// 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 engine;

import 'dart:async';
import 'dart:collection';
import 'dart:math' as math;

import 'package:analyzer/source/embedder.dart';
import 'package:analyzer/src/cancelable_future.dart';
import 'package:analyzer/src/context/cache.dart' as cache;
import 'package:analyzer/src/context/context.dart' as newContext;
import 'package:analyzer/src/generated/incremental_resolution_validator.dart';
import 'package:analyzer/src/plugin/command_line_plugin.dart';
import 'package:analyzer/src/plugin/engine_plugin.dart';
import 'package:analyzer/src/plugin/options_plugin.dart';
import 'package:analyzer/src/services/lint.dart';
import 'package:analyzer/src/task/manager.dart';
import 'package:analyzer/task/dart.dart';
import 'package:analyzer/task/model.dart' as newContext;
import 'package:analyzer/task/model.dart';
import 'package:html/dom.dart' show Document;
import 'package:path/path.dart' as pathos;
import 'package:plugin/manager.dart';
import 'package:plugin/plugin.dart';

import '../../instrumentation/instrumentation.dart';
import 'ast.dart';
import 'constant.dart';
import 'element.dart';
import 'error.dart';
import 'error_verifier.dart';
import 'html.dart' as ht;
import 'incremental_resolver.dart'
    show IncrementalResolver, PoorMansIncrementalResolver;
import 'incremental_scanner.dart';
import 'java_core.dart';
import 'java_engine.dart';
import 'parser.dart' show Parser, IncrementalParser;
import 'resolver.dart';
import 'scanner.dart';
import 'sdk.dart' show DartSdk;
import 'source.dart';
import 'utilities_collection.dart';
import 'utilities_general.dart';

/**
 * Used by [AnalysisOptions] to allow function bodies to be analyzed in some
 * sources but not others.
 */
typedef bool AnalyzeFunctionBodiesPredicate(Source source);

/**
 * Type of callback functions used by PendingFuture.  Functions of this type
 * should perform a computation based on the data in [sourceEntry] and return
 * it.  If the computation can't be performed yet because more analysis is
 * needed, null should be returned.
 *
 * The function may also throw an exception, in which case the corresponding
 * future will be completed with failure.
 *
 * Since this function is called while the state of analysis is being updated,
 * it should be free of side effects so that it doesn't cause reentrant
 * changes to the analysis state.
 */
typedef T PendingFutureComputer<T>(SourceEntry sourceEntry);

/**
 * An LRU cache of information related to analysis.
 */
class AnalysisCache {
  /**
   * A flag used to control whether trace information should be produced when
   * the content of the cache is modified.
   */
  static bool _TRACE_CHANGES = false;

  /**
   * A list containing the partitions of which this cache is comprised.
   */
  final List<CachePartition> _partitions;

  /**
   * Initialize a newly created cache to have the given [_partitions]. The
   * partitions will be searched in the order in which they appear in the list,
   * so the most specific partition (usually an [SdkCachePartition]) should be
   * first and the most general (usually a [UniversalCachePartition]) last.
   */
  AnalysisCache(this._partitions);

  /**
   * Return the number of entries in this cache that have an AST associated with
   * them.
   */
  int get astSize => _partitions[_partitions.length - 1].astSize;

  /**
   * Return information about each of the partitions in this cache.
   */
  List<AnalysisContextStatistics_PartitionData> get partitionData {
    int count = _partitions.length;
    List<AnalysisContextStatistics_PartitionData> data =
        new List<AnalysisContextStatistics_PartitionData>(count);
    for (int i = 0; i < count; i++) {
      CachePartition partition = _partitions[i];
      data[i] = new AnalysisContextStatisticsImpl_PartitionDataImpl(
          partition.astSize, partition.map.length);
    }
    return data;
  }

  /**
   * Record that the AST associated with the given [source] was just read from
   * the cache.
   */
  void accessedAst(Source source) {
    int count = _partitions.length;
    for (int i = 0; i < count; i++) {
      if (_partitions[i].contains(source)) {
        _partitions[i].accessedAst(source);
        return;
      }
    }
  }

  /**
   * Return the entry associated with the given [source].
   */
  SourceEntry get(Source source) {
    int count = _partitions.length;
    for (int i = 0; i < count; i++) {
      if (_partitions[i].contains(source)) {
        return _partitions[i].get(source);
      }
    }
    //
    // We should never get to this point because the last partition should
    // always be a universal partition, except in the case of the SDK context,
    // in which case the source should always be part of the SDK.
    //
    return null;
  }

  /**
   * Return context that owns the given [source].
   */
  InternalAnalysisContext getContextFor(Source source) {
    int count = _partitions.length;
    for (int i = 0; i < count; i++) {
      if (_partitions[i].contains(source)) {
        return _partitions[i].context;
      }
    }
    //
    // We should never get to this point because the last partition should
    // always be a universal partition, except in the case of the SDK context,
    // in which case the source should always be part of the SDK.
    //
    AnalysisEngine.instance.logger.logInformation(
        "Could not find context for ${source.fullName}",
        new CaughtException(new AnalysisException(), null));
    return null;
  }

  /**
   * Return an iterator returning all of the map entries mapping sources to
   * cache entries.
   */
  MapIterator<Source, SourceEntry> iterator() {
    int count = _partitions.length;
    List<Map<Source, SourceEntry>> maps =
        new List<Map<Source, SourceEntry>>(count);
    for (int i = 0; i < count; i++) {
      maps[i] = _partitions[i].map;
    }
    return new MultipleMapIterator<Source, SourceEntry>(maps);
  }

  /**
   * Associate the given [entry] with the given [source].
   */
  void put(Source source, SourceEntry entry) {
    entry.fixExceptionState();
    int count = _partitions.length;
    for (int i = 0; i < count; i++) {
      if (_partitions[i].contains(source)) {
        if (_TRACE_CHANGES) {
          try {
            SourceEntry oldEntry = _partitions[i].get(source);
            if (oldEntry == null) {
              AnalysisEngine.instance.logger.logInformation(
                  "Added a cache entry for '${source.fullName}'.");
            } else {
              AnalysisEngine.instance.logger.logInformation(
                  "Modified the cache entry for ${source.fullName}'. Diff = ${entry.getDiff(oldEntry)}");
            }
          } catch (exception) {
            // Ignored
            JavaSystem.currentTimeMillis();
          }
        }
        _partitions[i].put(source, entry);
        return;
      }
    }
  }

  /**
   * Remove all information related to the given [source] from this cache.
   * Return the entry associated with the source, or `null` if there was cache
   * entry for the source.
   */
  SourceEntry remove(Source source) {
    int count = _partitions.length;
    for (int i = 0; i < count; i++) {
      if (_partitions[i].contains(source)) {
        if (_TRACE_CHANGES) {
          try {
            AnalysisEngine.instance.logger.logInformation(
                "Removed the cache entry for ${source.fullName}'.");
          } catch (exception) {
            // Ignored
            JavaSystem.currentTimeMillis();
          }
        }
        return _partitions[i].remove(source);
      }
    }
    return null;
  }

  /**
   * Record that the AST associated with the given [source] was just removed
   * from the cache.
   */
  void removedAst(Source source) {
    int count = _partitions.length;
    for (int i = 0; i < count; i++) {
      if (_partitions[i].contains(source)) {
        _partitions[i].removedAst(source);
        return;
      }
    }
  }

  /**
   * Return the number of sources that are mapped to cache entries.
   */
  int size() {
    int size = 0;
    int count = _partitions.length;
    for (int i = 0; i < count; i++) {
      size += _partitions[i].size();
    }
    return size;
  }

  /**
   * Record that the AST associated with the given [source] was just stored to
   * the cache.
   */
  void storedAst(Source source) {
    int count = _partitions.length;
    for (int i = 0; i < count; i++) {
      if (_partitions[i].contains(source)) {
        _partitions[i].storedAst(source);
        return;
      }
    }
  }
}

/**
 * A context in which a single analysis can be performed and incrementally
 * maintained. The context includes such information as the version of the SDK
 * being analyzed against as well as the package-root used to resolve 'package:'
 * URI's. (Both of which are known indirectly through the [SourceFactory].)
 *
 * An analysis context also represents the state of the analysis, which includes
 * knowing which sources have been included in the analysis (either directly or
 * indirectly) and the results of the analysis. Sources must be added and
 * removed from the context using the method [applyChanges], which is also used
 * to notify the context when sources have been modified and, consequently,
 * previously known results might have been invalidated.
 *
 * There are two ways to access the results of the analysis. The most common is
 * to use one of the 'get' methods to access the results. The 'get' methods have
 * the advantage that they will always return quickly, but have the disadvantage
 * that if the results are not currently available they will return either
 * nothing or in some cases an incomplete result. The second way to access
 * results is by using one of the 'compute' methods. The 'compute' methods will
 * always attempt to compute the requested results but might block the caller
 * for a significant period of time.
 *
 * When results have been invalidated, have never been computed (as is the case
 * for newly added sources), or have been removed from the cache, they are
 * <b>not</b> automatically recreated. They will only be recreated if one of the
 * 'compute' methods is invoked.
 *
 * However, this is not always acceptable. Some clients need to keep the
 * analysis results up-to-date. For such clients there is a mechanism that
 * allows them to incrementally perform needed analysis and get notified of the
 * consequent changes to the analysis results. This mechanism is realized by the
 * method [performAnalysisTask].
 *
 * Analysis engine allows for having more than one context. This can be used,
 * for example, to perform one analysis based on the state of files on disk and
 * a separate analysis based on the state of those files in open editors. It can
 * also be used to perform an analysis based on a proposed future state, such as
 * the state after a refactoring.
 */
abstract class AnalysisContext {
  /**
   * An empty list of contexts.
   */
  static const List<AnalysisContext> EMPTY_LIST = const <AnalysisContext>[];

  /**
   * Return the set of analysis options controlling the behavior of this
   * context. Clients should not modify the returned set of options. The options
   * should only be set by invoking the method [setAnalysisOptions].
   */
  AnalysisOptions get analysisOptions;

  /**
   * Set the set of analysis options controlling the behavior of this context to
   * the given [options]. Clients can safely assume that all necessary analysis
   * results have been invalidated.
   */
  void set analysisOptions(AnalysisOptions options);

  /**
   * Set the order in which sources will be analyzed by [performAnalysisTask] to
   * match the order of the sources in the given list of [sources]. If a source
   * that needs to be analyzed is not contained in the list, then it will be
   * treated as if it were at the end of the list. If the list is empty (or
   * `null`) then no sources will be given priority over other sources.
   *
   * Changes made to the list after this method returns will <b>not</b> be
   * reflected in the priority order.
   */
  void set analysisPriorityOrder(List<Source> sources);

  /**
   * Return the set of declared variables used when computing constant values.
   */
  DeclaredVariables get declaredVariables;

  /**
   * Return a list containing all of the sources known to this context that
   * represent HTML files. The contents of the list can be incomplete.
   */
  List<Source> get htmlSources;

  /**
   * The stream that is notified when a source either starts or stops being
   * analyzed implicitly.
   */
  Stream<ImplicitAnalysisEvent> get implicitAnalysisEvents;

  /**
   * Returns `true` if this context was disposed using [dispose].
   */
  bool get isDisposed;

  /**
   * Return a list containing all of the sources known to this context that
   * represent the defining compilation unit of a library that can be run within
   * a browser. The sources that are returned represent libraries that have a
   * 'main' method and are either referenced by an HTML file or import, directly
   * or indirectly, a client-only library. The contents of the list can be
   * incomplete.
   */
  List<Source> get launchableClientLibrarySources;

  /**
   * Return a list containing all of the sources known to this context that
   * represent the defining compilation unit of a library that can be run
   * outside of a browser. The contents of the list can be incomplete.
   */
  List<Source> get launchableServerLibrarySources;

  /**
   * Return a list containing all of the sources known to this context that
   * represent the defining compilation unit of a library. The contents of the
   * list can be incomplete.
   */
  List<Source> get librarySources;

  /**
   * Return a client-provided name used to identify this context, or `null` if
   * the client has not provided a name.
   */
  String get name;

  /**
   * Set the client-provided name used to identify this context to the given
   * [name].
   */
  set name(String name);

  /**
   * The stream that is notified when sources have been added or removed,
   * or the source's content has changed.
   */
  Stream<SourcesChangedEvent> get onSourcesChanged;

  /**
   * Return the source factory used to create the sources that can be analyzed
   * in this context.
   */
  SourceFactory get sourceFactory;

  /**
   * Set the source factory used to create the sources that can be analyzed in
   * this context to the given source [factory]. Clients can safely assume that
   * all analysis results have been invalidated.
   */
  void set sourceFactory(SourceFactory factory);

  /**
   * Return a list containing all of the sources known to this context.
   */
  List<Source> get sources;

  /**
   * Return a type provider for this context or throw [AnalysisException] if
   * either `dart:core` or `dart:async` cannot be resolved.
   */
  TypeProvider get typeProvider;

  /**
   * Return a type system for this context.
   */
  TypeSystem get typeSystem;

  /**
   * Add the given [listener] to the list of objects that are to be notified
   * when various analysis results are produced in this context.
   */
  void addListener(AnalysisListener listener);

  /**
   * Apply the given [delta] to change the level of analysis that will be
   * performed for the sources known to this context.
   */
  void applyAnalysisDelta(AnalysisDelta delta);

  /**
   * Apply the changes specified by the given [changeSet] to this context. Any
   * analysis results that have been invalidated by these changes will be
   * removed.
   */
  ApplyChangesStatus applyChanges(ChangeSet changeSet);

  /**
   * Return the documentation comment for the given [element] as it appears in
   * the original source (complete with the beginning and ending delimiters) for
   * block documentation comments, or lines starting with `"///"` and separated
   * with `"\n"` characters for end-of-line documentation comments, or `null` if
   * the element does not have a documentation comment associated with it. This
   * can be a long-running operation if the information needed to access the
   * comment is not cached.
   *
   * Throws an [AnalysisException] if the documentation comment could not be
   * determined because the analysis could not be performed.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  String computeDocumentationComment(Element element);

  /**
   * Return a list containing all of the errors associated with the given
   * [source]. If the errors are not already known then the source will be
   * analyzed in order to determine the errors associated with it.
   *
   * Throws an [AnalysisException] if the errors could not be determined because
   * the analysis could not be performed.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   *
   * See [getErrors].
   */
  List<AnalysisError> computeErrors(Source source);

  /**
   * Return the element model corresponding to the HTML file defined by the
   * given [source]. If the element model does not yet exist it will be created.
   * The process of creating an element model for an HTML file can be
   * long-running, depending on the size of the file and the number of libraries
   * that are defined in it (via script tags) that also need to have a model
   * built for them.
   *
   * Throws AnalysisException if the element model could not be determined
   * because the analysis could not be performed.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   *
   * See [getHtmlElement].
   */
  @deprecated
  HtmlElement computeHtmlElement(Source source);

  /**
   * Return the kind of the given [source], computing it's kind if it is not
   * already known. Return [SourceKind.UNKNOWN] if the source is not contained
   * in this context.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   *
   * See [getKindOf].
   */
  SourceKind computeKindOf(Source source);

  /**
   * Return the element model corresponding to the library defined by the given
   * [source]. If the element model does not yet exist it will be created. The
   * process of creating an element model for a library can long-running,
   * depending on the size of the library and the number of libraries that are
   * imported into it that also need to have a model built for them.
   *
   * Throws an [AnalysisException] if the element model could not be determined
   * because the analysis could not be performed.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   *
   * See [getLibraryElement].
   */
  LibraryElement computeLibraryElement(Source source);

  /**
   * Return the line information for the given [source], or `null` if the source
   * is not of a recognized kind (neither a Dart nor HTML file). If the line
   * information was not previously known it will be created. The line
   * information is used to map offsets from the beginning of the source to line
   * and column pairs.
   *
   * Throws an [AnalysisException] if the line information could not be
   * determined because the analysis could not be performed.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   *
   * See [getLineInfo].
   */
  LineInfo computeLineInfo(Source source);

  /**
   * Return a future which will be completed with the fully resolved AST for a
   * single compilation unit within the given library, once that AST is up to
   * date.
   *
   * If the resolved AST can't be computed for some reason, the future will be
   * completed with an error.  One possible error is AnalysisNotScheduledError,
   * which means that the resolved AST can't be computed because the given
   * source file is not scheduled to be analyzed within the context of the
   * given library.
   */
  CancelableFuture<CompilationUnit> computeResolvedCompilationUnitAsync(
      Source source, Source librarySource);

  /**
   * Perform work until the given [result] has been computed for the given
   * [target]. Return the computed value.
   */
  Object /*V*/ computeResult(
      AnalysisTarget target, ResultDescriptor /*<V>*/ result);

  /**
   * Notifies the context that the client is going to stop using this context.
   */
  void dispose();

  /**
   * Return `true` if the given [source] exists.
   *
   * This method should be used rather than the method [Source.exists] because
   * contexts can have local overrides of the content of a source that the
   * source is not aware of and a source with local content is considered to
   * exist even if there is no file on disk.
   */
  bool exists(Source source);

  /**
   * Return the element model corresponding to the compilation unit defined by
   * the given [unitSource] in the library defined by the given [librarySource],
   * or `null` if the element model does not currently exist or if the library
   * cannot be analyzed for some reason.
   */
  CompilationUnitElement getCompilationUnitElement(
      Source unitSource, Source librarySource);

  /**
   * Return configuration data associated with the given key or the [key]'s
   * default value if no state has been associated.
   *
   * See [setConfigurationData].
   */
  Object getConfigurationData(ResultDescriptor key);

  /**
   * Return the contents and timestamp of the given [source].
   *
   * This method should be used rather than the method [Source.getContents]
   * because contexts can have local overrides of the content of a source that
   * the source is not aware of.
   */
  TimestampedData<String> getContents(Source source);

  /**
   * Return the element referenced by the given [location], or `null` if the
   * element is not immediately available or if there is no element with the
   * given location. The latter condition can occur, for example, if the
   * location describes an element from a different context or if the element
   * has been removed from this context as a result of some change since it was
   * originally obtained.
   */
  Element getElement(ElementLocation location);

  /**
   * Return an analysis error info containing the list of all of the errors and
   * the line info associated with the given [source]. The list of errors will
   * be empty if the source is not known to this context or if there are no
   * errors in the source. The errors contained in the list can be incomplete.
   *
   * See [computeErrors].
   */
  AnalysisErrorInfo getErrors(Source source);

  /**
   * Return the element model corresponding to the HTML file defined by the
   * given [source], or `null` if the source does not represent an HTML file,
   * the element representing the file has not yet been created, or the analysis
   * of the HTML file failed for some reason.
   *
   * See [computeHtmlElement].
   */
  @deprecated
  HtmlElement getHtmlElement(Source source);

  /**
   * Return the sources for the HTML files that reference the compilation unit
   * with the given [source]. If the source does not represent a Dart source or
   * is not known to this context, the returned list will be empty. The contents
   * of the list can be incomplete.
   */
  List<Source> getHtmlFilesReferencing(Source source);

  /**
   * Return the kind of the given [source], or `null` if the kind is not known
   * to this context.
   *
   * See [computeKindOf].
   */
  SourceKind getKindOf(Source source);

  /**
   * Return the sources for the defining compilation units of any libraries of
   * which the given [source] is a part. The list will normally contain a single
   * library because most Dart sources are only included in a single library,
   * but it is possible to have a part that is contained in multiple identically
   * named libraries. If the source represents the defining compilation unit of
   * a library, then the returned list will contain the given source as its only
   * element. If the source does not represent a Dart source or is not known to
   * this context, the returned list will be empty. The contents of the list can
   * be incomplete.
   */
  List<Source> getLibrariesContaining(Source source);

  /**
   * Return the sources for the defining compilation units of any libraries that
   * depend on the library defined by the given [librarySource]. One library
   * depends on another if it either imports or exports that library.
   */
  List<Source> getLibrariesDependingOn(Source librarySource);

  /**
   * Return the sources for the defining compilation units of any libraries that
   * are referenced from the HTML file defined by the given [htmlSource].
   */
  List<Source> getLibrariesReferencedFromHtml(Source htmlSource);

  /**
   * Return the element model corresponding to the library defined by the given
   * [source], or `null` if the element model does not currently exist or if the
   * library cannot be analyzed for some reason.
   */
  LibraryElement getLibraryElement(Source source);

  /**
   * Return the line information for the given [source], or `null` if the line
   * information is not known. The line information is used to map offsets from
   * the beginning of the source to line and column pairs.
   *
   * See [computeLineInfo].
   */
  LineInfo getLineInfo(Source source);

  /**
   * Return the modification stamp for the [source], or a negative value if the
   * source does not exist. A modification stamp is a non-negative integer with
   * the property that if the contents of the source have not been modified
   * since the last time the modification stamp was accessed then the same value
   * will be returned, but if the contents of the source have been modified one
   * or more times (even if the net change is zero) the stamps will be different.
   *
   * This method should be used rather than the method
   * [Source.getModificationStamp] because contexts can have local overrides of
   * the content of a source that the source is not aware of.
   */
  int getModificationStamp(Source source);

  /**
   * Return a fully resolved AST for the compilation unit defined by the given
   * [unitSource] within the given [library], or `null` if the resolved AST is
   * not already computed.
   *
   * See [resolveCompilationUnit].
   */
  CompilationUnit getResolvedCompilationUnit(
      Source unitSource, LibraryElement library);

  /**
   * Return a fully resolved AST for the compilation unit defined by the given
   * [unitSource] within the library defined by the given [librarySource], or
   * `null` if the resolved AST is not already computed.
   *
   * See [resolveCompilationUnit2].
   */
  CompilationUnit getResolvedCompilationUnit2(
      Source unitSource, Source librarySource);

  /**
   * Return the fully resolved HTML unit defined by the given [htmlSource], or
   * `null` if the resolved unit is not already computed.
   *
   * See [resolveHtmlUnit].
   */
  @deprecated
  ht.HtmlUnit getResolvedHtmlUnit(Source htmlSource);

  /**
   * Return the value of the given [result] for the given [target].
   *
   * If the corresponding [target] does not exist, or the [result] is not
   * computed yet, then the default value is returned.
   */
  Object /*V*/ getResult(
      AnalysisTarget target, ResultDescriptor /*<V>*/ result);

  /**
   * Return a list of the sources being analyzed in this context whose full path
   * is equal to the given [path].
   */
  List<Source> getSourcesWithFullName(String path);

  /**
   * Invalidates hints in the given [librarySource] and included parts.
   */
  void invalidateLibraryHints(Source librarySource);

  /**
   * Return `true` if the given [librarySource] is known to be the defining
   * compilation unit of a library that can be run on a client (references
   * 'dart:html', either directly or indirectly).
   *
   * <b>Note:</b> In addition to the expected case of returning `false` if the
   * source is known to be a library that cannot be run on a client, this method
   * will also return `false` if the source is not known to be a library or if
   * we do not know whether it can be run on a client.
   */
  bool isClientLibrary(Source librarySource);

  /**
   * Return `true` if the given [librarySource] is known to be the defining
   * compilation unit of a library that can be run on the server (does not
   * reference 'dart:html', either directly or indirectly).
   *
   * <b>Note:</b> In addition to the expected case of returning `false` if the
   * source is known to be a library that cannot be run on the server, this
   * method will also return `false` if the source is not known to be a library
   * or if we do not know whether it can be run on the server.
   */
  bool isServerLibrary(Source librarySource);

  /**
   * Return the stream that is notified when a new value for the given
   * [descriptor] is computed.
   */
  Stream<ComputedResult> onResultComputed(ResultDescriptor descriptor);

  /**
   * Parse the content of the given [source] to produce an AST structure. The
   * resulting AST structure may or may not be resolved, and may have a slightly
   * different structure depending upon whether it is resolved.
   *
   * Throws an [AnalysisException] if the analysis could not be performed
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  CompilationUnit parseCompilationUnit(Source source);

  /**
   * Parse a single HTML [source] to produce a document model.
   *
   * Throws an [AnalysisException] if the analysis could not be performed
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Document parseHtmlDocument(Source source);

  /**
   * Parse a single HTML [source] to produce an AST structure. The resulting
   * HTML AST structure may or may not be resolved, and may have a slightly
   * different structure depending upon whether it is resolved.
   *
   * Throws an [AnalysisException] if the analysis could not be performed
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  @deprecated // use parseHtmlDocument(source)
  ht.HtmlUnit parseHtmlUnit(Source source);

  /**
   * Perform the next unit of work required to keep the analysis results
   * up-to-date and return information about the consequent changes to the
   * analysis results. This method can be long running.
   *
   * The implementation that uses the task model notifies subscribers of
   * [onResultComputed] about computed results.
   *
   * The following results are computed for Dart sources.
   *
   * 1. For explicit and implicit sources:
   *    [PARSED_UNIT]
   *    [RESOLVED_UNIT]
   *
   * 2. For explicit sources:
   *    [DART_ERRORS].
   *
   * 3. For explicit and implicit library sources:
   *    [LIBRARY_ELEMENT].
   */
  AnalysisResult performAnalysisTask();

  /**
   * Remove the given [listener] from the list of objects that are to be
   * notified when various analysis results are produced in this context.
   */
  void removeListener(AnalysisListener listener);

  /**
   * Return a fully resolved AST for the compilation unit defined by the given
   * [unitSource] within the given [library].
   *
   * Throws an [AnalysisException] if the analysis could not be performed.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   *
   * See [getResolvedCompilationUnit].
   */
  CompilationUnit resolveCompilationUnit(
      Source unitSource, LibraryElement library);

  /**
   * Return a fully resolved AST for the compilation unit defined by the given
   * [unitSource] within the library defined by the given [librarySource].
   *
   * Throws an [AnalysisException] if the analysis could not be performed.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   *
   * See [getResolvedCompilationUnit2].
   */
  CompilationUnit resolveCompilationUnit2(
      Source unitSource, Source librarySource);

  /**
   * Parse and resolve a single [htmlSource] within the given context to produce
   * a fully resolved AST.
   *
   * Throws an [AnalysisException] if the analysis could not be performed.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  @deprecated
  ht.HtmlUnit resolveHtmlUnit(Source htmlSource);

  /**
   * Set the contents of the given [source] to the given [contents] and mark the
   * source as having changed. The additional [offset] and [length] information
   * is used by the context to determine what reanalysis is necessary.
   */
  void setChangedContents(
      Source source, String contents, int offset, int oldLength, int newLength);

  /**
   * Associate this configuration [data] object with the given descriptor [key].
   *
   * See [getConfigurationData].
   */
  void setConfigurationData(ResultDescriptor key, Object data);

  /**
   * Set the contents of the given [source] to the given [contents] and mark the
   * source as having changed. This has the effect of overriding the default
   * contents of the source. If the contents are `null` the override is removed
   * so that the default contents will be returned.
   */
  void setContents(Source source, String contents);

  /**
   * Check the cache for any invalid entries (entries whose modification time
   * does not match the modification time of the source associated with the
   * entry). Invalid entries will be marked as invalid so that the source will
   * be re-analyzed. Return `true` if at least one entry was invalid.
   */
  bool validateCacheConsistency();
}

/**
 * An [AnalysisContext].
 */
class AnalysisContextImpl implements InternalAnalysisContext {
  /**
   * The difference between the maximum cache size and the maximum priority
   * order size. The priority list must be capped so that it is less than the
   * cache size. Failure to do so can result in an infinite loop in
   * performAnalysisTask() because re-caching one AST structure can cause
   * another priority source's AST structure to be flushed.
   */
  static int _PRIORITY_ORDER_SIZE_DELTA = 4;

  /**
   * A flag indicating whether trace output should be produced as analysis tasks
   * are performed. Used for debugging.
   */
  static bool _TRACE_PERFORM_TASK = false;

  /**
   * The next context identifier.
   */
  static int _NEXT_ID = 0;

  /**
   * The unique identifier of this context.
   */
  final int _id = _NEXT_ID++;

  /**
   * A client-provided name used to identify this context, or `null` if the
   * client has not provided a name.
   */
  String name;

  /**
   * Configuration data associated with this context.
   */
  final HashMap<ResultDescriptor, Object> _configurationData =
      new HashMap<ResultDescriptor, Object>();

  /**
   * The set of analysis options controlling the behavior of this context.
   */
  AnalysisOptionsImpl _options = new AnalysisOptionsImpl();

  /// The embedder yaml locator for this context.
  EmbedderYamlLocator _embedderYamlLocator = new EmbedderYamlLocator(null);

  /**
   * A flag indicating whether errors related to implicitly analyzed sources
   * should be generated and reported.
   */
  bool _generateImplicitErrors = true;

  /**
   * A flag indicating whether errors related to sources in the SDK should be
   * generated and reported.
   */
  bool _generateSdkErrors = true;

  /**
   * A flag indicating whether this context is disposed.
   */
  bool _disposed = false;

  /**
   * A cache of content used to override the default content of a source.
   */
  ContentCache _contentCache = new ContentCache();

  /**
   * The source factory used to create the sources that can be analyzed in this
   * context.
   */
  SourceFactory _sourceFactory;

  /**
   * The set of declared variables used when computing constant values.
   */
  DeclaredVariables _declaredVariables = new DeclaredVariables();

  /**
   * A source representing the core library.
   */
  Source _coreLibrarySource;

  /**
   * A source representing the async library.
   */
  Source _asyncLibrarySource;

  /**
   * The partition that contains analysis results that are not shared with other
   * contexts.
   */
  CachePartition _privatePartition;

  /**
   * A table mapping the sources known to the context to the information known
   * about the source.
   */
  AnalysisCache _cache;

  /**
   * A list containing sources for which data should not be flushed.
   */
  List<Source> _priorityOrder = Source.EMPTY_LIST;

  /**
   * A map from all sources for which there are futures pending to a list of
   * the corresponding PendingFuture objects.  These sources will be analyzed
   * in the same way as priority sources, except with higher priority.
   *
   * TODO(paulberry): since the size of this map is not constrained (as it is
   * for _priorityOrder), we run the risk of creating an analysis loop if
   * re-caching one AST structure causes the AST structure for another source
   * with pending futures to be flushed.  However, this is unlikely to happen
   * in practice since sources are removed from this hash set as soon as their
   * futures have completed.
   */
  HashMap<Source, List<PendingFuture>> _pendingFutureSources =
      new HashMap<Source, List<PendingFuture>>();

  /**
   * A list containing sources whose AST structure is needed in order to resolve
   * the next library to be resolved.
   */
  HashSet<Source> _neededForResolution = null;

  /**
   * A table mapping sources to the change notices that are waiting to be
   * returned related to that source.
   */
  HashMap<Source, ChangeNoticeImpl> _pendingNotices =
      new HashMap<Source, ChangeNoticeImpl>();

  /**
   * The object used to record the results of performing an analysis task.
   */
  AnalysisContextImpl_AnalysisTaskResultRecorder _resultRecorder;

  /**
   * Cached information used in incremental analysis or `null` if none.
   */
  IncrementalAnalysisCache _incrementalAnalysisCache;

  /**
   * The [TypeProvider] for this context, `null` if not yet created.
   */
  TypeProvider _typeProvider;

  /**
   * The [TypeSystem] for this context, `null` if not yet created.
   */
  TypeSystem _typeSystem;

  /**
   * The object used to manage the list of sources that need to be analyzed.
   */
  WorkManager _workManager = new WorkManager();

  /**
   * The [Stopwatch] of the current "perform tasks cycle".
   */
  Stopwatch _performAnalysisTaskStopwatch;

  /**
   * The controller for sending [SourcesChangedEvent]s.
   */
  StreamController<SourcesChangedEvent> _onSourcesChangedController;

  /**
   * A subscription for a stream of events indicating when files are (and are
   * not) being implicitly analyzed.
   */
  StreamController<ImplicitAnalysisEvent> _implicitAnalysisEventsController;

  /**
   * The listeners that are to be notified when various analysis results are
   * produced in this context.
   */
  List<AnalysisListener> _listeners = new List<AnalysisListener>();

  /**
   * The most recently incrementally resolved source, or `null` when it was
   * already validated, or the most recent change was not incrementally resolved.
   */
  Source incrementalResolutionValidation_lastUnitSource;

  /**
   * The most recently incrementally resolved library source, or `null` when it
   * was already validated, or the most recent change was not incrementally
   * resolved.
   */
  Source incrementalResolutionValidation_lastLibrarySource;

  /**
   * The result of incremental resolution result of
   * [incrementalResolutionValidation_lastSource].
   */
  CompilationUnit incrementalResolutionValidation_lastUnit;

  /**
   * A factory to override how the [ResolverVisitor] is created.
   */
  ResolverVisitorFactory resolverVisitorFactory;

  /**
   * A factory to override how the [TypeResolverVisitor] is created.
   */
  TypeResolverVisitorFactory typeResolverVisitorFactory;

  /**
   * A factory to override how [LibraryResolver] is created.
   */
  LibraryResolverFactory libraryResolverFactory;

  /**
   * Initialize a newly created analysis context.
   */
  AnalysisContextImpl() {
    _resultRecorder = new AnalysisContextImpl_AnalysisTaskResultRecorder(this);
    _privatePartition = new UniversalCachePartition(
        this,
        AnalysisOptionsImpl.DEFAULT_CACHE_SIZE,
        new AnalysisContextImpl_ContextRetentionPolicy(this));
    _cache = createCacheFromSourceFactory(null);
    _onSourcesChangedController =
        new StreamController<SourcesChangedEvent>.broadcast();
    _implicitAnalysisEventsController =
        new StreamController<ImplicitAnalysisEvent>.broadcast();
  }

  @override
  AnalysisCache get analysisCache => _cache;

  @override
  AnalysisOptions get analysisOptions => _options;

  @override
  void set analysisOptions(AnalysisOptions options) {
    bool needsRecompute = this._options.analyzeFunctionBodiesPredicate !=
            options.analyzeFunctionBodiesPredicate ||
        this._options.generateImplicitErrors !=
            options.generateImplicitErrors ||
        this._options.generateSdkErrors != options.generateSdkErrors ||
        this._options.dart2jsHint != options.dart2jsHint ||
        (this._options.hint && !options.hint) ||
        this._options.preserveComments != options.preserveComments ||
        this._options.strongMode != options.strongMode ||
        ((options is AnalysisOptionsImpl)
            ? this._options.strongModeHints != options.strongModeHints
            : false) ||
        this._options.enableStrictCallChecks !=
            options.enableStrictCallChecks ||
        this._options.enableSuperMixins != options.enableSuperMixins;
    int cacheSize = options.cacheSize;
    if (this._options.cacheSize != cacheSize) {
      this._options.cacheSize = cacheSize;
      //cache.setMaxCacheSize(cacheSize);
      _privatePartition.maxCacheSize = cacheSize;
      //
      // Cap the size of the priority list to being less than the cache size.
      // Failure to do so can result in an infinite loop in
      // performAnalysisTask() because re-caching one AST structure
      // can cause another priority source's AST structure to be flushed.
      //
      // TODO(brianwilkerson) Remove this constraint when the new task model is
      // implemented.
      //
      int maxPriorityOrderSize = cacheSize - _PRIORITY_ORDER_SIZE_DELTA;
      if (_priorityOrder.length > maxPriorityOrderSize) {
        _priorityOrder = _priorityOrder.sublist(0, maxPriorityOrderSize);
      }
    }
    this._options.analyzeFunctionBodiesPredicate =
        options.analyzeFunctionBodiesPredicate;
    this._options.generateImplicitErrors = options.generateImplicitErrors;
    this._options.generateSdkErrors = options.generateSdkErrors;
    this._options.dart2jsHint = options.dart2jsHint;
    this._options.enableStrictCallChecks = options.enableStrictCallChecks;
    this._options.enableSuperMixins = options.enableSuperMixins;
    this._options.hint = options.hint;
    this._options.incremental = options.incremental;
    this._options.incrementalApi = options.incrementalApi;
    this._options.incrementalValidation = options.incrementalValidation;
    this._options.lint = options.lint;
    this._options.preserveComments = options.preserveComments;
    this._options.strongMode = options.strongMode;
    if (options is AnalysisOptionsImpl) {
      this._options.strongModeHints = options.strongModeHints;
    }
    _generateImplicitErrors = options.generateImplicitErrors;
    _generateSdkErrors = options.generateSdkErrors;
    if (needsRecompute) {
      _invalidateAllLocalResolutionInformation(false);
    }
  }

  @override
  void set analysisPriorityOrder(List<Source> sources) {
    if (sources == null || sources.isEmpty) {
      _priorityOrder = Source.EMPTY_LIST;
    } else {
      while (sources.remove(null)) {
        // Nothing else to do.
      }
      if (sources.isEmpty) {
        _priorityOrder = Source.EMPTY_LIST;
      }
      //
      // Cap the size of the priority list to being less than the cache size.
      // Failure to do so can result in an infinite loop in
      // performAnalysisTask() because re-caching one AST structure
      // can cause another priority source's AST structure to be flushed.
      //
      int count = math.min(
          sources.length, _options.cacheSize - _PRIORITY_ORDER_SIZE_DELTA);
      _priorityOrder = new List<Source>(count);
      for (int i = 0; i < count; i++) {
        _priorityOrder[i] = sources[i];
      }
      // Ensure entries for every priority source.
      for (var source in _priorityOrder) {
        SourceEntry entry = _getReadableSourceEntry(source);
        if (entry == null) {
          _createSourceEntry(source, false);
        }
      }
    }
  }

  @override
  set contentCache(ContentCache value) {
    _contentCache = value;
  }

  @override
  DeclaredVariables get declaredVariables => _declaredVariables;

  @override
  EmbedderYamlLocator get embedderYamlLocator => _embedderYamlLocator;

  @override
  List<AnalysisTarget> get explicitTargets {
    List<AnalysisTarget> targets = <AnalysisTarget>[];
    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
    while (iterator.moveNext()) {
      if (iterator.value.explicitlyAdded) {
        targets.add(iterator.key);
      }
    }
    return targets;
  }

  @override
  List<Source> get htmlSources => _getSources(SourceKind.HTML);

  @override
  Stream<ImplicitAnalysisEvent> get implicitAnalysisEvents =>
      _implicitAnalysisEventsController.stream;

  @override
  bool get isDisposed => _disposed;

  @override
  List<Source> get launchableClientLibrarySources {
    // TODO(brianwilkerson) This needs to filter out libraries that do not
    // reference dart:html, either directly or indirectly.
    List<Source> sources = new List<Source>();
    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
    while (iterator.moveNext()) {
      Source source = iterator.key;
      SourceEntry sourceEntry = iterator.value;
      if (sourceEntry.kind == SourceKind.LIBRARY && !source.isInSystemLibrary) {
//          DartEntry dartEntry = (DartEntry) sourceEntry;
//          if (dartEntry.getValue(DartEntry.IS_LAUNCHABLE) && dartEntry.getValue(DartEntry.IS_CLIENT)) {
        sources.add(source);
//          }
      }
    }
    return sources;
  }

  @override
  List<Source> get launchableServerLibrarySources {
    // TODO(brianwilkerson) This needs to filter out libraries that reference
    // dart:html, either directly or indirectly.
    List<Source> sources = new List<Source>();
    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
    while (iterator.moveNext()) {
      Source source = iterator.key;
      SourceEntry sourceEntry = iterator.value;
      if (sourceEntry.kind == SourceKind.LIBRARY && !source.isInSystemLibrary) {
//          DartEntry dartEntry = (DartEntry) sourceEntry;
//          if (dartEntry.getValue(DartEntry.IS_LAUNCHABLE) && !dartEntry.getValue(DartEntry.IS_CLIENT)) {
        sources.add(source);
//          }
      }
    }
    return sources;
  }

  @override
  List<Source> get librarySources => _getSources(SourceKind.LIBRARY);

  /**
   * Look through the cache for a task that needs to be performed. Return the
   * task that was found, or `null` if there is no more work to be done.
   */
  AnalysisTask get nextAnalysisTask {
    bool hintsEnabled = _options.hint;
    bool lintsEnabled = _options.lint;
    bool hasBlockedTask = false;
    //
    // Look for incremental analysis
    //
    if (_incrementalAnalysisCache != null &&
        _incrementalAnalysisCache.hasWork) {
      AnalysisTask task =
          new IncrementalAnalysisTask(this, _incrementalAnalysisCache);
      _incrementalAnalysisCache = null;
      return task;
    }
    //
    // Look for a source that needs to be analyzed because it has futures
    // pending.
    //
    if (_pendingFutureSources.isNotEmpty) {
      List<Source> sourcesToRemove = <Source>[];
      AnalysisTask task;
      for (Source source in _pendingFutureSources.keys) {
        SourceEntry sourceEntry = _cache.get(source);
        List<PendingFuture> pendingFutures = _pendingFutureSources[source];
        for (int i = 0; i < pendingFutures.length;) {
          if (pendingFutures[i].evaluate(sourceEntry)) {
            pendingFutures.removeAt(i);
          } else {
            i++;
          }
        }
        if (pendingFutures.isEmpty) {
          sourcesToRemove.add(source);
          continue;
        }
        AnalysisContextImpl_TaskData taskData = _getNextAnalysisTaskForSource(
            source, sourceEntry, true, hintsEnabled, lintsEnabled);
        task = taskData.task;
        if (task != null) {
          break;
        } else if (taskData.isBlocked) {
          hasBlockedTask = true;
        } else {
          // There is no more work to do for this task, so forcibly complete
          // all its pending futures.
          for (PendingFuture pendingFuture in pendingFutures) {
            pendingFuture.forciblyComplete();
          }
          sourcesToRemove.add(source);
        }
      }
      for (Source source in sourcesToRemove) {
        _pendingFutureSources.remove(source);
      }
      if (task != null) {
        return task;
      }
    }
    //
    // Look for a priority source that needs to be analyzed.
    //
    int priorityCount = _priorityOrder.length;
    for (int i = 0; i < priorityCount; i++) {
      Source source = _priorityOrder[i];
      AnalysisContextImpl_TaskData taskData = _getNextAnalysisTaskForSource(
          source, _cache.get(source), true, hintsEnabled, lintsEnabled);
      AnalysisTask task = taskData.task;
      if (task != null) {
        return task;
      } else if (taskData.isBlocked) {
        hasBlockedTask = true;
      }
    }
    if (_neededForResolution != null) {
      List<Source> sourcesToRemove = new List<Source>();
      for (Source source in _neededForResolution) {
        SourceEntry sourceEntry = _cache.get(source);
        if (sourceEntry is DartEntry) {
          DartEntry dartEntry = sourceEntry;
          if (!dartEntry.hasResolvableCompilationUnit) {
            if (dartEntry.getState(DartEntry.PARSED_UNIT) == CacheState.ERROR) {
              sourcesToRemove.add(source);
            } else {
              AnalysisContextImpl_TaskData taskData =
                  _createParseDartTask(source, dartEntry);
              AnalysisTask task = taskData.task;
              if (task != null) {
                return task;
              } else if (taskData.isBlocked) {
                hasBlockedTask = true;
              }
            }
          }
        }
      }
      int count = sourcesToRemove.length;
      for (int i = 0; i < count; i++) {
        _neededForResolution.remove(sourcesToRemove[i]);
      }
    }
    //
    // Look for a non-priority source that needs to be analyzed.
    //
    List<Source> sourcesToRemove = new List<Source>();
    WorkManager_WorkIterator sources = _workManager.iterator();
    try {
      while (sources.hasNext) {
        Source source = sources.next();
        AnalysisContextImpl_TaskData taskData = _getNextAnalysisTaskForSource(
            source, _cache.get(source), false, hintsEnabled, lintsEnabled);
        AnalysisTask task = taskData.task;
        if (task != null) {
          return task;
        } else if (taskData.isBlocked) {
          hasBlockedTask = true;
        } else {
          sourcesToRemove.add(source);
        }
      }
    } finally {
      int count = sourcesToRemove.length;
      for (int i = 0; i < count; i++) {
        _workManager.remove(sourcesToRemove[i]);
      }
    }
    if (hasBlockedTask) {
      // All of the analysis work is blocked waiting for an asynchronous task
      // to complete.
      return WaitForAsyncTask.instance;
    }
    return null;
  }

  @override
  Stream<SourcesChangedEvent> get onSourcesChanged =>
      _onSourcesChangedController.stream;

  /**
   * Make _pendingFutureSources available to unit tests.
   */
  HashMap<Source, List<PendingFuture>> get pendingFutureSources_forTesting =>
      _pendingFutureSources;

  @override
  List<Source> get prioritySources => _priorityOrder;

  @override
  List<AnalysisTarget> get priorityTargets => prioritySources;

  @override
  CachePartition get privateAnalysisCachePartition => _privatePartition;

  @override
  SourceFactory get sourceFactory => _sourceFactory;

  @override
  void set sourceFactory(SourceFactory factory) {
    if (identical(_sourceFactory, factory)) {
      return;
    } else if (factory.context != null) {
      throw new IllegalStateException(
          "Source factories cannot be shared between contexts");
    }
    if (_sourceFactory != null) {
      _sourceFactory.context = null;
    }
    factory.context = this;
    _sourceFactory = factory;
    _coreLibrarySource = _sourceFactory.forUri(DartSdk.DART_CORE);
    _asyncLibrarySource = _sourceFactory.forUri(DartSdk.DART_ASYNC);
    _cache = createCacheFromSourceFactory(factory);
    _invalidateAllLocalResolutionInformation(true);
  }

  @override
  List<Source> get sources {
    List<Source> sources = new List<Source>();
    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
    while (iterator.moveNext()) {
      sources.add(iterator.key);
    }
    return sources;
  }

  /**
   * Return a list of the sources that would be processed by
   * [performAnalysisTask]. This method duplicates, and must therefore be kept
   * in sync with, [getNextAnalysisTask]. This method is intended to be used for
   * testing purposes only.
   */
  List<Source> get sourcesNeedingProcessing {
    HashSet<Source> sources = new HashSet<Source>();
    bool hintsEnabled = _options.hint;
    bool lintsEnabled = _options.lint;

    //
    // Look for priority sources that need to be analyzed.
    //
    for (Source source in _priorityOrder) {
      _getSourcesNeedingProcessing(source, _cache.get(source), true,
          hintsEnabled, lintsEnabled, sources);
    }
    //
    // Look for non-priority sources that need to be analyzed.
    //
    WorkManager_WorkIterator iterator = _workManager.iterator();
    while (iterator.hasNext) {
      Source source = iterator.next();
      _getSourcesNeedingProcessing(source, _cache.get(source), false,
          hintsEnabled, lintsEnabled, sources);
    }
    return new List<Source>.from(sources);
  }

  @override
  AnalysisContextStatistics get statistics {
    AnalysisContextStatisticsImpl statistics =
        new AnalysisContextStatisticsImpl();
    visitCacheItems(statistics._internalPutCacheItem);
    statistics.partitionData = _cache.partitionData;
    return statistics;
  }

  IncrementalAnalysisCache get test_incrementalAnalysisCache {
    return _incrementalAnalysisCache;
  }

  set test_incrementalAnalysisCache(IncrementalAnalysisCache value) {
    _incrementalAnalysisCache = value;
  }

  List<Source> get test_priorityOrder => _priorityOrder;

  @override
  TypeProvider get typeProvider {
    if (_typeProvider != null) {
      return _typeProvider;
    }
    Source coreSource = sourceFactory.forUri(DartSdk.DART_CORE);
    if (coreSource == null) {
      throw new AnalysisException("Could not create a source for dart:core");
    }
    LibraryElement coreElement = computeLibraryElement(coreSource);
    if (coreElement == null) {
      throw new AnalysisException("Could not create an element for dart:core");
    }
    Source asyncSource = sourceFactory.forUri(DartSdk.DART_ASYNC);
    if (asyncSource == null) {
      throw new AnalysisException("Could not create a source for dart:async");
    }
    LibraryElement asyncElement = computeLibraryElement(asyncSource);
    if (asyncElement == null) {
      throw new AnalysisException("Could not create an element for dart:async");
    }
    _typeProvider = new TypeProviderImpl(coreElement, asyncElement);
    return _typeProvider;
  }

  /**
   * Sets the [TypeProvider] for this context.
   */
  void set typeProvider(TypeProvider typeProvider) {
    _typeProvider = typeProvider;
  }

  @override
  TypeSystem get typeSystem {
    if (_typeSystem == null) {
      _typeSystem = TypeSystem.create(this);
    }
    return _typeSystem;
  }

  @override
  List<newContext.WorkManager> get workManagers {
    throw new NotImplementedException('In not task-based AnalysisContext.');
  }

  @override
  void addListener(AnalysisListener listener) {
    if (!_listeners.contains(listener)) {
      _listeners.add(listener);
    }
  }

  @override
  void applyAnalysisDelta(AnalysisDelta delta) {
    ChangeSet changeSet = new ChangeSet();
    delta.analysisLevels.forEach((Source source, AnalysisLevel level) {
      if (level == AnalysisLevel.NONE) {
        changeSet.removedSource(source);
      } else {
        changeSet.addedSource(source);
      }
    });
    applyChanges(changeSet);
  }

  @override
  ApplyChangesStatus applyChanges(ChangeSet changeSet) {
    if (changeSet.isEmpty) {
      return new ApplyChangesStatus(false);
    }
    //
    // First, compute the list of sources that have been removed.
    //
    List<Source> removedSources =
        new List<Source>.from(changeSet.removedSources);
    for (SourceContainer container in changeSet.removedContainers) {
      _addSourcesInContainer(removedSources, container);
    }
    //
    // Then determine which cached results are no longer valid.
    //
    for (Source source in changeSet.addedSources) {
      _sourceAvailable(source);
    }
    for (Source source in changeSet.changedSources) {
      if (_contentCache.getContents(source) != null) {
        // This source is overridden in the content cache, so the change will
        // have no effect. Just ignore it to avoid wasting time doing
        // re-analysis.
        continue;
      }
      _sourceChanged(source);
    }
    changeSet.changedContents.forEach((Source key, String value) {
      _contentsChanged(key, value, false);
    });
    changeSet.changedRanges
        .forEach((Source source, ChangeSet_ContentChange change) {
      _contentRangeChanged(source, change.contents, change.offset,
          change.oldLength, change.newLength);
    });
    for (Source source in changeSet.deletedSources) {
      _sourceDeleted(source);
    }
    for (Source source in removedSources) {
      _sourceRemoved(source);
    }
    _onSourcesChangedController.add(new SourcesChangedEvent(changeSet));
    return new ApplyChangesStatus(true);
  }

  @override
  String computeDocumentationComment(Element element) {
    if (element == null) {
      return null;
    }
    Source source = element.source;
    if (source == null) {
      return null;
    }
    SourceRange docRange = element.docRange;
    if (docRange == null) {
      return null;
    }
    String code = getContents(source).data;
    String comment = code.substring(docRange.offset, docRange.end);
    return comment.replaceAll('\r\n', '\n');
  }

  @override
  List<AnalysisError> computeErrors(Source source) {
    bool enableHints = _options.hint;
    bool enableLints = _options.lint;

    SourceEntry sourceEntry = _getReadableSourceEntry(source);
    if (sourceEntry is DartEntry) {
      List<AnalysisError> errors = new List<AnalysisError>();
      try {
        DartEntry dartEntry = sourceEntry;
        ListUtilities.addAll(
            errors, _getDartScanData(source, dartEntry, DartEntry.SCAN_ERRORS));
        dartEntry = _getReadableDartEntry(source);
        ListUtilities.addAll(errors,
            _getDartParseData(source, dartEntry, DartEntry.PARSE_ERRORS));
        dartEntry = _getReadableDartEntry(source);
        if (dartEntry.getValue(DartEntry.SOURCE_KIND) == SourceKind.LIBRARY) {
          ListUtilities.addAll(
              errors,
              _getDartResolutionData(
                  source, source, dartEntry, DartEntry.RESOLUTION_ERRORS));
          dartEntry = _getReadableDartEntry(source);
          ListUtilities.addAll(
              errors,
              _getDartVerificationData(
                  source, source, dartEntry, DartEntry.VERIFICATION_ERRORS));
          if (enableHints) {
            dartEntry = _getReadableDartEntry(source);
            ListUtilities.addAll(errors,
                _getDartHintData(source, source, dartEntry, DartEntry.HINTS));
          }
          if (enableLints) {
            dartEntry = _getReadableDartEntry(source);
            ListUtilities.addAll(errors,
                _getDartLintData(source, source, dartEntry, DartEntry.LINTS));
          }
        } else {
          List<Source> libraries = getLibrariesContaining(source);
          for (Source librarySource in libraries) {
            ListUtilities.addAll(
                errors,
                _getDartResolutionData(source, librarySource, dartEntry,
                    DartEntry.RESOLUTION_ERRORS));
            dartEntry = _getReadableDartEntry(source);
            ListUtilities.addAll(
                errors,
                _getDartVerificationData(source, librarySource, dartEntry,
                    DartEntry.VERIFICATION_ERRORS));
            if (enableHints) {
              dartEntry = _getReadableDartEntry(source);
              ListUtilities.addAll(
                  errors,
                  _getDartHintData(
                      source, librarySource, dartEntry, DartEntry.HINTS));
            }
            if (enableLints) {
              dartEntry = _getReadableDartEntry(source);
              ListUtilities.addAll(
                  errors,
                  _getDartLintData(
                      source, librarySource, dartEntry, DartEntry.LINTS));
            }
          }
        }
      } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
        AnalysisEngine.instance.logger.logInformation(
            "Could not compute errors",
            new CaughtException(exception, stackTrace));
      }
      if (errors.isEmpty) {
        return AnalysisError.NO_ERRORS;
      }
      return errors;
    } else if (sourceEntry is HtmlEntry) {
      HtmlEntry htmlEntry = sourceEntry;
      try {
        return _getHtmlResolutionData2(
            source, htmlEntry, HtmlEntry.RESOLUTION_ERRORS);
      } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
        AnalysisEngine.instance.logger.logInformation(
            "Could not compute errors",
            new CaughtException(exception, stackTrace));
      }
    }
    return AnalysisError.NO_ERRORS;
  }

  @override
  List<Source> computeExportedLibraries(Source source) => _getDartParseData2(
      source, DartEntry.EXPORTED_LIBRARIES, Source.EMPTY_LIST);

  @override
  @deprecated
  HtmlElement computeHtmlElement(Source source) =>
      _getHtmlResolutionData(source, HtmlEntry.ELEMENT, null);

  @override
  List<Source> computeImportedLibraries(Source source) => _getDartParseData2(
      source, DartEntry.IMPORTED_LIBRARIES, Source.EMPTY_LIST);

  @override
  SourceKind computeKindOf(Source source) {
    SourceEntry sourceEntry = _getReadableSourceEntry(source);
    if (sourceEntry == null) {
      return SourceKind.UNKNOWN;
    } else if (sourceEntry is DartEntry) {
      try {
        return _getDartParseData(source, sourceEntry, DartEntry.SOURCE_KIND);
      } on AnalysisException {
        return SourceKind.UNKNOWN;
      }
    }
    return sourceEntry.kind;
  }

  @override
  LibraryElement computeLibraryElement(Source source) =>
      _getDartResolutionData2(source, source, DartEntry.ELEMENT, null);

  @override
  LineInfo computeLineInfo(Source source) {
    SourceEntry sourceEntry = _getReadableSourceEntry(source);
    try {
      if (sourceEntry is HtmlEntry) {
        return _getHtmlParseData(source, SourceEntry.LINE_INFO, null);
      } else if (sourceEntry is DartEntry) {
        return _getDartScanData2(source, SourceEntry.LINE_INFO, null);
      }
    } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
      AnalysisEngine.instance.logger.logInformation(
          "Could not compute ${SourceEntry.LINE_INFO}",
          new CaughtException(exception, stackTrace));
    }
    return null;
  }

  @override
  CompilationUnit computeResolvableCompilationUnit(Source source) {
    DartEntry dartEntry = _getReadableDartEntry(source);
    if (dartEntry == null) {
      throw new AnalysisException(
          "computeResolvableCompilationUnit for non-Dart: ${source.fullName}");
    }
    dartEntry = _cacheDartParseData(source, dartEntry, DartEntry.PARSED_UNIT);
    CompilationUnit unit = dartEntry.resolvableCompilationUnit;
    if (unit == null) {
      throw new AnalysisException(
          "Internal error: computeResolvableCompilationUnit could not parse ${source.fullName}",
          new CaughtException(dartEntry.exception, null));
    }
    return unit;
  }

  @override
  CancelableFuture<CompilationUnit> computeResolvedCompilationUnitAsync(
      Source unitSource, Source librarySource) {
    return new _AnalysisFutureHelper<CompilationUnit>(this)
        .computeAsync(unitSource, (SourceEntry sourceEntry) {
      if (sourceEntry is DartEntry) {
        if (sourceEntry.getStateInLibrary(
                DartEntry.RESOLVED_UNIT, librarySource) ==
            CacheState.ERROR) {
          throw sourceEntry.exception;
        }
        return sourceEntry.getValueInLibrary(
            DartEntry.RESOLVED_UNIT, librarySource);
      }
      throw new AnalysisNotScheduledError();
    });
  }

  @override
  Object computeResult(AnalysisTarget target, ResultDescriptor result) {
    return result.defaultValue;
  }

  /**
   * Create an analysis cache based on the given source [factory].
   */
  AnalysisCache createCacheFromSourceFactory(SourceFactory factory) {
    if (factory == null) {
      return new AnalysisCache(<CachePartition>[_privatePartition]);
    }
    DartSdk sdk = factory.dartSdk;
    if (sdk == null) {
      return new AnalysisCache(<CachePartition>[_privatePartition]);
    }
    return new AnalysisCache(<CachePartition>[
      AnalysisEngine.instance.partitionManager.forSdk(sdk),
      _privatePartition
    ]);
  }

  @override
  void dispose() {
    _disposed = true;
    for (List<PendingFuture> pendingFutures in _pendingFutureSources.values) {
      for (PendingFuture pendingFuture in pendingFutures) {
        pendingFuture.forciblyComplete();
      }
    }
    _pendingFutureSources.clear();
  }

  @override
  List<CompilationUnit> ensureResolvedDartUnits(Source unitSource) {
    SourceEntry sourceEntry = _cache.get(unitSource);
    if (sourceEntry is! DartEntry) {
      return null;
    }
    DartEntry dartEntry = sourceEntry;
    // Check every library.
    List<CompilationUnit> units = <CompilationUnit>[];
    List<Source> containingLibraries = dartEntry.containingLibraries;
    for (Source librarySource in containingLibraries) {
      CompilationUnit unit =
          dartEntry.getValueInLibrary(DartEntry.RESOLVED_UNIT, librarySource);
      if (unit == null) {
        units = null;
        break;
      }
      units.add(unit);
    }
    // Invalidate the flushed RESOLVED_UNIT to force it eventually.
    if (units == null) {
      bool shouldBeScheduled = false;
      for (Source librarySource in containingLibraries) {
        if (dartEntry.getStateInLibrary(
                DartEntry.RESOLVED_UNIT, librarySource) ==
            CacheState.FLUSHED) {
          dartEntry.setStateInLibrary(
              DartEntry.RESOLVED_UNIT, librarySource, CacheState.INVALID);
          shouldBeScheduled = true;
        }
      }
      if (shouldBeScheduled) {
        _workManager.add(unitSource, SourcePriority.UNKNOWN);
      }
      // We cannot provide resolved units right now,
      // but the future analysis will.
      return null;
    }
    // done
    return units;
  }

  @override
  bool exists(Source source) {
    if (source == null) {
      return false;
    }
    if (_contentCache.getContents(source) != null) {
      return true;
    }
    return source.exists();
  }

  @override
  cache.CacheEntry getCacheEntry(AnalysisTarget target) {
    return null;
  }

  @override
  CompilationUnitElement getCompilationUnitElement(
      Source unitSource, Source librarySource) {
    LibraryElement libraryElement = getLibraryElement(librarySource);
    if (libraryElement != null) {
      // try defining unit
      CompilationUnitElement definingUnit =
          libraryElement.definingCompilationUnit;
      if (definingUnit.source == unitSource) {
        return definingUnit;
      }
      // try parts
      for (CompilationUnitElement partUnit in libraryElement.parts) {
        if (partUnit.source == unitSource) {
          return partUnit;
        }
      }
    }
    return null;
  }

  @override
  Object getConfigurationData(ResultDescriptor key) => _configurationData[key];

  @override
  TimestampedData<String> getContents(Source source) {
    String contents = _contentCache.getContents(source);
    if (contents != null) {
      return new TimestampedData<String>(
          _contentCache.getModificationStamp(source), contents);
    }
    return source.contents;
  }

  @override
  InternalAnalysisContext getContextFor(Source source) {
    InternalAnalysisContext context = _cache.getContextFor(source);
    return context == null ? this : context;
  }

  @override
  Element getElement(ElementLocation location) {
    // TODO(brianwilkerson) This should not be a "get" method.
    try {
      List<String> components = location.components;
      Source source = _computeSourceFromEncoding(components[0]);
      String sourceName = source.shortName;
      if (AnalysisEngine.isDartFileName(sourceName)) {
        ElementImpl element = computeLibraryElement(source) as ElementImpl;
        for (int i = 1; i < components.length; i++) {
          if (element == null) {
            return null;
          }
          element = element.getChild(components[i]);
        }
        return element;
      }
      if (AnalysisEngine.isHtmlFileName(sourceName)) {
        return computeHtmlElement(source);
      }
    } catch (exception) {
      // If the location cannot be decoded for some reason then the underlying
      // cause should have been logged already and we can fall though to return
      // null.
    }
    return null;
  }

  @override
  AnalysisErrorInfo getErrors(Source source) {
    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
    if (sourceEntry is DartEntry) {
      DartEntry dartEntry = sourceEntry;
      return new AnalysisErrorInfoImpl(
          dartEntry.allErrors, dartEntry.getValue(SourceEntry.LINE_INFO));
    } else if (sourceEntry is HtmlEntry) {
      HtmlEntry htmlEntry = sourceEntry;
      return new AnalysisErrorInfoImpl(
          htmlEntry.allErrors, htmlEntry.getValue(SourceEntry.LINE_INFO));
    }
    return new AnalysisErrorInfoImpl(AnalysisError.NO_ERRORS, null);
  }

  @override
  @deprecated
  HtmlElement getHtmlElement(Source source) {
    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
    if (sourceEntry is HtmlEntry) {
      return sourceEntry.getValue(HtmlEntry.ELEMENT);
    }
    return null;
  }

  @override
  List<Source> getHtmlFilesReferencing(Source source) {
    SourceKind sourceKind = getKindOf(source);
    if (sourceKind == null) {
      return Source.EMPTY_LIST;
    }
    List<Source> htmlSources = new List<Source>();
    while (true) {
      if (sourceKind == SourceKind.PART) {
        List<Source> librarySources = getLibrariesContaining(source);
        MapIterator<Source, SourceEntry> partIterator = _cache.iterator();
        while (partIterator.moveNext()) {
          SourceEntry sourceEntry = partIterator.value;
          if (sourceEntry.kind == SourceKind.HTML) {
            List<Source> referencedLibraries = (sourceEntry as HtmlEntry)
                .getValue(HtmlEntry.REFERENCED_LIBRARIES);
            if (_containsAny(referencedLibraries, librarySources)) {
              htmlSources.add(partIterator.key);
            }
          }
        }
      } else {
        MapIterator<Source, SourceEntry> iterator = _cache.iterator();
        while (iterator.moveNext()) {
          SourceEntry sourceEntry = iterator.value;
          if (sourceEntry.kind == SourceKind.HTML) {
            List<Source> referencedLibraries = (sourceEntry as HtmlEntry)
                .getValue(HtmlEntry.REFERENCED_LIBRARIES);
            if (_contains(referencedLibraries, source)) {
              htmlSources.add(iterator.key);
            }
          }
        }
      }
      break;
    }
    if (htmlSources.isEmpty) {
      return Source.EMPTY_LIST;
    }
    return htmlSources;
  }

  @override
  SourceKind getKindOf(Source source) {
    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
    if (sourceEntry == null) {
      return SourceKind.UNKNOWN;
    }
    return sourceEntry.kind;
  }

  @override
  List<Source> getLibrariesContaining(Source source) {
    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
    if (sourceEntry is DartEntry) {
      return sourceEntry.containingLibraries;
    }
    return Source.EMPTY_LIST;
  }

  @override
  List<Source> getLibrariesDependingOn(Source librarySource) {
    List<Source> dependentLibraries = new List<Source>();
    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
    while (iterator.moveNext()) {
      SourceEntry sourceEntry = iterator.value;
      if (sourceEntry.kind == SourceKind.LIBRARY) {
        if (_contains(
            (sourceEntry as DartEntry).getValue(DartEntry.EXPORTED_LIBRARIES),
            librarySource)) {
          dependentLibraries.add(iterator.key);
        }
        if (_contains(
            (sourceEntry as DartEntry).getValue(DartEntry.IMPORTED_LIBRARIES),
            librarySource)) {
          dependentLibraries.add(iterator.key);
        }
      }
    }
    if (dependentLibraries.isEmpty) {
      return Source.EMPTY_LIST;
    }
    return dependentLibraries;
  }

  @override
  List<Source> getLibrariesReferencedFromHtml(Source htmlSource) {
    SourceEntry sourceEntry = getReadableSourceEntryOrNull(htmlSource);
    if (sourceEntry is HtmlEntry) {
      HtmlEntry htmlEntry = sourceEntry;
      return htmlEntry.getValue(HtmlEntry.REFERENCED_LIBRARIES);
    }
    return Source.EMPTY_LIST;
  }

  @override
  LibraryElement getLibraryElement(Source source) {
    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
    if (sourceEntry is DartEntry) {
      return sourceEntry.getValue(DartEntry.ELEMENT);
    }
    return null;
  }

  @override
  LineInfo getLineInfo(Source source) {
    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
    if (sourceEntry != null) {
      return sourceEntry.getValue(SourceEntry.LINE_INFO);
    }
    return null;
  }

  @override
  int getModificationStamp(Source source) {
    int stamp = _contentCache.getModificationStamp(source);
    if (stamp != null) {
      return stamp;
    }
    return source.modificationStamp;
  }

  @override
  ChangeNoticeImpl getNotice(Source source) {
    ChangeNoticeImpl notice = _pendingNotices[source];
    if (notice == null) {
      notice = new ChangeNoticeImpl(source);
      _pendingNotices[source] = notice;
    }
    return notice;
  }

  @override
  Namespace getPublicNamespace(LibraryElement library) {
    // TODO(brianwilkerson) Rename this to not start with 'get'.
    // Note that this is not part of the API of the interface.
    Source source = library.definingCompilationUnit.source;
    DartEntry dartEntry = _getReadableDartEntry(source);
    if (dartEntry == null) {
      return null;
    }
    Namespace namespace = null;
    if (identical(dartEntry.getValue(DartEntry.ELEMENT), library)) {
      namespace = dartEntry.getValue(DartEntry.PUBLIC_NAMESPACE);
    }
    if (namespace == null) {
      NamespaceBuilder builder = new NamespaceBuilder();
      namespace = builder.createPublicNamespaceForLibrary(library);
      if (dartEntry == null) {
        AnalysisEngine.instance.logger.logError(
            "Could not compute the public namespace for ${library.source.fullName}",
            new CaughtException(
                new AnalysisException(
                    "A Dart file became a non-Dart file: ${source.fullName}"),
                null));
        return null;
      }
      if (identical(dartEntry.getValue(DartEntry.ELEMENT), library)) {
        dartEntry.setValue(DartEntry.PUBLIC_NAMESPACE, namespace);
      }
    }
    return namespace;
  }

  /**
   * Return the cache entry associated with the given [source], or `null` if
   * there is no entry associated with the source.
   */
  SourceEntry getReadableSourceEntryOrNull(Source source) => _cache.get(source);

  @override
  CompilationUnit getResolvedCompilationUnit(
      Source unitSource, LibraryElement library) {
    if (library == null) {
      return null;
    }
    return getResolvedCompilationUnit2(unitSource, library.source);
  }

  @override
  CompilationUnit getResolvedCompilationUnit2(
      Source unitSource, Source librarySource) {
    SourceEntry sourceEntry = getReadableSourceEntryOrNull(unitSource);
    if (sourceEntry is DartEntry) {
      return sourceEntry.getValueInLibrary(
          DartEntry.RESOLVED_UNIT, librarySource);
    }
    return null;
  }

  @override
  @deprecated
  ht.HtmlUnit getResolvedHtmlUnit(Source htmlSource) {
    SourceEntry sourceEntry = getReadableSourceEntryOrNull(htmlSource);
    if (sourceEntry is HtmlEntry) {
      HtmlEntry htmlEntry = sourceEntry;
      return htmlEntry.getValue(HtmlEntry.RESOLVED_UNIT);
    }
    return null;
  }

  @override
  Object getResult(AnalysisTarget target, ResultDescriptor result) {
    return result.defaultValue;
  }

  @override
  List<Source> getSourcesWithFullName(String path) {
    List<Source> sources = <Source>[];
    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
    while (iterator.moveNext()) {
      if (iterator.key.fullName == path) {
        sources.add(iterator.key);
      }
    }
    return sources;
  }

  @override
  bool handleContentsChanged(
      Source source, String originalContents, String newContents, bool notify) {
    SourceEntry sourceEntry = _cache.get(source);
    if (sourceEntry == null) {
      return false;
    }
    bool changed = newContents != originalContents;
    if (newContents != null) {
      if (changed) {
        _incrementalAnalysisCache =
            IncrementalAnalysisCache.clear(_incrementalAnalysisCache, source);
        if (!analysisOptions.incremental ||
            !_tryPoorMansIncrementalResolution(source, newContents)) {
          _sourceChanged(source);
        }
        sourceEntry.modificationTime =
            _contentCache.getModificationStamp(source);
        sourceEntry.setValue(SourceEntry.CONTENT, newContents);
      } else {
        sourceEntry.modificationTime =
            _contentCache.getModificationStamp(source);
      }
    } else if (originalContents != null) {
      _incrementalAnalysisCache =
          IncrementalAnalysisCache.clear(_incrementalAnalysisCache, source);
      // We are removing the overlay for the file, check if the file's
      // contents is the same as it was in the overlay.
      try {
        TimestampedData<String> fileContents = getContents(source);
        newContents = fileContents.data;
        sourceEntry.modificationTime = fileContents.modificationTime;
        if (newContents == originalContents) {
          sourceEntry.setValue(SourceEntry.CONTENT, newContents);
          changed = false;
        }
      } catch (e) {}
      // If not the same content (e.g. the file is being closed without save),
      // then force analysis.
      if (changed) {
        if (!analysisOptions.incremental ||
            !_tryPoorMansIncrementalResolution(source, newContents)) {
          _sourceChanged(source);
        }
      }
    }
    if (notify && changed) {
      _onSourcesChangedController
          .add(new SourcesChangedEvent.changedContent(source, newContents));
    }
    return changed;
  }

  @override
  void invalidateLibraryHints(Source librarySource) {
    SourceEntry sourceEntry = _cache.get(librarySource);
    if (sourceEntry is! DartEntry) {
      return;
    }
    DartEntry dartEntry = sourceEntry;
    // Prepare sources to invalidate hints in.
    List<Source> sources = <Source>[librarySource];
    sources.addAll(dartEntry.getValue(DartEntry.INCLUDED_PARTS));
    // Invalidate hints and lints.
    for (Source source in sources) {
      DartEntry dartEntry = _cache.get(source);
      if (dartEntry.getStateInLibrary(DartEntry.HINTS, librarySource) ==
          CacheState.VALID) {
        dartEntry.setStateInLibrary(
            DartEntry.HINTS, librarySource, CacheState.INVALID);
      }
      if (dartEntry.getStateInLibrary(DartEntry.LINTS, librarySource) ==
          CacheState.VALID) {
        dartEntry.setStateInLibrary(
            DartEntry.LINTS, librarySource, CacheState.INVALID);
      }
    }
  }

  @override
  bool isClientLibrary(Source librarySource) {
    SourceEntry sourceEntry = _getReadableSourceEntry(librarySource);
    if (sourceEntry is DartEntry) {
      DartEntry dartEntry = sourceEntry;
      return dartEntry.getValue(DartEntry.IS_CLIENT) &&
          dartEntry.getValue(DartEntry.IS_LAUNCHABLE);
    }
    return false;
  }

  @override
  bool isServerLibrary(Source librarySource) {
    SourceEntry sourceEntry = _getReadableSourceEntry(librarySource);
    if (sourceEntry is DartEntry) {
      DartEntry dartEntry = sourceEntry;
      return !dartEntry.getValue(DartEntry.IS_CLIENT) &&
          dartEntry.getValue(DartEntry.IS_LAUNCHABLE);
    }
    return false;
  }

  @override
  Stream<ComputedResult> onResultComputed(ResultDescriptor descriptor) {
    throw new NotImplementedException('In not task-based AnalysisContext.');
  }

  @override
  CompilationUnit parseCompilationUnit(Source source) =>
      _getDartParseData2(source, DartEntry.PARSED_UNIT, null);

  @override
  Document parseHtmlDocument(Source source) {
    return null;
  }

  @override
  @deprecated
  ht.HtmlUnit parseHtmlUnit(Source source) =>
      _getHtmlParseData(source, HtmlEntry.PARSED_UNIT, null);

  @override
  AnalysisResult performAnalysisTask() {
    if (_TRACE_PERFORM_TASK) {
      print("----------------------------------------");
    }
    return PerformanceStatistics.performAnaysis.makeCurrentWhile(() {
      int getStart = JavaSystem.currentTimeMillis();
      AnalysisTask task = PerformanceStatistics.nextTask
          .makeCurrentWhile(() => nextAnalysisTask);
      int getEnd = JavaSystem.currentTimeMillis();
      if (task == null) {
        _validateLastIncrementalResolutionResult();
        if (_performAnalysisTaskStopwatch != null) {
          AnalysisEngine.instance.instrumentationService.logPerformance(
              AnalysisPerformanceKind.FULL,
              _performAnalysisTaskStopwatch,
              'context_id=$_id');
          _performAnalysisTaskStopwatch = null;
        }
        return new AnalysisResult(
            _getChangeNotices(true), getEnd - getStart, null, -1);
      }
      if (_performAnalysisTaskStopwatch == null) {
        _performAnalysisTaskStopwatch = new Stopwatch()..start();
      }
      String taskDescription = task.toString();
      _notifyAboutToPerformTask(taskDescription);
      if (_TRACE_PERFORM_TASK) {
        print(taskDescription);
      }
      int performStart = JavaSystem.currentTimeMillis();
      try {
        task.perform(_resultRecorder);
      } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
        AnalysisEngine.instance.logger.logInformation(
            "Could not perform analysis task: $taskDescription",
            new CaughtException(exception, stackTrace));
      } on AnalysisException catch (exception, stackTrace) {
        if (exception.cause is! JavaIOException) {
          AnalysisEngine.instance.logger.logError(
              "Internal error while performing the task: $task",
              new CaughtException(exception, stackTrace));
        }
      }
      int performEnd = JavaSystem.currentTimeMillis();
      List<ChangeNotice> notices = _getChangeNotices(false);
      int noticeCount = notices.length;
      for (int i = 0; i < noticeCount; i++) {
        ChangeNotice notice = notices[i];
        Source source = notice.source;
        // TODO(brianwilkerson) Figure out whether the compilation unit is
        // always resolved, or whether we need to decide whether to invoke the
        // "parsed" or "resolved" method. This might be better done when
        // recording task results in order to reduce the chance of errors.
//        if (notice.getCompilationUnit() != null) {
//          notifyResolvedDart(source, notice.getCompilationUnit());
//        } else if (notice.getHtmlUnit() != null) {
//          notifyResolvedHtml(source, notice.getHtmlUnit());
//        }
        _notifyErrors(source, notice.errors, notice.lineInfo);
      }
      return new AnalysisResult(notices, getEnd - getStart,
          task.runtimeType.toString(), performEnd - performStart);
    });
  }

  @override
  void recordLibraryElements(Map<Source, LibraryElement> elementMap) {
    Source htmlSource = _sourceFactory.forUri(DartSdk.DART_HTML);
    elementMap.forEach((Source librarySource, LibraryElement library) {
      //
      // Cache the element in the library's info.
      //
      DartEntry dartEntry = _getReadableDartEntry(librarySource);
      if (dartEntry != null) {
        _recordElementData(dartEntry, library, library.source, htmlSource);
        dartEntry.setState(SourceEntry.CONTENT, CacheState.FLUSHED);
        dartEntry.setValue(SourceEntry.LINE_INFO, new LineInfo(<int>[0]));
        // DartEntry.ELEMENT - set in recordElementData
        dartEntry.setValue(DartEntry.EXPORTED_LIBRARIES, Source.EMPTY_LIST);
        dartEntry.setValue(DartEntry.IMPORTED_LIBRARIES, Source.EMPTY_LIST);
        dartEntry.setValue(DartEntry.INCLUDED_PARTS, Source.EMPTY_LIST);
        // DartEntry.IS_CLIENT - set in recordElementData
        // DartEntry.IS_LAUNCHABLE - set in recordElementData
        dartEntry.setValue(DartEntry.PARSE_ERRORS, AnalysisError.NO_ERRORS);
        dartEntry.setState(DartEntry.PARSED_UNIT, CacheState.FLUSHED);
        dartEntry.setState(DartEntry.PUBLIC_NAMESPACE, CacheState.FLUSHED);
        dartEntry.setValue(DartEntry.SCAN_ERRORS, AnalysisError.NO_ERRORS);
        dartEntry.setValue(DartEntry.SOURCE_KIND, SourceKind.LIBRARY);
        dartEntry.setState(DartEntry.TOKEN_STREAM, CacheState.FLUSHED);
        dartEntry.setValueInLibrary(DartEntry.RESOLUTION_ERRORS, librarySource,
            AnalysisError.NO_ERRORS);
        dartEntry.setStateInLibrary(
            DartEntry.RESOLVED_UNIT, librarySource, CacheState.FLUSHED);
        dartEntry.setValueInLibrary(DartEntry.VERIFICATION_ERRORS,
            librarySource, AnalysisError.NO_ERRORS);
        dartEntry.setValueInLibrary(
            DartEntry.HINTS, librarySource, AnalysisError.NO_ERRORS);
        dartEntry.setValueInLibrary(
            DartEntry.LINTS, librarySource, AnalysisError.NO_ERRORS);
      }
    });
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  DartEntry recordResolveDartLibraryCycleTaskResults(
      ResolveDartLibraryCycleTask task) {
    LibraryResolver2 resolver = task.libraryResolver;
    CaughtException thrownException = task.exception;
    Source unitSource = task.unitSource;
    DartEntry unitEntry = _getReadableDartEntry(unitSource);
    if (resolver != null) {
      //
      // The resolver should only be null if an exception was thrown before (or
      // while) it was being created.
      //
      List<ResolvableLibrary> resolvedLibraries = resolver.resolvedLibraries;
      if (resolvedLibraries == null) {
        //
        // The resolved libraries should only be null if an exception was thrown
        // during resolution.
        //
        if (thrownException == null) {
          var message = "In recordResolveDartLibraryCycleTaskResults, "
              "resolvedLibraries was null and there was no thrown exception";
          unitEntry.recordResolutionError(
              new CaughtException(new AnalysisException(message), null));
        } else {
          unitEntry.recordResolutionError(thrownException);
        }
        _removeFromCache(unitSource);
        if (thrownException != null) {
          throw new AnalysisException('<rethrow>', thrownException);
        }
        return unitEntry;
      }
      Source htmlSource = sourceFactory.forUri(DartSdk.DART_HTML);
      RecordingErrorListener errorListener = resolver.errorListener;
      for (ResolvableLibrary library in resolvedLibraries) {
        Source librarySource = library.librarySource;
        for (Source source in library.compilationUnitSources) {
          CompilationUnit unit = library.getAST(source);
          List<AnalysisError> errors = errorListener.getErrorsForSource(source);
          LineInfo lineInfo = getLineInfo(source);
          DartEntry dartEntry = _cache.get(source);
          if (thrownException == null) {
            dartEntry.setState(DartEntry.PARSED_UNIT, CacheState.FLUSHED);
            dartEntry.setValueInLibrary(
                DartEntry.RESOLVED_UNIT, librarySource, unit);
            dartEntry.setValueInLibrary(
                DartEntry.RESOLUTION_ERRORS, librarySource, errors);
            if (source == librarySource) {
              _recordElementData(
                  dartEntry, library.libraryElement, librarySource, htmlSource);
            }
            _cache.storedAst(source);
          } else {
            dartEntry.recordResolutionErrorInLibrary(
                librarySource, thrownException);
          }
          if (source != librarySource) {
            _workManager.add(source, SourcePriority.PRIORITY_PART);
          }
          ChangeNoticeImpl notice = getNotice(source);
          notice.resolvedDartUnit = unit;
          notice.setErrors(dartEntry.allErrors, lineInfo);
        }
      }
    }
    if (thrownException != null) {
      throw new AnalysisException('<rethrow>', thrownException);
    }
    return unitEntry;
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  DartEntry recordResolveDartLibraryTaskResults(ResolveDartLibraryTask task) {
    LibraryResolver resolver = task.libraryResolver;
    CaughtException thrownException = task.exception;
    Source unitSource = task.unitSource;
    DartEntry unitEntry = _getReadableDartEntry(unitSource);
    if (resolver != null) {
      //
      // The resolver should only be null if an exception was thrown before (or
      // while) it was being created.
      //
      Set<Library> resolvedLibraries = resolver.resolvedLibraries;
      if (resolvedLibraries == null) {
        //
        // The resolved libraries should only be null if an exception was thrown
        // during resolution.
        //
        if (thrownException == null) {
          String message = "In recordResolveDartLibraryTaskResults, "
              "resolvedLibraries was null and there was no thrown exception";
          unitEntry.recordResolutionError(
              new CaughtException(new AnalysisException(message), null));
        } else {
          unitEntry.recordResolutionError(thrownException);
        }
        _removeFromCache(unitSource);
        if (thrownException != null) {
          throw new AnalysisException('<rethrow>', thrownException);
        }
        return unitEntry;
      }
      Source htmlSource = sourceFactory.forUri(DartSdk.DART_HTML);
      RecordingErrorListener errorListener = resolver.errorListener;
      for (Library library in resolvedLibraries) {
        Source librarySource = library.librarySource;
        for (Source source in library.compilationUnitSources) {
          CompilationUnit unit = library.getAST(source);
          List<AnalysisError> errors = errorListener.getErrorsForSource(source);
          LineInfo lineInfo = getLineInfo(source);
          DartEntry dartEntry = _cache.get(source);
          if (thrownException == null) {
            dartEntry.setValue(SourceEntry.LINE_INFO, lineInfo);
            dartEntry.setState(DartEntry.PARSED_UNIT, CacheState.FLUSHED);
            dartEntry.setValueInLibrary(
                DartEntry.RESOLVED_UNIT, librarySource, unit);
            dartEntry.setValueInLibrary(
                DartEntry.RESOLUTION_ERRORS, librarySource, errors);
            if (source == librarySource) {
              _recordElementData(
                  dartEntry, library.libraryElement, librarySource, htmlSource);
            }
            _cache.storedAst(source);
          } else {
            dartEntry.recordResolutionErrorInLibrary(
                librarySource, thrownException);
            _removeFromCache(source);
          }
          if (source != librarySource) {
            _workManager.add(source, SourcePriority.PRIORITY_PART);
          }
          ChangeNoticeImpl notice = getNotice(source);
          notice.resolvedDartUnit = unit;
          notice.setErrors(dartEntry.allErrors, lineInfo);
        }
      }
    }
    if (thrownException != null) {
      throw new AnalysisException('<rethrow>', thrownException);
    }
    return unitEntry;
  }

  @override
  void removeListener(AnalysisListener listener) {
    _listeners.remove(listener);
  }

  @override
  CompilationUnit resolveCompilationUnit(
      Source unitSource, LibraryElement library) {
    if (library == null) {
      return null;
    }
    return resolveCompilationUnit2(unitSource, library.source);
  }

  @override
  CompilationUnit resolveCompilationUnit2(
          Source unitSource, Source librarySource) =>
      _getDartResolutionData2(
          unitSource, librarySource, DartEntry.RESOLVED_UNIT, null);

  @override
  @deprecated
  ht.HtmlUnit resolveHtmlUnit(Source htmlSource) {
    computeHtmlElement(htmlSource);
    return parseHtmlUnit(htmlSource);
  }

  @override
  void setChangedContents(Source source, String contents, int offset,
      int oldLength, int newLength) {
    if (_contentRangeChanged(source, contents, offset, oldLength, newLength)) {
      _onSourcesChangedController.add(new SourcesChangedEvent.changedRange(
          source, contents, offset, oldLength, newLength));
    }
  }

  @override
  void setConfigurationData(ResultDescriptor key, Object data) {
    _configurationData[key] = data;
  }

  @override
  void setContents(Source source, String contents) {
    _contentsChanged(source, contents, true);
  }

  @override
  bool shouldErrorsBeAnalyzed(Source source, Object entry) {
    DartEntry dartEntry = entry;
    if (source.isInSystemLibrary) {
      return _generateSdkErrors;
    } else if (!dartEntry.explicitlyAdded) {
      return _generateImplicitErrors;
    } else {
      return true;
    }
  }

  @override
  void test_flushAstStructures(Source source) {
    DartEntry dartEntry = getReadableSourceEntryOrNull(source);
    dartEntry.flushAstStructures();
  }

  @override
  bool validateCacheConsistency() {
    int consistencyCheckStart = JavaSystem.nanoTime();
    List<Source> changedSources = new List<Source>();
    List<Source> missingSources = new List<Source>();
    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
    while (iterator.moveNext()) {
      Source source = iterator.key;
      SourceEntry sourceEntry = iterator.value;
      int sourceTime = getModificationStamp(source);
      if (sourceTime != sourceEntry.modificationTime) {
        changedSources.add(source);
      }
      if (sourceEntry.exception != null) {
        if (!exists(source)) {
          missingSources.add(source);
        }
      }
    }
    int count = changedSources.length;
    for (int i = 0; i < count; i++) {
      _sourceChanged(changedSources[i]);
    }
    int removalCount = 0;
    for (Source source in missingSources) {
      if (getLibrariesContaining(source).isEmpty &&
          getLibrariesDependingOn(source).isEmpty) {
        _removeFromCache(source);
        removalCount++;
      }
    }
    int consistencyCheckEnd = JavaSystem.nanoTime();
    if (changedSources.length > 0 || missingSources.length > 0) {
      StringBuffer buffer = new StringBuffer();
      buffer.write("Consistency check took ");
      buffer.write((consistencyCheckEnd - consistencyCheckStart) / 1000000.0);
      buffer.writeln(" ms and found");
      buffer.write("  ");
      buffer.write(changedSources.length);
      buffer.writeln(" inconsistent entries");
      buffer.write("  ");
      buffer.write(missingSources.length);
      buffer.write(" missing sources (");
      buffer.write(removalCount);
      buffer.writeln(" removed");
      for (Source source in missingSources) {
        buffer.write("    ");
        buffer.writeln(source.fullName);
      }
      _logInformation(buffer.toString());
    }
    return changedSources.length > 0;
  }

  @deprecated
  @override
  void visitCacheItems(void callback(Source source, SourceEntry dartEntry,
      DataDescriptor rowDesc, CacheState state)) {
    bool hintsEnabled = _options.hint;
    bool lintsEnabled = _options.lint;
    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
    while (iterator.moveNext()) {
      Source source = iterator.key;
      SourceEntry sourceEntry = iterator.value;
      for (DataDescriptor descriptor in sourceEntry.descriptors) {
        if (descriptor == DartEntry.SOURCE_KIND) {
          // The source kind is always valid, so the state isn't interesting.
          continue;
        } else if (descriptor == DartEntry.CONTAINING_LIBRARIES) {
          // The list of containing libraries is always valid, so the state
          // isn't interesting.
          continue;
        } else if (descriptor == DartEntry.PUBLIC_NAMESPACE) {
          // The public namespace isn't computed by performAnalysisTask()
          // and therefore isn't interesting.
          continue;
        } else if (descriptor == HtmlEntry.HINTS) {
          // We are not currently recording any hints related to HTML.
          continue;
        }
        callback(
            source, sourceEntry, descriptor, sourceEntry.getState(descriptor));
      }
      if (sourceEntry is DartEntry) {
        // get library-specific values
        List<Source> librarySources = getLibrariesContaining(source);
        for (Source librarySource in librarySources) {
          for (DataDescriptor descriptor in sourceEntry.libraryDescriptors) {
            if (descriptor == DartEntry.BUILT_ELEMENT ||
                descriptor == DartEntry.BUILT_UNIT) {
              // These values are not currently being computed, so their state
              // is not interesting.
              continue;
            } else if (!sourceEntry.explicitlyAdded &&
                !_generateImplicitErrors &&
                (descriptor == DartEntry.VERIFICATION_ERRORS ||
                    descriptor == DartEntry.HINTS ||
                    descriptor == DartEntry.LINTS)) {
              continue;
            } else if (source.isInSystemLibrary &&
                !_generateSdkErrors &&
                (descriptor == DartEntry.VERIFICATION_ERRORS ||
                    descriptor == DartEntry.HINTS ||
                    descriptor == DartEntry.LINTS)) {
              continue;
            } else if (!hintsEnabled && descriptor == DartEntry.HINTS) {
              continue;
            } else if (!lintsEnabled && descriptor == DartEntry.LINTS) {
              continue;
            }
            callback(librarySource, sourceEntry, descriptor,
                sourceEntry.getStateInLibrary(descriptor, librarySource));
          }
        }
      }
    }
  }

  @override
  void visitContentCache(ContentCacheVisitor visitor) {
    _contentCache.accept(visitor);
  }

  /**
   * Record that we have accessed the AST structure associated with the given
   * [source]. At the moment, there is no differentiation between the parsed and
   * resolved forms of the AST.
   */
  void _accessedAst(Source source) {
    _cache.accessedAst(source);
  }

  /**
   * Add all of the sources contained in the given source [container] to the
   * given list of [sources].
   */
  void _addSourcesInContainer(List<Source> sources, SourceContainer container) {
    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
    while (iterator.moveNext()) {
      Source source = iterator.key;
      if (container.contains(source)) {
        sources.add(source);
      }
    }
  }

  /**
   * Given the [unitSource] of a Dart file and the [librarySource] of the
   * library that contains it, return a cache entry in which the state of the
   * data represented by the given [descriptor] is either [CacheState.VALID] or
   * [CacheState.ERROR]. This method assumes that the data can be produced by
   * generating hints for the library if the data is not already cached. The
   * [dartEntry] is the cache entry associated with the Dart file.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be parsed.
   */
  DartEntry _cacheDartHintData(Source unitSource, Source librarySource,
      DartEntry dartEntry, DataDescriptor descriptor) {
    //
    // Check to see whether we already have the information being requested.
    //
    CacheState state = dartEntry.getStateInLibrary(descriptor, librarySource);
    while (state != CacheState.ERROR && state != CacheState.VALID) {
      //
      // If not, compute the information.
      // Unless the modification date of the source continues to change,
      // this loop will eventually terminate.
      //
      DartEntry libraryEntry = _getReadableDartEntry(librarySource);
      libraryEntry = _cacheDartResolutionData(
          librarySource, librarySource, libraryEntry, DartEntry.ELEMENT);
      LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
      CompilationUnitElement definingUnit =
          libraryElement.definingCompilationUnit;
      List<CompilationUnitElement> parts = libraryElement.parts;
      List<TimestampedData<CompilationUnit>> units =
          new List<TimestampedData<CompilationUnit>>(parts.length + 1);
      units[0] = _getResolvedUnit(definingUnit, librarySource);
      if (units[0] == null) {
        Source source = definingUnit.source;
        units[0] = new TimestampedData<CompilationUnit>(
            getModificationStamp(source),
            resolveCompilationUnit(source, libraryElement));
      }
      for (int i = 0; i < parts.length; i++) {
        units[i + 1] = _getResolvedUnit(parts[i], librarySource);
        if (units[i + 1] == null) {
          Source source = parts[i].source;
          units[i + 1] = new TimestampedData<CompilationUnit>(
              getModificationStamp(source),
              resolveCompilationUnit(source, libraryElement));
        }
      }
      dartEntry = new GenerateDartHintsTask(
              this, units, getLibraryElement(librarySource))
          .perform(_resultRecorder) as DartEntry;
      state = dartEntry.getStateInLibrary(descriptor, librarySource);
    }
    return dartEntry;
  }

  /**
   * Given a source for a Dart file and the library that contains it, return a
   * cache entry in which the state of the data represented by the given
   * descriptor is either [CacheState.VALID] or [CacheState.ERROR]. This method
   * assumes that the data can be produced by generating lints for the library
   * if the data is not already cached.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  DartEntry _cacheDartLintData(Source unitSource, Source librarySource,
      DartEntry dartEntry, DataDescriptor descriptor) {
    //
    // Check to see whether we already have the information being requested.
    //
    CacheState state = dartEntry.getStateInLibrary(descriptor, librarySource);
    while (state != CacheState.ERROR && state != CacheState.VALID) {
      //
      // If not, compute the information.
      // Unless the modification date of the source continues to change,
      // this loop will eventually terminate.
      //
      DartEntry libraryEntry = _getReadableDartEntry(librarySource);
      libraryEntry = _cacheDartResolutionData(
          librarySource, librarySource, libraryEntry, DartEntry.ELEMENT);
      LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
      CompilationUnitElement definingUnit =
          libraryElement.definingCompilationUnit;
      List<CompilationUnitElement> parts = libraryElement.parts;
      List<TimestampedData<CompilationUnit>> units =
          new List<TimestampedData<CompilationUnit>>(parts.length + 1);
      units[0] = _getResolvedUnit(definingUnit, librarySource);
      if (units[0] == null) {
        Source source = definingUnit.source;
        units[0] = new TimestampedData<CompilationUnit>(
            getModificationStamp(source),
            resolveCompilationUnit(source, libraryElement));
      }
      for (int i = 0; i < parts.length; i++) {
        units[i + 1] = _getResolvedUnit(parts[i], librarySource);
        if (units[i + 1] == null) {
          Source source = parts[i].source;
          units[i + 1] = new TimestampedData<CompilationUnit>(
              getModificationStamp(source),
              resolveCompilationUnit(source, libraryElement));
        }
      }
      //TODO(pquitslund): revisit if we need all units or whether one will do
      dartEntry = new GenerateDartLintsTask(
              this, units, getLibraryElement(librarySource))
          .perform(_resultRecorder) as DartEntry;
      state = dartEntry.getStateInLibrary(descriptor, librarySource);
    }
    return dartEntry;
  }

  /**
   * Given a source for a Dart file, return a cache entry in which the state of
   * the data represented by the given descriptor is either [CacheState.VALID]
   * or [CacheState.ERROR]. This method assumes that the data can be produced by
   * parsing the source if it is not already cached.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  DartEntry _cacheDartParseData(
      Source source, DartEntry dartEntry, DataDescriptor descriptor) {
    if (identical(descriptor, DartEntry.PARSED_UNIT)) {
      if (dartEntry.hasResolvableCompilationUnit) {
        return dartEntry;
      }
    }
    //
    // Check to see whether we already have the information being requested.
    //
    CacheState state = dartEntry.getState(descriptor);
    while (state != CacheState.ERROR && state != CacheState.VALID) {
      //
      // If not, compute the information. Unless the modification date of the
      // source continues to change, this loop will eventually terminate.
      //
      dartEntry = _cacheDartScanData(source, dartEntry, DartEntry.TOKEN_STREAM);
      dartEntry = new ParseDartTask(
              this,
              source,
              dartEntry.getValue(DartEntry.TOKEN_STREAM),
              dartEntry.getValue(SourceEntry.LINE_INFO))
          .perform(_resultRecorder) as DartEntry;
      state = dartEntry.getState(descriptor);
    }
    return dartEntry;
  }

  /**
   * Given a source for a Dart file and the library that contains it, return a
   * cache entry in which the state of the data represented by the given
   * descriptor is either [CacheState.VALID] or [CacheState.ERROR]. This method
   * assumes that the data can be produced by resolving the source in the
   * context of the library if it is not already cached.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  DartEntry _cacheDartResolutionData(Source unitSource, Source librarySource,
      DartEntry dartEntry, DataDescriptor descriptor) {
    //
    // Check to see whether we already have the information being requested.
    //
    CacheState state = (identical(descriptor, DartEntry.ELEMENT))
        ? dartEntry.getState(descriptor)
        : dartEntry.getStateInLibrary(descriptor, librarySource);
    while (state != CacheState.ERROR && state != CacheState.VALID) {
      //
      // If not, compute the information. Unless the modification date of the
      // source continues to change, this loop will eventually terminate.
      //
      // TODO(brianwilkerson) As an optimization, if we already have the
      // element model for the library we can use ResolveDartUnitTask to produce
      // the resolved AST structure much faster.
      dartEntry = new ResolveDartLibraryTask(this, unitSource, librarySource)
          .perform(_resultRecorder) as DartEntry;
      state = (identical(descriptor, DartEntry.ELEMENT))
          ? dartEntry.getState(descriptor)
          : dartEntry.getStateInLibrary(descriptor, librarySource);
    }
    return dartEntry;
  }

  /**
   * Given a source for a Dart file, return a cache entry in which the state of
   * the data represented by the given descriptor is either [CacheState.VALID]
   * or [CacheState.ERROR]. This method assumes that the data can be produced by
   * scanning the source if it is not already cached.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  DartEntry _cacheDartScanData(
      Source source, DartEntry dartEntry, DataDescriptor descriptor) {
    //
    // Check to see whether we already have the information being requested.
    //
    CacheState state = dartEntry.getState(descriptor);
    while (state != CacheState.ERROR && state != CacheState.VALID) {
      //
      // If not, compute the information. Unless the modification date of the
      // source continues to change, this loop will eventually terminate.
      //
      try {
        if (dartEntry.getState(SourceEntry.CONTENT) != CacheState.VALID) {
          dartEntry = new GetContentTask(this, source).perform(_resultRecorder)
              as DartEntry;
        }
        dartEntry = new ScanDartTask(
                this, source, dartEntry.getValue(SourceEntry.CONTENT))
            .perform(_resultRecorder) as DartEntry;
      } on AnalysisException catch (exception) {
        throw exception;
      } catch (exception, stackTrace) {
        throw new AnalysisException(
            "Exception", new CaughtException(exception, stackTrace));
      }
      state = dartEntry.getState(descriptor);
    }
    return dartEntry;
  }

  /**
   * Given a source for a Dart file and the library that contains it, return a
   * cache entry in which the state of the data represented by the given
   * descriptor is either [CacheState.VALID] or [CacheState.ERROR]. This method
   * assumes that the data can be produced by verifying the source in the given
   * library if the data is not already cached.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  DartEntry _cacheDartVerificationData(Source unitSource, Source librarySource,
      DartEntry dartEntry, DataDescriptor descriptor) {
    //
    // Check to see whether we already have the information being requested.
    //
    CacheState state = dartEntry.getStateInLibrary(descriptor, librarySource);
    while (state != CacheState.ERROR && state != CacheState.VALID) {
      //
      // If not, compute the information. Unless the modification date of the
      // source continues to change, this loop will eventually terminate.
      //
      LibraryElement library = computeLibraryElement(librarySource);
      CompilationUnit unit = resolveCompilationUnit(unitSource, library);
      if (unit == null) {
        throw new AnalysisException(
            "Could not resolve compilation unit ${unitSource.fullName} in ${librarySource.fullName}");
      }
      dartEntry = new GenerateDartErrorsTask(this, unitSource, unit, library)
          .perform(_resultRecorder) as DartEntry;
      state = dartEntry.getStateInLibrary(descriptor, librarySource);
    }
    return dartEntry;
  }

  /**
   * Given a source for an HTML file, return a cache entry in which all of the
   * data represented by the state of the given descriptors is either
   * [CacheState.VALID] or [CacheState.ERROR]. This method assumes that the data
   * can be produced by parsing the source if it is not already cached.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  HtmlEntry _cacheHtmlParseData(
      Source source, HtmlEntry htmlEntry, DataDescriptor descriptor) {
    if (identical(descriptor, HtmlEntry.PARSED_UNIT)) {
      ht.HtmlUnit unit = htmlEntry.anyParsedUnit;
      if (unit != null) {
        return htmlEntry;
      }
    }
    //
    // Check to see whether we already have the information being requested.
    //
    CacheState state = htmlEntry.getState(descriptor);
    while (state != CacheState.ERROR && state != CacheState.VALID) {
      //
      // If not, compute the information. Unless the modification date of the
      // source continues to change, this loop will eventually terminate.
      //
      try {
        if (htmlEntry.getState(SourceEntry.CONTENT) != CacheState.VALID) {
          htmlEntry = new GetContentTask(this, source).perform(_resultRecorder)
              as HtmlEntry;
        }
        htmlEntry = new ParseHtmlTask(
                this, source, htmlEntry.getValue(SourceEntry.CONTENT))
            .perform(_resultRecorder) as HtmlEntry;
      } on AnalysisException catch (exception) {
        throw exception;
      } catch (exception, stackTrace) {
        throw new AnalysisException(
            "Exception", new CaughtException(exception, stackTrace));
      }
      state = htmlEntry.getState(descriptor);
    }
    return htmlEntry;
  }

  /**
   * Given a source for an HTML file, return a cache entry in which the state of
   * the data represented by the given descriptor is either [CacheState.VALID]
   * or [CacheState.ERROR]. This method assumes that the data can be produced by
   * resolving the source if it is not already cached.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  HtmlEntry _cacheHtmlResolutionData(
      Source source, HtmlEntry htmlEntry, DataDescriptor descriptor) {
    //
    // Check to see whether we already have the information being requested.
    //
    CacheState state = htmlEntry.getState(descriptor);
    while (state != CacheState.ERROR && state != CacheState.VALID) {
      //
      // If not, compute the information. Unless the modification date of the
      // source continues to change, this loop will eventually terminate.
      //
      htmlEntry = _cacheHtmlParseData(source, htmlEntry, HtmlEntry.PARSED_UNIT);
      htmlEntry = new ResolveHtmlTask(this, source, htmlEntry.modificationTime,
              htmlEntry.getValue(HtmlEntry.PARSED_UNIT))
          .perform(_resultRecorder) as HtmlEntry;
      state = htmlEntry.getState(descriptor);
    }
    return htmlEntry;
  }

  /**
   * Remove the given [pendingFuture] from [_pendingFutureSources], since the
   * client has indicated its computation is not needed anymore.
   */
  void _cancelFuture(PendingFuture pendingFuture) {
    List<PendingFuture> pendingFutures =
        _pendingFutureSources[pendingFuture.source];
    if (pendingFutures != null) {
      pendingFutures.remove(pendingFuture);
      if (pendingFutures.isEmpty) {
        _pendingFutureSources.remove(pendingFuture.source);
      }
    }
  }

  /**
   * Compute the transitive closure of all libraries that depend on the given
   * [library] by adding such libraries to the given collection of
   * [librariesToInvalidate].
   */
  void _computeAllLibrariesDependingOn(
      Source library, HashSet<Source> librariesToInvalidate) {
    if (librariesToInvalidate.add(library)) {
      for (Source dependentLibrary in getLibrariesDependingOn(library)) {
        _computeAllLibrariesDependingOn(
            dependentLibrary, librariesToInvalidate);
      }
    }
  }

  /**
   * Return the priority that should be used when the source associated with
   * the given [dartEntry] is added to the work manager.
   */
  SourcePriority _computePriority(DartEntry dartEntry) {
    SourceKind kind = dartEntry.kind;
    if (kind == SourceKind.LIBRARY) {
      return SourcePriority.LIBRARY;
    } else if (kind == SourceKind.PART) {
      return SourcePriority.NORMAL_PART;
    }
    return SourcePriority.UNKNOWN;
  }

  /**
   * Given the encoded form of a source ([encoding]), use the source factory to
   * reconstitute the original source.
   */
  Source _computeSourceFromEncoding(String encoding) =>
      _sourceFactory.fromEncoding(encoding);

  /**
   * Return `true` if the given list of [sources] contains the given
   * [targetSource].
   */
  bool _contains(List<Source> sources, Source targetSource) {
    for (Source source in sources) {
      if (source == targetSource) {
        return true;
      }
    }
    return false;
  }

  /**
   * Return `true` if the given list of [sources] contains any of the given
   * [targetSources].
   */
  bool _containsAny(List<Source> sources, List<Source> targetSources) {
    for (Source targetSource in targetSources) {
      if (_contains(sources, targetSource)) {
        return true;
      }
    }
    return false;
  }

  /**
   * Set the contents of the given [source] to the given [contents] and mark the
   * source as having changed. The additional [offset], [oldLength] and
   * [newLength] information is used by the context to determine what reanalysis
   * is necessary. The method [setChangedContents] triggers a source changed
   * event where as this method does not.
   */
  bool _contentRangeChanged(Source source, String contents, int offset,
      int oldLength, int newLength) {
    bool changed = false;
    String originalContents = _contentCache.setContents(source, contents);
    if (contents != null) {
      if (contents != originalContents) {
        if (_options.incremental) {
          _incrementalAnalysisCache = IncrementalAnalysisCache.update(
              _incrementalAnalysisCache,
              source,
              originalContents,
              contents,
              offset,
              oldLength,
              newLength,
              _getReadableSourceEntry(source));
        }
        _sourceChanged(source);
        changed = true;
        SourceEntry sourceEntry = _cache.get(source);
        if (sourceEntry != null) {
          sourceEntry.modificationTime =
              _contentCache.getModificationStamp(source);
          sourceEntry.setValue(SourceEntry.CONTENT, contents);
        }
      }
    } else if (originalContents != null) {
      _incrementalAnalysisCache =
          IncrementalAnalysisCache.clear(_incrementalAnalysisCache, source);
      _sourceChanged(source);
      changed = true;
    }
    return changed;
  }

  /**
   * Set the contents of the given [source] to the given [contents] and mark the
   * source as having changed. This has the effect of overriding the default
   * contents of the source. If the contents are `null` the override is removed
   * so that the default contents will be returned. If [notify] is true, a
   * source changed event is triggered.
   */
  void _contentsChanged(Source source, String contents, bool notify) {
    String originalContents = _contentCache.setContents(source, contents);
    handleContentsChanged(source, originalContents, contents, notify);
  }

  /**
   * Create a [GenerateDartErrorsTask] for the given [unitSource], marking the
   * verification errors as being in-process. The compilation unit and the
   * library can be the same if the compilation unit is the defining compilation
   * unit of the library.
   */
  AnalysisContextImpl_TaskData _createGenerateDartErrorsTask(Source unitSource,
      DartEntry unitEntry, Source librarySource, DartEntry libraryEntry) {
    if (unitEntry.getStateInLibrary(DartEntry.RESOLVED_UNIT, librarySource) !=
            CacheState.VALID ||
        libraryEntry.getState(DartEntry.ELEMENT) != CacheState.VALID) {
      return _createResolveDartLibraryTask(librarySource, libraryEntry);
    }
    CompilationUnit unit =
        unitEntry.getValueInLibrary(DartEntry.RESOLVED_UNIT, librarySource);
    if (unit == null) {
      CaughtException exception = new CaughtException(
          new AnalysisException(
              "Entry has VALID state for RESOLVED_UNIT but null value for ${unitSource.fullName} in ${librarySource.fullName}"),
          null);
      AnalysisEngine.instance.logger
          .logInformation(exception.toString(), exception);
      unitEntry.recordResolutionError(exception);
      return new AnalysisContextImpl_TaskData(null, false);
    }
    LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
    return new AnalysisContextImpl_TaskData(
        new GenerateDartErrorsTask(this, unitSource, unit, libraryElement),
        false);
  }

  /**
   * Create a [GenerateDartHintsTask] for the given [source], marking the hints
   * as being in-process.
   */
  AnalysisContextImpl_TaskData _createGenerateDartHintsTask(Source source,
      DartEntry dartEntry, Source librarySource, DartEntry libraryEntry) {
    if (libraryEntry.getState(DartEntry.ELEMENT) != CacheState.VALID) {
      return _createResolveDartLibraryTask(librarySource, libraryEntry);
    }
    LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
    CompilationUnitElement definingUnit =
        libraryElement.definingCompilationUnit;
    List<CompilationUnitElement> parts = libraryElement.parts;
    List<TimestampedData<CompilationUnit>> units =
        new List<TimestampedData<CompilationUnit>>(parts.length + 1);
    units[0] = _getResolvedUnit(definingUnit, librarySource);
    if (units[0] == null) {
      // TODO(brianwilkerson) We should return a ResolveDartUnitTask
      // (unless there are multiple ASTs that need to be resolved).
      return _createResolveDartLibraryTask(librarySource, libraryEntry);
    }
    for (int i = 0; i < parts.length; i++) {
      units[i + 1] = _getResolvedUnit(parts[i], librarySource);
      if (units[i + 1] == null) {
        // TODO(brianwilkerson) We should return a ResolveDartUnitTask
        // (unless there are multiple ASTs that need to be resolved).
        return _createResolveDartLibraryTask(librarySource, libraryEntry);
      }
    }
    return new AnalysisContextImpl_TaskData(
        new GenerateDartHintsTask(this, units, libraryElement), false);
  }

  /**
   * Create a [GenerateDartLintsTask] for the given [source], marking the lints
   * as being in-process.
   */
  AnalysisContextImpl_TaskData _createGenerateDartLintsTask(Source source,
      DartEntry dartEntry, Source librarySource, DartEntry libraryEntry) {
    if (libraryEntry.getState(DartEntry.ELEMENT) != CacheState.VALID) {
      return _createResolveDartLibraryTask(librarySource, libraryEntry);
    }
    LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
    CompilationUnitElement definingUnit =
        libraryElement.definingCompilationUnit;
    List<CompilationUnitElement> parts = libraryElement.parts;
    List<TimestampedData<CompilationUnit>> units =
        new List<TimestampedData<CompilationUnit>>(parts.length + 1);
    units[0] = _getResolvedUnit(definingUnit, librarySource);
    if (units[0] == null) {
      // TODO(brianwilkerson) We should return a ResolveDartUnitTask
      // (unless there are multiple ASTs that need to be resolved).
      return _createResolveDartLibraryTask(librarySource, libraryEntry);
    }
    for (int i = 0; i < parts.length; i++) {
      units[i + 1] = _getResolvedUnit(parts[i], librarySource);
      if (units[i + 1] == null) {
        // TODO(brianwilkerson) We should return a ResolveDartUnitTask
        // (unless there are multiple ASTs that need to be resolved).
        return _createResolveDartLibraryTask(librarySource, libraryEntry);
      }
    }
    //TODO(pquitslund): revisit if we need all units or whether one will do
    return new AnalysisContextImpl_TaskData(
        new GenerateDartLintsTask(this, units, libraryElement), false);
  }

  /**
   * Create a [GetContentTask] for the given [source], marking the content as
   * being in-process.
   */
  AnalysisContextImpl_TaskData _createGetContentTask(
      Source source, SourceEntry sourceEntry) {
    return new AnalysisContextImpl_TaskData(
        new GetContentTask(this, source), false);
  }

  /**
   * Create a [ParseDartTask] for the given [source].
   */
  AnalysisContextImpl_TaskData _createParseDartTask(
      Source source, DartEntry dartEntry) {
    if (dartEntry.getState(DartEntry.TOKEN_STREAM) != CacheState.VALID ||
        dartEntry.getState(SourceEntry.LINE_INFO) != CacheState.VALID) {
      return _createScanDartTask(source, dartEntry);
    }
    Token tokenStream = dartEntry.getValue(DartEntry.TOKEN_STREAM);
    dartEntry.setState(DartEntry.TOKEN_STREAM, CacheState.FLUSHED);
    return new AnalysisContextImpl_TaskData(
        new ParseDartTask(this, source, tokenStream,
            dartEntry.getValue(SourceEntry.LINE_INFO)),
        false);
  }

  /**
   * Create a [ParseHtmlTask] for the given [source].
   */
  AnalysisContextImpl_TaskData _createParseHtmlTask(
      Source source, HtmlEntry htmlEntry) {
    if (htmlEntry.getState(SourceEntry.CONTENT) != CacheState.VALID) {
      return _createGetContentTask(source, htmlEntry);
    }
    String content = htmlEntry.getValue(SourceEntry.CONTENT);
    htmlEntry.setState(SourceEntry.CONTENT, CacheState.FLUSHED);
    return new AnalysisContextImpl_TaskData(
        new ParseHtmlTask(this, source, content), false);
  }

  /**
   * Create a [ResolveDartLibraryTask] for the given [source], marking ? as
   * being in-process.
   */
  AnalysisContextImpl_TaskData _createResolveDartLibraryTask(
      Source source, DartEntry dartEntry) {
    try {
      AnalysisContextImpl_CycleBuilder builder =
          new AnalysisContextImpl_CycleBuilder(this);
      PerformanceStatistics.cycles.makeCurrentWhile(() {
        builder.computeCycleContaining(source);
      });
      AnalysisContextImpl_TaskData taskData = builder.taskData;
      if (taskData != null) {
        return taskData;
      }
      return new AnalysisContextImpl_TaskData(
          new ResolveDartLibraryCycleTask(
              this, source, source, builder.librariesInCycle),
          false);
    } on AnalysisException catch (exception, stackTrace) {
      dartEntry
          .recordResolutionError(new CaughtException(exception, stackTrace));
      AnalysisEngine.instance.logger.logError(
          "Internal error trying to create a ResolveDartLibraryTask",
          new CaughtException(exception, stackTrace));
    }
    return new AnalysisContextImpl_TaskData(null, false);
  }

  /**
   * Create a [ResolveHtmlTask] for the given [source], marking the resolved
   * unit as being in-process.
   */
  AnalysisContextImpl_TaskData _createResolveHtmlTask(
      Source source, HtmlEntry htmlEntry) {
    if (htmlEntry.getState(HtmlEntry.PARSED_UNIT) != CacheState.VALID) {
      return _createParseHtmlTask(source, htmlEntry);
    }
    return new AnalysisContextImpl_TaskData(
        new ResolveHtmlTask(this, source, htmlEntry.modificationTime,
            htmlEntry.getValue(HtmlEntry.PARSED_UNIT)),
        false);
  }

  /**
   * Create a [ScanDartTask] for the given [source], marking the scan errors as
   * being in-process.
   */
  AnalysisContextImpl_TaskData _createScanDartTask(
      Source source, DartEntry dartEntry) {
    if (dartEntry.getState(SourceEntry.CONTENT) != CacheState.VALID) {
      return _createGetContentTask(source, dartEntry);
    }
    String content = dartEntry.getValue(SourceEntry.CONTENT);
    dartEntry.setState(SourceEntry.CONTENT, CacheState.FLUSHED);
    return new AnalysisContextImpl_TaskData(
        new ScanDartTask(this, source, content), false);
  }

  /**
   * Create a source entry for the given [source]. Return the source entry that
   * was created, or `null` if the source should not be tracked by this context.
   */
  SourceEntry _createSourceEntry(Source source, bool explicitlyAdded) {
    String name = source.shortName;
    if (AnalysisEngine.isHtmlFileName(name)) {
      HtmlEntry htmlEntry = new HtmlEntry();
      htmlEntry.modificationTime = getModificationStamp(source);
      htmlEntry.explicitlyAdded = explicitlyAdded;
      _cache.put(source, htmlEntry);
      if (!explicitlyAdded) {
        _implicitAnalysisEventsController
            .add(new ImplicitAnalysisEvent(source, true));
      }
      return htmlEntry;
    } else {
      DartEntry dartEntry = new DartEntry();
      dartEntry.modificationTime = getModificationStamp(source);
      dartEntry.explicitlyAdded = explicitlyAdded;
      _cache.put(source, dartEntry);
      if (!explicitlyAdded) {
        _implicitAnalysisEventsController
            .add(new ImplicitAnalysisEvent(source, true));
      }
      return dartEntry;
    }
  }

  /**
   * Return a list containing all of the change notices that are waiting to be
   * returned. If there are no notices, then return either `null` or an empty
   * list, depending on the value of [nullIfEmpty].
   */
  List<ChangeNotice> _getChangeNotices(bool nullIfEmpty) {
    if (_pendingNotices.isEmpty) {
      if (nullIfEmpty) {
        return null;
      }
      return ChangeNoticeImpl.EMPTY_LIST;
    }
    List<ChangeNotice> notices = new List.from(_pendingNotices.values);
    _pendingNotices.clear();
    return notices;
  }

  /**
   * Given a source for a Dart file and the library that contains it, return the
   * data represented by the given descriptor that is associated with that
   * source. This method assumes that the data can be produced by generating
   * hints for the library if it is not already cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be resolved.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getDartHintData(Source unitSource, Source librarySource,
      DartEntry dartEntry, DataDescriptor descriptor) {
    dartEntry =
        _cacheDartHintData(unitSource, librarySource, dartEntry, descriptor);
    if (identical(descriptor, DartEntry.ELEMENT)) {
      return dartEntry.getValue(descriptor);
    }
    return dartEntry.getValueInLibrary(descriptor, librarySource);
  }

  /**
   * Given a source for a Dart file and the library that contains it, return the
   * data represented by the given descriptor that is associated with that
   * source. This method assumes that the data can be produced by generating
   * lints for the library if it is not already cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be resolved.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getDartLintData(Source unitSource, Source librarySource,
      DartEntry dartEntry, DataDescriptor descriptor) {
    dartEntry =
        _cacheDartLintData(unitSource, librarySource, dartEntry, descriptor);
    if (identical(descriptor, DartEntry.ELEMENT)) {
      return dartEntry.getValue(descriptor);
    }
    return dartEntry.getValueInLibrary(descriptor, librarySource);
  }

  /**
   * Given a source for a Dart file, return the data represented by the given
   * descriptor that is associated with that source. This method assumes that
   * the data can be produced by parsing the source if it is not already cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be parsed.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getDartParseData(
      Source source, DartEntry dartEntry, DataDescriptor descriptor) {
    dartEntry = _cacheDartParseData(source, dartEntry, descriptor);
    if (identical(descriptor, DartEntry.PARSED_UNIT)) {
      _accessedAst(source);
      return dartEntry.anyParsedCompilationUnit;
    }
    return dartEntry.getValue(descriptor);
  }

  /**
   * Given a source for a Dart file, return the data represented by the given
   * descriptor that is associated with that source, or the given default value
   * if the source is not a Dart file. This method assumes that the data can be
   * produced by parsing the source if it is not already cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be parsed.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getDartParseData2(
      Source source, DataDescriptor descriptor, Object defaultValue) {
    DartEntry dartEntry = _getReadableDartEntry(source);
    if (dartEntry == null) {
      return defaultValue;
    }
    try {
      return _getDartParseData(source, dartEntry, descriptor);
    } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
      AnalysisEngine.instance.logger.logInformation(
          "Could not compute $descriptor",
          new CaughtException(exception, stackTrace));
      return defaultValue;
    }
  }

  /**
   * Given a source for a Dart file and the library that contains it, return the
   * data represented by the given descriptor that is associated with that
   * source. This method assumes that the data can be produced by resolving the
   * source in the context of the library if it is not already cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be resolved.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getDartResolutionData(Source unitSource, Source librarySource,
      DartEntry dartEntry, DataDescriptor descriptor) {
    dartEntry = _cacheDartResolutionData(
        unitSource, librarySource, dartEntry, descriptor);
    if (identical(descriptor, DartEntry.ELEMENT)) {
      return dartEntry.getValue(descriptor);
    } else if (identical(descriptor, DartEntry.RESOLVED_UNIT)) {
      _accessedAst(unitSource);
    }
    return dartEntry.getValueInLibrary(descriptor, librarySource);
  }

  /**
   * Given a source for a Dart file and the library that contains it, return the
   * data represented by the given descriptor that is associated with that
   * source, or the given default value if the source is not a Dart file. This
   * method assumes that the data can be produced by resolving the source in the
   * context of the library if it is not already cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be resolved.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getDartResolutionData2(Source unitSource, Source librarySource,
      DataDescriptor descriptor, Object defaultValue) {
    DartEntry dartEntry = _getReadableDartEntry(unitSource);
    if (dartEntry == null) {
      return defaultValue;
    }
    try {
      return _getDartResolutionData(
          unitSource, librarySource, dartEntry, descriptor);
    } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
      AnalysisEngine.instance.logger.logInformation(
          "Could not compute $descriptor",
          new CaughtException(exception, stackTrace));
      return defaultValue;
    }
  }

  /**
   * Given a source for a Dart file, return the data represented by the given
   * descriptor that is associated with that source. This method assumes that
   * the data can be produced by scanning the source if it is not already
   * cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be scanned.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getDartScanData(
      Source source, DartEntry dartEntry, DataDescriptor descriptor) {
    dartEntry = _cacheDartScanData(source, dartEntry, descriptor);
    return dartEntry.getValue(descriptor);
  }

  /**
   * Given a source for a Dart file, return the data represented by the given
   * descriptor that is associated with that source, or the given default value
   * if the source is not a Dart file. This method assumes that the data can be
   * produced by scanning the source if it is not already cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be scanned.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getDartScanData2(
      Source source, DataDescriptor descriptor, Object defaultValue) {
    DartEntry dartEntry = _getReadableDartEntry(source);
    if (dartEntry == null) {
      return defaultValue;
    }
    try {
      return _getDartScanData(source, dartEntry, descriptor);
    } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
      AnalysisEngine.instance.logger.logInformation(
          "Could not compute $descriptor",
          new CaughtException(exception, stackTrace));
      return defaultValue;
    }
  }

  /**
   * Given a source for a Dart file and the library that contains it, return the
   * data represented by the given descriptor that is associated with that
   * source. This method assumes that the data can be produced by verifying the
   * source within the given library if it is not already cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be resolved.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getDartVerificationData(Source unitSource, Source librarySource,
      DartEntry dartEntry, DataDescriptor descriptor) {
    dartEntry = _cacheDartVerificationData(
        unitSource, librarySource, dartEntry, descriptor);
    return dartEntry.getValueInLibrary(descriptor, librarySource);
  }

  /**
   * Given a source for an HTML file, return the data represented by the given
   * descriptor that is associated with that source, or the given default value
   * if the source is not an HTML file. This method assumes that the data can be
   * produced by parsing the source if it is not already cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be parsed.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getHtmlParseData(
      Source source, DataDescriptor descriptor, Object defaultValue) {
    HtmlEntry htmlEntry = _getReadableHtmlEntry(source);
    if (htmlEntry == null) {
      return defaultValue;
    }
    htmlEntry = _cacheHtmlParseData(source, htmlEntry, descriptor);
    if (identical(descriptor, HtmlEntry.PARSED_UNIT)) {
      _accessedAst(source);
      return htmlEntry.anyParsedUnit;
    }
    return htmlEntry.getValue(descriptor);
  }

  /**
   * Given a source for an HTML file, return the data represented by the given
   * descriptor that is associated with that source, or the given default value
   * if the source is not an HTML file. This method assumes that the data can be
   * produced by resolving the source if it is not already cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be resolved.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getHtmlResolutionData(
      Source source, DataDescriptor descriptor, Object defaultValue) {
    HtmlEntry htmlEntry = _getReadableHtmlEntry(source);
    if (htmlEntry == null) {
      return defaultValue;
    }
    try {
      return _getHtmlResolutionData2(source, htmlEntry, descriptor);
    } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
      AnalysisEngine.instance.logger.logInformation(
          "Could not compute $descriptor",
          new CaughtException(exception, stackTrace));
      return defaultValue;
    }
  }

  /**
   * Given a source for an HTML file, return the data represented by the given
   * descriptor that is associated with that source. This method assumes that
   * the data can be produced by resolving the source if it is not already
   * cached.
   *
   * Throws an [AnalysisException] if data could not be returned because the
   * source could not be resolved.
   *
   * <b>Note:</b> This method cannot be used in an async environment.
   */
  Object _getHtmlResolutionData2(
      Source source, HtmlEntry htmlEntry, DataDescriptor descriptor) {
    htmlEntry = _cacheHtmlResolutionData(source, htmlEntry, descriptor);
    if (identical(descriptor, HtmlEntry.RESOLVED_UNIT)) {
      _accessedAst(source);
    }
    return htmlEntry.getValue(descriptor);
  }

  /**
   * Look at the given [source] to see whether a task needs to be performed
   * related to it. Return the task that should be performed, or `null` if there
   * is no more work to be done for the source.
   */
  AnalysisContextImpl_TaskData _getNextAnalysisTaskForSource(
      Source source,
      SourceEntry sourceEntry,
      bool isPriority,
      bool hintsEnabled,
      bool lintsEnabled) {
    // Refuse to generate tasks for html based files that are above 1500 KB
    if (_isTooBigHtmlSourceEntry(source, sourceEntry)) {
      // TODO (jwren) we still need to report an error of some kind back to the
      // client.
      return new AnalysisContextImpl_TaskData(null, false);
    }
    if (sourceEntry == null) {
      return new AnalysisContextImpl_TaskData(null, false);
    }
    CacheState contentState = sourceEntry.getState(SourceEntry.CONTENT);
    if (contentState == CacheState.INVALID) {
      return _createGetContentTask(source, sourceEntry);
    } else if (contentState == CacheState.IN_PROCESS) {
      // We are already in the process of getting the content.
      // There's nothing else we can do with this source until that's complete.
      return new AnalysisContextImpl_TaskData(null, true);
    } else if (contentState == CacheState.ERROR) {
      // We have done all of the analysis we can for this source because we
      // cannot get its content.
      return new AnalysisContextImpl_TaskData(null, false);
    }
    if (sourceEntry is DartEntry) {
      DartEntry dartEntry = sourceEntry;
      CacheState scanErrorsState = dartEntry.getState(DartEntry.SCAN_ERRORS);
      if (scanErrorsState == CacheState.INVALID ||
          (isPriority && scanErrorsState == CacheState.FLUSHED)) {
        return _createScanDartTask(source, dartEntry);
      }
      CacheState parseErrorsState = dartEntry.getState(DartEntry.PARSE_ERRORS);
      if (parseErrorsState == CacheState.INVALID ||
          (isPriority && parseErrorsState == CacheState.FLUSHED)) {
        return _createParseDartTask(source, dartEntry);
      }
      if (isPriority && parseErrorsState != CacheState.ERROR) {
        if (!dartEntry.hasResolvableCompilationUnit) {
          return _createParseDartTask(source, dartEntry);
        }
      }
      SourceKind kind = dartEntry.getValue(DartEntry.SOURCE_KIND);
      if (kind == SourceKind.UNKNOWN) {
        return _createParseDartTask(source, dartEntry);
      } else if (kind == SourceKind.LIBRARY) {
        CacheState elementState = dartEntry.getState(DartEntry.ELEMENT);
        if (elementState == CacheState.INVALID) {
          return _createResolveDartLibraryTask(source, dartEntry);
        }
      }
      List<Source> librariesContaining = dartEntry.containingLibraries;
      for (Source librarySource in librariesContaining) {
        SourceEntry librarySourceEntry = _cache.get(librarySource);
        if (librarySourceEntry is DartEntry) {
          DartEntry libraryEntry = librarySourceEntry;
          CacheState elementState = libraryEntry.getState(DartEntry.ELEMENT);
          if (elementState == CacheState.INVALID ||
              (isPriority && elementState == CacheState.FLUSHED)) {
//            return createResolveDartLibraryTask(librarySource, (DartEntry) libraryEntry);
            return new AnalysisContextImpl_TaskData(
                new ResolveDartLibraryTask(this, source, librarySource), false);
          }
          CacheState resolvedUnitState = dartEntry.getStateInLibrary(
              DartEntry.RESOLVED_UNIT, librarySource);
          if (resolvedUnitState == CacheState.INVALID ||
              (isPriority && resolvedUnitState == CacheState.FLUSHED)) {
            //
            // The commented out lines below are an optimization that doesn't
            // quite work yet. The problem is that if the source was not
            // resolved because it wasn't part of any library, then there won't
            // be any elements in the element model that we can use to resolve
            // it.
            //
//            LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
//            if (libraryElement != null) {
//              return new ResolveDartUnitTask(this, source, libraryElement);
//            }
            // Possibly replace with:
//             return createResolveDartLibraryTask(librarySource, (DartEntry) libraryEntry);
            return new AnalysisContextImpl_TaskData(
                new ResolveDartLibraryTask(this, source, librarySource), false);
          }
          if (shouldErrorsBeAnalyzed(source, dartEntry)) {
            CacheState verificationErrorsState = dartEntry.getStateInLibrary(
                DartEntry.VERIFICATION_ERRORS, librarySource);
            if (verificationErrorsState == CacheState.INVALID ||
                (isPriority && verificationErrorsState == CacheState.FLUSHED)) {
              return _createGenerateDartErrorsTask(
                  source, dartEntry, librarySource, libraryEntry);
            }
            if (hintsEnabled) {
              CacheState hintsState =
                  dartEntry.getStateInLibrary(DartEntry.HINTS, librarySource);
              if (hintsState == CacheState.INVALID ||
                  (isPriority && hintsState == CacheState.FLUSHED)) {
                return _createGenerateDartHintsTask(
                    source, dartEntry, librarySource, libraryEntry);
              }
            }
            if (lintsEnabled) {
              CacheState lintsState =
                  dartEntry.getStateInLibrary(DartEntry.LINTS, librarySource);
              if (lintsState == CacheState.INVALID ||
                  (isPriority && lintsState == CacheState.FLUSHED)) {
                return _createGenerateDartLintsTask(
                    source, dartEntry, librarySource, libraryEntry);
              }
            }
          }
        }
      }
    } else if (sourceEntry is HtmlEntry) {
      HtmlEntry htmlEntry = sourceEntry;
      CacheState parseErrorsState = htmlEntry.getState(HtmlEntry.PARSE_ERRORS);
      if (parseErrorsState == CacheState.INVALID ||
          (isPriority && parseErrorsState == CacheState.FLUSHED)) {
        return _createParseHtmlTask(source, htmlEntry);
      }
      if (isPriority && parseErrorsState != CacheState.ERROR) {
        ht.HtmlUnit parsedUnit = htmlEntry.anyParsedUnit;
        if (parsedUnit == null) {
          return _createParseHtmlTask(source, htmlEntry);
        }
      }
      CacheState resolvedUnitState =
          htmlEntry.getState(HtmlEntry.RESOLVED_UNIT);
      if (resolvedUnitState == CacheState.INVALID ||
          (isPriority && resolvedUnitState == CacheState.FLUSHED)) {
        return _createResolveHtmlTask(source, htmlEntry);
      }
    }
    return new AnalysisContextImpl_TaskData(null, false);
  }

  /**
   * Return the cache entry associated with the given [source], or `null` if the
   * source is not a Dart file.
   *
   * @param source the source for which a cache entry is being sought
   * @return the source cache entry associated with the given source
   */
  DartEntry _getReadableDartEntry(Source source) {
    SourceEntry sourceEntry = _cache.get(source);
    if (sourceEntry == null) {
      sourceEntry = _createSourceEntry(source, false);
    }
    if (sourceEntry is DartEntry) {
      return sourceEntry;
    }
    return null;
  }

  /**
   * Return the cache entry associated with the given [source], or `null` if the
   * source is not an HTML file.
   */
  HtmlEntry _getReadableHtmlEntry(Source source) {
    SourceEntry sourceEntry = _cache.get(source);
    if (sourceEntry == null) {
      sourceEntry = _createSourceEntry(source, false);
    }
    if (sourceEntry is HtmlEntry) {
      return sourceEntry;
    }
    return null;
  }

  /**
   * Return the cache entry associated with the given [source], creating it if
   * necessary.
   */
  SourceEntry _getReadableSourceEntry(Source source) {
    SourceEntry sourceEntry = _cache.get(source);
    if (sourceEntry == null) {
      sourceEntry = _createSourceEntry(source, false);
    }
    return sourceEntry;
  }

  /**
   * Return a resolved compilation unit corresponding to the given [element] in
   * the library defined by the given [librarySource], or `null` if the
   * information is not cached.
   */
  TimestampedData<CompilationUnit> _getResolvedUnit(
      CompilationUnitElement element, Source librarySource) {
    SourceEntry sourceEntry = _cache.get(element.source);
    if (sourceEntry is DartEntry) {
      DartEntry dartEntry = sourceEntry;
      if (dartEntry.getStateInLibrary(DartEntry.RESOLVED_UNIT, librarySource) ==
          CacheState.VALID) {
        return new TimestampedData<CompilationUnit>(
            dartEntry.modificationTime,
            dartEntry.getValueInLibrary(
                DartEntry.RESOLVED_UNIT, librarySource));
      }
    }
    return null;
  }

  /**
   * Return a list containing all of the sources known to this context that have
   * the given [kind].
   */
  List<Source> _getSources(SourceKind kind) {
    List<Source> sources = new List<Source>();
    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
    while (iterator.moveNext()) {
      if (iterator.value.kind == kind) {
        sources.add(iterator.key);
      }
    }
    return sources;
  }

  /**
   * Look at the given [source] to see whether a task needs to be performed
   * related to it. If so, add the source to the set of sources that need to be
   * processed. This method duplicates, and must therefore be kept in sync with,
   * [_getNextAnalysisTaskForSource]. This method is intended to be used for
   * testing purposes only.
   */
  void _getSourcesNeedingProcessing(
      Source source,
      SourceEntry sourceEntry,
      bool isPriority,
      bool hintsEnabled,
      bool lintsEnabled,
      HashSet<Source> sources) {
    if (sourceEntry is DartEntry) {
      DartEntry dartEntry = sourceEntry;
      CacheState scanErrorsState = dartEntry.getState(DartEntry.SCAN_ERRORS);
      if (scanErrorsState == CacheState.INVALID ||
          (isPriority && scanErrorsState == CacheState.FLUSHED)) {
        sources.add(source);
        return;
      }
      CacheState parseErrorsState = dartEntry.getState(DartEntry.PARSE_ERRORS);
      if (parseErrorsState == CacheState.INVALID ||
          (isPriority && parseErrorsState == CacheState.FLUSHED)) {
        sources.add(source);
        return;
      }
      if (isPriority) {
        if (!dartEntry.hasResolvableCompilationUnit) {
          sources.add(source);
          return;
        }
      }
      for (Source librarySource in getLibrariesContaining(source)) {
        SourceEntry libraryEntry = _cache.get(librarySource);
        if (libraryEntry is DartEntry) {
          CacheState elementState = libraryEntry.getState(DartEntry.ELEMENT);
          if (elementState == CacheState.INVALID ||
              (isPriority && elementState == CacheState.FLUSHED)) {
            sources.add(source);
            return;
          }
          CacheState resolvedUnitState = dartEntry.getStateInLibrary(
              DartEntry.RESOLVED_UNIT, librarySource);
          if (resolvedUnitState == CacheState.INVALID ||
              (isPriority && resolvedUnitState == CacheState.FLUSHED)) {
            LibraryElement libraryElement =
                libraryEntry.getValue(DartEntry.ELEMENT);
            if (libraryElement != null) {
              sources.add(source);
              return;
            }
          }
          if (shouldErrorsBeAnalyzed(source, dartEntry)) {
            CacheState verificationErrorsState = dartEntry.getStateInLibrary(
                DartEntry.VERIFICATION_ERRORS, librarySource);
            if (verificationErrorsState == CacheState.INVALID ||
                (isPriority && verificationErrorsState == CacheState.FLUSHED)) {
              LibraryElement libraryElement =
                  libraryEntry.getValue(DartEntry.ELEMENT);
              if (libraryElement != null) {
                sources.add(source);
                return;
              }
            }
            if (hintsEnabled) {
              CacheState hintsState =
                  dartEntry.getStateInLibrary(DartEntry.HINTS, librarySource);
              if (hintsState == CacheState.INVALID ||
                  (isPriority && hintsState == CacheState.FLUSHED)) {
                LibraryElement libraryElement =
                    libraryEntry.getValue(DartEntry.ELEMENT);
                if (libraryElement != null) {
                  sources.add(source);
                  return;
                }
              }
            }
            if (lintsEnabled) {
              CacheState lintsState =
                  dartEntry.getStateInLibrary(DartEntry.LINTS, librarySource);
              if (lintsState == CacheState.INVALID ||
                  (isPriority && lintsState == CacheState.FLUSHED)) {
                LibraryElement libraryElement =
                    libraryEntry.getValue(DartEntry.ELEMENT);
                if (libraryElement != null) {
                  sources.add(source);
                  return;
                }
              }
            }
          }
        }
      }
    } else if (sourceEntry is HtmlEntry) {
      HtmlEntry htmlEntry = sourceEntry;
      CacheState parsedUnitState = htmlEntry.getState(HtmlEntry.PARSED_UNIT);
      if (parsedUnitState == CacheState.INVALID ||
          (isPriority && parsedUnitState == CacheState.FLUSHED)) {
        sources.add(source);
        return;
      }
      CacheState resolvedUnitState =
          htmlEntry.getState(HtmlEntry.RESOLVED_UNIT);
      if (resolvedUnitState == CacheState.INVALID ||
          (isPriority && resolvedUnitState == CacheState.FLUSHED)) {
        sources.add(source);
        return;
      }
    }
  }

  /**
   * Invalidate all of the resolution results computed by this context. The flag
   * [invalidateUris] should be `true` if the cached results of converting URIs
   * to source files should also be invalidated.
   */
  void _invalidateAllLocalResolutionInformation(bool invalidateUris) {
    HashMap<Source, List<Source>> oldPartMap =
        new HashMap<Source, List<Source>>();
    MapIterator<Source, SourceEntry> iterator = _privatePartition.iterator();
    while (iterator.moveNext()) {
      Source source = iterator.key;
      SourceEntry sourceEntry = iterator.value;
      if (sourceEntry is HtmlEntry) {
        HtmlEntry htmlEntry = sourceEntry;
        htmlEntry.invalidateAllResolutionInformation(invalidateUris);
        iterator.value = htmlEntry;
        _workManager.add(source, SourcePriority.HTML);
      } else if (sourceEntry is DartEntry) {
        DartEntry dartEntry = sourceEntry;
        oldPartMap[source] = dartEntry.getValue(DartEntry.INCLUDED_PARTS);
        dartEntry.invalidateAllResolutionInformation(invalidateUris);
        iterator.value = dartEntry;
        _workManager.add(source, _computePriority(dartEntry));
      }
    }
    _removeFromPartsUsingMap(oldPartMap);
  }

  /**
   * In response to a change to at least one of the compilation units in the
   * library defined by the given [librarySource], invalidate any results that
   * are dependent on the result of resolving that library.
   *
   * <b>Note:</b> Any cache entries that were accessed before this method was
   * invoked must be re-accessed after this method returns.
   */
  void _invalidateLibraryResolution(Source librarySource) {
    // TODO(brianwilkerson) This could be optimized. There's no need to flush
    // all of these entries if the public namespace hasn't changed, which will
    // be a fairly common case. The question is whether we can afford the time
    // to compute the namespace to look for differences.
    DartEntry libraryEntry = _getReadableDartEntry(librarySource);
    if (libraryEntry != null) {
      List<Source> includedParts =
          libraryEntry.getValue(DartEntry.INCLUDED_PARTS);
      libraryEntry.invalidateAllResolutionInformation(false);
      _workManager.add(librarySource, SourcePriority.LIBRARY);
      for (Source partSource in includedParts) {
        SourceEntry partEntry = _cache.get(partSource);
        if (partEntry is DartEntry) {
          partEntry.invalidateAllResolutionInformation(false);
        }
      }
    }
  }

  /**
   * Return `true` if the given [library] is, or depends on, 'dart:html'. The
   * [visitedLibraries] is a collection of the libraries that have been visited,
   * used to prevent infinite recursion.
   */
  bool _isClient(LibraryElement library, Source htmlSource,
      HashSet<LibraryElement> visitedLibraries) {
    if (visitedLibraries.contains(library)) {
      return false;
    }
    if (library.source == htmlSource) {
      return true;
    }
    visitedLibraries.add(library);
    for (LibraryElement imported in library.importedLibraries) {
      if (_isClient(imported, htmlSource, visitedLibraries)) {
        return true;
      }
    }
    for (LibraryElement exported in library.exportedLibraries) {
      if (_isClient(exported, htmlSource, visitedLibraries)) {
        return true;
      }
    }
    return false;
  }

  bool _isTooBigHtmlSourceEntry(Source source, SourceEntry sourceEntry) =>
      false;

//  /**
//   * Notify all of the analysis listeners that the given source is no longer included in the set of
//   * sources that are being analyzed.
//   *
//   * @param source the source that is no longer being analyzed
//   */
//  void _notifyExcludedSource(Source source) {
//    int count = _listeners.length;
//    for (int i = 0; i < count; i++) {
//      _listeners[i].excludedSource(this, source);
//    }
//  }

//  /**
//   * Notify all of the analysis listeners that the given source is now included in the set of
//   * sources that are being analyzed.
//   *
//   * @param source the source that is now being analyzed
//   */
//  void _notifyIncludedSource(Source source) {
//    int count = _listeners.length;
//    for (int i = 0; i < count; i++) {
//      _listeners[i].includedSource(this, source);
//    }
//  }

//  /**
//   * Notify all of the analysis listeners that the given Dart source was parsed.
//   *
//   * @param source the source that was parsed
//   * @param unit the result of parsing the source
//   */
//  void _notifyParsedDart(Source source, CompilationUnit unit) {
//    int count = _listeners.length;
//    for (int i = 0; i < count; i++) {
//      _listeners[i].parsedDart(this, source, unit);
//    }
//  }

//  /**
//   * Notify all of the analysis listeners that the given HTML source was parsed.
//   *
//   * @param source the source that was parsed
//   * @param unit the result of parsing the source
//   */
//  void _notifyParsedHtml(Source source, ht.HtmlUnit unit) {
//    int count = _listeners.length;
//    for (int i = 0; i < count; i++) {
//      _listeners[i].parsedHtml(this, source, unit);
//    }
//  }

//  /**
//   * Notify all of the analysis listeners that the given Dart source was resolved.
//   *
//   * @param source the source that was resolved
//   * @param unit the result of resolving the source
//   */
//  void _notifyResolvedDart(Source source, CompilationUnit unit) {
//    int count = _listeners.length;
//    for (int i = 0; i < count; i++) {
//      _listeners[i].resolvedDart(this, source, unit);
//    }
//  }

//  /**
//   * Notify all of the analysis listeners that the given HTML source was resolved.
//   *
//   * @param source the source that was resolved
//   * @param unit the result of resolving the source
//   */
//  void _notifyResolvedHtml(Source source, ht.HtmlUnit unit) {
//    int count = _listeners.length;
//    for (int i = 0; i < count; i++) {
//      _listeners[i].resolvedHtml(this, source, unit);
//    }
//  }

  /**
   * Log the given debugging [message].
   */
  void _logInformation(String message) {
    AnalysisEngine.instance.logger.logInformation(message);
  }

  /**
   * Notify all of the analysis listeners that a task is about to be performed.
   */
  void _notifyAboutToPerformTask(String taskDescription) {
    int count = _listeners.length;
    for (int i = 0; i < count; i++) {
      _listeners[i].aboutToPerformTask(this, taskDescription);
    }
  }

  /**
   * Notify all of the analysis listeners that the errors associated with the
   * given [source] has been updated to the given [errors].
   */
  void _notifyErrors(
      Source source, List<AnalysisError> errors, LineInfo lineInfo) {
    int count = _listeners.length;
    for (int i = 0; i < count; i++) {
      _listeners[i].computedErrors(this, source, errors, lineInfo);
    }
  }

  /**
   * Given that the given [source] (with the corresponding [sourceEntry]) has
   * been invalidated, invalidate all of the libraries that depend on it.
   */
  void _propagateInvalidation(Source source, SourceEntry sourceEntry) {
    if (sourceEntry is HtmlEntry) {
      HtmlEntry htmlEntry = sourceEntry;
      htmlEntry.modificationTime = getModificationStamp(source);
      htmlEntry.invalidateAllInformation();
      _cache.removedAst(source);
      _workManager.add(source, SourcePriority.HTML);
    } else if (sourceEntry is DartEntry) {
      List<Source> containingLibraries = getLibrariesContaining(source);
      List<Source> dependentLibraries = getLibrariesDependingOn(source);
      HashSet<Source> librariesToInvalidate = new HashSet<Source>();
      for (Source containingLibrary in containingLibraries) {
        _computeAllLibrariesDependingOn(
            containingLibrary, librariesToInvalidate);
      }
      for (Source dependentLibrary in dependentLibraries) {
        _computeAllLibrariesDependingOn(
            dependentLibrary, librariesToInvalidate);
      }
      for (Source library in librariesToInvalidate) {
        _invalidateLibraryResolution(library);
      }
      DartEntry dartEntry = _cache.get(source);
      _removeFromParts(source, dartEntry);
      dartEntry.modificationTime = getModificationStamp(source);
      dartEntry.invalidateAllInformation();
      _cache.removedAst(source);
      _workManager.add(source, SourcePriority.UNKNOWN);
    }
    // reset unit in the notification, it is out of date now
    ChangeNoticeImpl notice = _pendingNotices[source];
    if (notice != null) {
      notice.resolvedDartUnit = null;
      notice.resolvedHtmlUnit = null;
    }
  }

  /**
   * Given a [dartEntry] and a [library] element, record the library element and
   * other information gleaned from the element in the cache entry.
   */
  void _recordElementData(DartEntry dartEntry, LibraryElement library,
      Source librarySource, Source htmlSource) {
    dartEntry.setValue(DartEntry.ELEMENT, library);
    dartEntry.setValue(DartEntry.IS_LAUNCHABLE, library.entryPoint != null);
    dartEntry.setValue(DartEntry.IS_CLIENT,
        _isClient(library, htmlSource, new HashSet<LibraryElement>()));
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  DartEntry _recordGenerateDartErrorsTask(GenerateDartErrorsTask task) {
    Source source = task.source;
    DartEntry dartEntry = _cache.get(source);
    Source librarySource = task.libraryElement.source;
    CaughtException thrownException = task.exception;
    if (thrownException != null) {
      dartEntry.recordVerificationErrorInLibrary(
          librarySource, thrownException);
      throw new AnalysisException('<rethrow>', thrownException);
    }
    dartEntry.setValueInLibrary(
        DartEntry.VERIFICATION_ERRORS, librarySource, task.errors);
    ChangeNoticeImpl notice = getNotice(source);
    LineInfo lineInfo = dartEntry.getValue(SourceEntry.LINE_INFO);
    notice.setErrors(dartEntry.allErrors, lineInfo);
    return dartEntry;
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  DartEntry _recordGenerateDartHintsTask(GenerateDartHintsTask task) {
    Source librarySource = task.libraryElement.source;
    CaughtException thrownException = task.exception;
    DartEntry libraryEntry = null;
    HashMap<Source, List<AnalysisError>> hintMap = task.hintMap;
    if (hintMap == null) {
      // We don't have any information about which sources to mark as invalid
      // other than the library source.
      DartEntry libraryEntry = _cache.get(librarySource);
      if (thrownException == null) {
        String message = "GenerateDartHintsTask returned a null hint map "
            "without throwing an exception: ${librarySource.fullName}";
        thrownException =
            new CaughtException(new AnalysisException(message), null);
      }
      libraryEntry.recordHintErrorInLibrary(librarySource, thrownException);
      throw new AnalysisException('<rethrow>', thrownException);
    }
    hintMap.forEach((Source unitSource, List<AnalysisError> hints) {
      DartEntry dartEntry = _cache.get(unitSource);
      if (unitSource == librarySource) {
        libraryEntry = dartEntry;
      }
      if (thrownException == null) {
        dartEntry.setValueInLibrary(DartEntry.HINTS, librarySource, hints);
        ChangeNoticeImpl notice = getNotice(unitSource);
        LineInfo lineInfo = dartEntry.getValue(SourceEntry.LINE_INFO);
        notice.setErrors(dartEntry.allErrors, lineInfo);
      } else {
        dartEntry.recordHintErrorInLibrary(librarySource, thrownException);
      }
    });
    if (thrownException != null) {
      throw new AnalysisException('<rethrow>', thrownException);
    }
    return libraryEntry;
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  DartEntry _recordGenerateDartLintsTask(GenerateDartLintsTask task) {
    Source librarySource = task.libraryElement.source;
    CaughtException thrownException = task.exception;
    DartEntry libraryEntry = null;
    HashMap<Source, List<AnalysisError>> lintMap = task.lintMap;
    if (lintMap == null) {
      // We don't have any information about which sources to mark as invalid
      // other than the library source.
      DartEntry libraryEntry = _cache.get(librarySource);
      if (thrownException == null) {
        String message = "GenerateDartLintsTask returned a null lint map "
            "without throwing an exception: ${librarySource.fullName}";
        thrownException =
            new CaughtException(new AnalysisException(message), null);
      }
      libraryEntry.recordLintErrorInLibrary(librarySource, thrownException);
      throw new AnalysisException('<rethrow>', thrownException);
    }
    lintMap.forEach((Source unitSource, List<AnalysisError> lints) {
      DartEntry dartEntry = _cache.get(unitSource);
      if (unitSource == librarySource) {
        libraryEntry = dartEntry;
      }
      if (thrownException == null) {
        dartEntry.setValueInLibrary(DartEntry.LINTS, librarySource, lints);
        ChangeNoticeImpl notice = getNotice(unitSource);
        LineInfo lineInfo = dartEntry.getValue(SourceEntry.LINE_INFO);
        notice.setErrors(dartEntry.allErrors, lineInfo);
      } else {
        dartEntry.recordLintErrorInLibrary(librarySource, thrownException);
      }
    });
    if (thrownException != null) {
      throw new AnalysisException('<rethrow>', thrownException);
    }
    return libraryEntry;
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  SourceEntry _recordGetContentsTask(GetContentTask task) {
    if (!task.isComplete) {
      return null;
    }
    Source source = task.source;
    SourceEntry sourceEntry = _cache.get(source);
    CaughtException thrownException = task.exception;
    if (thrownException != null) {
      sourceEntry.recordContentError(thrownException);
      {
        sourceEntry.setValue(SourceEntry.CONTENT_ERRORS, task.errors);
        ChangeNoticeImpl notice = getNotice(source);
        notice.setErrors(sourceEntry.allErrors, null);
      }
      _workManager.remove(source);
      throw new AnalysisException('<rethrow>', thrownException);
    }
    sourceEntry.modificationTime = task.modificationTime;
    sourceEntry.setValue(SourceEntry.CONTENT, task.content);
    return sourceEntry;
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  DartEntry _recordIncrementalAnalysisTaskResults(
      IncrementalAnalysisTask task) {
    CompilationUnit unit = task.compilationUnit;
    if (unit != null) {
      ChangeNoticeImpl notice = getNotice(task.source);
      notice.resolvedDartUnit = unit;
      _incrementalAnalysisCache =
          IncrementalAnalysisCache.cacheResult(task.cache, unit);
    }
    return null;
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  DartEntry _recordParseDartTaskResults(ParseDartTask task) {
    Source source = task.source;
    DartEntry dartEntry = _cache.get(source);
    _removeFromParts(source, dartEntry);
    CaughtException thrownException = task.exception;
    if (thrownException != null) {
      _removeFromParts(source, dartEntry);
      dartEntry.recordParseError(thrownException);
      _cache.removedAst(source);
      throw new AnalysisException('<rethrow>', thrownException);
    }
    if (task.hasNonPartOfDirective) {
      dartEntry.setValue(DartEntry.SOURCE_KIND, SourceKind.LIBRARY);
      dartEntry.containingLibrary = source;
      _workManager.add(source, SourcePriority.LIBRARY);
    } else if (task.hasPartOfDirective) {
      dartEntry.setValue(DartEntry.SOURCE_KIND, SourceKind.PART);
      dartEntry.removeContainingLibrary(source);
      _workManager.add(source, SourcePriority.NORMAL_PART);
    } else {
      // The file contains no directives.
      List<Source> containingLibraries = dartEntry.containingLibraries;
      if (containingLibraries.length > 1 ||
          (containingLibraries.length == 1 &&
              containingLibraries[0] != source)) {
        dartEntry.setValue(DartEntry.SOURCE_KIND, SourceKind.PART);
        dartEntry.removeContainingLibrary(source);
        _workManager.add(source, SourcePriority.NORMAL_PART);
      } else {
        dartEntry.setValue(DartEntry.SOURCE_KIND, SourceKind.LIBRARY);
        dartEntry.containingLibrary = source;
        _workManager.add(source, SourcePriority.LIBRARY);
      }
    }
    List<Source> newParts = task.includedSources;
    for (int i = 0; i < newParts.length; i++) {
      Source partSource = newParts[i];
      DartEntry partEntry = _getReadableDartEntry(partSource);
      if (partEntry != null && !identical(partEntry, dartEntry)) {
        // TODO(brianwilkerson) Change the kind of the "part" if it was marked
        // as a library and it has no directives.
        partEntry.addContainingLibrary(source);
      }
    }
    dartEntry.setValue(DartEntry.PARSED_UNIT, task.compilationUnit);
    dartEntry.setValue(DartEntry.PARSE_ERRORS, task.errors);
    dartEntry.setValue(DartEntry.EXPORTED_LIBRARIES, task.exportedSources);
    dartEntry.setValue(DartEntry.IMPORTED_LIBRARIES, task.importedSources);
    dartEntry.setValue(DartEntry.INCLUDED_PARTS, newParts);
    _cache.storedAst(source);
    ChangeNoticeImpl notice = getNotice(source);
    if (notice.resolvedDartUnit == null) {
      notice.parsedDartUnit = task.compilationUnit;
    }
    notice.setErrors(dartEntry.allErrors, task.lineInfo);
    // Verify that the incrementally parsed and resolved unit in the incremental
    // cache is structurally equivalent to the fully parsed unit
    _incrementalAnalysisCache = IncrementalAnalysisCache.verifyStructure(
        _incrementalAnalysisCache, source, task.compilationUnit);
    return dartEntry;
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  HtmlEntry _recordParseHtmlTaskResults(ParseHtmlTask task) {
    Source source = task.source;
    HtmlEntry htmlEntry = _cache.get(source);
    CaughtException thrownException = task.exception;
    if (thrownException != null) {
      htmlEntry.recordParseError(thrownException);
      _cache.removedAst(source);
      throw new AnalysisException('<rethrow>', thrownException);
    }
    LineInfo lineInfo = task.lineInfo;
    htmlEntry.setValue(SourceEntry.LINE_INFO, lineInfo);
    htmlEntry.setValue(HtmlEntry.PARSED_UNIT, task.htmlUnit);
    htmlEntry.setValue(HtmlEntry.PARSE_ERRORS, task.errors);
    htmlEntry.setValue(
        HtmlEntry.REFERENCED_LIBRARIES, task.referencedLibraries);
    _cache.storedAst(source);
    ChangeNoticeImpl notice = getNotice(source);
    notice.setErrors(htmlEntry.allErrors, lineInfo);
    return htmlEntry;
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  DartEntry _recordResolveDartUnitTaskResults(ResolveDartUnitTask task) {
    Source unitSource = task.source;
    DartEntry dartEntry = _cache.get(unitSource);
    Source librarySource = task.librarySource;
    CaughtException thrownException = task.exception;
    if (thrownException != null) {
      dartEntry.recordResolutionErrorInLibrary(librarySource, thrownException);
      _cache.removedAst(unitSource);
      throw new AnalysisException('<rethrow>', thrownException);
    }
    dartEntry.setValueInLibrary(
        DartEntry.RESOLVED_UNIT, librarySource, task.resolvedUnit);
    _cache.storedAst(unitSource);
    return dartEntry;
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  HtmlEntry _recordResolveHtmlTaskResults(ResolveHtmlTask task) {
    Source source = task.source;
    HtmlEntry htmlEntry = _cache.get(source);
    CaughtException thrownException = task.exception;
    if (thrownException != null) {
      htmlEntry.recordResolutionError(thrownException);
      _cache.removedAst(source);
      throw new AnalysisException('<rethrow>', thrownException);
    }
    htmlEntry.setState(HtmlEntry.PARSED_UNIT, CacheState.FLUSHED);
    htmlEntry.setValue(HtmlEntry.RESOLVED_UNIT, task.resolvedUnit);
    htmlEntry.setValue(HtmlEntry.ELEMENT, task.element);
    htmlEntry.setValue(HtmlEntry.RESOLUTION_ERRORS, task.resolutionErrors);
    _cache.storedAst(source);
    ChangeNoticeImpl notice = getNotice(source);
    notice.resolvedHtmlUnit = task.resolvedUnit;
    LineInfo lineInfo = htmlEntry.getValue(SourceEntry.LINE_INFO);
    notice.setErrors(htmlEntry.allErrors, lineInfo);
    return htmlEntry;
  }

  /**
   * Record the results produced by performing a [task] and return the cache
   * entry associated with the results.
   */
  DartEntry _recordScanDartTaskResults(ScanDartTask task) {
    Source source = task.source;
    DartEntry dartEntry = _cache.get(source);
    CaughtException thrownException = task.exception;
    if (thrownException != null) {
      _removeFromParts(source, dartEntry);
      dartEntry.recordScanError(thrownException);
      _cache.removedAst(source);
      throw new AnalysisException('<rethrow>', thrownException);
    }
    LineInfo lineInfo = task.lineInfo;
    dartEntry.setValue(SourceEntry.LINE_INFO, lineInfo);
    dartEntry.setValue(DartEntry.TOKEN_STREAM, task.tokenStream);
    dartEntry.setValue(DartEntry.SCAN_ERRORS, task.errors);
    _cache.storedAst(source);
    ChangeNoticeImpl notice = getNotice(source);
    notice.setErrors(dartEntry.allErrors, lineInfo);
    return dartEntry;
  }

  void _removeFromCache(Source source) {
    SourceEntry entry = _cache.remove(source);
    if (entry != null && !entry.explicitlyAdded) {
      _implicitAnalysisEventsController
          .add(new ImplicitAnalysisEvent(source, false));
    }
  }

  /**
   * Remove the given [librarySource] from the list of containing libraries for
   * all of the parts referenced by the given [dartEntry].
   */
  void _removeFromParts(Source librarySource, DartEntry dartEntry) {
    List<Source> oldParts = dartEntry.getValue(DartEntry.INCLUDED_PARTS);
    for (int i = 0; i < oldParts.length; i++) {
      Source partSource = oldParts[i];
      DartEntry partEntry = _getReadableDartEntry(partSource);
      if (partEntry != null && !identical(partEntry, dartEntry)) {
        partEntry.removeContainingLibrary(librarySource);
        if (partEntry.containingLibraries.length == 0 && !exists(partSource)) {
          _removeFromCache(partSource);
        }
      }
    }
  }

  /**
   * Remove the given libraries that are keys in the given map from the list of
   * containing libraries for each of the parts in the corresponding value.
   */
  void _removeFromPartsUsingMap(HashMap<Source, List<Source>> oldPartMap) {
    oldPartMap.forEach((Source librarySource, List<Source> oldParts) {
      for (int i = 0; i < oldParts.length; i++) {
        Source partSource = oldParts[i];
        if (partSource != librarySource) {
          DartEntry partEntry = _getReadableDartEntry(partSource);
          if (partEntry != null) {
            partEntry.removeContainingLibrary(librarySource);
            if (partEntry.containingLibraries.length == 0 &&
                !exists(partSource)) {
              _removeFromCache(partSource);
            }
          }
        }
      }
    });
  }

  /**
   * Remove the given [source] from the priority order if it is in the list.
   */
  void _removeFromPriorityOrder(Source source) {
    int count = _priorityOrder.length;
    List<Source> newOrder = new List<Source>();
    for (int i = 0; i < count; i++) {
      if (_priorityOrder[i] != source) {
        newOrder.add(_priorityOrder[i]);
      }
    }
    if (newOrder.length < count) {
      analysisPriorityOrder = newOrder;
    }
  }

  /**
   * Create an entry for the newly added [source] and invalidate any sources
   * that referenced the source before it existed.
   */
  void _sourceAvailable(Source source) {
    // TODO(brianwilkerson) This method needs to check whether the source was
    // previously being implicitly analyzed. If so, the cache entry needs to be
    // update to reflect the new status and an event needs to be generated to
    // inform clients that it is no longer being implicitly analyzed.
    SourceEntry sourceEntry = _cache.get(source);
    if (sourceEntry == null) {
      sourceEntry = _createSourceEntry(source, true);
    } else {
      _propagateInvalidation(source, sourceEntry);
      sourceEntry = _cache.get(source);
    }
    if (sourceEntry is HtmlEntry) {
      _workManager.add(source, SourcePriority.HTML);
    } else if (sourceEntry is DartEntry) {
      _workManager.add(source, _computePriority(sourceEntry));
    }
  }

  /**
   * Invalidate the [source] that was changed and any sources that referenced
   * the source before it existed.
   */
  void _sourceChanged(Source source) {
    SourceEntry sourceEntry = _cache.get(source);
    // If the source is removed, we don't care about it.
    if (sourceEntry == null) {
      return;
    }
    // Check if the content of the source is the same as it was the last time.
    String sourceContent = sourceEntry.getValue(SourceEntry.CONTENT);
    if (sourceContent != null) {
      sourceEntry.setState(SourceEntry.CONTENT, CacheState.FLUSHED);
      try {
        TimestampedData<String> fileContents = getContents(source);
        if (fileContents.data == sourceContent) {
          return;
        }
      } catch (e) {}
    }
    // We have to invalidate the cache.
    _propagateInvalidation(source, sourceEntry);
  }

  /**
   * Record that the give [source] has been deleted.
   */
  void _sourceDeleted(Source source) {
    SourceEntry sourceEntry = _cache.get(source);
    if (sourceEntry is HtmlEntry) {
      HtmlEntry htmlEntry = sourceEntry;
      htmlEntry.recordContentError(new CaughtException(
          new AnalysisException("This source was marked as being deleted"),
          null));
    } else if (sourceEntry is DartEntry) {
      DartEntry dartEntry = sourceEntry;
      HashSet<Source> libraries = new HashSet<Source>();
      for (Source librarySource in getLibrariesContaining(source)) {
        libraries.add(librarySource);
        for (Source dependentLibrary
            in getLibrariesDependingOn(librarySource)) {
          libraries.add(dependentLibrary);
        }
      }
      for (Source librarySource in libraries) {
        _invalidateLibraryResolution(librarySource);
      }
      dartEntry.recordContentError(new CaughtException(
          new AnalysisException("This source was marked as being deleted"),
          null));
    }
    _workManager.remove(source);
    _removeFromPriorityOrder(source);
  }

  /**
   * Record that the given [source] has been removed.
   */
  void _sourceRemoved(Source source) {
    SourceEntry sourceEntry = _cache.get(source);
    if (sourceEntry is HtmlEntry) {} else if (sourceEntry is DartEntry) {
      HashSet<Source> libraries = new HashSet<Source>();
      for (Source librarySource in getLibrariesContaining(source)) {
        libraries.add(librarySource);
        for (Source dependentLibrary
            in getLibrariesDependingOn(librarySource)) {
          libraries.add(dependentLibrary);
        }
      }
      for (Source librarySource in libraries) {
        _invalidateLibraryResolution(librarySource);
      }
    }
    _removeFromCache(source);
    _workManager.remove(source);
    _removeFromPriorityOrder(source);
  }

  /**
   * TODO(scheglov) A hackish, limited incremental resolution implementation.
   */
  bool _tryPoorMansIncrementalResolution(Source unitSource, String newCode) {
    return PerformanceStatistics.incrementalAnalysis.makeCurrentWhile(() {
      incrementalResolutionValidation_lastUnitSource = null;
      incrementalResolutionValidation_lastLibrarySource = null;
      incrementalResolutionValidation_lastUnit = null;
      // prepare the entry
      DartEntry dartEntry = _cache.get(unitSource);
      if (dartEntry == null) {
        return false;
      }
      // prepare the (only) library source
      List<Source> librarySources = getLibrariesContaining(unitSource);
      if (librarySources.length != 1) {
        return false;
      }
      Source librarySource = librarySources[0];
      // prepare the library element
      LibraryElement libraryElement = getLibraryElement(librarySource);
      if (libraryElement == null) {
        return false;
      }
      // prepare the existing unit
      CompilationUnit oldUnit =
          getResolvedCompilationUnit2(unitSource, librarySource);
      if (oldUnit == null) {
        return false;
      }
      // do resolution
      Stopwatch perfCounter = new Stopwatch()..start();
      PoorMansIncrementalResolver resolver = new PoorMansIncrementalResolver(
          typeProvider,
          unitSource,
          getReadableSourceEntryOrNull(unitSource),
          null,
          null,
          oldUnit,
          analysisOptions.incrementalApi);
      bool success = resolver.resolve(newCode);
      AnalysisEngine.instance.instrumentationService.logPerformance(
          AnalysisPerformanceKind.INCREMENTAL,
          perfCounter,
          'success=$success,context_id=$_id,code_length=${newCode.length}');
      if (!success) {
        return false;
      }
      // if validation, remember the result, but throw it away
      if (analysisOptions.incrementalValidation) {
        incrementalResolutionValidation_lastUnitSource = oldUnit.element.source;
        incrementalResolutionValidation_lastLibrarySource =
            oldUnit.element.library.source;
        incrementalResolutionValidation_lastUnit = oldUnit;
        return false;
      }
      // prepare notice
      {
        LineInfo lineInfo = getLineInfo(unitSource);
        ChangeNoticeImpl notice = getNotice(unitSource);
        notice.resolvedDartUnit = oldUnit;
        notice.setErrors(dartEntry.allErrors, lineInfo);
      }
      // OK
      return true;
    });
  }

  void _validateLastIncrementalResolutionResult() {
    if (incrementalResolutionValidation_lastUnitSource == null ||
        incrementalResolutionValidation_lastLibrarySource == null ||
        incrementalResolutionValidation_lastUnit == null) {
      return;
    }
    CompilationUnit fullUnit = getResolvedCompilationUnit2(
        incrementalResolutionValidation_lastUnitSource,
        incrementalResolutionValidation_lastLibrarySource);
    if (fullUnit != null) {
      try {
        assertSameResolution(
            incrementalResolutionValidation_lastUnit, fullUnit);
      } on IncrementalResolutionMismatch catch (mismatch, stack) {
        String failure = mismatch.message;
        String message =
            'Incremental resolution mismatch:\n$failure\nat\n$stack';
        AnalysisEngine.instance.logger.logError(message);
      }
    }
    incrementalResolutionValidation_lastUnitSource = null;
    incrementalResolutionValidation_lastLibrarySource = null;
    incrementalResolutionValidation_lastUnit = null;
  }
}

/**
 * An object used by an analysis context to record the results of a task.
 */
class AnalysisContextImpl_AnalysisTaskResultRecorder
    implements AnalysisTaskVisitor<SourceEntry> {
  final AnalysisContextImpl AnalysisContextImpl_this;

  AnalysisContextImpl_AnalysisTaskResultRecorder(this.AnalysisContextImpl_this);

  @override
  DartEntry visitGenerateDartErrorsTask(GenerateDartErrorsTask task) =>
      AnalysisContextImpl_this._recordGenerateDartErrorsTask(task);

  @override
  DartEntry visitGenerateDartHintsTask(GenerateDartHintsTask task) =>
      AnalysisContextImpl_this._recordGenerateDartHintsTask(task);

  @override
  DartEntry visitGenerateDartLintsTask(GenerateDartLintsTask task) =>
      AnalysisContextImpl_this._recordGenerateDartLintsTask(task);

  @override
  SourceEntry visitGetContentTask(GetContentTask task) =>
      AnalysisContextImpl_this._recordGetContentsTask(task);

  @override
  DartEntry visitIncrementalAnalysisTask(IncrementalAnalysisTask task) =>
      AnalysisContextImpl_this._recordIncrementalAnalysisTaskResults(task);

  @override
  DartEntry visitParseDartTask(ParseDartTask task) =>
      AnalysisContextImpl_this._recordParseDartTaskResults(task);

  @override
  HtmlEntry visitParseHtmlTask(ParseHtmlTask task) =>
      AnalysisContextImpl_this._recordParseHtmlTaskResults(task);

  @override
  DartEntry visitResolveDartLibraryCycleTask(
          ResolveDartLibraryCycleTask task) =>
      AnalysisContextImpl_this.recordResolveDartLibraryCycleTaskResults(task);

  @override
  DartEntry visitResolveDartLibraryTask(ResolveDartLibraryTask task) =>
      AnalysisContextImpl_this.recordResolveDartLibraryTaskResults(task);

  @override
  DartEntry visitResolveDartUnitTask(ResolveDartUnitTask task) =>
      AnalysisContextImpl_this._recordResolveDartUnitTaskResults(task);

  @override
  HtmlEntry visitResolveHtmlTask(ResolveHtmlTask task) =>
      AnalysisContextImpl_this._recordResolveHtmlTaskResults(task);

  @override
  DartEntry visitScanDartTask(ScanDartTask task) =>
      AnalysisContextImpl_this._recordScanDartTaskResults(task);
}

class AnalysisContextImpl_ContextRetentionPolicy
    implements CacheRetentionPolicy {
  final AnalysisContextImpl AnalysisContextImpl_this;

  AnalysisContextImpl_ContextRetentionPolicy(this.AnalysisContextImpl_this);

  @override
  RetentionPriority getAstPriority(Source source, SourceEntry sourceEntry) {
    int priorityCount = AnalysisContextImpl_this._priorityOrder.length;
    for (int i = 0; i < priorityCount; i++) {
      if (source == AnalysisContextImpl_this._priorityOrder[i]) {
        return RetentionPriority.HIGH;
      }
    }
    if (AnalysisContextImpl_this._neededForResolution != null &&
        AnalysisContextImpl_this._neededForResolution.contains(source)) {
      return RetentionPriority.HIGH;
    }
    if (sourceEntry is DartEntry) {
      DartEntry dartEntry = sourceEntry;
      if (_astIsNeeded(dartEntry)) {
        return RetentionPriority.MEDIUM;
      }
    }
    return RetentionPriority.LOW;
  }

  bool _astIsNeeded(DartEntry dartEntry) =>
      dartEntry.hasInvalidData(DartEntry.HINTS) ||
          dartEntry.hasInvalidData(DartEntry.LINTS) ||
          dartEntry.hasInvalidData(DartEntry.VERIFICATION_ERRORS) ||
          dartEntry.hasInvalidData(DartEntry.RESOLUTION_ERRORS);
}

/**
 * An object used to construct a list of the libraries that must be resolved
 * together in order to resolve any one of the libraries.
 */
class AnalysisContextImpl_CycleBuilder {
  final AnalysisContextImpl AnalysisContextImpl_this;

  /**
   * A table mapping the sources of the defining compilation units of libraries
   * to the representation of the library that has the information needed to
   * resolve the library.
   */
  HashMap<Source, ResolvableLibrary> _libraryMap =
      new HashMap<Source, ResolvableLibrary>();

  /**
   * The dependency graph used to compute the libraries in the cycle.
   */
  DirectedGraph<ResolvableLibrary> _dependencyGraph;

  /**
   * A list containing the libraries that are ready to be resolved.
   */
  List<ResolvableLibrary> _librariesInCycle;

  /**
   * The analysis task that needs to be performed before the cycle of libraries
   * can be resolved, or `null` if the libraries are ready to be resolved.
   */
  AnalysisContextImpl_TaskData _taskData;

  /**
   * Initialize a newly created cycle builder.
   */
  AnalysisContextImpl_CycleBuilder(this.AnalysisContextImpl_this) : super();

  /**
   * Return a list containing the libraries that are ready to be resolved
   * (assuming that [getTaskData] returns `null`).
   */
  List<ResolvableLibrary> get librariesInCycle => _librariesInCycle;

  /**
   * Return a representation of an analysis task that needs to be performed
   * before the cycle of libraries can be resolved, or `null` if the libraries
   * are ready to be resolved.
   */
  AnalysisContextImpl_TaskData get taskData => _taskData;

  /**
   * Compute a list of the libraries that need to be resolved together in orde
   *  to resolve the given [librarySource].
   */
  void computeCycleContaining(Source librarySource) {
    //
    // Create the object representing the library being resolved.
    //
    ResolvableLibrary targetLibrary = _createLibrary(librarySource);
    //
    // Compute the set of libraries that need to be resolved together.
    //
    _dependencyGraph = new DirectedGraph<ResolvableLibrary>();
    _computeLibraryDependencies(targetLibrary);
    if (_taskData != null) {
      return;
    }
    _librariesInCycle = _dependencyGraph.findCycleContaining(targetLibrary);
    //
    // Ensure that all of the data needed to resolve them has been computed.
    //
    _ensureImportsAndExports();
    if (_taskData != null) {
      // At least one imported library needs to be resolved before the target
      // library.
      AnalysisTask task = _taskData.task;
      if (task is ResolveDartLibraryTask) {
        AnalysisContextImpl_this._workManager
            .addFirst(task.librarySource, SourcePriority.LIBRARY);
      }
      return;
    }
    _computePartsInCycle(librarySource);
    if (_taskData != null) {
      // At least one part needs to be parsed.
      return;
    }
    // All of the AST's necessary to perform a resolution of the library cycle
    // have been gathered, so it is no longer necessary to retain them in the
    // cache.
    AnalysisContextImpl_this._neededForResolution = null;
  }

  bool _addDependency(ResolvableLibrary dependant, Source dependency,
      List<ResolvableLibrary> dependencyList) {
    if (dependant.librarySource == dependency) {
      // Don't add a dependency of a library on itself; there's no point.
      return true;
    }
    ResolvableLibrary importedLibrary = _libraryMap[dependency];
    if (importedLibrary == null) {
      importedLibrary = _createLibraryOrNull(dependency);
      if (importedLibrary != null) {
        _computeLibraryDependencies(importedLibrary);
        if (_taskData != null) {
          return false;
        }
      }
    }
    if (importedLibrary != null) {
      if (dependencyList != null) {
        dependencyList.add(importedLibrary);
      }
      _dependencyGraph.addEdge(dependant, importedLibrary);
    }
    return true;
  }

  /**
   * Recursively traverse the libraries reachable from the given [library],
   * creating instances of the class [Library] to represent them, and record the
   * references in the library objects.
   *
   * Throws an [AnalysisException] if some portion of the library graph could
   * not be traversed.
   */
  void _computeLibraryDependencies(ResolvableLibrary library) {
    Source librarySource = library.librarySource;
    DartEntry dartEntry =
        AnalysisContextImpl_this._getReadableDartEntry(librarySource);
    List<Source> importedSources =
        _getSources(librarySource, dartEntry, DartEntry.IMPORTED_LIBRARIES);
    if (_taskData != null) {
      return;
    }
    List<Source> exportedSources =
        _getSources(librarySource, dartEntry, DartEntry.EXPORTED_LIBRARIES);
    if (_taskData != null) {
      return;
    }
    _computeLibraryDependenciesFromDirectives(
        library, importedSources, exportedSources);
  }

  /**
   * Recursively traverse the libraries reachable from the given [library],
   * creating instances of the class [Library] to represent them, and record the
   * references in the library objects. The [importedSources] is a list
   * containing the sources that are imported into the given library. The
   * [exportedSources] is a list containing the sources that are exported from
   * the given library.
   */
  void _computeLibraryDependenciesFromDirectives(ResolvableLibrary library,
      List<Source> importedSources, List<Source> exportedSources) {
    int importCount = importedSources.length;
    List<ResolvableLibrary> importedLibraries = new List<ResolvableLibrary>();
    bool explicitlyImportsCore = false;
    bool importsAsync = false;
    for (int i = 0; i < importCount; i++) {
      Source importedSource = importedSources[i];
      if (importedSource == AnalysisContextImpl_this._coreLibrarySource) {
        explicitlyImportsCore = true;
      } else if (importedSource ==
          AnalysisContextImpl_this._asyncLibrarySource) {
        importsAsync = true;
      }
      if (!_addDependency(library, importedSource, importedLibraries)) {
        return;
      }
    }
    library.explicitlyImportsCore = explicitlyImportsCore;
    if (!explicitlyImportsCore) {
      if (!_addDependency(library, AnalysisContextImpl_this._coreLibrarySource,
          importedLibraries)) {
        return;
      }
    }
    if (!importsAsync) {
      // Add a dependency on async to ensure that the Future element will be
      // built before we generate errors and warnings for async methods.  Also
      // include it in importedLibraries, so that it will be picked up by
      // LibraryResolver2._buildLibraryMap().
      // TODO(paulberry): this is a bit of a hack, since the async library
      // isn't actually being imported.  Also, it's not clear whether it should
      // be necessary: in theory, dart:core already (indirectly) imports
      // dart:async, so if core has been built, async should have been built
      // too.  However, removing this code causes unit test failures.
      if (!_addDependency(library, AnalysisContextImpl_this._asyncLibrarySource,
          importedLibraries)) {
        return;
      }
    }
    library.importedLibraries = importedLibraries;
    int exportCount = exportedSources.length;
    if (exportCount > 0) {
      List<ResolvableLibrary> exportedLibraries = new List<ResolvableLibrary>();
      for (int i = 0; i < exportCount; i++) {
        Source exportedSource = exportedSources[i];
        if (!_addDependency(library, exportedSource, exportedLibraries)) {
          return;
        }
      }
      library.exportedLibraries = exportedLibraries;
    }
  }

  /**
   * Gather the resolvable AST structures for each of the compilation units in
   * each of the libraries in the cycle. This is done in two phases: first we
   * ensure that we have cached an AST structure for each compilation unit, then
   * we gather them. We split the work this way because getting the AST
   * structures can change the state of the cache in such a way that we would
   * have more work to do if any compilation unit didn't have a resolvable AST
   * structure.
   */
  void _computePartsInCycle(Source librarySource) {
    int count = _librariesInCycle.length;
    List<CycleBuilder_LibraryPair> libraryData =
        new List<CycleBuilder_LibraryPair>();
    for (int i = 0; i < count; i++) {
      ResolvableLibrary library = _librariesInCycle[i];
      libraryData.add(new CycleBuilder_LibraryPair(
          library, _ensurePartsInLibrary(library)));
    }
    AnalysisContextImpl_this._neededForResolution = _gatherSources(libraryData);
    if (AnalysisContextImpl._TRACE_PERFORM_TASK) {
      print(
          "  preserve resolution data for ${AnalysisContextImpl_this._neededForResolution.length} sources while resolving ${librarySource.fullName}");
    }
    if (_taskData != null) {
      return;
    }
    for (int i = 0; i < count; i++) {
      _computePartsInLibrary(libraryData[i]);
    }
  }

  /**
   * Gather the resolvable compilation units for each of the compilation units
   * in the library represented by the [libraryPair].
   */
  void _computePartsInLibrary(CycleBuilder_LibraryPair libraryPair) {
    ResolvableLibrary library = libraryPair.library;
    List<CycleBuilder_SourceEntryPair> entryPairs = libraryPair.entryPairs;
    int count = entryPairs.length;
    List<ResolvableCompilationUnit> units =
        new List<ResolvableCompilationUnit>(count);
    for (int i = 0; i < count; i++) {
      CycleBuilder_SourceEntryPair entryPair = entryPairs[i];
      Source source = entryPair.source;
      DartEntry dartEntry = entryPair.entry;
      units[i] = new ResolvableCompilationUnit(
          source, dartEntry.resolvableCompilationUnit);
    }
    library.resolvableCompilationUnits = units;
  }

  /**
   * Create an object to represent the information about the library defined by
   * the compilation unit with the given [librarySource].
   */
  ResolvableLibrary _createLibrary(Source librarySource) {
    ResolvableLibrary library = new ResolvableLibrary(librarySource);
    SourceEntry sourceEntry =
        AnalysisContextImpl_this._cache.get(librarySource);
    if (sourceEntry is DartEntry) {
      LibraryElementImpl libraryElement =
          sourceEntry.getValue(DartEntry.ELEMENT) as LibraryElementImpl;
      if (libraryElement != null) {
        library.libraryElement = libraryElement;
      }
    }
    _libraryMap[librarySource] = library;
    return library;
  }

  /**
   * Create an object to represent the information about the library defined by
   * the compilation unit with the given [librarySource].
   */
  ResolvableLibrary _createLibraryOrNull(Source librarySource) {
    ResolvableLibrary library = new ResolvableLibrary(librarySource);
    SourceEntry sourceEntry =
        AnalysisContextImpl_this._cache.get(librarySource);
    if (sourceEntry is DartEntry) {
      LibraryElementImpl libraryElement =
          sourceEntry.getValue(DartEntry.ELEMENT) as LibraryElementImpl;
      if (libraryElement != null) {
        library.libraryElement = libraryElement;
      }
    }
    _libraryMap[librarySource] = library;
    return library;
  }

  /**
   * Ensure that the given [library] has an element model built for it. If
   * another task needs to be executed first in order to build the element
   * model, that task is placed in [taskData].
   */
  void _ensureElementModel(ResolvableLibrary library) {
    Source librarySource = library.librarySource;
    DartEntry libraryEntry =
        AnalysisContextImpl_this._getReadableDartEntry(librarySource);
    if (libraryEntry != null &&
        libraryEntry.getState(DartEntry.PARSED_UNIT) != CacheState.ERROR) {
      AnalysisContextImpl_this._workManager
          .addFirst(librarySource, SourcePriority.LIBRARY);
      if (_taskData == null) {
        _taskData = AnalysisContextImpl_this._createResolveDartLibraryTask(
            librarySource, libraryEntry);
      }
    }
  }

  /**
   * Ensure that all of the libraries that are exported by the given [library]
   * (but are not themselves in the cycle) have element models built for them.
   * If another task needs to be executed first in order to build the element
   * model, that task is placed in [taskData].
   */
  void _ensureExports(
      ResolvableLibrary library, HashSet<Source> visitedLibraries) {
    List<ResolvableLibrary> dependencies = library.exports;
    int dependencyCount = dependencies.length;
    for (int i = 0; i < dependencyCount; i++) {
      ResolvableLibrary dependency = dependencies[i];
      if (!_librariesInCycle.contains(dependency) &&
          visitedLibraries.add(dependency.librarySource)) {
        if (dependency.libraryElement == null) {
          _ensureElementModel(dependency);
        } else {
          _ensureExports(dependency, visitedLibraries);
        }
        if (_taskData != null) {
          return;
        }
      }
    }
  }

  /**
   * Ensure that all of the libraries that are exported by the given [library]
   * (but are not themselves in the cycle) have element models built for them.
   * If another task needs to be executed first in order to build the element
   * model, that task is placed in [taskData].
   */
  void _ensureImports(ResolvableLibrary library) {
    List<ResolvableLibrary> dependencies = library.imports;
    int dependencyCount = dependencies.length;
    for (int i = 0; i < dependencyCount; i++) {
      ResolvableLibrary dependency = dependencies[i];
      if (!_librariesInCycle.contains(dependency) &&
          dependency.libraryElement == null) {
        _ensureElementModel(dependency);
        if (_taskData != null) {
          return;
        }
      }
    }
  }

  /**
   * Ensure that all of the libraries that are either imported or exported by
   * libraries in the cycle (but are not themselves in the cycle) have element
   * models built for them.
   */
  void _ensureImportsAndExports() {
    HashSet<Source> visitedLibraries = new HashSet<Source>();
    int libraryCount = _librariesInCycle.length;
    for (int i = 0; i < libraryCount; i++) {
      ResolvableLibrary library = _librariesInCycle[i];
      _ensureImports(library);
      if (_taskData != null) {
        return;
      }
      _ensureExports(library, visitedLibraries);
      if (_taskData != null) {
        return;
      }
    }
  }

  /**
   * Ensure that there is a resolvable compilation unit available for all of the
   * compilation units in the given [library].
   */
  List<CycleBuilder_SourceEntryPair> _ensurePartsInLibrary(
      ResolvableLibrary library) {
    List<CycleBuilder_SourceEntryPair> pairs =
        new List<CycleBuilder_SourceEntryPair>();
    Source librarySource = library.librarySource;
    DartEntry libraryEntry =
        AnalysisContextImpl_this._getReadableDartEntry(librarySource);
    if (libraryEntry == null) {
      throw new AnalysisException(
          "Cannot find entry for ${librarySource.fullName}");
    } else if (libraryEntry.getState(DartEntry.PARSED_UNIT) ==
        CacheState.ERROR) {
      String message =
          "Cannot compute parsed unit for ${librarySource.fullName}";
      CaughtException exception = libraryEntry.exception;
      if (exception == null) {
        throw new AnalysisException(message);
      }
      throw new AnalysisException(
          message, new CaughtException(exception, null));
    }
    _ensureResolvableCompilationUnit(librarySource, libraryEntry);
    pairs.add(new CycleBuilder_SourceEntryPair(librarySource, libraryEntry));
    List<Source> partSources =
        _getSources(librarySource, libraryEntry, DartEntry.INCLUDED_PARTS);
    int count = partSources.length;
    for (int i = 0; i < count; i++) {
      Source partSource = partSources[i];
      DartEntry partEntry =
          AnalysisContextImpl_this._getReadableDartEntry(partSource);
      if (partEntry != null &&
          partEntry.getState(DartEntry.PARSED_UNIT) != CacheState.ERROR) {
        _ensureResolvableCompilationUnit(partSource, partEntry);
        pairs.add(new CycleBuilder_SourceEntryPair(partSource, partEntry));
      }
    }
    return pairs;
  }

  /**
   * Ensure that there is a resolvable compilation unit available for the given
   * [source].
   */
  void _ensureResolvableCompilationUnit(Source source, DartEntry dartEntry) {
    // The entry will be null if the source represents a non-Dart file.
    if (dartEntry != null && !dartEntry.hasResolvableCompilationUnit) {
      if (_taskData == null) {
        _taskData =
            AnalysisContextImpl_this._createParseDartTask(source, dartEntry);
      }
    }
  }

  HashSet<Source> _gatherSources(List<CycleBuilder_LibraryPair> libraryData) {
    int libraryCount = libraryData.length;
    HashSet<Source> sources = new HashSet<Source>();
    for (int i = 0; i < libraryCount; i++) {
      List<CycleBuilder_SourceEntryPair> entryPairs = libraryData[i].entryPairs;
      int entryCount = entryPairs.length;
      for (int j = 0; j < entryCount; j++) {
        sources.add(entryPairs[j].source);
      }
    }
    return sources;
  }

  /**
   * Return the sources described by the given [descriptor].
   */
  List<Source> _getSources(Source source, DartEntry dartEntry,
      DataDescriptor<List<Source>> descriptor) {
    if (dartEntry == null) {
      return Source.EMPTY_LIST;
    }
    CacheState exportState = dartEntry.getState(descriptor);
    if (exportState == CacheState.ERROR) {
      return Source.EMPTY_LIST;
    } else if (exportState != CacheState.VALID) {
      if (_taskData == null) {
        _taskData =
            AnalysisContextImpl_this._createParseDartTask(source, dartEntry);
      }
      return Source.EMPTY_LIST;
    }
    return dartEntry.getValue(descriptor);
  }
}

/**
 * Information about the next task to be performed. Each data has an implicit
 * associated source: the source that might need to be analyzed. There are
 * essentially three states that can be represented:
 *
 * * If [getTask] returns a non-`null` value, then that is the task that should
 *   be executed to further analyze the associated source.
 * * Otherwise, if [isBlocked] returns `true`, then there is no work that can be
 *   done, but analysis for the associated source is not complete.
 * * Otherwise, [getDependentSource] should return a source that needs to be
 *   analyzed before the analysis of the associated source can be completed.
 */
class AnalysisContextImpl_TaskData {
  /**
   * The task that is to be performed.
   */
  final AnalysisTask task;

  /**
   * A flag indicating whether the associated source is blocked waiting for its
   * contents to be loaded.
   */
  final bool _blocked;

  /**
   * Initialize a newly created data holder.
   */
  AnalysisContextImpl_TaskData(this.task, this._blocked);

  /**
   * Return `true` if the associated source is blocked waiting for its contents
   * to be loaded.
   */
  bool get isBlocked => _blocked;

  @override
  String toString() {
    if (task == null) {
      return "blocked: $_blocked";
    }
    return task.toString();
  }
}

/**
 * Statistics and information about a single [AnalysisContext].
 */
abstract class AnalysisContextStatistics {
  /**
   * Return the statistics for each kind of cached data.
   */
  List<AnalysisContextStatistics_CacheRow> get cacheRows;

  /**
   * Return the exceptions that caused some entries to have a state of
   * [CacheState.ERROR].
   */
  List<CaughtException> get exceptions;

  /**
   * Return information about each of the partitions in the cache.
   */
  List<AnalysisContextStatistics_PartitionData> get partitionData;

  /**
   * Return a list containing all of the sources in the cache.
   */
  List<Source> get sources;
}

/**
 * Information about single piece of data in the cache.
 */
abstract class AnalysisContextStatistics_CacheRow {
  /**
   * List of possible states which can be queried.
   */
  static const List<CacheState> STATES = const <CacheState>[
    CacheState.ERROR,
    CacheState.FLUSHED,
    CacheState.IN_PROCESS,
    CacheState.INVALID,
    CacheState.VALID
  ];

  /**
   * Return the number of entries whose state is [CacheState.ERROR].
   */
  int get errorCount;

  /**
   * Return the number of entries whose state is [CacheState.FLUSHED].
   */
  int get flushedCount;

  /**
   * Return the number of entries whose state is [CacheState.IN_PROCESS].
   */
  int get inProcessCount;

  /**
   * Return the number of entries whose state is [CacheState.INVALID].
   */
  int get invalidCount;

  /**
   * Return the name of the data represented by this object.
   */
  String get name;

  /**
   * Return the number of entries whose state is [CacheState.VALID].
   */
  int get validCount;

  /**
   * Return the number of entries whose state is [state].
   */
  int getCount(CacheState state);
}

/**
 * Information about a single partition in the cache.
 */
abstract class AnalysisContextStatistics_PartitionData {
  /**
   * Return the number of entries in the partition that have an AST structure in
   * one state or another.
   */
  int get astCount;

  /**
   * Return the total number of entries in the partition.
   */
  int get totalCount;
}

/**
 * Implementation of the [AnalysisContextStatistics].
 */
class AnalysisContextStatisticsImpl implements AnalysisContextStatistics {
  Map<String, AnalysisContextStatistics_CacheRow> _dataMap =
      new HashMap<String, AnalysisContextStatistics_CacheRow>();

  List<Source> _sources = new List<Source>();

  HashSet<CaughtException> _exceptions = new HashSet<CaughtException>();

  List<AnalysisContextStatistics_PartitionData> _partitionData;

  @override
  List<AnalysisContextStatistics_CacheRow> get cacheRows =>
      _dataMap.values.toList();

  @override
  List<CaughtException> get exceptions => new List.from(_exceptions);

  @override
  List<AnalysisContextStatistics_PartitionData> get partitionData =>
      _partitionData;

  /**
   * Set the partition data returned by this object to the given data.
   */
  void set partitionData(List<AnalysisContextStatistics_PartitionData> data) {
    _partitionData = data;
  }

  @override
  List<Source> get sources => _sources;

  void addSource(Source source) {
    _sources.add(source);
  }

  void _internalPutCacheItem(Source source, SourceEntry dartEntry,
      DataDescriptor rowDesc, CacheState state) {
    String rowName = rowDesc.toString();
    AnalysisContextStatisticsImpl_CacheRowImpl row =
        _dataMap[rowName] as AnalysisContextStatisticsImpl_CacheRowImpl;
    if (row == null) {
      row = new AnalysisContextStatisticsImpl_CacheRowImpl(rowName);
      _dataMap[rowName] = row;
    }
    row._incState(state);
    if (state == CacheState.ERROR) {
      CaughtException exception = dartEntry.exception;
      if (exception != null) {
        _exceptions.add(exception);
      }
    }
  }
}

class AnalysisContextStatisticsImpl_CacheRowImpl
    implements AnalysisContextStatistics_CacheRow {
  final String name;

  Map<CacheState, int> _counts = <CacheState, int>{};

  AnalysisContextStatisticsImpl_CacheRowImpl(this.name);

  @override
  int get errorCount => getCount(CacheState.ERROR);

  @override
  int get flushedCount => getCount(CacheState.FLUSHED);

  @override
  int get hashCode => name.hashCode;

  @override
  int get inProcessCount => getCount(CacheState.IN_PROCESS);

  @override
  int get invalidCount => getCount(CacheState.INVALID);

  @override
  int get validCount => getCount(CacheState.VALID);

  @override
  bool operator ==(Object obj) =>
      obj is AnalysisContextStatisticsImpl_CacheRowImpl && obj.name == name;

  @override
  int getCount(CacheState state) {
    int count = _counts[state];
    if (count != null) {
      return count;
    } else {
      return 0;
    }
  }

  void _incState(CacheState state) {
    if (_counts[state] == null) {
      _counts[state] = 1;
    } else {
      _counts[state]++;
    }
  }
}

class AnalysisContextStatisticsImpl_PartitionDataImpl
    implements AnalysisContextStatistics_PartitionData {
  final int astCount;

  final int totalCount;

  AnalysisContextStatisticsImpl_PartitionDataImpl(
      this.astCount, this.totalCount);
}

/**
 * A representation of changes to the types of analysis that should be
 * performed.
 */
class AnalysisDelta {
  /**
   * A mapping from source to what type of analysis should be performed on that
   * source.
   */
  HashMap<Source, AnalysisLevel> _analysisMap =
      new HashMap<Source, AnalysisLevel>();

  /**
   * Return a collection of the sources that have been added. This is equivalent
   * to calling [getAnalysisLevels] and collecting all sources that do not have
   * an analysis level of [AnalysisLevel.NONE].
   */
  List<Source> get addedSources {
    List<Source> result = new List<Source>();
    _analysisMap.forEach((Source source, AnalysisLevel level) {
      if (level != AnalysisLevel.NONE) {
        result.add(source);
      }
    });
    return result;
  }

  /**
   * Return a mapping of sources to the level of analysis that should be
   * performed.
   */
  Map<Source, AnalysisLevel> get analysisLevels => _analysisMap;

  /**
   * Record that the given [source] should be analyzed at the given [level].
   */
  void setAnalysisLevel(Source source, AnalysisLevel level) {
    _analysisMap[source] = level;
  }

  @override
  String toString() {
    StringBuffer buffer = new StringBuffer();
    bool needsSeparator = _appendSources(buffer, false, AnalysisLevel.ALL);
    needsSeparator =
        _appendSources(buffer, needsSeparator, AnalysisLevel.RESOLVED);
    _appendSources(buffer, needsSeparator, AnalysisLevel.NONE);
    return buffer.toString();
  }

  /**
   * Appendto the given [buffer] all sources with the given analysis [level],
   * prefixed with a label and a separator if [needsSeparator] is `true`.
   */
  bool _appendSources(
      StringBuffer buffer, bool needsSeparator, AnalysisLevel level) {
    bool first = true;
    _analysisMap.forEach((Source source, AnalysisLevel sourceLevel) {
      if (sourceLevel == level) {
        if (first) {
          first = false;
          if (needsSeparator) {
            buffer.write("; ");
          }
          buffer.write(level);
          buffer.write(" ");
        } else {
          buffer.write(", ");
        }
        buffer.write(source.fullName);
      }
    });
    return needsSeparator || !first;
  }
}

/**
 * The entry point for the functionality provided by the analysis engine. There
 * is a single instance of this class.
 */
class AnalysisEngine {
  /**
   * The suffix used for Dart source files.
   */
  static const String SUFFIX_DART = "dart";

  /**
   * The short suffix used for HTML files.
   */
  static const String SUFFIX_HTM = "htm";

  /**
   * The long suffix used for HTML files.
   */
  static const String SUFFIX_HTML = "html";

  /**
   * The file name used for analysis options files.
   */
  static const String ANALYSIS_OPTIONS_FILE = '.analysis_options';

  /**
   * The unique instance of this class.
   */
  static final AnalysisEngine instance = new AnalysisEngine._();

  /**
   * The logger that should receive information about errors within the analysis
   * engine.
   */
  Logger _logger = Logger.NULL;

  /**
   * The plugin that defines the extension points and extensions that are defined by
   * command-line applications using the analysis engine.
   */
  final CommandLinePlugin commandLinePlugin = new CommandLinePlugin();

  /**
   * The plugin that defines the extension points and extensions that are
   * inherently defined by the analysis engine.
   */
  final EnginePlugin enginePlugin = new EnginePlugin();

  /***
   * The plugin that defines the extension points and extensions that are defined
   * by applications that want to consume options defined in the analysis
   * options file.
   */
  final OptionsPlugin optionsPlugin = new OptionsPlugin();

  /**
   * The instrumentation service that is to be used by this analysis engine.
   */
  InstrumentationService _instrumentationService =
      InstrumentationService.NULL_SERVICE;

  /**
   * The list of supported plugins for processing by clients.
   */
  List<Plugin> _supportedPlugins;

  /**
   * The partition manager being used to manage the shared partitions.
   */
  final PartitionManager partitionManager = new PartitionManager();

  /**
   * The partition manager being used to manage the shared partitions.
   */
  final newContext.PartitionManager partitionManager_new =
      new newContext.PartitionManager();

  /**
   * A flag indicating whether the (new) task model should be used to perform
   * analysis.
   */
  bool useTaskModel = true;

  /**
   * A flag indicating whether the task model should attempt to limit
   * invalidation after a change.
   */
  bool limitInvalidationInTaskModel = false;

  /**
   * The plugins that are defined outside the `analyzer` package.
   */
  List<Plugin> _userDefinedPlugins = <Plugin>[];

  /**
   * The task manager used to manage the tasks used to analyze code.
   */
  TaskManager _taskManager;

  AnalysisEngine._();

  /**
   * Return the instrumentation service that is to be used by this analysis
   * engine.
   */
  InstrumentationService get instrumentationService => _instrumentationService;

  /**
   * Set the instrumentation service that is to be used by this analysis engine
   * to the given [service].
   */
  void set instrumentationService(InstrumentationService service) {
    if (service == null) {
      _instrumentationService = InstrumentationService.NULL_SERVICE;
    } else {
      _instrumentationService = service;
    }
  }

  /**
   * Return the logger that should receive information about errors within the
   * analysis engine.
   */
  Logger get logger => _logger;

  /**
   * Set the logger that should receive information about errors within the
   * analysis engine to the given [logger].
   */
  void set logger(Logger logger) {
    this._logger = logger == null ? Logger.NULL : logger;
  }

  /**
   * Return the list of supported plugins for processing by clients.
   */
  List<Plugin> get supportedPlugins {
    if (_supportedPlugins == null) {
      _supportedPlugins = <Plugin>[
        enginePlugin,
        commandLinePlugin,
        optionsPlugin
      ];
      _supportedPlugins.addAll(_userDefinedPlugins);
    }
    return _supportedPlugins;
  }

  /**
   * Return the task manager used to manage the tasks used to analyze code.
   */
  TaskManager get taskManager {
    if (_taskManager == null) {
      new ExtensionManager().processPlugins(supportedPlugins);
      _taskManager = new TaskManager();
      _taskManager.addTaskDescriptors(enginePlugin.taskDescriptors);
      // TODO(brianwilkerson) Create a way to associate different results with
      // different file suffixes, then make this pluggable.
      _taskManager.addGeneralResult(DART_ERRORS);
    }
    return _taskManager;
  }

  /**
   * Set plugins that are defined outside the `analyzer` package.
   */
  void set userDefinedPlugins(List<Plugin> plugins) {
    if (plugins == null) {
      plugins = <Plugin>[];
    }
    _userDefinedPlugins = plugins;
    _supportedPlugins = null;
    _taskManager = null;
  }

  /**
   * Clear any caches holding on to analysis results so that a full re-analysis
   * will be performed the next time an analysis context is created.
   */
  void clearCaches() {
    partitionManager.clearCache();
  }

  /**
   * Create and return a new context in which analysis can be performed.
   */
  AnalysisContext createAnalysisContext() {
    if (useTaskModel) {
      return new newContext.AnalysisContextImpl();
    }
    return new AnalysisContextImpl();
  }

  /**
   * Return `true` if the given [fileName] is an analysis options file.
   */
  static bool isAnalysisOptionsFileName(String fileName,
      [pathos.Context context]) {
    if (fileName == null) {
      return false;
    }
    return (context ?? pathos.posix).basename(fileName) ==
        ANALYSIS_OPTIONS_FILE;
  }

  /**
   * Return `true` if the given [fileName] is assumed to contain Dart source
   * code.
   */
  static bool isDartFileName(String fileName) {
    if (fileName == null) {
      return false;
    }
    return javaStringEqualsIgnoreCase(
        FileNameUtilities.getExtension(fileName), SUFFIX_DART);
  }

  /**
   * Return `true` if the given [fileName] is assumed to contain HTML.
   */
  static bool isHtmlFileName(String fileName) {
    if (fileName == null) {
      return false;
    }
    String extension = FileNameUtilities.getExtension(fileName);
    return javaStringEqualsIgnoreCase(extension, SUFFIX_HTML) ||
        javaStringEqualsIgnoreCase(extension, SUFFIX_HTM);
  }
}

/**
 * The analysis errors and line information for the errors.
 */
abstract class AnalysisErrorInfo {
  /**
   * Return the errors that as a result of the analysis, or `null` if there were
   * no errors.
   */
  List<AnalysisError> get errors;

  /**
   * Return the line information associated with the errors, or `null` if there
   * were no errors.
   */
  LineInfo get lineInfo;
}

/**
 * The analysis errors and line info associated with a source.
 */
class AnalysisErrorInfoImpl implements AnalysisErrorInfo {
  /**
   * The analysis errors associated with a source, or `null` if there are no
   * errors.
   */
  final List<AnalysisError> errors;

  /**
   * The line information associated with the errors, or `null` if there are no
   * errors.
   */
  final LineInfo lineInfo;

  /**
   * Initialize an newly created error info with the given [errors] and
   * [lineInfo].
   */
  AnalysisErrorInfoImpl(this.errors, this.lineInfo);
}

/**
 * The levels at which a source can be analyzed.
 */
class AnalysisLevel extends Enum<AnalysisLevel> {
  /**
   * Indicates a source should be fully analyzed.
   */
  static const AnalysisLevel ALL = const AnalysisLevel('ALL', 0);

  /**
   * Indicates a source should be resolved and that errors, warnings and hints are needed.
   */
  static const AnalysisLevel ERRORS = const AnalysisLevel('ERRORS', 1);

  /**
   * Indicates a source should be resolved, but that errors, warnings and hints are not needed.
   */
  static const AnalysisLevel RESOLVED = const AnalysisLevel('RESOLVED', 2);

  /**
   * Indicates a source is not of interest to the client.
   */
  static const AnalysisLevel NONE = const AnalysisLevel('NONE', 3);

  static const List<AnalysisLevel> values = const [ALL, ERRORS, RESOLVED, NONE];

  const AnalysisLevel(String name, int ordinal) : super(name, ordinal);
}

/**
 * An object that is listening for results being produced by an analysis
 * context.
 */
abstract class AnalysisListener {
  /**
   * Reports that a task, described by the given [taskDescription] is about to
   * be performed by the given [context].
   */
  void aboutToPerformTask(AnalysisContext context, String taskDescription);

  /**
   * Reports that the [errors] associated with the given [source] in the given
   * [context] has been updated to the given errors. The [lineInfo] is the line
   * information associated with the source.
   */
  void computedErrors(AnalysisContext context, Source source,
      List<AnalysisError> errors, LineInfo lineInfo);

  /**
   * Reports that the given [source] is no longer included in the set of sources
   * that are being analyzed by the given analysis [context].
   */
  void excludedSource(AnalysisContext context, Source source);

  /**
   * Reports that the given [source] is now included in the set of sources that
   * are being analyzed by the given analysis [context].
   */
  void includedSource(AnalysisContext context, Source source);

  /**
   * Reports that the given Dart [source] was parsed in the given [context],
   * producing the given [unit].
   */
  void parsedDart(AnalysisContext context, Source source, CompilationUnit unit);

  /**
   * Reports that the given HTML [source] was parsed in the given [context].
   */
  @deprecated
  void parsedHtml(AnalysisContext context, Source source, ht.HtmlUnit unit);

  /**
   * Reports that the given Dart [source] was resolved in the given [context].
   */
  void resolvedDart(
      AnalysisContext context, Source source, CompilationUnit unit);

  /**
   * Reports that the given HTML [source] was resolved in the given [context].
   */
  @deprecated
  void resolvedHtml(AnalysisContext context, Source source, ht.HtmlUnit unit);
}

/**
 * Futures returned by [AnalysisContext] for pending analysis results will
 * complete with this error if it is determined that analysis results will
 * never become available (e.g. because the requested source is not subject to
 * analysis, or because the requested source is a part file which is not a part
 * of any known library).
 */
class AnalysisNotScheduledError implements Exception {}

/**
 * A set of analysis options used to control the behavior of an analysis
 * context.
 */
abstract class AnalysisOptions {
  /**
   * If analysis is to parse and analyze all function bodies, return `true`.
   * If analysis is to skip all function bodies, return `false`.  If analysis
   * is to parse and analyze function bodies in some sources and not in others,
   * throw an exception.
   *
   * This getter is deprecated; consider using [analyzeFunctionBodiesPredicate]
   * instead.
   */
  @deprecated // Use this.analyzeFunctionBodiesPredicate
  bool get analyzeFunctionBodies;

  /**
   * Function that returns `true` if analysis is to parse and analyze function
   * bodies for a given source.
   */
  AnalyzeFunctionBodiesPredicate get analyzeFunctionBodiesPredicate;

  /**
   * Return the maximum number of sources for which AST structures should be
   * kept in the cache.
   */
  int get cacheSize;

  /**
   * Return `true` if analysis is to generate dart2js related hint results.
   */
  bool get dart2jsHint;

  /**
   * Return `true` if analysis is to include the new async support.
   */
  @deprecated // Always true
  bool get enableAsync;

  /**
   * Return `true` if analysis is to include the new deferred loading support.
   */
  @deprecated // Always true
  bool get enableDeferredLoading;

  /**
   * Return `true` if analysis is to include the new enum support.
   */
  @deprecated // Always true
  bool get enableEnum;

  /**
   * Return `true` to enable generic methods (DEP 22).
   */
  bool get enableGenericMethods => null;

  /**
   * Return `true` to enable null-aware operators (DEP 9).
   */
  @deprecated // Always true
  bool get enableNullAwareOperators;

  /**
   * Return `true` to strictly follow the specification when generating
   * warnings on "call" methods (fixes dartbug.com/21938).
   */
  bool get enableStrictCallChecks;

  /**
   * Return `true` if mixins are allowed to inherit from types other than
   * Object, and are allowed to reference `super`.
   */
  bool get enableSuperMixins;

  /**
   * Return `true` if errors, warnings and hints should be generated for sources
   * that are implicitly being analyzed. The default value is `true`.
   */
  bool get generateImplicitErrors;

  /**
   * Return `true` if errors, warnings and hints should be generated for sources
   * in the SDK. The default value is `false`.
   */
  bool get generateSdkErrors;

  /**
   * Return `true` if analysis is to generate hint results (e.g. type inference
   * based information and pub best practices).
   */
  bool get hint;

  /**
   * Return `true` if incremental analysis should be used.
   */
  bool get incremental;

  /**
   * A flag indicating whether incremental analysis should be used for API
   * changes.
   */
  bool get incrementalApi;

  /**
   * A flag indicating whether validation should be performed after incremental
   * analysis.
   */
  bool get incrementalValidation;

  /**
   * Return `true` if analysis is to generate lint warnings.
   */
  bool get lint;

  /**
   * Return `true` if analysis is to parse comments.
   */
  bool get preserveComments;

  /**
   * Return `true` if strong mode analysis should be used.
   */
  bool get strongMode;
}

/**
 * A set of analysis options used to control the behavior of an analysis
 * context.
 */
class AnalysisOptionsImpl implements AnalysisOptions {
  /**
   * The maximum number of sources for which data should be kept in the cache.
   */
  static const int DEFAULT_CACHE_SIZE = 64;

  /**
   * The default value for enabling deferred loading.
   */
  @deprecated
  static bool DEFAULT_ENABLE_DEFERRED_LOADING = true;

  /**
   * The default value for enabling enum support.
   */
  @deprecated
  static bool DEFAULT_ENABLE_ENUM = true;

  /**
   * A predicate indicating whether analysis is to parse and analyze function
   * bodies.
   */
  AnalyzeFunctionBodiesPredicate _analyzeFunctionBodiesPredicate =
      _analyzeAllFunctionBodies;

  /**
   * The maximum number of sources for which AST structures should be kept in
   * the cache.
   */
  int cacheSize = DEFAULT_CACHE_SIZE;

  /**
   * A flag indicating whether analysis is to generate dart2js related hint
   * results.
   */
  bool dart2jsHint = false;

  /**
   * A flag indicating whether generic methods are to be supported (DEP 22).
   */
  bool enableGenericMethods = false;

  /**
   * A flag indicating whether analysis is to strictly follow the specification
   * when generating warnings on "call" methods (fixes dartbug.com/21938).
   */
  bool enableStrictCallChecks = false;

  /**
   * A flag indicating whether mixins are allowed to inherit from types other
   * than Object, and are allowed to reference `super`.
   */
  bool enableSuperMixins = false;

  /**
   * A flag indicating whether errors, warnings and hints should be generated
   * for sources that are implicitly being analyzed.
   */
  bool generateImplicitErrors = true;

  /**
   * A flag indicating whether errors, warnings and hints should be generated
   * for sources in the SDK.
   */
  bool generateSdkErrors = false;

  /**
   * A flag indicating whether analysis is to generate hint results (e.g. type
   * inference based information and pub best practices).
   */
  bool hint = true;

  /**
   * A flag indicating whether incremental analysis should be used.
   */
  bool incremental = false;

  /**
   * A flag indicating whether incremental analysis should be used for API
   * changes.
   */
  bool incrementalApi = false;

  /**
   * A flag indicating whether validation should be performed after incremental
   * analysis.
   */
  bool incrementalValidation = false;

  /**
   * A flag indicating whether analysis is to generate lint warnings.
   */
  bool lint = false;

  /**
   * A flag indicating whether analysis is to parse comments.
   */
  bool preserveComments = true;

  /**
   * A flag indicating whether strong-mode analysis should be used.
   */
  bool strongMode = false;

  /**
   * A flag indicating whether strong-mode inference hints should be
   * used.  This flag is not exposed in the interface, and should be
   * replaced by something more general.
   */
  // TODO(leafp): replace this with something more general
  bool strongModeHints = false;

  /**
   * Initialize a newly created set of analysis options to have their default
   * values.
   */
  AnalysisOptionsImpl();

  /**
   * Initialize a newly created set of analysis options to have the same values
   * as those in the given set of analysis [options].
   */
  @deprecated // Use new AnalysisOptionsImpl.from(options)
  AnalysisOptionsImpl.con1(AnalysisOptions options) {
    analyzeFunctionBodiesPredicate = options.analyzeFunctionBodiesPredicate;
    cacheSize = options.cacheSize;
    dart2jsHint = options.dart2jsHint;
    enableStrictCallChecks = options.enableStrictCallChecks;
    enableGenericMethods = options.enableGenericMethods;
    enableSuperMixins = options.enableSuperMixins;
    generateImplicitErrors = options.generateImplicitErrors;
    generateSdkErrors = options.generateSdkErrors;
    hint = options.hint;
    incremental = options.incremental;
    incrementalApi = options.incrementalApi;
    incrementalValidation = options.incrementalValidation;
    lint = options.lint;
    preserveComments = options.preserveComments;
    strongMode = options.strongMode;
    if (options is AnalysisOptionsImpl) {
      strongModeHints = options.strongModeHints;
    }
  }

  /**
   * Initialize a newly created set of analysis options to have the same values
   * as those in the given set of analysis [options].
   */
  AnalysisOptionsImpl.from(AnalysisOptions options) {
    analyzeFunctionBodiesPredicate = options.analyzeFunctionBodiesPredicate;
    cacheSize = options.cacheSize;
    dart2jsHint = options.dart2jsHint;
    enableStrictCallChecks = options.enableStrictCallChecks;
    enableGenericMethods = options.enableGenericMethods;
    enableSuperMixins = options.enableSuperMixins;
    generateImplicitErrors = options.generateImplicitErrors;
    generateSdkErrors = options.generateSdkErrors;
    hint = options.hint;
    incremental = options.incremental;
    incrementalApi = options.incrementalApi;
    incrementalValidation = options.incrementalValidation;
    lint = options.lint;
    preserveComments = options.preserveComments;
    strongMode = options.strongMode;
    if (options is AnalysisOptionsImpl) {
      strongModeHints = options.strongModeHints;
    }
  }

  bool get analyzeFunctionBodies {
    if (identical(analyzeFunctionBodiesPredicate, _analyzeAllFunctionBodies)) {
      return true;
    } else if (identical(
        analyzeFunctionBodiesPredicate, _analyzeNoFunctionBodies)) {
      return false;
    } else {
      throw new StateError('analyzeFunctionBodiesPredicate in use');
    }
  }

  set analyzeFunctionBodies(bool value) {
    if (value) {
      analyzeFunctionBodiesPredicate = _analyzeAllFunctionBodies;
    } else {
      analyzeFunctionBodiesPredicate = _analyzeNoFunctionBodies;
    }
  }

  @override
  AnalyzeFunctionBodiesPredicate get analyzeFunctionBodiesPredicate =>
      _analyzeFunctionBodiesPredicate;

  set analyzeFunctionBodiesPredicate(AnalyzeFunctionBodiesPredicate value) {
    if (value == null) {
      throw new ArgumentError.notNull('analyzeFunctionBodiesPredicate');
    }
    _analyzeFunctionBodiesPredicate = value;
  }

  @deprecated
  @override
  bool get enableAsync => true;

  @deprecated
  void set enableAsync(bool enable) {
    // Async support cannot be disabled
  }

  @deprecated
  @override
  bool get enableDeferredLoading => true;

  @deprecated
  void set enableDeferredLoading(bool enable) {
    // Deferred loading support cannot be disabled
  }

  @deprecated
  @override
  bool get enableEnum => true;

  @deprecated
  void set enableEnum(bool enable) {
    // Enum support cannot be disabled
  }

  @deprecated
  @override
  bool get enableNullAwareOperators => true;

  @deprecated
  void set enableNullAwareOperators(bool enable) {
    // Null-aware operator support cannot be disabled
  }

  /**
   * Predicate used for [analyzeFunctionBodiesPredicate] when
   * [analyzeFunctionBodies] is set to `true`.
   */
  static bool _analyzeAllFunctionBodies(Source _) => true;

  /**
   * Predicate used for [analyzeFunctionBodiesPredicate] when
   * [analyzeFunctionBodies] is set to `false`.
   */
  static bool _analyzeNoFunctionBodies(Source _) => false;
}

/**
 *
 */
class AnalysisResult {
  /**
   * The change notices associated with this result, or `null` if there were no
   * changes and there is no more work to be done.
   */
  final List<ChangeNotice> _notices;

  /**
   * The number of milliseconds required to determine which task was to be
   * performed.
   */
  final int getTime;

  /**
   * The name of the class of the task that was performed.
   */
  final String taskClassName;

  /**
   * The number of milliseconds required to perform the task.
   */
  final int performTime;

  /**
   * Initialize a newly created analysis result to have the given values. The
   * [notices] is the change notices associated with this result. The [getTime]
   * is the number of milliseconds required to determine which task was to be
   * performed. The [taskClassName] is the name of the class of the task that
   * was performed. The [performTime] is the number of milliseconds required to
   * perform the task.
   */
  AnalysisResult(
      this._notices, this.getTime, this.taskClassName, this.performTime);

  /**
   * Return the change notices associated with this result, or `null` if there
   * were no changes and there is no more work to be done.
   */
  List<ChangeNotice> get changeNotices => _notices;

  /**
   * Return `true` if there is more to be performed after the task that was
   * performed.
   */
  bool get hasMoreWork => _notices != null;
}

/**
 * An analysis task.
 */
abstract class AnalysisTask {
  /**
   * The context in which the task is to be performed.
   */
  final InternalAnalysisContext context;

  /**
   * The exception that was thrown while performing this task, or `null` if the
   * task completed successfully.
   */
  CaughtException _thrownException;

  /**
   * Initialize a newly created task to perform analysis within the given
   * [context].
   */
  AnalysisTask(this.context);

  /**
   * Return the exception that was thrown while performing this task, or `null`
   * if the task completed successfully.
   */
  CaughtException get exception => _thrownException;

  /**
   * Return a textual description of this task.
   */
  String get taskDescription;

  /**
   * Use the given [visitor] to visit this task. Throws an [AnalysisException]
   * if the visitor throws the exception.
   */
  accept(AnalysisTaskVisitor visitor);

  /**
   * Perform this analysis task, protected by an exception handler. Throws an
   * [AnalysisException] if an exception occurs while performing the task.
   */
  void internalPerform();

  /**
   * Perform this analysis task and use the given [visitor] to visit this task
   * after it has completed. Throws an [AnalysisException] if the visitor throws
   * the exception.
   */
  Object perform(AnalysisTaskVisitor visitor) {
    try {
      _safelyPerform();
    } on AnalysisException catch (exception, stackTrace) {
      _thrownException = new CaughtException(exception, stackTrace);
      AnalysisEngine.instance.logger.logInformation(
          "Task failed: $taskDescription",
          new CaughtException(exception, stackTrace));
    }
    return PerformanceStatistics.analysisTaskVisitor
        .makeCurrentWhile(() => accept(visitor));
  }

  @override
  String toString() => taskDescription;

  /**
   * Perform this analysis task, ensuring that all exceptions are wrapped in an
   * [AnalysisException]. Throws an [AnalysisException] if any exception occurs
   * while performing the task
   */
  void _safelyPerform() {
    try {
      String contextName = context.name;
      if (contextName == null) {
        contextName = 'unnamed';
      }
      AnalysisEngine.instance.instrumentationService
          .logAnalysisTask(contextName, taskDescription);
      internalPerform();
    } on AnalysisException {
      rethrow;
    } catch (exception, stackTrace) {
      throw new AnalysisException(
          exception.toString(), new CaughtException(exception, stackTrace));
    }
  }
}

/**
 * An object used to visit tasks. While tasks are not structured in any
 * interesting way, this class provides the ability to dispatch to an
 * appropriate method.
 */
abstract class AnalysisTaskVisitor<E> {
  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitGenerateDartErrorsTask(GenerateDartErrorsTask task);

  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitGenerateDartHintsTask(GenerateDartHintsTask task);

  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitGenerateDartLintsTask(GenerateDartLintsTask task);

  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitGetContentTask(GetContentTask task);

  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitIncrementalAnalysisTask(
      IncrementalAnalysisTask incrementalAnalysisTask);

  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitParseDartTask(ParseDartTask task);

  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitParseHtmlTask(ParseHtmlTask task);

  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitResolveDartLibraryCycleTask(ResolveDartLibraryCycleTask task);

  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitResolveDartLibraryTask(ResolveDartLibraryTask task);

  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitResolveDartUnitTask(ResolveDartUnitTask task);

  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitResolveHtmlTask(ResolveHtmlTask task);

  /**
   * Visit the given [task], returning the result of the visit. This method will
   * throw an AnalysisException if the visitor throws an exception.
   */
  E visitScanDartTask(ScanDartTask task);
}

/**
 * The result of applying a [ChangeSet] to a [AnalysisContext].
 */
class ApplyChangesStatus {
  /**
   * Is `true` if the given [ChangeSet] caused any changes in the context.
   */
  final bool hasChanges;

  ApplyChangesStatus(this.hasChanges);
}

/**
 * A `CachedResult` is a single analysis result that is stored in a
 * [SourceEntry].
 */
class CachedResult<E> {
  /**
   * The state of the cached value.
   */
  CacheState state;

  /**
   * The value being cached, or `null` if there is no value (for example, when
   * the [state] is [CacheState.INVALID].
   */
  E value;

  /**
   * Initialize a newly created result holder to represent the value of data
   * described by the given [descriptor].
   */
  CachedResult(DataDescriptor descriptor) {
    state = CacheState.INVALID;
    value = descriptor.defaultValue;
  }
}

/**
 * A single partition in an LRU cache of information related to analysis.
 */
abstract class CachePartition {
  /**
   * The context that owns this partition. Multiple contexts can reference a
   * partition, but only one context can own it.
   */
  final InternalAnalysisContext context;

  /**
   * The maximum number of sources for which AST structures should be kept in
   * the cache.
   */
  int _maxCacheSize = 0;

  /**
   * The policy used to determine which pieces of data to remove from the cache.
   */
  final CacheRetentionPolicy _retentionPolicy;

  /**
   * A table mapping the sources belonging to this partition to the information
   * known about those sources.
   */
  HashMap<Source, SourceEntry> _sourceMap = new HashMap<Source, SourceEntry>();

  /**
   * A list containing the most recently accessed sources with the most recently
   * used at the end of the list. When more sources are added than the maximum
   * allowed then the least recently used source will be removed and will have
   * it's cached AST structure flushed.
   */
  List<Source> _recentlyUsed;

  /**
   * Initialize a newly created cache to maintain at most [maxCacheSize] AST
   * structures in the cache. The cache is owned by the give [context], and the
   * [retentionPolicy] will be used to determine which pieces of data to remove
   * from the cache.
   */
  CachePartition(this.context, this._maxCacheSize, this._retentionPolicy) {
    _recentlyUsed = new List<Source>();
  }

  /**
   * Return the number of entries in this partition that have an AST associated
   * with them.
   */
  int get astSize {
    int astSize = 0;
    int count = _recentlyUsed.length;
    for (int i = 0; i < count; i++) {
      Source source = _recentlyUsed[i];
      SourceEntry sourceEntry = _sourceMap[source];
      if (sourceEntry is DartEntry) {
        if (sourceEntry.anyParsedCompilationUnit != null) {
          astSize++;
        }
      } else if (sourceEntry is HtmlEntry) {
        if (sourceEntry.anyParsedUnit != null) {
          astSize++;
        }
      }
    }
    return astSize;
  }

  /**
   * Return a table mapping the sources known to the context to the information
   * known about the source.
   *
   * <b>Note:</b> This method is only visible for use by [AnalysisCache] and
   * should not be used for any other purpose.
   */
  Map<Source, SourceEntry> get map => _sourceMap;

  /**
   * Set the maximum size of the cache to the given [size].
   */
  void set maxCacheSize(int size) {
    _maxCacheSize = size;
    while (_recentlyUsed.length > _maxCacheSize) {
      if (!_flushAstFromCache()) {
        break;
      }
    }
  }

  /**
   * Record that the AST associated with the given source was just read from the
   * cache.
   */
  void accessedAst(Source source) {
    if (_recentlyUsed.remove(source)) {
      _recentlyUsed.add(source);
      return;
    }
    while (_recentlyUsed.length >= _maxCacheSize) {
      if (!_flushAstFromCache()) {
        break;
      }
    }
    _recentlyUsed.add(source);
  }

  /**
   * Return `true` if the given [source] is contained in this partition.
   */
  bool contains(Source source);

  /**
   * Return the entry associated with the given [source].
   */
  SourceEntry get(Source source) => _sourceMap[source];

  /**
   * Return an iterator returning all of the map entries mapping sources to
   * cache entries.
   */
  MapIterator<Source, SourceEntry> iterator() =>
      new SingleMapIterator<Source, SourceEntry>(_sourceMap);

  /**
   * Associate the given [entry] with the given [source].
   */
  void put(Source source, SourceEntry entry) {
    entry.fixExceptionState();
    _sourceMap[source] = entry;
  }

  /**
   * Remove all information related to the given [source] from this partition.
   * Return the entry associated with the source, or `null` if there was cache
   * entry for the source.
   */
  SourceEntry remove(Source source) {
    _recentlyUsed.remove(source);
    return _sourceMap.remove(source);
  }

  /**
   * Record that the AST associated with the given [source] was just removed
   * from the cache.
   */
  void removedAst(Source source) {
    _recentlyUsed.remove(source);
  }

  /**
   * Return the number of sources that are mapped to cache entries.
   */
  int size() => _sourceMap.length;

  /**
   * Record that the AST associated with the given [source] was just stored to
   * the cache.
   */
  void storedAst(Source source) {
    if (_recentlyUsed.contains(source)) {
      return;
    }
    while (_recentlyUsed.length >= _maxCacheSize) {
      if (!_flushAstFromCache()) {
        break;
      }
    }
    _recentlyUsed.add(source);
  }

  /**
   * Attempt to flush one AST structure from the cache. Return `true` if a
   * structure was flushed.
   */
  bool _flushAstFromCache() {
    Source removedSource = _removeAstToFlush();
    if (removedSource == null) {
      return false;
    }
    SourceEntry sourceEntry = _sourceMap[removedSource];
    if (sourceEntry is HtmlEntry) {
      HtmlEntry htmlEntry = sourceEntry;
      htmlEntry.flushAstStructures();
    } else if (sourceEntry is DartEntry) {
      DartEntry dartEntry = sourceEntry;
      dartEntry.flushAstStructures();
    }
    return true;
  }

  /**
   * Remove and return one source from the list of recently used sources whose
   * AST structure can be flushed from the cache. The source that will be
   * returned will be the source that has been unreferenced for the longest
   * period of time but that is not a priority for analysis.
   */
  Source _removeAstToFlush() {
    int sourceToRemove = -1;
    for (int i = 0; i < _recentlyUsed.length; i++) {
      Source source = _recentlyUsed[i];
      RetentionPriority priority =
          _retentionPolicy.getAstPriority(source, _sourceMap[source]);
      if (priority == RetentionPriority.LOW) {
        return _recentlyUsed.removeAt(i);
      } else if (priority == RetentionPriority.MEDIUM && sourceToRemove < 0) {
        sourceToRemove = i;
      }
    }
    if (sourceToRemove < 0) {
      // This happens if the retention policy returns a priority of HIGH for all
      // of the sources that have been recently used. This is the case, for
      // example, when the list of priority sources is bigger than the current
      // cache size.
      return null;
    }
    return _recentlyUsed.removeAt(sourceToRemove);
  }
}

/**
 * An object used to determine how important it is for data to be retained in
 * the analysis cache.
 */
abstract class CacheRetentionPolicy {
  /**
   * Return the priority of retaining the AST structure for the given [source].
   */
  RetentionPriority getAstPriority(Source source, SourceEntry sourceEntry);
}

/**
 * The possible states of cached data.
 */
class CacheState extends Enum<CacheState> {
  /**
   * The data is not in the cache and the last time an attempt was made to
   * compute the data an exception occurred, making it pointless to attempt to
   * compute the data again.
   *
   * Valid Transitions:
   * * [INVALID] if a source was modified that might cause the data to be
   *   computable
   */
  static const CacheState ERROR = const CacheState('ERROR', 0);

  /**
   * The data is not in the cache because it was flushed from the cache in order
   * to control memory usage. If the data is recomputed, results do not need to
   * be reported.
   *
   * Valid Transitions:
   * * [IN_PROCESS] if the data is being recomputed
   * * [INVALID] if a source was modified that causes the data to need to be
   *   recomputed
   */
  static const CacheState FLUSHED = const CacheState('FLUSHED', 1);

  /**
   * The data might or might not be in the cache but is in the process of being
   * recomputed.
   *
   * Valid Transitions:
   * * [ERROR] if an exception occurred while trying to compute the data
   * * [VALID] if the data was successfully computed and stored in the cache
   */
  static const CacheState IN_PROCESS = const CacheState('IN_PROCESS', 2);

  /**
   * The data is not in the cache and needs to be recomputed so that results can
   * be reported.
   *
   * Valid Transitions:
   * * [IN_PROCESS] if an attempt is being made to recompute the data
   */
  static const CacheState INVALID = const CacheState('INVALID', 3);

  /**
   * The data is in the cache and up-to-date.
   *
   * Valid Transitions:
   * * [FLUSHED] if the data is removed in order to manage memory usage
   * * [INVALID] if a source was modified in such a way as to invalidate the
   *   previous data
   */
  static const CacheState VALID = const CacheState('VALID', 4);

  static const List<CacheState> values = const [
    ERROR,
    FLUSHED,
    IN_PROCESS,
    INVALID,
    VALID
  ];

  const CacheState(String name, int ordinal) : super(name, ordinal);
}

/**
 * An object that represents a change to the analysis results associated with a
 * given source.
 */
abstract class ChangeNotice implements AnalysisErrorInfo {
  /**
   * The parsed, but maybe not resolved Dart AST that changed as a result of
   * the analysis, or `null` if the AST was not changed.
   */
  CompilationUnit get parsedDartUnit;

  /**
   * The fully resolved Dart AST that changed as a result of the analysis, or
   * `null` if the AST was not changed.
   */
  CompilationUnit get resolvedDartUnit;

  /**
   * The fully resolved HTML AST that changed as a result of the analysis, or
   * `null` if the AST was not changed.
   */
  @deprecated
  ht.HtmlUnit get resolvedHtmlUnit;

  /**
   * Return the source for which the result is being reported.
   */
  Source get source;
}

/**
 * An implementation of a [ChangeNotice].
 */
class ChangeNoticeImpl implements ChangeNotice {
  /**
   * An empty list of change notices.
   */
  static const List<ChangeNoticeImpl> EMPTY_LIST = const <ChangeNoticeImpl>[];

  /**
   * The source for which the result is being reported.
   */
  final Source source;

  /**
   * The parsed, but maybe not resolved Dart AST that changed as a result of
   * the analysis, or `null` if the AST was not changed.
   */
  CompilationUnit parsedDartUnit;

  /**
   * The fully resolved Dart AST that changed as a result of the analysis, or
   * `null` if the AST was not changed.
   */
  CompilationUnit resolvedDartUnit;

  /**
   * The fully resolved HTML AST that changed as a result of the analysis, or
   * `null` if the AST was not changed.
   */
  @deprecated
  ht.HtmlUnit resolvedHtmlUnit;

  /**
   * The errors that changed as a result of the analysis, or `null` if errors
   * were not changed.
   */
  List<AnalysisError> _errors;

  /**
   * The line information associated with the source, or `null` if errors were
   * not changed.
   */
  LineInfo _lineInfo;

  /**
   * Initialize a newly created notice associated with the given source.
   *
   * @param source the source for which the change is being reported
   */
  ChangeNoticeImpl(this.source);

  @override
  List<AnalysisError> get errors => _errors;

  @override
  LineInfo get lineInfo => _lineInfo;

  /**
   * Set the errors that changed as a result of the analysis to the given
   * [errors] and set the line information to the given [lineInfo].
   */
  void setErrors(List<AnalysisError> errors, LineInfo lineInfo) {
    this._errors = errors;
    this._lineInfo = lineInfo;
    if (lineInfo == null) {
      AnalysisEngine.instance.logger.logInformation("No line info: $source",
          new CaughtException(new AnalysisException(), null));
    }
  }

  @override
  String toString() => "Changes for ${source.fullName}";
}

/**
 * An indication of which sources have been added, changed, removed, or deleted.
 * In the case of a changed source, there are multiple ways of indicating the
 * nature of the change.
 *
 * No source should be added to the change set more than once, either with the
 * same or a different kind of change. It does not make sense, for example, for
 * a source to be both added and removed, and it is redundant for a source to be
 * marked as changed in its entirety and changed in some specific range.
 */
class ChangeSet {
  /**
   * A list containing the sources that have been added.
   */
  final List<Source> addedSources = new List<Source>();

  /**
   * A list containing the sources that have been changed.
   */
  final List<Source> changedSources = new List<Source>();

  /**
   * A table mapping the sources whose content has been changed to the current
   * content of those sources.
   */
  HashMap<Source, String> _changedContent = new HashMap<Source, String>();

  /**
   * A table mapping the sources whose content has been changed within a single
   * range to the current content of those sources and information about the
   * affected range.
   */
  final HashMap<Source, ChangeSet_ContentChange> changedRanges =
      new HashMap<Source, ChangeSet_ContentChange>();

  /**
   * A list containing the sources that have been removed.
   */
  final List<Source> removedSources = new List<Source>();

  /**
   * A list containing the source containers specifying additional sources that
   * have been removed.
   */
  final List<SourceContainer> removedContainers = new List<SourceContainer>();

  /**
   * A list containing the sources that have been deleted.
   */
  final List<Source> deletedSources = new List<Source>();

  /**
   * Return a table mapping the sources whose content has been changed to the
   * current content of those sources.
   */
  Map<Source, String> get changedContents => _changedContent;

  /**
   * Return `true` if this change set does not contain any changes.
   */
  bool get isEmpty => addedSources.isEmpty &&
      changedSources.isEmpty &&
      _changedContent.isEmpty &&
      changedRanges.isEmpty &&
      removedSources.isEmpty &&
      removedContainers.isEmpty &&
      deletedSources.isEmpty;

  /**
   * Record that the specified [source] has been added and that its content is
   * the default contents of the source.
   */
  void addedSource(Source source) {
    addedSources.add(source);
  }

  /**
   * Record that the specified [source] has been changed and that its content is
   * the given [contents].
   */
  void changedContent(Source source, String contents) {
    _changedContent[source] = contents;
  }

  /**
   * Record that the specified [source] has been changed and that its content is
   * the given [contents]. The [offset] is the offset into the current contents.
   * The [oldLength] is the number of characters in the original contents that
   * were replaced. The [newLength] is the number of characters in the
   * replacement text.
   */
  void changedRange(Source source, String contents, int offset, int oldLength,
      int newLength) {
    changedRanges[source] =
        new ChangeSet_ContentChange(contents, offset, oldLength, newLength);
  }

  /**
   * Record that the specified [source] has been changed. If the content of the
   * source was previously overridden, this has no effect (the content remains
   * overridden). To cancel (or change) the override, use [changedContent]
   * instead.
   */
  void changedSource(Source source) {
    changedSources.add(source);
  }

  /**
   * Record that the specified [source] has been deleted.
   */
  void deletedSource(Source source) {
    deletedSources.add(source);
  }

  /**
   * Record that the specified source [container] has been removed.
   */
  void removedContainer(SourceContainer container) {
    if (container != null) {
      removedContainers.add(container);
    }
  }

  /**
   * Record that the specified [source] has been removed.
   */
  void removedSource(Source source) {
    if (source != null) {
      removedSources.add(source);
    }
  }

  @override
  String toString() {
    StringBuffer buffer = new StringBuffer();
    bool needsSeparator =
        _appendSources(buffer, addedSources, false, "addedSources");
    needsSeparator = _appendSources(
        buffer, changedSources, needsSeparator, "changedSources");
    needsSeparator = _appendSources2(
        buffer, _changedContent, needsSeparator, "changedContent");
    needsSeparator =
        _appendSources2(buffer, changedRanges, needsSeparator, "changedRanges");
    needsSeparator = _appendSources(
        buffer, deletedSources, needsSeparator, "deletedSources");
    needsSeparator = _appendSources(
        buffer, removedSources, needsSeparator, "removedSources");
    int count = removedContainers.length;
    if (count > 0) {
      if (removedSources.isEmpty) {
        if (needsSeparator) {
          buffer.write("; ");
        }
        buffer.write("removed: from ");
        buffer.write(count);
        buffer.write(" containers");
      } else {
        buffer.write(", and more from ");
        buffer.write(count);
        buffer.write(" containers");
      }
    }
    return buffer.toString();
  }

  /**
   * Append the given [sources] to the given [buffer], prefixed with the given
   * [label] and a separator if [needsSeparator] is `true`. Return `true` if
   * future lists of sources will need a separator.
   */
  bool _appendSources(StringBuffer buffer, List<Source> sources,
      bool needsSeparator, String label) {
    if (sources.isEmpty) {
      return needsSeparator;
    }
    if (needsSeparator) {
      buffer.write("; ");
    }
    buffer.write(label);
    String prefix = " ";
    for (Source source in sources) {
      buffer.write(prefix);
      buffer.write(source.fullName);
      prefix = ", ";
    }
    return true;
  }

  /**
   * Append the given [sources] to the given [builder], prefixed with the given
   * [label] and a separator if [needsSeparator] is `true`. Return `true` if
   * future lists of sources will need a separator.
   */
  bool _appendSources2(StringBuffer buffer, HashMap<Source, dynamic> sources,
      bool needsSeparator, String label) {
    if (sources.isEmpty) {
      return needsSeparator;
    }
    if (needsSeparator) {
      buffer.write("; ");
    }
    buffer.write(label);
    String prefix = " ";
    for (Source source in sources.keys.toSet()) {
      buffer.write(prefix);
      buffer.write(source.fullName);
      prefix = ", ";
    }
    return true;
  }
}

/**
 * A change to the content of a source.
 */
class ChangeSet_ContentChange {
  /**
   * The new contents of the source.
   */
  final String contents;

  /**
   * The offset into the current contents.
   */
  final int offset;

  /**
   * The number of characters in the original contents that were replaced
   */
  final int oldLength;

  /**
   * The number of characters in the replacement text.
   */
  final int newLength;

  /**
   * Initialize a newly created change object to represent a change to the
   * content of a source. The [contents] is the new contents of the source. The
   * [offse] ist the offset into the current contents. The [oldLength] is the
   * number of characters in the original contents that were replaced. The
   * [newLength] is the number of characters in the replacement text.
   */
  ChangeSet_ContentChange(
      this.contents, this.offset, this.oldLength, this.newLength);
}

/**
 * [ComputedResult] describes a value computed for a [ResultDescriptor].
 */
class ComputedResult<V> {
  /**
   * The context in which the value was computed.
   */
  final AnalysisContext context;

  /**
   * The descriptor of the result which was computed.
   */
  final ResultDescriptor<V> descriptor;

  /**
   * The target for which the result was computed.
   */
  final AnalysisTarget target;

  /**
   * The computed value.
   */
  final V value;

  ComputedResult(this.context, this.descriptor, this.target, this.value);

  @override
  String toString() => '$descriptor of $target in $context';
}

/**
 * A pair containing a library and a list of the (source, entry) pairs for
 * compilation units in the library.
 */
class CycleBuilder_LibraryPair {
  /**
   * The library containing the compilation units.
   */
  ResolvableLibrary library;

  /**
   * The (source, entry) pairs representing the compilation units in the
   * library.
   */
  List<CycleBuilder_SourceEntryPair> entryPairs;

  /**
   * Initialize a newly created pair from the given [library] and [entryPairs].
   */
  CycleBuilder_LibraryPair(this.library, this.entryPairs);
}

/**
 * A pair containing a source and the cache entry associated with that source.
 * They are used to reduce the number of times an entry must be looked up in the
 * cache.
 */
class CycleBuilder_SourceEntryPair {
  /**
   * The source associated with the entry.
   */
  Source source;

  /**
   * The entry associated with the source.
   */
  DartEntry entry;

  /**
   * Initialize a newly created pair from the given [source] and [entry].
   */
  CycleBuilder_SourceEntryPair(this.source, this.entry);
}

/**
 * The information cached by an analysis context about an individual Dart file.
 */
class DartEntry extends SourceEntry {
  /**
   * The data descriptor representing the element model representing a single
   * compilation unit. This model is incomplete and should not be used except as
   * input to another task.
   */
  static final DataDescriptor<List<AnalysisError>> BUILT_ELEMENT =
      new DataDescriptor<List<AnalysisError>>("DartEntry.BUILT_ELEMENT");

  /**
   * The data descriptor representing the AST structure after the element model
   * has been built (and declarations are resolved) but before other resolution
   * has been performed.
   */
  static final DataDescriptor<CompilationUnit> BUILT_UNIT =
      new DataDescriptor<CompilationUnit>("DartEntry.BUILT_UNIT");

  /**
   * The data descriptor representing the list of libraries that contain this
   * compilation unit.
   */
  static final DataDescriptor<List<Source>> CONTAINING_LIBRARIES =
      new DataDescriptor<List<Source>>(
          "DartEntry.CONTAINING_LIBRARIES", Source.EMPTY_LIST);

  /**
   * The data descriptor representing the library element for the library. This
   * data is only available for Dart files that are the defining compilation
   * unit of a library.
   */
  static final DataDescriptor<LibraryElement> ELEMENT =
      new DataDescriptor<LibraryElement>("DartEntry.ELEMENT");

  /**
   * The data descriptor representing the list of exported libraries. This data
   * is only available for Dart files that are the defining compilation unit of
   * a library.
   */
  static final DataDescriptor<List<Source>> EXPORTED_LIBRARIES =
      new DataDescriptor<List<Source>>(
          "DartEntry.EXPORTED_LIBRARIES", Source.EMPTY_LIST);

  /**
   * The data descriptor representing the hints resulting from auditing the
   * source.
   */
  static final DataDescriptor<List<AnalysisError>> HINTS =
      new DataDescriptor<List<AnalysisError>>(
          "DartEntry.HINTS", AnalysisError.NO_ERRORS);

  /**
   * The data descriptor representing the list of imported libraries. This data
   * is only available for Dart files that are the defining compilation unit of
   * a library.
   */
  static final DataDescriptor<List<Source>> IMPORTED_LIBRARIES =
      new DataDescriptor<List<Source>>(
          "DartEntry.IMPORTED_LIBRARIES", Source.EMPTY_LIST);

  /**
   * The data descriptor representing the list of included parts. This data is
   * only available for Dart files that are the defining compilation unit of a
   * library.
   */
  static final DataDescriptor<List<Source>> INCLUDED_PARTS =
      new DataDescriptor<List<Source>>(
          "DartEntry.INCLUDED_PARTS", Source.EMPTY_LIST);

  /**
   * The data descriptor representing the client flag. This data is only
   * available for Dart files that are the defining compilation unit of a
   * library.
   */
  static final DataDescriptor<bool> IS_CLIENT =
      new DataDescriptor<bool>("DartEntry.IS_CLIENT", false);

  /**
   * The data descriptor representing the launchable flag. This data is only
   * available for Dart files that are the defining compilation unit of a
   * library.
   */
  static final DataDescriptor<bool> IS_LAUNCHABLE =
      new DataDescriptor<bool>("DartEntry.IS_LAUNCHABLE", false);

  /**
   * The data descriptor representing lint warnings resulting from auditing the
   * source.
   */
  static final DataDescriptor<List<AnalysisError>> LINTS =
      new DataDescriptor<List<AnalysisError>>(
          "DartEntry.LINTS", AnalysisError.NO_ERRORS);

  /**
   * The data descriptor representing the errors resulting from parsing the
   * source.
   */
  static final DataDescriptor<List<AnalysisError>> PARSE_ERRORS =
      new DataDescriptor<List<AnalysisError>>(
          "DartEntry.PARSE_ERRORS", AnalysisError.NO_ERRORS);

  /**
   * The data descriptor representing the parsed AST structure.
   */
  static final DataDescriptor<CompilationUnit> PARSED_UNIT =
      new DataDescriptor<CompilationUnit>("DartEntry.PARSED_UNIT");

  /**
   * The data descriptor representing the public namespace of the library. This
   * data is only available for Dart files that are the defining compilation
   * unit of a library.
   */
  static final DataDescriptor<Namespace> PUBLIC_NAMESPACE =
      new DataDescriptor<Namespace>("DartEntry.PUBLIC_NAMESPACE");

  /**
   * The data descriptor representing the errors resulting from resolving the
   * source.
   */
  static final DataDescriptor<List<AnalysisError>> RESOLUTION_ERRORS =
      new DataDescriptor<List<AnalysisError>>(
          "DartEntry.RESOLUTION_ERRORS", AnalysisError.NO_ERRORS);

  /**
   * The data descriptor representing the resolved AST structure.
   */
  static final DataDescriptor<CompilationUnit> RESOLVED_UNIT =
      new DataDescriptor<CompilationUnit>("DartEntry.RESOLVED_UNIT");

  /**
   * The data descriptor representing the errors resulting from scanning the
   * source.
   */
  static final DataDescriptor<List<AnalysisError>> SCAN_ERRORS =
      new DataDescriptor<List<AnalysisError>>(
          "DartEntry.SCAN_ERRORS", AnalysisError.NO_ERRORS);

  /**
   * The data descriptor representing the source kind.
   */
  static final DataDescriptor<SourceKind> SOURCE_KIND =
      new DataDescriptor<SourceKind>(
          "DartEntry.SOURCE_KIND", SourceKind.UNKNOWN);

  /**
   * The data descriptor representing the token stream.
   */
  static final DataDescriptor<Token> TOKEN_STREAM =
      new DataDescriptor<Token>("DartEntry.TOKEN_STREAM");

  /**
   * The data descriptor representing the errors resulting from verifying the
   * source.
   */
  static final DataDescriptor<List<AnalysisError>> VERIFICATION_ERRORS =
      new DataDescriptor<List<AnalysisError>>(
          "DartEntry.VERIFICATION_ERRORS", AnalysisError.NO_ERRORS);

  /**
   * The list of libraries that contain this compilation unit. The list will be
   * empty if there are no known libraries that contain this compilation unit.
   */
  List<Source> _containingLibraries = new List<Source>();

  /**
   * The information known as a result of resolving this compilation unit as
   * part of the library that contains this unit. This field will never be
   * `null`.
   */
  ResolutionState _resolutionState = new ResolutionState();

  /**
   * Return all of the errors associated with the compilation unit that are
   * currently cached.
   */
  List<AnalysisError> get allErrors {
    List<AnalysisError> errors = new List<AnalysisError>();
    errors.addAll(super.allErrors);
    errors.addAll(getValue(SCAN_ERRORS));
    errors.addAll(getValue(PARSE_ERRORS));
    ResolutionState state = _resolutionState;
    while (state != null) {
      errors.addAll(state.getValue(RESOLUTION_ERRORS));
      errors.addAll(state.getValue(VERIFICATION_ERRORS));
      errors.addAll(state.getValue(HINTS));
      errors.addAll(state.getValue(LINTS));
      state = state._nextState;
    }
    if (errors.length == 0) {
      return AnalysisError.NO_ERRORS;
    }
    return errors;
  }

  /**
   * Return a valid parsed compilation unit, either an unresolved AST structure
   * or the result of resolving the AST structure in the context of some
   * library, or `null` if there is no parsed compilation unit available.
   */
  CompilationUnit get anyParsedCompilationUnit {
    if (getState(PARSED_UNIT) == CacheState.VALID) {
      return getValue(PARSED_UNIT);
    }
    ResolutionState state = _resolutionState;
    while (state != null) {
      if (state.getState(BUILT_UNIT) == CacheState.VALID) {
        return state.getValue(BUILT_UNIT);
      }
      state = state._nextState;
    }

    return anyResolvedCompilationUnit;
  }

  /**
   * Return the result of resolving the compilation unit as part of any library,
   * or `null` if there is no cached resolved compilation unit.
   */
  CompilationUnit get anyResolvedCompilationUnit {
    ResolutionState state = _resolutionState;
    while (state != null) {
      if (state.getState(RESOLVED_UNIT) == CacheState.VALID) {
        return state.getValue(RESOLVED_UNIT);
      }
      state = state._nextState;
    }
    return null;
  }

  /**
   * The libraries that are known to contain this part.
   */
  List<Source> get containingLibraries => _containingLibraries;

  /**
   * Set the list of libraries that contain this compilation unit to contain
   * only the given [librarySource]. This method should only be invoked on
   * entries that represent a library.
   */
  void set containingLibrary(Source librarySource) {
    _containingLibraries.clear();
    _containingLibraries.add(librarySource);
  }

  @override
  List<DataDescriptor> get descriptors {
    List<DataDescriptor> result = super.descriptors;
    result.addAll(<DataDescriptor>[
      DartEntry.SOURCE_KIND,
      DartEntry.CONTAINING_LIBRARIES,
      DartEntry.PARSE_ERRORS,
      DartEntry.PARSED_UNIT,
      DartEntry.SCAN_ERRORS,
      DartEntry.SOURCE_KIND,
      DartEntry.TOKEN_STREAM
    ]);
    SourceKind kind = getValue(DartEntry.SOURCE_KIND);
    if (kind == SourceKind.LIBRARY) {
      result.addAll(<DataDescriptor>[
        DartEntry.ELEMENT,
        DartEntry.EXPORTED_LIBRARIES,
        DartEntry.IMPORTED_LIBRARIES,
        DartEntry.INCLUDED_PARTS,
        DartEntry.IS_CLIENT,
        DartEntry.IS_LAUNCHABLE,
        DartEntry.PUBLIC_NAMESPACE
      ]);
    }
    return result;
  }

  /**
   * Return `true` if this entry has an AST structure that can be resolved, even
   * if it needs to be copied. Returning `true` implies that the method
   * [resolvableCompilationUnit] will return a non-`null` result.
   */
  bool get hasResolvableCompilationUnit {
    if (getState(PARSED_UNIT) == CacheState.VALID) {
      return true;
    }
    ResolutionState state = _resolutionState;
    while (state != null) {
      if (state.getState(BUILT_UNIT) == CacheState.VALID ||
          state.getState(RESOLVED_UNIT) == CacheState.VALID) {
        return true;
      }
      state = state._nextState;
    }

    return false;
  }

  @override
  SourceKind get kind => getValue(SOURCE_KIND);

  /**
   * The library sources containing the receiver's source.
   */
  List<Source> get librariesContaining {
    ResolutionState state = _resolutionState;
    List<Source> result = new List<Source>();
    while (state != null) {
      if (state._librarySource != null) {
        result.add(state._librarySource);
      }
      state = state._nextState;
    }
    return result;
  }

  /**
   * Get a list of all the library-dependent descriptors for which values may
   * be stored in this SourceEntry.
   */
  List<DataDescriptor> get libraryDescriptors {
    return <DataDescriptor>[
      DartEntry.BUILT_ELEMENT,
      DartEntry.BUILT_UNIT,
      DartEntry.RESOLUTION_ERRORS,
      DartEntry.RESOLVED_UNIT,
      DartEntry.VERIFICATION_ERRORS,
      DartEntry.HINTS,
      DartEntry.LINTS
    ];
  }

  /**
   * A compilation unit that has not been accessed by any other client and can
   * therefore safely be modified by the reconciler, or `null` if the source has
   * not been parsed.
   */
  CompilationUnit get resolvableCompilationUnit {
    if (getState(PARSED_UNIT) == CacheState.VALID) {
      CompilationUnit unit = getValue(PARSED_UNIT);
      setState(PARSED_UNIT, CacheState.FLUSHED);
      return unit;
    }
    ResolutionState state = _resolutionState;
    while (state != null) {
      if (state.getState(BUILT_UNIT) == CacheState.VALID) {
        // TODO(brianwilkerson) We're cloning the structure to remove any
        // previous resolution data, but I'm not sure that's necessary.
        return state.getValue(BUILT_UNIT).accept(new AstCloner());
      }
      if (state.getState(RESOLVED_UNIT) == CacheState.VALID) {
        return state.getValue(RESOLVED_UNIT).accept(new AstCloner());
      }
      state = state._nextState;
    }
    return null;
  }

  /**
   * Add the given [librarySource] to the list of libraries that contain this
   * part. This method should only be invoked on entries that represent a part.
   */
  void addContainingLibrary(Source librarySource) {
    _containingLibraries.add(librarySource);
  }

  /**
   * Flush any AST structures being maintained by this entry.
   */
  void flushAstStructures() {
    _flush(TOKEN_STREAM);
    _flush(PARSED_UNIT);
    _resolutionState.flushAstStructures();
  }

  /**
   * Return the state of the data represented by the given [descriptor] in the
   * context of the given [librarySource].
   */
  CacheState getStateInLibrary(
      DataDescriptor descriptor, Source librarySource) {
    if (!_isValidLibraryDescriptor(descriptor)) {
      throw new ArgumentError("Invalid descriptor: $descriptor");
    }
    ResolutionState state = _resolutionState;
    while (state != null) {
      if (librarySource == state._librarySource) {
        return state.getState(descriptor);
      }
      state = state._nextState;
    }
    return CacheState.INVALID;
  }

  /**
   * Return the value of the data represented by the given [descriptor] in the
   * context of the given [librarySource], or `null` if the data represented by
   * the descriptor is not in the cache.
   */
  Object getValueInLibrary(DataDescriptor descriptor, Source librarySource) {
    if (!_isValidLibraryDescriptor(descriptor)) {
      throw new ArgumentError("Invalid descriptor: $descriptor");
    }
    ResolutionState state = _resolutionState;
    while (state != null) {
      if (librarySource == state._librarySource) {
        return state.getValue(descriptor);
      }
      state = state._nextState;
    }
    return descriptor.defaultValue;
  }

  /**
   * Return `true` if the data represented by the given [descriptor] is marked
   * as being invalid. If the descriptor represents library-specific data then
   * this method will return `true` if the data associated with any library it
   * marked as invalid.
   */
  bool hasInvalidData(DataDescriptor descriptor) {
    if (_isValidDescriptor(descriptor)) {
      return getState(descriptor) == CacheState.INVALID;
    } else if (_isValidLibraryDescriptor(descriptor)) {
      ResolutionState state = _resolutionState;
      while (state != null) {
        if (state.getState(descriptor) == CacheState.INVALID) {
          return true;
        }
        state = state._nextState;
      }
    }
    return false;
  }

  @override
  void invalidateAllInformation() {
    super.invalidateAllInformation();
    setState(SCAN_ERRORS, CacheState.INVALID);
    setState(TOKEN_STREAM, CacheState.INVALID);
    setState(SOURCE_KIND, CacheState.INVALID);
    setState(PARSE_ERRORS, CacheState.INVALID);
    setState(PARSED_UNIT, CacheState.INVALID);
    _discardCachedResolutionInformation(true);
  }

  /**
   * Invalidate all of the resolution information associated with the
   * compilation unit. The flag [invalidateUris] should be `true` if the cached
   * results of converting URIs to source files should also be invalidated.
   */
  void invalidateAllResolutionInformation(bool invalidateUris) {
    if (getState(PARSED_UNIT) == CacheState.FLUSHED) {
      ResolutionState state = _resolutionState;
      while (state != null) {
        if (state.getState(BUILT_UNIT) == CacheState.VALID) {
          CompilationUnit unit = state.getValue(BUILT_UNIT);
          setValue(PARSED_UNIT, unit.accept(new AstCloner()));
          break;
        } else if (state.getState(RESOLVED_UNIT) == CacheState.VALID) {
          CompilationUnit unit = state.getValue(RESOLVED_UNIT);
          setValue(PARSED_UNIT, unit.accept(new AstCloner()));
          break;
        }
        state = state._nextState;
      }
    }
    _discardCachedResolutionInformation(invalidateUris);
  }

  /**
   * Invalidate all of the parse and resolution information associated with
   * this source.
   */
  void invalidateParseInformation() {
    setState(SOURCE_KIND, CacheState.INVALID);
    setState(PARSE_ERRORS, CacheState.INVALID);
    setState(PARSED_UNIT, CacheState.INVALID);
    _containingLibraries.clear();
    _discardCachedResolutionInformation(true);
  }

  /**
   * Record that an [exception] occurred while attempting to build the element
   * model for the source represented by this entry in the context of the given
   * [library]. This will set the state of all resolution-based information as
   * being in error, but will not change the state of any parse results.
   */
  void recordBuildElementErrorInLibrary(
      Source librarySource, CaughtException exception) {
    setStateInLibrary(BUILT_ELEMENT, librarySource, CacheState.ERROR);
    setStateInLibrary(BUILT_UNIT, librarySource, CacheState.ERROR);
    recordResolutionErrorInLibrary(librarySource, exception);
  }

  @override
  void recordContentError(CaughtException exception) {
    super.recordContentError(exception);
    recordScanError(exception);
  }

  /**
   * Record that an error occurred while attempting to generate hints for the
   * source represented by this entry. This will set the state of all
   * verification information as being in error. The [librarySource] is the
   * source of the library in which hints were being generated. The [exception]
   * is the exception that shows where the error occurred.
   */
  void recordHintErrorInLibrary(
      Source librarySource, CaughtException exception) {
    this.exception = exception;
    ResolutionState state = _getOrCreateResolutionState(librarySource);
    state.recordHintError();
  }

  /**
   * Record that an error occurred while attempting to generate lints for the
   * source represented by this entry. This will set the state of all
   * verification information as being in error. The [librarySource] is the
   * source of the library in which lints were being generated. The [exception]
   * is the exception that shows where the error occurred.
   */
  void recordLintErrorInLibrary(
      Source librarySource, CaughtException exception) {
    this.exception = exception;
    ResolutionState state = _getOrCreateResolutionState(librarySource);
    state.recordLintError();
  }

  /**
   * Record that an [exception] occurred while attempting to scan or parse the
   * entry represented by this entry. This will set the state of all information,
   * including any resolution-based information, as being in error.
   */
  void recordParseError(CaughtException exception) {
    setState(SOURCE_KIND, CacheState.ERROR);
    setState(PARSE_ERRORS, CacheState.ERROR);
    setState(PARSED_UNIT, CacheState.ERROR);
    setState(EXPORTED_LIBRARIES, CacheState.ERROR);
    setState(IMPORTED_LIBRARIES, CacheState.ERROR);
    setState(INCLUDED_PARTS, CacheState.ERROR);
    recordResolutionError(exception);
  }

  /**
   * Record that an [exception] occurred while attempting to resolve the source
   * represented by this entry. This will set the state of all resolution-based
   * information as being in error, but will not change the state of any parse
   * results.
   */
  void recordResolutionError(CaughtException exception) {
    this.exception = exception;
    setState(ELEMENT, CacheState.ERROR);
    setState(IS_CLIENT, CacheState.ERROR);
    setState(IS_LAUNCHABLE, CacheState.ERROR);
    setState(PUBLIC_NAMESPACE, CacheState.ERROR);
    _resolutionState.recordResolutionErrorsInAllLibraries();
  }

  /**
   * Record that an error occurred while attempting to resolve the source
   * represented by this entry. This will set the state of all resolution-based
   * information as being in error, but will not change the state of any parse
   * results. The [librarySource] is the source of the library in which
   * resolution was being performed. The [exception] is the exception that shows
   * where the error occurred.
   */
  void recordResolutionErrorInLibrary(
      Source librarySource, CaughtException exception) {
    this.exception = exception;
    setState(ELEMENT, CacheState.ERROR);
    setState(IS_CLIENT, CacheState.ERROR);
    setState(IS_LAUNCHABLE, CacheState.ERROR);
    setState(PUBLIC_NAMESPACE, CacheState.ERROR);
    ResolutionState state = _getOrCreateResolutionState(librarySource);
    state.recordResolutionError();
  }

  /**
   * Record that an [exception] occurred while attempting to scan or parse the
   * entry represented by this entry. This will set the state of all
   * information, including any resolution-based information, as being in error.
   */
  @override
  void recordScanError(CaughtException exception) {
    super.recordScanError(exception);
    setState(SCAN_ERRORS, CacheState.ERROR);
    setState(TOKEN_STREAM, CacheState.ERROR);
    recordParseError(exception);
  }

  /**
   * Record that an [exception] occurred while attempting to generate errors and
   * warnings for the source represented by this entry. This will set the state
   * of all verification information as being in error. The [librarySource] is
   * the source of the library in which verification was being performed. The
   * [exception] is the exception that shows where the error occurred.
   */
  void recordVerificationErrorInLibrary(
      Source librarySource, CaughtException exception) {
    this.exception = exception;
    ResolutionState state = _getOrCreateResolutionState(librarySource);
    state.recordVerificationError();
  }

  /**
   * Remove the given [library] from the list of libraries that contain this
   * part. This method should only be invoked on entries that represent a part.
   */
  void removeContainingLibrary(Source library) {
    _containingLibraries.remove(library);
  }

  /**
   * Remove any resolution information associated with this compilation unit
   * being part of the given [library], presumably because it is no longer part
   * of the library.
   */
  void removeResolution(Source library) {
    if (library != null) {
      if (library == _resolutionState._librarySource) {
        if (_resolutionState._nextState == null) {
          _resolutionState.invalidateAllResolutionInformation();
        } else {
          _resolutionState = _resolutionState._nextState;
        }
      } else {
        ResolutionState priorState = _resolutionState;
        ResolutionState state = _resolutionState._nextState;
        while (state != null) {
          if (library == state._librarySource) {
            priorState._nextState = state._nextState;
            break;
          }
          priorState = state;
          state = state._nextState;
        }
      }
    }
  }

  /**
   * Set the state of the data represented by the given [descriptor] in the
   * context of the given [library] to the given [state].
   */
  void setStateInLibrary(
      DataDescriptor descriptor, Source library, CacheState state) {
    if (!_isValidLibraryDescriptor(descriptor)) {
      throw new ArgumentError("Invalid descriptor: $descriptor");
    }
    ResolutionState resolutionState = _getOrCreateResolutionState(library);
    resolutionState.setState(descriptor, state);
  }

  /**
   * Set the value of the data represented by the given [descriptor] in the
   * context of the given [library] to the given [value], and set the state of
   * that data to [CacheState.VALID].
   */
  void setValueInLibrary(
      DataDescriptor descriptor, Source library, Object value) {
    if (!_isValidLibraryDescriptor(descriptor)) {
      throw new ArgumentError("Invalid descriptor: $descriptor");
    }
    ResolutionState state = _getOrCreateResolutionState(library);
    state.setValue(descriptor, value);
  }

  /**
   * Invalidate all of the resolution information associated with the
   * compilation unit. The flag [invalidateUris] should be `true` if the cached
   * results of converting URIs to source files should also be invalidated.
   */
  void _discardCachedResolutionInformation(bool invalidateUris) {
    setState(ELEMENT, CacheState.INVALID);
    setState(IS_CLIENT, CacheState.INVALID);
    setState(IS_LAUNCHABLE, CacheState.INVALID);
    setState(PUBLIC_NAMESPACE, CacheState.INVALID);
    _resolutionState.invalidateAllResolutionInformation();
    if (invalidateUris) {
      setState(EXPORTED_LIBRARIES, CacheState.INVALID);
      setState(IMPORTED_LIBRARIES, CacheState.INVALID);
      setState(INCLUDED_PARTS, CacheState.INVALID);
    }
  }

  /**
   * Return a resolution state for the specified [library], creating one as
   * necessary.
   */
  ResolutionState _getOrCreateResolutionState(Source library) {
    ResolutionState state = _resolutionState;
    if (state._librarySource == null) {
      state._librarySource = library;
      return state;
    }
    while (state._librarySource != library) {
      if (state._nextState == null) {
        ResolutionState newState = new ResolutionState();
        newState._librarySource = library;
        state._nextState = newState;
        return newState;
      }
      state = state._nextState;
    }
    return state;
  }

  @override
  bool _isValidDescriptor(DataDescriptor descriptor) {
    return descriptor == CONTAINING_LIBRARIES ||
        descriptor == ELEMENT ||
        descriptor == EXPORTED_LIBRARIES ||
        descriptor == IMPORTED_LIBRARIES ||
        descriptor == INCLUDED_PARTS ||
        descriptor == IS_CLIENT ||
        descriptor == IS_LAUNCHABLE ||
        descriptor == PARSED_UNIT ||
        descriptor == PARSE_ERRORS ||
        descriptor == PUBLIC_NAMESPACE ||
        descriptor == SCAN_ERRORS ||
        descriptor == SOURCE_KIND ||
        descriptor == TOKEN_STREAM ||
        super._isValidDescriptor(descriptor);
  }

  /**
   * Return `true` if the [descriptor] is valid for this entry when the data is
   * relative to a library.
   */
  bool _isValidLibraryDescriptor(DataDescriptor descriptor) {
    return descriptor == BUILT_ELEMENT ||
        descriptor == BUILT_UNIT ||
        descriptor == HINTS ||
        descriptor == LINTS ||
        descriptor == RESOLUTION_ERRORS ||
        descriptor == RESOLVED_UNIT ||
        descriptor == VERIFICATION_ERRORS;
  }

  @override
  bool _writeDiffOn(StringBuffer buffer, SourceEntry oldEntry) {
    bool needsSeparator = super._writeDiffOn(buffer, oldEntry);
    if (oldEntry is! DartEntry) {
      if (needsSeparator) {
        buffer.write("; ");
      }
      buffer.write("entry type changed; was ");
      buffer.write(oldEntry.runtimeType.toString());
      return true;
    }
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "tokenStream",
        DartEntry.TOKEN_STREAM, oldEntry);
    needsSeparator = _writeStateDiffOn(
        buffer, needsSeparator, "scanErrors", DartEntry.SCAN_ERRORS, oldEntry);
    needsSeparator = _writeStateDiffOn(
        buffer, needsSeparator, "sourceKind", DartEntry.SOURCE_KIND, oldEntry);
    needsSeparator = _writeStateDiffOn(
        buffer, needsSeparator, "parsedUnit", DartEntry.PARSED_UNIT, oldEntry);
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "parseErrors",
        DartEntry.PARSE_ERRORS, oldEntry);
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
        "importedLibraries", DartEntry.IMPORTED_LIBRARIES, oldEntry);
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
        "exportedLibraries", DartEntry.EXPORTED_LIBRARIES, oldEntry);
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "includedParts",
        DartEntry.INCLUDED_PARTS, oldEntry);
    needsSeparator = _writeStateDiffOn(
        buffer, needsSeparator, "element", DartEntry.ELEMENT, oldEntry);
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
        "publicNamespace", DartEntry.PUBLIC_NAMESPACE, oldEntry);
    needsSeparator = _writeStateDiffOn(
        buffer, needsSeparator, "clientServer", DartEntry.IS_CLIENT, oldEntry);
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "launchable",
        DartEntry.IS_LAUNCHABLE, oldEntry);
    // TODO(brianwilkerson) Add better support for containingLibraries.
    // It would be nice to be able to report on size-preserving changes.
    int oldLibraryCount = (oldEntry as DartEntry)._containingLibraries.length;
    int libraryCount = _containingLibraries.length;
    if (oldLibraryCount != libraryCount) {
      if (needsSeparator) {
        buffer.write("; ");
      }
      buffer.write("containingLibraryCount = ");
      buffer.write(oldLibraryCount);
      buffer.write(" -> ");
      buffer.write(libraryCount);
      needsSeparator = true;
    }
    //
    // Report change to the per-library state.
    //
    HashMap<Source, ResolutionState> oldStateMap =
        new HashMap<Source, ResolutionState>();
    ResolutionState state = (oldEntry as DartEntry)._resolutionState;
    while (state != null) {
      Source librarySource = state._librarySource;
      if (librarySource != null) {
        oldStateMap[librarySource] = state;
      }
      state = state._nextState;
    }
    state = _resolutionState;
    while (state != null) {
      Source librarySource = state._librarySource;
      if (librarySource != null) {
        ResolutionState oldState = oldStateMap.remove(librarySource);
        if (oldState == null) {
          if (needsSeparator) {
            buffer.write("; ");
          }
          buffer.write("added resolution for ");
          buffer.write(librarySource.fullName);
          needsSeparator = true;
        } else {
          needsSeparator = oldState._writeDiffOn(
              buffer, needsSeparator, oldEntry as DartEntry);
        }
      }
      state = state._nextState;
    }
    for (Source librarySource in oldStateMap.keys.toSet()) {
      if (needsSeparator) {
        buffer.write("; ");
      }
      buffer.write("removed resolution for ");
      buffer.write(librarySource.fullName);
      needsSeparator = true;
    }
    return needsSeparator;
  }

  @override
  void _writeOn(StringBuffer buffer) {
    buffer.write("Dart: ");
    super._writeOn(buffer);
    _writeStateOn(buffer, "tokenStream", TOKEN_STREAM);
    _writeStateOn(buffer, "scanErrors", SCAN_ERRORS);
    _writeStateOn(buffer, "sourceKind", SOURCE_KIND);
    _writeStateOn(buffer, "parsedUnit", PARSED_UNIT);
    _writeStateOn(buffer, "parseErrors", PARSE_ERRORS);
    _writeStateOn(buffer, "exportedLibraries", EXPORTED_LIBRARIES);
    _writeStateOn(buffer, "importedLibraries", IMPORTED_LIBRARIES);
    _writeStateOn(buffer, "includedParts", INCLUDED_PARTS);
    _writeStateOn(buffer, "element", ELEMENT);
    _writeStateOn(buffer, "publicNamespace", PUBLIC_NAMESPACE);
    _writeStateOn(buffer, "clientServer", IS_CLIENT);
    _writeStateOn(buffer, "launchable", IS_LAUNCHABLE);
    _resolutionState._writeOn(buffer);
  }
}

/**
 * An immutable constant representing data that can be stored in the cache.
 */
class DataDescriptor<E> {
  /**
   * The next artificial hash code.
   */
  static int _NEXT_HASH_CODE = 0;

  /**
   * The artifitial hash code for this object.
   */
  final int _hashCode = _NEXT_HASH_CODE++;

  /**
   * The name of the descriptor, used for debugging purposes.
   */
  final String _name;

  /**
   * The default value used when the data does not exist.
   */
  final E defaultValue;

  /**
   * Initialize a newly created descriptor to have the given [name] and
   * [defaultValue].
   */
  DataDescriptor(this._name, [this.defaultValue = null]);

  @override
  int get hashCode => _hashCode;

  @override
  String toString() => _name;
}

/**
 * A retention policy that will keep AST's in the cache if there is analysis
 * information that needs to be computed for a source, where the computation is
 * dependent on having the AST.
 */
class DefaultRetentionPolicy implements CacheRetentionPolicy {
  /**
   * An instance of this class that can be shared.
   */
  static DefaultRetentionPolicy POLICY = new DefaultRetentionPolicy();

  /**
   * Return `true` if there is analysis information in the given [dartEntry]
   * that needs to be computed, where the computation is dependent on having the
   * AST.
   */
  bool astIsNeeded(DartEntry dartEntry) =>
      dartEntry.hasInvalidData(DartEntry.HINTS) ||
          dartEntry.hasInvalidData(DartEntry.LINTS) ||
          dartEntry.hasInvalidData(DartEntry.VERIFICATION_ERRORS) ||
          dartEntry.hasInvalidData(DartEntry.RESOLUTION_ERRORS);

  @override
  RetentionPriority getAstPriority(Source source, SourceEntry sourceEntry) {
    if (sourceEntry is DartEntry) {
      DartEntry dartEntry = sourceEntry;
      if (astIsNeeded(dartEntry)) {
        return RetentionPriority.MEDIUM;
      }
    }
    return RetentionPriority.LOW;
  }
}

/**
 * Instances of the class `GenerateDartErrorsTask` generate errors and warnings for a single
 * Dart source.
 */
class GenerateDartErrorsTask extends AnalysisTask {
  /**
   * The source for which errors and warnings are to be produced.
   */
  final Source source;

  /**
   * The compilation unit used to resolve the dependencies.
   */
  final CompilationUnit _unit;

  /**
   * The element model for the library containing the source.
   */
  final LibraryElement libraryElement;

  /**
   * The errors that were generated for the source.
   */
  List<AnalysisError> _errors;

  /**
   * Initialize a newly created task to perform analysis within the given context.
   *
   * @param context the context in which the task is to be performed
   * @param source the source for which errors and warnings are to be produced
   * @param unit the compilation unit used to resolve the dependencies
   * @param libraryElement the element model for the library containing the source
   */
  GenerateDartErrorsTask(InternalAnalysisContext context, this.source,
      this._unit, this.libraryElement)
      : super(context);

  /**
   * Return the errors that were generated for the source.
   *
   * @return the errors that were generated for the source
   */
  List<AnalysisError> get errors => _errors;

  @override
  String get taskDescription =>
      "generate errors and warnings for ${source.fullName}";

  @override
  accept(AnalysisTaskVisitor visitor) =>
      visitor.visitGenerateDartErrorsTask(this);

  @override
  void internalPerform() {
    PerformanceStatistics.errors.makeCurrentWhile(() {
      RecordingErrorListener errorListener = new RecordingErrorListener();
      ErrorReporter errorReporter = new ErrorReporter(errorListener, source);
      TypeProvider typeProvider = context.typeProvider;
      //
      // Validate the directives
      //
      validateDirectives(context, source, _unit, errorListener);
      //
      // Use the ConstantVerifier to verify the use of constants.
      // This needs to happen before using the ErrorVerifier because some error
      // codes need the computed constant values.
      //
      // TODO(paulberry): as a temporary workaround for issue 21572,
      // ConstantVerifier is being run right after ConstantValueComputer, so we
      // don't need to run it here.  Once issue 21572 is fixed, re-enable the
      // call to ConstantVerifier.
//      ConstantVerifier constantVerifier = new ConstantVerifier(errorReporter, libraryElement, typeProvider);
//      _unit.accept(constantVerifier);
      //
      // Use the ErrorVerifier to compute the rest of the errors.
      //
      ErrorVerifier errorVerifier = new ErrorVerifier(
          errorReporter,
          libraryElement,
          typeProvider,
          new InheritanceManager(libraryElement),
          context.analysisOptions.enableSuperMixins);
      _unit.accept(errorVerifier);
      _errors = errorListener.getErrorsForSource(source);
    });
  }

  /**
   * Check each directive in the given compilation unit to see if the referenced source exists and
   * report an error if it does not.
   *
   * @param context the context in which the library exists
   * @param librarySource the source representing the library containing the directives
   * @param unit the compilation unit containing the directives to be validated
   * @param errorListener the error listener to which errors should be reported
   */
  static void validateDirectives(AnalysisContext context, Source librarySource,
      CompilationUnit unit, AnalysisErrorListener errorListener) {
    for (Directive directive in unit.directives) {
      if (directive is UriBasedDirective) {
        validateReferencedSource(
            context, librarySource, directive, errorListener);
      }
    }
  }

  /**
   * Check the given directive to see if the referenced source exists and report an error if it does
   * not.
   *
   * @param context the context in which the library exists
   * @param librarySource the source representing the library containing the directive
   * @param directive the directive to be verified
   * @param errorListener the error listener to which errors should be reported
   */
  static void validateReferencedSource(
      AnalysisContext context,
      Source librarySource,
      UriBasedDirective directive,
      AnalysisErrorListener errorListener) {
    Source source = directive.source;
    if (source != null) {
      if (context.exists(source)) {
        return;
      }
    } else {
      // Don't report errors already reported by ParseDartTask.resolveDirective
      if (directive.validate() != null) {
        return;
      }
    }
    StringLiteral uriLiteral = directive.uri;
    errorListener.onError(new AnalysisError(
        librarySource,
        uriLiteral.offset,
        uriLiteral.length,
        CompileTimeErrorCode.URI_DOES_NOT_EXIST,
        [directive.uriContent]));
  }
}

/**
 * Instances of the class `GenerateDartHintsTask` generate hints for a single Dart library.
 */
class GenerateDartHintsTask extends AnalysisTask {
  /**
   * The compilation units that comprise the library, with the defining compilation unit appearing
   * first in the list.
   */
  final List<TimestampedData<CompilationUnit>> _units;

  /**
   * The element model for the library being analyzed.
   */
  final LibraryElement libraryElement;

  /**
   * A table mapping the sources that were analyzed to the hints that were
   * generated for the sources.
   */
  HashMap<Source, List<AnalysisError>> _hintMap;

  /**
   * Initialize a newly created task to perform analysis within the given context.
   *
   * @param context the context in which the task is to be performed
   * @param units the compilation units that comprise the library, with the defining compilation
   *          unit appearing first in the list
   * @param libraryElement the element model for the library being analyzed
   */
  GenerateDartHintsTask(
      InternalAnalysisContext context, this._units, this.libraryElement)
      : super(context);

  /**
   * Return a table mapping the sources that were analyzed to the hints that were generated for the
   * sources, or `null` if the task has not been performed or if the analysis did not complete
   * normally.
   *
   * @return a table mapping the sources that were analyzed to the hints that were generated for the
   *         sources
   */
  HashMap<Source, List<AnalysisError>> get hintMap => _hintMap;

  @override
  String get taskDescription {
    Source librarySource = libraryElement.source;
    if (librarySource == null) {
      return "generate Dart hints for library without source";
    }
    return "generate Dart hints for ${librarySource.fullName}";
  }

  @override
  accept(AnalysisTaskVisitor visitor) =>
      visitor.visitGenerateDartHintsTask(this);

  @override
  void internalPerform() {
    //
    // Gather the compilation units.
    //
    int unitCount = _units.length;
    List<CompilationUnit> compilationUnits =
        new List<CompilationUnit>(unitCount);
    for (int i = 0; i < unitCount; i++) {
      compilationUnits[i] = _units[i].data;
    }
    //
    // Analyze all of the units.
    //
    RecordingErrorListener errorListener = new RecordingErrorListener();
    HintGenerator hintGenerator =
        new HintGenerator(compilationUnits, context, errorListener);
    hintGenerator.generateForLibrary();
    //
    // Store the results.
    //
    _hintMap = new HashMap<Source, List<AnalysisError>>();
    for (int i = 0; i < unitCount; i++) {
      Source source = _units[i].data.element.source;
      _hintMap[source] = errorListener.getErrorsForSource(source);
    }
  }
}

/// Generates lint feedback for a single Dart library.
class GenerateDartLintsTask extends AnalysisTask {
  ///The compilation units that comprise the library, with the defining
  ///compilation unit appearing first in the list.
  final List<TimestampedData<CompilationUnit>> _units;

  /// The element model for the library being analyzed.
  final LibraryElement libraryElement;

  /// A mapping of analyzed sources to their associated lint warnings.
  /// May be [null] if the task has not been performed or if analysis did not
  /// complete normally.
  HashMap<Source, List<AnalysisError>> lintMap;

  /// Initialize a newly created task to perform lint checking over these
  /// [_units] belonging to this [libraryElement] within the given [context].
  GenerateDartLintsTask(context, this._units, this.libraryElement)
      : super(context);

  @override
  String get taskDescription {
    Source librarySource = libraryElement.source;
    return (librarySource == null)
        ? "generate Dart lints for library without source"
        : "generate Dart lints for ${librarySource.fullName}";
  }

  @override
  accept(AnalysisTaskVisitor visitor) =>
      visitor.visitGenerateDartLintsTask(this);

  @override
  void internalPerform() {
    Iterable<CompilationUnit> compilationUnits =
        _units.map((TimestampedData<CompilationUnit> unit) => unit.data);
    RecordingErrorListener errorListener = new RecordingErrorListener();
    LintGenerator lintGenerator =
        new LintGenerator(compilationUnits, errorListener);
    lintGenerator.generate();

    lintMap = new HashMap<Source, List<AnalysisError>>();
    compilationUnits.forEach((CompilationUnit unit) {
      Source source = unit.element.source;
      lintMap[source] = errorListener.getErrorsForSource(source);
    });
  }
}

/**
 * Instances of the class `GetContentTask` get the contents of a source.
 */
class GetContentTask extends AnalysisTask {
  /**
   * The source to be read.
   */
  final Source source;

  /**
   * A flag indicating whether this task is complete.
   */
  bool _complete = false;

  /**
   * The contents of the source.
   */
  String _content;

  /**
   * The errors that were produced by getting the source content.
   */
  final List<AnalysisError> errors = <AnalysisError>[];

  /**
   * The time at which the contents of the source were last modified.
   */
  int _modificationTime = -1;

  /**
   * Initialize a newly created task to perform analysis within the given context.
   *
   * @param context the context in which the task is to be performed
   * @param source the source to be parsed
   * @param contentData the time-stamped contents of the source
   */
  GetContentTask(InternalAnalysisContext context, this.source)
      : super(context) {
    if (source == null) {
      throw new IllegalArgumentException("Cannot get contents of null source");
    }
  }

  /**
   * Return the contents of the source, or `null` if the task has not completed or if there
   * was an exception while getting the contents.
   *
   * @return the contents of the source
   */
  String get content => _content;

  /**
   * Return `true` if this task is complete. Unlike most tasks, this task is allowed to be
   * visited more than once in order to support asynchronous IO. If the task is not complete when it
   * is visited synchronously as part of the [AnalysisTask.perform]
   * method, it will be visited again, using the same visitor, when the IO operation has been
   * performed.
   *
   * @return `true` if this task is complete
   */
  bool get isComplete => _complete;

  /**
   * Return the time at which the contents of the source that was parsed were last modified, or a
   * negative value if the task has not yet been performed or if an exception occurred.
   *
   * @return the time at which the contents of the source that was parsed were last modified
   */
  int get modificationTime => _modificationTime;

  @override
  String get taskDescription => "get contents of ${source.fullName}";

  @override
  accept(AnalysisTaskVisitor visitor) => visitor.visitGetContentTask(this);

  @override
  void internalPerform() {
    _complete = true;
    try {
      TimestampedData<String> data = context.getContents(source);
      _content = data.data;
      _modificationTime = data.modificationTime;
      AnalysisEngine.instance.instrumentationService
          .logFileRead(source.fullName, _modificationTime, _content);
    } catch (exception, stackTrace) {
      if (source.exists()) {
        errors.add(new AnalysisError(
            source, 0, 0, ScannerErrorCode.UNABLE_GET_CONTENT, [exception]));
      }
      throw new AnalysisException("Could not get contents of $source",
          new CaughtException(exception, stackTrace));
    }
  }
}

/**
 * The information cached by an analysis context about an individual HTML file.
 */
class HtmlEntry extends SourceEntry {
  /**
   * The data descriptor representing the HTML element.
   */
  static final DataDescriptor<HtmlElement> ELEMENT =
      new DataDescriptor<HtmlElement>("HtmlEntry.ELEMENT");

  /**
   * The data descriptor representing the hints resulting from auditing the
   * source.
   */
  static final DataDescriptor<List<AnalysisError>> HINTS =
      new DataDescriptor<List<AnalysisError>>(
          "HtmlEntry.HINTS", AnalysisError.NO_ERRORS);

  /**
   * The data descriptor representing the errors resulting from parsing the
   * source.
   */
  static final DataDescriptor<List<AnalysisError>> PARSE_ERRORS =
      new DataDescriptor<List<AnalysisError>>(
          "HtmlEntry.PARSE_ERRORS", AnalysisError.NO_ERRORS);

  /**
   * The data descriptor representing the parsed AST structure.
   */
  static final DataDescriptor<ht.HtmlUnit> PARSED_UNIT =
      new DataDescriptor<ht.HtmlUnit>("HtmlEntry.PARSED_UNIT");

  /**
   * The data descriptor representing the resolved AST structure.
   */
  static final DataDescriptor<ht.HtmlUnit> RESOLVED_UNIT =
      new DataDescriptor<ht.HtmlUnit>("HtmlEntry.RESOLVED_UNIT");

  /**
   * The data descriptor representing the list of referenced libraries.
   */
  static final DataDescriptor<List<Source>> REFERENCED_LIBRARIES =
      new DataDescriptor<List<Source>>(
          "HtmlEntry.REFERENCED_LIBRARIES", Source.EMPTY_LIST);

  /**
   * The data descriptor representing the errors resulting from resolving the
   * source.
   */
  static final DataDescriptor<List<AnalysisError>> RESOLUTION_ERRORS =
      new DataDescriptor<List<AnalysisError>>(
          "HtmlEntry.RESOLUTION_ERRORS", AnalysisError.NO_ERRORS);

  /**
   * Return all of the errors associated with the HTML file that are currently
   * cached.
   */
  List<AnalysisError> get allErrors {
    List<AnalysisError> errors = new List<AnalysisError>();
    errors.addAll(super.allErrors);
    errors.addAll(getValue(PARSE_ERRORS));
    errors.addAll(getValue(RESOLUTION_ERRORS));
    errors.addAll(getValue(HINTS));
    if (errors.length == 0) {
      return AnalysisError.NO_ERRORS;
    }
    return errors;
  }

  /**
   * Return a valid parsed unit, either an unresolved AST structure or the
   * result of resolving the AST structure, or `null` if there is no parsed unit
   * available.
   */
  ht.HtmlUnit get anyParsedUnit {
    if (getState(PARSED_UNIT) == CacheState.VALID) {
      return getValue(PARSED_UNIT);
    }
    if (getState(RESOLVED_UNIT) == CacheState.VALID) {
      return getValue(RESOLVED_UNIT);
    }
    return null;
  }

  @override
  List<DataDescriptor> get descriptors {
    List<DataDescriptor> result = super.descriptors;
    result.addAll([
      HtmlEntry.ELEMENT,
      HtmlEntry.PARSE_ERRORS,
      HtmlEntry.PARSED_UNIT,
      HtmlEntry.RESOLUTION_ERRORS,
      HtmlEntry.RESOLVED_UNIT,
      HtmlEntry.HINTS
    ]);
    return result;
  }

  @override
  SourceKind get kind => SourceKind.HTML;

  /**
   * Flush any AST structures being maintained by this entry.
   */
  void flushAstStructures() {
    _flush(PARSED_UNIT);
    _flush(RESOLVED_UNIT);
  }

  @override
  void invalidateAllInformation() {
    super.invalidateAllInformation();
    setState(PARSE_ERRORS, CacheState.INVALID);
    setState(PARSED_UNIT, CacheState.INVALID);
    setState(RESOLVED_UNIT, CacheState.INVALID);
    invalidateAllResolutionInformation(true);
  }

  /**
   * Invalidate all of the resolution information associated with the HTML file.
   * If [invalidateUris] is `true`, the cached results of converting URIs to
   * source files should also be invalidated.
   */
  void invalidateAllResolutionInformation(bool invalidateUris) {
    setState(RESOLVED_UNIT, CacheState.INVALID);
    setState(ELEMENT, CacheState.INVALID);
    setState(RESOLUTION_ERRORS, CacheState.INVALID);
    setState(HINTS, CacheState.INVALID);
    if (invalidateUris) {
      setState(REFERENCED_LIBRARIES, CacheState.INVALID);
    }
  }

  /**
   * Invalidate all of the parse and resolution information associated with
   * this source.
   */
  void invalidateParseInformation() {
    setState(PARSE_ERRORS, CacheState.INVALID);
    setState(PARSED_UNIT, CacheState.INVALID);
    invalidateAllResolutionInformation(true);
  }

  @override
  void recordContentError(CaughtException exception) {
    super.recordContentError(exception);
    recordParseError(exception);
  }

  /**
   * Record that an [exception] was encountered while attempting to parse the
   * source associated with this entry.
   */
  void recordParseError(CaughtException exception) {
    // If the scanning and parsing of HTML are separated,
    // the following line can be removed.
    recordScanError(exception);
    setState(PARSE_ERRORS, CacheState.ERROR);
    setState(PARSED_UNIT, CacheState.ERROR);
    setState(REFERENCED_LIBRARIES, CacheState.ERROR);
    recordResolutionError(exception);
  }

  /**
   * Record that an [exception] was encountered while attempting to resolve the
   * source associated with this entry.
   */
  void recordResolutionError(CaughtException exception) {
    this.exception = exception;
    setState(RESOLVED_UNIT, CacheState.ERROR);
    setState(ELEMENT, CacheState.ERROR);
    setState(RESOLUTION_ERRORS, CacheState.ERROR);
    setState(HINTS, CacheState.ERROR);
  }

  @override
  bool _isValidDescriptor(DataDescriptor descriptor) {
    return descriptor == ELEMENT ||
        descriptor == HINTS ||
        descriptor == PARSED_UNIT ||
        descriptor == PARSE_ERRORS ||
        descriptor == REFERENCED_LIBRARIES ||
        descriptor == RESOLUTION_ERRORS ||
        descriptor == RESOLVED_UNIT ||
        super._isValidDescriptor(descriptor);
  }

  @override
  bool _writeDiffOn(StringBuffer buffer, SourceEntry oldEntry) {
    bool needsSeparator = super._writeDiffOn(buffer, oldEntry);
    if (oldEntry is! HtmlEntry) {
      if (needsSeparator) {
        buffer.write("; ");
      }
      buffer.write("entry type changed; was ");
      buffer.write(oldEntry.runtimeType);
      return true;
    }
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "parseErrors",
        HtmlEntry.PARSE_ERRORS, oldEntry);
    needsSeparator = _writeStateDiffOn(
        buffer, needsSeparator, "parsedUnit", HtmlEntry.PARSED_UNIT, oldEntry);
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "resolvedUnit",
        HtmlEntry.RESOLVED_UNIT, oldEntry);
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
        "resolutionErrors", HtmlEntry.RESOLUTION_ERRORS, oldEntry);
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
        "referencedLibraries", HtmlEntry.REFERENCED_LIBRARIES, oldEntry);
    needsSeparator = _writeStateDiffOn(
        buffer, needsSeparator, "element", HtmlEntry.ELEMENT, oldEntry);
    return needsSeparator;
  }

  @override
  void _writeOn(StringBuffer buffer) {
    buffer.write("Html: ");
    super._writeOn(buffer);
    _writeStateOn(buffer, "parseErrors", PARSE_ERRORS);
    _writeStateOn(buffer, "parsedUnit", PARSED_UNIT);
    _writeStateOn(buffer, "resolvedUnit", RESOLVED_UNIT);
    _writeStateOn(buffer, "resolutionErrors", RESOLUTION_ERRORS);
    _writeStateOn(buffer, "referencedLibraries", REFERENCED_LIBRARIES);
    _writeStateOn(buffer, "element", ELEMENT);
  }
}

/**
 * An event indicating when a source either starts or stops being implicitly
 * analyzed.
 */
class ImplicitAnalysisEvent {
  /**
   * The source whose status has changed.
   */
  final Source source;

  /**
   * A flag indicating whether the source is now being analyzed.
   */
  final bool isAnalyzed;

  /**
   * Initialize a newly created event to indicate that the given [source] has
   * changed it status to match the [isAnalyzed] flag.
   */
  ImplicitAnalysisEvent(this.source, this.isAnalyzed);

  @override
  String toString() =>
      '${isAnalyzed ? '' : 'not '}analyzing ${source.fullName}';
}

/**
 * Instances of the class `IncrementalAnalysisCache` hold information used to perform
 * incremental analysis.
 *
 * See [AnalysisContextImpl.setChangedContents].
 */
class IncrementalAnalysisCache {
  final Source librarySource;

  final Source source;

  final String oldContents;

  final CompilationUnit resolvedUnit;

  String _newContents;

  int _offset = 0;

  int _oldLength = 0;

  int _newLength = 0;

  IncrementalAnalysisCache(
      this.librarySource,
      this.source,
      this.resolvedUnit,
      this.oldContents,
      this._newContents,
      this._offset,
      this._oldLength,
      this._newLength);

  /**
   * Determine if the cache contains source changes that need to be analyzed
   *
   * @return `true` if the cache contains changes to be analyzed, else `false`
   */
  bool get hasWork => _oldLength > 0 || _newLength > 0;

  /**
   * Return the current contents for the receiver's source.
   *
   * @return the contents (not `null`)
   */
  String get newContents => _newContents;

  /**
   * Return the number of characters in the replacement text.
   *
   * @return the replacement length (zero or greater)
   */
  int get newLength => _newLength;

  /**
   * Return the character position of the first changed character.
   *
   * @return the offset (zero or greater)
   */
  int get offset => _offset;

  /**
   * Return the number of characters that were replaced.
   *
   * @return the replaced length (zero or greater)
   */
  int get oldLength => _oldLength;

  /**
   * Determine if the incremental analysis result can be cached for the next incremental analysis.
   *
   * @param cache the prior incremental analysis cache
   * @param unit the incrementally updated compilation unit
   * @return the cache used for incremental analysis or `null` if incremental analysis results
   *         cannot be cached for the next incremental analysis
   */
  static IncrementalAnalysisCache cacheResult(
      IncrementalAnalysisCache cache, CompilationUnit unit) {
    if (cache != null && unit != null) {
      return new IncrementalAnalysisCache(cache.librarySource, cache.source,
          unit, cache._newContents, cache._newContents, 0, 0, 0);
    }
    return null;
  }

  /**
   * Determine if the cache should be cleared.
   *
   * @param cache the prior cache or `null` if none
   * @param source the source being updated (not `null`)
   * @return the cache used for incremental analysis or `null` if incremental analysis cannot
   *         be performed
   */
  static IncrementalAnalysisCache clear(
      IncrementalAnalysisCache cache, Source source) {
    if (cache == null || cache.source == source) {
      return null;
    }
    return cache;
  }

  /**
   * Determine if incremental analysis can be performed from the given information.
   *
   * @param cache the prior cache or `null` if none
   * @param source the source being updated (not `null`)
   * @param oldContents the original source contents prior to this update (may be `null`)
   * @param newContents the new contents after this incremental change (not `null`)
   * @param offset the offset at which the change occurred
   * @param oldLength the length of the text being replaced
   * @param newLength the length of the replacement text
   * @param sourceEntry the cached entry for the given source or `null` if none
   * @return the cache used for incremental analysis or `null` if incremental analysis cannot
   *         be performed
   */
  static IncrementalAnalysisCache update(
      IncrementalAnalysisCache cache,
      Source source,
      String oldContents,
      String newContents,
      int offset,
      int oldLength,
      int newLength,
      SourceEntry sourceEntry) {
    // Determine the cache resolved unit
    Source librarySource = null;
    CompilationUnit unit = null;
    if (sourceEntry is DartEntry) {
      DartEntry dartEntry = sourceEntry;
      List<Source> librarySources = dartEntry.librariesContaining;
      if (librarySources.length == 1) {
        librarySource = librarySources[0];
        if (librarySource != null) {
          unit = dartEntry.getValueInLibrary(
              DartEntry.RESOLVED_UNIT, librarySource);
        }
      }
    }
    // Create a new cache if there is not an existing cache or the source is
    // different or a new resolved compilation unit is available.
    if (cache == null || cache.source != source || unit != null) {
      if (unit == null) {
        return null;
      }
      if (oldContents == null) {
        if (oldLength != 0) {
          return null;
        }
        oldContents =
            "${newContents.substring(0, offset)}${newContents.substring(offset + newLength)}";
      }
      return new IncrementalAnalysisCache(librarySource, source, unit,
          oldContents, newContents, offset, oldLength, newLength);
    }
    // Update the existing cache if the change is contiguous
    if (cache._oldLength == 0 && cache._newLength == 0) {
      cache._offset = offset;
      cache._oldLength = oldLength;
      cache._newLength = newLength;
    } else {
      if (cache._offset > offset || offset > cache._offset + cache._newLength) {
        return null;
      }
      cache._newLength += newLength - oldLength;
    }
    cache._newContents = newContents;
    return cache;
  }

  /**
   * Verify that the incrementally parsed and resolved unit in the incremental cache is structurally
   * equivalent to the fully parsed unit.
   *
   * @param cache the prior cache or `null` if none
   * @param source the source of the compilation unit that was parsed (not `null`)
   * @param unit the compilation unit that was just parsed
   * @return the cache used for incremental analysis or `null` if incremental analysis results
   *         cannot be cached for the next incremental analysis
   */
  static IncrementalAnalysisCache verifyStructure(
      IncrementalAnalysisCache cache, Source source, CompilationUnit unit) {
    if (cache != null && unit != null && cache.source == source) {
      if (!AstComparator.equalNodes(cache.resolvedUnit, unit)) {
        return null;
      }
    }
    return cache;
  }
}

/**
 * Instances of the class `IncrementalAnalysisTask` incrementally update existing analysis.
 */
class IncrementalAnalysisTask extends AnalysisTask {
  /**
   * The information used to perform incremental analysis.
   */
  final IncrementalAnalysisCache cache;

  /**
   * The compilation unit that was produced by incrementally updating the existing unit.
   */
  CompilationUnit _updatedUnit;

  /**
   * Initialize a newly created task to perform analysis within the given context.
   *
   * @param context the context in which the task is to be performed
   * @param cache the incremental analysis cache used to perform the analysis
   */
  IncrementalAnalysisTask(InternalAnalysisContext context, this.cache)
      : super(context);

  /**
   * Return the compilation unit that was produced by incrementally updating the existing
   * compilation unit, or `null` if the task has not yet been performed, could not be
   * performed, or if an exception occurred.
   *
   * @return the compilation unit
   */
  CompilationUnit get compilationUnit => _updatedUnit;

  /**
   * Return the source that is to be incrementally analyzed.
   *
   * @return the source
   */
  Source get source => cache != null ? cache.source : null;

  @override
  String get taskDescription =>
      "incremental analysis ${cache != null ? cache.source : "null"}";

  /**
   * Return the type provider used for incremental resolution.
   *
   * @return the type provider (or `null` if an exception occurs)
   */
  TypeProvider get typeProvider {
    try {
      return context.typeProvider;
    } on AnalysisException {
      return null;
    }
  }

  @override
  accept(AnalysisTaskVisitor visitor) =>
      visitor.visitIncrementalAnalysisTask(this);

  @override
  void internalPerform() {
    if (cache == null) {
      return;
    }
    // Only handle small changes
    if (cache.oldLength > 0 || cache.newLength > 30) {
      return;
    }
    // Produce an updated token stream
    CharacterReader reader = new CharSequenceReader(cache.newContents);
    BooleanErrorListener errorListener = new BooleanErrorListener();
    IncrementalScanner scanner = new IncrementalScanner(
        cache.source, reader, errorListener, context.analysisOptions);
    scanner.rescan(cache.resolvedUnit.beginToken, cache.offset, cache.oldLength,
        cache.newLength);
    if (errorListener.errorReported) {
      return;
    }
    // Produce an updated AST
    IncrementalParser parser = new IncrementalParser(
        cache.source, scanner.tokenMap, AnalysisErrorListener.NULL_LISTENER);
    _updatedUnit = parser.reparse(cache.resolvedUnit, scanner.leftToken,
        scanner.rightToken, cache.offset, cache.offset + cache.oldLength);
    // Update the resolution
    TypeProvider typeProvider = this.typeProvider;
    if (_updatedUnit != null && typeProvider != null) {
      CompilationUnitElement element = _updatedUnit.element;
      if (element != null) {
        LibraryElement library = element.library;
        if (library != null) {
          IncrementalResolver resolver = new IncrementalResolver(null, null,
              null, element, cache.offset, cache.oldLength, cache.newLength);
          resolver.resolve(parser.updatedNode);
        }
      }
    }
  }
}

/**
 * Additional behavior for an analysis context that is required by internal
 * users of the context.
 */
abstract class InternalAnalysisContext implements AnalysisContext {
  /**
   * A table mapping the sources known to the context to the information known
   * about the source.
   *
   * TODO(scheglov) add the type, once we have only one cache.
   */
  dynamic get analysisCache;

  /**
   * Allow the client to supply its own content cache.  This will take the
   * place of the content cache created by default, allowing clients to share
   * the content cache between contexts.
   */
  set contentCache(ContentCache value);

  /// Get the [EmbedderYamlLocator] for this context.
  EmbedderYamlLocator get embedderYamlLocator;

  /**
   * Return a list of the explicit targets being analyzed by this context.
   */
  List<AnalysisTarget> get explicitTargets;

  /**
   * A factory to override how [LibraryResolver] is created.
   */
  LibraryResolverFactory get libraryResolverFactory;

  /**
   * Return a list containing all of the sources that have been marked as
   * priority sources. Clients must not modify the returned list.
   */
  List<Source> get prioritySources;

  /**
   * Return a list of the priority targets being analyzed by this context.
   */
  List<AnalysisTarget> get priorityTargets;

  /**
   * The partition that contains analysis results that are not shared with other
   * contexts.
   *
   * TODO(scheglov) add the type, once we have only one cache.
   */
  dynamic get privateAnalysisCachePartition;

  /**
   * A factory to override how [ResolverVisitor] is created.
   */
  ResolverVisitorFactory get resolverVisitorFactory;

  /**
   * Returns a statistics about this context.
   */
  AnalysisContextStatistics get statistics;

  /**
   * Sets the [TypeProvider] for this context.
   */
  void set typeProvider(TypeProvider typeProvider);

  /**
   * A factory to override how [TypeResolverVisitor] is created.
   */
  TypeResolverVisitorFactory get typeResolverVisitorFactory;

  /**
   * A list of all [WorkManager]s used by this context.
   */
  List<newContext.WorkManager> get workManagers;

  /**
   * Return a list containing the sources of the libraries that are exported by
   * the library with the given [source]. The list will be empty if the given
   * source is invalid, if the given source does not represent a library, or if
   * the library does not export any other libraries.
   *
   * Throws an [AnalysisException] if the exported libraries could not be
   * computed.
   */
  List<Source> computeExportedLibraries(Source source);

  /**
   * Return a list containing the sources of the libraries that are imported by
   * the library with the given [source]. The list will be empty if the given
   * source is invalid, if the given source does not represent a library, or if
   * the library does not import any other libraries.
   *
   * Throws an [AnalysisException] if the imported libraries could not be
   * computed.
   */
  List<Source> computeImportedLibraries(Source source);

  /**
   * Return an AST structure corresponding to the given [source], but ensure
   * that the structure has not already been resolved and will not be resolved
   * by any other threads or in any other library.
   *
   * Throws an [AnalysisException] if the analysis could not be performed.
   *
   * <b>Note:</b> This method cannot be used in an async environment
   */
  CompilationUnit computeResolvableCompilationUnit(Source source);

  /**
   * Return all the resolved [CompilationUnit]s for the given [source] if not
   * flushed, otherwise return `null` and ensures that the [CompilationUnit]s
   * will be eventually returned to the client from [performAnalysisTask].
   */
  List<CompilationUnit> ensureResolvedDartUnits(Source source);

  /**
   * Return the cache entry associated with the given [target].
   */
  cache.CacheEntry getCacheEntry(AnalysisTarget target);

  /**
   * Return context that owns the given [source].
   */
  InternalAnalysisContext getContextFor(Source source);

  /**
   * Return a change notice for the given [source], creating one if one does not
   * already exist.
   */
  ChangeNoticeImpl getNotice(Source source);

  /**
   * Return a namespace containing mappings for all of the public names defined
   * by the given [library].
   */
  Namespace getPublicNamespace(LibraryElement library);

  /**
   * Respond to a change which has been made to the given [source] file.
   * [originalContents] is the former contents of the file, and [newContents]
   * is the updated contents.  If [notify] is true, a source changed event is
   * triggered.
   *
   * Normally it should not be necessary for clients to call this function,
   * since it will be automatically invoked in response to a call to
   * [applyChanges] or [setContents].  However, if this analysis context is
   * sharing its content cache with other contexts, then the client must
   * manually update the content cache and call this function for each context.
   *
   * Return `true` if the change was significant to this context (i.e. [source]
   * is either implicitly or explicitly analyzed by this context, and a change
   * actually occurred).
   */
  bool handleContentsChanged(
      Source source, String originalContents, String newContents, bool notify);

  /**
   * Given an [elementMap] mapping the source for the libraries represented by
   * the corresponding elements to the elements representing the libraries,
   * record those mappings.
   */
  void recordLibraryElements(Map<Source, LibraryElement> elementMap);

  /**
   * Return `true` if errors should be produced for the given [source].
   * The [entry] associated with the source is passed in for efficiency.
   *
   * TODO(scheglov) remove [entry] after migration to the new task model.
   * It is not used there anyway.
   */
  bool shouldErrorsBeAnalyzed(Source source, Object entry);

  /**
   * For testing only: flush all representations of the AST (both resolved and
   * unresolved) for the given [source] out of the cache.
   */
  void test_flushAstStructures(Source source);

  /**
   * Call the given callback function for eache cache item in the context.
   */
  @deprecated
  void visitCacheItems(void callback(Source source, SourceEntry dartEntry,
      DataDescriptor rowDesc, CacheState state));

  /**
   * Visit all entries of the content cache.
   */
  void visitContentCache(ContentCacheVisitor visitor);
}

/**
 * An object that can be used to receive information about errors within the
 * analysis engine. Implementations usually write this information to a file,
 * but can also record the information for later use (such as during testing) or
 * even ignore the information.
 */
abstract class Logger {
  /**
   * A logger that ignores all logging.
   */
  static final Logger NULL = new NullLogger();

  /**
   * Log the given message as an error. The [message] is expected to be an
   * explanation of why the error occurred or what it means. The [exception] is
   * expected to be the reason for the error. At least one argument must be
   * provided.
   */
  void logError(String message, [CaughtException exception]);

  /**
   * Log the given [exception] as one representing an error. The [message] is an
   * explanation of why the error occurred or what it means.
   */
  @deprecated // Use logError(message, exception)
  void logError2(String message, Object exception);

  /**
   * Log the given informational message. The [message] is expected to be an
   * explanation of why the error occurred or what it means. The [exception] is
   * expected to be the reason for the error.
   */
  void logInformation(String message, [CaughtException exception]);

  /**
   * Log the given [exception] as one representing an informational message. The
   * [message] is an explanation of why the error occurred or what it means.
   */
  @deprecated // Use logInformation(message, exception)
  void logInformation2(String message, Object exception);
}

/**
 * An implementation of [Logger] that does nothing.
 */
class NullLogger implements Logger {
  @override
  void logError(String message, [CaughtException exception]) {}

  @override
  void logError2(String message, Object exception) {}

  @override
  void logInformation(String message, [CaughtException exception]) {}

  @override
  void logInformation2(String message, Object exception) {}
}

/**
 * An exception created when an analysis attempt fails because a source was
 * deleted between the time the analysis started and the time the results of the
 * analysis were ready to be recorded.
 */
class ObsoleteSourceAnalysisException extends AnalysisException {
  /**
   * The source that was removed while it was being analyzed.
   */
  Source _source;

  /**
   * Initialize a newly created exception to represent the removal of the given
   * [source].
   */
  ObsoleteSourceAnalysisException(Source source)
      : super(
            "The source '${source.fullName}' was removed while it was being analyzed") {
    this._source = source;
  }

  /**
   * Return the source that was removed while it was being analyzed.
   */
  Source get source => _source;
}

/**
 * Instances of the class `ParseDartTask` parse a specific source as a Dart file.
 */
class ParseDartTask extends AnalysisTask {
  /**
   * The source to be parsed.
   */
  final Source source;

  /**
   * The head of the token stream used for parsing.
   */
  final Token _tokenStream;

  /**
   * The line information associated with the source.
   */
  final LineInfo lineInfo;

  /**
   * The compilation unit that was produced by parsing the source.
   */
  CompilationUnit _unit;

  /**
   * A flag indicating whether the source contains a 'part of' directive.
   */
  bool _containsPartOfDirective = false;

  /**
   * A flag indicating whether the source contains any directive other than a 'part of' directive.
   */
  bool _containsNonPartOfDirective = false;

  /**
   * A set containing the sources referenced by 'export' directives.
   */
  HashSet<Source> _exportedSources = new HashSet<Source>();

  /**
   * A set containing the sources referenced by 'import' directives.
   */
  HashSet<Source> _importedSources = new HashSet<Source>();

  /**
   * A set containing the sources referenced by 'part' directives.
   */
  HashSet<Source> _includedSources = new HashSet<Source>();

  /**
   * The errors that were produced by scanning and parsing the source.
   */
  List<AnalysisError> _errors = AnalysisError.NO_ERRORS;

  /**
   * Initialize a newly created task to perform analysis within the given context.
   *
   * @param context the context in which the task is to be performed
   * @param source the source to be parsed
   * @param tokenStream the head of the token stream used for parsing
   * @param lineInfo the line information associated with the source
   */
  ParseDartTask(InternalAnalysisContext context, this.source, this._tokenStream,
      this.lineInfo)
      : super(context);

  /**
   * Return the compilation unit that was produced by parsing the source, or `null` if the
   * task has not yet been performed or if an exception occurred.
   *
   * @return the compilation unit that was produced by parsing the source
   */
  CompilationUnit get compilationUnit => _unit;

  /**
   * Return the errors that were produced by scanning and parsing the source, or an empty list if
   * the task has not yet been performed or if an exception occurred.
   *
   * @return the errors that were produced by scanning and parsing the source
   */
  List<AnalysisError> get errors => _errors;

  /**
   * Return a list containing the sources referenced by 'export' directives, or an empty list if
   * the task has not yet been performed or if an exception occurred.
   *
   * @return an list containing the sources referenced by 'export' directives
   */
  List<Source> get exportedSources => _toArray(_exportedSources);

  /**
   * Return `true` if the source contains any directive other than a 'part of' directive, or
   * `false` if the task has not yet been performed or if an exception occurred.
   *
   * @return `true` if the source contains any directive other than a 'part of' directive
   */
  bool get hasNonPartOfDirective => _containsNonPartOfDirective;

  /**
   * Return `true` if the source contains a 'part of' directive, or `false` if the task
   * has not yet been performed or if an exception occurred.
   *
   * @return `true` if the source contains a 'part of' directive
   */
  bool get hasPartOfDirective => _containsPartOfDirective;

  /**
   * Return a list containing the sources referenced by 'import' directives, or an empty list if
   * the task has not yet been performed or if an exception occurred.
   *
   * @return a list containing the sources referenced by 'import' directives
   */
  List<Source> get importedSources => _toArray(_importedSources);

  /**
   * Return a list containing the sources referenced by 'part' directives, or an empty list if
   * the task has not yet been performed or if an exception occurred.
   *
   * @return a list containing the sources referenced by 'part' directives
   */
  List<Source> get includedSources => _toArray(_includedSources);

  @override
  String get taskDescription {
    if (source == null) {
      return "parse as dart null source";
    }
    return "parse as dart ${source.fullName}";
  }

  @override
  accept(AnalysisTaskVisitor visitor) => visitor.visitParseDartTask(this);

  @override
  void internalPerform() {
    //
    // Then parse the token stream.
    //
    PerformanceStatistics.parse.makeCurrentWhile(() {
      RecordingErrorListener errorListener = new RecordingErrorListener();
      Parser parser = new Parser(source, errorListener);
      AnalysisOptions options = context.analysisOptions;
      parser.parseFunctionBodies =
          options.analyzeFunctionBodiesPredicate(source);
      parser.parseGenericMethods = options.enableGenericMethods;
      _unit = parser.parseCompilationUnit(_tokenStream);
      _unit.lineInfo = lineInfo;
      AnalysisContext analysisContext = context;
      for (Directive directive in _unit.directives) {
        if (directive is PartOfDirective) {
          _containsPartOfDirective = true;
        } else {
          _containsNonPartOfDirective = true;
          if (directive is UriBasedDirective) {
            Source referencedSource = resolveDirective(
                analysisContext, source, directive, errorListener);
            if (referencedSource != null) {
              if (directive is ExportDirective) {
                _exportedSources.add(referencedSource);
              } else if (directive is ImportDirective) {
                _importedSources.add(referencedSource);
              } else if (directive is PartDirective) {
                if (referencedSource != source) {
                  _includedSources.add(referencedSource);
                }
              } else {
                throw new AnalysisException(
                    "$runtimeType failed to handle a ${directive.runtimeType}");
              }
            }
          }
        }
      }
      _errors = errorListener.getErrorsForSource(source);
    });
  }

  /**
   * Efficiently convert the given set of [sources] to a list.
   */
  List<Source> _toArray(HashSet<Source> sources) {
    int size = sources.length;
    if (size == 0) {
      return Source.EMPTY_LIST;
    }
    return new List.from(sources);
  }

  /**
   * Return the result of resolving the URI of the given URI-based directive against the URI of the
   * given library, or `null` if the URI is not valid.
   *
   * @param context the context in which the resolution is to be performed
   * @param librarySource the source representing the library containing the directive
   * @param directive the directive which URI should be resolved
   * @param errorListener the error listener to which errors should be reported
   * @return the result of resolving the URI against the URI of the library
   */
  static Source resolveDirective(AnalysisContext context, Source librarySource,
      UriBasedDirective directive, AnalysisErrorListener errorListener) {
    StringLiteral uriLiteral = directive.uri;
    String uriContent = uriLiteral.stringValue;
    if (uriContent != null) {
      uriContent = uriContent.trim();
      directive.uriContent = uriContent;
    }
    UriValidationCode code = directive.validate();
    if (code == null) {
      String encodedUriContent = Uri.encodeFull(uriContent);
      try {
        Source source =
            context.sourceFactory.resolveUri(librarySource, encodedUriContent);
        directive.source = source;
        return source;
      } on JavaIOException {
        code = UriValidationCode.INVALID_URI;
      }
    }
    if (code == UriValidationCode.URI_WITH_DART_EXT_SCHEME) {
      return null;
    }
    if (code == UriValidationCode.URI_WITH_INTERPOLATION) {
      errorListener.onError(new AnalysisError(librarySource, uriLiteral.offset,
          uriLiteral.length, CompileTimeErrorCode.URI_WITH_INTERPOLATION));
      return null;
    }
    if (code == UriValidationCode.INVALID_URI) {
      errorListener.onError(new AnalysisError(librarySource, uriLiteral.offset,
          uriLiteral.length, CompileTimeErrorCode.INVALID_URI, [uriContent]));
      return null;
    }
    throw new RuntimeException(
        message: "Failed to handle validation code: $code");
  }
}

/**
 * Instances of the class `ParseHtmlTask` parse a specific source as an HTML file.
 */
class ParseHtmlTask extends AnalysisTask {
  /**
   * The name of the 'src' attribute in a HTML tag.
   */
  static String _ATTRIBUTE_SRC = "src";

  /**
   * The name of the 'script' tag in an HTML file.
   */
  static String _TAG_SCRIPT = "script";

  /**
   * The source to be parsed.
   */
  final Source source;

  /**
   * The contents of the source.
   */
  final String _content;

  /**
   * The line information that was produced.
   */
  LineInfo _lineInfo;

  /**
   * The HTML unit that was produced by parsing the source.
   */
  ht.HtmlUnit _unit;

  /**
   * The errors that were produced by scanning and parsing the source.
   */
  List<AnalysisError> _errors = AnalysisError.NO_ERRORS;

  /**
   * A list containing the sources of the libraries that are referenced within the HTML.
   */
  List<Source> _referencedLibraries = Source.EMPTY_LIST;

  /**
   * Initialize a newly created task to perform analysis within the given context.
   *
   * @param context the context in which the task is to be performed
   * @param source the source to be parsed
   * @param content the contents of the source
   */
  ParseHtmlTask(InternalAnalysisContext context, this.source, this._content)
      : super(context);

  /**
   * Return the errors that were produced by scanning and parsing the source, or `null` if the
   * task has not yet been performed or if an exception occurred.
   *
   * @return the errors that were produced by scanning and parsing the source
   */
  List<AnalysisError> get errors => _errors;

  /**
   * Return the HTML unit that was produced by parsing the source.
   *
   * @return the HTML unit that was produced by parsing the source
   */
  ht.HtmlUnit get htmlUnit => _unit;

  /**
   * Return the sources of libraries that are referenced in the specified HTML file.
   *
   * @return the sources of libraries that are referenced in the HTML file
   */
  List<Source> get librarySources {
    List<Source> libraries = new List<Source>();
    _unit.accept(new ParseHtmlTask_getLibrarySources(this, libraries));
    if (libraries.isEmpty) {
      return Source.EMPTY_LIST;
    }
    return libraries;
  }

  /**
   * Return the line information that was produced, or `null` if the task has not yet been
   * performed or if an exception occurred.
   *
   * @return the line information that was produced
   */
  LineInfo get lineInfo => _lineInfo;

  /**
   * Return a list containing the sources of the libraries that are referenced within the HTML.
   *
   * @return the sources of the libraries that are referenced within the HTML
   */
  List<Source> get referencedLibraries => _referencedLibraries;

  @override
  String get taskDescription {
    if (source == null) {
      return "parse as html null source";
    }
    return "parse as html ${source.fullName}";
  }

  @override
  accept(AnalysisTaskVisitor visitor) => visitor.visitParseHtmlTask(this);

  @override
  void internalPerform() {
    try {
      ht.AbstractScanner scanner = new ht.StringScanner(source, _content);
      scanner.passThroughElements = <String>[_TAG_SCRIPT];
      ht.Token token = scanner.tokenize();
      _lineInfo = new LineInfo(scanner.lineStarts);
      RecordingErrorListener errorListener = new RecordingErrorListener();
      _unit = new ht.HtmlParser(source, errorListener, context.analysisOptions)
          .parse(token, _lineInfo);
      _unit.accept(new RecursiveXmlVisitor_ParseHtmlTask_internalPerform(
          this, errorListener));
      _errors = errorListener.getErrorsForSource(source);
      _referencedLibraries = librarySources;
    } catch (exception, stackTrace) {
      throw new AnalysisException(
          "Exception", new CaughtException(exception, stackTrace));
    }
  }

  /**
   * Resolves directives in the given [CompilationUnit].
   */
  void _resolveScriptDirectives(
      CompilationUnit script, AnalysisErrorListener errorListener) {
    if (script == null) {
      return;
    }
    AnalysisContext analysisContext = context;
    for (Directive directive in script.directives) {
      if (directive is UriBasedDirective) {
        ParseDartTask.resolveDirective(
            analysisContext, source, directive, errorListener);
      }
    }
  }
}

class ParseHtmlTask_getLibrarySources extends ht.RecursiveXmlVisitor<Object> {
  final ParseHtmlTask _task;

  List<Source> libraries;

  ParseHtmlTask_getLibrarySources(this._task, this.libraries) : super();

  @override
  Object visitHtmlScriptTagNode(ht.HtmlScriptTagNode node) {
    ht.XmlAttributeNode scriptAttribute = null;
    for (ht.XmlAttributeNode attribute in node.attributes) {
      if (javaStringEqualsIgnoreCase(
          attribute.name, ParseHtmlTask._ATTRIBUTE_SRC)) {
        scriptAttribute = attribute;
      }
    }
    if (scriptAttribute != null) {
      try {
        Uri uri = Uri.parse(scriptAttribute.text);
        String fileName = uri.path;
        Source librarySource =
            _task.context.sourceFactory.resolveUri(_task.source, fileName);
        if (_task.context.exists(librarySource)) {
          libraries.add(librarySource);
        }
      } on FormatException {
        // ignored - invalid URI reported during resolution phase
      }
    }
    return super.visitHtmlScriptTagNode(node);
  }
}

/**
 * An object that manages the partitions that can be shared between analysis
 * contexts.
 */
class PartitionManager {
  /**
   * The default cache size for a Dart SDK partition.
   */
  static int _DEFAULT_SDK_CACHE_SIZE = 256;

  /**
   * A table mapping SDK's to the partitions used for those SDK's.
   */
  HashMap<DartSdk, SdkCachePartition> _sdkPartitions =
      new HashMap<DartSdk, SdkCachePartition>();

  /**
   * Clear any cached data being maintained by this manager.
   */
  void clearCache() {
    _sdkPartitions.clear();
  }

  /**
   * Return the partition being used for the given [sdk], creating the partition
   * if necessary.
   */
  SdkCachePartition forSdk(DartSdk sdk) {
    // Call sdk.context now, because when it creates a new
    // InternalAnalysisContext instance, it calls forSdk() again, so creates an
    // SdkCachePartition instance.
    // So, if we initialize context after "partition == null", we end up
    // with two SdkCachePartition instances.
    InternalAnalysisContext sdkContext = sdk.context;
    // Check cache for an existing partition.
    SdkCachePartition partition = _sdkPartitions[sdk];
    if (partition == null) {
      partition = new SdkCachePartition(sdkContext, _DEFAULT_SDK_CACHE_SIZE);
      _sdkPartitions[sdk] = partition;
    }
    return partition;
  }
}

/**
 * Representation of a pending computation which is based on the results of
 * analysis that may or may not have been completed.
 */
class PendingFuture<T> {
  /**
   * The context in which this computation runs.
   */
  final AnalysisContextImpl _context;

  /**
   * The source used by this computation to compute its value.
   */
  final Source source;

  /**
   * The function which implements the computation.
   */
  final PendingFutureComputer<T> _computeValue;

  /**
   * The completer that should be completed once the computation has succeeded.
   */
  CancelableCompleter<T> _completer;

  PendingFuture(this._context, this.source, this._computeValue) {
    _completer = new CancelableCompleter<T>(_onCancel);
  }

  /**
   * Retrieve the future which will be completed when this object is
   * successfully evaluated.
   */
  CancelableFuture<T> get future => _completer.future;

  /**
   * Execute [_computeValue], passing it the given [sourceEntry], and complete
   * the pending future if it's appropriate to do so.  If the pending future is
   * completed by this call, true is returned; otherwise false is returned.
   *
   * Once this function has returned true, it should not be called again.
   *
   * Other than completing the future, this method is free of side effects.
   * Note that any code the client has attached to the future will be executed
   * in a microtask, so there is no danger of side effects occurring due to
   * client callbacks.
   */
  bool evaluate(SourceEntry sourceEntry) {
    assert(!_completer.isCompleted);
    try {
      T result = _computeValue(sourceEntry);
      if (result == null) {
        return false;
      } else {
        _completer.complete(result);
        return true;
      }
    } catch (exception, stackTrace) {
      _completer.completeError(exception, stackTrace);
      return true;
    }
  }

  /**
   * No further analysis updates are expected which affect this future, so
   * complete it with an AnalysisNotScheduledError in order to avoid
   * deadlocking the client.
   */
  void forciblyComplete() {
    try {
      throw new AnalysisNotScheduledError();
    } catch (exception, stackTrace) {
      _completer.completeError(exception, stackTrace);
    }
  }

  void _onCancel() {
    _context._cancelFuture(this);
  }
}

/**
 * Container with global [AnalysisContext] performance statistics.
 */
class PerformanceStatistics {
  /**
   * The [PerformanceTag] for time spent in reading files.
   */
  static PerformanceTag io = new PerformanceTag('io');

  /**
   * The [PerformanceTag] for time spent in scanning.
   */
  static PerformanceTag scan = new PerformanceTag('scan');

  /**
   * The [PerformanceTag] for time spent in parsing.
   */
  static PerformanceTag parse = new PerformanceTag('parse');

  /**
   * The [PerformanceTag] for time spent in resolving.
   */
  static PerformanceTag resolve = new PerformanceTag('resolve');

  /**
   * The [PerformanceTag] for time spent in error verifier.
   */
  static PerformanceTag errors = new PerformanceTag('errors');

  /**
   * The [PerformanceTag] for time spent in hints generator.
   */
  static PerformanceTag hints = new PerformanceTag('hints');

  /**
   * The [PerformanceTag] for time spent in linting.
   */
  static PerformanceTag lint = new PerformanceTag('lint');

  /**
   * The [PerformanceTag] for time spent computing cycles.
   */
  static PerformanceTag cycles = new PerformanceTag('cycles');

  /**
   * The [PerformanceTag] for time spent in other phases of analysis.
   */
  static PerformanceTag performAnaysis = new PerformanceTag('performAnaysis');

  /**
   * The [PerformanceTag] for time spent in the analysis task visitor after
   * tasks are complete.
   */
  static PerformanceTag analysisTaskVisitor =
      new PerformanceTag('analysisTaskVisitor');

  /**
   * The [PerformanceTag] for time spent in the getter
   * AnalysisContextImpl.nextAnalysisTask.
   */
  static var nextTask = new PerformanceTag('nextAnalysisTask');

  /**
   * The [PerformanceTag] for time spent during otherwise not accounted parts
   * incremental of analysis.
   */
  static PerformanceTag incrementalAnalysis =
      new PerformanceTag('incrementalAnalysis');
}

/**
 * An error listener that will record the errors that are reported to it in a
 * way that is appropriate for caching those errors within an analysis context.
 */
class RecordingErrorListener implements AnalysisErrorListener {
  /**
   * A map of sets containing the errors that were collected, keyed by each
   * source.
   */
  Map<Source, HashSet<AnalysisError>> _errors =
      new HashMap<Source, HashSet<AnalysisError>>();

  /**
   * Return the errors collected by the listener.
   */
  List<AnalysisError> get errors {
    int numEntries = _errors.length;
    if (numEntries == 0) {
      return AnalysisError.NO_ERRORS;
    }
    List<AnalysisError> resultList = new List<AnalysisError>();
    for (HashSet<AnalysisError> errors in _errors.values) {
      resultList.addAll(errors);
    }
    return resultList;
  }

  /**
   * Add all of the errors recorded by the given [listener] to this listener.
   */
  void addAll(RecordingErrorListener listener) {
    for (AnalysisError error in listener.errors) {
      onError(error);
    }
  }

  /**
   * Return the errors collected by the listener for the given [source].
   */
  List<AnalysisError> getErrorsForSource(Source source) {
    HashSet<AnalysisError> errorsForSource = _errors[source];
    if (errorsForSource == null) {
      return AnalysisError.NO_ERRORS;
    } else {
      return new List.from(errorsForSource);
    }
  }

  @override
  void onError(AnalysisError error) {
    Source source = error.source;
    HashSet<AnalysisError> errorsForSource = _errors[source];
    if (_errors[source] == null) {
      errorsForSource = new HashSet<AnalysisError>();
      _errors[source] = errorsForSource;
    }
    errorsForSource.add(error);
  }
}

class RecursiveXmlVisitor_ParseHtmlTask_internalPerform
    extends ht.RecursiveXmlVisitor<Object> {
  final ParseHtmlTask ParseHtmlTask_this;

  RecordingErrorListener errorListener;

  RecursiveXmlVisitor_ParseHtmlTask_internalPerform(
      this.ParseHtmlTask_this, this.errorListener)
      : super();

  @override
  Object visitHtmlScriptTagNode(ht.HtmlScriptTagNode node) {
    ParseHtmlTask_this._resolveScriptDirectives(node.script, errorListener);
    return null;
  }
}

class RecursiveXmlVisitor_ResolveHtmlTask_internalPerform
    extends ht.RecursiveXmlVisitor<Object> {
  final ResolveHtmlTask ResolveHtmlTask_this;

  RecordingErrorListener errorListener;

  RecursiveXmlVisitor_ResolveHtmlTask_internalPerform(
      this.ResolveHtmlTask_this, this.errorListener)
      : super();

  @override
  Object visitHtmlScriptTagNode(ht.HtmlScriptTagNode node) {
    CompilationUnit script = node.script;
    if (script != null) {
      GenerateDartErrorsTask.validateDirectives(ResolveHtmlTask_this.context,
          ResolveHtmlTask_this.source, script, errorListener);
    }
    return null;
  }
}

/**
 * An visitor that removes any resolution information from an AST structure when
 * used to visit that structure.
 */
class ResolutionEraser extends GeneralizingAstVisitor<Object> {
  /**
   * A flag indicating whether the elements associated with declarations should
   * be erased.
   */
  bool eraseDeclarations = true;

  @override
  Object visitAssignmentExpression(AssignmentExpression node) {
    node.staticElement = null;
    node.propagatedElement = null;
    return super.visitAssignmentExpression(node);
  }

  @override
  Object visitBinaryExpression(BinaryExpression node) {
    node.staticElement = null;
    node.propagatedElement = null;
    return super.visitBinaryExpression(node);
  }

  @override
  Object visitBreakStatement(BreakStatement node) {
    node.target = null;
    return super.visitBreakStatement(node);
  }

  @override
  Object visitCompilationUnit(CompilationUnit node) {
    if (eraseDeclarations) {
      node.element = null;
    }
    return super.visitCompilationUnit(node);
  }

  @override
  Object visitConstructorDeclaration(ConstructorDeclaration node) {
    if (eraseDeclarations) {
      node.element = null;
    }
    return super.visitConstructorDeclaration(node);
  }

  @override
  Object visitConstructorName(ConstructorName node) {
    node.staticElement = null;
    return super.visitConstructorName(node);
  }

  @override
  Object visitContinueStatement(ContinueStatement node) {
    node.target = null;
    return super.visitContinueStatement(node);
  }

  @override
  Object visitDirective(Directive node) {
    if (eraseDeclarations) {
      node.element = null;
    }
    return super.visitDirective(node);
  }

  @override
  Object visitExpression(Expression node) {
    node.staticType = null;
    node.propagatedType = null;
    return super.visitExpression(node);
  }

  @override
  Object visitFunctionExpression(FunctionExpression node) {
    if (eraseDeclarations) {
      node.element = null;
    }
    return super.visitFunctionExpression(node);
  }

  @override
  Object visitFunctionExpressionInvocation(FunctionExpressionInvocation node) {
    node.staticElement = null;
    node.propagatedElement = null;
    return super.visitFunctionExpressionInvocation(node);
  }

  @override
  Object visitIndexExpression(IndexExpression node) {
    node.staticElement = null;
    node.propagatedElement = null;
    return super.visitIndexExpression(node);
  }

  @override
  Object visitInstanceCreationExpression(InstanceCreationExpression node) {
    node.staticElement = null;
    return super.visitInstanceCreationExpression(node);
  }

  @override
  Object visitPostfixExpression(PostfixExpression node) {
    node.staticElement = null;
    node.propagatedElement = null;
    return super.visitPostfixExpression(node);
  }

  @override
  Object visitPrefixExpression(PrefixExpression node) {
    node.staticElement = null;
    node.propagatedElement = null;
    return super.visitPrefixExpression(node);
  }

  @override
  Object visitRedirectingConstructorInvocation(
      RedirectingConstructorInvocation node) {
    node.staticElement = null;
    return super.visitRedirectingConstructorInvocation(node);
  }

  @override
  Object visitSimpleIdentifier(SimpleIdentifier node) {
    if (eraseDeclarations || !node.inDeclarationContext()) {
      node.staticElement = null;
    }
    node.propagatedElement = null;
    return super.visitSimpleIdentifier(node);
  }

  @override
  Object visitSuperConstructorInvocation(SuperConstructorInvocation node) {
    node.staticElement = null;
    return super.visitSuperConstructorInvocation(node);
  }

  /**
   * Remove any resolution information from the given AST structure.
   */
  static void erase(AstNode node, {bool eraseDeclarations: true}) {
    ResolutionEraser eraser = new ResolutionEraser();
    eraser.eraseDeclarations = eraseDeclarations;
    node.accept(eraser);
  }
}

/**
 * The information produced by resolving a compilation unit as part of a
 * specific library.
 */
class ResolutionState {
  /**
   * The next resolution state or `null` if none.
   */
  ResolutionState _nextState;

  /**
   * The source for the defining compilation unit of the library that contains
   * this unit. If this unit is the defining compilation unit for it's library,
   * then this will be the source for this unit.
   */
  Source _librarySource;

  /**
   * A table mapping descriptors to the cached results for those descriptors.
   * If there is no entry for a given descriptor then the state is implicitly
   * [CacheState.INVALID] and the value is implicitly the default value.
   */
  Map<DataDescriptor, CachedResult> resultMap =
      new HashMap<DataDescriptor, CachedResult>();

  /**
   * Flush any AST structures being maintained by this state.
   */
  void flushAstStructures() {
    _flush(DartEntry.BUILT_UNIT);
    _flush(DartEntry.RESOLVED_UNIT);
    if (_nextState != null) {
      _nextState.flushAstStructures();
    }
  }

  /**
   * Return the state of the data represented by the given [descriptor].
   */
  CacheState getState(DataDescriptor descriptor) {
    CachedResult result = resultMap[descriptor];
    if (result == null) {
      return CacheState.INVALID;
    }
    return result.state;
  }

  /**
   * Return the value of the data represented by the given [descriptor], or
   * `null` if the data represented by the descriptor is not valid.
   */
  /*<V>*/ dynamic /*V*/ getValue(DataDescriptor /*<V>*/ descriptor) {
    CachedResult result = resultMap[descriptor];
    if (result == null) {
      return descriptor.defaultValue;
    }
    return result.value;
  }

  /**
   * Return `true` if the state of any data value is [CacheState.ERROR].
   */
  bool hasErrorState() {
    for (CachedResult result in resultMap.values) {
      if (result.state == CacheState.ERROR) {
        return true;
      }
    }
    return false;
  }

  /**
   * Invalidate all of the resolution information associated with the compilation unit.
   */
  void invalidateAllResolutionInformation() {
    _nextState = null;
    _librarySource = null;
    setState(DartEntry.BUILT_UNIT, CacheState.INVALID);
    setState(DartEntry.BUILT_ELEMENT, CacheState.INVALID);
    setState(DartEntry.HINTS, CacheState.INVALID);
    setState(DartEntry.LINTS, CacheState.INVALID);
    setState(DartEntry.RESOLVED_UNIT, CacheState.INVALID);
    setState(DartEntry.RESOLUTION_ERRORS, CacheState.INVALID);
    setState(DartEntry.VERIFICATION_ERRORS, CacheState.INVALID);
  }

  /**
   * Record that an exception occurred while attempting to build the element
   * model for the source associated with this state.
   */
  void recordBuildElementError() {
    setState(DartEntry.BUILT_UNIT, CacheState.ERROR);
    setState(DartEntry.BUILT_ELEMENT, CacheState.ERROR);
    recordResolutionError();
  }

  /**
   * Record that an exception occurred while attempting to generate hints for
   * the source associated with this entry. This will set the state of all
   * verification information as being in error.
   */
  void recordHintError() {
    setState(DartEntry.HINTS, CacheState.ERROR);
  }

  /**
   * Record that an exception occurred while attempting to generate lints for
   * the source associated with this entry. This will set the state of all
   * verification information as being in error.
   */
  void recordLintError() {
    setState(DartEntry.LINTS, CacheState.ERROR);
  }

  /**
   * Record that an exception occurred while attempting to resolve the source
   * associated with this state.
   */
  void recordResolutionError() {
    setState(DartEntry.RESOLVED_UNIT, CacheState.ERROR);
    setState(DartEntry.RESOLUTION_ERRORS, CacheState.ERROR);
    recordVerificationError();
  }

  /**
   * Record that an exception occurred while attempting to scan or parse the
   * source associated with this entry. This will set the state of all
   * resolution-based information as being in error.
   */
  void recordResolutionErrorsInAllLibraries() {
    recordBuildElementError();
    if (_nextState != null) {
      _nextState.recordResolutionErrorsInAllLibraries();
    }
  }

  /**
   * Record that an exception occurred while attempting to generate errors and
   * warnings for the source associated with this entry. This will set the state
   * of all verification information as being in error.
   */
  void recordVerificationError() {
    setState(DartEntry.VERIFICATION_ERRORS, CacheState.ERROR);
    recordHintError();
  }

  /**
   * Set the state of the data represented by the given [descriptor] to the
   * given [state].
   */
  void setState(DataDescriptor descriptor, CacheState state) {
    if (state == CacheState.VALID) {
      throw new ArgumentError("use setValue() to set the state to VALID");
    }
    if (state == CacheState.INVALID) {
      resultMap.remove(descriptor);
    } else {
      CachedResult result =
          resultMap.putIfAbsent(descriptor, () => new CachedResult(descriptor));
      result.state = state;
      if (state != CacheState.IN_PROCESS) {
        //
        // If the state is in-process, we can leave the current value in the
        // cache for any 'get' methods to access.
        //
        result.value = descriptor.defaultValue;
      }
    }
  }

  /**
   * Set the value of the data represented by the given [descriptor] to the
   * given [value].
   */
  void setValue(DataDescriptor /*<V>*/ descriptor, dynamic /*V*/ value) {
    CachedResult result =
        resultMap.putIfAbsent(descriptor, () => new CachedResult(descriptor));
    SourceEntry.countTransition(descriptor, result);
    result.state = CacheState.VALID;
    result.value = value == null ? descriptor.defaultValue : value;
  }

  /**
   * Flush the value of the data described by the [descriptor].
   */
  void _flush(DataDescriptor descriptor) {
    CachedResult result = resultMap[descriptor];
    if (result != null && result.state == CacheState.VALID) {
      result.state = CacheState.FLUSHED;
      result.value = descriptor.defaultValue;
    }
  }

  /**
   * Write a textual representation of the difference between the old entry and
   * this entry to the given string [buffer]. A separator will be written before
   * the first difference if [needsSeparator] is `true`. The [oldEntry] is the
   * entry that was replaced by this entry. Return `true` is a separator is
   * needed before writing any subsequent differences.
   */
  bool _writeDiffOn(
      StringBuffer buffer, bool needsSeparator, DartEntry oldEntry) {
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "resolvedUnit",
        DartEntry.RESOLVED_UNIT, oldEntry);
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
        "resolutionErrors", DartEntry.RESOLUTION_ERRORS, oldEntry);
    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
        "verificationErrors", DartEntry.VERIFICATION_ERRORS, oldEntry);
    needsSeparator = _writeStateDiffOn(
        buffer, needsSeparator, "hints", DartEntry.HINTS, oldEntry);
    needsSeparator = _writeStateDiffOn(
        buffer, needsSeparator, "lints", DartEntry.LINTS, oldEntry);
    return needsSeparator;
  }

  /**
   * Write a textual representation of this state to the given [buffer]. The
   * result will only be used for debugging purposes.
   */
  void _writeOn(StringBuffer buffer) {
    if (_librarySource != null) {
      _writeStateOn(buffer, "builtElement", DartEntry.BUILT_ELEMENT);
      _writeStateOn(buffer, "builtUnit", DartEntry.BUILT_UNIT);
      _writeStateOn(buffer, "resolvedUnit", DartEntry.RESOLVED_UNIT);
      _writeStateOn(buffer, "resolutionErrors", DartEntry.RESOLUTION_ERRORS);
      _writeStateOn(
          buffer, "verificationErrors", DartEntry.VERIFICATION_ERRORS);
      _writeStateOn(buffer, "hints", DartEntry.HINTS);
      _writeStateOn(buffer, "lints", DartEntry.LINTS);
      if (_nextState != null) {
        _nextState._writeOn(buffer);
      }
    }
  }

  /**
   * Write a textual representation of the difference between the state of the
   * value described by the given [descriptor] between the [oldEntry] and this
   * entry to the given [buffer]. Return `true` if some difference was written.
   */
  bool _writeStateDiffOn(StringBuffer buffer, bool needsSeparator, String label,
      DataDescriptor descriptor, SourceEntry oldEntry) {
    CacheState oldState = oldEntry.getState(descriptor);
    CacheState newState = getState(descriptor);
    if (oldState != newState) {
      if (needsSeparator) {
        buffer.write("; ");
      }
      buffer.write(label);
      buffer.write(" = ");
      buffer.write(oldState);
      buffer.write(" -> ");
      buffer.write(newState);
      return true;
    }
    return needsSeparator;
  }

  /**
   * Write a textual representation of the state of the value described by the
   * given [descriptor] to the given bugger, prefixed by the given [label] to
   * the given [buffer].
   */
  void _writeStateOn(
      StringBuffer buffer, String label, DataDescriptor descriptor) {
    CachedResult result = resultMap[descriptor];
    buffer.write("; ");
    buffer.write(label);
    buffer.write(" = ");
    buffer.write(result == null ? CacheState.INVALID : result.state);
  }
}

/**
 * A compilation unit that is not referenced by any other objects. It is used by
 * the [LibraryResolver] to resolve a library.
 */
class ResolvableCompilationUnit {
  /**
   * The source of the compilation unit.
   */
  final Source source;

  /**
   * The compilation unit.
   */
  final CompilationUnit compilationUnit;

  /**
   * Initialize a newly created holder to hold the given [source] and
   * [compilationUnit].
   */
  ResolvableCompilationUnit(this.source, this.compilationUnit);
}

/**
 * Instances of the class `ResolveDartLibraryTask` resolve a specific Dart library.
 */
class ResolveDartLibraryCycleTask extends AnalysisTask {
  /**
   * The source representing the file whose compilation unit is to be returned. TODO(brianwilkerson)
   * This should probably be removed, but is being left in for now to ease the transition.
   */
  final Source unitSource;

  /**
   * The source representing the library to be resolved.
   */
  final Source librarySource;

  /**
   * The libraries that are part of the cycle containing the library to be resolved.
   */
  final List<ResolvableLibrary> _librariesInCycle;

  /**
   * The library resolver holding information about the libraries that were resolved.
   */
  LibraryResolver2 _resolver;

  /**
   * Initialize a newly created task to perform analysis within the given context.
   *
   * @param context the context in which the task is to be performed
   * @param unitSource the source representing the file whose compilation unit is to be returned
   * @param librarySource the source representing the library to be resolved
   * @param librariesInCycle the libraries that are part of the cycle containing the library to be
   *          resolved
   */
  ResolveDartLibraryCycleTask(InternalAnalysisContext context, this.unitSource,
      this.librarySource, this._librariesInCycle)
      : super(context);

  /**
   * Return the library resolver holding information about the libraries that were resolved.
   *
   * @return the library resolver holding information about the libraries that were resolved
   */
  LibraryResolver2 get libraryResolver => _resolver;

  @override
  String get taskDescription {
    if (librarySource == null) {
      return "resolve library null source";
    }
    return "resolve library ${librarySource.fullName}";
  }

  @override
  accept(AnalysisTaskVisitor visitor) =>
      visitor.visitResolveDartLibraryCycleTask(this);

  @override
  void internalPerform() {
    _resolver = new LibraryResolver2(context);
    _resolver.resolveLibrary(librarySource, _librariesInCycle);
  }
}

/**
 * Instances of the class `ResolveDartLibraryTask` resolve a specific Dart library.
 */
class ResolveDartLibraryTask extends AnalysisTask {
  /**
   * The source representing the file whose compilation unit is to be returned.
   */
  final Source unitSource;

  /**
   * The source representing the library to be resolved.
   */
  final Source librarySource;

  /**
   * The library resolver holding information about the libraries that were resolved.
   */
  LibraryResolver _resolver;

  /**
   * Initialize a newly created task to perform analysis within the given context.
   *
   * @param context the context in which the task is to be performed
   * @param unitSource the source representing the file whose compilation unit is to be returned
   * @param librarySource the source representing the library to be resolved
   */
  ResolveDartLibraryTask(
      InternalAnalysisContext context, this.unitSource, this.librarySource)
      : super(context);

  /**
   * Return the library resolver holding information about the libraries that were resolved.
   *
   * @return the library resolver holding information about the libraries that were resolved
   */
  LibraryResolver get libraryResolver => _resolver;

  @override
  String get taskDescription {
    if (librarySource == null) {
      return "resolve library null source";
    }
    return "resolve library ${librarySource.fullName}";
  }

  @override
  accept(AnalysisTaskVisitor visitor) =>
      visitor.visitResolveDartLibraryTask(this);

  @override
  void internalPerform() {
    LibraryResolverFactory resolverFactory = context.libraryResolverFactory;
    _resolver = resolverFactory == null
        ? new LibraryResolver(context)
        : resolverFactory(context);
    _resolver.resolveLibrary(librarySource, true);
  }
}

/**
 * Instances of the class `ResolveDartUnitTask` resolve a single Dart file based on a existing
 * element model.
 */
class ResolveDartUnitTask extends AnalysisTask {
  /**
   * The source that is to be resolved.
   */
  final Source source;

  /**
   * The element model for the library containing the source.
   */
  final LibraryElement _libraryElement;

  /**
   * The compilation unit that was resolved by this task.
   */
  CompilationUnit _resolvedUnit;

  /**
   * Initialize a newly created task to perform analysis within the given context.
   *
   * @param context the context in which the task is to be performed
   * @param source the source to be parsed
   * @param libraryElement the element model for the library containing the source
   */
  ResolveDartUnitTask(
      InternalAnalysisContext context, this.source, this._libraryElement)
      : super(context);

  /**
   * Return the source for the library containing the source that is to be resolved.
   *
   * @return the source for the library containing the source that is to be resolved
   */
  Source get librarySource => _libraryElement.source;

  /**
   * Return the compilation unit that was resolved by this task.
   *
   * @return the compilation unit that was resolved by this task
   */
  CompilationUnit get resolvedUnit => _resolvedUnit;

  @override
  String get taskDescription {
    Source librarySource = _libraryElement.source;
    if (librarySource == null) {
      return "resolve unit null source";
    }
    return "resolve unit ${librarySource.fullName}";
  }

  @override
  accept(AnalysisTaskVisitor visitor) => visitor.visitResolveDartUnitTask(this);

  @override
  void internalPerform() {
    TypeProvider typeProvider = _libraryElement.context.typeProvider;
    CompilationUnit unit = context.computeResolvableCompilationUnit(source);
    if (unit == null) {
      throw new AnalysisException(
          "Internal error: computeResolvableCompilationUnit returned a value without a parsed Dart unit");
    }
    //
    // Resolve names in declarations.
    //
    new DeclarationResolver().resolve(unit, _find(_libraryElement, source));
    //
    // Resolve the type names.
    //
    RecordingErrorListener errorListener = new RecordingErrorListener();
    TypeResolverVisitor typeResolverVisitor = new TypeResolverVisitor(
        _libraryElement, source, typeProvider, errorListener);
    unit.accept(typeResolverVisitor);
    //
    // Resolve the rest of the structure
    //
    InheritanceManager inheritanceManager =
        new InheritanceManager(_libraryElement);
    ResolverVisitor resolverVisitor = new ResolverVisitor(
        _libraryElement, source, typeProvider, errorListener,
        inheritanceManager: inheritanceManager);
    unit.accept(resolverVisitor);
    //
    // Perform additional error checking.
    //
    PerformanceStatistics.errors.makeCurrentWhile(() {
      ErrorReporter errorReporter = new ErrorReporter(errorListener, source);
      ErrorVerifier errorVerifier = new ErrorVerifier(
          errorReporter,
          _libraryElement,
          typeProvider,
          inheritanceManager,
          context.analysisOptions.enableSuperMixins);
      unit.accept(errorVerifier);
      // TODO(paulberry): as a temporary workaround for issue 21572,
      // ConstantVerifier is being run right after ConstantValueComputer, so we
      // don't need to run it here.  Once issue 21572 is fixed, re-enable the
      // call to ConstantVerifier.
//       ConstantVerifier constantVerifier = new ConstantVerifier(errorReporter, _libraryElement, typeProvider);
//       unit.accept(constantVerifier);
    });
    //
    // Capture the results.
    //
    _resolvedUnit = unit;
  }

  /**
   * Search the compilation units that are part of the given library and return the element
   * representing the compilation unit with the given source. Return `null` if there is no
   * such compilation unit.
   *
   * @param libraryElement the element representing the library being searched through
   * @param unitSource the source for the compilation unit whose element is to be returned
   * @return the element representing the compilation unit
   */
  CompilationUnitElement _find(
      LibraryElement libraryElement, Source unitSource) {
    CompilationUnitElement element = libraryElement.definingCompilationUnit;
    if (element.source == unitSource) {
      return element;
    }
    for (CompilationUnitElement partElement in libraryElement.parts) {
      if (partElement.source == unitSource) {
        return partElement;
      }
    }
    return null;
  }
}

/**
 * Instances of the class `ResolveHtmlTask` resolve a specific source as an HTML file.
 */
class ResolveHtmlTask extends AnalysisTask {
  /**
   * The source to be resolved.
   */
  final Source source;

  /**
   * The time at which the contents of the source were last modified.
   */
  final int modificationTime;

  /**
   * The HTML unit to be resolved.
   */
  final ht.HtmlUnit _unit;

  /**
   * The [HtmlUnit] that was resolved by this task.
   */
  ht.HtmlUnit _resolvedUnit;

  /**
   * The element produced by resolving the source.
   */
  HtmlElement _element = null;

  /**
   * The resolution errors that were discovered while resolving the source.
   */
  List<AnalysisError> _resolutionErrors = AnalysisError.NO_ERRORS;

  /**
   * Initialize a newly created task to perform analysis within the given context.
   *
   * @param context the context in which the task is to be performed
   * @param source the source to be resolved
   * @param modificationTime the time at which the contents of the source were last modified
   * @param unit the HTML unit to be resolved
   */
  ResolveHtmlTask(InternalAnalysisContext context, this.source,
      this.modificationTime, this._unit)
      : super(context);

  HtmlElement get element => _element;

  List<AnalysisError> get resolutionErrors => _resolutionErrors;

  /**
   * Return the [HtmlUnit] that was resolved by this task.
   *
   * @return the [HtmlUnit] that was resolved by this task
   */
  ht.HtmlUnit get resolvedUnit => _resolvedUnit;

  @override
  String get taskDescription {
    if (source == null) {
      return "resolve as html null source";
    }
    return "resolve as html ${source.fullName}";
  }

  @override
  accept(AnalysisTaskVisitor visitor) => visitor.visitResolveHtmlTask(this);

  @override
  void internalPerform() {
    //
    // Build the standard HTML element.
    //
    HtmlUnitBuilder builder = new HtmlUnitBuilder(context);
    _element = builder.buildHtmlElement(source, _unit);
    RecordingErrorListener errorListener = builder.errorListener;
    //
    // Validate the directives
    //
    _unit.accept(new RecursiveXmlVisitor_ResolveHtmlTask_internalPerform(
        this, errorListener));
    //
    // Record all resolution errors.
    //
    _resolutionErrors = errorListener.getErrorsForSource(source);
    //
    // Remember the resolved unit.
    //
    _resolvedUnit = _unit;
  }
}

/**
 * The priority of data in the cache in terms of the desirability of retaining
 * some specified data about a specified source.
 */
class RetentionPriority extends Enum<RetentionPriority> {
  /**
   * A priority indicating that a given piece of data can be removed from the
   * cache without reservation.
   */
  static const RetentionPriority LOW = const RetentionPriority('LOW', 0);

  /**
   * A priority indicating that a given piece of data should not be removed from
   * the cache unless there are no sources for which the corresponding data has
   * a lower priority. Currently used for data that is needed in order to finish
   * some outstanding analysis task.
   */
  static const RetentionPriority MEDIUM = const RetentionPriority('MEDIUM', 1);

  /**
   * A priority indicating that a given piece of data should not be removed from
   * the cache. Currently used for data related to a priority source.
   */
  static const RetentionPriority HIGH = const RetentionPriority('HIGH', 2);

  static const List<RetentionPriority> values = const [LOW, MEDIUM, HIGH];

  const RetentionPriority(String name, int ordinal) : super(name, ordinal);
}

/**
 * Instances of the class `ScanDartTask` scan a specific source as a Dart file.
 */
class ScanDartTask extends AnalysisTask {
  /**
   * The source to be scanned.
   */
  final Source source;

  /**
   * The contents of the source.
   */
  final String _content;

  /**
   * The token stream that was produced by scanning the source.
   */
  Token _tokenStream;

  /**
   * The line information that was produced.
   */
  LineInfo _lineInfo;

  /**
   * The errors that were produced by scanning the source.
   */
  List<AnalysisError> _errors = AnalysisError.NO_ERRORS;

  /**
   * Initialize a newly created task to perform analysis within the given context.
   *
   * @param context the context in which the task is to be performed
   * @param source the source to be parsed
   * @param content the contents of the source
   */
  ScanDartTask(InternalAnalysisContext context, this.source, this._content)
      : super(context);

  /**
   * Return the errors that were produced by scanning the source, or `null` if the task has
   * not yet been performed or if an exception occurred.
   *
   * @return the errors that were produced by scanning the source
   */
  List<AnalysisError> get errors => _errors;

  /**
   * Return the line information that was produced, or `null` if the task has not yet been
   * performed or if an exception occurred.
   *
   * @return the line information that was produced
   */
  LineInfo get lineInfo => _lineInfo;

  @override
  String get taskDescription {
    if (source == null) {
      return "scan as dart null source";
    }
    return "scan as dart ${source.fullName}";
  }

  /**
   * Return the token stream that was produced by scanning the source, or `null` if the task
   * has not yet been performed or if an exception occurred.
   *
   * @return the token stream that was produced by scanning the source
   */
  Token get tokenStream => _tokenStream;

  @override
  accept(AnalysisTaskVisitor visitor) => visitor.visitScanDartTask(this);

  @override
  void internalPerform() {
    PerformanceStatistics.scan.makeCurrentWhile(() {
      RecordingErrorListener errorListener = new RecordingErrorListener();
      try {
        Scanner scanner = new Scanner(
            source, new CharSequenceReader(_content), errorListener);
        scanner.preserveComments = context.analysisOptions.preserveComments;
        _tokenStream = scanner.tokenize();
        _lineInfo = new LineInfo(scanner.lineStarts);
        _errors = errorListener.getErrorsForSource(source);
      } catch (exception, stackTrace) {
        throw new AnalysisException(
            "Exception", new CaughtException(exception, stackTrace));
      }
    });
  }
}

/**
 * An [AnalysisContext] that only contains sources for a Dart SDK.
 */
class SdkAnalysisContext extends AnalysisContextImpl {
  @override
  AnalysisCache createCacheFromSourceFactory(SourceFactory factory) {
    if (factory == null) {
      return super.createCacheFromSourceFactory(factory);
    }
    DartSdk sdk = factory.dartSdk;
    if (sdk == null) {
      throw new IllegalArgumentException(
          "The source factory for an SDK analysis context must have a DartUriResolver");
    }
    return new AnalysisCache(
        <CachePartition>[AnalysisEngine.instance.partitionManager.forSdk(sdk)]);
  }
}

/**
 * A cache partition that contains all of the sources in the SDK.
 */
class SdkCachePartition extends CachePartition {
  /**
   * Initialize a newly created partition. The [context] is the context that
   * owns this partition. The [maxCacheSize] is the maximum number of sources
   * for which AST structures should be kept in the cache.
   */
  SdkCachePartition(InternalAnalysisContext context, int maxCacheSize)
      : super(context, maxCacheSize, DefaultRetentionPolicy.POLICY);

  @override
  bool contains(Source source) => source.isInSystemLibrary;
}

/**
 * The information cached by an analysis context about an individual source, no
 * matter what kind of source it is.
 */
abstract class SourceEntry {
  /**
   * The data descriptor representing the contents of the source.
   */
  static final DataDescriptor<String> CONTENT =
      new DataDescriptor<String>("SourceEntry.CONTENT");

  /**
   * The data descriptor representing the errors resulting from reading the
   * source content.
   */
  static final DataDescriptor<List<AnalysisError>> CONTENT_ERRORS =
      new DataDescriptor<List<AnalysisError>>(
          "SourceEntry.CONTENT_ERRORS", AnalysisError.NO_ERRORS);

  /**
   * The data descriptor representing the line information.
   */
  static final DataDescriptor<LineInfo> LINE_INFO =
      new DataDescriptor<LineInfo>("SourceEntry.LINE_INFO");

  /**
   * The index of the flag indicating whether the source was explicitly added to
   * the context or whether the source was implicitly added because it was
   * referenced by another source.
   */
  static int _EXPLICITLY_ADDED_FLAG = 0;

  /**
   * A table mapping data descriptors to a count of the number of times a value
   * was set when in a given state.
   */
  static final Map<DataDescriptor, Map<CacheState, int>> transitionMap =
      new HashMap<DataDescriptor, Map<CacheState, int>>();

  /**
   * The most recent time at which the state of the source matched the state
   * represented by this entry.
   */
  int modificationTime = 0;

  /**
   * The exception that caused one or more values to have a state of
   * [CacheState.ERROR].
   */
  CaughtException exception;

  /**
   * A bit-encoding of boolean flags associated with this element.
   */
  int _flags = 0;

  /**
   * A table mapping data descriptors to the cached results for those
   * descriptors.
   */
  Map<DataDescriptor, CachedResult> resultMap =
      new HashMap<DataDescriptor, CachedResult>();

  /**
   * Return all of the errors associated with this entry.
   */
  List<AnalysisError> get allErrors {
    return getValue(CONTENT_ERRORS);
  }

  /**
   * Get a list of all the library-independent descriptors for which values may
   * be stored in this SourceEntry.
   */
  List<DataDescriptor> get descriptors {
    return <DataDescriptor>[CONTENT, CONTENT_ERRORS, LINE_INFO];
  }

  /**
   * Return `true` if the source was explicitly added to the context or `false`
   * if the source was implicitly added because it was referenced by another
   * source.
   */
  bool get explicitlyAdded => _getFlag(_EXPLICITLY_ADDED_FLAG);

  /**
   * Set whether the source was explicitly added to the context to match the
   * [explicitlyAdded] flag.
   */
  void set explicitlyAdded(bool explicitlyAdded) {
    _setFlag(_EXPLICITLY_ADDED_FLAG, explicitlyAdded);
  }

  /**
   * Return the kind of the source, or `null` if the kind is not currently
   * cached.
   */
  SourceKind get kind;

  /**
   * Fix the state of the [exception] to match the current state of the entry.
   */
  void fixExceptionState() {
    if (hasErrorState()) {
      if (exception == null) {
        //
        // This code should never be reached, but is a fail-safe in case an
        // exception is not recorded when it should be.
        //
        String message = "State set to ERROR without setting an exception";
        exception = new CaughtException(new AnalysisException(message), null);
      }
    } else {
      exception = null;
    }
  }

  /**
   * Return a textual representation of the difference between the [oldEntry]
   * and this entry. The difference is represented as a sequence of fields whose
   * value would change if the old entry were converted into the new entry.
   */
  String getDiff(SourceEntry oldEntry) {
    StringBuffer buffer = new StringBuffer();
    _writeDiffOn(buffer, oldEntry);
    return buffer.toString();
  }

  /**
   * Return the state of the data represented by the given [descriptor].
   */
  CacheState getState(DataDescriptor descriptor) {
    if (!_isValidDescriptor(descriptor)) {
      throw new ArgumentError("Invalid descriptor: $descriptor");
    }
    CachedResult result = resultMap[descriptor];
    if (result == null) {
      return CacheState.INVALID;
    }
    return result.state;
  }

  /**
   * Return the value of the data represented by the given [descriptor], or
   * `null` if the data represented by the descriptor is not valid.
   */
  /*<V>*/ dynamic /*V*/ getValue(DataDescriptor /*<V>*/ descriptor) {
    if (!_isValidDescriptor(descriptor)) {
      throw new ArgumentError("Invalid descriptor: $descriptor");
    }
    CachedResult result = resultMap[descriptor];
    if (result == null) {
      return descriptor.defaultValue;
    }
    return result.value;
  }

  /**
   * Return `true` if the state of any data value is [CacheState.ERROR].
   */
  bool hasErrorState() {
    for (CachedResult result in resultMap.values) {
      if (result.state == CacheState.ERROR) {
        return true;
      }
    }
    return false;
  }

  /**
   * Invalidate all of the information associated with this source.
   */
  void invalidateAllInformation() {
    setState(CONTENT, CacheState.INVALID);
    setState(CONTENT_ERRORS, CacheState.INVALID);
    setState(LINE_INFO, CacheState.INVALID);
  }

  /**
   * Record that an [exception] occurred while attempting to get the contents of
   * the source represented by this entry. This will set the state of all
   * information, including any resolution-based information, as being in error.
   */
  void recordContentError(CaughtException exception) {
    setState(CONTENT, CacheState.ERROR);
    recordScanError(exception);
  }

  /**
   * Record that an [exception] occurred while attempting to scan or parse the
   * entry represented by this entry. This will set the state of all
   * information, including any resolution-based information, as being in error.
   */
  void recordScanError(CaughtException exception) {
    this.exception = exception;
    setState(LINE_INFO, CacheState.ERROR);
  }

  /**
   * Set the state of the data represented by the given [descriptor] to the
   * given [state].
   */
  void setState(DataDescriptor descriptor, CacheState state) {
    if (!_isValidDescriptor(descriptor)) {
      throw new ArgumentError("Invalid descriptor: $descriptor");
    }
    if (state == CacheState.VALID) {
      throw new ArgumentError("use setValue() to set the state to VALID");
    }
    _validateStateChange(descriptor, state);
    if (state == CacheState.INVALID) {
      resultMap.remove(descriptor);
    } else {
      CachedResult result =
          resultMap.putIfAbsent(descriptor, () => new CachedResult(descriptor));
      result.state = state;
      if (state != CacheState.IN_PROCESS) {
        //
        // If the state is in-process, we can leave the current value in the
        // cache for any 'get' methods to access.
        //
        result.value = descriptor.defaultValue;
      }
    }
  }

  /**
   * Set the value of the data represented by the given [descriptor] to the
   * given [value].
   */
  void setValue(DataDescriptor /*<V>*/ descriptor, dynamic /*V*/ value) {
    if (!_isValidDescriptor(descriptor)) {
      throw new ArgumentError("Invalid descriptor: $descriptor");
    }
    _validateStateChange(descriptor, CacheState.VALID);
    CachedResult result =
        resultMap.putIfAbsent(descriptor, () => new CachedResult(descriptor));
    countTransition(descriptor, result);
    result.state = CacheState.VALID;
    result.value = value == null ? descriptor.defaultValue : value;
  }

  @override
  String toString() {
    StringBuffer buffer = new StringBuffer();
    _writeOn(buffer);
    return buffer.toString();
  }

  /**
   * Flush the value of the data described by the [descriptor].
   */
  void _flush(DataDescriptor descriptor) {
    CachedResult result = resultMap[descriptor];
    if (result != null && result.state == CacheState.VALID) {
      _validateStateChange(descriptor, CacheState.FLUSHED);
      result.state = CacheState.FLUSHED;
      result.value = descriptor.defaultValue;
    }
  }

  /**
   * Return the value of the flag with the given [index].
   */
  bool _getFlag(int index) => BooleanArray.get(_flags, index);

  /**
   * Return `true` if the [descriptor] is valid for this entry.
   */
  bool _isValidDescriptor(DataDescriptor descriptor) {
    return descriptor == CONTENT ||
        descriptor == CONTENT_ERRORS ||
        descriptor == LINE_INFO;
  }

  /**
   * Set the value of the flag with the given [index] to the given [value].
   */
  void _setFlag(int index, bool value) {
    _flags = BooleanArray.set(_flags, index, value);
  }

  /**
   * If the state of the value described by the given [descriptor] is changing
   * from ERROR to anything else, capture the information. This is an attempt to
   * discover the underlying cause of a long-standing bug.
   */
  void _validateStateChange(DataDescriptor descriptor, CacheState newState) {
    // TODO(brianwilkerson) Decide whether we still want to capture this data.
//    if (descriptor != CONTENT) {
//      return;
//    }
//    CachedResult result = resultMap[CONTENT];
//    if (result != null && result.state == CacheState.ERROR) {
//      String message =
//          "contentState changing from ${result.state} to $newState";
//      InstrumentationBuilder builder =
//          Instrumentation.builder2("SourceEntry-validateStateChange");
//      builder.data3("message", message);
//      //builder.data("source", source.getFullName());
//      builder.record(new CaughtException(new AnalysisException(message), null));
//      builder.log();
//    }
  }

  /**
   * Write a textual representation of the difference between the [oldEntry] and
   * this entry to the given string [buffer]. Return `true` if some difference
   * was written.
   */
  bool _writeDiffOn(StringBuffer buffer, SourceEntry oldEntry) {
    bool needsSeparator = false;
    CaughtException oldException = oldEntry.exception;
    if (!identical(oldException, exception)) {
      buffer.write("exception = ");
      buffer.write(oldException.runtimeType);
      buffer.write(" -> ");
      buffer.write(exception.runtimeType);
      needsSeparator = true;
    }
    int oldModificationTime = oldEntry.modificationTime;
    if (oldModificationTime != modificationTime) {
      if (needsSeparator) {
        buffer.write("; ");
      }
      buffer.write("time = ");
      buffer.write(oldModificationTime);
      buffer.write(" -> ");
      buffer.write(modificationTime);
      needsSeparator = true;
    }
    needsSeparator =
        _writeStateDiffOn(buffer, needsSeparator, "content", CONTENT, oldEntry);
    needsSeparator = _writeStateDiffOn(
        buffer, needsSeparator, "contentErrors", CONTENT_ERRORS, oldEntry);
    needsSeparator = _writeStateDiffOn(
        buffer, needsSeparator, "lineInfo", LINE_INFO, oldEntry);
    return needsSeparator;
  }

  /**
   * Write a textual representation of this entry to the given [buffer]. The
   * result should only be used for debugging purposes.
   */
  void _writeOn(StringBuffer buffer) {
    buffer.write("time = ");
    buffer.write(modificationTime);
    _writeStateOn(buffer, "content", CONTENT);
    _writeStateOn(buffer, "contentErrors", CONTENT_ERRORS);
    _writeStateOn(buffer, "lineInfo", LINE_INFO);
  }

  /**
   * Write a textual representation of the difference between the state of the
   * value described by the given [descriptor] between the [oldEntry] and this
   * entry to the given [buffer]. Return `true` if some difference was written.
   */
  bool _writeStateDiffOn(StringBuffer buffer, bool needsSeparator, String label,
      DataDescriptor descriptor, SourceEntry oldEntry) {
    CacheState oldState = oldEntry.getState(descriptor);
    CacheState newState = getState(descriptor);
    if (oldState != newState) {
      if (needsSeparator) {
        buffer.write("; ");
      }
      buffer.write(label);
      buffer.write(" = ");
      buffer.write(oldState);
      buffer.write(" -> ");
      buffer.write(newState);
      return true;
    }
    return needsSeparator;
  }

  /**
   * Write a textual representation of the state of the value described by the
   * given [descriptor] to the given bugger, prefixed by the given [label] to
   * the given [buffer].
   */
  void _writeStateOn(
      StringBuffer buffer, String label, DataDescriptor descriptor) {
    CachedResult result = resultMap[descriptor];
    buffer.write("; ");
    buffer.write(label);
    buffer.write(" = ");
    buffer.write(result == null ? CacheState.INVALID : result.state);
  }

  /**
   * Increment the count of the number of times that data represented by the
   * given [descriptor] was transitioned from the current state (as found in the
   * given [result] to a valid state.
   */
  static void countTransition(DataDescriptor descriptor, CachedResult result) {
    Map<CacheState, int> countMap = transitionMap.putIfAbsent(
        descriptor, () => new HashMap<CacheState, int>());
    int count = countMap[result.state];
    countMap[result.state] = count == null ? 1 : count + 1;
  }
}

/**
 * The priority levels used to return sources in an optimal order. A smaller
 * ordinal value equates to a higher priority.
 */
class SourcePriority extends Enum<SourcePriority> {
  /**
   * Used for a Dart source that is known to be a part contained in a library
   * that was recently resolved. These parts are given a higher priority because
   * there is a high probability that their AST structure is still in the cache
   * and therefore would not need to be re-created.
   */
  static const SourcePriority PRIORITY_PART =
      const SourcePriority('PRIORITY_PART', 0);

  /**
   * Used for a Dart source that is known to be a library.
   */
  static const SourcePriority LIBRARY = const SourcePriority('LIBRARY', 1);

  /**
   * Used for a Dart source whose kind is unknown.
   */
  static const SourcePriority UNKNOWN = const SourcePriority('UNKNOWN', 2);

  /**
   * Used for a Dart source that is known to be a part but whose library has not
   * yet been resolved.
   */
  static const SourcePriority NORMAL_PART =
      const SourcePriority('NORMAL_PART', 3);

  /**
   * Used for an HTML source.
   */
  static const SourcePriority HTML = const SourcePriority('HTML', 4);

  static const List<SourcePriority> values = const [
    PRIORITY_PART,
    LIBRARY,
    UNKNOWN,
    NORMAL_PART,
    HTML
  ];

  const SourcePriority(String name, int ordinal) : super(name, ordinal);
}

/**
 * [SourcesChangedEvent] indicates which sources have been added, removed,
 * or whose contents have changed.
 */
class SourcesChangedEvent {
  /**
   * The internal representation of what has changed. Clients should not access
   * this field directly.
   */
  final ChangeSet _changeSet;

  /**
   * Construct an instance representing the given changes.
   */
  SourcesChangedEvent(ChangeSet changeSet) : _changeSet = changeSet;

  /**
   * Construct an instance representing a source content change.
   */
  factory SourcesChangedEvent.changedContent(Source source, String contents) {
    ChangeSet changeSet = new ChangeSet();
    changeSet.changedContent(source, contents);
    return new SourcesChangedEvent(changeSet);
  }

  /**
   * Construct an instance representing a source content change.
   */
  factory SourcesChangedEvent.changedRange(Source source, String contents,
      int offset, int oldLength, int newLength) {
    ChangeSet changeSet = new ChangeSet();
    changeSet.changedRange(source, contents, offset, oldLength, newLength);
    return new SourcesChangedEvent(changeSet);
  }

  /**
   * Return the collection of sources for which content has changed.
   */
  Iterable<Source> get changedSources {
    List<Source> changedSources = new List.from(_changeSet.changedSources);
    changedSources.addAll(_changeSet.changedContents.keys);
    changedSources.addAll(_changeSet.changedRanges.keys);
    return changedSources;
  }

  /**
   * Return `true` if any sources were added.
   */
  bool get wereSourcesAdded => _changeSet.addedSources.length > 0;

  /**
   * Return `true` if any sources were removed or deleted.
   */
  bool get wereSourcesRemovedOrDeleted =>
      _changeSet.removedSources.length > 0 ||
          _changeSet.removedContainers.length > 0 ||
          _changeSet.deletedSources.length > 0;
}

/**
 * Analysis data for which we have a modification time.
 */
class TimestampedData<E> {
  /**
   * The modification time of the source from which the data was created.
   */
  final int modificationTime;

  /**
   * The data that was created from the source.
   */
  final E data;

  /**
   * Initialize a newly created holder to associate the given [data] with the
   * given [modificationTime].
   */
  TimestampedData(this.modificationTime, this.data);
}

/**
 * A cache partition that contains all sources not contained in other
 * partitions.
 */
class UniversalCachePartition extends CachePartition {
  /**
   * Initialize a newly created partition. The [context] is the context that
   * owns this partition. The [maxCacheSize] is the maximum number of sources
   * for which AST structures should be kept in the cache. The [retentionPolicy]
   * is the policy used to determine which pieces of data to remove from the
   * cache.
   */
  UniversalCachePartition(InternalAnalysisContext context, int maxCacheSize,
      CacheRetentionPolicy retentionPolicy)
      : super(context, maxCacheSize, retentionPolicy);

  @override
  bool contains(Source source) => true;
}

/**
 * The unique instances of the class `WaitForAsyncTask` represents a state in which there is
 * no analysis work that can be done until some asynchronous task (such as IO) has completed, but
 * where analysis is not yet complete.
 */
class WaitForAsyncTask extends AnalysisTask {
  /**
   * The unique instance of this class.
   */
  static WaitForAsyncTask _UniqueInstance = new WaitForAsyncTask();

  /**
   * Return the unique instance of this class.
   *
   * @return the unique instance of this class
   */
  static WaitForAsyncTask get instance => _UniqueInstance;

  /**
   * Prevent the creation of instances of this class.
   */
  WaitForAsyncTask() : super(null);

  @override
  String get taskDescription => "Waiting for async analysis";

  @override
  accept(AnalysisTaskVisitor visitor) => null;

  @override
  void internalPerform() {
    // There is no work to be done.
  }
}

/**
 * An object that manages a list of sources that need to have analysis work
 * performed on them.
 */
class WorkManager {
  /**
   * A list containing the various queues is priority order.
   */
  List<List<Source>> _workQueues;

  /**
   * Initialize a newly created manager to have no work queued up.
   */
  WorkManager() {
    int queueCount = SourcePriority.values.length;
    _workQueues = new List<List<Source>>(queueCount);
    for (int i = 0; i < queueCount; i++) {
      _workQueues[i] = new List<Source>();
    }
  }

  /**
   * Record that the given [source] needs to be analyzed. The [priority] level
   * is used to control when the source will be analyzed with respect to other
   * sources. If the source was previously added then it's priority is updated.
   * If it was previously added with the same priority then it's position in the
   * queue is unchanged.
   */
  void add(Source source, SourcePriority priority) {
    int queueCount = _workQueues.length;
    int ordinal = priority.ordinal;
    for (int i = 0; i < queueCount; i++) {
      List<Source> queue = _workQueues[i];
      if (i == ordinal) {
        if (!queue.contains(source)) {
          queue.add(source);
        }
      } else {
        queue.remove(source);
      }
    }
  }

  /**
   * Record that the given [source] needs to be analyzed. The [priority] level
   * is used to control when the source will be analyzed with respect to other
   * sources. If the source was previously added then it's priority is updated.
   * In either case, it will be analyzed before other sources of the same
   * priority.
   */
  void addFirst(Source source, SourcePriority priority) {
    int queueCount = _workQueues.length;
    int ordinal = priority.ordinal;
    for (int i = 0; i < queueCount; i++) {
      List<Source> queue = _workQueues[i];
      if (i == ordinal) {
        queue.remove(source);
        queue.insert(0, source);
      } else {
        queue.remove(source);
      }
    }
  }

  /**
   * Return an iterator that can be used to access the sources to be analyzed in
   * the order in which they should be analyzed.
   *
   * <b>Note:</b> As with other iterators, no sources can be added or removed
   * from this work manager while the iterator is being used. Unlike some
   * implementations, however, the iterator will not detect when this
   * requirement has been violated; it might work correctly, it might return the
   * wrong source, or it might throw an exception.
   */
  WorkManager_WorkIterator iterator() => new WorkManager_WorkIterator(this);

  /**
   * Record that the given source is fully analyzed.
   */
  void remove(Source source) {
    int queueCount = _workQueues.length;
    for (int i = 0; i < queueCount; i++) {
      _workQueues[i].remove(source);
    }
  }

  @override
  String toString() {
    StringBuffer buffer = new StringBuffer();
    List<SourcePriority> priorities = SourcePriority.values;
    bool needsSeparator = false;
    int queueCount = _workQueues.length;
    for (int i = 0; i < queueCount; i++) {
      List<Source> queue = _workQueues[i];
      if (!queue.isEmpty) {
        if (needsSeparator) {
          buffer.write("; ");
        }
        buffer.write(priorities[i]);
        buffer.write(": ");
        int queueSize = queue.length;
        for (int j = 0; j < queueSize; j++) {
          if (j > 0) {
            buffer.write(", ");
          }
          buffer.write(queue[j].fullName);
        }
        needsSeparator = true;
      }
    }
    return buffer.toString();
  }
}

/**
 * An iterator that returns the sources in a work manager in the order in which
 * they are to be analyzed.
 */
class WorkManager_WorkIterator {
  final WorkManager _manager;

  /**
   * The index of the work queue through which we are currently iterating.
   */
  int _queueIndex = 0;

  /**
   * The index of the next element of the work queue to be returned.
   */
  int _index = -1;

  /**
   * Initialize a newly created iterator to be ready to return the first element
   * in the iteration.
   */
  WorkManager_WorkIterator(this._manager) {
    _advance();
  }

  /**
   * Return `true` if there is another [Source] available for processing.
   */
  bool get hasNext => _queueIndex < _manager._workQueues.length;

  /**
   * Return the next [Source] available for processing and advance so that the
   * returned source will not be returned again.
   */
  Source next() {
    if (!hasNext) {
      throw new NoSuchElementException();
    }
    Source source = _manager._workQueues[_queueIndex][_index];
    _advance();
    return source;
  }

  /**
   * Increment the [index] and [queueIndex] so that they are either indicating
   * the next source to be returned or are indicating that there are no more
   * sources to be returned.
   */
  void _advance() {
    _index++;
    if (_index >= _manager._workQueues[_queueIndex].length) {
      _index = 0;
      _queueIndex++;
      while (_queueIndex < _manager._workQueues.length &&
          _manager._workQueues[_queueIndex].isEmpty) {
        _queueIndex++;
      }
    }
  }
}

/**
 * A helper class used to create futures for AnalysisContextImpl. Using a helper
 * class allows us to preserve the generic parameter T.
 */
class _AnalysisFutureHelper<T> {
  final AnalysisContextImpl _context;

  _AnalysisFutureHelper(this._context);

  /**
   * Return a future that will be completed with the result of calling
   * [computeValue].  If [computeValue] returns non-null, the future will be
   * completed immediately with the resulting value.  If it returns null, then
   * it will be re-executed in the future, after the next time the cached
   * information for [source] has changed.  If [computeValue] throws an
   * exception, the future will fail with that exception.
   *
   * If the [computeValue] still returns null after there is no further
   * analysis to be done for [source], then the future will be completed with
   * the error AnalysisNotScheduledError.
   *
   * Since [computeValue] will be called while the state of analysis is being
   * updated, it should be free of side effects so that it doesn't cause
   * reentrant changes to the analysis state.
   */
  CancelableFuture<T> computeAsync(
      Source source, T computeValue(SourceEntry sourceEntry)) {
    if (_context.isDisposed) {
      // No further analysis is expected, so return a future that completes
      // immediately with AnalysisNotScheduledError.
      return new CancelableFuture.error(new AnalysisNotScheduledError());
    }
    SourceEntry sourceEntry = _context.getReadableSourceEntryOrNull(source);
    if (sourceEntry == null) {
      return new CancelableFuture.error(new AnalysisNotScheduledError());
    }
    PendingFuture pendingFuture =
        new PendingFuture<T>(_context, source, computeValue);
    if (!pendingFuture.evaluate(sourceEntry)) {
      _context._pendingFutureSources
          .putIfAbsent(source, () => <PendingFuture>[])
          .add(pendingFuture);
    }
    return pendingFuture.future;
  }
}