pkg/analysis_server/lib/src/utilities/extensions/ast.dart - sdk.git - Git at Google

 // Copyright (c) 2020, 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:analysis_server/src/services/correction/namespace.dart';
 import 'package:analysis_server/src/utilities/extensions/element.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/source/source.dart';
 import 'package:analyzer/src/dart/ast/element_locator.dart';
 import 'package:analyzer/src/dart/ast/token.dart';
 import 'package:analyzer/src/utilities/extensions/ast.dart';
 import 'package:analyzer/src/utilities/extensions/collection.dart';
 import 'package:analyzer/src/utilities/extensions/element.dart';

 class ThrowStatement {
   final ExpressionStatement statement;
   final ThrowExpression expression;

   ThrowStatement({required this.statement, required this.expression});
 }

 class _ReferencedUnprefixedNamesCollector extends RecursiveAstVisitor<void> {
   final Set<String> names = <String>{};

   @override
   void visitNamedType(NamedType node) {
     if (node.importPrefix == null) {
       names.add(node.name.lexeme);
     }

     super.visitNamedType(node);
   }

   @override
   void visitSimpleIdentifier(SimpleIdentifier node) {
     if (!_isPrefixed(node) && !_isLabelName(node)) {
       names.add(node.name);
     }
   }

   @override
   visitVariableDeclaration(VariableDeclaration node) {
     names.add(node.name.lexeme);
     return super.visitVariableDeclaration(node);
   }

   static bool _isLabelName(SimpleIdentifier node) {
     return node.parent is Label;
   }

   static bool _isPrefixed(SimpleIdentifier node) {
     var parent = node.parent;
     return parent is ConstructorName && parent.name == node ||
         parent is MethodInvocation &&
             parent.methodName == node &&
             parent.realTarget != null ||
         parent is PrefixedIdentifier && parent.identifier == node ||
         parent is PropertyAccess && parent.target == node;
   }
 }

 extension AnnotatedNodeExtension on AnnotatedNode {
   /// Return the first token in this node that is not a comment.
   Token get firstNonCommentToken {
     var metadata = this.metadata;
     if (metadata.isEmpty) {
       return firstTokenAfterCommentAndMetadata;
     }
     return metadata.beginToken!;
   }
 }

 extension AstNodeExtension on AstNode {
   /// Return the [IfStatement] associated with `this`.
   IfStatement? get enclosingIfStatement {
     for (var node in withParents) {
       if (node is IfStatement) {
         return node;
       } else if (node is! Expression) {
         return null;
       }
     }
     return null;
   }

   /// Return `true` if this node has an `override` annotation.
   bool get hasOverride {
     var node = this;
     if (node is AnnotatedNode) {
       for (var annotation in node.metadata) {
         if (annotation.name.name == 'override' &&
             annotation.arguments == null) {
           return true;
         }
       }
     }
     return false;
   }

   bool get inAsyncMethodOrFunction {
     var body = thisOrAncestorOfType<FunctionBody>();
     return body != null && body.isAsynchronous && body.star == null;
   }

   bool get inAsyncStarOrSyncStarMethodOrFunction {
     var body = thisOrAncestorOfType<FunctionBody>();
     return body != null && body.keyword != null && body.star != null;
   }

   bool get inCatchClause => thisOrAncestorOfType<CatchClause>() != null;

   bool get inClassMemberBody {
     var node = this;
     while (true) {
       var body = node.thisOrAncestorOfType<FunctionBody>();
       if (body == null) {
         return false;
       }
       var parent = body.parent;
       if (parent is ConstructorDeclaration || parent is MethodDeclaration) {
         return true;
       } else if (parent == null) {
         return false;
       }
       node = parent;
     }
   }

   bool get inDoLoop => thisOrAncestorOfType<DoStatement>() != null;

   bool get inForLoop =>
       thisOrAncestorMatching((p) => p is ForStatement) != null;

   bool get inLoop => inDoLoop || inForLoop || inWhileLoop;

   bool get inSwitch => thisOrAncestorOfType<SwitchStatement>() != null;

   bool get inWhileLoop => thisOrAncestorOfType<WhileStatement>() != null;

   /// The [Token]s contained within `this`.
   List<Token> get tokens {
     var result = <Token>[];
     for (var token = beginToken; ; token = token.next!) {
       result.add(token);
       if (token == endToken) {
         break;
       }
     }
     return result;
   }

   /// Returns the [ExpressionStatement] associated with `this` if `this` points
   /// to the identifier for a simple `print`, and `null` otherwise.
   ExpressionStatement? findSimplePrintInvocation() {
     var parent = this.parent;
     var grandparent = parent?.parent;
     if (this case SimpleIdentifier(:var element)) {
       if (element is TopLevelFunctionElement &&
           element.name3 == 'print' &&
           element.library2.isDartCore &&
           parent is MethodInvocation &&
           grandparent is ExpressionStatement) {
         return grandparent;
       }
     }
     return null;
   }

   /// Returns the element associated with `this`.
   ///
   /// If [useMockForImport] is `true` then a [MockLibraryImportElement] will be
   /// returned when an import directive or a prefix element is associated with
   /// `this`. The rename-prefix refactoring should be updated to not require
   /// this work-around.
   ///
   /// Returns `null` if `this` is `null` or doesn't have an element.
   Element? getElement({bool useMockForImport = false}) {
     AstNode? node = this;
     if (node is SimpleIdentifier && node.parent is LibraryIdentifier) {
       node = node.parent;
     }
     if (node is LibraryIdentifier) {
       node = node.parent;
     }
     if (node is StringLiteral && node.parent is UriBasedDirective) {
       return null;
     }

     Element? element;
     if (useMockForImport && node is ImportDirective) {
       element = MockLibraryImportElement(node.libraryImport!);
     } else {
       element = ElementLocator.locate2(node);
     }
     if (useMockForImport &&
         node is SimpleIdentifier &&
         element is PrefixElement) {
       element = MockLibraryImportElement(getImportElement(node)!);
     }
     return element;
   }
 }

 extension BinaryExpressionExtension on BinaryExpression {
   bool get isNotEqNull {
     return operator.type == TokenType.BANG_EQ && rightOperand is NullLiteral;
   }
 }

 extension CompilationUnitExtension on CompilationUnit {
   /// Return the list of tokens that comprise the file header comment for this
   /// compilation unit.
   ///
   /// If there is no file comment the list will be empty. If the file comment is
   /// a block comment the list will contain a single token. If the file comment
   /// is comprised of one or more single line comments, then the list will
   /// contain all of the tokens, and the comment is assumed to stop at the first
   /// line that contains anything other than a single line comment (either a
   /// blank line, a directive, a declaration, or a multi-line comment). The list
   /// will never include a documentation comment.
   List<Token> get fileHeader {
     var lineInfo = this.lineInfo;
     var firstToken = beginToken;
     if (firstToken.type == TokenType.SCRIPT_TAG) {
       firstToken = firstToken.next!;
     }
     var firstComment = firstToken.precedingComments;
     if (firstComment == null ||
         firstComment.lexeme.startsWith('/**') ||
         firstComment.lexeme.startsWith('///')) {
       return const [];
     } else if (firstComment.lexeme.startsWith('/*')) {
       return [firstComment];
     } else if (!firstComment.lexeme.startsWith('//')) {
       return const [];
     }
     var header = <Token>[firstComment];
     var previousLine = lineInfo.getLocation(firstComment.offset).lineNumber;
     var currentToken = firstComment.next;
     while (currentToken != null) {
       if (!currentToken.lexeme.startsWith('//') ||
           currentToken.lexeme.startsWith('///')) {
         return header;
       }
       var currentLine = lineInfo.getLocation(currentToken.offset).lineNumber;
       if (currentLine != previousLine + 1) {
         return header;
       }
       header.add(currentToken);
       currentToken = currentToken.next;
       previousLine = currentLine;
     }
     return header;
   }

   /// Returns names of elements that might conflict with a new local variable
   /// declared at [offset].
   Set<String> findPossibleLocalVariableConflicts(int offset) {
     var enclosingNode = nodeCovering(offset: offset)!;
     var enclosingBlock = enclosingNode.thisOrAncestorOfType<Block>();
     if (enclosingBlock == null) {
       return {};
     }

     var visitor = _ReferencedUnprefixedNamesCollector();
     enclosingBlock.accept(visitor);
     return visitor.names;
   }
 }

 extension DeclaredVariablePatternExtension on DeclaredVariablePattern {
   Token? get finalKeyword {
     return keyword.asFinalKeyword;
   }

   Token? get varKeyword {
     return keyword.asVarKeyword;
   }
 }

 extension DirectiveExtension on Directive {
   /// If the target imports or exports a [LibraryElement], returns it.
   LibraryElement? get referencedLibrary {
     switch (this) {
       case ExportDirective directive:
         return directive.libraryExport?.exportedLibrary2;
       case ImportDirective directive:
         return directive.libraryImport?.importedLibrary2;
       default:
         return null;
     }
   }

   /// If [referencedUri] is a [DirectiveUriWithSource], returns the [Source]
   /// from it.
   Source? get referencedSource {
     var uri = referencedUri;
     if (uri is DirectiveUriWithSource) {
       return uri.source;
     }
     return null;
   }

   /// Returns the [DirectiveUri] from the element.
   DirectiveUri? get referencedUri {
     switch (this) {
       case ExportDirective directive:
         return directive.libraryExport?.uri;
       case ImportDirective directive:
         return directive.libraryImport?.uri;
       case PartDirective directive:
         return directive.partInclude?.uri;
       default:
         return null;
     }
   }
 }

 extension ExpressionExtension on Expression {
   /// Whether this [Expression] should be wrapped with parentheses when we want
   /// to use it as operand of a logical and-expression.
   bool get shouldWrapParenthesisBeforeAnd {
     var self = this;
     if (self is! BinaryExpression) {
       return false;
     }
     var precedence = self.operator.type.precedence;
     return precedence < TokenClass.LOGICAL_AND_OPERATOR.precedence;
   }
 }

 extension FunctionBodyExtension on FunctionBody {
   bool get isEmpty =>
       this is EmptyFunctionBody ||
       (this is BlockFunctionBody && beginToken.isSynthetic);
 }

 extension MethodDeclarationExtension on MethodDeclaration {
   Token? get propertyKeywordGet {
     var propertyKeyword = this.propertyKeyword;
     return propertyKeyword != null && propertyKeyword.keyword == Keyword.GET
         ? propertyKeyword
         : null;
   }
 }

 extension MethodInvocationExtension on MethodInvocation {
   /// Returns whether this expression is an invocation of the method `cast`
   /// from either Iterable`, `List`, `Map`, or `Set`.
   bool get isCastMethodInvocation {
     var element = methodName.element;
     return element is MethodElement && element.isCastMethod;
   }

   /// Returns whether this expression is an invocation of the method `toList`
   /// from `Iterable`.
   bool get isToListMethodInvocation {
     var element = methodName.element;
     return element is MethodElement && element.isToListMethod;
   }

   /// Returns whether this expression is an invocation of the method `toSet`
   /// from `Iterable`.
   bool get isToSetMethodInvocation {
     var element = methodName.element;
     return element is MethodElement && element.isToSetMethod;
   }
 }

 extension NamedTypeExtension on NamedType {
   String get qualifiedName {
     var importPrefix = this.importPrefix;
     if (importPrefix != null) {
       return '${importPrefix.name.lexeme}.${name.lexeme}';
     } else {
       return name.lexeme;
     }
   }
 }

 extension NodeListExtension<E extends AstNode> on NodeList<E> {
   /// Return the last element of the list whose end is at or before the
   /// [offset], or `null` if the list is empty or if the offset is before the
   /// end of the first element.
   E? elementBefore(int offset) {
     for (var i = length - 1; i >= 0; i--) {
       var element = this[i];
       if (element.end <= offset) {
         return element;
       }
     }
     return null;
   }
 }

 extension StatementExtension on Statement {
   ThrowStatement? get followingThrow {
     var block = parent;
     if (block is Block) {
       var next = block.statements.nextOrNull(this);
       if (next is ExpressionStatement) {
         var throwExpression = next.expression;
         if (throwExpression is ThrowExpression) {
           return ThrowStatement(statement: next, expression: throwExpression);
         }
       }
     }
     return null;
   }

   List<Statement> get selfOrBlockStatements {
     var self = this;
     return self is Block ? self.statements : [self];
   }
 }

 extension TokenQuestionExtension on Token? {
   Token? get asFinalKeyword {
     var self = this;
     return self != null && self.keyword == Keyword.FINAL ? self : null;
   }

   Token? get asVarKeyword {
     var self = this;
     return self != null && self.keyword == Keyword.VAR ? self : null;
   }
 }

 extension VariableDeclarationListExtension on VariableDeclarationList {
   Token? get finalKeyword {
     return keyword.asFinalKeyword;
   }

   Token? get varKeyword {
     return keyword.asVarKeyword;
   }
 }
	// Copyright (c) 2020, 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:analysis_server/src/services/correction/namespace.dart';
	import 'package:analysis_server/src/utilities/extensions/element.dart';
	import 'package:analyzer/dart/ast/ast.dart';
	import 'package:analyzer/dart/ast/token.dart';
	import 'package:analyzer/dart/ast/visitor.dart';
	import 'package:analyzer/dart/element/element.dart';
	import 'package:analyzer/source/source.dart';
	import 'package:analyzer/src/dart/ast/element_locator.dart';
	import 'package:analyzer/src/dart/ast/token.dart';
	import 'package:analyzer/src/utilities/extensions/ast.dart';
	import 'package:analyzer/src/utilities/extensions/collection.dart';
	import 'package:analyzer/src/utilities/extensions/element.dart';

	class ThrowStatement {
	final ExpressionStatement statement;
	final ThrowExpression expression;

	ThrowStatement({required this.statement, required this.expression});
	}

	class _ReferencedUnprefixedNamesCollector extends RecursiveAstVisitor<void> {
	final Set<String> names = <String>{};

	@override
	void visitNamedType(NamedType node) {
	if (node.importPrefix == null) {
	names.add(node.name.lexeme);
	}

	super.visitNamedType(node);
	}

	@override
	void visitSimpleIdentifier(SimpleIdentifier node) {
	if (!_isPrefixed(node) && !_isLabelName(node)) {
	names.add(node.name);
	}
	}

	@override
	visitVariableDeclaration(VariableDeclaration node) {
	names.add(node.name.lexeme);
	return super.visitVariableDeclaration(node);
	}

	static bool _isLabelName(SimpleIdentifier node) {
	return node.parent is Label;
	}

	static bool _isPrefixed(SimpleIdentifier node) {
	var parent = node.parent;
	return parent is ConstructorName && parent.name == node \|\|
	parent is MethodInvocation &&
	parent.methodName == node &&
	parent.realTarget != null \|\|
	parent is PrefixedIdentifier && parent.identifier == node \|\|
	parent is PropertyAccess && parent.target == node;
	}
	}

	extension AnnotatedNodeExtension on AnnotatedNode {
	/// Return the first token in this node that is not a comment.
	Token get firstNonCommentToken {
	var metadata = this.metadata;
	if (metadata.isEmpty) {
	return firstTokenAfterCommentAndMetadata;
	}
	return metadata.beginToken!;
	}
	}

	extension AstNodeExtension on AstNode {
	/// Return the [IfStatement] associated with `this`.
	IfStatement? get enclosingIfStatement {
	for (var node in withParents) {
	if (node is IfStatement) {
	return node;
	} else if (node is! Expression) {
	return null;
	}
	}
	return null;
	}

	/// Return `true` if this node has an `override` annotation.
	bool get hasOverride {
	var node = this;
	if (node is AnnotatedNode) {
	for (var annotation in node.metadata) {
	if (annotation.name.name == 'override' &&
	annotation.arguments == null) {
	return true;
	}
	}
	}
	return false;
	}

	bool get inAsyncMethodOrFunction {
	var body = thisOrAncestorOfType<FunctionBody>();
	return body != null && body.isAsynchronous && body.star == null;
	}

	bool get inAsyncStarOrSyncStarMethodOrFunction {
	var body = thisOrAncestorOfType<FunctionBody>();
	return body != null && body.keyword != null && body.star != null;
	}

	bool get inCatchClause => thisOrAncestorOfType<CatchClause>() != null;

	bool get inClassMemberBody {
	var node = this;
	while (true) {
	var body = node.thisOrAncestorOfType<FunctionBody>();
	if (body == null) {
	return false;
	}
	var parent = body.parent;
	if (parent is ConstructorDeclaration \|\| parent is MethodDeclaration) {
	return true;
	} else if (parent == null) {
	return false;
	}
	node = parent;
	}
	}

	bool get inDoLoop => thisOrAncestorOfType<DoStatement>() != null;

	bool get inForLoop =>
	thisOrAncestorMatching((p) => p is ForStatement) != null;

	bool get inLoop => inDoLoop \|\| inForLoop \|\| inWhileLoop;

	bool get inSwitch => thisOrAncestorOfType<SwitchStatement>() != null;

	bool get inWhileLoop => thisOrAncestorOfType<WhileStatement>() != null;

	/// The [Token]s contained within `this`.
	List<Token> get tokens {
	var result = <Token>[];
	for (var token = beginToken; ; token = token.next!) {
	result.add(token);
	if (token == endToken) {
	break;
	}
	}
	return result;
	}

	/// Returns the [ExpressionStatement] associated with `this` if `this` points
	/// to the identifier for a simple `print`, and `null` otherwise.
	ExpressionStatement? findSimplePrintInvocation() {
	var parent = this.parent;
	var grandparent = parent?.parent;
	if (this case SimpleIdentifier(:var element)) {
	if (element is TopLevelFunctionElement &&
	element.name3 == 'print' &&
	element.library2.isDartCore &&
	parent is MethodInvocation &&
	grandparent is ExpressionStatement) {
	return grandparent;
	}
	}
	return null;
	}

	/// Returns the element associated with `this`.
	///
	/// If [useMockForImport] is `true` then a [MockLibraryImportElement] will be
	/// returned when an import directive or a prefix element is associated with
	/// `this`. The rename-prefix refactoring should be updated to not require
	/// this work-around.
	///
	/// Returns `null` if `this` is `null` or doesn't have an element.
	Element? getElement({bool useMockForImport = false}) {
	AstNode? node = this;
	if (node is SimpleIdentifier && node.parent is LibraryIdentifier) {
	node = node.parent;
	}
	if (node is LibraryIdentifier) {
	node = node.parent;
	}
	if (node is StringLiteral && node.parent is UriBasedDirective) {
	return null;
	}

	Element? element;
	if (useMockForImport && node is ImportDirective) {
	element = MockLibraryImportElement(node.libraryImport!);
	} else {
	element = ElementLocator.locate2(node);
	}
	if (useMockForImport &&
	node is SimpleIdentifier &&
	element is PrefixElement) {
	element = MockLibraryImportElement(getImportElement(node)!);
	}
	return element;
	}
	}

	extension BinaryExpressionExtension on BinaryExpression {
	bool get isNotEqNull {
	return operator.type == TokenType.BANG_EQ && rightOperand is NullLiteral;
	}
	}

	extension CompilationUnitExtension on CompilationUnit {
	/// Return the list of tokens that comprise the file header comment for this
	/// compilation unit.
	///
	/// If there is no file comment the list will be empty. If the file comment is
	/// a block comment the list will contain a single token. If the file comment
	/// is comprised of one or more single line comments, then the list will
	/// contain all of the tokens, and the comment is assumed to stop at the first
	/// line that contains anything other than a single line comment (either a
	/// blank line, a directive, a declaration, or a multi-line comment). The list
	/// will never include a documentation comment.
	List<Token> get fileHeader {
	var lineInfo = this.lineInfo;
	var firstToken = beginToken;
	if (firstToken.type == TokenType.SCRIPT_TAG) {
	firstToken = firstToken.next!;
	}
	var firstComment = firstToken.precedingComments;
	if (firstComment == null \|\|
	firstComment.lexeme.startsWith('/**') \|\|
	firstComment.lexeme.startsWith('///')) {
	return const [];
	} else if (firstComment.lexeme.startsWith('/*')) {
	return [firstComment];
	} else if (!firstComment.lexeme.startsWith('//')) {
	return const [];
	}
	var header = <Token>[firstComment];
	var previousLine = lineInfo.getLocation(firstComment.offset).lineNumber;
	var currentToken = firstComment.next;
	while (currentToken != null) {
	if (!currentToken.lexeme.startsWith('//') \|\|
	currentToken.lexeme.startsWith('///')) {
	return header;
	}
	var currentLine = lineInfo.getLocation(currentToken.offset).lineNumber;
	if (currentLine != previousLine + 1) {
	return header;
	}
	header.add(currentToken);
	currentToken = currentToken.next;
	previousLine = currentLine;
	}
	return header;
	}

	/// Returns names of elements that might conflict with a new local variable
	/// declared at [offset].
	Set<String> findPossibleLocalVariableConflicts(int offset) {
	var enclosingNode = nodeCovering(offset: offset)!;
	var enclosingBlock = enclosingNode.thisOrAncestorOfType<Block>();
	if (enclosingBlock == null) {
	return {};
	}

	var visitor = _ReferencedUnprefixedNamesCollector();
	enclosingBlock.accept(visitor);
	return visitor.names;
	}
	}

	extension DeclaredVariablePatternExtension on DeclaredVariablePattern {
	Token? get finalKeyword {
	return keyword.asFinalKeyword;
	}

	Token? get varKeyword {
	return keyword.asVarKeyword;
	}
	}

	extension DirectiveExtension on Directive {
	/// If the target imports or exports a [LibraryElement], returns it.
	LibraryElement? get referencedLibrary {
	switch (this) {
	case ExportDirective directive:
	return directive.libraryExport?.exportedLibrary2;
	case ImportDirective directive:
	return directive.libraryImport?.importedLibrary2;
	default:
	return null;
	}
	}

	/// If [referencedUri] is a [DirectiveUriWithSource], returns the [Source]
	/// from it.
	Source? get referencedSource {
	var uri = referencedUri;
	if (uri is DirectiveUriWithSource) {
	return uri.source;
	}
	return null;
	}

	/// Returns the [DirectiveUri] from the element.
	DirectiveUri? get referencedUri {
	switch (this) {
	case ExportDirective directive:
	return directive.libraryExport?.uri;
	case ImportDirective directive:
	return directive.libraryImport?.uri;
	case PartDirective directive:
	return directive.partInclude?.uri;
	default:
	return null;
	}
	}
	}

	extension ExpressionExtension on Expression {
	/// Whether this [Expression] should be wrapped with parentheses when we want
	/// to use it as operand of a logical and-expression.
	bool get shouldWrapParenthesisBeforeAnd {
	var self = this;
	if (self is! BinaryExpression) {
	return false;
	}
	var precedence = self.operator.type.precedence;
	return precedence < TokenClass.LOGICAL_AND_OPERATOR.precedence;
	}
	}

	extension FunctionBodyExtension on FunctionBody {
	bool get isEmpty =>
	this is EmptyFunctionBody \|\|
	(this is BlockFunctionBody && beginToken.isSynthetic);
	}

	extension MethodDeclarationExtension on MethodDeclaration {
	Token? get propertyKeywordGet {
	var propertyKeyword = this.propertyKeyword;
	return propertyKeyword != null && propertyKeyword.keyword == Keyword.GET
	? propertyKeyword
	: null;
	}
	}

	extension MethodInvocationExtension on MethodInvocation {
	/// Returns whether this expression is an invocation of the method `cast`
	/// from either Iterable`, `List`, `Map`, or `Set`.
	bool get isCastMethodInvocation {
	var element = methodName.element;
	return element is MethodElement && element.isCastMethod;
	}

	/// Returns whether this expression is an invocation of the method `toList`
	/// from `Iterable`.
	bool get isToListMethodInvocation {
	var element = methodName.element;
	return element is MethodElement && element.isToListMethod;
	}

	/// Returns whether this expression is an invocation of the method `toSet`
	/// from `Iterable`.
	bool get isToSetMethodInvocation {
	var element = methodName.element;
	return element is MethodElement && element.isToSetMethod;
	}
	}

	extension NamedTypeExtension on NamedType {
	String get qualifiedName {
	var importPrefix = this.importPrefix;
	if (importPrefix != null) {
	return '${importPrefix.name.lexeme}.${name.lexeme}';
	} else {
	return name.lexeme;
	}
	}
	}

	extension NodeListExtension<E extends AstNode> on NodeList<E> {
	/// Return the last element of the list whose end is at or before the
	/// [offset], or `null` if the list is empty or if the offset is before the
	/// end of the first element.
	E? elementBefore(int offset) {
	for (var i = length - 1; i >= 0; i--) {
	var element = this[i];
	if (element.end <= offset) {
	return element;
	}
	}
	return null;
	}
	}

	extension StatementExtension on Statement {
	ThrowStatement? get followingThrow {
	var block = parent;
	if (block is Block) {
	var next = block.statements.nextOrNull(this);
	if (next is ExpressionStatement) {
	var throwExpression = next.expression;
	if (throwExpression is ThrowExpression) {
	return ThrowStatement(statement: next, expression: throwExpression);
	}
	}
	}
	return null;
	}

	List<Statement> get selfOrBlockStatements {
	var self = this;
	return self is Block ? self.statements : [self];
	}
	}

	extension TokenQuestionExtension on Token? {
	Token? get asFinalKeyword {
	var self = this;
	return self != null && self.keyword == Keyword.FINAL ? self : null;
	}

	Token? get asVarKeyword {
	var self = this;
	return self != null && self.keyword == Keyword.VAR ? self : null;
	}
	}

	extension VariableDeclarationListExtension on VariableDeclarationList {
	Token? get finalKeyword {
	return keyword.asFinalKeyword;
	}

	Token? get varKeyword {
	return keyword.asVarKeyword;
	}
	}