pkg/analysis_server/lib/src/services/correction/dart/abstract_producer.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 'dart:math' as math;

 import 'package:_fe_analyzer_shared/src/scanner/token.dart';
 import 'package:analysis_server/plugin/edit/fix/fix_dart.dart';
 import 'package:analysis_server/src/services/correction/fix/dart/top_level_declarations.dart';
 import 'package:analysis_server/src/services/correction/util.dart';
 import 'package:analysis_server/src/utilities/flutter.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/dart/element/type_provider.dart';
 import 'package:analyzer/dart/element/type_system.dart';
 import 'package:analyzer/diagnostic/diagnostic.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/source/source_range.dart';
 import 'package:analyzer/src/dart/analysis/session_helper.dart';
 import 'package:analyzer/src/dart/ast/utilities.dart';
 import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer_plugin/utilities/assist/assist.dart';
 import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
 import 'package:analyzer_plugin/utilities/change_builder/change_builder_dart.dart';
 import 'package:analyzer_plugin/utilities/change_builder/change_workspace.dart';
 import 'package:analyzer_plugin/utilities/fixes/fixes.dart';
 import 'package:analyzer_plugin/utilities/range_factory.dart';
 import 'package:meta/meta.dart';

 /// An object that can compute a correction (fix or assist) in a Dart file.
 abstract class CorrectionProducer extends SingleCorrectionProducer {
   /// Return the type for the class `bool` from `dart:core`.
   DartType get coreTypeBool => resolvedResult.typeProvider.boolType;

   /// Returns `true` if [node] is in a static context.
   bool get inStaticContext {
     // constructor initializer cannot reference "this"
     if (node.thisOrAncestorOfType<ConstructorInitializer>() != null) {
       return true;
     }
     // field initializer cannot reference "this"
     if (node.thisOrAncestorOfType<FieldDeclaration>() != null) {
       return true;
     }
     // static method
     var method = node.thisOrAncestorOfType<MethodDeclaration>();
     return method != null && method.isStatic;
   }

   Future<void> compute(ChangeBuilder builder);

   /// Return the class, enum or mixin declaration for the given [element].
   Future<ClassOrMixinDeclaration> getClassOrMixinDeclaration(
       ClassElement element) async {
     var result = await sessionHelper.getElementDeclaration(element);
     if (result.node is ClassOrMixinDeclaration) {
       return result.node;
     }
     return null;
   }

   /// Return the extension declaration for the given [element].
   Future<ExtensionDeclaration> getExtensionDeclaration(
       ExtensionElement element) async {
     var result = await sessionHelper.getElementDeclaration(element);
     if (result.node is ExtensionDeclaration) {
       return result.node;
     }
     return null;
   }

   /// Return the class element associated with the [target], or `null` if there
   /// is no such class element.
   ClassElement getTargetClassElement(Expression target) {
     var type = target.staticType;
     if (type is InterfaceType) {
       return type.element;
     } else if (target is Identifier) {
       var element = target.staticElement;
       if (element is ClassElement) {
         return element;
       }
     }
     return null;
   }

   /// Returns an expected [DartType] of [expression], may be `null` if cannot be
   /// inferred.
   DartType inferUndefinedExpressionType(Expression expression) {
     var parent = expression.parent;
     // myFunction();
     if (parent is ExpressionStatement) {
       if (expression is MethodInvocation) {
         return VoidTypeImpl.instance;
       }
     }
     // return myFunction();
     if (parent is ReturnStatement) {
       var executable = getEnclosingExecutableElement(expression);
       return executable?.returnType;
     }
     // int v = myFunction();
     if (parent is VariableDeclaration) {
       var variableDeclaration = parent;
       if (variableDeclaration.initializer == expression) {
         var variableElement = variableDeclaration.declaredElement;
         if (variableElement != null) {
           return variableElement.type;
         }
       }
     }
     // myField = 42;
     if (parent is AssignmentExpression) {
       var assignment = parent;
       if (assignment.leftHandSide == expression) {
         var rhs = assignment.rightHandSide;
         if (rhs != null) {
           return rhs.staticType;
         }
       }
     }
     // v = myFunction();
     if (parent is AssignmentExpression) {
       var assignment = parent;
       if (assignment.rightHandSide == expression) {
         if (assignment.operator.type == TokenType.EQ) {
           // v = myFunction();
           return assignment.writeType;
         } else {
           // v += myFunction();
           var method = assignment.staticElement;
           if (method != null) {
             var parameters = method.parameters;
             if (parameters.length == 1) {
               return parameters[0].type;
             }
           }
         }
       }
     }
     // v + myFunction();
     if (parent is BinaryExpression) {
       var binary = parent;
       var method = binary.staticElement;
       if (method != null) {
         if (binary.rightOperand == expression) {
           var parameters = method.parameters;
           return parameters.length == 1 ? parameters[0].type : null;
         }
       }
     }
     // foo( myFunction() );
     if (parent is ArgumentList) {
       var parameter = expression.staticParameterElement;
       return parameter?.type;
     }
     // bool
     {
       // assert( myFunction() );
       if (parent is AssertStatement) {
         var statement = parent;
         if (statement.condition == expression) {
           return coreTypeBool;
         }
       }
       // if ( myFunction() ) {}
       if (parent is IfStatement) {
         var statement = parent;
         if (statement.condition == expression) {
           return coreTypeBool;
         }
       }
       // while ( myFunction() ) {}
       if (parent is WhileStatement) {
         var statement = parent;
         if (statement.condition == expression) {
           return coreTypeBool;
         }
       }
       // do {} while ( myFunction() );
       if (parent is DoStatement) {
         var statement = parent;
         if (statement.condition == expression) {
           return coreTypeBool;
         }
       }
       // !myFunction()
       if (parent is PrefixExpression) {
         var prefixExpression = parent;
         if (prefixExpression.operator.type == TokenType.BANG) {
           return coreTypeBool;
         }
       }
       // binary expression '&&' or '||'
       if (parent is BinaryExpression) {
         var binaryExpression = parent;
         var operatorType = binaryExpression.operator.type;
         if (operatorType == TokenType.AMPERSAND_AMPERSAND ||
             operatorType == TokenType.BAR_BAR) {
           return coreTypeBool;
         }
       }
     }
     // we don't know
     return null;
   }
 }

 class CorrectionProducerContext {
   final int selectionOffset;
   final int selectionLength;
   final int selectionEnd;

   final CompilationUnit unit;
   final CorrectionUtils utils;
   final String file;

   final TypeProvider typeProvider;

   final AnalysisSession session;
   final AnalysisSessionHelper sessionHelper;
   final ResolvedUnitResult resolvedResult;
   final ChangeWorkspace workspace;
   final DartFixContext dartFixContext;

   /// A flag indicating whether the correction producers will be run in the
   /// context of applying bulk fixes.
   final bool applyingBulkFixes;

   final Diagnostic diagnostic;

   AstNode _node;

   CorrectionProducerContext({
     @required this.resolvedResult,
     @required this.workspace,
     this.applyingBulkFixes = false,
     this.dartFixContext,
     this.diagnostic,
     this.selectionOffset = -1,
     this.selectionLength = 0,
   })  : file = resolvedResult.path,
         session = resolvedResult.session,
         sessionHelper = AnalysisSessionHelper(resolvedResult.session),
         typeProvider = resolvedResult.typeProvider,
         selectionEnd = (selectionOffset ?? 0) + (selectionLength ?? 0),
         unit = resolvedResult.unit,
         utils = CorrectionUtils(resolvedResult);

   AstNode get node => _node;

   /// Return `true` if the lint with the given [name] is enabled.
   bool isLintEnabled(String name) {
     var analysisOptions = session.analysisContext.analysisOptions;
     return analysisOptions.isLintEnabled(name);
   }

   bool setupCompute() {
     final locator = NodeLocator(selectionOffset, selectionEnd);
     _node = locator.searchWithin(resolvedResult.unit);
     return _node != null;
   }
 }

 /// An object that can dynamically compute multiple corrections (fixes or
 /// assists).
 abstract class MultiCorrectionProducer extends _AbstractCorrectionProducer {
   /// Return each of the individual producers generated by this producer.
   Iterable<CorrectionProducer> get producers;
 }

 /// An object that can compute a correction (fix or assist) in a Dart file.
 abstract class SingleCorrectionProducer extends _AbstractCorrectionProducer {
   /// Return the arguments that should be used when composing the message for an
   /// assist, or `null` if the assist message has no parameters or if this
   /// producer doesn't support assists.
   List<Object> get assistArguments => null;

   /// Return the assist kind that should be used to build an assist, or `null`
   /// if this producer doesn't support assists.
   AssistKind get assistKind => null;

   /// Return the length of the error message being fixed, or `null` if there is
   /// no diagnostic.
   int get errorLength => diagnostic?.problemMessage?.length;

   /// Return the text of the error message being fixed, or `null` if there is
   /// no diagnostic.
   String get errorMessage => diagnostic?.problemMessage?.message;

   /// Return the offset of the error message being fixed, or `null` if there is
   /// no diagnostic.
   int get errorOffset => diagnostic?.problemMessage?.offset;

   /// Return the arguments that should be used when composing the message for a
   /// fix, or `null` if the fix message has no parameters or if this producer
   /// doesn't support fixes.
   List<Object> get fixArguments => null;

   /// Return the fix kind that should be used to build a fix, or `null` if this
   /// producer doesn't support fixes.
   FixKind get fixKind => null;
 }

 /// The behavior shared by [CorrectionProducer] and [MultiCorrectionProducer].
 abstract class _AbstractCorrectionProducer {
   /// The context used to produce corrections.
   CorrectionProducerContext _context;

   /// The most deeply nested node that completely covers the highlight region of
   /// the diagnostic, or `null` if there is no diagnostic, such a node does not
   /// exist, or if it hasn't been computed yet. Use [coveredNode] to access this
   /// field.
   AstNode _coveredNode;

   /// Initialize a newly created producer.
   _AbstractCorrectionProducer();

   bool get applyingBulkFixes => _context.applyingBulkFixes;

   /// The most deeply nested node that completely covers the highlight region of
   /// the diagnostic, or `null` if there is no diagnostic or if such a node does
   /// not exist.
   AstNode get coveredNode {
     // TODO(brianwilkerson) Consider renaming this to `coveringNode`.
     if (_coveredNode == null) {
       var diagnostic = this.diagnostic;
       if (diagnostic == null) {
         return null;
       }
       var errorOffset = diagnostic.problemMessage.offset;
       var errorLength = diagnostic.problemMessage.length;
       _coveredNode =
           NodeLocator2(errorOffset, math.max(errorOffset + errorLength - 1, 0))
               .searchWithin(unit);
     }
     return _coveredNode;
   }

   /// Return the diagnostic being fixed, or `null` if this producer is being
   /// used to produce an assist.
   Diagnostic get diagnostic => _context.diagnostic;

   /// Returns the EOL to use for this [CompilationUnit].
   String get eol => utils.endOfLine;

   String get file => _context.file;

   Flutter get flutter => Flutter.instance;

   /// Return the library element for the library in which a correction is being
   /// produced.
   LibraryElement get libraryElement => resolvedResult.libraryElement;

   AstNode get node => _context.node;

   ResolvedUnitResult get resolvedResult => _context.resolvedResult;

   /// Return the resource provider used to access the file system.
   ResourceProvider get resourceProvider =>
       resolvedResult.session.resourceProvider;

   int get selectionEnd => _context.selectionEnd;

   int get selectionLength => _context.selectionLength;

   int get selectionOffset => _context.selectionOffset;

   AnalysisSessionHelper get sessionHelper => _context.sessionHelper;

   TypeProvider get typeProvider => _context.typeProvider;

   /// Return the type system appropriate to the library in which the correction
   /// was requested.
   TypeSystem get typeSystem => _context.resolvedResult.typeSystem;

   CompilationUnit get unit => _context.unit;

   CorrectionUtils get utils => _context.utils;

   /// Configure this producer based on the [context].
   void configure(CorrectionProducerContext context) {
     _context = context;
   }

   /// Return the text that should be displayed to users when referring to the
   /// given [type].
   String displayStringForType(DartType type) => type.getDisplayString(
       withNullability: libraryElement.isNonNullableByDefault);

   /// Return the function body of the most deeply nested method or function that
   /// encloses the [node], or `null` if the node is not in a method or function.
   FunctionBody getEnclosingFunctionBody() {
     var closure = node.thisOrAncestorOfType<FunctionExpression>();
     if (closure != null) {
       return closure.body;
     }
     var function = node.thisOrAncestorOfType<FunctionDeclaration>();
     if (function != null) {
       return function.functionExpression.body;
     }
     var constructor = node.thisOrAncestorOfType<ConstructorDeclaration>();
     if (constructor != null) {
       return constructor.body;
     }
     var method = node.thisOrAncestorOfType<MethodDeclaration>();
     if (method != null) {
       return method.body;
     }
     return null;
   }

   /// Return the text of the given [range] in the unit.
   String getRangeText(SourceRange range) {
     return utils.getRangeText(range);
   }

   /// Return the top-level declarations with the [name] in libraries that are
   /// available to this context.
   List<TopLevelDeclaration> getTopLevelDeclarations(String name) =>
       _context.dartFixContext.getTopLevelDeclarations(name);

   /// Return `true` the lint with the given [name] is enabled.
   bool isLintEnabled(String name) {
     return _context.isLintEnabled(name);
   }

   /// Return `true` if the selection covers an operator of the given
   /// [binaryExpression].
   bool isOperatorSelected(BinaryExpression binaryExpression) {
     AstNode left = binaryExpression.leftOperand;
     AstNode right = binaryExpression.rightOperand;
     // between the nodes
     if (selectionOffset >= left.end &&
         selectionOffset + selectionLength <= right.offset) {
       return true;
     }
     // or exactly select the node (but not with infix expressions)
     if (selectionOffset == left.offset &&
         selectionOffset + selectionLength == right.end) {
       if (left is BinaryExpression || right is BinaryExpression) {
         return false;
       }
       return true;
     }
     // invalid selection (part of node, etc)
     return false;
   }

   /// Return `true` if the given [node] is in a location where an implicit
   /// constructor invocation would be allowed.
   bool mightBeImplicitConstructor(AstNode node) {
     if (node is SimpleIdentifier) {
       var parent = node.parent;
       if (parent is MethodInvocation) {
         return parent.realTarget == null;
       }
     }
     return false;
   }

   /// Return `true` if the [node] might be a type name.
   bool mightBeTypeIdentifier(AstNode node) {
     if (node is SimpleIdentifier) {
       var parent = node.parent;
       if (parent is TypeName) {
         return true;
       }
       return _isNameOfType(node.name);
     }
     return false;
   }

   /// Replace all occurrences of the [oldIndent] with the [newIndent] within the
   /// [source].
   String replaceSourceIndent(
       String source, String oldIndent, String newIndent) {
     return source.replaceAll(RegExp('^$oldIndent', multiLine: true), newIndent);
   }

   /// Return `true` if the given [expression] should be wrapped with parenthesis
   /// when we want to use it as operand of a logical `and` expression.
   bool shouldWrapParenthesisBeforeAnd(Expression expression) {
     if (expression is BinaryExpression) {
       var binary = expression;
       var precedence = binary.operator.type.precedence;
       return precedence < TokenClass.LOGICAL_AND_OPERATOR.precedence;
     }
     return false;
   }

   /// Return `true` if the [name] is capitalized.
   bool _isNameOfType(String name) {
     if (name.isEmpty) {
       return false;
     }
     var firstLetter = name.substring(0, 1);
     if (firstLetter.toUpperCase() != firstLetter) {
       return false;
     }
     return true;
   }
 }

 extension DartFileEditBuilderExtension on DartFileEditBuilder {
   /// Add edits to the [builder] to remove any parentheses enclosing the
   /// [expression].
   // TODO(brianwilkerson) Consider moving this to DartFileEditBuilder.
   void removeEnclosingParentheses(Expression expression) {
     var precedence = getExpressionPrecedence(expression);
     while (expression.parent is ParenthesizedExpression) {
       var parenthesized = expression.parent as ParenthesizedExpression;
       if (getExpressionParentPrecedence(parenthesized) > precedence) {
         break;
       }
       addDeletion(range.token(parenthesized.leftParenthesis));
       addDeletion(range.token(parenthesized.rightParenthesis));
       expression = parenthesized;
     }
   }
 }
	// 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 'dart:math' as math;

	import 'package:_fe_analyzer_shared/src/scanner/token.dart';
	import 'package:analysis_server/plugin/edit/fix/fix_dart.dart';
	import 'package:analysis_server/src/services/correction/fix/dart/top_level_declarations.dart';
	import 'package:analysis_server/src/services/correction/util.dart';
	import 'package:analysis_server/src/utilities/flutter.dart';
	import 'package:analyzer/dart/analysis/results.dart';
	import 'package:analyzer/dart/analysis/session.dart';
	import 'package:analyzer/dart/ast/ast.dart';
	import 'package:analyzer/dart/ast/token.dart';
	import 'package:analyzer/dart/element/element.dart';
	import 'package:analyzer/dart/element/type.dart';
	import 'package:analyzer/dart/element/type_provider.dart';
	import 'package:analyzer/dart/element/type_system.dart';
	import 'package:analyzer/diagnostic/diagnostic.dart';
	import 'package:analyzer/file_system/file_system.dart';
	import 'package:analyzer/source/source_range.dart';
	import 'package:analyzer/src/dart/analysis/session_helper.dart';
	import 'package:analyzer/src/dart/ast/utilities.dart';
	import 'package:analyzer/src/dart/element/type.dart';
	import 'package:analyzer_plugin/utilities/assist/assist.dart';
	import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
	import 'package:analyzer_plugin/utilities/change_builder/change_builder_dart.dart';
	import 'package:analyzer_plugin/utilities/change_builder/change_workspace.dart';
	import 'package:analyzer_plugin/utilities/fixes/fixes.dart';
	import 'package:analyzer_plugin/utilities/range_factory.dart';
	import 'package:meta/meta.dart';

	/// An object that can compute a correction (fix or assist) in a Dart file.
	abstract class CorrectionProducer extends SingleCorrectionProducer {
	/// Return the type for the class `bool` from `dart:core`.
	DartType get coreTypeBool => resolvedResult.typeProvider.boolType;

	/// Returns `true` if [node] is in a static context.
	bool get inStaticContext {
	// constructor initializer cannot reference "this"
	if (node.thisOrAncestorOfType<ConstructorInitializer>() != null) {
	return true;
	}
	// field initializer cannot reference "this"
	if (node.thisOrAncestorOfType<FieldDeclaration>() != null) {
	return true;
	}
	// static method
	var method = node.thisOrAncestorOfType<MethodDeclaration>();
	return method != null && method.isStatic;
	}

	Future<void> compute(ChangeBuilder builder);

	/// Return the class, enum or mixin declaration for the given [element].
	Future<ClassOrMixinDeclaration> getClassOrMixinDeclaration(
	ClassElement element) async {
	var result = await sessionHelper.getElementDeclaration(element);
	if (result.node is ClassOrMixinDeclaration) {
	return result.node;
	}
	return null;
	}

	/// Return the extension declaration for the given [element].
	Future<ExtensionDeclaration> getExtensionDeclaration(
	ExtensionElement element) async {
	var result = await sessionHelper.getElementDeclaration(element);
	if (result.node is ExtensionDeclaration) {
	return result.node;
	}
	return null;
	}

	/// Return the class element associated with the [target], or `null` if there
	/// is no such class element.
	ClassElement getTargetClassElement(Expression target) {
	var type = target.staticType;
	if (type is InterfaceType) {
	return type.element;
	} else if (target is Identifier) {
	var element = target.staticElement;
	if (element is ClassElement) {
	return element;
	}
	}
	return null;
	}

	/// Returns an expected [DartType] of [expression], may be `null` if cannot be
	/// inferred.
	DartType inferUndefinedExpressionType(Expression expression) {
	var parent = expression.parent;
	// myFunction();
	if (parent is ExpressionStatement) {
	if (expression is MethodInvocation) {
	return VoidTypeImpl.instance;
	}
	}
	// return myFunction();
	if (parent is ReturnStatement) {
	var executable = getEnclosingExecutableElement(expression);
	return executable?.returnType;
	}
	// int v = myFunction();
	if (parent is VariableDeclaration) {
	var variableDeclaration = parent;
	if (variableDeclaration.initializer == expression) {
	var variableElement = variableDeclaration.declaredElement;
	if (variableElement != null) {
	return variableElement.type;
	}
	}
	}
	// myField = 42;
	if (parent is AssignmentExpression) {
	var assignment = parent;
	if (assignment.leftHandSide == expression) {
	var rhs = assignment.rightHandSide;
	if (rhs != null) {
	return rhs.staticType;
	}
	}
	}
	// v = myFunction();
	if (parent is AssignmentExpression) {
	var assignment = parent;
	if (assignment.rightHandSide == expression) {
	if (assignment.operator.type == TokenType.EQ) {
	// v = myFunction();
	return assignment.writeType;
	} else {
	// v += myFunction();
	var method = assignment.staticElement;
	if (method != null) {
	var parameters = method.parameters;
	if (parameters.length == 1) {
	return parameters[0].type;
	}
	}
	}
	}
	}
	// v + myFunction();
	if (parent is BinaryExpression) {
	var binary = parent;
	var method = binary.staticElement;
	if (method != null) {
	if (binary.rightOperand == expression) {
	var parameters = method.parameters;
	return parameters.length == 1 ? parameters[0].type : null;
	}
	}
	}
	// foo( myFunction() );
	if (parent is ArgumentList) {
	var parameter = expression.staticParameterElement;
	return parameter?.type;
	}
	// bool
	{
	// assert( myFunction() );
	if (parent is AssertStatement) {
	var statement = parent;
	if (statement.condition == expression) {
	return coreTypeBool;
	}
	}
	// if ( myFunction() ) {}
	if (parent is IfStatement) {
	var statement = parent;
	if (statement.condition == expression) {
	return coreTypeBool;
	}
	}
	// while ( myFunction() ) {}
	if (parent is WhileStatement) {
	var statement = parent;
	if (statement.condition == expression) {
	return coreTypeBool;
	}
	}
	// do {} while ( myFunction() );
	if (parent is DoStatement) {
	var statement = parent;
	if (statement.condition == expression) {
	return coreTypeBool;
	}
	}
	// !myFunction()
	if (parent is PrefixExpression) {
	var prefixExpression = parent;
	if (prefixExpression.operator.type == TokenType.BANG) {
	return coreTypeBool;
	}
	}
	// binary expression '&&' or '\|\|'
	if (parent is BinaryExpression) {
	var binaryExpression = parent;
	var operatorType = binaryExpression.operator.type;
	if (operatorType == TokenType.AMPERSAND_AMPERSAND \|\|
	operatorType == TokenType.BAR_BAR) {
	return coreTypeBool;
	}
	}
	}
	// we don't know
	return null;
	}
	}

	class CorrectionProducerContext {
	final int selectionOffset;
	final int selectionLength;
	final int selectionEnd;

	final CompilationUnit unit;
	final CorrectionUtils utils;
	final String file;

	final TypeProvider typeProvider;

	final AnalysisSession session;
	final AnalysisSessionHelper sessionHelper;
	final ResolvedUnitResult resolvedResult;
	final ChangeWorkspace workspace;
	final DartFixContext dartFixContext;

	/// A flag indicating whether the correction producers will be run in the
	/// context of applying bulk fixes.
	final bool applyingBulkFixes;

	final Diagnostic diagnostic;

	AstNode _node;

	CorrectionProducerContext({
	@required this.resolvedResult,
	@required this.workspace,
	this.applyingBulkFixes = false,
	this.dartFixContext,
	this.diagnostic,
	this.selectionOffset = -1,
	this.selectionLength = 0,
	}) : file = resolvedResult.path,
	session = resolvedResult.session,
	sessionHelper = AnalysisSessionHelper(resolvedResult.session),
	typeProvider = resolvedResult.typeProvider,
	selectionEnd = (selectionOffset ?? 0) + (selectionLength ?? 0),
	unit = resolvedResult.unit,
	utils = CorrectionUtils(resolvedResult);

	AstNode get node => _node;

	/// Return `true` if the lint with the given [name] is enabled.
	bool isLintEnabled(String name) {
	var analysisOptions = session.analysisContext.analysisOptions;
	return analysisOptions.isLintEnabled(name);
	}

	bool setupCompute() {
	final locator = NodeLocator(selectionOffset, selectionEnd);
	_node = locator.searchWithin(resolvedResult.unit);
	return _node != null;
	}
	}

	/// An object that can dynamically compute multiple corrections (fixes or
	/// assists).
	abstract class MultiCorrectionProducer extends _AbstractCorrectionProducer {
	/// Return each of the individual producers generated by this producer.
	Iterable<CorrectionProducer> get producers;
	}

	/// An object that can compute a correction (fix or assist) in a Dart file.
	abstract class SingleCorrectionProducer extends _AbstractCorrectionProducer {
	/// Return the arguments that should be used when composing the message for an
	/// assist, or `null` if the assist message has no parameters or if this
	/// producer doesn't support assists.
	List<Object> get assistArguments => null;

	/// Return the assist kind that should be used to build an assist, or `null`
	/// if this producer doesn't support assists.
	AssistKind get assistKind => null;

	/// Return the length of the error message being fixed, or `null` if there is
	/// no diagnostic.
	int get errorLength => diagnostic?.problemMessage?.length;

	/// Return the text of the error message being fixed, or `null` if there is
	/// no diagnostic.
	String get errorMessage => diagnostic?.problemMessage?.message;

	/// Return the offset of the error message being fixed, or `null` if there is
	/// no diagnostic.
	int get errorOffset => diagnostic?.problemMessage?.offset;

	/// Return the arguments that should be used when composing the message for a
	/// fix, or `null` if the fix message has no parameters or if this producer
	/// doesn't support fixes.
	List<Object> get fixArguments => null;

	/// Return the fix kind that should be used to build a fix, or `null` if this
	/// producer doesn't support fixes.
	FixKind get fixKind => null;
	}

	/// The behavior shared by [CorrectionProducer] and [MultiCorrectionProducer].
	abstract class _AbstractCorrectionProducer {
	/// The context used to produce corrections.
	CorrectionProducerContext _context;

	/// The most deeply nested node that completely covers the highlight region of
	/// the diagnostic, or `null` if there is no diagnostic, such a node does not
	/// exist, or if it hasn't been computed yet. Use [coveredNode] to access this
	/// field.
	AstNode _coveredNode;

	/// Initialize a newly created producer.
	_AbstractCorrectionProducer();

	bool get applyingBulkFixes => _context.applyingBulkFixes;

	/// The most deeply nested node that completely covers the highlight region of
	/// the diagnostic, or `null` if there is no diagnostic or if such a node does
	/// not exist.
	AstNode get coveredNode {
	// TODO(brianwilkerson) Consider renaming this to `coveringNode`.
	if (_coveredNode == null) {
	var diagnostic = this.diagnostic;
	if (diagnostic == null) {
	return null;
	}
	var errorOffset = diagnostic.problemMessage.offset;
	var errorLength = diagnostic.problemMessage.length;
	_coveredNode =
	NodeLocator2(errorOffset, math.max(errorOffset + errorLength - 1, 0))
	.searchWithin(unit);
	}
	return _coveredNode;
	}

	/// Return the diagnostic being fixed, or `null` if this producer is being
	/// used to produce an assist.
	Diagnostic get diagnostic => _context.diagnostic;

	/// Returns the EOL to use for this [CompilationUnit].
	String get eol => utils.endOfLine;

	String get file => _context.file;

	Flutter get flutter => Flutter.instance;

	/// Return the library element for the library in which a correction is being
	/// produced.
	LibraryElement get libraryElement => resolvedResult.libraryElement;

	AstNode get node => _context.node;

	ResolvedUnitResult get resolvedResult => _context.resolvedResult;

	/// Return the resource provider used to access the file system.
	ResourceProvider get resourceProvider =>
	resolvedResult.session.resourceProvider;

	int get selectionEnd => _context.selectionEnd;

	int get selectionLength => _context.selectionLength;

	int get selectionOffset => _context.selectionOffset;

	AnalysisSessionHelper get sessionHelper => _context.sessionHelper;

	TypeProvider get typeProvider => _context.typeProvider;

	/// Return the type system appropriate to the library in which the correction
	/// was requested.
	TypeSystem get typeSystem => _context.resolvedResult.typeSystem;

	CompilationUnit get unit => _context.unit;

	CorrectionUtils get utils => _context.utils;

	/// Configure this producer based on the [context].
	void configure(CorrectionProducerContext context) {
	_context = context;
	}

	/// Return the text that should be displayed to users when referring to the
	/// given [type].
	String displayStringForType(DartType type) => type.getDisplayString(
	withNullability: libraryElement.isNonNullableByDefault);

	/// Return the function body of the most deeply nested method or function that
	/// encloses the [node], or `null` if the node is not in a method or function.
	FunctionBody getEnclosingFunctionBody() {
	var closure = node.thisOrAncestorOfType<FunctionExpression>();
	if (closure != null) {
	return closure.body;
	}
	var function = node.thisOrAncestorOfType<FunctionDeclaration>();
	if (function != null) {
	return function.functionExpression.body;
	}
	var constructor = node.thisOrAncestorOfType<ConstructorDeclaration>();
	if (constructor != null) {
	return constructor.body;
	}
	var method = node.thisOrAncestorOfType<MethodDeclaration>();
	if (method != null) {
	return method.body;
	}
	return null;
	}

	/// Return the text of the given [range] in the unit.
	String getRangeText(SourceRange range) {
	return utils.getRangeText(range);
	}

	/// Return the top-level declarations with the [name] in libraries that are
	/// available to this context.
	List<TopLevelDeclaration> getTopLevelDeclarations(String name) =>
	_context.dartFixContext.getTopLevelDeclarations(name);

	/// Return `true` the lint with the given [name] is enabled.
	bool isLintEnabled(String name) {
	return _context.isLintEnabled(name);
	}

	/// Return `true` if the selection covers an operator of the given
	/// [binaryExpression].
	bool isOperatorSelected(BinaryExpression binaryExpression) {
	AstNode left = binaryExpression.leftOperand;
	AstNode right = binaryExpression.rightOperand;
	// between the nodes
	if (selectionOffset >= left.end &&
	selectionOffset + selectionLength <= right.offset) {
	return true;
	}
	// or exactly select the node (but not with infix expressions)
	if (selectionOffset == left.offset &&
	selectionOffset + selectionLength == right.end) {
	if (left is BinaryExpression \|\| right is BinaryExpression) {
	return false;
	}
	return true;
	}
	// invalid selection (part of node, etc)
	return false;
	}

	/// Return `true` if the given [node] is in a location where an implicit
	/// constructor invocation would be allowed.
	bool mightBeImplicitConstructor(AstNode node) {
	if (node is SimpleIdentifier) {
	var parent = node.parent;
	if (parent is MethodInvocation) {
	return parent.realTarget == null;
	}
	}
	return false;
	}

	/// Return `true` if the [node] might be a type name.
	bool mightBeTypeIdentifier(AstNode node) {
	if (node is SimpleIdentifier) {
	var parent = node.parent;
	if (parent is TypeName) {
	return true;
	}
	return _isNameOfType(node.name);
	}
	return false;
	}

	/// Replace all occurrences of the [oldIndent] with the [newIndent] within the
	/// [source].
	String replaceSourceIndent(
	String source, String oldIndent, String newIndent) {
	return source.replaceAll(RegExp('^$oldIndent', multiLine: true), newIndent);
	}

	/// Return `true` if the given [expression] should be wrapped with parenthesis
	/// when we want to use it as operand of a logical `and` expression.
	bool shouldWrapParenthesisBeforeAnd(Expression expression) {
	if (expression is BinaryExpression) {
	var binary = expression;
	var precedence = binary.operator.type.precedence;
	return precedence < TokenClass.LOGICAL_AND_OPERATOR.precedence;
	}
	return false;
	}

	/// Return `true` if the [name] is capitalized.
	bool _isNameOfType(String name) {
	if (name.isEmpty) {
	return false;
	}
	var firstLetter = name.substring(0, 1);
	if (firstLetter.toUpperCase() != firstLetter) {
	return false;
	}
	return true;
	}
	}

	extension DartFileEditBuilderExtension on DartFileEditBuilder {
	/// Add edits to the [builder] to remove any parentheses enclosing the
	/// [expression].
	// TODO(brianwilkerson) Consider moving this to DartFileEditBuilder.
	void removeEnclosingParentheses(Expression expression) {
	var precedence = getExpressionPrecedence(expression);
	while (expression.parent is ParenthesizedExpression) {
	var parenthesized = expression.parent as ParenthesizedExpression;
	if (getExpressionParentPrecedence(parenthesized) > precedence) {
	break;
	}
	addDeletion(range.token(parenthesized.leftParenthesis));
	addDeletion(range.token(parenthesized.rightParenthesis));
	expression = parenthesized;
	}
	}
	}