First pass at build dependency graph for barback.

pkg/barback/lib/src/asset_id.dart

Index: pkg/barback/lib/src/asset_id.dart
diff --git a/pkg/barback/lib/src/asset_id.dart b/pkg/barback/lib/src/asset_id.dart
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+++ b/pkg/barback/lib/src/asset_id.dart
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+// Copyright (c) 2013, 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 barback.asset_id;
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:pathos/path.dart' as pathos;
+
+/// AssetIDs always use POSIX style paths regardless of the host platform.
+final _posix = new pathos.Builder(style: pathos.Style.posix);
+
+/// Identifies an asset within a package.
+class AssetId {
+  /// The name of the package containing this asset.
+  final String package;
+
+  /// The path to the asset relative to the root directory of [package].
+  ///
+  /// Source (i.e. read from disk) and generated (i.e. the output of a
+  /// [Transformer]) assets all have paths. Even intermediate assets that are
+  /// generated and then consumed by later transformations will still have
+  /// a path used to identify it.
+  ///
+  /// Asset paths always use forward slashes as path separators, regardless of
+  /// the host platform.
+  final String path;
+
+  /// Gets the file extension of the asset, if it has one, including the ".".
+  String get extension => pathos.extension(path);
+
+  /// Creates a new AssetId at [path] within [package].
+  AssetId(this.package, String path)
+      : path = _posix.normalize(path);
+
+  /// Parses an [AssetId] string of the form "package|path/to/asset.txt".
+  factory AssetId.parse(String description) {
+    var parts = description.split("|");
+    if (parts.length != 2) {
+      throw new FormatException('Could not parse "$description".');
+    }
+
+    if (parts[0].isEmpty) {
+      throw new FormatException(
+          'Cannot have empty package name in "$description".');
+    }
+
+    if (parts[1].isEmpty) {
+      throw new FormatException(
+          'Cannot have empty path in "$description".');
+    }
+
+    return new AssetId(parts[0], parts[1]);
+  }
+
+  /// Deserializes an [AssetId] from [data], which must be the result of
+  /// calling [serialize] on an existing [AssetId].
+  ///
+  /// Note that this is intended for communicating ids across isolates and not
+  /// for persistent storage of asset identifiers. There is no guarantee of
+  /// backwards compatibility in serialization form across versions.
+  AssetId.deserialize(data)
+      : package = data[0],
+        path = data[1];
+
+  /// Returns `true` of [other] is an [AssetId] with the same package and path.
+  operator ==(other) =>
+      other is AssetId &&
+      package == other.package &&
+      path == other.path;
+
+  int get hashCode => package.hashCode ^ path.hashCode;
+
+  /// Returns a new [AssetId] with the same [package] as this one and with the
+  /// [path] extended to include [extension].
+  AssetId addExtension(String extension) =>
+      new AssetId(package, "$path$extension");
+
+  /// Returns a new [AssetId] with the same [package] and [path] as this one
+  /// but with file extension [newExtension].
+  AssetId changeExtension(String newExtension) =>
+      new AssetId(package, pathos.withoutExtension(path) + newExtension);
+
+  String toString() => "$package|$path";
+
+  /// Serializes this [AssetId] to an object that can be sent across isolates
+  /// and passed to [deserialize].
+  serialize() => [package, path];
+}