'Inline Method' refactoring.

pkg/analysis_server/lib/src/services/refactoring/inline_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.inline_method;
+
+import 'dart:async';
+
+import 'package:analysis_server/src/protocol.dart' hide Element;
+import 'package:analysis_server/src/services/correction/source_range.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/refactoring.dart';
+import 'package:analysis_server/src/services/refactoring/refactoring_internal.dart';
+import 'package:analysis_server/src/services/search/element_visitors.dart';
+import 'package:analysis_server/src/services/search/hierarchy.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/scanner.dart';
+import 'package:analyzer/src/generated/source.dart';
+
+
+/**
+ * Resolver sets [ParameterElement] for the most cases, but not for setter invocation.
+ *
+ * Returns the best available [ParameterElement] for which the given [Expression] is used.
+ */
+ParameterElement _getBestParameterElement(Expression expr) {
+  // TODO(scheglov) investigate why AssignmentExpression "f = 0" doesn't have
+  // an element.
+  // setter invocation
+  if (expr.parent is AssignmentExpression) {
+    AssignmentExpression assignment = expr.parent as AssignmentExpression;
+    if (assignment.rightHandSide == expr &&
+        assignment.operator.type == TokenType.EQ) {
+      Expression lhs = assignment.leftHandSide;
+      Element lhsElement = null;
+      if (lhs is Identifier) {
+        lhsElement = lhs.bestElement;
+      }
+      if (lhs is PropertyAccess) {
+        lhsElement = lhs.propertyName.bestElement;
+      }
+      if (lhsElement is PropertyAccessorElement) {
+        List<ParameterElement> parameters = lhsElement.parameters;
+        if (parameters.length != 0) {
+          return parameters[0];
+        }
+      }
+    }
+  }
+  // use resolver
+  return expr.bestParameterElement;
+}
+
+
+/**
+ * Returns the [SourceRange] to find conflicting locals in.
+ */
+SourceRange _getLocalsConflictingRange(AstNode node) {
+  // maybe Block
+  Block block = node.getAncestor((node) => node is Block);
+  if (block != null) {
+    int offset = node.offset;
+    int endOffset = block.end;
+    return rangeStartEnd(offset, endOffset);
+  }
+  // maybe whole executable
+  AstNode executableNode = getEnclosingExecutableNode(node);
+  if (executableNode != null) {
+    return rangeNode(executableNode);
+  }
+  // not a part of a declaration with locals
+  return SourceRange.EMPTY;
+}
+
+
+/**
+ * Returns the source which should replace given invocation with given
+ * arguments.
+ */
+String _getMethodSourceForInvocation(_SourcePart part, CorrectionUtils utils,
+    AstNode contextNode, Expression targetExpression, List<Expression> arguments) {
+  // prepare edits to replace parameters with arguments
+  List<SourceEdit> edits = <SourceEdit>[];
+  part._parameters.forEach(
+      (ParameterElement parameter, List<_ParameterOccurrence> occurrences) {
+    // prepare argument
+    Expression argument = null;
+    for (Expression arg in arguments) {
+      if (_getBestParameterElement(arg) == parameter) {
+        argument = arg;
+        break;
+      }
+    }
+    if (argument is NamedExpression) {
+      argument = (argument as NamedExpression).expression;
+    }
+    int argumentPrecedence = getExpressionPrecedence(argument);
+    String argumentSource = utils.getNodeText(argument);
+    // replace all occurrences of this parameter
+    for (_ParameterOccurrence occurrence in occurrences) {
+      SourceRange range = occurrence.range;
+      // prepare argument source to apply at this occurrence
+      String occurrenceArgumentSource;
+      if (argumentPrecedence < occurrence.parentPrecedence) {
+        occurrenceArgumentSource = "(${argumentSource})";
+      } else {
+        occurrenceArgumentSource = argumentSource;
+      }
+      // do replace
+      edits.add(new SourceEdit.range(range, occurrenceArgumentSource));
+    }
+  });
+  // replace static field "qualifier" with invocation target
+  part._staticFieldQualifiers.forEach(
+      (String className, List<SourceRange> ranges) {
+    for (SourceRange range in ranges) {
+      edits.add(new SourceEdit.range(range, className + '.'));
+    }
+  });
+  // replace instance field "qualifier" with invocation target
+  if (targetExpression != null) {
+    String targetSource = utils.getNodeText(targetExpression) + '.';
+    for (SourceRange qualifierRange in part._instanceFieldQualifiers) {
+      edits.add(new SourceEdit.range(qualifierRange, targetSource));
+    }
+  }
+  // prepare edits to replace conflicting variables
+  Set<String> conflictingNames = _getNamesConflictingAt(contextNode);
+  part._variables.forEach((VariableElement variable, List<SourceRange> ranges) {
+    String originalName = variable.displayName;
+    // prepare unique name
+    String uniqueName;
+    {
+      uniqueName = originalName;
+      int uniqueIndex = 2;
+      while (conflictingNames.contains(uniqueName)) {
+        uniqueName = originalName + uniqueIndex.toString();
+        uniqueIndex++;
+      }
+    }
+    // update references, if name was change
+    if (uniqueName != originalName) {
+      for (SourceRange range in ranges) {
+        edits.add(new SourceEdit.range(range, uniqueName));
+      }
+    }
+  });
+  // prepare source with applied arguments
+  edits.sort((SourceEdit a, SourceEdit b) => b.offset - a.offset);
+  return SourceEdit.applySequence(part._source, edits);
+}
+
+
+/**
+ * Returns the names which will shadow or will be shadowed by any declaration
+ * at [node].
+ */
+Set<String> _getNamesConflictingAt(AstNode node) {
+  Set<String> result = new Set<String>();
+  // local variables and functions
+  {
+    SourceRange localsRange = _getLocalsConflictingRange(node);
+    ExecutableElement enclosingExecutable = getEnclosingExecutableElement(node);
+    if (enclosingExecutable != null) {
+      visitChildren(enclosingExecutable, (element) {
+        if (element is LocalElement) {
+          SourceRange elementRange = element.visibleRange;
+          if (elementRange != null && elementRange.intersects(localsRange)) {
+            result.add(element.displayName);
+          }
+        }
+        return true;
+      });
+    }
+  }
+  // fields
+  {
+    ClassElement enclosingClassElement = getEnclosingClassElement(node);
+    if (enclosingClassElement != null) {
+      Set<ClassElement> elements = new Set<ClassElement>();
+      elements.add(enclosingClassElement);
+      elements.addAll(getSuperClasses(enclosingClassElement));
+      for (ClassElement classElement in elements) {
+        List<Element> classMembers = getChildren(classElement);
+        for (Element classMemberElement in classMembers) {
+          result.add(classMemberElement.displayName);
+        }
+      }
+    }
+  }
+  // done
+  return result;
+}
+
+
+/**
+ * [InlineMethodRefactoring] implementation.
+ */
+class InlineMethodRefactoringImpl extends RefactoringImpl implements
+    InlineMethodRefactoring {
+  final SearchEngine searchEngine;
+  final CompilationUnit unit;
+  final int offset;
+  String file;
+  CorrectionUtils utils;
+  SourceChange change;
+
+  bool deleteSource = false;
+  bool inlineAll = true;
+
+  ExecutableElement _methodElement;
+  String _methodFile;
+  CompilationUnit _methodUnit;
+  CorrectionUtils _methodUtils;
+  AstNode _methodNode;
+  FormalParameterList _methodParameters;
+  FunctionBody _methodBody;
+  Expression _methodExpression;
+  _SourcePart _methodExpressionPart;
+  _SourcePart _methodStatementsPart;
+  List<_ReferenceProcessor> _referenceProcessors = [];
+
+  InlineMethodRefactoringImpl(this.searchEngine, this.unit, this.offset) {
+    file = unit.element.source.fullName;
+    utils = new CorrectionUtils(unit);
+  }
+
+  @override
+  String get refactoringName {
+    if (_methodElement is MethodElement) {
+      return "Inline Method";
+    } else {
+      return "Inline Function";
+    }
+  }
+
+  @override
+  Future<RefactoringStatus> checkFinalConditions() {
+    change = new SourceChange(refactoringName);
+    RefactoringStatus result = new RefactoringStatus();
+    // check for compatibility of "deleteSource" and "inlineAll"
+    if (deleteSource && !inlineAll) {
+      result.addError('All references must be inlined to remove the source.');
+    }
+    // prepare changes
+    for (_ReferenceProcessor processor in _referenceProcessors) {
+      processor._process(result);
+    }
+    // delete method
+    if (deleteSource && inlineAll) {
+      SourceRange methodRange = rangeNode(_methodNode);
+      SourceRange linesRange = _methodUtils.getLinesRange(methodRange);
+      change.addEdit(_methodFile, new SourceEdit.range(linesRange, ""));
+    }
+    // done
+    return new Future.value(result);
+  }
+
+  @override
+  Future<RefactoringStatus> checkInitialConditions() {
+    RefactoringStatus result = new RefactoringStatus();
+    // prepare method information
+    result.addStatus(_prepareMethod());
+    if (result.hasFatalError) {
+      return new Future.value(result);
+    }
+    // maybe operator
+    if (_methodElement.isOperator) {
+      result = new RefactoringStatus.fatal('Cannot inline operator.');
+      return new Future.value(result);
+    }
+    // analyze method body
+    result.addStatus(_prepareMethodParts());
+    // process references
+    return searchEngine.searchReferences(_methodElement).then((references) {
+      _referenceProcessors.clear();
+      for (SearchMatch reference in references) {
+        _ReferenceProcessor processor =
+            new _ReferenceProcessor(this, reference);
+        _referenceProcessors.add(processor);
+      }
+    }).then((_) {
+      return result;
+    });
+  }
+
+  @override
+  Future<SourceChange> createChange() {
+    return new Future.value(change);
+  }
+
+  @override
+  bool requiresPreview() => false;
+
+  _SourcePart _createSourcePart(SourceRange range) {
+    String source = _methodUtils.getRangeText(range);
+    String prefix = getLinePrefix(source);
+    _SourcePart result = new _SourcePart(range.offset, source, prefix);
+    // remember parameters and variables occurrences
+    _methodUnit.accept(new _VariablesVisitor(_methodElement, range, result));
+    // done
+    return result;
+  }
+
+  /**
+   * Initializes [_methodElement] and related fields.
+   */
+  RefactoringStatus _prepareMethod() {
+    _methodElement = null;
+    _methodParameters = null;
+    _methodBody = null;
+    deleteSource = false;
+    inlineAll = false;
+    // prepare selected SimpleIdentifier
+    AstNode selectedNode = new NodeLocator.con1(offset).searchWithin(unit);
+    if (selectedNode is! SimpleIdentifier) {
+      return new RefactoringStatus.fatal(
+          'Method declaration or reference must be selected to activate this refactoring.');
+    }
+    SimpleIdentifier selectedIdentifier = selectedNode as SimpleIdentifier;
+    // prepare selected ExecutableElement
+    Element selectedElement = selectedIdentifier.bestElement;
+    if (selectedElement is! ExecutableElement) {
+      return new RefactoringStatus.fatal(
+          'Method declaration or reference must be selected to activate this refactoring.');
+    }
+    _methodElement = selectedElement as ExecutableElement;
+    _methodFile = _methodElement.source.fullName;
+    _methodUnit = selectedElement.unit;
+    _methodUtils = new CorrectionUtils(_methodUnit);
+    if (selectedElement is MethodElement ||
+        selectedElement is PropertyAccessorElement) {
+      MethodDeclaration methodDeclaration =
+          _methodElement.node as MethodDeclaration;
+      _methodNode = methodDeclaration;
+      _methodParameters = methodDeclaration.parameters;
+      _methodBody = methodDeclaration.body;
+      // prepare mode
+      deleteSource = selectedNode == methodDeclaration.name;
+      inlineAll = deleteSource;
+    }
+    if (selectedElement is FunctionElement) {
+      FunctionDeclaration functionDeclaration =
+          _methodElement.node as FunctionDeclaration;
+      _methodNode = functionDeclaration;
+      _methodParameters = functionDeclaration.functionExpression.parameters;
+      _methodBody = functionDeclaration.functionExpression.body;
+      // prepare mode
+      deleteSource = selectedNode == functionDeclaration.name;
+      inlineAll = deleteSource;
+    }
+    // OK
+    return new RefactoringStatus();
+  }
+
+  /**
+   * Analyze [_methodBody] to fill [_methodExpressionPart] and
+   * [_methodStatementsPart].
+   */
+  RefactoringStatus _prepareMethodParts() {
+    RefactoringStatus result = new RefactoringStatus();
+    if (_methodBody is ExpressionFunctionBody) {
+      ExpressionFunctionBody body = _methodBody as ExpressionFunctionBody;
+      _methodExpression = body.expression;
+      SourceRange methodExpressionRange = rangeNode(_methodExpression);
+      _methodExpressionPart = _createSourcePart(methodExpressionRange);
+    } else if (_methodBody is BlockFunctionBody) {
+      Block body = (_methodBody as BlockFunctionBody).block;
+      List<Statement> statements = body.statements;
+      if (statements.length >= 1) {
+        Statement lastStatement = statements[statements.length - 1];
+        // "return" statement requires special handling
+        if (lastStatement is ReturnStatement) {
+          _methodExpression = lastStatement.expression;
+          SourceRange methodExpressionRange = rangeNode(_methodExpression);
+          _methodExpressionPart = _createSourcePart(methodExpressionRange);
+          // exclude "return" statement from statements
+          statements = statements.sublist(0, statements.length - 1);
+        }
+        // if there are statements, process them
+        if (!statements.isEmpty) {
+          SourceRange statementsRange =
+              _methodUtils.getLinesRangeStatements(statements);
+          _methodStatementsPart = _createSourcePart(statementsRange);
+        }
+      }
+      // check if more than one return
+      body.accept(new _ReturnsValidatorVisitor(result));
+    } else {
+      return new RefactoringStatus.fatal('Cannot inline method without body.');
+    }
+    return result;
+  }
+}
+
+
+class _ParameterOccurrence {
+  final int parentPrecedence;
+  final SourceRange range;
+  _ParameterOccurrence(this.parentPrecedence, this.range);
+}
+
+
+/**
+ * Processor for single [SearchMatch] reference to [methodElement].
+ */
+class _ReferenceProcessor {
+  final InlineMethodRefactoringImpl ref;
+
+  String _refFile;
+  CorrectionUtils _refUtils;
+  AstNode _node;
+  SourceRange _refLineRange;
+  String _refPrefix;
+
+  _ReferenceProcessor(this.ref, SearchMatch reference) {
+    // prepare SourceChange to update
+    Element refElement = reference.element;
+    _refFile = refElement.source.fullName;
+    // prepare CorrectionUtils
+    CompilationUnit refUnit = refElement.unit;
+    _refUtils = new CorrectionUtils(refUnit);
+    // prepare node and environment
+    _node = _refUtils.findNode(reference.sourceRange.offset);
+    Statement refStatement = _node.getAncestor((node) => node is Statement);
+    if (refStatement != null) {
+      _refLineRange = _refUtils.getLinesRangeStatements([refStatement]);
+      _refPrefix = _refUtils.getNodePrefix(refStatement);
+    } else {
+      _refLineRange = null;
+      _refPrefix = _refUtils.getLinePrefix(_node.offset);
+    }
+  }
+
+  bool _canInlineBody(AstNode usage) {
+    // no statements, usually just expression
+    if (ref._methodStatementsPart == null) {
+      // empty method, inline as closure
+      if (ref._methodExpressionPart == null) {
+        return false;
+      }
+      // OK, just expression
+      return true;
+    }
+    // analyze point of invocation
+    AstNode parent = usage.parent;
+    AstNode parent2 = parent.parent;
+    // OK, if statement in block
+    if (parent is Statement) {
+      return parent2 is Block;
+    }
+    // maybe assignment, in block
+    if (parent is AssignmentExpression) {
+      AssignmentExpression assignment = parent;
+      // inlining setter
+      if (assignment.leftHandSide == usage) {
+        return parent2 is Statement && parent2.parent is Block;
+      }
+      // inlining initializer
+      return ref._methodExpressionPart != null;
+    }
+    // maybe value for variable initializer, in block
+    if (ref._methodExpressionPart != null) {
+      if (parent is VariableDeclaration) {
+        if (parent2 is VariableDeclarationList) {
+          AstNode parent3 = parent2.parent;
+          return parent3 is VariableDeclarationStatement &&
+              parent3.parent is Block;
+        }
+      }
+    }
+    // not in block, cannot inline body
+    return false;
+  }
+
+  void _inlineMethodInvocation(RefactoringStatus status, Expression methodUsage,
+      bool cascaded, Expression target, List<Expression> arguments) {
+    // we don't support cascade
+    if (cascaded) {
+      status.addError(
+          'Cannot inline cascade invocation.',
+          new Location.fromNode(methodUsage));
+    }
+    // can we inline method body into "methodUsage" block?
+    if (_canInlineBody(methodUsage)) {
+      // insert non-return statements
+      if (ref._methodStatementsPart != null) {
+        // prepare statements source for invocation
+        String source = _getMethodSourceForInvocation(
+            ref._methodStatementsPart,
+            _refUtils,
+            methodUsage,
+            target,
+            arguments);
+        source = _refUtils.replaceSourceIndent(
+            source,
+            ref._methodStatementsPart._prefix,
+            _refPrefix);
+        // do insert
+        SourceRange range = rangeStartLength(_refLineRange, 0);
+        SourceEdit edit = new SourceEdit.range(range, source);
+        ref.change.addEdit(_refFile, edit);
+      }
+      // replace invocation with return expression
+      if (ref._methodExpressionPart != null) {
+        // prepare expression source for invocation
+        String source = _getMethodSourceForInvocation(
+            ref._methodExpressionPart,
+            _refUtils,
+            methodUsage,
+            target,
+            arguments);
+        if (getExpressionPrecedence(ref._methodExpression) <
+            getExpressionParentPrecedence(methodUsage)) {
+          source = "(${source})";
+        }
+        // do replace
+        SourceRange methodUsageRange = rangeNode(methodUsage);
+        SourceEdit edit = new SourceEdit.range(methodUsageRange, source);
+        ref.change.addEdit(_refFile, edit);
+      } else {
+        SourceEdit edit = new SourceEdit.range(_refLineRange, "");
+        ref.change.addEdit(_refFile, edit);
+      }
+      return;
+    }
+    // inline as closure invocation
+    String source;
+    {
+      source = ref._methodUtils.getRangeText(
+          rangeStartEnd(ref._methodParameters.leftParenthesis, ref._methodNode));
+      String methodPrefix =
+          ref._methodUtils.getLinePrefix(ref._methodNode.offset);
+      source = _refUtils.replaceSourceIndent(source, methodPrefix, _refPrefix);
+      source = source.trim();
+    }
+    // do insert
+    SourceRange range = rangeNode(_node);
+    SourceEdit edit = new SourceEdit.range(range, source);
+    ref.change.addEdit(_refFile, edit);
+  }
+
+  void _process(RefactoringStatus status) {
+    AstNode nodeParent = _node.parent;
+    // may be only single place should be inlined
+    if (!_shouldProcess()) {
+      return;
+    }
+    // may be invocation of inline method
+    if (nodeParent is MethodInvocation) {
+      MethodInvocation invocation = nodeParent;
+      Expression target = invocation.target;
+      List<Expression> arguments = invocation.argumentList.arguments;
+      _inlineMethodInvocation(
+          status,
+          invocation,
+          invocation.isCascaded,
+          target,
+          arguments);
+    } else {
+      // cannot inline reference to method: var v = new A().method;
+      if (ref._methodElement is MethodElement) {
+        status.addFatalError(
+            'Cannot inline class method reference.',
+            new Location.fromNode(_node));
+        return;
+      }
+      // PropertyAccessorElement
+      if (ref._methodElement is PropertyAccessorElement) {
+        Expression target = null;
+        bool cascade = false;
+        if (nodeParent is PrefixedIdentifier) {
+          PrefixedIdentifier propertyAccess = nodeParent;
+          target = propertyAccess.prefix;
+          cascade = false;
+        }
+        if (nodeParent is PropertyAccess) {
+          PropertyAccess propertyAccess = nodeParent;
+          target = propertyAccess.realTarget;
+          cascade = propertyAccess.isCascaded;
+        }
+        // prepare arguments
+        List<Expression> arguments = [];
+        if ((_node as SimpleIdentifier).inSetterContext()) {
+          arguments.add(
+              (nodeParent.parent as AssignmentExpression).rightHandSide);
+        }
+        // inline body
+        _inlineMethodInvocation(
+            status,
+            nodeParent as Expression,
+            cascade,
+            target,
+            arguments);
+        return;
+      }
+      // not invocation, just reference to function
+      String source;
+      {
+        source = ref._methodUtils.getRangeText(
+            rangeStartEnd(ref._methodParameters.leftParenthesis, ref._methodNode));
+        String methodPrefix =
+            ref._methodUtils.getLinePrefix(ref._methodNode.offset);
+        source =
+            _refUtils.replaceSourceIndent(source, methodPrefix, _refPrefix);
+        source = source.trim();
+      }
+      // do insert
+      SourceRange range = rangeNode(_node);
+      SourceEdit edit = new SourceEdit.range(range, source);
+      ref.change.addEdit(_refFile, edit);
+    }
+  }
+
+  bool _shouldProcess() {
+    if (!ref.inlineAll) {
+      SourceRange parentRange = rangeNode(_node);
+      return parentRange.contains(ref.offset);
+    }
+    return true;
+  }
+}
+
+class _ReturnsValidatorVisitor extends RecursiveAstVisitor {
+  final RefactoringStatus result;
+  int _numReturns = 0;
+
+  _ReturnsValidatorVisitor(this.result);
+
+  @override
+  visitReturnStatement(ReturnStatement node) {
+    _numReturns++;
+    if (_numReturns == 2) {
+      result.addError('Ambiguous return value.', new Location.fromNode(node));
+    }
+  }
+}
+
+/**
+ * Information about the source of a method being inlined.
+ */
+class _SourcePart {
+  /**
+   * The base for all [SourceRange]s.
+   */
+  final int _base;
+
+  /**
+   * The source of the method.
+   */
+  final String _source;
+
+  /**
+   * The original prefix of the method.
+   */
+  final String _prefix;
+
+  /**
+   * The occurrences of the method parameters.
+   */
+  Map<ParameterElement, List<_ParameterOccurrence>> _parameters = {};
+
+  /**
+   * The occurrences of the method local variables.
+   */
+  Map<VariableElement, List<SourceRange>> _variables = {};
+
+  /**
+   * The source ranges of the qualifiers in instance field references.
+   * Some of them have length `0`.
+   */
+  List<SourceRange> _instanceFieldQualifiers = [];
+
+  /**
+   * The source ranges of the qualifiers in instance field references.
+   * Some of them have length `0`.
+   */
+  Map<String, List<SourceRange>> _staticFieldQualifiers = {};
+
+  _SourcePart(this._base, this._source, this._prefix);
+
+  void addInstanceFieldQualifier(SourceRange range) {
+    range = rangeFromBase(range, _base);
+    _instanceFieldQualifiers.add(range);
+  }
+
+  void addParameterOccurrence(ParameterElement parameter, SourceRange range,
+      int precedence) {
+    if (parameter != null) {
+      List<_ParameterOccurrence> occurrences = _parameters[parameter];
+      if (occurrences == null) {
+        occurrences = [];
+        _parameters[parameter] = occurrences;
+      }
+      range = rangeFromBase(range, _base);
+      occurrences.add(new _ParameterOccurrence(precedence, range));
+    }
+  }
+
+  void addStaticFieldQualifier(String className, SourceRange range) {
+    List<SourceRange> ranges = _staticFieldQualifiers[className];
+    if (ranges == null) {
+      ranges = [];
+      _staticFieldQualifiers[className] = ranges;
+    }
+    range = rangeFromBase(range, _base);
+    ranges.add(range);
+  }
+
+  void addVariable(VariableElement element, SourceRange range) {
+    List<SourceRange> ranges = _variables[element];
+    if (ranges == null) {
+      ranges = [];
+      _variables[element] = ranges;
+    }
+    range = rangeFromBase(range, _base);
+    ranges.add(range);
+  }
+}
+
+/**
+ * A visitor that fills [_SourcePart] with fields, parameters and variables.
+ */
+class _VariablesVisitor extends GeneralizingAstVisitor {
+  /**
+   * The [ExecutableElement] being inlined.
+   */
+  final ExecutableElement methodElement;
+
+  /**
+   * The [SourceRange] of the element body.
+   */
+  SourceRange bodyRange;
+
+  /**
+   * The [_SourcePart] to record reference into.
+   */
+  _SourcePart result;
+
+  _VariablesVisitor(this.methodElement, this.bodyRange, this.result);
+
+  @override
+  visitNode(AstNode node) {
+    SourceRange nodeRange = rangeNode(node);
+    if (!bodyRange.intersects(nodeRange)) {
+      return null;
+    }
+    super.visitNode(node);
+  }
+
+  @override
+  visitSimpleIdentifier(SimpleIdentifier node) {
+    SourceRange nodeRange = rangeNode(node);
+    if (bodyRange.covers(nodeRange)) {
+      _addInstanceFieldQualifier(node);
+      _addParameter(node);
+      _addVariable(node);
+    }
+  }
+
+  void _addInstanceFieldQualifier(SimpleIdentifier node) {
+    PropertyAccessorElement accessor = getPropertyAccessorElement(node);
+    if (isClassFieldAccessorElement(accessor)) {
+      AstNode qualifier = getNodeQualifier(node);
+      if (qualifier == null || qualifier is ThisExpression) {
+        if (accessor.isStatic) {
+          String className = accessor.enclosingElement.displayName;
+          if (qualifier == null) {
+            SourceRange qualifierRange = rangeStartLength(node, 0);
+            result.addStaticFieldQualifier(className, qualifierRange);
+          }
+        } else {
+          SourceRange qualifierRange;
+          if (qualifier != null) {
+            qualifierRange = rangeStartStart(qualifier, node);
+          } else {
+            qualifierRange = rangeStartLength(node, 0);
+          }
+          result.addInstanceFieldQualifier(qualifierRange);
+        }
+      }
+    }
+  }
+
+  void _addParameter(SimpleIdentifier node) {
+    ParameterElement parameterElement = getParameterElement(node);
+    // not a parameter
+    if (parameterElement == null) {
+      return;
+    }
+    // not a parameter of the function being inlined
+    if (!methodElement.parameters.contains(parameterElement)) {
+      return;
+    }
+    // OK, add occurrence
+    SourceRange nodeRange = rangeNode(node);
+    int parentPrecedence = getExpressionParentPrecedence(node);
+    result.addParameterOccurrence(
+        parameterElement,
+        nodeRange,
+        parentPrecedence);
+  }
+
+  void _addVariable(SimpleIdentifier node) {
+    VariableElement variableElement = getLocalVariableElement(node);
+    if (variableElement != null) {
+      SourceRange nodeRange = rangeNode(node);
+      result.addVariable(variableElement, nodeRange);
+    }
+  }
+}