Add an SDK source.

lib/src/source/sdk.dart

Index: lib/src/source/sdk.dart
diff --git a/lib/src/source/sdk.dart b/lib/src/source/sdk.dart
new file mode 100644
index 0000000000000000000000000000000000000000..c04d7fd2e0554d94610e1a34406d06dd7c4e5ee9
--- /dev/null
+++ b/lib/src/source/sdk.dart
@@ -0,0 +1,109 @@
+// 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 'package:pub_semver/pub_semver.dart';
+
+import '../exceptions.dart';
+import '../flutter.dart' as flutter;
+import '../io.dart';
+import '../package.dart';
+import '../pubspec.dart';
+import '../source.dart';
+import '../system_cache.dart';
+
+/// A package [Source] that gets packages from a hard-coded SDK.
+class SdkSource extends Source {
+  final name = 'sdk';
+
+  BoundSource bind(SystemCache systemCache) =>
+      new BoundSdkSource(this, systemCache);
+
+  /// Returns a reference to an SDK package named [name] from [sdk].
+  PackageRef refFor(String name, String sdk) => new PackageRef(name, this, sdk);
+
+  /// Returns an ID for an SDK package with the given [name] and [version] from
+  /// [sdk].
+  PackageId idFor(String name, Version version, String sdk) =>
+      new PackageId(name, this, version, sdk);
+
+  /// Parses an SDK dependency.
+  PackageRef parseRef(String name, description, {String containingPath}) {
+    if (description is! String) {
+      throw new FormatException("The description must be an SDK name.");
+    }
+
+    return new PackageRef(name, this, description);
+  }
+
+  PackageId parseId(String name, Version version, description) {
+    if (description is! String) {
+      throw new FormatException("The description must be an SDK name.");
+    }
+
+    return new PackageId(name, this, version, description);
+  }
+
+  bool descriptionsEqual(description1, description2) =>
+      description1 == description2;
+
+  int hashDescription(description) => description.hashCode;
+}
+
+/// The [BoundSource] for [SdkSource].
+class BoundSdkSource extends BoundSource {
+  final SdkSource source;
+
+  final SystemCache systemCache;
+
+  BoundSdkSource(this.source, this.systemCache);
+
+  Future<List<PackageId>> doGetVersions(PackageRef ref) async {
+    var sdk = ref.description as String;
+    if (sdk == 'dart') {
+      throw new PackageNotFoundException(
+          'Could not find package ${ref.name} in the Dart SDK.');
+    } else if (sdk != 'flutter') {
+      throw new PackageNotFoundException('Unknown SDK "$sdk".');
+    }
+
+    var pubspec = _loadPubspec(ref.name);
+    var id = new PackageId(ref.name, source, pubspec.version, sdk);
+    memoizePubspec(id, pubspec);
+    return [id];
+  }
+
+  Future<Pubspec> doDescribe(PackageId id) async => _loadPubspec(id.name);
+
+  /// Loads the pubspec for the Flutter package named [name].
+  ///
+  /// Throws a [PackageNotFoundException] if Flutter is unavaialable or doesn't
+  /// contain the package.
+  Pubspec _loadPubspec(String name) =>
+      new Pubspec.load(_verifiedPackagePath(name), systemCache.sources,
+          expectedName: name);
+
+  Future get(PackageId id, String symlink) async {
+    createPackageSymlink(id.name, _verifiedPackagePath(id.name), symlink);
+  }
+
+  /// Returns the path in the Flutter SDK for the package named [name].
+  ///
+  /// Throws a [PackageNotFoundException] if Flutter is unavailable or doesn't
+  /// contain the package.
+  String _verifiedPackagePath(String name) {
+    if (!flutter.isAvailable) {
+      throw new PackageNotFoundException('The Flutter SDK is not available.');
+    }
+
+    var path = flutter.packagePath(name);
+    if (dirExists(path)) return path;
+
+    throw new PackageNotFoundException(
+        'Could not find package $name in the Flutter SDK.');
+  }
+
+  String getDirectory(PackageId id) => flutter.packagePath(id.name);
+}