Improve barback/pub logging.

pkg/barback/lib/src/asset_cascade.dart

Index: pkg/barback/lib/src/asset_cascade.dart
diff --git a/pkg/barback/lib/src/asset_cascade.dart b/pkg/barback/lib/src/asset_cascade.dart
index f123cf38376ca0ea6bb2bf46a7b59ebc0511719c..9eec80041c467d9fec3eb872676b90fb399c150f 100644
--- a/pkg/barback/lib/src/asset_cascade.dart
+++ b/pkg/barback/lib/src/asset_cascade.dart
@@ -11,6 +11,7 @@ import 'asset.dart';
 import 'asset_id.dart';
 import 'asset_node.dart';
 import 'asset_set.dart';
+import 'barback_logger.dart';
 import 'build_result.dart';
 import 'cancelable_future.dart';
 import 'errors.dart';
@@ -84,11 +85,20 @@ class AssetCascade {
   /// A controller whose stream feeds into [_onDirtyPool].
   final _onDirtyController = new StreamController.broadcast(sync: true);
 
+  /// A stream that emits an event whenever any transforms in this cascade log

[nweiz, 2013/10/16 19:41:27]

"log" -> "logs"

[Bob Nystrom, 2013/10/28 23:45:56]

Done.

+  /// an entry.
+  Stream<LogEntry> get onLog => _onLogPool.stream;
+  final _onLogPool = new StreamPool<LogEntry>.broadcast();
+
   /// The errors that have occurred since the current build started.
   ///
   /// This will be empty if no build is occurring.
   Queue<BarbackException> _accumulatedErrors;
 
+  /// The number of errors that have been logged since the current build
+  /// started.
+  int _numLogErrors;
+
   /// A future that completes when the currently running build process finishes.
   ///
   /// If no build it in progress, is `null`.
@@ -108,6 +118,11 @@ class AssetCascade {
   AssetCascade(this.graph, this.package) {
     _onDirtyPool.add(_onDirtyController.stream);
     _addPhase(new Phase(this, []));
+
+    // Keep track of logged errors so we can know that the build failed.
+    onLog.listen((entry) {
+      if (entry.level == LogLevel.ERROR) _numLogErrors++;
+    });
   }
 
   /// Gets the asset identified by [id].
@@ -222,6 +237,7 @@ class AssetCascade {
   /// Add [phase] to the end of [_phases] and watch its [onDirty] stream.
   void _addPhase(Phase phase) {
     _onDirtyPool.add(phase.onDirty);
+    _onLogPool.add(phase.onLog);
     phase.onDirty.listen((_) {
       _newChanges = true;
       _waitForProcess();
@@ -240,10 +256,12 @@ class AssetCascade {
     if (_processDone != null) return _processDone;
 
     _accumulatedErrors = new Queue();
+    _numLogErrors = 0;
     return _processDone = _process().then((_) {
       // Report the build completion.
       // TODO(rnystrom): Put some useful data in here.
-      _resultsController.add(new BuildResult(_accumulatedErrors));
+      _resultsController.add(
+          new BuildResult(_accumulatedErrors, _numLogErrors));
     }).catchError((error) {
       // If we get here, it's an unexpected error. Runtime errors like missing
       // assets should be handled earlier. Errors from transformers or other