipMissingElementWarning &&
	_elements[extendsTag] == null &&
	isCustomTagName(extendsTag)) {
	_logger.warning(CUSTOM_ELEMENT_NOT_FOUND.create({'tag': extendsTag}),
	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 && src.endsWith('web_components/dart_support.js')) {
	_logger.warning(DART_SUPPORT_NO_LONGER_REQUIRED, span: node.sourceSpan);
	}

	if (src != null && src.contains('web_components/webcomponents.')) {
	_logger.warning(WEB_COMPONENTS_NO_LONGER_REQUIRED, span: node.sourceSpan);
	}

	if (src != null && src.contains('web_components/platform.')) {
	_logger.warning(PLATFORM_JS_RENAMED, span: node.sourceSpan);
	}

	var isEmpty = node.innerHtml.trim() == '';

	if (src == null) {
	if (isDart && isEmpty) {
	_logger.warning(SCRIPT_TAG_SEEMS_EMPTY, span: node.sourceSpan);
	}
	return;
	}

	if (src.endsWith('.dart') && !isDart) {
	_logger.warning(EXPECTED_DART_MIME_TYPE, span: node.sourceSpan);
	return;
	}

	if (!src.endsWith('.dart') && isDart) {
	_logger.warning(EXPECTED_DART_EXTENSION, span: node.sourceSpan);
	return;
	}

	if (!isEmpty) {
	_logger.warning(FOUND_BOTH_SCRIPT_SRC_AND_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 \|\|
	INTERNALLY_DEFINED_ELEMENTS.contains(customTagName)) {
	return;
	}

	var info = _elements[customTagName];
	if (info == null) {
	if (!_skipMissingElementWarning && _isEntryPoint) {
	_logger.warning(CUSTOM_ELEMENT_NOT_FOUND.create({'tag': customTagName}),
	span: node.sourceSpan);
	}
	return;
	}

	var baseTag = info.baseExtendsTag;
	if (baseTag != null && !hasIsAttribute) {
	_logger.warning(BAD_INSTANTIATION_MISSING_BASE_TAG
	.create({'tag': customTagName, 'base': baseTag}),
	span: node.sourceSpan);
	return;
	}

	if (hasIsAttribute && baseTag == null) {
	_logger.warning(BAD_INSTANTIATION_BOGUS_BASE_TAG
	.create({'tag': customTagName, 'base': nodeTag}),
	span: node.sourceSpan);
	return;
	}

	if (hasIsAttribute && baseTag != nodeTag) {
	_logger.warning(BAD_INSTANTIATION_WRONG_BASE_TAG
	.create({'tag': customTagName, 'base': baseTag}),
	span: node.sourceSpan);
	}

	// FOUC check, if content is supplied
	if (_isEntryPoint && !node.innerHtml.isEmpty) {
	var parent = node;
	var hasFoucFix = false;
	while (parent != null && !hasFoucFix) {
	if (parent.localName == 'polymer-element' \|\|
	parent.attributes['unresolved'] != null) {
	hasFoucFix = true;
	}
	if (parent.localName == 'body') break;
	parent = parent.parent;
	}
	if (!hasFoucFix) _logger.warning(POSSIBLE_FUOC, 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);
	var alternative = '"$newName" or "${newName.toLowerCase()}"';
	_logger.warning(NO_DASHES_IN_CUSTOM_ATTRIBUTES
	.create({'name': name, 'alternative': alternative}), 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 && !_inAutoBindingElement) {
	_logger.warning(EVENT_HANDLERS_ONLY_WITHIN_POLYMER,
	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.create({'value': value, 'name': name}),
	span: node.attributeSpans[name]);
	}
	}
	}

	Message usePolymerHtmlMessageFrom(AssetId id) {
	var segments = path.url.split(id.path);
	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;
	}
	var reachOutPrefix = '../' * upDirCount;
	return USE_POLYMER_HTML.create({'reachOutPrefix': reachOutPrefix});
	}

	const List<String> INTERNALLY_DEFINED_ELEMENTS = const [
	'auto-binding-dart',
	'polymer-element'
	];
	const List<String> AUTO_BINDING_ELEMENTS = const [
	'auto-binding-dart',
	'auto-binding'
	];