// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:async';
import 'dart:collection';
import 'dart:typed_data';

import 'package:analyzer/context/declared_variables.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/element/element.dart' show CompilationUnitElement;
import 'package:analyzer/error/error.dart';
import 'package:analyzer/error/listener.dart';
import 'package:analyzer/exception/exception.dart';
import 'package:analyzer/file_system/file_system.dart';
import 'package:analyzer/src/context/context.dart';
import 'package:analyzer/src/dart/analysis/byte_store.dart';
import 'package:analyzer/src/dart/analysis/file_state.dart';
import 'package:analyzer/src/dart/analysis/index.dart';
import 'package:analyzer/src/dart/analysis/search.dart';
import 'package:analyzer/src/dart/analysis/status.dart';
import 'package:analyzer/src/dart/analysis/top_level_declaration.dart';
import 'package:analyzer/src/generated/engine.dart'
    show AnalysisContext, AnalysisEngine, AnalysisOptions;
import 'package:analyzer/src/generated/source.dart';
import 'package:analyzer/src/services/lint.dart';
import 'package:analyzer/src/summary/api_signature.dart';
import 'package:analyzer/src/summary/format.dart';
import 'package:analyzer/src/summary/idl.dart';
import 'package:analyzer/src/summary/link.dart';
import 'package:analyzer/src/summary/package_bundle_reader.dart';
import 'package:analyzer/src/task/dart.dart' show COMPILATION_UNIT_ELEMENT;
import 'package:analyzer/task/dart.dart' show LibrarySpecificUnit;
import 'package:meta/meta.dart';

/**
 * This class computes [AnalysisResult]s for Dart files.
 *
 * Let the set of "explicitly analyzed files" denote the set of paths that have
 * been passed to [addFile] but not subsequently passed to [removeFile]. Let
 * the "current analysis results" denote the map from the set of explicitly
 * analyzed files to the most recent [AnalysisResult] delivered to [results]
 * for each file. Let the "current file state" represent a map from file path
 * to the file contents most recently read from that file, or fetched from the
 * content cache (considering all possible possible file paths, regardless of
 * whether they're in the set of explicitly analyzed files). Let the
 * "analysis state" be either "analyzing" or "idle".
 *
 * (These are theoretical constructs; they may not necessarily reflect data
 * structures maintained explicitly by the driver).
 *
 * Then we make the following guarantees:
 *
 *    - Whenever the analysis state is idle, the current analysis results are
 *      consistent with the current file state.
 *
 *    - A call to [addFile] or [changeFile] causes the analysis state to
 *      transition to "analyzing", and schedules the contents of the given
 *      files to be read into the current file state prior to the next time
 *      the analysis state transitions back to "idle".
 *
 *    - If at any time the client stops making calls to [addFile], [changeFile],
 *      and [removeFile], the analysis state will eventually transition back to
 *      "idle" after a finite amount of processing.
 *
 * As a result of these guarantees, a client may ensure that the analysis
 * results are "eventually consistent" with the file system by simply calling
 * [changeFile] any time the contents of a file on the file system have changed.
 *
 *
 * TODO(scheglov) Clean up the list of implicitly analyzed files.
 */
class AnalysisDriver {
  /**
   * The version of data format, should be incremented on every format change.
   */
  static const int DATA_VERSION = 13;

  /**
   * The name of the driver, e.g. the name of the folder.
   */
  final String name;

  /**
   * The scheduler that schedules analysis work in this, and possibly other
   * analysis drivers.
   */
  final AnalysisDriverScheduler _scheduler;

  /**
   * The logger to write performed operations and performance to.
   */
  final PerformanceLog _logger;

  /**
   * The resource provider for working with files.
   */
  final ResourceProvider _resourceProvider;

  /**
   * The byte storage to get and put serialized data.
   *
   * It can be shared with other [AnalysisDriver]s.
   */
  final ByteStore _byteStore;

  /**
   * This [ContentCache] is consulted for a file content before reading
   * the content from the file.
   */
  final FileContentOverlay _contentOverlay;

  /**
   * The analysis options to analyze with.
   */
  AnalysisOptions _analysisOptions;

  /**
   * The optional SDK bundle, used when the client cannot read SDK files.
   */
  final PackageBundle _sdkBundle;

  /**
   * The [SourceFactory] is used to resolve URIs to paths and restore URIs
   * from file paths.
   */
  SourceFactory _sourceFactory;

  /**
   * The declared environment variables.
   */
  final DeclaredVariables declaredVariables = new DeclaredVariables();

  /**
   * The salt to mix into all hashes used as keys for serialized data.
   */
  final Uint32List _salt = new Uint32List(1 + AnalysisOptions.signatureLength);

  /**
   * The current file system state.
   */
  FileSystemState _fsState;

  /**
   * The set of added files.
   */
  final _addedFiles = new LinkedHashSet<String>();

  /**
   * The set of priority files, that should be analyzed sooner.
   */
  final _priorityFiles = new LinkedHashSet<String>();

  /**
   * The mapping from the files for which analysis was requested using
   * [getResult] to the [Completer]s to report the result.
   */
  final _requestedFiles = <String, List<Completer<AnalysisResult>>>{};

  /**
   * The list of tasks to compute files referencing a name.
   */
  final _referencingNameTasks = <_FilesReferencingNameTask>[];

  /**
   * The list of tasks to compute top-level declarations of a name.
   */
  final _topLevelNameDeclarationsTasks = <_TopLevelNameDeclarationsTask>[];

  /**
   * The mapping from the files for which the index was requested using
   * [getIndex] to the [Completer]s to report the result.
   */
  final _indexRequestedFiles =
      <String, List<Completer<AnalysisDriverUnitIndex>>>{};

  /**
   * The mapping from the files for which the index was requested using
   * [getIndex] to the [Completer]s to report the result.
   */
  final _unitElementRequestedFiles =
      <String, List<Completer<CompilationUnitElement>>>{};

  /**
   * The set of files were reported as changed through [changeFile] and not
   * checked for actual changes yet.
   */
  final _changedFiles = new LinkedHashSet<String>();

  /**
   * The set of files that are currently scheduled for analysis.
   */
  final _filesToAnalyze = new LinkedHashSet<String>();

  /**
   * The mapping from the files for which analysis was requested using
   * [getResult], and which were found to be parts without known libraries,
   * to the [Completer]s to report the result.
   */
  final _requestedParts = <String, List<Completer<AnalysisResult>>>{};

  /**
   * The set of part files that are currently scheduled for analysis.
   */
  final _partsToAnalyze = new LinkedHashSet<String>();

  /**
   * The controller for the [results] stream.
   */
  final _resultController = new StreamController<AnalysisResult>();

  /**
   * Cached results for [_priorityFiles].
   */
  final Map<String, AnalysisResult> _priorityResults = {};

  /**
   * The instance of the status helper.
   */
  final StatusSupport _statusSupport = new StatusSupport();

  /**
   * The controller for the [exceptions] stream.
   */
  final StreamController<ExceptionResult> _exceptionController =
      new StreamController<ExceptionResult>();

  /**
   * The instance of the [Search] helper.
   */
  Search _search;

  AnalysisDriverTestView _testView;

  /**
   * Create a new instance of [AnalysisDriver].
   *
   * The given [SourceFactory] is cloned to ensure that it does not contain a
   * reference to a [AnalysisContext] in which it could have been used.
   */
  AnalysisDriver(
      this._scheduler,
      this._logger,
      this._resourceProvider,
      this._byteStore,
      this._contentOverlay,
      this.name,
      SourceFactory sourceFactory,
      this._analysisOptions,
      {PackageBundle sdkBundle})
      : _sourceFactory = sourceFactory.clone(),
        _sdkBundle = sdkBundle {
    _testView = new AnalysisDriverTestView(this);
    _fillSalt();
    _fsState = new FileSystemState(_logger, _byteStore, _contentOverlay,
        _resourceProvider, sourceFactory, _analysisOptions, _salt);
    _scheduler._add(this);
    _search = new Search(this);
  }

  /**
   * Return the set of files explicitly added to analysis using [addFile].
   */
  Set<String> get addedFiles => _addedFiles;

  /**
   * Return the analysis options used to control analysis.
   */
  AnalysisOptions get analysisOptions => _analysisOptions;

  /**
   * Return the stream that produces [ExceptionResult]s.
   */
  Stream<ExceptionResult> get exceptions => _exceptionController.stream;

  /**
   * The current file system state.
   */
  FileSystemState get fsState => _fsState;

  /**
   * Return `true` if the driver has a file to analyze.
   */
  bool get hasFilesToAnalyze {
    return _changedFiles.isNotEmpty ||
        _requestedFiles.isNotEmpty ||
        _requestedParts.isNotEmpty ||
        _filesToAnalyze.isNotEmpty ||
        _partsToAnalyze.isNotEmpty;
  }

  /**
   * Return the set of files that are known at this moment. This set does not
   * always include all added files or all implicitly used file. If a file has
   * not been processed yet, it might be missing.
   */
  Set<String> get knownFiles => _fsState.knownFilePaths;

  /**
   * Return the number of files scheduled for analysis.
   */
  int get numberOfFilesToAnalyze => _filesToAnalyze.length;

  /**
   * Return the list of files that the driver should try to analyze sooner.
   */
  List<String> get priorityFiles => _priorityFiles.toList(growable: false);

  /**
   * Set the list of files that the driver should try to analyze sooner.
   *
   * Every path in the list must be absolute and normalized.
   *
   * The driver will produce the results through the [results] stream. The
   * exact order in which results are produced is not defined, neither
   * between priority files, nor between priority and non-priority files.
   */
  void set priorityFiles(List<String> priorityPaths) {
    _priorityResults.keys
        .toSet()
        .difference(priorityPaths.toSet())
        .forEach(_priorityResults.remove);
    _priorityFiles.clear();
    _priorityFiles.addAll(priorityPaths);
    _statusSupport.transitionToAnalyzing();
    _scheduler._notify(this);
  }

  /**
   * Return the [Stream] that produces [AnalysisResult]s for added files.
   *
   * Note that the stream supports only one single subscriber.
   *
   * Analysis starts when the [AnalysisDriverScheduler] is started and the
   * driver is added to it. The analysis state transitions to "analyzing" and
   * an analysis result is produced for every added file prior to the next time
   * the analysis state transitions to "idle".
   *
   * At least one analysis result is produced for every file passed to
   * [addFile] or [changeFile] prior to the next time the analysis state
   * transitions to "idle", unless the file is later removed from analysis
   * using [removeFile]. Analysis results for other files are produced only if
   * the changes affect analysis results of other files.
   *
   * More than one result might be produced for the same file, even if the
   * client does not change the state of the files.
   *
   * Results might be produced even for files that have never been added
   * using [addFile], for example when [getResult] was called for a file.
   */
  Stream<AnalysisResult> get results => _resultController.stream;

  /**
   * Return the search support for the driver.
   */
  Search get search => _search;

  /**
   * Return the source factory used to resolve URIs to paths and restore URIs
   * from file paths.
   */
  SourceFactory get sourceFactory => _sourceFactory;

  /**
   * Return the stream that produces [AnalysisStatus] events.
   */
  Stream<AnalysisStatus> get status => _statusSupport.stream;

  @visibleForTesting
  AnalysisDriverTestView get test => _testView;

  /**
   * Return the priority of work that the driver needs to perform.
   */
  AnalysisDriverPriority get _workPriority {
    if (_requestedFiles.isNotEmpty) {
      return AnalysisDriverPriority.interactive;
    }
    if (_referencingNameTasks.isNotEmpty) {
      return AnalysisDriverPriority.interactive;
    }
    if (_indexRequestedFiles.isNotEmpty) {
      return AnalysisDriverPriority.interactive;
    }
    if (_unitElementRequestedFiles.isNotEmpty) {
      return AnalysisDriverPriority.interactive;
    }
    if (_topLevelNameDeclarationsTasks.isNotEmpty) {
      return AnalysisDriverPriority.interactive;
    }
    if (_priorityFiles.isNotEmpty) {
      for (String path in _priorityFiles) {
        if (_filesToAnalyze.contains(path)) {
          return AnalysisDriverPriority.priority;
        }
      }
    }
    if (_filesToAnalyze.isNotEmpty) {
      return AnalysisDriverPriority.general;
    }
    if (_changedFiles.isNotEmpty) {
      return AnalysisDriverPriority.general;
    }
    if (_requestedParts.isNotEmpty || _partsToAnalyze.isNotEmpty) {
      return AnalysisDriverPriority.general;
    }
    _statusSupport.transitionToIdle();
    return AnalysisDriverPriority.nothing;
  }

  /**
   * Add the file with the given [path] to the set of files to analyze.
   *
   * The [path] must be absolute and normalized.
   *
   * The results of analysis are eventually produced by the [results] stream.
   */
  void addFile(String path) {
    if (AnalysisEngine.isDartFileName(path)) {
      _addedFiles.add(path);
      _filesToAnalyze.add(path);
      _priorityResults.clear();
    }
    _statusSupport.transitionToAnalyzing();
    _scheduler._notify(this);
  }

  /**
   * The file with the given [path] might have changed - updated, added or
   * removed. Or not, we don't know. Or it might have, but then changed back.
   *
   * The [path] must be absolute and normalized.
   *
   * The [path] can be any file - explicitly or implicitly analyzed, or neither.
   *
   * Causes the analysis state to transition to "analyzing" (if it is not in
   * that state already). Schedules the file contents for [path] to be read
   * into the current file state prior to the next time the analysis state
   * transitions to "idle".
   *
   * Invocation of this method will not prevent a [Future] returned from
   * [getResult] from completing with a result, but the result is not
   * guaranteed to be consistent with the new current file state after this
   * [changeFile] invocation.
   */
  void changeFile(String path) {
    _changedFiles.add(path);
    if (_addedFiles.contains(path)) {
      _filesToAnalyze.add(path);
    }
    _priorityResults.clear();
    _statusSupport.transitionToAnalyzing();
    _scheduler._notify(this);
  }

  /**
   * Some state on which analysis depends has changed, so the driver needs to be
   * re-configured with the new state.
   *
   * At least one of the optional parameters should be provided, but only those
   * that represent state that has actually changed need be provided.
   */
  void configure(
      {AnalysisOptions analysisOptions, SourceFactory sourceFactory}) {
    if (analysisOptions != null) {
      _analysisOptions = analysisOptions;
    }
    if (sourceFactory != null) {
      _sourceFactory = sourceFactory;
    }
    _fillSalt();
    _fsState = new FileSystemState(_logger, _byteStore, _contentOverlay,
        _resourceProvider, _sourceFactory, _analysisOptions, _salt);
    _filesToAnalyze.addAll(_addedFiles);
    _statusSupport.transitionToAnalyzing();
    _scheduler._notify(this);
  }

  /**
   * Notify the driver that the client is going to stop using it.
   */
  void dispose() {
    _scheduler._remove(this);
  }

  /**
   * Return a [Future] that completes with the list of added files that
   * reference the given external [name].
   */
  Future<List<String>> getFilesReferencingName(String name) {
    var task = new _FilesReferencingNameTask(this, name);
    _referencingNameTasks.add(task);
    _statusSupport.transitionToAnalyzing();
    _scheduler._notify(this);
    return task.completer.future;
  }

  /**
   * Return a [Future] that completes with the [AnalysisDriverUnitIndex] for
   * the file with the given [path].
   */
  Future<AnalysisDriverUnitIndex> getIndex(String path) {
    var completer = new Completer<AnalysisDriverUnitIndex>();
    _indexRequestedFiles
        .putIfAbsent(path, () => <Completer<AnalysisDriverUnitIndex>>[])
        .add(completer);
    _statusSupport.transitionToAnalyzing();
    _scheduler._notify(this);
    return completer.future;
  }

  /**
   * Return a [Future] that completes with a [AnalysisResult] for the Dart
   * file with the given [path]. If the file is not a Dart file, the [Future]
   * completes with `null`.
   *
   * The [path] must be absolute and normalized.
   *
   * The [path] can be any file - explicitly or implicitly analyzed, or neither.
   *
   * If the driver has the cached analysis result for the file, it is returned.
   *
   * Otherwise causes the analysis state to transition to "analyzing" (if it is
   * not in that state already), the driver will read the file and produce the
   * analysis result for it, which is consistent with the current file state
   * (including the new state of the file), prior to the next time the analysis
   * state transitions to "idle".
   */
  Future<AnalysisResult> getResult(String path) {
    // Return the cached result.
    {
      AnalysisResult result = _priorityResults[path];
      if (result != null) {
        return new Future.value(result);
      }
    }

    // Schedule analysis.
    var completer = new Completer<AnalysisResult>();
    _requestedFiles
        .putIfAbsent(path, () => <Completer<AnalysisResult>>[])
        .add(completer);
    _statusSupport.transitionToAnalyzing();
    _scheduler._notify(this);
    return completer.future;
  }

  /**
   * Return a [Future] that completes with top-level declarations with the
   * given [name] in all known libraries.
   */
  Future<List<TopLevelDeclarationInSource>> getTopLevelNameDeclarations(
      String name) {
    var task = new _TopLevelNameDeclarationsTask(this, name);
    _topLevelNameDeclarationsTasks.add(task);
    _statusSupport.transitionToAnalyzing();
    _scheduler._notify(this);
    return task.completer.future;
  }

  /**
   * Return a [Future] that completes with the [CompilationUnitElement] for the
   * file with the given [path].
   */
  Future<CompilationUnitElement> getUnitElement(String path) {
    var completer = new Completer<CompilationUnitElement>();
    _unitElementRequestedFiles
        .putIfAbsent(path, () => <Completer<CompilationUnitElement>>[])
        .add(completer);
    _statusSupport.transitionToAnalyzing();
    _scheduler._notify(this);
    return completer.future;
  }

  /**
   * Return a [Future] that completes with a [ParseResult] for the file
   * with the given [path].
   *
   * The [path] must be absolute and normalized.
   *
   * The [path] can be any file - explicitly or implicitly analyzed, or neither.
   *
   * The parsing is performed in the method itself, and the result is not
   * produced through the [results] stream (just because it is not a fully
   * resolved unit).
   */
  Future<ParseResult> parseFile(String path) async {
    FileState file = _verifyApiSignature(path);
    RecordingErrorListener listener = new RecordingErrorListener();
    CompilationUnit unit = file.parse(listener);
    return new ParseResult(file.path, file.uri, file.content, file.contentHash,
        unit.lineInfo, unit, listener.errors);
  }

  /**
   * Remove the file with the given [path] from the list of files to analyze.
   *
   * The [path] must be absolute and normalized.
   *
   * The results of analysis of the file might still be produced by the
   * [results] stream. The driver will try to stop producing these results,
   * but does not guarantee this.
   */
  void removeFile(String path) {
    _addedFiles.remove(path);
    _filesToAnalyze.remove(path);
    _fsState.removeFile(path);
    _filesToAnalyze.addAll(_addedFiles);
    _priorityResults.clear();
    _statusSupport.transitionToAnalyzing();
    _scheduler._notify(this);
  }

  /**
   * Return a future that will be completed the next time the status is idle.
   *
   * If the status is currently idle, the returned future will be signaled
   * immediately.
   */
  Future<Null> waitForIdle() => _statusSupport.waitForIdle();

  /**
   * Return the cached or newly computed analysis result of the file with the
   * given [path].
   *
   * The result will have the fully resolved unit and will always be newly
   * compute only if [withUnit] is `true`.
   *
   * Return `null` if the file is a part of an unknown library, so cannot be
   * analyzed yet. But [asIsIfPartWithoutLibrary] is `true`, then the file is
   * analyzed anyway, even without a library.
   */
  AnalysisResult _computeAnalysisResult(String path,
      {bool withUnit: false, bool asIsIfPartWithoutLibrary: false}) {
    /**
     * If the [file] is a library, return the [file] itself.
     * If the [file] is a part, return a library it is known to be a part of.
     * If there is no such library, return `null`.
     */
    FileState getLibraryFile(FileState file) {
      FileState libraryFile = file.isPart ? file.library : file;
      if (libraryFile == null && asIsIfPartWithoutLibrary) {
        libraryFile = file;
      }
      return libraryFile;
    }

    // If we don't need the fully resolved unit, check for the cached result.
    if (!withUnit) {
      FileState file = _fsState.getFileForPath(path);

      // Prepare the library file - the file itself, or the known library.
      FileState libraryFile = getLibraryFile(file);
      if (libraryFile == null) {
        return null;
      }

      // Check for the cached result.
      String key = _getResolvedUnitKey(libraryFile, file);
      List<int> bytes = _byteStore.get(key);
      if (bytes != null) {
        return _getAnalysisResultFromBytes(file, bytes);
      }
    }

    // We need the fully resolved unit, or the result is not cached.
    return _logger.run('Compute analysis result for $path', () {
      FileState file = _verifyApiSignature(path);

      // Prepare the library file - the file itself, or the known library.
      FileState libraryFile = getLibraryFile(file);
      if (libraryFile == null) {
        return null;
      }

      _LibraryContext libraryContext = _createLibraryContext(libraryFile);
      AnalysisContext analysisContext = _createAnalysisContext(libraryContext);
      try {
        CompilationUnit resolvedUnit = analysisContext.resolveCompilationUnit2(
            file.source, libraryFile.source);
        List<AnalysisError> errors = analysisContext.computeErrors(file.source);
        AnalysisDriverUnitIndexBuilder index = indexUnit(resolvedUnit);

        // Store the result into the cache.
        List<int> bytes;
        {
          bytes = new AnalysisDriverResolvedUnitBuilder(
                  errors: errors
                      .map((error) => new AnalysisDriverUnitErrorBuilder(
                          offset: error.offset,
                          length: error.length,
                          uniqueName: error.errorCode.uniqueName,
                          message: error.message,
                          correction: error.correction))
                      .toList(),
                  index: index)
              .toBuffer();
          String key = _getResolvedUnitKey(libraryFile, file);
          _byteStore.put(key, bytes);
        }

        // Return the result, full or partial.
        _logger.writeln('Computed new analysis result.');
        AnalysisResult result = _getAnalysisResultFromBytes(file, bytes,
            content: withUnit ? file.content : null,
            withErrors: _addedFiles.contains(path),
            resolvedUnit: withUnit ? resolvedUnit : null);
        if (withUnit && _priorityFiles.contains(path)) {
          _priorityResults[path] = result;
        }
        return result;
      } finally {
        analysisContext.dispose();
      }
    });
  }

  AnalysisDriverUnitIndex _computeIndex(String path) {
    AnalysisResult analysisResult = _computeAnalysisResult(path,
        withUnit: false, asIsIfPartWithoutLibrary: true);
    return analysisResult._index;
  }

  CompilationUnitElement _computeUnitElement(String path) {
    FileState file = _fsState.getFileForPath(path);
    FileState libraryFile = file.library ?? file;

    // Create the AnalysisContext to resynthesize elements in.
    _LibraryContext libraryContext = _createLibraryContext(libraryFile);
    AnalysisContext analysisContext = _createAnalysisContext(libraryContext);

    // Resynthesize the CompilationUnitElement in the context.
    try {
      return analysisContext.computeResult(
          new LibrarySpecificUnit(libraryFile.source, file.source),
          COMPILATION_UNIT_ELEMENT);
    } finally {
      analysisContext.dispose();
    }
  }

  AnalysisContext _createAnalysisContext(_LibraryContext libraryContext) {
    AnalysisContextImpl analysisContext =
        AnalysisEngine.instance.createAnalysisContext();
    analysisContext.useSdkCachePartition = false;
    analysisContext.analysisOptions = _analysisOptions;
    analysisContext.declaredVariables.addAll(declaredVariables);
    analysisContext.sourceFactory = _sourceFactory.clone();
    analysisContext.contentCache = new _ContentCacheWrapper(_fsState);
    analysisContext.resultProvider =
        new InputPackagesResultProvider(analysisContext, libraryContext.store);
    return analysisContext;
  }

  /**
   * Return the context in which the [library] should be analyzed it.
   */
  _LibraryContext _createLibraryContext(FileState library) {
    return _logger.run('Create library context', () {
      Map<String, FileState> libraries = <String, FileState>{};
      SummaryDataStore store = new SummaryDataStore(const <String>[]);

      if (_sdkBundle != null) {
        store.addBundle(null, _sdkBundle);
      }

      void appendLibraryFiles(FileState library) {
        if (!libraries.containsKey(library.uriStr)) {
          // Serve 'dart:' URIs from the SDK bundle.
          if (_sdkBundle != null && library.uri.scheme == 'dart') {
            return;
          }

          libraries[library.uriStr] = library;

          // Append the defining unit.
          store.addUnlinkedUnit(library.uriStr, library.unlinked);

          // Append parts.
          for (FileState part in library.partedFiles) {
            store.addUnlinkedUnit(part.uriStr, part.unlinked);
          }

          // Append referenced libraries.
          library.importedFiles.forEach(appendLibraryFiles);
          library.exportedFiles.forEach(appendLibraryFiles);
        }
      }

      _logger.run('Append library files', () {
        return appendLibraryFiles(library);
      });

      Set<String> libraryUrisToLink = new Set<String>();
      _logger.run('Load linked bundles', () {
        for (FileState library in libraries.values) {
          if (library.exists) {
            String key = '${library.transitiveSignature}.linked';
            List<int> bytes = _byteStore.get(key);
            if (bytes != null) {
              LinkedLibrary linked = new LinkedLibrary.fromBuffer(bytes);
              store.addLinkedLibrary(library.uriStr, linked);
            } else {
              libraryUrisToLink.add(library.uriStr);
            }
          }
        }
        int numOfLoaded = libraries.length - libraryUrisToLink.length;
        _logger.writeln('Loaded $numOfLoaded linked bundles.');
      });

      Map<String, LinkedLibraryBuilder> linkedLibraries = {};
      _logger.run('Link bundles', () {
        linkedLibraries = link(libraryUrisToLink, (String uri) {
          LinkedLibrary linkedLibrary = store.linkedMap[uri];
          return linkedLibrary;
        }, (String uri) {
          UnlinkedUnit unlinkedUnit = store.unlinkedMap[uri];
          return unlinkedUnit;
        }, (_) => null, _analysisOptions.strongMode);
        _logger.writeln('Linked ${linkedLibraries.length} bundles.');
      });

      linkedLibraries.forEach((uri, linkedBuilder) {
        FileState library = libraries[uri];
        String key = '${library.transitiveSignature}.linked';
        List<int> bytes = linkedBuilder.toBuffer();
        LinkedLibrary linked = new LinkedLibrary.fromBuffer(bytes);
        store.addLinkedLibrary(uri, linked);
        _byteStore.put(key, bytes);
      });

      return new _LibraryContext(library, store);
    });
  }

  /**
   * Fill [_salt] with data.
   */
  void _fillSalt() {
    _salt[0] = DATA_VERSION;
    List<int> crossContextOptions = _analysisOptions.signature;
    assert(crossContextOptions.length == AnalysisOptions.signatureLength);
    for (int i = 0; i < crossContextOptions.length; i++) {
      _salt[i + 1] = crossContextOptions[i];
    }
  }

  /**
   * Load the [AnalysisResult] for the given [file] from the [bytes]. Set
   * optional [content] and [resolvedUnit].
   */
  AnalysisResult _getAnalysisResultFromBytes(FileState file, List<int> bytes,
      {String content, bool withErrors: true, CompilationUnit resolvedUnit}) {
    var unit = new AnalysisDriverResolvedUnit.fromBuffer(bytes);
    List<AnalysisError> errors = withErrors
        ? _getErrorsFromSerialized(file, unit.errors)
        : const <AnalysisError>[];
    return new AnalysisResult(
        this,
        _sourceFactory,
        file.path,
        file.uri,
        file.exists,
        content,
        file.contentHash,
        file.lineInfo,
        resolvedUnit,
        errors,
        unit.index);
  }

  /**
   * Return [AnalysisError]s for the given [serialized] errors.
   */
  List<AnalysisError> _getErrorsFromSerialized(
      FileState file, List<AnalysisDriverUnitError> serialized) {
    return serialized.map((error) {
      String errorName = error.uniqueName;
      ErrorCode errorCode =
          errorCodeByUniqueName(errorName) ?? _lintCodeByUniqueName(errorName);
      if (errorCode == null) {
        // This could fail because the error code is no longer defined, or, in
        // the case of a lint rule, if the lint rule has been disabled since the
        // errors were written.
        throw new StateError('No ErrorCode for $errorName in $file');
      }
      return new AnalysisError.forValues(file.source, error.offset,
          error.length, errorCode, error.message, error.correction);
    }).toList();
  }

  /**
   * Return the key to store fully resolved results for the [file] in the
   * [library] into the cache. Return `null` if the dependency signature is
   * not known yet.
   */
  String _getResolvedUnitKey(FileState library, FileState file) {
    ApiSignature signature = new ApiSignature();
    signature.addUint32List(_salt);
    signature.addString(library.transitiveSignature);
    signature.addString(file.contentHash);
    return '${signature.toHex()}.resolved';
  }

  /**
   * Return the lint code with the given [errorName], or `null` if there is no
   * lint registered with that name or the lint is not enabled in the analysis
   * options.
   */
  ErrorCode _lintCodeByUniqueName(String errorName) {
    if (errorName.startsWith('_LintCode.')) {
      String lintName = errorName.substring(10);
      List<Linter> lintRules = _analysisOptions.lintRules;
      for (Linter linter in lintRules) {
        if (linter.name == lintName) {
          return linter.lintCode;
        }
      }
    }
    return null;
  }

  /**
   * Perform a single chunk of work and produce [results].
   */
  Future<Null> _performWork() async {
    // Verify all changed files one at a time.
    if (_changedFiles.isNotEmpty) {
      String path = _removeFirst(_changedFiles);
      // If the file has not been accessed yet, we either will eventually read
      // it later while analyzing one of the added files, or don't need it.
      if (_fsState.knownFilePaths.contains(path)) {
        _verifyApiSignature(path);
      }
      return;
    }

    // Analyze a requested file.
    if (_requestedFiles.isNotEmpty) {
      String path = _requestedFiles.keys.first;
      try {
        AnalysisResult result = _computeAnalysisResult(path, withUnit: true);
        // If a part without a library, delay its analysis.
        if (result == null) {
          _requestedParts
              .putIfAbsent(path, () => [])
              .addAll(_requestedFiles.remove(path));
          return;
        }
        // Notify the completers.
        _requestedFiles.remove(path).forEach((completer) {
          completer.complete(result);
        });
        // Remove from to be analyzed and produce it now.
        _filesToAnalyze.remove(path);
        _resultController.add(result);
      } catch (exception, stackTrace) {
        _filesToAnalyze.remove(path);
        _requestedFiles.remove(path).forEach((completer) {
          completer.completeError(exception, stackTrace);
        });
      }
      return;
    }

    // Process an index request.
    if (_indexRequestedFiles.isNotEmpty) {
      String path = _indexRequestedFiles.keys.first;
      AnalysisDriverUnitIndex index = _computeIndex(path);
      _indexRequestedFiles.remove(path).forEach((completer) {
        completer.complete(index);
      });
      return;
    }

    // Process a unit request.
    if (_unitElementRequestedFiles.isNotEmpty) {
      String path = _unitElementRequestedFiles.keys.first;
      CompilationUnitElement unitElement = _computeUnitElement(path);
      _unitElementRequestedFiles.remove(path).forEach((completer) {
        completer.complete(unitElement);
      });
      return;
    }

    // Compute files referencing a name.
    if (_referencingNameTasks.isNotEmpty) {
      _FilesReferencingNameTask task = _referencingNameTasks.first;
      bool isDone = await task.perform();
      if (isDone) {
        _referencingNameTasks.remove(task);
      }
      return;
    }

    // Compute top-level declarations.
    if (_topLevelNameDeclarationsTasks.isNotEmpty) {
      _TopLevelNameDeclarationsTask task = _topLevelNameDeclarationsTasks.first;
      bool isDone = await task.perform();
      if (isDone) {
        _topLevelNameDeclarationsTasks.remove(task);
      }
      return;
    }

    // Analyze a priority file.
    if (_priorityFiles.isNotEmpty) {
      for (String path in _priorityFiles) {
        if (_filesToAnalyze.remove(path)) {
          try {
            AnalysisResult result =
                _computeAnalysisResult(path, withUnit: true);
            if (result == null) {
              _partsToAnalyze.add(path);
            } else {
              _resultController.add(result);
            }
          } catch (exception, stackTrace) {
            _reportError(path, exception, stackTrace);
          }
          return;
        }
      }
    }

    // Analyze a general file.
    if (_filesToAnalyze.isNotEmpty) {
      String path = _removeFirst(_filesToAnalyze);
      try {
        AnalysisResult result = _computeAnalysisResult(path, withUnit: false);
        if (result == null) {
          _partsToAnalyze.add(path);
        } else {
          _resultController.add(result);
        }
      } catch (exception, stackTrace) {
        _reportError(path, exception, stackTrace);
      }
      return;
    }

    // Analyze a requested part file.
    if (_requestedParts.isNotEmpty) {
      String path = _requestedParts.keys.first;
      try {
        AnalysisResult result = _computeAnalysisResult(path,
            withUnit: true, asIsIfPartWithoutLibrary: true);
        // Notify the completers.
        _requestedParts.remove(path).forEach((completer) {
          completer.complete(result);
        });
        // Remove from to be analyzed and produce it now.
        _partsToAnalyze.remove(path);
        _resultController.add(result);
      } catch (exception, stackTrace) {
        _partsToAnalyze.remove(path);
        _requestedParts.remove(path).forEach((completer) {
          completer.completeError(exception, stackTrace);
        });
      }
      return;
    }

    // Analyze a general part.
    if (_partsToAnalyze.isNotEmpty) {
      String path = _removeFirst(_partsToAnalyze);
      try {
        AnalysisResult result = _computeAnalysisResult(path,
            withUnit: _priorityFiles.contains(path),
            asIsIfPartWithoutLibrary: true);
        _resultController.add(result);
      } catch (exception, stackTrace) {
        _reportError(path, exception, stackTrace);
      }
      return;
    }
  }

  void _reportError(String path, exception, StackTrace stackTrace) {
    CaughtException caught = new CaughtException(exception, stackTrace);
    _exceptionController.add(new ExceptionResult(path, caught));
  }

  /**
   * Verify the API signature for the file with the given [path], and decide
   * which linked libraries should be invalidated, and files reanalyzed.
   */
  FileState _verifyApiSignature(String path) {
    return _logger.run('Verify API signature of $path', () {
      bool anyApiChanged = false;
      List<FileState> files = _fsState.getFilesForPath(path);
      for (FileState file in files) {
        bool apiChanged = file.refresh();
        if (apiChanged) {
          anyApiChanged = true;
        }
      }
      if (anyApiChanged) {
        _logger.writeln('API signatures mismatch found for $path');
        // TODO(scheglov) schedule analysis of only affected files
        _filesToAnalyze.addAll(_addedFiles);
      }
      return files[0];
    });
  }

  /**
   * Remove and return the first item in the given [set].
   */
  static Object/*=T*/ _removeFirst/*<T>*/(LinkedHashSet<Object/*=T*/ > set) {
    Object/*=T*/ element = set.first;
    set.remove(element);
    return element;
  }
}

/**
 * Priorities of [AnalysisDriver] work. The farther a priority to the beginning
 * of the list, the earlier the corresponding [AnalysisDriver] should be asked
 * to perform work.
 */
enum AnalysisDriverPriority { nothing, general, priority, interactive }

/**
 * Instances of this class schedule work in multiple [AnalysisDriver]s so that
 * work with the highest priority is performed first.
 */
class AnalysisDriverScheduler {
  /**
   * Time interval in milliseconds before pumping the event queue.
   *
   * Relinquishing execution flow and running the event loop after every task
   * has too much overhead. Instead we use a fixed length of time, so we can
   * spend less time overall and still respond quickly enough.
   */
  static const int _MS_BEFORE_PUMPING_EVENT_QUEUE = 2;

  /**
   * Event queue pumping is required to allow IO and other asynchronous data
   * processing while analysis is active. For example Analysis Server needs to
   * be able to process `updateContent` or `setPriorityFiles` requests while
   * background analysis is in progress.
   *
   * The number of pumpings is arbitrary, might be changed if we see that
   * analysis or other data processing tasks are starving. Ideally we would
   * need to run all asynchronous operations using a single global scheduler.
   */
  static const int _NUMBER_OF_EVENT_QUEUE_PUMPINGS = 128;

  final PerformanceLog _logger;
  final List<AnalysisDriver> _drivers = [];
  final Monitor _hasWork = new Monitor();
  final StatusSupport _statusSupport = new StatusSupport();

  bool _started = false;

  AnalysisDriverScheduler(this._logger);

  /**
   * Return `true` if we are currently analyzing code.
   */
  bool get isAnalyzing => _hasFilesToAnalyze;

  /**
   * Return the stream that produces [AnalysisStatus] events.
   */
  Stream<AnalysisStatus> get status => _statusSupport.stream;

  /**
   * Return `true` if there is a driver with a file to analyze.
   */
  bool get _hasFilesToAnalyze {
    for (AnalysisDriver driver in _drivers) {
      if (driver.hasFilesToAnalyze) {
        return true;
      }
    }
    return false;
  }

  /**
   * Start the scheduler, so that any [AnalysisDriver] created before or
   * after will be asked to perform work.
   */
  void start() {
    if (_started) {
      throw new StateError('The scheduler has already been started.');
    }
    _started = true;
    _run();
  }

  /**
   * Add the given [driver] and schedule it to perform its work.
   */
  void _add(AnalysisDriver driver) {
    _drivers.add(driver);
    _hasWork.notify();
  }

  /**
   * Notify that there is a change to the [driver], it it might need to
   * perform some work.
   */
  void _notify(AnalysisDriver driver) {
    _hasWork.notify();
  }

  /**
   * Remove the given [driver] from the scheduler, so that it will not be
   * asked to perform any new work.
   */
  void _remove(AnalysisDriver driver) {
    _drivers.remove(driver);
    _hasWork.notify();
  }

  /**
   * Run infinitely analysis cycle, selecting the drivers with the highest
   * priority first.
   */
  Future<Null> _run() async {
    Stopwatch timer = new Stopwatch()..start();
    PerformanceLogSection analysisSection;
    while (true) {
      // Pump the event queue.
      if (timer.elapsedMilliseconds > _MS_BEFORE_PUMPING_EVENT_QUEUE) {
        await _pumpEventQueue(_NUMBER_OF_EVENT_QUEUE_PUMPINGS);
        timer.reset();
      }

      await _hasWork.signal;

      // Transition to analyzing if there are files to analyze.
      if (_hasFilesToAnalyze) {
        _statusSupport.transitionToAnalyzing();
        analysisSection ??= _logger.enter('Analyzing');
      }

      // Find the driver with the highest priority.
      AnalysisDriver bestDriver;
      AnalysisDriverPriority bestPriority = AnalysisDriverPriority.nothing;
      for (AnalysisDriver driver in _drivers) {
        AnalysisDriverPriority priority = driver._workPriority;
        if (bestPriority == null || priority.index > bestPriority.index) {
          bestDriver = driver;
          bestPriority = priority;
        }
      }

      // Transition to idle if no files to analyze.
      if (!_hasFilesToAnalyze) {
        _statusSupport.transitionToIdle();
        analysisSection?.exit();
        analysisSection = null;
      }

      // Continue to sleep if no work to do.
      if (bestPriority == AnalysisDriverPriority.nothing) {
        continue;
      }

      // Ask the driver to perform a chunk of work.
      await bestDriver._performWork();

      // Schedule one more cycle.
      _hasWork.notify();
    }
  }

  /**
   * Returns a [Future] that completes after performing [times] pumpings of
   * the event queue.
   */
  static Future _pumpEventQueue(int times) {
    if (times == 0) {
      return new Future.value();
    }
    return new Future.delayed(Duration.ZERO, () => _pumpEventQueue(times - 1));
  }
}

@visibleForTesting
class AnalysisDriverTestView {
  final AnalysisDriver driver;

  AnalysisDriverTestView(this.driver);

  Set<String> get filesToAnalyze => driver._filesToAnalyze;

  Map<String, AnalysisResult> get priorityResults => driver._priorityResults;
}

/**
 * The result of analyzing of a single file.
 *
 * These results are self-consistent, i.e. [content], [contentHash], the
 * resolved [unit] correspond to each other. All referenced elements, even
 * external ones, are also self-consistent. But none of the results is
 * guaranteed to be consistent with the state of the files.
 *
 * Every result is independent, and is not guaranteed to be consistent with
 * any previously returned result, even inside of the same library.
 */
class AnalysisResult {
  /**
   * The [AnalysisDriver] that produced this result.
   */
  final AnalysisDriver driver;

  /**
   * The [SourceFactory] with which the file was analyzed.
   */
  final SourceFactory sourceFactory;

  /**
   * The path of the analysed file, absolute and normalized.
   */
  final String path;

  /**
   * The URI of the file that corresponded to the [path] in the used
   * [SourceFactory] at some point. Is it not guaranteed to be still consistent
   * to the [path], and provided as FYI.
   */
  final Uri uri;

  /**
   * Return `true` if the file exists.
   */
  final bool exists;

  /**
   * The content of the file that was scanned, parsed and resolved.
   */
  final String content;

  /**
   * The MD5 hash of the [content].
   */
  final String contentHash;

  /**
   * Information about lines in the [content].
   */
  final LineInfo lineInfo;

  /**
   * The fully resolved compilation unit for the [content].
   */
  final CompilationUnit unit;

  /**
   * The full list of computed analysis errors, both syntactic and semantic.
   */
  final List<AnalysisError> errors;

  /**
   * The index of the unit.
   */
  final AnalysisDriverUnitIndex _index;

  AnalysisResult(
      this.driver,
      this.sourceFactory,
      this.path,
      this.uri,
      this.exists,
      this.content,
      this.contentHash,
      this.lineInfo,
      this.unit,
      this.errors,
      this._index);
}

/**
 * Exception that happened during analysis.
 */
class ExceptionResult {
  /**
   * The path of the file being analyzed when the [exception] happened.
   *
   * Absolute and normalized.
   */
  final String path;

  /**
   * The exception during analysis of the file with the [path].
   */
  final CaughtException exception;

  ExceptionResult(this.path, this.exception);
}

/**
 * The result of parsing of a single file.
 *
 * These results are self-consistent, i.e. [content], [contentHash], the
 * resolved [unit] correspond to each other. But none of the results is
 * guaranteed to be consistent with the state of the files.
 */
class ParseResult {
  /**
   * The path of the parsed file, absolute and normalized.
   */
  final String path;

  /**
   * The URI of the file that corresponded to the [path].
   */
  final Uri uri;

  /**
   * The content of the file that was scanned and parsed.
   */
  final String content;

  /**
   * The MD5 hash of the [content].
   */
  final String contentHash;

  /**
   * Information about lines in the [content].
   */
  final LineInfo lineInfo;

  /**
   * The parsed, unresolved compilation unit for the [content].
   */
  final CompilationUnit unit;

  /**
   * The scanning and parsing errors.
   */
  final List<AnalysisError> errors;

  ParseResult(this.path, this.uri, this.content, this.contentHash,
      this.lineInfo, this.unit, this.errors);
}

/**
 * This class is used to gather and print performance information.
 */
class PerformanceLog {
  final StringSink sink;
  int _level = 0;

  PerformanceLog(this.sink);

  /**
   * Enter a new execution section, which starts at one point of code, runs
   * some time, and then ends at the other point of code.
   *
   * The client must call [PerformanceLogSection.exit] for every [enter].
   */
  PerformanceLogSection enter(String msg) {
    writeln('+++ $msg.');
    _level++;
    return new PerformanceLogSection(this, msg);
  }

  /**
   * Return the result of the function [f] invocation and log the elapsed time.
   *
   * Each invocation of [run] creates a new enclosed section in the log,
   * which begins with printing [msg], then any log output produced during
   * [f] invocation, and ends with printing [msg] with the elapsed time.
   */
  /*=T*/ run/*<T>*/(String msg, /*=T*/ f()) {
    Stopwatch timer = new Stopwatch()..start();
    try {
      writeln('+++ $msg.');
      _level++;
      return f();
    } finally {
      _level--;
      int ms = timer.elapsedMilliseconds;
      writeln('--- $msg in $ms ms.');
    }
  }

  /**
   * Write a new line into the log.
   */
  void writeln(String msg) {
    if (sink != null) {
      String indent = '\t' * _level;
      sink.writeln('$indent$msg');
    }
  }
}

/**
 * The performance measurement section for operations that start and end
 * at different place in code, so cannot be run using [PerformanceLog.run].
 *
 * The client must call [exit] for every [PerformanceLog.enter].
 */
class PerformanceLogSection {
  final PerformanceLog _logger;
  final String _msg;
  final Stopwatch _timer = new Stopwatch()..start();

  PerformanceLogSection(this._logger, this._msg);

  /**
   * Stop the timer, log the time.
   */
  void exit() {
    _timer.stop();
    _logger._level--;
    int ms = _timer.elapsedMilliseconds;
    _logger.writeln('--- $_msg in $ms ms.');
  }
}

/**
 * [ContentCache] wrapper around [FileContentOverlay].
 */
class _ContentCacheWrapper implements ContentCache {
  final FileSystemState fsState;

  _ContentCacheWrapper(this.fsState);

  @override
  void accept(ContentCacheVisitor visitor) {
    throw new UnimplementedError();
  }

  @override
  String getContents(Source source) {
    return _getFileForSource(source).content;
  }

  @override
  bool getExists(Source source) {
    if (source.isInSystemLibrary) {
      return true;
    }
    return _getFileForSource(source).exists;
  }

  @override
  int getModificationStamp(Source source) {
    if (source.isInSystemLibrary) {
      return 0;
    }
    return _getFileForSource(source).exists ? 0 : -1;
  }

  @override
  String setContents(Source source, String contents) {
    throw new UnimplementedError();
  }

  FileState _getFileForSource(Source source) {
    String path = source.fullName;
    return fsState.getFileForPath(path);
  }
}

/**
 * Task that computes the list of files that were added to the driver and
 * have at least one reference to an identifier [name] defined outside of the
 * file.
 */
class _FilesReferencingNameTask {
  static const int _MS_WORK_INTERVAL = 5;

  final AnalysisDriver driver;
  final String name;
  final Completer<List<String>> completer = new Completer<List<String>>();

  final List<String> referencingFiles = <String>[];
  final Set<String> checkedFiles = new Set<String>();
  final List<String> filesToCheck = <String>[];

  _FilesReferencingNameTask(this.driver, this.name);

  /**
   * Perform work for a fixed length of time, and complete the [completer] to
   * either return `true` to indicate that the task is done, or return `false`
   * to indicate that the task should continue to be run.
   *
   * Each invocation of an asynchronous method has overhead, which looks as
   * `_SyncCompleter.complete` invocation, we see as much as 62% in some
   * scenarios. Instead we use a fixed length of time, so we can spend less time
   * overall and keep quick enough response time.
   */
  Future<bool> perform() async {
    Stopwatch timer = new Stopwatch()..start();
    while (timer.elapsedMilliseconds < _MS_WORK_INTERVAL) {
      // Prepare files to check.
      if (filesToCheck.isEmpty) {
        Set<String> newFiles = driver.addedFiles.difference(checkedFiles);
        filesToCheck.addAll(newFiles);
      }

      // If no more files to check, complete and done.
      if (filesToCheck.isEmpty) {
        completer.complete(referencingFiles);
        return true;
      }

      // Check the next file.
      String path = filesToCheck.removeLast();
      FileState file = driver._fsState.getFileForPath(path);
      if (file.referencedNames.contains(name)) {
        referencingFiles.add(path);
      }
      checkedFiles.add(path);
    }

    // We're not done yet.
    return false;
  }
}

/**
 * TODO(scheglov) document
 */
class _LibraryContext {
  final FileState file;
  final SummaryDataStore store;
  _LibraryContext(this.file, this.store);
}

/**
 * Task that computes top-level declarations for a certain name in all
 * known libraries.
 */
class _TopLevelNameDeclarationsTask {
  final AnalysisDriver driver;
  final String name;
  final Completer<List<TopLevelDeclarationInSource>> completer =
      new Completer<List<TopLevelDeclarationInSource>>();

  final List<TopLevelDeclarationInSource> libraryDeclarations =
      <TopLevelDeclarationInSource>[];
  final Set<String> checkedFiles = new Set<String>();
  final List<String> filesToCheck = <String>[];

  _TopLevelNameDeclarationsTask(this.driver, this.name);

  /**
   * Perform a single piece of work, and either complete the [completer] and
   * return `true` to indicate that the task is done, return `false` to indicate
   * that the task should continue to be run.
   */
  Future<bool> perform() async {
    // Prepare files to check.
    if (filesToCheck.isEmpty) {
      filesToCheck.addAll(driver.addedFiles.difference(checkedFiles));
      filesToCheck.addAll(driver.knownFiles.difference(checkedFiles));
    }

    // If no more files to check, complete and done.
    if (filesToCheck.isEmpty) {
      completer.complete(libraryDeclarations);
      return true;
    }

    // Check the next file.
    String path = filesToCheck.removeLast();
    if (checkedFiles.add(path)) {
      FileState file = driver._fsState.getFileForPath(path);
      if (!file.isPart) {
        bool isExported = false;
        TopLevelDeclaration declaration = file.topLevelDeclarations[name];
        for (FileState part in file.partedFiles) {
          declaration ??= part.topLevelDeclarations[name];
        }
        if (declaration == null) {
          declaration = file.exportedTopLevelDeclarations[name];
          isExported = true;
        }
        if (declaration != null) {
          libraryDeclarations.add(new TopLevelDeclarationInSource(
              file.source, declaration, isExported));
        }
      }
    }

    // We're not done yet.
    return false;
  }
}