Removed fixed dependencies

packages/analyzer/lib/src/summary/pub_summary.dart

+// 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:core';
+
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
+import 'package:analyzer/error/listener.dart';
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer/src/dart/scanner/reader.dart';
+import 'package:analyzer/src/dart/scanner/scanner.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/parser.dart';
+import 'package:analyzer/src/generated/source.dart';
+import 'package:analyzer/src/generated/utilities_collection.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'
+    show ResynthesizerResultProvider, SummaryDataStore;
+import 'package:analyzer/src/summary/summarize_ast.dart'
+    show serializeAstUnlinked;
+import 'package:analyzer/src/summary/summarize_elements.dart'
+    show PackageBundleAssembler;
+import 'package:analyzer/src/util/fast_uri.dart';
+import 'package:convert/convert.dart';
+import 'package:crypto/crypto.dart';
+import 'package:meta/meta.dart';
+import 'package:path/path.dart' as pathos;
+
+/**
+ * Unlinked and linked information about a [PubPackage].
+ */
+class LinkedPubPackage {
+  final PubPackage package;
+  final PackageBundle unlinked;
+  final PackageBundle linked;
+
+  final String linkedHash;
+
+  LinkedPubPackage(this.package, this.unlinked, this.linked, this.linkedHash);
+
+  @override
+  String toString() => package.toString();
+}
+
+/**
+ * A package in the pub cache.
+ */
+class PubPackage {
+  final String name;
+  final Folder libFolder;
+
+  PubPackage(this.name, this.libFolder);
+
+  Folder get folder => libFolder.parent;
+
+  @override
+  int get hashCode => libFolder.hashCode;
+
+  @override
+  bool operator ==(other) {
+    return other is PubPackage && other.libFolder == libFolder;
+  }
+
+  @override
+  String toString() => '($name in $folder)';
+}
+
+/**
+ * Class that manages summaries for pub packages.
+ *
+ * The client should call [getLinkedBundles] after creating a new
+ * [AnalysisContext] and configuring its source factory, but before computing
+ * any analysis results.  The returned linked bundles can be used to create and
+ * configure [ResynthesizerResultProvider] for the context.
+ */
+class PubSummaryManager {
+  static const UNLINKED_NAME = 'unlinked.ds';
+  static const UNLINKED_SPEC_NAME = 'unlinked_spec.ds';
+
+  /**
+   * If `true` (by default), then linking new bundles is allowed.
+   * Otherwise only using existing cached bundles can be used.
+   */
+  final bool allowLinking;
+
+  /**
+   * See [PackageBundleAssembler.currentMajorVersion].
+   */
+  final int majorVersion;
+
+  final ResourceProvider resourceProvider;
+
+  /**
+   * The name of the temporary file that is used for atomic writes.
+   */
+  final String tempFileName;
+
+  /**
+   * The map from [PubPackage]s to their unlinked [PackageBundle]s in the pub
+   * cache.
+   */
+  final Map<PubPackage, PackageBundle> unlinkedBundleMap =
+      new HashMap<PubPackage, PackageBundle>();
+
+  /**
+   * The map from linked file paths to the corresponding linked bundles.
+   */
+  final Map<String, PackageBundle> linkedBundleMap =
+      new HashMap<String, PackageBundle>();
+
+  /**
+   * The set of packages to compute unlinked summaries for.
+   */
+  final Set<PubPackage> packagesToComputeUnlinked = new Set<PubPackage>();
+
+  /**
+   * The set of already processed packages, which we have already checked
+   * for their unlinked bundle existence, or scheduled its computing.
+   */
+  final Set<PubPackage> seenPackages = new Set<PubPackage>();
+
+  /**
+   * The [Completer] that completes when computing of all scheduled unlinked
+   * bundles is complete.
+   */
+  Completer _onUnlinkedCompleteCompleter;
+
+  PubSummaryManager(this.resourceProvider, this.tempFileName,
+      {@visibleForTesting this.allowLinking: true,
+      @visibleForTesting this.majorVersion:
+          PackageBundleAssembler.currentMajorVersion});
+
+  /**
+   * The [Future] that completes when computing of all scheduled unlinked
+   * bundles is complete.
+   */
+  Future get onUnlinkedComplete {
+    if (packagesToComputeUnlinked.isEmpty) {
+      return new Future.value();
+    }
+    _onUnlinkedCompleteCompleter ??= new Completer();
+    return _onUnlinkedCompleteCompleter.future;
+  }
+
+  /**
+   * Return the [pathos.Context] corresponding to the [resourceProvider].
+   */
+  pathos.Context get pathContext => resourceProvider.pathContext;
+
+  /**
+   * Complete when the unlinked bundles for the package with the given [name]
+   * and the [libFolder] are computed and written to the files.
+   *
+   * This method is intended to be used for generating unlinked bundles for
+   * the `Flutter` packages.
+   */
+  Future<Null> computeUnlinkedForFolder(String name, Folder libFolder) async {
+    PubPackage package = new PubPackage(name, libFolder);
+    _scheduleUnlinked(package);
+    await onUnlinkedComplete;
+  }
+
+  /**
+   * Return the list of linked [LinkedPubPackage]s that can be provided at this
+   * time for a subset of the packages used by the given [context].  If
+   * information about some of the used packages is not available yet, schedule
+   * its computation, so that it might be available later for other contexts
+   * referencing the same packages.
+   */
+  List<LinkedPubPackage> getLinkedBundles(AnalysisContext context) {
+    return new _ContextLinker(this, context).getLinkedBundles();
+  }
+
+  /**
+   * Return all available unlinked [PackageBundle]s for the given [context],
+   * maybe an empty map, but not `null`.
+   */
+  @visibleForTesting
+  Map<PubPackage, PackageBundle> getUnlinkedBundles(AnalysisContext context) {
+    bool strong = context.analysisOptions.strongMode;
+    Map<PubPackage, PackageBundle> unlinkedBundles =
+        new HashMap<PubPackage, PackageBundle>();
+    Map<String, List<Folder>> packageMap = context.sourceFactory.packageMap;
+    if (packageMap != null) {
+      packageMap.forEach((String packageName, List<Folder> libFolders) {
+        if (libFolders.length == 1) {
+          Folder libFolder = libFolders.first;
+          PubPackage package = new PubPackage(packageName, libFolder);
+          PackageBundle unlinkedBundle =
+              _getUnlinkedOrSchedule(package, strong);
+          if (unlinkedBundle != null) {
+            unlinkedBundles[package] = unlinkedBundle;
+          }
+        }
+      });
+    }
+    return unlinkedBundles;
+  }
+
+  /**
+   * Compute unlinked bundle for a package from [packagesToComputeUnlinked],
+   * and schedule delayed computation for the next package, if any.
+   */
+  void _computeNextUnlinked() {
+    if (packagesToComputeUnlinked.isNotEmpty) {
+      PubPackage package = packagesToComputeUnlinked.first;
+      _computeUnlinked(package, false);
+      _computeUnlinked(package, true);
+      packagesToComputeUnlinked.remove(package);
+      _scheduleNextUnlinked();
+    } else {
+      if (_onUnlinkedCompleteCompleter != null) {
+        _onUnlinkedCompleteCompleter.complete(true);
+        _onUnlinkedCompleteCompleter = null;
+      }
+    }
+  }
+
+  /**
+   * Compute the unlinked bundle for the package with the given path, put
+   * it in the [unlinkedBundleMap] and store into the [resourceProvider].
+   *
+   * TODO(scheglov) Consider moving into separate isolate(s).
+   */
+  void _computeUnlinked(PubPackage package, bool strong) {
+    Folder libFolder = package.libFolder;
+    String libPath = libFolder.path + pathContext.separator;
+    PackageBundleAssembler assembler = new PackageBundleAssembler();
+
+    /**
+     * Return the `package` [Uri] for the given [path] in the `lib` folder
+     * of the current package.
+     */
+    Uri getUri(String path) {
+      String pathInLib = path.substring(libPath.length);
+      String uriPath = pathos.posix.joinAll(pathContext.split(pathInLib));
+      String uriStr = 'package:${package.name}/$uriPath';
+      return FastUri.parse(uriStr);
+    }
+
+    /**
+     * If the given [file] is a Dart file, add its unlinked unit.
+     */
+    void addDartFile(File file) {
+      String path = file.path;
+      if (AnalysisEngine.isDartFileName(path)) {
+        Uri uri = getUri(path);
+        Source source = file.createSource(uri);
+        CompilationUnit unit = _parse(source, strong);
+        UnlinkedUnitBuilder unlinkedUnit = serializeAstUnlinked(unit);
+        assembler.addUnlinkedUnit(source, unlinkedUnit);
+      }
+    }
+
+    /**
+     * Visit the [folder] recursively.
+     */
+    void addDartFiles(Folder folder) {
+      List<Resource> children = folder.getChildren();
+      for (Resource child in children) {
+        if (child is File) {
+          addDartFile(child);
+        }
+      }
+      for (Resource child in children) {
+        if (child is Folder) {
+          addDartFiles(child);
+        }
+      }
+    }
+
+    try {
+      addDartFiles(libFolder);
+      PackageBundleBuilder bundleWriter = assembler.assemble();
+      bundleWriter.majorVersion = majorVersion;
+      List<int> bytes = bundleWriter.toBuffer();
+      String fileName = _getUnlinkedName(strong);
+      _writeAtomic(package.folder, fileName, bytes);
+    } on FileSystemException {
+      // Ignore file system exceptions.
+    }
+  }
+
+  /**
+   * Return the name of the file for an unlinked bundle, in strong or spec mode.
+   */
+  String _getUnlinkedName(bool strong) {
+    if (strong) {
+      return UNLINKED_NAME;
+    } else {
+      return UNLINKED_SPEC_NAME;
+    }
+  }
+
+  /**
+   * Return the unlinked [PackageBundle] for the given [package]. If the bundle
+   * has not been compute yet, return `null` and schedule its computation.
+   */
+  PackageBundle _getUnlinkedOrSchedule(PubPackage package, bool strong) {
+    // Try to find in the cache.
+    PackageBundle bundle = unlinkedBundleMap[package];
+    if (bundle != null) {
+      return bundle;
+    }
+
+    // Try to read from the file system.
+    String fileName = _getUnlinkedName(strong);
+    File file = package.folder.getChildAssumingFile(fileName);
+    if (file.exists) {
+      try {
+        List<int> bytes = file.readAsBytesSync();
+        bundle = new PackageBundle.fromBuffer(bytes);
+      } on FileSystemException {
+        // Ignore file system exceptions.
+      }
+    }
+
+    // Verify compatibility and consistency.
+    bool isInPubCache = isPathInPubCache(pathContext, package.folder.path);
+    if (bundle != null &&
+        bundle.majorVersion == majorVersion &&
+        (isInPubCache || _isConsistent(package, bundle))) {
+      unlinkedBundleMap[package] = bundle;
+      return bundle;
+    }
+
+    // Schedule computation in the background, if in the pub cache.
+    if (isInPubCache) {
+      if (seenPackages.add(package)) {
+        _scheduleUnlinked(package);
+      }
+    }
+
+    // The bundle is not available.
+    return null;
+  }
+
+  /**
+   * Return `true` if content hashes for the [package] library files are the
+   * same the hashes in the unlinked [bundle].
+   */
+  bool _isConsistent(PubPackage package, PackageBundle bundle) {
+    List<String> actualHashes = <String>[];
+
+    /**
+     * If the given [file] is a Dart file, add its content hash.
+     */
+    void hashDartFile(File file) {
+      String path = file.path;
+      if (AnalysisEngine.isDartFileName(path)) {
+        List<int> fileBytes = file.readAsBytesSync();
+        List<int> hashBytes = md5.convert(fileBytes).bytes;
+        String hashHex = hex.encode(hashBytes);
+        actualHashes.add(hashHex);
+      }
+    }
+
+    /**
+     * Visit the [folder] recursively.
+     */
+    void hashDartFiles(Folder folder) {
+      List<Resource> children = folder.getChildren();
+      for (Resource child in children) {
+        if (child is File) {
+          hashDartFile(child);
+        } else if (child is Folder) {
+          hashDartFiles(child);
+        }
+      }
+    }
+
+    // Recursively compute hashes of the `lib` folder Dart files.
+    try {
+      hashDartFiles(package.libFolder);
+    } on FileSystemException {
+      return false;
+    }
+
+    // Compare sorted actual and bundle unit hashes.
+    List<String> bundleHashes = bundle.unlinkedUnitHashes.toList()..sort();
+    actualHashes.sort();
+    return listsEqual(actualHashes, bundleHashes);
+  }
+
+  /**
+   * Parse the given [source] into AST.
+   */
+  CompilationUnit _parse(Source source, bool strong) {
+    String code = source.contents.data;
+    AnalysisErrorListener errorListener = AnalysisErrorListener.NULL_LISTENER;
+    CharSequenceReader reader = new CharSequenceReader(code);
+    Scanner scanner = new Scanner(source, reader, errorListener);
+    scanner.scanGenericMethodComments = strong;
+    Token token = scanner.tokenize();
+    LineInfo lineInfo = new LineInfo(scanner.lineStarts);
+    Parser parser = new Parser(source, errorListener);
+    parser.parseGenericMethodComments = strong;
+    CompilationUnit unit = parser.parseCompilationUnit(token);
+    unit.lineInfo = lineInfo;
+    return unit;
+  }
+
+  /**
+   * Schedule delayed computation of the next package unlinked bundle from the
+   * set of [packagesToComputeUnlinked].  We delay each computation because we
+   * want operations in analysis server to proceed, and computing bundles of
+   * packages is a background task.
+   */
+  void _scheduleNextUnlinked() {
+    new Future.delayed(new Duration(milliseconds: 10), _computeNextUnlinked);
+  }
+
+  /**
+   * Schedule computing unlinked bundles for the given [package].
+   */
+  void _scheduleUnlinked(PubPackage package) {
+    if (packagesToComputeUnlinked.isEmpty) {
+      _scheduleNextUnlinked();
+    }
+    packagesToComputeUnlinked.add(package);
+  }
+
+  /**
+   * Atomically write the given [bytes] into the file in the [folder].
+   */
+  void _writeAtomic(Folder folder, String fileName, List<int> bytes) {
+    String filePath = folder.getChildAssumingFile(fileName).path;
+    File tempFile = folder.getChildAssumingFile(tempFileName);
+    tempFile.writeAsBytesSync(bytes);
+    tempFile.renameSync(filePath);
+  }
+
+  /**
+   * If the given [uri] has the `package` scheme, return the name of the
+   * package that contains the referenced resource.  Otherwise return `null`.
+   *
+   * For example `package:foo/bar.dart` => `foo`.
+   */
+  static String getPackageName(String uri) {
+    const String PACKAGE_SCHEME = 'package:';
+    if (uri.startsWith(PACKAGE_SCHEME)) {
+      int index = uri.indexOf('/');
+      if (index != -1) {
+        return uri.substring(PACKAGE_SCHEME.length, index);
+      }
+    }
+    return null;
+  }
+
+  /**
+   * Return `true` if the given absolute [path] is in the pub cache.
+   */
+  static bool isPathInPubCache(pathos.Context pathContext, String path) {
+    List<String> parts = pathContext.split(path);
+    for (int i = 0; i < parts.length - 1; i++) {
+      if (parts[i] == '.pub-cache') {
+        return true;
+      }
+      if (parts[i] == 'Pub' && parts[i + 1] == 'Cache') {
+        return true;
+      }
+    }
+    return false;
+  }
+}
+
+class _ContextLinker {
+  final PubSummaryManager manager;
+  final AnalysisContext context;
+
+  final strong;
+  final _ListedPackages listedPackages;
+  final PackageBundle sdkBundle;
+
+  final List<_LinkNode> nodes = <_LinkNode>[];
+  final Map<String, _LinkNode> packageToNode = <String, _LinkNode>{};
+
+  _ContextLinker(this.manager, AnalysisContext context)
+      : context = context,
+        strong = context.analysisOptions.strongMode,
+        listedPackages = new _ListedPackages(context.sourceFactory),
+        sdkBundle = context.sourceFactory.dartSdk.getLinkedBundle();
+
+  /**
+   * Return the list of linked [LinkedPubPackage]s that can be provided at this
+   * time for a subset of the packages used by the [context].
+   */
+  List<LinkedPubPackage> getLinkedBundles() {
+//    Stopwatch timer = new Stopwatch()..start();
+
+    if (sdkBundle == null) {
+      return const <LinkedPubPackage>[];
+    }
+
+    Map<PubPackage, PackageBundle> unlinkedBundles =
+        manager.getUnlinkedBundles(context);
+
+    // TODO(scheglov) remove debug output after optimizing
+//    print('LOADED ${unlinkedBundles.length} unlinked bundles'
+//        ' in ${timer.elapsedMilliseconds} ms');
+//    timer..reset();
+
+    // If no unlinked bundles, there is nothing we can try to link.
+    if (unlinkedBundles.isEmpty) {
+      return const <LinkedPubPackage>[];
+    }
+
+    // Create nodes for packages.
+    unlinkedBundles.forEach((package, unlinked) {
+      _LinkNode node = new _LinkNode(this, package, unlinked);
+      nodes.add(node);
+      packageToNode[package.name] = node;
+    });
+
+    // Compute transitive dependencies, mark some nodes as failed.
+    for (_LinkNode node in nodes) {
+      node.computeTransitiveDependencies();
+    }
+
+    // Attempt to read existing linked bundles.
+    for (_LinkNode node in nodes) {
+      _readLinked(node);
+    }
+
+    // Link new packages, if allowed.
+    if (manager.allowLinking) {
+      _link();
+    }
+
+    // Create successfully linked packages.
+    List<LinkedPubPackage> linkedPackages = <LinkedPubPackage>[];
+    for (_LinkNode node in nodes) {
+      if (node.linked != null) {
+        linkedPackages.add(new LinkedPubPackage(
+            node.package, node.unlinked, node.linked, node.linkedHash));
+      }
+    }
+
+    // TODO(scheglov) remove debug output after optimizing
+//    print('LINKED ${linkedPackages.length} bundles'
+//        ' in ${timer.elapsedMilliseconds} ms');
+
+    // Done.
+    return linkedPackages;
+  }
+
+  String _getDeclaredVariable(String name) {
+    return context.declaredVariables.get(name);
+  }
+
+  /**
+   * Return the name of the file for a linked bundle, in strong or spec mode.
+   */
+  String _getLinkedName(String hash) {
+    if (strong) {
+      return 'linked_$hash.ds';
+    } else {
+      return 'linked_spec_$hash.ds';
+    }
+  }
+
+  void _link() {
+    // Fill the store with bundles.
+    // Append the linked SDK bundle.
+    // Append unlinked and (if read from a cache) linked package bundles.
+    SummaryDataStore store = new SummaryDataStore(const <String>[]);
+    store.addBundle(null, sdkBundle);
+    for (_LinkNode node in nodes) {
+      store.addBundle(null, node.unlinked);
+      if (node.linked != null) {
+        store.addBundle(null, node.linked);
+      }
+    }
+
+    // Prepare URIs to link.
+    Map<String, _LinkNode> uriToNode = <String, _LinkNode>{};
+    for (_LinkNode node in nodes) {
+      if (!node.isReady) {
+        for (String uri in node.unlinked.unlinkedUnitUris) {
+          uriToNode[uri] = node;
+        }
+      }
+    }
+    Set<String> libraryUris = uriToNode.keys.toSet();
+
+    // Perform linking.
+    Map<String, LinkedLibraryBuilder> linkedLibraries =
+        link(libraryUris, (String uri) {
+      return store.linkedMap[uri];
+    }, (String uri) {
+      return store.unlinkedMap[uri];
+    }, _getDeclaredVariable, strong);
+
+    // Assemble newly linked bundles.
+    for (_LinkNode node in nodes) {
+      if (!node.isReady) {
+        PackageBundleAssembler assembler = new PackageBundleAssembler();
+        linkedLibraries.forEach((uri, linkedLibrary) {
+          if (identical(uriToNode[uri], node)) {
+            assembler.addLinkedLibrary(uri, linkedLibrary);
+          }
+        });
+        List<int> bytes = assembler.assemble().toBuffer();
+        node.linkedNewBytes = bytes;
+        node.linked = new PackageBundle.fromBuffer(bytes);
+      }
+    }
+
+    // Write newly linked bundles.
+    for (_LinkNode node in nodes) {
+      _writeLinked(node);
+    }
+  }
+
+  /**
+   * Attempt to find the linked bundle that corresponds to the given [node]
+   * with all its transitive dependencies and put it into [_LinkNode.linked].
+   */
+  void _readLinked(_LinkNode node) {
+    String hash = node.linkedHash;
+    if (hash != null) {
+      String fileName = _getLinkedName(hash);
+      File file = node.package.folder.getChildAssumingFile(fileName);
+      // Try to find in the cache.
+      PackageBundle linked = manager.linkedBundleMap[file.path];
+      if (linked != null) {
+        node.linked = linked;
+        return;
+      }
+      // Try to read from the file system.
+      if (file.exists) {
+        try {
+          List<int> bytes = file.readAsBytesSync();
+          linked = new PackageBundle.fromBuffer(bytes);
+          manager.linkedBundleMap[file.path] = linked;
+          node.linked = linked;
+        } on FileSystemException {
+          // Ignore file system exceptions.
+        }
+      }
+    }
+  }
+
+  /**
+   * If a new linked bundle was linked for the given [node], write the bundle
+   * into the memory cache and the file system.
+   */
+  void _writeLinked(_LinkNode node) {
+    String hash = node.linkedHash;
+    if (hash != null && node.linkedNewBytes != null) {
+      String fileName = _getLinkedName(hash);
+      File file = node.package.folder.getChildAssumingFile(fileName);
+      manager.linkedBundleMap[file.path] = node.linked;
+      manager._writeAtomic(node.package.folder, fileName, node.linkedNewBytes);
+    }
+  }
+}
+
+/**
+ * Information about a package to link.
+ */
+class _LinkNode {
+  final _ContextLinker linker;
+  final PubPackage package;
+  final PackageBundle unlinked;
+
+  bool failed = false;
+  Set<_LinkNode> transitiveDependencies;
+
+  List<_LinkNode> _dependencies;
+  String _linkedHash;
+
+  List<int> linkedNewBytes;
+  PackageBundle linked;
+
+  _LinkNode(this.linker, this.package, this.unlinked);
+
+  /**
+   * Retrieve the dependencies of this node.
+   */
+  List<_LinkNode> get dependencies {
+    if (_dependencies == null) {
+      Set<_LinkNode> dependencies = new Set<_LinkNode>();
+
+      void appendDependency(String uriStr) {
+        Uri uri = FastUri.parse(uriStr);
+        if (!uri.hasScheme) {
+          // A relative path in this package, skip it.
+        } else if (uri.scheme == 'dart') {
+          // Dependency on the SDK is implicit and always added.
+          // The SDK linked bundle is precomputed before linking packages.
+        } else if (uriStr.startsWith('package:')) {
+          String package = PubSummaryManager.getPackageName(uriStr);
+          _LinkNode packageNode = linker.packageToNode[package];
+          if (packageNode == null && linker.listedPackages.isListed(uriStr)) {
+            failed = true;
+          }
+          if (packageNode != null) {
+            dependencies.add(packageNode);
+          }
+        } else {
+          failed = true;
+        }
+      }
+
+      for (UnlinkedUnit unit in unlinked.unlinkedUnits) {
+        for (UnlinkedImport import in unit.imports) {
+          if (!import.isImplicit) {
+            appendDependency(import.uri);
+          }
+        }
+        for (UnlinkedExportPublic export in unit.publicNamespace.exports) {
+          appendDependency(export.uri);
+        }
+      }
+
+      _dependencies = dependencies.toList();
+    }
+    return _dependencies;
+  }
+
+  /**
+   * Return `true` is the node is ready - has the linked bundle or failed (does
+   * not have all required dependencies).
+   */
+  bool get isReady => linked != null || failed;
+
+  /**
+   * Return the hash string that corresponds to this linked bundle in the
+   * context of its SDK bundle and transitive dependencies.  Return `null` if
+   * the hash computation fails, because for example the full transitive
+   * dependencies cannot computed.
+   */
+  String get linkedHash {
+    if (_linkedHash == null && transitiveDependencies != null) {
+      ApiSignature signature = new ApiSignature();
+      // Add all unlinked API signatures.
+      List<String> signatures = <String>[];
+      signatures.add(linker.sdkBundle.apiSignature);
+      transitiveDependencies
+          .map((node) => node.unlinked.apiSignature)
+          .forEach(signatures.add);
+      signatures.sort();
+      signatures.forEach(signature.addString);
+      // Combine into a single hash.
+      appendDeclaredVariables(signature);
+      _linkedHash = signature.toHex();
+    }
+    return _linkedHash;
+  }
+
+  /**
+   * Append names and values of all referenced declared variables (even the
+   * ones without actually declared values) to the given [signature].
+   */
+  void appendDeclaredVariables(ApiSignature signature) {
+    Set<String> nameSet = new Set<String>();
+    for (_LinkNode node in transitiveDependencies) {
+      for (UnlinkedUnit unit in node.unlinked.unlinkedUnits) {
+        for (UnlinkedImport import in unit.imports) {
+          for (UnlinkedConfiguration configuration in import.configurations) {
+            nameSet.add(configuration.name);
+          }
+        }
+        for (UnlinkedExportPublic export in unit.publicNamespace.exports) {
+          for (UnlinkedConfiguration configuration in export.configurations) {
+            nameSet.add(configuration.name);
+          }
+        }
+      }
+    }
+    List<String> sortedNameList = nameSet.toList()..sort();
+    signature.addInt(sortedNameList.length);
+    for (String name in sortedNameList) {
+      signature.addString(name);
+      signature.addString(linker._getDeclaredVariable(name) ?? '');
+    }
+  }
+
+  /**
+   * Compute the set of existing transitive dependencies for this node.
+   * If any `package` dependency cannot be resolved, but it is one of the
+   * [listedPackages] then set [failed] to `true`.
+   * Only [unlinked] is used, so this method can be called before linking.
+   */
+  void computeTransitiveDependencies() {
+    if (transitiveDependencies == null) {
+      transitiveDependencies = new Set<_LinkNode>();
+
+      void appendDependencies(_LinkNode node) {
+        if (transitiveDependencies.add(node)) {
+          node.dependencies.forEach(appendDependencies);
+        }
+      }
+
+      appendDependencies(this);
+      if (transitiveDependencies.any((node) => node.failed)) {
+        failed = true;
+      }
+    }
+  }
+
+  @override
+  String toString() => package.toString();
+}
+
+/**
+ * The set of package names that are listed in the `.packages` file of a
+ * context.  These are the only packages, references to which can
+ * be possibly resolved in the context.  Nodes that reference a `package:` URI
+ * without the unlinked bundle, so without the node, cannot be linked.
+ */
+class _ListedPackages {
+  final Set<String> names = new Set<String>();
+
+  _ListedPackages(SourceFactory sourceFactory) {
+    Map<String, List<Folder>> map = sourceFactory.packageMap;
+    if (map != null) {
+      names.addAll(map.keys);
+    }
+  }
+
+  /**
+   * Check whether the given `package:` [uri] is listed in the package map.
+   */
+  bool isListed(String uri) {
+    String package = PubSummaryManager.getPackageName(uri);
+    return names.contains(package);
+  }
+}