Start sketching out a buildAll() method.

pkg/barback/lib/src/package_graph.dart

 // 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.package_graph;
 
 import 'dart:async';
 
 import 'asset_cascade.dart';
 import 'asset_id.dart';
 import 'asset_node.dart';
+import 'asset_set.dart';
 import 'build_result.dart';
 import 'errors.dart';
 import 'package_provider.dart';
 import 'utils.dart';
 
 /// The collection of [AssetCascade]s for an entire application.
 ///
 /// This tracks each package's [AssetCascade] and routes asset requests between
 /// them.
 class PackageGraph {
@@ skipping 63 matching lines @@
   /// has been created and return it. This means that the returned asset will
   /// always be [AssetState.AVAILABLE].
   ///
   /// If the asset cannot be found, returns null.
   Future<AssetNode> getAssetNode(AssetId id) {
     var cascade = _cascades[id.package];
     if (cascade != null) return cascade.getAssetNode(id);
     return new Future.value(null);
   }
 
+  /// Gets all output assets.
+  ///
+  /// If a build is currently in progress, waits until it completes. The
+  /// returned future will complete with an error if the build is not
+  /// successful.
+  Future<AssetSet> getAllAssets() {
+    if (_cascadeResults.values.contains(null)) {
+      // A build is still ongoing, so wait for it to complete and try again.
+      return results.first.then((_) => getAllAssets());
+    }
+
+    // If the build completed with an error, complete the future with it.
+    var errors = unionAll(
+        _cascadeResults.values.map((result) => result.errors));
+    if (errors.isNotEmpty) {
+      return new Future.error(BarbackException.aggregate(errors));
+    }
+
+    // Otherwise, return all of the final output assets.
+    var assets = unionAll(_cascades.values.map(
+        (cascade) => cascade.availableOutputs.toSet()));
+
+    return new Future.value(new AssetSet.from(assets));
+  }
+
   /// Adds [sources] to the graph's known set of source assets.
   ///
   /// Begins applying any transforms that can consume any of the sources. If a
   /// given source is already known, it is considered modified and all
   /// transforms that use it will be re-applied.
   void updateSources(Iterable<AssetId> sources) {
     groupBy(sources, (id) => id.package).forEach((package, ids) {
       var cascade = _cascades[package];
       if (cascade == null) throw new ArgumentError("Unknown package $package.");
       _cascadeResults[package] = null;
       cascade.updateSources(ids);
     });
   }
 
   /// Removes [removed] from the graph's known set of source assets.
   void removeSources(Iterable<AssetId> sources) {
     groupBy(sources, (id) => id.package).forEach((package, ids) {
       var cascade = _cascades[package];
       if (cascade == null) throw new ArgumentError("Unknown package $package.");
       _cascadeResults[package] = null;
       cascade.removeSources(ids);
     });
   }
 }