Refactor Source.

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

Index: sdk/lib/_internal/pub/lib/src/source/unknown.dart
diff --git a/sdk/lib/_internal/pub/lib/src/source/unknown.dart b/sdk/lib/_internal/pub/lib/src/source/unknown.dart
new file mode 100644
index 0000000000000000000000000000000000000000..40cd11118ba359b811728598ba2cb5810b2579d5
--- /dev/null
+++ b/sdk/lib/_internal/pub/lib/src/source/unknown.dart
@@ -0,0 +1,47 @@
+// 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.unknown;
+
+import 'dart:async';
+
+import '../package.dart';
+import '../pubspec.dart';
+import '../source.dart';
+
+/// A [Null Object] that represents a source not recognized by pub.
+///
+/// It provides some default behavior so that pub can work with sources it
+/// doesn't recognize.
+///
+/// [null object]: http://en.wikipedia.org/wiki/Null_Object_pattern
+class UnknownSource extends Source {
+  final String name;
+
+  UnknownSource(this.name);
+
+  /// Two unknown sources are the same if their names are the same.
+  bool operator==(other) =>
+      other is UnknownSource &&
+      other.name == name;
+
+  int get hashCode => name.hashCode;
+
+  Future<Pubspec> onDescribe(PackageId id) => throw new UnsupportedError(
+      "Cannot describe a package from unknown source '$name'.");
+
+  Future<bool> get(PackageId id, String path) => throw new UnsupportedError(
+      "Cannot get a package from an unknown source '$name'.");
+
+  /// Returns the directory where this package can be found locally.
+  Future<String> getDirectory(PackageId id) => throw new UnsupportedError(
+      "Cannot find a package from an unknown source '$name'.");
+
+  bool descriptionsEqual(description1, description2) =>
+      description1 == description2;
+
+  /// Unknown sources do no validation.
+  dynamic parseDescription(String containingPath, description,
+                           {bool fromLockFile: false}) => description;
+}