Revert "cleanup unused incremental resolution"

pkg/analyzer/lib/src/generated/incremental_resolver.dart

Index: pkg/analyzer/lib/src/generated/incremental_resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/incremental_resolver.dart b/pkg/analyzer/lib/src/generated/incremental_resolver.dart
index f1b26100b1dc4069e922b3324772b1a2d3a8f900..a9da4e95d45afc1cff82317b8ed5f8f32eec97f2 100644
--- a/pkg/analyzer/lib/src/generated/incremental_resolver.dart
+++ b/pkg/analyzer/lib/src/generated/incremental_resolver.dart
@@ -4,10 +4,1038 @@
 
 library analyzer.src.generated.incremental_resolver;
 
+import 'dart:collection';
+import 'dart:math' as math;
+
 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/visitor.dart';
+import 'package:analyzer/error/error.dart';
+import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/exception/exception.dart';
+import 'package:analyzer/src/context/cache.dart';
+import 'package:analyzer/src/dart/ast/token.dart';
+import 'package:analyzer/src/dart/ast/utilities.dart';
+import 'package:analyzer/src/dart/element/builder.dart';
+import 'package:analyzer/src/dart/element/element.dart';
+import 'package:analyzer/src/dart/resolver/inheritance_manager.dart';
+import 'package:analyzer/src/dart/scanner/reader.dart';
+import 'package:analyzer/src/dart/scanner/scanner.dart';
+import 'package:analyzer/src/generated/constant.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/error_verifier.dart';
+import 'package:analyzer/src/generated/incremental_logger.dart'
+    show logger, LoggingTimer;
+import 'package:analyzer/src/generated/parser.dart';
 import 'package:analyzer/src/generated/resolver.dart';
+import 'package:analyzer/src/generated/source.dart';
+import 'package:analyzer/src/generated/utilities_dart.dart';
+import 'package:analyzer/src/task/dart.dart';
+import 'package:analyzer/task/dart.dart';
+import 'package:analyzer/task/general.dart' show CONTENT, LINE_INFO;
+import 'package:analyzer/task/model.dart';
+
+/**
+ * The [Delta] implementation used by incremental resolver.
+ * It keeps Dart results that are either don't change or are updated.
+ */
+class IncrementalBodyDelta extends Delta {
+  /**
+   * The offset of the changed contents.
+   */
+  final int updateOffset;
+
+  /**
+   * The end of the changed contents in the old unit.
+   */
+  final int updateEndOld;
+
+  /**
+   * The end of the changed contents in the new unit.
+   */
+  final int updateEndNew;
+
+  /**
+   * The delta between [updateEndNew] and [updateEndOld].
+   */
+  final int updateDelta;
+
+  IncrementalBodyDelta(Source source, this.updateOffset, this.updateEndOld,
+      this.updateEndNew, this.updateDelta)
+      : super(source);
+
+  @override
+  DeltaResult validate(InternalAnalysisContext context, AnalysisTarget target,
+      ResultDescriptor descriptor, Object value) {
+    // A body change delta should never leak outside its source.
+    // It can cause invalidation of results (e.g. hints) in other sources,
+    // but only when a result in the updated source is INVALIDATE_NO_DELTA.
+    if (target.source != source) {
+      return DeltaResult.STOP;
+    }
+    // don't invalidate results of standard Dart tasks
+    bool isByTask(TaskDescriptor taskDescriptor) {
+      return taskDescriptor.results.contains(descriptor);
+    }
+
+    if (descriptor == CONTENT) {
+      return DeltaResult.KEEP_CONTINUE;
+    }
+    if (target is LibrarySpecificUnit && target.unit != source) {
+      if (isByTask(GatherUsedLocalElementsTask.DESCRIPTOR) ||
+          isByTask(GatherUsedImportedElementsTask.DESCRIPTOR)) {
+        return DeltaResult.KEEP_CONTINUE;
+      }
+    }
+    if (isByTask(BuildCompilationUnitElementTask.DESCRIPTOR) ||
+        isByTask(BuildDirectiveElementsTask.DESCRIPTOR) ||
+        isByTask(BuildEnumMemberElementsTask.DESCRIPTOR) ||
+        isByTask(BuildExportNamespaceTask.DESCRIPTOR) ||
+        isByTask(BuildLibraryElementTask.DESCRIPTOR) ||
+        isByTask(BuildPublicNamespaceTask.DESCRIPTOR) ||
+        isByTask(BuildSourceExportClosureTask.DESCRIPTOR) ||
+        isByTask(ComputeConstantDependenciesTask.DESCRIPTOR) ||
+        isByTask(ComputeConstantValueTask.DESCRIPTOR) ||
+        isByTask(ComputeInferableStaticVariableDependenciesTask.DESCRIPTOR) ||
+        isByTask(ComputeLibraryCycleTask.DESCRIPTOR) ||
+        isByTask(DartErrorsTask.DESCRIPTOR) ||
+        isByTask(ReadyLibraryElement2Task.DESCRIPTOR) ||
+        isByTask(ReadyLibraryElement5Task.DESCRIPTOR) ||
+        isByTask(ReadyLibraryElement7Task.DESCRIPTOR) ||
+        isByTask(ReadyResolvedUnitTask.DESCRIPTOR) ||
+        isByTask(EvaluateUnitConstantsTask.DESCRIPTOR) ||
+        isByTask(GenerateHintsTask.DESCRIPTOR) ||
+        isByTask(InferInstanceMembersInUnitTask.DESCRIPTOR) ||
+        isByTask(InferStaticVariableTypesInUnitTask.DESCRIPTOR) ||
+        isByTask(InferStaticVariableTypeTask.DESCRIPTOR) ||
+        isByTask(LibraryErrorsReadyTask.DESCRIPTOR) ||
+        isByTask(LibraryUnitErrorsTask.DESCRIPTOR) ||
+        isByTask(ParseDartTask.DESCRIPTOR) ||
+        isByTask(PartiallyResolveUnitReferencesTask.DESCRIPTOR) ||
+        isByTask(ScanDartTask.DESCRIPTOR) ||
+        isByTask(ResolveConstantExpressionTask.DESCRIPTOR) ||
+        isByTask(ResolveDirectiveElementsTask.DESCRIPTOR) ||
+        isByTask(ResolvedUnit7InLibraryClosureTask.DESCRIPTOR) ||
+        isByTask(ResolvedUnit7InLibraryTask.DESCRIPTOR) ||
+        isByTask(ResolveInstanceFieldsInUnitTask.DESCRIPTOR) ||
+        isByTask(ResolveLibraryReferencesTask.DESCRIPTOR) ||
+        isByTask(ResolveLibraryTask.DESCRIPTOR) ||
+        isByTask(ResolveLibraryTypeNamesTask.DESCRIPTOR) ||
+        isByTask(ResolveTopLevelLibraryTypeBoundsTask.DESCRIPTOR) ||
+        isByTask(ResolveTopLevelUnitTypeBoundsTask.DESCRIPTOR) ||
+        isByTask(ResolveUnitTask.DESCRIPTOR) ||
+        isByTask(ResolveUnitTypeNamesTask.DESCRIPTOR) ||
+        isByTask(ResolveVariableReferencesTask.DESCRIPTOR) ||
+        isByTask(StrongModeVerifyUnitTask.DESCRIPTOR) ||
+        isByTask(VerifyUnitTask.DESCRIPTOR)) {
+      return DeltaResult.KEEP_CONTINUE;
+    }
+    // invalidate all the other results
+    return DeltaResult.INVALIDATE_NO_DELTA;
+  }
+}
+
+/**
+ * Instances of the class [IncrementalResolver] resolve the smallest portion of
+ * an AST structure that we currently know how to resolve.
+ */
+class IncrementalResolver {
+  /**
+   * The element of the compilation unit being resolved.
+   */
+  final CompilationUnitElementImpl _definingUnit;
+
+  /**
+   * The context the compilation unit being resolved in.
+   */
+  final AnalysisContext _context;
+
+  /**
+   * The object used to access the types from the core library.
+   */
+  final TypeProvider _typeProvider;
+
+  /**
+   * The type system primitives.
+   */
+  final TypeSystem _typeSystem;
+
+  /**
+   * The element for the library containing the compilation unit being resolved.
+   */
+  final LibraryElementImpl _definingLibrary;
+
+  final AnalysisCache _cache;
+
+  /**
+   * The [CacheEntry] corresponding to the source being resolved.
+   */
+  final CacheEntry newSourceEntry;
+
+  /**
+   * The [CacheEntry] corresponding to the [LibrarySpecificUnit] being resolved.
+   */
+  final CacheEntry newUnitEntry;
+
+  /**
+   * The source representing the compilation unit being visited.
+   */
+  final Source _source;
+
+  /**
+   * The source representing the library of the compilation unit being visited.
+   */
+  final Source _librarySource;
+
+  /**
+   * The offset of the changed contents.
+   */
+  final int _updateOffset;
+
+  /**
+   * The end of the changed contents in the old unit.
+   */
+  final int _updateEndOld;
+
+  /**
+   * The end of the changed contents in the new unit.
+   */
+  final int _updateEndNew;
+
+  /**
+   * The delta between [_updateEndNew] and [_updateEndOld].
+   */
+  final int _updateDelta;
+
+  /**
+   * The set of [AnalysisError]s that have been already shifted.
+   */
+  final Set<AnalysisError> _alreadyShiftedErrors = new HashSet.identity();
+
+  final RecordingErrorListener errorListener = new RecordingErrorListener();
+  ResolutionContext _resolutionContext;
+
+  List<AnalysisError> _resolveErrors = AnalysisError.NO_ERRORS;
+  List<AnalysisError> _verifyErrors = AnalysisError.NO_ERRORS;
+
+  /**
+   * Initialize a newly created incremental resolver to resolve a node in the
+   * given source in the given library.
+   */
+  IncrementalResolver(
+      this._cache,
+      this.newSourceEntry,
+      this.newUnitEntry,
+      CompilationUnitElementImpl definingUnit,
+      this._updateOffset,
+      int updateEndOld,
+      int updateEndNew)
+      : _definingUnit = definingUnit,
+        _context = definingUnit.context,
+        _typeProvider = definingUnit.context.typeProvider,
+        _typeSystem = definingUnit.context.typeSystem,
+        _definingLibrary = definingUnit.library,
+        _source = definingUnit.source,
+        _librarySource = definingUnit.library.source,
+        _updateEndOld = updateEndOld,
+        _updateEndNew = updateEndNew,
+        _updateDelta = updateEndNew - updateEndOld;
+
+  /**
+   * Resolve [body], reporting any errors or warnings to the given listener.
+   *
+   * [body] - the root of the AST structure to be resolved.
+   */
+  void resolve(BlockFunctionBody body) {
+    logger.enter('resolve: $_definingUnit');
+    try {
+      Declaration executable = _findResolutionRoot(body);
+      _prepareResolutionContext(executable);
+      // update elements
+      _updateCache();
+      _updateElementNameOffsets();
+      _buildElements(executable, body);
+      // resolve
+      _resolveReferences(executable);
+      _computeConstants(executable);
+      _resolveErrors = errorListener.getErrorsForSource(_source);
+      // verify
+      _verify(executable);
+      _context.invalidateLibraryHints(_librarySource);
+      // update entry errors
+      _updateEntry();
+    } finally {
+      logger.exit();
+    }
+  }
+
+  void _buildElements(Declaration executable, AstNode node) {
+    LoggingTimer timer = logger.startTimer();
+    try {
+      ElementHolder holder = new ElementHolder();
+      node.accept(new LocalElementBuilder(holder, _definingUnit));
+      // Move local elements into the ExecutableElementImpl.
+      ExecutableElementImpl executableElement =
+          executable.element as ExecutableElementImpl;
+      executableElement.localVariables = holder.localVariables;
+      executableElement.functions = holder.functions;
+      executableElement.labels = holder.labels;
+      holder.validate();
+    } finally {
+      timer.stop('build elements');
+    }
+  }
+
+  /**
+   * Compute a value for all of the constants in the given [node].
+   */
+  void _computeConstants(AstNode node) {
+    // compute values
+    {
+      CompilationUnit unit = node.getAncestor((n) => n is CompilationUnit);
+      ConstantValueComputer computer = new ConstantValueComputer(
+          _typeProvider, _context.declaredVariables, null, _typeSystem);
+      computer.add(unit);
+      computer.computeValues();
+    }
+    // validate
+    {
+      ErrorReporter errorReporter = new ErrorReporter(errorListener, _source);
+      ConstantVerifier constantVerifier = new ConstantVerifier(errorReporter,
+          _definingLibrary, _typeProvider, _context.declaredVariables);
+      node.accept(constantVerifier);
+    }
+  }
+
+  /**
+   * Starting at [node], find the smallest AST node that can be resolved
+   * independently of any other nodes. Return the node that was found.
+   *
+   * [node] - the node at which the search is to begin
+   *
+   * Throws [AnalysisException] if there is no such node.
+   */
+  Declaration _findResolutionRoot(AstNode node) {
+    while (node != null) {
+      if (node is ConstructorDeclaration ||
+          node is FunctionDeclaration ||
+          node is MethodDeclaration) {
+        return node;
+      }
+      node = node.parent;
+    }
+    throw new AnalysisException("Cannot resolve node: no resolvable node");
+  }
+
+  void _prepareResolutionContext(AstNode node) {
+    if (_resolutionContext == null) {
+      _resolutionContext = ResolutionContextBuilder.contextFor(node);
+    }
+  }
+
+  _resolveReferences(AstNode node) {
+    LoggingTimer timer = logger.startTimer();
+    try {
+      _prepareResolutionContext(node);
+      Scope scope = _resolutionContext.scope;
+      // resolve types
+      {
+        TypeResolverVisitor visitor = new TypeResolverVisitor(
+            _definingLibrary, _source, _typeProvider, errorListener,
+            nameScope: scope);
+        node.accept(visitor);
+      }
+      // resolve variables
+      {
+        VariableResolverVisitor visitor = new VariableResolverVisitor(
+            _definingLibrary, _source, _typeProvider, errorListener,
+            nameScope: scope);
+        node.accept(visitor);
+      }
+      // resolve references
+      {
+        ResolverVisitor visitor = new ResolverVisitor(
+            _definingLibrary, _source, _typeProvider, errorListener,
+            nameScope: scope);
+        if (_resolutionContext.enclosingClassDeclaration != null) {
+          visitor.visitClassDeclarationIncrementally(
+              _resolutionContext.enclosingClassDeclaration);
+        }
+        if (node is Comment) {
+          visitor.resolveOnlyCommentInFunctionBody = true;
+          node = node.parent;
+        }
+        visitor.initForIncrementalResolution();
+        node.accept(visitor);
+      }
+    } finally {
+      timer.stop('resolve references');
+    }
+  }
+
+  void _shiftEntryErrors() {
+    _shiftErrors_NEW(HINTS);
+    _shiftErrors_NEW(LINTS);
+    _shiftErrors_NEW(LIBRARY_UNIT_ERRORS);
+    _shiftErrors_NEW(RESOLVE_TYPE_NAMES_ERRORS);
+    _shiftErrors_NEW(RESOLVE_TYPE_BOUNDS_ERRORS);
+    _shiftErrors_NEW(RESOLVE_UNIT_ERRORS);
+    _shiftErrors_NEW(STATIC_VARIABLE_RESOLUTION_ERRORS_IN_UNIT);
+    _shiftErrors_NEW(STRONG_MODE_ERRORS);
+    _shiftErrors_NEW(VARIABLE_REFERENCE_ERRORS);
+    _shiftErrors_NEW(VERIFY_ERRORS);
+  }
+
+  void _shiftErrors(List<AnalysisError> errors) {
+    for (AnalysisError error in errors) {
+      if (_alreadyShiftedErrors.add(error)) {
+        int errorOffset = error.offset;
+        if (errorOffset > _updateOffset) {
+          error.offset += _updateDelta;
+        }
+      }
+    }
+  }
+
+  void _shiftErrors_NEW(ResultDescriptor<List<AnalysisError>> descriptor) {
+    List<AnalysisError> errors = newUnitEntry.getValue(descriptor);
+    _shiftErrors(errors);
+  }
+
+  void _updateCache() {
+    if (newSourceEntry != null) {
+      LoggingTimer timer = logger.startTimer();
+      try {
+        newSourceEntry.setState(CONTENT, CacheState.INVALID,
+            delta: new IncrementalBodyDelta(_source, _updateOffset,
+                _updateEndOld, _updateEndNew, _updateDelta));
+      } finally {
+        timer.stop('invalidate cache with delta');
+      }
+    }
+  }
+
+  void _updateElementNameOffsets() {
+    LoggingTimer timer = logger.startTimer();
+    try {
+      _definingUnit.accept(
+          new _ElementOffsetUpdater(_updateOffset, _updateDelta, _cache));
+      _definingUnit.afterIncrementalResolution();
+    } finally {
+      timer.stop('update element offsets');
+    }
+  }
+
+  void _updateEntry() {
+    _updateErrors_NEW(RESOLVE_TYPE_NAMES_ERRORS, []);
+    _updateErrors_NEW(RESOLVE_TYPE_BOUNDS_ERRORS, []);
+    _updateErrors_NEW(RESOLVE_UNIT_ERRORS, _resolveErrors);
+    _updateErrors_NEW(VARIABLE_REFERENCE_ERRORS, []);
+    _updateErrors_NEW(VERIFY_ERRORS, _verifyErrors);
+    // invalidate results we don't update incrementally
+    newUnitEntry.setState(STRONG_MODE_ERRORS, CacheState.INVALID);
+    newUnitEntry.setState(USED_IMPORTED_ELEMENTS, CacheState.INVALID);
+    newUnitEntry.setState(USED_LOCAL_ELEMENTS, CacheState.INVALID);
+    newUnitEntry.setState(HINTS, CacheState.INVALID);
+    newUnitEntry.setState(LINTS, CacheState.INVALID);
+  }
+
+  List<AnalysisError> _updateErrors(
+      List<AnalysisError> oldErrors, List<AnalysisError> newErrors) {
+    List<AnalysisError> errors = new List<AnalysisError>();
+    // add updated old errors
+    for (AnalysisError error in oldErrors) {
+      int errorOffset = error.offset;
+      if (errorOffset < _updateOffset) {
+        errors.add(error);
+      } else if (errorOffset > _updateEndOld) {
+        error.offset += _updateDelta;
+        errors.add(error);
+      }
+    }
+    // add new errors
+    for (AnalysisError error in newErrors) {
+      int errorOffset = error.offset;
+      if (errorOffset > _updateOffset && errorOffset < _updateEndNew) {
+        errors.add(error);
+      }
+    }
+    // done
+    return errors;
+  }
+
+  void _updateErrors_NEW(ResultDescriptor<List<AnalysisError>> descriptor,
+      List<AnalysisError> newErrors) {
+    List<AnalysisError> oldErrors = newUnitEntry.getValue(descriptor);
+    List<AnalysisError> errors = _updateErrors(oldErrors, newErrors);
+    newUnitEntry.setValueIncremental(descriptor, errors, true);
+  }
+
+  void _verify(AstNode node) {
+    LoggingTimer timer = logger.startTimer();
+    try {
+      RecordingErrorListener errorListener = new RecordingErrorListener();
+      ErrorReporter errorReporter = new ErrorReporter(errorListener, _source);
+      ErrorVerifier errorVerifier = new ErrorVerifier(
+          errorReporter,
+          _definingLibrary,
+          _typeProvider,
+          new InheritanceManager(_definingLibrary),
+          _context.analysisOptions.enableSuperMixins);
+      if (_resolutionContext.enclosingClassDeclaration != null) {
+        errorVerifier.visitClassDeclarationIncrementally(
+            _resolutionContext.enclosingClassDeclaration);
+      }
+      node.accept(errorVerifier);
+      _verifyErrors = errorListener.getErrorsForSource(_source);
+    } finally {
+      timer.stop('verify');
+    }
+  }
+}
+
+class PoorMansIncrementalResolver {
+  final TypeProvider _typeProvider;
+  final Source _unitSource;
+  final AnalysisCache _cache;
+
+  /**
+   * The [CacheEntry] corresponding to the source being resolved.
+   */
+  final CacheEntry _sourceEntry;
+
+  /**
+   * The [CacheEntry] corresponding to the [LibrarySpecificUnit] being resolved.
+   */
+  final CacheEntry _unitEntry;
+
+  final CompilationUnit _oldUnit;
+  CompilationUnitElement _unitElement;
+
+  int _updateOffset;
+  int _updateDelta;
+  int _updateEndOld;
+  int _updateEndNew;
+
+  LineInfo _newLineInfo;
+  List<AnalysisError> _newScanErrors = <AnalysisError>[];
+  List<AnalysisError> _newParseErrors = <AnalysisError>[];
+
+  PoorMansIncrementalResolver(
+      this._typeProvider,
+      this._unitSource,
+      this._cache,
+      this._sourceEntry,
+      this._unitEntry,
+      this._oldUnit,
+      bool resolveApiChanges);
+
+  /**
+   * Attempts to update [_oldUnit] to the state corresponding to [newCode].
+   * Returns `true` if success, or `false` otherwise.
+   * The [_oldUnit] might be damaged.
+   */
+  bool resolve(String newCode) {
+    logger.enter('diff/resolve $_unitSource');
+    try {
+      // prepare old unit
+      if (!_areCurlyBracketsBalanced(_oldUnit.beginToken)) {
+        logger.log('Unbalanced number of curly brackets in the old unit.');
+        return false;
+      }
+      _unitElement = _oldUnit.element;
+      // prepare new unit
+      CompilationUnit newUnit = _parseUnit(newCode);
+      if (!_areCurlyBracketsBalanced(newUnit.beginToken)) {
+        logger.log('Unbalanced number of curly brackets in the new unit.');
+        return false;
+      }
+      // find difference
+      _TokenPair firstPair =
+          _findFirstDifferentToken(_oldUnit.beginToken, newUnit.beginToken);
+      _TokenPair lastPair =
+          _findLastDifferentToken(_oldUnit.endToken, newUnit.endToken);
+      if (firstPair != null && lastPair != null) {
+        int firstOffsetOld = firstPair.oldToken.offset;
+        int firstOffsetNew = firstPair.newToken.offset;
+        int lastOffsetOld = lastPair.oldToken.end;
+        int lastOffsetNew = lastPair.newToken.end;
+        int beginOffsetOld = math.min(firstOffsetOld, lastOffsetOld);
+        int endOffsetOld = math.max(firstOffsetOld, lastOffsetOld);
+        int beginOffsetNew = math.min(firstOffsetNew, lastOffsetNew);
+        int endOffsetNew = math.max(firstOffsetNew, lastOffsetNew);
+        // A pure whitespace change.
+        if (identical(firstPair.oldToken, lastPair.oldToken) &&
+            identical(firstPair.newToken, lastPair.newToken) &&
+            firstPair.kind == _TokenDifferenceKind.OFFSET) {
+          _updateOffset = beginOffsetOld - 1;
+          _updateEndOld = endOffsetOld;
+          _updateEndNew = endOffsetNew;
+          _updateDelta = newUnit.length - _oldUnit.length;
+          logger.log('Whitespace change.');
+          _shiftTokens(firstPair.oldToken, true);
+          IncrementalResolver incrementalResolver = new IncrementalResolver(
+              _cache,
+              _sourceEntry,
+              _unitEntry,
+              _unitElement,
+              _updateOffset,
+              _updateEndOld,
+              _updateEndNew);
+          incrementalResolver._updateCache();
+          incrementalResolver._updateElementNameOffsets();
+          incrementalResolver._shiftEntryErrors();
+          _updateEntry();
+          logger.log('Success.');
+          return true;
+        }
+        // A Dart documentation comment change.
+        {
+          Token firstOldToken = firstPair.oldToken;
+          Token firstNewToken = firstPair.newToken;
+          Token lastOldToken = lastPair.oldToken;
+          Token lastNewToken = lastPair.newToken;
+          if (firstOldToken is DocumentationCommentToken &&
+              firstNewToken is DocumentationCommentToken &&
+              lastOldToken is DocumentationCommentToken &&
+              lastNewToken is DocumentationCommentToken &&
+              identical(firstOldToken.parent, lastOldToken.parent) &&
+              identical(firstNewToken.parent, lastNewToken.parent)) {
+            _updateOffset = beginOffsetOld;
+            _updateEndOld = firstOldToken.parent.offset;
+            _updateEndNew = firstNewToken.parent.offset;
+            _updateDelta = newUnit.length - _oldUnit.length;
+            bool success =
+                _resolveCommentDoc(newUnit, firstOldToken, firstNewToken);
+            logger.log('Documentation comment resolved: $success');
+            return success;
+          }
+        }
+        // Find nodes covering the "old" and "new" token ranges.
+        AstNode oldNode =
+            _findNodeCovering(_oldUnit, beginOffsetOld, endOffsetOld - 1);
+        AstNode newNode =
+            _findNodeCovering(newUnit, beginOffsetNew, endOffsetNew - 1);
+        logger.log(() => 'oldNode: $oldNode');
+        logger.log(() => 'newNode: $newNode');
+        // Try to find the smallest common node, a FunctionBody currently.
+        {
+          List<AstNode> oldParents = _getParents(oldNode);
+          List<AstNode> newParents = _getParents(newNode);
+          // fail if an initializer change
+          if (oldParents.any((n) => n is ConstructorInitializer) ||
+              newParents.any((n) => n is ConstructorInitializer)) {
+            logger.log('Failure: a change in a constructor initializer');
+            return false;
+          }
+          // find matching methods / bodies
+          int length = math.min(oldParents.length, newParents.length);
+          bool found = false;
+          for (int i = 0; i < length; i++) {
+            AstNode oldParent = oldParents[i];
+            AstNode newParent = newParents[i];
+            if (oldParent is CompilationUnit && newParent is CompilationUnit) {
+              int oldLength = oldParent.declarations.length;
+              int newLength = newParent.declarations.length;
+              if (oldLength != newLength) {
+                logger.log(
+                    'Failure: unit declarations mismatch $oldLength vs. $newLength');
+                return false;
+              }
+            } else if (oldParent is ClassDeclaration &&
+                newParent is ClassDeclaration) {
+              int oldLength = oldParent.members.length;
+              int newLength = newParent.members.length;
+              if (oldLength != newLength) {
+                logger.log(
+                    'Failure: class declarations mismatch $oldLength vs. $newLength');
+                return false;
+              }
+            } else if (oldParent is FunctionDeclaration &&
+                    newParent is FunctionDeclaration ||
+                oldParent is ConstructorDeclaration &&
+                    newParent is ConstructorDeclaration ||
+                oldParent is MethodDeclaration &&
+                    newParent is MethodDeclaration) {
+              if (oldParents.length == i || newParents.length == i) {
+                return false;
+              }
+            } else if (oldParent is FunctionBody && newParent is FunctionBody) {
+              if (oldParent is BlockFunctionBody &&
+                  newParent is BlockFunctionBody) {
+                if (oldParent.isAsynchronous != newParent.isAsynchronous) {
+                  logger.log('Failure: body async mismatch.');
+                  return false;
+                }
+                if (oldParent.isGenerator != newParent.isGenerator) {
+                  logger.log('Failure: body generator mismatch.');
+                  return false;
+                }
+                oldNode = oldParent;
+                newNode = newParent;
+                found = true;
+                break;
+              }
+              logger.log('Failure: not a block function body.');
+              return false;
+            } else if (oldParent is FunctionExpression &&
+                newParent is FunctionExpression) {
+              // skip
+            } else {
+              logger.log('Failure: old and new parent mismatch'
+                  ' ${oldParent.runtimeType} vs. ${newParent.runtimeType}');
+              return false;
+            }
+          }
+          if (!found) {
+            logger.log('Failure: no enclosing function body or executable.');
+            return false;
+          }
+        }
+        logger.log(() => 'oldNode: $oldNode');
+        logger.log(() => 'newNode: $newNode');
+        // prepare update range
+        _updateOffset = oldNode.offset;
+        _updateEndOld = oldNode.end;
+        _updateEndNew = newNode.end;
+        _updateDelta = _updateEndNew - _updateEndOld;
+        // replace node
+        NodeReplacer.replace(oldNode, newNode);
+        // update token references
+        {
+          Token oldBeginToken = _getBeginTokenNotComment(oldNode);
+          Token newBeginToken = _getBeginTokenNotComment(newNode);
+          if (oldBeginToken.previous.type == TokenType.EOF) {
+            _oldUnit.beginToken = newBeginToken;
+          } else {
+            oldBeginToken.previous.setNext(newBeginToken);
+          }
+          newNode.endToken.setNext(oldNode.endToken.next);
+          _shiftTokens(oldNode.endToken.next);
+        }
+        // perform incremental resolution
+        IncrementalResolver incrementalResolver = new IncrementalResolver(
+            _cache,
+            _sourceEntry,
+            _unitEntry,
+            _unitElement,
+            _updateOffset,
+            _updateEndOld,
+            _updateEndNew);
+        incrementalResolver.resolve(newNode);
+        // update DartEntry
+        _updateEntry();
+        logger.log('Success.');
+        return true;
+      }
+    } catch (e, st) {
+      logger.logException(e, st);
+      logger.log('Failure: exception.');
+      // The incremental resolver log is usually turned off,
+      // so also log the exception to the instrumentation log.
+      AnalysisEngine.instance.logger.logError(
+          'Failure in incremental resolver', new CaughtException(e, st));
+    } finally {
+      logger.exit();
+    }
+    return false;
+  }
+
+  CompilationUnit _parseUnit(String code) {
+    LoggingTimer timer = logger.startTimer();
+    try {
+      Token token = _scan(code);
+      RecordingErrorListener errorListener = new RecordingErrorListener();
+      Parser parser = new Parser(_unitSource, errorListener);
+      AnalysisOptions options = _unitElement.context.analysisOptions;
+      parser.parseGenericMethodComments = options.strongMode;
+      CompilationUnit unit = parser.parseCompilationUnit(token);
+      _newParseErrors = errorListener.errors;
+      return unit;
+    } finally {
+      timer.stop('parse');
+    }
+  }
+
+  /**
+   * Attempts to resolve a documentation comment change.
+   * Returns `true` if success.
+   */
+  bool _resolveCommentDoc(
+      CompilationUnit newUnit, CommentToken oldToken, CommentToken newToken) {
+    if (oldToken == null || newToken == null) {
+      return false;
+    }
+    // find nodes
+    int offset = oldToken.offset;
+    logger.log('offset: $offset');
+    AstNode oldNode = _findNodeCovering(_oldUnit, offset, offset);
+    AstNode newNode = _findNodeCovering(newUnit, offset, offset);
+    if (oldNode is! Comment || newNode is! Comment) {
+      return false;
+    }
+    Comment oldComment = oldNode;
+    Comment newComment = newNode;
+    logger.log('oldComment.beginToken: ${oldComment.beginToken}');
+    logger.log('newComment.beginToken: ${newComment.beginToken}');
+    // update token references
+    _shiftTokens(oldToken.parent);
+    _setPrecedingComments(oldToken.parent, newComment.tokens.first);
+    // replace node
+    NodeReplacer.replace(oldComment, newComment);
+    // update elements
+    IncrementalResolver incrementalResolver = new IncrementalResolver(
+        _cache,
+        _sourceEntry,
+        _unitEntry,
+        _unitElement,
+        _updateOffset,
+        _updateEndOld,
+        _updateEndNew);
+    incrementalResolver._updateCache();
+    incrementalResolver._updateElementNameOffsets();
+    incrementalResolver._shiftEntryErrors();
+    _updateEntry();
+    // resolve references in the comment
+    incrementalResolver._resolveReferences(newComment);
+    // update 'documentationComment' of the parent element(s)
+    {
+      AstNode parent = newComment.parent;
+      if (parent is AnnotatedNode) {
+        setElementDocumentationForVariables(VariableDeclarationList list) {
+          for (VariableDeclaration variable in list.variables) {
+            Element variableElement = variable.element;
+            if (variableElement is ElementImpl) {
+              setElementDocumentationComment(variableElement, parent);
+            }
+          }
+        }
+
+        Element parentElement = ElementLocator.locate(newComment.parent);
+        if (parentElement is ElementImpl) {
+          setElementDocumentationComment(parentElement, parent);
+        } else if (parent is FieldDeclaration) {
+          setElementDocumentationForVariables(parent.fields);
+        } else if (parent is TopLevelVariableDeclaration) {
+          setElementDocumentationForVariables(parent.variables);
+        }
+      }
+    }
+    // OK
+    return true;
+  }
+
+  Token _scan(String code) {
+    RecordingErrorListener errorListener = new RecordingErrorListener();
+    CharSequenceReader reader = new CharSequenceReader(code);
+    Scanner scanner = new Scanner(_unitSource, reader, errorListener);
+    AnalysisOptions options = _unitElement.context.analysisOptions;
+    scanner.scanGenericMethodComments = options.strongMode;
+    Token token = scanner.tokenize();
+    _newLineInfo = new LineInfo(scanner.lineStarts);
+    _newScanErrors = errorListener.errors;
+    return token;
+  }
+
+  /**
+   * Set the given [comment] as a "precedingComments" for [token].
+   */
+  void _setPrecedingComments(Token token, CommentToken comment) {
+    if (token is BeginTokenWithComment) {
+      token.precedingComments = comment;
+    } else if (token is KeywordTokenWithComment) {
+      token.precedingComments = comment;
+    } else if (token is StringTokenWithComment) {
+      token.precedingComments = comment;
+    } else if (token is TokenWithComment) {
+      token.precedingComments = comment;
+    } else {
+      Type parentType = token?.runtimeType;
+      throw new AnalysisException('Uknown parent token type: $parentType');
+    }
+  }
+
+  void _shiftTokens(Token token, [bool goUpComment = false]) {
+    while (token != null) {
+      if (goUpComment && token is CommentToken) {
+        token = (token as CommentToken).parent;
+      }
+      if (token.offset > _updateOffset) {
+        token.offset += _updateDelta;
+      }
+      // comments
+      _shiftTokens(token.precedingComments);
+      if (token is DocumentationCommentToken) {
+        for (Token reference in token.references) {
+          _shiftTokens(reference);
+        }
+      }
+      // next
+      if (token.type == TokenType.EOF) {
+        break;
+      }
+      token = token.next;
+    }
+  }
+
+  void _updateEntry() {
+    // scan results
+    _sourceEntry.setValueIncremental(SCAN_ERRORS, _newScanErrors, true);
+    _sourceEntry.setValueIncremental(LINE_INFO, _newLineInfo, false);
+    // parse results
+    _sourceEntry.setValueIncremental(PARSE_ERRORS, _newParseErrors, true);
+    _sourceEntry.setValueIncremental(PARSED_UNIT, _oldUnit, false);
+  }
+
+  /**
+   * Checks if [token] has a balanced number of open and closed curly brackets.
+   */
+  static bool _areCurlyBracketsBalanced(Token token) {
+    int numOpen = _getTokenCount(token, TokenType.OPEN_CURLY_BRACKET);
+    int numOpen2 =
+        _getTokenCount(token, TokenType.STRING_INTERPOLATION_EXPRESSION);
+    int numClosed = _getTokenCount(token, TokenType.CLOSE_CURLY_BRACKET);
+    return numOpen + numOpen2 == numClosed;
+  }
+
+  static _TokenDifferenceKind _compareToken(
+      Token oldToken, Token newToken, int delta) {
+    if (oldToken == null && newToken == null) {
+      return null;
+    }
+    if (oldToken == null || newToken == null) {
+      return _TokenDifferenceKind.CONTENT;
+    }
+    if (oldToken.type != newToken.type) {
+      return _TokenDifferenceKind.CONTENT;
+    }
+    if (oldToken.lexeme != newToken.lexeme) {
+      return _TokenDifferenceKind.CONTENT;
+    }
+    if (newToken.offset - oldToken.offset != delta) {
+      return _TokenDifferenceKind.OFFSET;
+    }
+    return null;
+  }
+
+  static _TokenPair _findFirstDifferentToken(Token oldToken, Token newToken) {
+    while (oldToken.type != TokenType.EOF || newToken.type != TokenType.EOF) {
+      if (oldToken.type == TokenType.EOF || newToken.type == TokenType.EOF) {
+        return new _TokenPair(_TokenDifferenceKind.CONTENT, oldToken, newToken);
+      }
+      // compare comments
+      {
+        Token oldComment = oldToken.precedingComments;
+        Token newComment = newToken.precedingComments;
+        while (true) {
+          _TokenDifferenceKind diffKind =
+              _compareToken(oldComment, newComment, 0);
+          if (diffKind != null) {
+            return new _TokenPair(
+                diffKind, oldComment ?? oldToken, newComment ?? newToken);
+          }
+          if (oldComment == null && newComment == null) {
+            break;
+          }
+          oldComment = oldComment.next;
+          newComment = newComment.next;
+        }
+      }
+      // compare tokens
+      _TokenDifferenceKind diffKind = _compareToken(oldToken, newToken, 0);
+      if (diffKind != null) {
+        return new _TokenPair(diffKind, oldToken, newToken);
+      }
+      // next tokens
+      oldToken = oldToken.next;
+      newToken = newToken.next;
+    }
+    // no difference
+    return null;
+  }
+
+  static _TokenPair _findLastDifferentToken(Token oldToken, Token newToken) {
+    int delta = newToken.offset - oldToken.offset;
+    Token prevOldToken;
+    Token prevNewToken;
+    while (oldToken.previous != oldToken && newToken.previous != newToken) {
+      // compare tokens
+      _TokenDifferenceKind diffKind = _compareToken(oldToken, newToken, delta);
+      if (diffKind != null) {
+        return new _TokenPair(diffKind, prevOldToken, prevNewToken);
+      }
+      prevOldToken = oldToken;
+      prevNewToken = newToken;
+      // compare comments
+      {
+        Token oldComment = oldToken.precedingComments;
+        Token newComment = newToken.precedingComments;
+        while (oldComment?.next != null) {
+          oldComment = oldComment.next;
+        }
+        while (newComment?.next != null) {
+          newComment = newComment.next;
+        }
+        while (true) {
+          _TokenDifferenceKind diffKind =
+              _compareToken(oldComment, newComment, delta);
+          if (diffKind != null) {
+            return new _TokenPair(
+                diffKind, oldComment ?? oldToken, newComment ?? newToken);
+          }
+          if (oldComment == null && newComment == null) {
+            break;
+          }
+          prevOldToken = oldComment;
+          prevNewToken = newComment;
+          oldComment = oldComment.previous;
+          newComment = newComment.previous;
+        }
+      }
+      // next tokens
+      oldToken = oldToken.previous;
+      newToken = newToken.previous;
+    }
+    return null;
+  }
+
+  static AstNode _findNodeCovering(AstNode root, int offset, int end) {
+    NodeLocator nodeLocator = new NodeLocator(offset, end);
+    return nodeLocator.searchWithin(root);
+  }
+
+  static Token _getBeginTokenNotComment(AstNode node) {
+    Token oldBeginToken = node.beginToken;
+    if (oldBeginToken is CommentToken) {
+      return oldBeginToken.parent;
+    }
+    return oldBeginToken;
+  }
+
+  static List<AstNode> _getParents(AstNode node) {
+    List<AstNode> parents = <AstNode>[];
+    while (node != null) {
+      parents.insert(0, node);
+      node = node.parent;
+    }
+    return parents;
+  }
+
+  /**
+   * Returns number of tokens with the given [type].
+   */
+  static int _getTokenCount(Token token, TokenType type) {
+    int count = 0;
+    while (token.type != TokenType.EOF) {
+      if (token.type == type) {
+        count++;
+      }
+      token = token.next;
+    }
+    return count;
+  }
+}
 
 /**
  * The context to resolve an [AstNode] in.
@@ -162,3 +1190,125 @@ class ResolutionContextBuilder {
     return context;
   }
 }
+
+/**
+ * Adjusts the location of each Element that moved.
+ *
+ * Since `==` and `hashCode` of a local variable or function Element are based
+ * on the element name offsets, we also need to remove these elements from the
+ * cache to avoid a memory leak. TODO(scheglov) fix and remove this
+ */
+class _ElementOffsetUpdater extends GeneralizingElementVisitor {
+  final int updateOffset;
+  final int updateDelta;
+  final AnalysisCache cache;
+
+  _ElementOffsetUpdater(this.updateOffset, this.updateDelta, this.cache);
+
+  @override
+  visitElement(Element element) {
+    // name offset
+    int nameOffset = element.nameOffset;
+    if (nameOffset > updateOffset) {
+      (element as ElementImpl).nameOffset = nameOffset + updateDelta;
+      if (element is ConstVariableElement) {
+        Expression initializer = element.constantInitializer;
+        if (initializer != null) {
+          _shiftTokens(initializer.beginToken);
+        }
+        _shiftErrors(element.evaluationResult?.errors);
+      }
+    }
+    // code range
+    if (element is ElementImpl) {
+      int oldOffset = element.codeOffset;
+      int oldLength = element.codeLength;
+      if (oldOffset != null) {
+        int newOffset = oldOffset;
+        int newLength = oldLength;
+        newOffset += oldOffset > updateOffset ? updateDelta : 0;
+        if (oldOffset <= updateOffset && updateOffset < oldOffset + oldLength) {
+          newLength += updateDelta;
+        }
+        if (newOffset != oldOffset || newLength != oldLength) {
+          element.setCodeRange(newOffset, newLength);
+        }
+      }
+    }
+    // visible range
+    if (element is LocalElement) {
+      SourceRange visibleRange = element.visibleRange;
+      if (visibleRange != null) {
+        int oldOffset = visibleRange.offset;
+        int oldLength = visibleRange.length;
+        int newOffset = oldOffset;
+        int newLength = oldLength;
+        newOffset += oldOffset > updateOffset ? updateDelta : 0;
+        newLength += visibleRange.contains(updateOffset) ? updateDelta : 0;
+        if (newOffset != oldOffset || newLength != oldLength) {
+          if (element is FunctionElementImpl) {
+            element.setVisibleRange(newOffset, newLength);
+          } else if (element is LocalVariableElementImpl) {
+            element.setVisibleRange(newOffset, newLength);
+          } else if (element is ParameterElementImpl) {
+            element.setVisibleRange(newOffset, newLength);
+          }
+        }
+      }
+    }
+    super.visitElement(element);
+  }
+
+  void _shiftErrors(List<AnalysisError> errors) {
+    if (errors != null) {
+      for (AnalysisError error in errors) {
+        int errorOffset = error.offset;
+        if (errorOffset > updateOffset) {
+          error.offset += updateDelta;
+        }
+      }
+    }
+  }
+
+  void _shiftTokens(Token token) {
+    while (token != null) {
+      if (token.offset > updateOffset) {
+        token.offset += updateDelta;
+      }
+      // comments
+      _shiftTokens(token.precedingComments);
+      if (token is DocumentationCommentToken) {
+        for (Token reference in token.references) {
+          _shiftTokens(reference);
+        }
+      }
+      // next
+      if (token.type == TokenType.EOF) {
+        break;
+      }
+      token = token.next;
+    }
+  }
+}
+
+/**
+ * Describes how two [Token]s are different.
+ */
+class _TokenDifferenceKind {
+  static const CONTENT = const _TokenDifferenceKind('CONTENT');
+  static const OFFSET = const _TokenDifferenceKind('OFFSET');
+
+  final String name;
+
+  const _TokenDifferenceKind(this.name);
+
+  @override
+  String toString() => name;
+}
+
+class _TokenPair {
+  final _TokenDifferenceKind kind;
+  final Token oldToken;
+  final Token newToken;
+  _TokenPair(this.kind, this.oldToken, this.newToken);
+}