Start pulling pub from its own repo.

sdk/lib/_internal/pub/lib/src/source/cached.dart

-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-library pub.source.cached;
-
-import 'dart:async';
-
-import 'package:path/path.dart' as path;
-
-import '../io.dart';
-import '../package.dart';
-import '../pubspec.dart';
-import '../source.dart';
-import '../utils.dart';
-
-/// Base class for a [Source] that installs packages into pub's [SystemCache].
-///
-/// A source should be cached if it requires network access to retrieve
-/// packages or the package needs to be "frozen" at the point in time that it's
-/// installed. (For example, Git packages are cached because installing from
-/// the same repo over time may yield different commits.)
-abstract class CachedSource extends Source {
-  /// The root directory of this source's cache within the system cache.
-  ///
-  /// This shouldn't be overridden by subclasses.
-  String get systemCacheRoot => path.join(systemCache.rootDir, name);
-
-  /// If [id] is already in the system cache, just loads it from there.
-  ///
-  /// Otherwise, defers to the subclass.
-  Future<Pubspec> doDescribe(PackageId id) {
-    return getDirectory(id).then((packageDir) {
-      if (fileExists(path.join(packageDir, "pubspec.yaml"))) {
-        return new Pubspec.load(packageDir, systemCache.sources,
-            expectedName: id.name);
-      }
-
-      return describeUncached(id);
-    });
-  }
-
-  /// Loads the (possibly remote) pubspec for the package version identified by
-  /// [id].
-  ///
-  /// This will only be called for packages that have not yet been installed in
-  /// the system cache.
-  Future<Pubspec> describeUncached(PackageId id);
-
-  Future get(PackageId id, String symlink) {
-    return downloadToSystemCache(id).then((pkg) {
-      createPackageSymlink(id.name, pkg.dir, symlink);
-    });
-  }
-
-  /// Determines if the package with [id] is already downloaded to the system
-  /// cache.
-  Future<bool> isInSystemCache(PackageId id) =>
-      getDirectory(id).then(dirExists);
-
-  /// Downloads the package identified by [id] to the system cache.
-  Future<Package> downloadToSystemCache(PackageId id);
-
-  /// Returns the [Package]s that have been downloaded to the system cache.
-  List<Package> getCachedPackages();
-
-  /// Reinstalls all packages that have been previously installed into the
-  /// system cache by this source.
-  ///
-  /// Returns a [Pair] whose first element is the number of packages
-  /// successfully repaired and the second is the number of failures.
-  Future<Pair<int, int>> repairCachedPackages();
-}