Initial 'Extract Method' refactoring implementation.

pkg/analysis_server/lib/src/services/refactoring/extract_method.dart

+// Copyright (c) 2014, 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.
+
+library services.src.refactoring.extract_method;
+
+import 'dart:async';
+
+import 'package:analysis_server/src/protocol2.dart' show Location,
+    RefactoringMethodParameter, RefactoringMethodParameterKind, SourceChange,
+    SourceEdit;
+import 'package:analysis_server/src/services/correction/selection_analyzer.dart';
+import 'package:analysis_server/src/services/correction/source_range.dart';
+import 'package:analysis_server/src/services/correction/statement_analyzer.dart';
+import 'package:analysis_server/src/services/correction/status.dart';
+import 'package:analysis_server/src/services/correction/util.dart';
+import 'package:analysis_server/src/services/refactoring/naming_conventions.dart';
+import 'package:analysis_server/src/services/refactoring/refactoring.dart';
+import 'package:analysis_server/src/services/refactoring/refactoring_internal.dart';
+import 'package:analysis_server/src/services/search/search_engine.dart';
+import 'package:analyzer/src/generated/ast.dart';
+import 'package:analyzer/src/generated/element.dart';
+import 'package:analyzer/src/generated/java_core.dart';
+import 'package:analyzer/src/generated/scanner.dart';
+import 'package:analyzer/src/generated/source.dart';
+
+
+const String _TOKEN_SEPARATOR = "\uFFFF";
+
+
+/**
+ * Returns the "normalized" version of the given source, which is reconstructed
+ * from tokens, so ignores all the comments and spaces.
+ */
+String _getNormalizedSource(String src) {
+  List<Token> selectionTokens = TokenUtils.getTokens(src);
+  return StringUtils.join(selectionTokens, _TOKEN_SEPARATOR);
+}
+
+
+/**
+ * Returns the [Map] which maps [map] values to their keys.
+ */
+Map<String, String> _inverseMap(Map map) {
+  Map result = {};
+  map.forEach((key, value) {
+    result[value] = key;
+  });
+  return result;
+}
+
+
+/**
+ * [ExtractMethodRefactoring] implementation.
+ */
+class ExtractMethodRefactoringImpl extends RefactoringImpl implements
+    ExtractMethodRefactoring {
+  final SearchEngine searchEngine;
+  final CompilationUnit unit;
+  final int selectionOffset;
+  final int selectionLength;
+  String file;
+  SourceRange selectionRange;
+  CorrectionUtils utils;
+
+  String returnType;
+  String name;
+  bool extractAll = true;
+  bool createGetter = false;
+  final List<String> names = <String>[];
+  final List<int> offsets = <int>[];
+  final List<int> lengths = <int>[];
+
+  Set<String> _usedNames = new Set<String>();
+  List<RefactoringMethodParameter> _parameters = <RefactoringMethodParameter>[];
+  Map<String, RefactoringMethodParameter> _parametersMap = <String,
+      RefactoringMethodParameter>{};
+  Map<String, List<SourceRange>> _parameterReferencesMap = <String,
+      List<SourceRange>>{};
+  DartType _returnType;
+  String _returnVariableName;
+  AstNode _parentMember;
+  Expression _selectionExpression;
+  FunctionExpression _selectionFunctionExpression;
+  List<Statement> _selectionStatements;
+  List<_Occurrence> _occurrences = [];
+  bool _staticContext = false;
+
+  ExtractMethodRefactoringImpl(this.searchEngine, this.unit,
+      this.selectionOffset, this.selectionLength) {
+    file = unit.element.source.fullName;
+    selectionRange = new SourceRange(selectionOffset, selectionLength);
+    utils = new CorrectionUtils(unit);
+  }
+
+  bool get canCreateGetter {
+    if (!parameters.isEmpty) {
+      return false;
+    }
+    if (_selectionExpression != null) {
+      if (_selectionExpression is AssignmentExpression) {
+        return false;
+      }
+    }
+    if (_selectionStatements != null) {
+      return returnType != null;
+    }
+    return true;
+  }
+
+  /**
+   * @return the selected [DartExpression] source, with applying new parameter names.
+   */
+  String get methodBodySource {
+    String source = utils.getRangeText(selectionRange);
+    // prepare ReplaceEdit operations to replace variables with parameters
+    // TODO: implement parameters
+    List<SourceEdit> replaceEdits = [];
+//    for (Parameter parameter in _parametersMap.values) {
+//      List<SourceRange> ranges = _parameterReferencesMap[parameter.oldName];
+//      if (ranges != null) {
+//        for (SourceRange range in ranges) {
+//          replaceEdits.add(new SourceEdit(range.offset - selectionRange.offset, range.length, parameter.newName));
+//        }
+//      }
+//    }
+    // apply replacements
+    source = SourceEdit.applySequence(source, replaceEdits);
+    // change indentation
+    if (_selectionFunctionExpression != null) {
+      AstNode baseNode =
+          _selectionFunctionExpression.getAncestor((node) => node is Statement);
+      if (baseNode != null) {
+        String baseIndent = utils.getNodePrefix(baseNode);
+        String targetIndent = utils.getNodePrefix(_parentMember);
+        source = utils.replaceSourceIndent(source, baseIndent, targetIndent);
+        source = source.trim();
+      }
+    }
+    if (_selectionStatements != null) {
+      String selectionIndent = utils.getNodePrefix(_selectionStatements[0]);
+      String targetIndent = utils.getNodePrefix(_parentMember) + '  ';
+      source = utils.replaceSourceIndent(source, selectionIndent, targetIndent);
+    }
+    // done
+    return source;
+  }
+
+  @override
+  List<RefactoringMethodParameter> get parameters => _parameters;
+
+  @override
+  void set parameters(List<RefactoringMethodParameter> parameters) {
+    // TODO: implement parameters
+  }
+
+  @override
+  String get refactoringName {
+    AstNode node = new NodeLocator.con1(selectionOffset).searchWithin(unit);
+    if (node != null &&
+        node.getAncestor((node) => node is ClassDeclaration) != null) {
+      return 'Extract Method';
+    }
+    return 'Extract Function';
+  }
+
+  String get signature {
+    StringBuffer sb = new StringBuffer();
+    if (createGetter) {
+      sb.write("get ");
+      sb.write(name);
+    } else {
+      sb.write(name);
+      sb.write("(");
+      // add all parameters
+      bool firstParameter = true;
+      for (RefactoringMethodParameter parameter in _parameters) {
+        // may be comma
+        if (firstParameter) {
+          firstParameter = false;
+        } else {
+          sb.write(', ');
+        }
+        // type
+        {
+          String typeSource = parameter.type;
+          if ('dynamic' != typeSource && '' != typeSource) {
+            sb.write(typeSource);
+            sb.write(" ");
+          }
+        }
+        // name
+        sb.write(parameter.name);
+      }
+      sb.write(")");
+    }
+    // done
+    return sb.toString();
+  }
+
+  @override
+  Future<RefactoringStatus> checkFinalConditions() {
+    RefactoringStatus result = new RefactoringStatus();
+    return new Future.value(result);
+    // TODO: implement checkFinalConditions
+  }
+
+  @override
+  Future<RefactoringStatus> checkInitialConditions() {
+    RefactoringStatus result = new RefactoringStatus();
+    // selection
+    result.addStatus(_checkSelection());
+    if (result.hasFatalError) {
+      return new Future.value(result);
+    }
+    // prepare parts
+    result.addStatus(_initializeParameters());
+    _initializeReturnType();
+    _initializeOccurrences();
+    _initializeGetter();
+    // closure cannot have parameters
+    if (_selectionFunctionExpression != null && !_parameters.isEmpty) {
+      String message = format(
+          'Cannot extract closure as method, it references {0} external variable(s).',
+          _parameters.length);
+      RefactoringStatus result = new RefactoringStatus.fatal(message);
+      return new Future.value(result);
+    }
+    return new Future.value(result);
+  }
+
+  @override
+  RefactoringStatus checkName() {
+    return validateMethodName(name);
+  }
+
+  @override
+  Future<SourceChange> createChange() {
+    SourceChange change = new SourceChange(refactoringName);
+    // replace occurrences with method invocation
+    for (_Occurrence occurence in _occurrences) {
+      SourceRange range = occurence.range;
+      // may be replacement of duplicates disabled
+      if (!extractAll && !occurence.isSelection) {
+        continue;
+      }
+      // prepare invocation source
+      String invocationSource;
+      if (_selectionFunctionExpression != null) {
+        invocationSource = name;
+      } else {
+        StringBuffer sb = new StringBuffer();
+        // may be returns value
+        if (returnType != null) {
+          // single variable assignment / return statement
+          if (_returnVariableName != null) {
+            String occurrenceName =
+                occurence._parameterOldToOccurrenceName[_returnVariableName];
+            // may be declare variable
+            if (!_parametersMap.containsKey(_returnVariableName)) {
+              if (returnType.isEmpty) {
+                sb.write('var ');
+              } else {
+                sb.write(returnType);
+                sb.write(' ');
+              }
+            }
+            // assign the return value
+            sb.write(occurrenceName);
+            sb.write(' = ');
+          } else {
+            sb.write('return ');
+          }
+        }
+        // invocation itself
+        sb.write(name);
+        if (!createGetter) {
+          sb.write("(");
+          bool firstParameter = true;
+          for (RefactoringMethodParameter parameter in _parameters) {
+            // may be comma
+            if (firstParameter) {
+              firstParameter = false;
+            } else {
+              sb.write(', ');
+            }
+            // argument name
+            {
+              String argumentName =
+                  occurence._parameterOldToOccurrenceName[parameter.id];
+              sb.write(argumentName);
+            }
+          }
+          sb.write(')');
+        }
+        invocationSource = sb.toString();
+        // statements as extracted with their ";", so add new after invocation
+        if (_selectionStatements != null) {
+          invocationSource += ';';
+        }
+      }
+      // add replace edit
+      SourceEdit edit = new SourceEdit.range(range, invocationSource);
+      change.addEdit(file, edit);
+    }
+    // add method declaration
+    {
+      // prepare environment
+      String prefix = utils.getNodePrefix(_parentMember);
+      String eol = utils.endOfLine;
+      // prepare annotations
+      String annotations = "";
+      {
+        // may be "static"
+        if (_staticContext) {
+          annotations = 'static ';
+        }
+      }
+      // prepare declaration source
+      String declarationSource = null;
+      {
+        String returnExpressionSource = methodBodySource;
+        // closure
+        if (_selectionFunctionExpression != null) {
+          declarationSource = "${name}${returnExpressionSource}";
+          if (_selectionFunctionExpression.body is ExpressionFunctionBody) {
+            declarationSource += ';';
+          }
+        }
+        // expression
+        if (_selectionExpression != null) {
+          // add return type
+          String returnTypeName =
+              utils.getExpressionTypeSource(_selectionExpression);
+          if (returnTypeName != null && returnTypeName != "dynamic") {
+            annotations += "${returnTypeName} ";
+          }
+          // just return expression
+          declarationSource =
+              "${annotations}${signature} => ${returnExpressionSource};";
+        }
+        // statements
+        if (_selectionStatements != null) {
+          if (returnType != null) {
+            if (returnType.isNotEmpty) {
+              annotations += returnType + ' ';
+            }
+          } else {
+            annotations += 'void ';
+          }
+          declarationSource = "${annotations}${signature} {${eol}";
+          declarationSource += returnExpressionSource;
+          if (_returnVariableName != null) {
+            declarationSource +=
+                '${prefix}  return ${_returnVariableName};$eol';
+          }
+          declarationSource += '${prefix}}';
+        }
+      }
+      // insert declaration
+      if (declarationSource != null) {
+        int offset = _parentMember.end;
+        SourceEdit edit =
+            new SourceEdit(offset, 0, '${eol}${eol}${prefix}${declarationSource}');
+        change.addEdit(file, edit);
+      }
+    }
+    // done
+    return new Future.value(change);
+  }
+
+  @override
+  bool requiresPreview() => false;
+
+  /**
+   * Adds a new reference to the parameter with the given name.
+   */
+  void _addParameterReference(String name, SourceRange range) {
+    List<SourceRange> references = _parameterReferencesMap[name];
+    if (references == null) {
+      references = [];
+      _parameterReferencesMap[name] = references;
+    }
+    references.add(range);
+  }
+
+  /**
+   * Checks if [selectionRange] selects [Expression] which can be extracted, and
+   * location of this [DartExpression] in AST allows extracting.
+   */
+  RefactoringStatus _checkSelection() {
+    _ExtractMethodAnalyzer selectionAnalyzer =
+        new _ExtractMethodAnalyzer(unit, selectionRange);
+    unit.accept(selectionAnalyzer);
+    // may be fatal error
+    {
+      RefactoringStatus status = selectionAnalyzer.status;
+      if (status.hasFatalError) {
+        return status;
+      }
+    }
+    // check selected nodes
+    List<AstNode> selectedNodes = selectionAnalyzer.selectedNodes;
+    if (!selectedNodes.isEmpty) {
+      AstNode coveringNode = selectionAnalyzer.coveringNode;
+      _parentMember = getEnclosingClassOrUnitMember(coveringNode);
+      // single expression selected
+      if (selectedNodes.length == 1 &&
+          !utils.selectionIncludesNonWhitespaceOutsideNode(
+              selectionRange,
+              selectionAnalyzer.firstSelectedNode)) {
+        AstNode selectedNode = selectionAnalyzer.firstSelectedNode;
+        if (selectedNode is Expression) {
+          _selectionExpression = selectedNode;
+          // additional check for closure
+          if (_selectionExpression is FunctionExpression) {
+            _selectionFunctionExpression =
+                _selectionExpression as FunctionExpression;
+            _selectionExpression = null;
+          }
+          // OK
+          return new RefactoringStatus();
+        }
+      }
+      // statements selected
+      {
+        List<Statement> selectedStatements = [];
+        for (AstNode selectedNode in selectedNodes) {
+          if (selectedNode is Statement) {
+            selectedStatements.add(selectedNode);
+          }
+        }
+        if (selectedStatements.length == selectedNodes.length) {
+          _selectionStatements = selectedStatements;
+          return new RefactoringStatus();
+        }
+      }
+    }
+    // invalid selection
+    return new RefactoringStatus.fatal(
+        'Can only extract a single expression or a set of statements.');
+  }
+
+  _SourcePattern _getSourcePattern(SourceRange range) {
+    String originalSource = utils.getText(range.offset, range.length);
+    _SourcePattern pattern = new _SourcePattern();
+    List<SourceEdit> replaceEdits = <SourceEdit>[];
+    unit.accept(new _GetSourcePatternVisitor(range, pattern, replaceEdits));
+    replaceEdits = replaceEdits.reversed.toList();
+    pattern.patternSource =
+        SourceEdit.applySequence(originalSource, replaceEdits);
+    return pattern;
+  }
+
+  /**
+   * Initializes [createGetter] flag.
+   */
+  void _initializeGetter() {
+    createGetter = false;
+    // maybe we cannot at all
+    if (!canCreateGetter) {
+      return;
+    }
+    // OK, just expression
+    if (_selectionExpression != null) {
+      createGetter = !_hasMethodInvocation(_selectionExpression);
+      return;
+    }
+    // allow code blocks without cycles
+    if (_selectionStatements != null) {
+      createGetter = true;
+      for (Statement statement in _selectionStatements) {
+        // method invocation is something heavy,
+        // so we don't want to extract it as a part of a getter
+        if (_hasMethodInvocation(statement)) {
+          createGetter = false;
+          return;
+        }
+        // don't allow cycles
+        statement.accept(new _ResetCanCreateGetterVisitor(this));
+      }
+    }
+  }
+
+  /**
+   * Fills [_occurrences] field.
+   */
+  void _initializeOccurrences() {
+    // prepare selection
+    _SourcePattern selectionPattern = _getSourcePattern(selectionRange);
+    String selectionSource =
+        _getNormalizedSource(selectionPattern.patternSource);
+    Map<String, String> patternToSelectionName =
+        _inverseMap(selectionPattern.originalToPatternNames);
+    // prepare an enclosing parent - class or unit
+    AstNode enclosingMemberParent = _parentMember.parent;
+    // visit nodes which will able to access extracted method
+    enclosingMemberParent.accept(
+        new _InitializeOccurrencesVisitor(
+            this,
+            selectionSource,
+            patternToSelectionName));
+  }
+
+  /**
+   * Prepares information about used variables, which should be turned into
+   * parameters.
+   */
+  RefactoringStatus _initializeParameters() {
+    _parameters.clear();
+    _parametersMap.clear();
+    _parameterReferencesMap.clear();
+    RefactoringStatus result = new RefactoringStatus();
+    List<VariableElement> assignedUsedVariables = [];
+    unit.accept(new _InitializeParametersVisitor(this, assignedUsedVariables));
+    // may be ends with "return" statement
+    if (_selectionStatements != null) {
+      Statement lastStatement =
+          _selectionStatements[_selectionStatements.length - 1];
+      if (lastStatement is ReturnStatement) {
+        Expression expression = lastStatement.expression;
+        if (expression != null) {
+          _returnType = expression.bestType;
+        }
+      }
+    }
+    // may be single variable to return
+    if (assignedUsedVariables.length == 1) {
+      // we cannot both return variable and have explicit return statement
+      if (_returnType != null) {
+        result.addFatalError(
+            "Ambiguous return value: Selected block contains assignment(s) to "
+                "local variables and return statement.");
+        return result;
+      }
+      // prepare to return an assigned variable
+      VariableElement returnVariable = assignedUsedVariables[0];
+      _returnType = returnVariable.type;
+      _returnVariableName = returnVariable.displayName;
+    }
+    // fatal, if multiple variables assigned and used after selection
+    if (assignedUsedVariables.length > 1) {
+      StringBuffer sb = new StringBuffer();
+      for (VariableElement variable in assignedUsedVariables) {
+        sb.write(variable.displayName);
+        sb.write("\n");
+      }
+      result.addFatalError(
+          format(
+              "Ambiguous return value: Selected block contains more than one "
+                  "assignment to local variables. Affected variables are:\n\n{0}",
+              sb.toString().trim()));
+    }
+    // done
+    return result;
+  }
+
+  void _initializeReturnType() {
+    if (_returnType == null) {
+      returnType = null;
+    } else {
+      returnType = utils.getTypeSource(_returnType);
+      if (returnType == 'dynamic') {
+        returnType = '';
+      }
+    }
+  }
+
+  /**
+   * Checks if the given [VariableElement] is declared in [selectionRange].
+   */
+  bool _isDeclaredInSelection(VariableElement element) {
+    return selectionRange.contains(element.nameOffset);
+  }
+
+  /**
+   * Checks if it is OK to extract the node with the given [SourceRange].
+   */
+  bool _isExtractable(SourceRange range) {
+    _ExtractMethodAnalyzer analyzer = new _ExtractMethodAnalyzer(unit, range);
+    utils.unit.accept(analyzer);
+    return analyzer.status.isOK;
+  }
+
+  /**
+   * Checks if [element] is referenced after [selectionRange].
+   */
+  bool _isUsedAfterSelection(VariableElement element) {
+    var visitor = new _IsUsedAfterSelectionVisitor(this, element);
+    _parentMember.accept(visitor);
+    return visitor.result;
+  }
+
+  /**
+   * Checks if [node] has a [MethodInvocation].
+   */
+  static bool _hasMethodInvocation(AstNode node) {
+    var visitor = new _HasMethodInvocationVisitor();
+    node.accept(visitor);
+    return visitor.result;
+  }
+}
+
+
+/**
+ * [SelectionAnalyzer] for [ExtractMethodRefactoringImpl].
+ */
+class _ExtractMethodAnalyzer extends StatementAnalyzer {
+  _ExtractMethodAnalyzer(CompilationUnit unit, SourceRange selection)
+      : super(unit, selection);
+
+  @override
+  void handleNextSelectedNode(AstNode node) {
+    super.handleNextSelectedNode(node);
+    _checkParent(node);
+  }
+
+  @override
+  void handleSelectionEndsIn(AstNode node) {
+    super.handleSelectionEndsIn(node);
+    invalidSelection(
+        "The selection does not cover a set of statements or an expression. "
+            "Extend selection to a valid range.");
+  }
+
+  @override
+  Object visitAssignmentExpression(AssignmentExpression node) {
+    super.visitAssignmentExpression(node);
+    Expression lhs = node.leftHandSide;
+    if (_isFirstSelectedNode(lhs)) {
+      invalidSelection(
+          'Cannot extract the left-hand side of an assignment.',
+          new Location.fromNode(lhs));
+    }
+    return null;
+  }
+
+  @override
+  Object visitConstructorInitializer(ConstructorInitializer node) {
+    super.visitConstructorInitializer(node);
+    if (_isFirstSelectedNode(node)) {
+      invalidSelection(
+          'Cannot extract a constructor initializer. '
+              'Select expression part of initializer.',
+          new Location.fromNode(node));
+    }
+    return null;
+  }
+
+  @override
+  Object visitForStatement(ForStatement node) {
+    super.visitForStatement(node);
+    if (identical(node.variables, firstSelectedNode)) {
+      invalidSelection(
+          "Cannot extract initialization part of a 'for' statement.");
+    } else if (node.updaters.contains(lastSelectedNode)) {
+      invalidSelection("Cannot extract increment part of a 'for' statement.");
+    }
+    return null;
+  }
+
+  @override
+  Object visitSimpleIdentifier(SimpleIdentifier node) {
+    super.visitSimpleIdentifier(node);
+    if (_isFirstSelectedNode(node)) {
+      // name of declaration
+      if (node.inDeclarationContext()) {
+        invalidSelection("Cannot extract the name part of a declaration.");
+      }
+      // method name
+      Element element = node.bestElement;
+      if (element is FunctionElement || element is MethodElement) {
+        invalidSelection("Cannot extract a single method name.");
+      }
+      // name in property access
+      if (node.parent is PrefixedIdentifier &&
+          (node.parent as PrefixedIdentifier).identifier == node) {
+        invalidSelection("Can not extract name part of a property access.");
+      }
+    }
+    return null;
+  }
+
+  @override
+  Object visitTypeName(TypeName node) {
+    super.visitTypeName(node);
+    if (_isFirstSelectedNode(node)) {
+      invalidSelection("Cannot extract a single type reference.");
+    }
+    return null;
+  }
+
+  @override
+  Object visitVariableDeclaration(VariableDeclaration node) {
+    super.visitVariableDeclaration(node);
+    if (_isFirstSelectedNode(node)) {
+      invalidSelection(
+          "Cannot extract a variable declaration fragment. "
+              "Select whole declaration statement.",
+          new Location.fromNode(node));
+    }
+    return null;
+  }
+
+  void _checkParent(AstNode node) {
+    AstNode firstParent = firstSelectedNode.parent;
+    do {
+      node = node.parent;
+      if (identical(node, firstParent)) {
+        return;
+      }
+    } while (node != null);
+    invalidSelection(
+        "Not all selected statements are enclosed by the same parent statement.");
+  }
+
+  bool _isFirstSelectedNode(AstNode node) => identical(firstSelectedNode, node);
+}
+
+
+class _GetSourcePatternVisitor extends GeneralizingAstVisitor {
+  final SourceRange partRange;
+  final _SourcePattern pattern;
+  final List<SourceEdit> replaceEdits;
+
+  _GetSourcePatternVisitor(this.partRange, this.pattern, this.replaceEdits);
+
+  @override
+  visitSimpleIdentifier(SimpleIdentifier node) {
+    SourceRange nodeRange = rangeNode(node);
+    if (partRange.covers(nodeRange)) {
+      VariableElement variableElement =
+          getLocalOrParameterVariableElement(node);
+      if (variableElement != null) {
+        // name of a named expression
+        if (isNamedExpressionName(node)) {
+          return;
+        }
+        // continue
+        String originalName = variableElement.displayName;
+        String patternName = pattern.originalToPatternNames[originalName];
+        if (patternName == null) {
+          patternName = '__refVar${pattern.originalToPatternNames.length}';
+          pattern.originalToPatternNames[originalName] = patternName;
+        }
+        replaceEdits.add(
+            new SourceEdit(
+                nodeRange.offset - partRange.offset,
+                nodeRange.length,
+                patternName));
+      }
+    }
+  }
+}
+
+
+
+class _HasMethodInvocationVisitor extends RecursiveAstVisitor {
+  bool result = false;
+
+  @override
+  visitMethodInvocation(MethodInvocation node) {
+    result = true;
+  }
+}
+
+
+class _InitializeOccurrencesVisitor extends GeneralizingAstVisitor<Object> {
+  final ExtractMethodRefactoringImpl ref;
+  final String selectionSource;
+  final Map<String, String> patternToSelectionName;
+
+  bool forceStatic = false;
+
+  _InitializeOccurrencesVisitor(this.ref, this.selectionSource,
+      this.patternToSelectionName);
+
+  @override
+  Object visitBlock(Block node) {
+    if (ref._selectionStatements != null) {
+      _visitStatements(node.statements);
+    }
+    return super.visitBlock(node);
+  }
+
+  @override
+  Object visitConstructorInitializer(ConstructorInitializer node) {
+    forceStatic = true;
+    try {
+      return super.visitConstructorInitializer(node);
+    } finally {
+      forceStatic = false;
+    }
+  }
+
+  @override
+  Object visitExpression(Expression node) {
+    if (ref._selectionFunctionExpression != null ||
+        ref._selectionExpression != null &&
+            node.runtimeType == ref._selectionExpression.runtimeType) {
+      SourceRange nodeRange = rangeNode(node);
+      _tryToFindOccurrence(nodeRange);
+    }
+    return super.visitExpression(node);
+  }
+
+  @override
+  Object visitMethodDeclaration(MethodDeclaration node) {
+    forceStatic = node.isStatic;
+    try {
+      return super.visitMethodDeclaration(node);
+    } finally {
+      forceStatic = false;
+    }
+  }
+
+  @override
+  Object visitSwitchMember(SwitchMember node) {
+    if (ref._selectionStatements != null) {
+      _visitStatements(node.statements);
+    }
+    return super.visitSwitchMember(node);
+  }
+
+  /**
+   * Checks if given [SourceRange] matched selection source and adds [_Occurrence].
+   */
+  bool _tryToFindOccurrence(SourceRange nodeRange) {
+    // check if can be extracted
+    if (!ref._isExtractable(nodeRange)) {
+      return false;
+    }
+    // prepare normalized node source
+    _SourcePattern nodePattern = ref._getSourcePattern(nodeRange);
+    String nodeSource = _getNormalizedSource(nodePattern.patternSource);
+    // if matches normalized node source, then add as occurrence
+    if (nodeSource == selectionSource) {
+      _Occurrence occurrence =
+          new _Occurrence(nodeRange, ref.selectionRange.intersects(nodeRange));
+      ref._occurrences.add(occurrence);
+      // prepare mapping of parameter names to the occurrence variables
+      for (MapEntry<String, String> entry in getMapEntrySet(
+          nodePattern.originalToPatternNames)) {
+        String patternName = entry.getValue();
+        String originalName = entry.getKey();
+        String selectionName = patternToSelectionName[patternName];
+        occurrence._parameterOldToOccurrenceName[selectionName] = originalName;
+      }
+      // update static
+      if (forceStatic) {
+        ref._staticContext = true;
+      }
+      // we have match
+      return true;
+    }
+    // no match
+    return false;
+  }
+
+  void _visitStatements(List<Statement> statements) {
+    int beginStatementIndex = 0;
+    int selectionCount = ref._selectionStatements.length;
+    while (beginStatementIndex + selectionCount <= statements.length) {
+      SourceRange nodeRange = rangeStartEnd(
+          statements[beginStatementIndex],
+          statements[beginStatementIndex + selectionCount - 1]);
+      bool found = _tryToFindOccurrence(nodeRange);
+      // next statement
+      if (found) {
+        beginStatementIndex += selectionCount;
+      } else {
+        beginStatementIndex++;
+      }
+    }
+  }
+}
+
+
+class _InitializeParametersVisitor extends GeneralizingAstVisitor<Object> {
+  final ExtractMethodRefactoringImpl ref;
+  final List<VariableElement> assignedUsedVariables;
+
+  _InitializeParametersVisitor(this.ref, this.assignedUsedVariables);
+
+  @override
+  Object visitSimpleIdentifier(SimpleIdentifier node) {
+    SourceRange nodeRange = rangeNode(node);
+    if (ref.selectionRange.covers(nodeRange)) {
+      // analyze local variable
+      VariableElement variableElement =
+          getLocalOrParameterVariableElement(node);
+      if (variableElement != null) {
+        // name of the named expression
+        if (isNamedExpressionName(node)) {
+          return null;
+        }
+        // if declared outside, add parameter
+        if (!ref._isDeclaredInSelection(variableElement)) {
+          String variableName = variableElement.displayName;
+          // add parameter
+          RefactoringMethodParameter parameter =
+              ref._parametersMap[variableName];
+          if (parameter == null) {
+            DartType parameterType = node.bestType;
+            String parameterTypeName = ref.utils.getTypeSource(parameterType);
+            parameter = new RefactoringMethodParameter(
+                RefactoringMethodParameterKind.REQUIRED,
+                parameterTypeName,
+                variableName,
+                id: variableName);
+            ref._parameters.add(parameter);
+            ref._parametersMap[variableName] = parameter;
+          }
+          // add reference to parameter
+          ref._addParameterReference(variableName, nodeRange);
+        }
+        // remember, if assigned and used after selection
+        if (isLeftHandOfAssignment(node) &&
+            ref._isUsedAfterSelection(variableElement)) {
+          if (!assignedUsedVariables.contains(variableElement)) {
+            assignedUsedVariables.add(variableElement);
+          }
+        }
+      }
+      // remember declaration names
+      if (node.inDeclarationContext()) {
+        ref._usedNames.add(node.name);
+      }
+    }
+    return null;
+  }
+}
+
+class _IsUsedAfterSelectionVisitor extends GeneralizingAstVisitor {
+  final ExtractMethodRefactoringImpl ref;
+  final VariableElement element;
+  bool result = false;
+
+  _IsUsedAfterSelectionVisitor(this.ref, this.element);
+
+  @override
+  visitSimpleIdentifier(SimpleIdentifier node) {
+    VariableElement nodeElement = getLocalVariableElement(node);
+    if (identical(nodeElement, element)) {
+      int nodeOffset = node.offset;
+      if (nodeOffset > ref.selectionRange.end) {
+        result = true;
+      }
+    }
+  }
+}
+
+
+/**
+ * Description of a single occurrence of the selected expression or set of
+ * statements.
+ */
+class _Occurrence {
+  final SourceRange range;
+  final bool isSelection;
+
+  Map<String, String> _parameterOldToOccurrenceName = <String, String>{};
+
+  _Occurrence(this.range, this.isSelection);
+}
+
+
+class _ResetCanCreateGetterVisitor extends RecursiveAstVisitor {
+  final ExtractMethodRefactoringImpl ref;
+
+  _ResetCanCreateGetterVisitor(this.ref);
+
+  @override
+  visitDoStatement(DoStatement node) {
+    ref.createGetter = false;
+    super.visitDoStatement(node);
+  }
+
+  @override
+  visitForEachStatement(ForEachStatement node) {
+    ref.createGetter = false;
+    super.visitForEachStatement(node);
+  }
+
+  @override
+  visitForStatement(ForStatement node) {
+    ref.createGetter = false;
+    super.visitForStatement(node);
+  }
+
+  @override
+  visitWhileStatement(WhileStatement node) {
+    ref.createGetter = false;
+    super.visitWhileStatement(node);
+  }
+}
+
+
+/**
+ * Generalized version of some source, in which references to the specific
+ * variables are replaced with pattern variables, with back mapping from the
+ * pattern to the original variable names.
+ */
+class _SourcePattern {
+  String patternSource;
+  Map<String, String> originalToPatternNames = {};
+}