pkg/analyzer/lib/src/manifest/manifest_validator.dart - sdk.git - Git at Google

 // Copyright (c) 2019, 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.

 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/manifest/charcodes.dart';
 import 'package:analyzer/src/manifest/manifest_values.dart';
 import 'package:analyzer/src/manifest/manifest_warning_code.dart';
 import 'package:collection/collection.dart';
 import 'package:meta/meta.dart';
 import 'package:source_span/source_span.dart';

 /// A rudimentary parser for Android Manifest files.
 ///
 /// Android Manifest files are written in XML. In order to validate an Android
 /// Manifest file, however, we do not need to parse or retain each element. This
 /// parser understands which elements are relevant to manifest validation.
 /// This parser does not validate the XML, and if it encounters an error while
 /// parsing, no exception is thrown. Instead, a parse result with
 /// [ParseResult.error] is returned.
 ///
 /// This parser does not understand
 ///
 /// * CDATA sections (https://www.w3.org/TR/xml/#sec-cdata-sect),
 /// * element type declarations (https://www.w3.org/TR/xml/#elemdecls),
 /// * attribute list declarations (https://www.w3.org/TR/xml/#attdecls),
 /// * conditional sections (https://www.w3.org/TR/xml/#sec-condition-sect),
 /// * entity declarations (https://www.w3.org/TR/xml/#sec-entity-decl),
 /// * notation declarations (https://www.w3.org/TR/xml/#Notations).
 ///
 /// This parser does not replace character or entity references
 /// (https://www.w3.org/TR/xml/#sec-references).
 class ManifestParser {
   /// Elements which are relevant to manifest validation.
   static const List<String> _relevantElements = [
     ACTIVITY_TAG,
     APPLICATION_TAG,
     MANIFEST_TAG,
     USES_FEATURE_TAG,
     USES_PERMISSION_TAG
   ];

   /// The text of the Android Manifest file.
   final String content;

   /// The source file representing the Android Manifest file, for source span
   /// purposes.
   final SourceFile sourceFile;

   /// The current offset in the source file.
   int _pos;

   ManifestParser(this.content, Uri uri)
       : sourceFile = SourceFile.fromString(content, url: uri),
         _pos = 0;

   /// Whether the current character is a tag-closing character (">").
   bool get _isClosing =>
       _pos < content.length && content.codeUnitAt(_pos) == $gt;

   /// Whether the current character and the following two characters make a
   /// comment closing ("-->").
   bool get _isCommentClosing =>
       _pos + 2 < content.length &&
       content.codeUnitAt(_pos) == $dash &&
       content.codeUnitAt(_pos + 1) == $dash &&
       content.codeUnitAt(_pos + 2) == $gt;

   /// Whether the following three characters make a comment opening ("<!--").
   bool get _isCommentOpening =>
       _pos + 3 < content.length &&
       content.codeUnitAt(_pos + 1) == $exclamation &&
       content.codeUnitAt(_pos + 2) == $dash &&
       content.codeUnitAt(_pos + 3) == $dash;

   /// Whether the following character makes a comment opening ("<!").
   bool get _isDeclarationOpening =>
       _pos + 1 < content.length && content.codeUnitAt(_pos + 1) == $exclamation;

   /// Whether the current character and the following character make a
   /// two-character closing.
   ///
   /// The "/>" and "?>" closings each represent an empty element.
   bool get _isTwoCharClosing =>
       _pos + 1 < content.length &&
       (content.codeUnitAt(_pos) == $question ||
           content.codeUnitAt(_pos) == $slash) &&
       content.codeUnitAt(_pos + 1) == $gt;

   bool get _isWhitespace {
     var char = content.codeUnitAt(_pos);
     return char == $space || char == $tab || char == $lf || char == $cr;
   }

   /// Parses an XML tag into a [ParseTagResult].
   ParseTagResult parseXmlTag() {
     // Walk until we find a tag.
     while (_pos < content.length && content.codeUnitAt(_pos) != $lt) {
       _pos++;
     }
     if (_pos >= content.length) {
       return ParseTagResult.eof;
     }
     if (_isCommentOpening) {
       return _parseComment();
     }
     if (_isDeclarationOpening) {
       return _parseDeclaration();
     }

     return _parseNormalTag();
   }

   /// Returns whether [name] represents an element that is relevant to manifest
   /// validation.
   bool _isRelevantElement(String name) => _relevantElements.contains(name);

   /// Parses any whitespace, returning `null` when non-whitespace is parsed.
   ParseResult? _parseAnyWhitespace() {
     if (_pos >= content.length) {
       return ParseResult.error;
     }

     while (_isWhitespace) {
       _pos++;
       if (_pos >= content.length) {
         return ParseResult.error;
       }
     }
     return null;
   }

   /// Parses an attribute.
   ParseAttributeResult _parseAttribute(bool isRelevant) {
     var attributes = <String, _XmlAttribute>{};
     bool isEmptyElement;

     while (true) {
       if (_pos >= content.length) {
         return ParseAttributeResult.error;
       }
       var char = content.codeUnitAt(_pos);

       // In each loop, [_pos] must either be whitespace, ">", "/>", or "?>" to
       // be valid.
       if (_isClosing) {
         isEmptyElement = false;
         break;
       } else if (_isTwoCharClosing) {
         isEmptyElement = true;
         _pos++;
         break;
       } else if (!_isWhitespace) {
         return ParseAttributeResult.error;
       }

       var parsedWhitespaceResult = _parseAnyWhitespace();
       if (parsedWhitespaceResult == ParseResult.error) {
         return ParseAttributeResult.error;
       }

       if (_isClosing) {
         isEmptyElement = false;
         break;
       } else if (_isTwoCharClosing) {
         isEmptyElement = true;
         _pos++;
         break;
       }

       // Parse attribute name.
       var attributeNamePos = _pos;
       late String attributeName;
       _pos++;
       if (_pos >= content.length) {
         return ParseAttributeResult.error;
       }

       while ((char = content.codeUnitAt(_pos)) != $equal) {
         if (_isWhitespace || _isClosing || _isTwoCharClosing) {
           // An attribute without a value, while allowed in HTML, is not allowed
           // in XML.
           return ParseAttributeResult.error;
         }
         _pos++;
         if (_pos >= content.length) {
           return ParseAttributeResult.error;
         }
       }

       if (isRelevant) {
         attributeName = content.substring(attributeNamePos, _pos).toLowerCase();
       }
       _pos++; // Walk past "=".
       if (_pos >= content.length) {
         return ParseAttributeResult.error;
       }

       // Parse attribute value.
       int quote;
       char = content.codeUnitAt(_pos);
       if (char == $apostrophe || char == $quote) {
         quote = char;
         _pos++;
       } else {
         // An attribute name, followed by "=", followed by ">" is an error.
         return ParseAttributeResult.error;
       }
       int attributeValuePos = _pos;

       while ((char = content.codeUnitAt(_pos)) != quote) {
         _pos++;
         if (_pos >= content.length) {
           return ParseAttributeResult.error;
         }
       }

       if (isRelevant) {
         var attributeValue = content.substring(attributeValuePos, _pos);
         var sourceSpan = sourceFile.span(attributeNamePos, _pos);
         attributes[attributeName] =
             _XmlAttribute(attributeName, attributeValue, sourceSpan);
       }
       _pos++;
     }

     var parseResult = isEmptyElement
         ? ParseResult.attributesWithEmptyElementClose
         : ParseResult.attributesWithTagClose;

     return ParseAttributeResult(parseResult, attributes);
   }

   /// Parses a comment tag, as per https://www.w3.org/TR/xml/#sec-comments.
   ParseTagResult _parseComment() {
     // Walk past "<!--"
     _pos += 4;
     if (_pos >= content.length) {
       return ParseTagResult.error;
     }
     while (!_isCommentClosing) {
       _pos++;
       if (_pos >= content.length) {
         return ParseTagResult.error;
       }
     }
     _pos += 2;

     return ParseTagResult(ParseResult.element, null);
   }

   /// Parses a general declaration.
   ///
   /// Declarations are not processed or stored. The parser just intends to read
   /// the tag and return.
   ParseTagResult _parseDeclaration() {
     // Walk past "<!"
     _pos += 2;
     if (_pos >= content.length) {
       return ParseTagResult.error;
     }
     while (!_isClosing) {
       _pos++;
       if (_pos >= content.length) {
         return ParseTagResult.error;
       }
     }

     return ParseTagResult(ParseResult.element, null);
   }

   /// Parses a normal tag starting with an '<' character at the current
   /// position.
   ParseTagResult _parseNormalTag() {
     var startPos = _pos;
     _pos++;

     if (_pos >= content.length) {
       return ParseTagResult.error;
     }

     if (_isWhitespace) {
       // A tag cannot begin with whitespace.
       return ParseTagResult.error;
     }

     var isEndTag = content.codeUnitAt(_pos) == $slash;
     if (isEndTag) _pos++;
     var tagClosingState = _TagClosingState.notClosed;

     // Parse name.
     var namePos = _pos;
     late String name;

     while (!_isClosing && !_isTwoCharClosing && !_isWhitespace) {
       _pos++;
       if (_pos >= content.length) {
         return ParseTagResult.error;
       }
     }

     if (_isClosing) {
       // End of tag name, and tag.
       name = content.substring(namePos, _pos).toLowerCase();
       tagClosingState = _TagClosingState.closed;
     } else if (_isTwoCharClosing) {
       // End of tag name, tag, and element.
       name = content.substring(namePos, _pos).toLowerCase();
       tagClosingState = _TagClosingState.closedEmptyElement;
       _pos++;
     } else if (_isWhitespace) {
       // End of tag name.
       name = content.substring(namePos, _pos).toLowerCase();
     }

     if (isEndTag) {
       var parsedWhitespaceResult = _parseAnyWhitespace();
       if (parsedWhitespaceResult == ParseResult.error) {
         return ParseTagResult.error;
       }
       if (_isClosing) {
         // End tags cannot have attributes.
         return ParseTagResult(
             ParseResult.endTag, _XmlElement(name, {}, [], null));
       } else {
         return ParseTagResult.error;
       }
     }

     var isRelevant = _isRelevantElement(name);

     Map<String, _XmlAttribute> attributes;
     bool isEmptyElement;
     if (tagClosingState == _TagClosingState.notClosed) {
       // Have not parsed the tag close yet; parse attributes.
       var attributeResult = _parseAttribute(isRelevant);
       var parseResult = attributeResult.parseResult;
       if (parseResult == ParseResult.error) {
         return ParseTagResult.error;
       }
       attributes = attributeResult.attributes!;
       isEmptyElement =
           parseResult == ParseResult.attributesWithEmptyElementClose;
     } else {
       attributes = {};
       isEmptyElement = tagClosingState == _TagClosingState.closedEmptyElement;
     }
     if (name.startsWith('!')) {
       // Declarations (generally beginning with '!', do not require end tags.
       isEmptyElement = true;
     }

     var children = <_XmlElement>[];
     if (!isEmptyElement) {
       ParseTagResult child;
       _pos++;
       // Parse any children, and end tag.
       while ((child = parseXmlTag()).parseResult != ParseResult.endTag) {
         if (child == ParseTagResult.eof || child == ParseTagResult.error) {
           return child;
         }
         if (child.element == null) {
           // Don't store an irrelevant element.
           continue;
         }
         children.add(child.element!);
         _pos++;
       }
     }

     // Finished parsing start tag.
     if (isRelevant) {
       var sourceSpan = sourceFile.span(startPos, _pos);
       return ParseTagResult(ParseResult.relevantElement,
           _XmlElement(name, attributes, children, sourceSpan));
     } else {
       // Discard all parsed children. This requires the notion that all relevant
       // tags are direct children of other relevant tags.
       return ParseTagResult(ParseResult.element, null);
     }
   }
 }

 class ManifestValidator {
   /// The source representing the file being validated.
   final Source source;

   /// Initialize a newly create validator to validate the content of the given
   /// [source].
   ManifestValidator(this.source);

   /// Validate the [contents] of the Android Manifest file.
   List<AnalysisError> validate(String content, bool checkManifest) {
     // TODO(srawlins): Simplify [checkManifest] notion. Why call the method if
     //  the caller always knows whether it should just return empty?
     if (!checkManifest) return [];

     RecordingErrorListener recorder = RecordingErrorListener();
     ErrorReporter reporter = ErrorReporter(
       recorder,
       source,
       isNonNullableByDefault: false,
     );

     var xmlParser = ManifestParser(content, source.uri);

     _checkManifestTag(xmlParser, reporter);
     return recorder.errors;
   }

   void _checkManifestTag(ManifestParser parser, ErrorReporter reporter) {
     ParseTagResult parseTagResult;
     while (
         (parseTagResult = parser.parseXmlTag()).element?.name != MANIFEST_TAG) {
       if (parseTagResult == ParseTagResult.eof ||
           parseTagResult == ParseTagResult.error) {
         return;
       }
     }

     var manifestElement = parseTagResult.element!;
     var features =
         manifestElement.children.where((e) => e.name == USES_FEATURE_TAG);
     var permissions =
         manifestElement.children.where((e) => e.name == USES_PERMISSION_TAG);
     _validateTouchScreenFeature(features, manifestElement, reporter);
     _validateFeatures(features, reporter);
     _validatePermissions(permissions, features, reporter);

     var application = manifestElement.children
         .firstWhereOrNull((e) => e.name == APPLICATION_TAG);
     if (application != null) {
       for (var activity
           in application.children.where((e) => e.name == ACTIVITY_TAG)) {
         _validateActivity(activity, reporter);
       }
     }
   }

   bool _hasFeatureCamera(Iterable<_XmlElement> features) => features
       .any((f) => f.attributes[ANDROID_NAME]?.value == HARDWARE_FEATURE_CAMERA);

   bool _hasFeatureCameraAutoFocus(Iterable<_XmlElement> features) =>
       features.any((f) =>
           f.attributes[ANDROID_NAME]?.value ==
           HARDWARE_FEATURE_CAMERA_AUTOFOCUS);

   /// Report an error for the given node.
   void _reportErrorForNode(ErrorReporter reporter, _XmlElement node,
       String? key, ErrorCode errorCode,
       [List<Object>? arguments]) {
     var span =
         key == null ? node.sourceSpan! : node.attributes[key]!.sourceSpan;
     reporter.reportErrorForOffset(
         errorCode, span.start.offset, span.length, arguments);
   }

   /// Validate the 'activity' tags.
   void _validateActivity(_XmlElement activity, ErrorReporter reporter) {
     var attributes = activity.attributes;
     if (attributes.containsKey(ATTRIBUTE_SCREEN_ORIENTATION)) {
       if (UNSUPPORTED_ORIENTATIONS
           .contains(attributes[ATTRIBUTE_SCREEN_ORIENTATION]?.value)) {
         _reportErrorForNode(reporter, activity, ATTRIBUTE_SCREEN_ORIENTATION,
             ManifestWarningCode.SETTING_ORIENTATION_ON_ACTIVITY);
       }
     }
     if (attributes.containsKey(ATTRIBUTE_RESIZEABLE_ACTIVITY)) {
       if (attributes[ATTRIBUTE_RESIZEABLE_ACTIVITY]?.value == 'false') {
         _reportErrorForNode(reporter, activity, ATTRIBUTE_RESIZEABLE_ACTIVITY,
             ManifestWarningCode.NON_RESIZABLE_ACTIVITY);
       }
     }
   }

   /// Validate the `uses-feature` tags.
   void _validateFeatures(
       Iterable<_XmlElement> features, ErrorReporter reporter) {
     var unsupported = features.where((element) => UNSUPPORTED_HARDWARE_FEATURES
         .contains(element.attributes[ANDROID_NAME]?.value));
     for (var element in unsupported) {
       if (!element.attributes.containsKey(ANDROID_REQUIRED)) {
         // Since `unsupported` is the list of elements for which
         // `elements.attributes[ANDROID_NAME]?.value` is contained in
         // [UNSUPPORTED_HARDWARE_FEATURES], which is a list of non-nullable
         // strings, it follows that `element.attributes[ANDROID_NAME]` is
         // non-`null`.
         _reportErrorForNode(
             reporter,
             element,
             ANDROID_NAME,
             ManifestWarningCode.UNSUPPORTED_CHROME_OS_HARDWARE,
             [element.attributes[ANDROID_NAME]!.value]);
       } else if (element.attributes[ANDROID_REQUIRED]?.value == 'true') {
         // Since `unsupported` is the list of elements for which
         // `elements.attributes[ANDROID_NAME]?.value` is contained in
         // [UNSUPPORTED_HARDWARE_FEATURES], which is a list of non-nullable
         // strings, it follows that `element.attributes[ANDROID_NAME]` is
         // non-`null`.
         _reportErrorForNode(
             reporter,
             element,
             ANDROID_NAME,
             ManifestWarningCode.UNSUPPORTED_CHROME_OS_FEATURE,
             [element.attributes[ANDROID_NAME]!.value]);
       }
     }
   }

   /// Validate the `uses-permission` tags.
   void _validatePermissions(Iterable<_XmlElement> permissions,
       Iterable<_XmlElement> features, ErrorReporter reporter) {
     for (var permission in permissions) {
       if (permission.attributes[ANDROID_NAME]?.value ==
           ANDROID_PERMISSION_CAMERA) {
         if (!_hasFeatureCamera(features) ||
             !_hasFeatureCameraAutoFocus(features)) {
           _reportErrorForNode(reporter, permission, ANDROID_NAME,
               ManifestWarningCode.CAMERA_PERMISSIONS_INCOMPATIBLE);
         }
       } else {
         var featureName = getImpliedUnsupportedHardware(
             permission.attributes[ANDROID_NAME]?.value);
         if (featureName != null) {
           _reportErrorForNode(
               reporter,
               permission,
               ANDROID_NAME,
               ManifestWarningCode.PERMISSION_IMPLIES_UNSUPPORTED_HARDWARE,
               [featureName]);
         }
       }
     }
   }

   /// Validate the presence/absence of the touchscreen feature tag.
   void _validateTouchScreenFeature(Iterable<_XmlElement> features,
       _XmlElement manifest, ErrorReporter reporter) {
     var feature = features.firstWhereOrNull((element) =>
         element.attributes[ANDROID_NAME]?.value ==
         HARDWARE_FEATURE_TOUCHSCREEN);
     if (feature != null) {
       if (!feature.attributes.containsKey(ANDROID_REQUIRED)) {
         _reportErrorForNode(
             reporter,
             feature,
             ANDROID_NAME,
             ManifestWarningCode.UNSUPPORTED_CHROME_OS_HARDWARE,
             [HARDWARE_FEATURE_TOUCHSCREEN]);
       } else if (feature.attributes[ANDROID_REQUIRED]?.value == 'true') {
         _reportErrorForNode(
             reporter,
             feature,
             ANDROID_NAME,
             ManifestWarningCode.UNSUPPORTED_CHROME_OS_FEATURE,
             [HARDWARE_FEATURE_TOUCHSCREEN]);
       }
     } else {
       _reportErrorForNode(
           reporter, manifest, null, ManifestWarningCode.NO_TOUCHSCREEN_FEATURE);
     }
   }
 }

 @visibleForTesting
 class ParseAttributeResult {
   static ParseAttributeResult error =
       ParseAttributeResult(ParseResult.error, null);

   final ParseResult parseResult;

   final Map<String, _XmlAttribute>? attributes;

   ParseAttributeResult(this.parseResult, this.attributes);
 }

 enum ParseResult {
   // Attributes were parsed, followed by a tag close like "/>", signifying an
   // empty element, as per https://www.w3.org/TR/xml/#sec-starttags.
   attributesWithEmptyElementClose,
   // Attributes were parsed, followed by a tag close, ">".
   attributesWithTagClose,
   // A start tag for an irrelevant element was parsed, as per
   // https://www.w3.org/TR/xml/#sec-starttags.
   element,
   // An end tag for an element was parsed, as per
   // https://www.w3.org/TR/xml/#sec-starttags.
   endTag,
   // The content's EOF was parsed.
   eof,
   // An error was encountered.
   error,
   // A relevant element was parsed.
   relevantElement,
 }

 @visibleForTesting
 class ParseTagResult {
   static ParseTagResult eof = ParseTagResult(ParseResult.eof, null);
   static ParseTagResult error = ParseTagResult(ParseResult.error, null);

   final ParseResult parseResult;

   final _XmlElement? element;

   ParseTagResult(this.parseResult, this.element);
 }

 enum _TagClosingState {
   // Represents that the tag's close has not been parsed.
   notClosed,
   // Represents that the tag's close has been parsed as ">".
   closed,
   // Represents that the tag's close has been parsed as "/>", "?>", indicating
   // an empty element, as per https://www.w3.org/TR/xml/#sec-starttags.
   closedEmptyElement,
 }

 class _XmlAttribute {
   final String name;
   final String value;
   final SourceSpan sourceSpan;

   _XmlAttribute(this.name, this.value, this.sourceSpan);
 }

 class _XmlElement {
   final String name;
   final Map<String, _XmlAttribute> attributes;
   final List<_XmlElement> children;
   final SourceSpan? sourceSpan;

   _XmlElement(this.name, this.attributes, this.children, this.sourceSpan);
 }
	// Copyright (c) 2019, 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.

	import 'package:analyzer/error/error.dart';
	import 'package:analyzer/error/listener.dart';
	import 'package:analyzer/src/generated/source.dart';
	import 'package:analyzer/src/manifest/charcodes.dart';
	import 'package:analyzer/src/manifest/manifest_values.dart';
	import 'package:analyzer/src/manifest/manifest_warning_code.dart';
	import 'package:collection/collection.dart';
	import 'package:meta/meta.dart';
	import 'package:source_span/source_span.dart';

	/// A rudimentary parser for Android Manifest files.
	///
	/// Android Manifest files are written in XML. In order to validate an Android
	/// Manifest file, however, we do not need to parse or retain each element. This
	/// parser understands which elements are relevant to manifest validation.
	/// This parser does not validate the XML, and if it encounters an error while
	/// parsing, no exception is thrown. Instead, a parse result with
	/// [ParseResult.error] is returned.
	///
	/// This parser does not understand
	///
	/// * CDATA sections (https://www.w3.org/TR/xml/#sec-cdata-sect),
	/// * element type declarations (https://www.w3.org/TR/xml/#elemdecls),
	/// * attribute list declarations (https://www.w3.org/TR/xml/#attdecls),
	/// * conditional sections (https://www.w3.org/TR/xml/#sec-condition-sect),
	/// * entity declarations (https://www.w3.org/TR/xml/#sec-entity-decl),
	/// * notation declarations (https://www.w3.org/TR/xml/#Notations).
	///
	/// This parser does not replace character or entity references
	/// (https://www.w3.org/TR/xml/#sec-references).
	class ManifestParser {
	/// Elements which are relevant to manifest validation.
	static const List<String> _relevantElements = [
	ACTIVITY_TAG,
	APPLICATION_TAG,
	MANIFEST_TAG,
	USES_FEATURE_TAG,
	USES_PERMISSION_TAG
	];

	/// The text of the Android Manifest file.
	final String content;

	/// The source file representing the Android Manifest file, for source span
	/// purposes.
	final SourceFile sourceFile;

	/// The current offset in the source file.
	int _pos;

	ManifestParser(this.content, Uri uri)
	: sourceFile = SourceFile.fromString(content, url: uri),
	_pos = 0;

	/// Whether the current character is a tag-closing character (">").
	bool get _isClosing =>
	_pos < content.length && content.codeUnitAt(_pos) == $gt;

	/// Whether the current character and the following two characters make a
	/// comment closing ("-->").
	bool get _isCommentClosing =>
	_pos + 2 < content.length &&
	content.codeUnitAt(_pos) == $dash &&
	content.codeUnitAt(_pos + 1) == $dash &&
	content.codeUnitAt(_pos + 2) == $gt;

	/// Whether the following three characters make a comment opening ("<!--").
	bool get _isCommentOpening =>
	_pos + 3 < content.length &&
	content.codeUnitAt(_pos + 1) == $exclamation &&
	content.codeUnitAt(_pos + 2) == $dash &&
	content.codeUnitAt(_pos + 3) == $dash;

	/// Whether the following character makes a comment opening ("<!").
	bool get _isDeclarationOpening =>
	_pos + 1 < content.length && content.codeUnitAt(_pos + 1) == $exclamation;

	/// Whether the current character and the following character make a
	/// two-character closing.
	///
	/// The "/>" and "?>" closings each represent an empty element.
	bool get _isTwoCharClosing =>
	_pos + 1 < content.length &&
	(content.codeUnitAt(_pos) == $question \|\|
	content.codeUnitAt(_pos) == $slash) &&
	content.codeUnitAt(_pos + 1) == $gt;

	bool get _isWhitespace {
	var char = content.codeUnitAt(_pos);
	return char == $space \|\| char == $tab \|\| char == $lf \|\| char == $cr;
	}

	/// Parses an XML tag into a [ParseTagResult].
	ParseTagResult parseXmlTag() {
	// Walk until we find a tag.
	while (_pos < content.length && content.codeUnitAt(_pos) != $lt) {
	_pos++;
	}
	if (_pos >= content.length) {
	return ParseTagResult.eof;
	}
	if (_isCommentOpening) {
	return _parseComment();
	}
	if (_isDeclarationOpening) {
	return _parseDeclaration();
	}

	return _parseNormalTag();
	}

	/// Returns whether [name] represents an element that is relevant to manifest
	/// validation.
	bool _isRelevantElement(String name) => _relevantElements.contains(name);

	/// Parses any whitespace, returning `null` when non-whitespace is parsed.
	ParseResult? _parseAnyWhitespace() {
	if (_pos >= content.length) {
	return ParseResult.error;
	}

	while (_isWhitespace) {
	_pos++;
	if (_pos >= content.length) {
	return ParseResult.error;
	}
	}
	return null;
	}

	/// Parses an attribute.
	ParseAttributeResult _parseAttribute(bool isRelevant) {
	var attributes = <String, _XmlAttribute>{};
	bool isEmptyElement;

	while (true) {
	if (_pos >= content.length) {
	return ParseAttributeResult.error;
	}
	var char = content.codeUnitAt(_pos);

	// In each loop, [_pos] must either be whitespace, ">", "/>", or "?>" to
	// be valid.
	if (_isClosing) {
	isEmptyElement = false;
	break;
	} else if (_isTwoCharClosing) {
	isEmptyElement = true;
	_pos++;
	break;
	} else if (!_isWhitespace) {
	return ParseAttributeResult.error;
	}

	var parsedWhitespaceResult = _parseAnyWhitespace();
	if (parsedWhitespaceResult == ParseResult.error) {
	return ParseAttributeResult.error;
	}

	if (_isClosing) {
	isEmptyElement = false;
	break;
	} else if (_isTwoCharClosing) {
	isEmptyElement = true;
	_pos++;
	break;
	}

	// Parse attribute name.
	var attributeNamePos = _pos;
	late String attributeName;
	_pos++;
	if (_pos >= content.length) {
	return ParseAttributeResult.error;
	}

	while ((char = content.codeUnitAt(_pos)) != $equal) {
	if (_isWhitespace \|\| _isClosing \|\| _isTwoCharClosing) {
	// An attribute without a value, while allowed in HTML, is not allowed
	// in XML.
	return ParseAttributeResult.error;
	}
	_pos++;
	if (_pos >= content.length) {
	return ParseAttributeResult.error;
	}
	}

	if (isRelevant) {
	attributeName = content.substring(attributeNamePos, _pos).toLowerCase();
	}
	_pos++; // Walk past "=".
	if (_pos >= content.length) {
	return ParseAttributeResult.error;
	}

	// Parse attribute value.
	int quote;
	char = content.codeUnitAt(_pos);
	if (char == $apostrophe \|\| char == $quote) {
	quote = char;
	_pos++;
	} else {
	// An attribute name, followed by "=", followed by ">" is an error.
	return ParseAttributeResult.error;
	}
	int attributeValuePos = _pos;

	while ((char = content.codeUnitAt(_pos)) != quote) {
	_pos++;
	if (_pos >= content.length) {
	return ParseAttributeResult.error;
	}
	}

	if (isRelevant) {
	var attributeValue = content.substring(attributeValuePos, _pos);
	var sourceSpan = sourceFile.span(attributeNamePos, _pos);
	attributes[attributeName] =
	_XmlAttribute(attributeName, attributeValue, sourceSpan);
	}
	_pos++;
	}

	var parseResult = isEmptyElement
	? ParseResult.attributesWithEmptyElementClose
	: ParseResult.attributesWithTagClose;

	return ParseAttributeResult(parseResult, attributes);
	}

	/// Parses a comment tag, as per https://www.w3.org/TR/xml/#sec-comments.
	ParseTagResult _parseComment() {
	// Walk past "<!--"
	_pos += 4;
	if (_pos >= content.length) {
	return ParseTagResult.error;
	}
	while (!_isCommentClosing) {
	_pos++;
	if (_pos >= content.length) {
	return ParseTagResult.error;
	}
	}
	_pos += 2;

	return ParseTagResult(ParseResult.element, null);
	}

	/// Parses a general declaration.
	///
	/// Declarations are not processed or stored. The parser just intends to read
	/// the tag and return.
	ParseTagResult _parseDeclaration() {
	// Walk past "<!"
	_pos += 2;
	if (_pos >= content.length) {
	return ParseTagResult.error;
	}
	while (!_isClosing) {
	_pos++;
	if (_pos >= content.length) {
	return ParseTagResult.error;
	}
	}

	return ParseTagResult(ParseResult.element, null);
	}

	/// Parses a normal tag starting with an '<' character at the current
	/// position.
	ParseTagResult _parseNormalTag() {
	var startPos = _pos;
	_pos++;

	if (_pos >= content.length) {
	return ParseTagResult.error;
	}

	if (_isWhitespace) {
	// A tag cannot begin with whitespace.
	return ParseTagResult.error;
	}

	var isEndTag = content.codeUnitAt(_pos) == $slash;
	if (isEndTag) _pos++;
	var tagClosingState = _TagClosingState.notClosed;

	// Parse name.
	var namePos = _pos;
	late String name;

	while (!_isClosing && !_isTwoCharClosing && !_isWhitespace) {
	_pos++;
	if (_pos >= content.length) {
	return ParseTagResult.error;
	}
	}

	if (_isClosing) {
	// End of tag name, and tag.
	name = content.substring(namePos, _pos).toLowerCase();
	tagClosingState = _TagClosingState.closed;
	} else if (_isTwoCharClosing) {
	// End of tag name, tag, and element.
	name = content.substring(namePos, _pos).toLowerCase();
	tagClosingState = _TagClosingState.closedEmptyElement;
	_pos++;
	} else if (_isWhitespace) {
	// End of tag name.
	name = content.substring(namePos, _pos).toLowerCase();
	}

	if (isEndTag) {
	var parsedWhitespaceResult = _parseAnyWhitespace();
	if (parsedWhitespaceResult == ParseResult.error) {
	return ParseTagResult.error;
	}
	if (_isClosing) {
	// End tags cannot have attributes.
	return ParseTagResult(
	ParseResult.endTag, _XmlElement(name, {}, [], null));
	} else {
	return ParseTagResult.error;
	}
	}

	var isRelevant = _isRelevantElement(name);

	Map<String, _XmlAttribute> attributes;
	bool isEmptyElement;
	if (tagClosingState == _TagClosingState.notClosed) {
	// Have not parsed the tag close yet; parse attributes.
	var attributeResult = _parseAttribute(isRelevant);
	var parseResult = attributeResult.parseResult;
	if (parseResult == ParseResult.error) {
	return ParseTagResult.error;
	}
	attributes = attributeResult.attributes!;
	isEmptyElement =
	parseResult == ParseResult.attributesWithEmptyElementClose;
	} else {
	attributes = {};
	isEmptyElement = tagClosingState == _TagClosingState.closedEmptyElement;
	}
	if (name.startsWith('!')) {
	// Declarations (generally beginning with '!', do not require end tags.
	isEmptyElement = true;
	}

	var children = <_XmlElement>[];
	if (!isEmptyElement) {
	ParseTagResult child;
	_pos++;
	// Parse any children, and end tag.
	while ((child = parseXmlTag()).parseResult != ParseResult.endTag) {
	if (child == ParseTagResult.eof \|\| child == ParseTagResult.error) {
	return child;
	}
	if (child.element == null) {
	// Don't store an irrelevant element.
	continue;
	}
	children.add(child.element!);
	_pos++;
	}
	}

	// Finished parsing start tag.
	if (isRelevant) {
	var sourceSpan = sourceFile.span(startPos, _pos);
	return ParseTagResult(ParseResult.relevantElement,
	_XmlElement(name, attributes, children, sourceSpan));
	} else {
	// Discard all parsed children. This requires the notion that all relevant
	// tags are direct children of other relevant tags.
	return ParseTagResult(ParseResult.element, null);
	}
	}
	}

	class ManifestValidator {
	/// The source representing the file being validated.
	final Source source;

	/// Initialize a newly create validator to validate the content of the given
	/// [source].
	ManifestValidator(this.source);

	/// Validate the [contents] of the Android Manifest file.
	List<AnalysisError> validate(String content, bool checkManifest) {
	// TODO(srawlins): Simplify [checkManifest] notion. Why call the method if
	// the caller always knows whether it should just return empty?
	if (!checkManifest) return [];

	RecordingErrorListener recorder = RecordingErrorListener();
	ErrorReporter reporter = ErrorReporter(
	recorder,
	source,
	isNonNullableByDefault: false,
	);

	var xmlParser = ManifestParser(content, source.uri);

	_checkManifestTag(xmlParser, reporter);
	return recorder.errors;
	}

	void _checkManifestTag(ManifestParser parser, ErrorReporter reporter) {
	ParseTagResult parseTagResult;
	while (
	(parseTagResult = parser.parseXmlTag()).element?.name != MANIFEST_TAG) {
	if (parseTagResult == ParseTagResult.eof \|\|
	parseTagResult == ParseTagResult.error) {
	return;
	}
	}

	var manifestElement = parseTagResult.element!;
	var features =
	manifestElement.children.where((e) => e.name == USES_FEATURE_TAG);
	var permissions =
	manifestElement.children.where((e) => e.name == USES_PERMISSION_TAG);
	_validateTouchScreenFeature(features, manifestElement, reporter);
	_validateFeatures(features, reporter);
	_validatePermissions(permissions, features, reporter);

	var application = manifestElement.children
	.firstWhereOrNull((e) => e.name == APPLICATION_TAG);
	if (application != null) {
	for (var activity
	in application.children.where((e) => e.name == ACTIVITY_TAG)) {
	_validateActivity(activity, reporter);
	}
	}
	}

	bool _hasFeatureCamera(Iterable<_XmlElement> features) => features
	.any((f) => f.attributes[ANDROID_NAME]?.value == HARDWARE_FEATURE_CAMERA);

	bool _hasFeatureCameraAutoFocus(Iterable<_XmlElement> features) =>
	features.any((f) =>
	f.attributes[ANDROID_NAME]?.value ==
	HARDWARE_FEATURE_CAMERA_AUTOFOCUS);

	/// Report an error for the given node.
	void _reportErrorForNode(ErrorReporter reporter, _XmlElement node,
	String? key, ErrorCode errorCode,
	[List<Object>? arguments]) {
	var span =
	key == null ? node.sourceSpan! : node.attributes[key]!.sourceSpan;
	reporter.reportErrorForOffset(
	errorCode, span.start.offset, span.length, arguments);
	}

	/// Validate the 'activity' tags.
	void _validateActivity(_XmlElement activity, ErrorReporter reporter) {
	var attributes = activity.attributes;
	if (attributes.containsKey(ATTRIBUTE_SCREEN_ORIENTATION)) {
	if (UNSUPPORTED_ORIENTATIONS
	.contains(attributes[ATTRIBUTE_SCREEN_ORIENTATION]?.value)) {
	_reportErrorForNode(reporter, activity, ATTRIBUTE_SCREEN_ORIENTATION,
	ManifestWarningCode.SETTING_ORIENTATION_ON_ACTIVITY);
	}
	}
	if (attributes.containsKey(ATTRIBUTE_RESIZEABLE_ACTIVITY)) {
	if (attributes[ATTRIBUTE_RESIZEABLE_ACTIVITY]?.value == 'false') {
	_reportErrorForNode(reporter, activity, ATTRIBUTE_RESIZEABLE_ACTIVITY,
	ManifestWarningCode.NON_RESIZABLE_ACTIVITY);
	}
	}
	}

	/// Validate the `uses-feature` tags.
	void _validateFeatures(
	Iterable<_XmlElement> features, ErrorReporter reporter) {
	var unsupported = features.where((element) => UNSUPPORTED_HARDWARE_FEATURES
	.contains(element.attributes[ANDROID_NAME]?.value));
	for (var element in unsupported) {
	if (!element.attributes.containsKey(ANDROID_REQUIRED)) {
	// Since `unsupported` is the list of elements for which
	// `elements.attributes[ANDROID_NAME]?.value` is contained in
	// [UNSUPPORTED_HARDWARE_FEATURES], which is a list of non-nullable
	// strings, it follows that `element.attributes[ANDROID_NAME]` is
	// non-`null`.
	_reportErrorForNode(
	reporter,
	element,
	ANDROID_NAME,
	ManifestWarningCode.UNSUPPORTED_CHROME_OS_HARDWARE,
	[element.attributes[ANDROID_NAME]!.value]);
	} else if (element.attributes[ANDROID_REQUIRED]?.value == 'true') {
	// Since `unsupported` is the list of elements for which
	// `elements.attributes[ANDROID_NAME]?.value` is contained in
	// [UNSUPPORTED_HARDWARE_FEATURES], which is a list of non-nullable
	// strings, it follows that `element.attributes[ANDROID_NAME]` is
	// non-`null`.
	_reportErrorForNode(
	reporter,
	element,
	ANDROID_NAME,
	ManifestWarningCode.UNSUPPORTED_CHROME_OS_FEATURE,
	[element.attributes[ANDROID_NAME]!.value]);
	}
	}
	}

	/// Validate the `uses-permission` tags.
	void _validatePermissions(Iterable<_XmlElement> permissions,
	Iterable<_XmlElement> features, ErrorReporter reporter) {
	for (var permission in permissions) {
	if (permission.attributes[ANDROID_NAME]?.value ==
	ANDROID_PERMISSION_CAMERA) {
	if (!_hasFeatureCamera(features) \|\|
	!_hasFeatureCameraAutoFocus(features)) {
	_reportErrorForNode(reporter, permission, ANDROID_NAME,
	ManifestWarningCode.CAMERA_PERMISSIONS_INCOMPATIBLE);
	}
	} else {
	var featureName = getImpliedUnsupportedHardware(
	permission.attributes[ANDROID_NAME]?.value);
	if (featureName != null) {
	_reportErrorForNode(
	reporter,
	permission,
	ANDROID_NAME,
	ManifestWarningCode.PERMISSION_IMPLIES_UNSUPPORTED_HARDWARE,
	[featureName]);
	}
	}
	}
	}

	/// Validate the presence/absence of the touchscreen feature tag.
	void _validateTouchScreenFeature(Iterable<_XmlElement> features,
	_XmlElement manifest, ErrorReporter reporter) {
	var feature = features.firstWhereOrNull((element) =>
	element.attributes[ANDROID_NAME]?.value ==
	HARDWARE_FEATURE_TOUCHSCREEN);
	if (feature != null) {
	if (!feature.attributes.containsKey(ANDROID_REQUIRED)) {
	_reportErrorForNode(
	reporter,
	feature,
	ANDROID_NAME,
	ManifestWarningCode.UNSUPPORTED_CHROME_OS_HARDWARE,
	[HARDWARE_FEATURE_TOUCHSCREEN]);
	} else if (feature.attributes[ANDROID_REQUIRED]?.value == 'true') {
	_reportErrorForNode(
	reporter,
	feature,
	ANDROID_NAME,
	ManifestWarningCode.UNSUPPORTED_CHROME_OS_FEATURE,
	[HARDWARE_FEATURE_TOUCHSCREEN]);
	}
	} else {
	_reportErrorForNode(
	reporter, manifest, null, ManifestWarningCode.NO_TOUCHSCREEN_FEATURE);
	}
	}
	}

	@visibleForTesting
	class ParseAttributeResult {
	static ParseAttributeResult error =
	ParseAttributeResult(ParseResult.error, null);

	final ParseResult parseResult;

	final Map<String, _XmlAttribute>? attributes;

	ParseAttributeResult(this.parseResult, this.attributes);
	}

	enum ParseResult {
	// Attributes were parsed, followed by a tag close like "/>", signifying an
	// empty element, as per https://www.w3.org/TR/xml/#sec-starttags.
	attributesWithEmptyElementClose,
	// Attributes were parsed, followed by a tag close, ">".
	attributesWithTagClose,
	// A start tag for an irrelevant element was parsed, as per
	// https://www.w3.org/TR/xml/#sec-starttags.
	element,
	// An end tag for an element was parsed, as per
	// https://www.w3.org/TR/xml/#sec-starttags.
	endTag,
	// The content's EOF was parsed.
	eof,
	// An error was encountered.
	error,
	// A relevant element was parsed.
	relevantElement,
	}

	@visibleForTesting
	class ParseTagResult {
	static ParseTagResult eof = ParseTagResult(ParseResult.eof, null);
	static ParseTagResult error = ParseTagResult(ParseResult.error, null);

	final ParseResult parseResult;

	final _XmlElement? element;

	ParseTagResult(this.parseResult, this.element);
	}

	enum _TagClosingState {
	// Represents that the tag's close has not been parsed.
	notClosed,
	// Represents that the tag's close has been parsed as ">".
	closed,
	// Represents that the tag's close has been parsed as "/>", "?>", indicating
	// an empty element, as per https://www.w3.org/TR/xml/#sec-starttags.
	closedEmptyElement,
	}

	class _XmlAttribute {
	final String name;
	final String value;
	final SourceSpan sourceSpan;

	_XmlAttribute(this.name, this.value, this.sourceSpan);
	}

	class _XmlElement {
	final String name;
	final Map<String, _XmlAttribute> attributes;
	final List<_XmlElement> children;
	final SourceSpan? sourceSpan;

	_XmlElement(this.name, this.attributes, this.children, this.sourceSpan);
	}