Add more metadata to non-programmatic barback exceptions.

pkg/barback/lib/src/phase.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.phase;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'asset.dart';
@@ skipping 51 matching lines @@
   /// Whenever an asset is added or modified, we need to asynchronously
   /// determine which transformers can use it as their primary input. We can't
   /// start processing until we know which transformers to run, and this allows
   /// us to wait until we do.
   var _adjustTransformersFutures = new Map<AssetId, Future>();
 
   /// New asset nodes that were added while [_adjustTransformers] was still
   /// being run on an old version of that asset.
   var _pendingNewInputs = new Map<AssetId, AssetNode>();
 
-  /// A map of output ids to the asset node outputs for those ids.
+  /// A map of output ids to the asset node outputs for those ids and the
+  /// transforms that produced those asset nodes.
   ///
   /// Usually there's only one node for a given output id. However, it's
   /// possible for multiple transformers in this phase to output an asset with
   /// the same id. In that case, the chronologically first output emitted is
   /// passed forward. We keep track of the other nodes so that if that output is
   /// removed, we know which asset to replace it with.
   final _outputs = new Map<AssetId, Queue<AssetNode>>();
 
   /// A stream that emits an event whenever this phase becomes dirty and needs
   /// to be run.
@@ skipping 247 matching lines @@
         }
       });
     })).then((_) {
       // Report collisions in a deterministic order.
       collisions = collisions.toList();
       collisions.sort((a, b) => a.compareTo(b));
       for (var collision in collisions) {
         // Ensure that there's still a collision. It's possible it was resolved
         // while another transform was running.
         if (_outputs[collision].length <= 1) continue;
-        cascade.reportError(new AssetCollisionException(collision));
+        cascade.reportError(new AssetCollisionException(
+            _outputs[collision].where((asset) => asset.transform != null)
+                .map((asset) => asset.transform.info),
+            collision));
       }
     });
   }
 
   /// Properly resolve collisions when [output] is removed.
   void _handleOutputRemoval(AssetNode output) {
     output.whenRemoved.then((_) {
       var assets = _outputs[output.id];
       if (assets.length == 1) {
         assert(assets.single == output);
         _outputs.remove(output.id);
         return;
       }
 
       // If there was more than one asset, we're resolving a collision --
       // possibly partially.
       var wasFirst = assets.first == output;
       assets.remove(output);
 
       // If this was the first asset, we need to pass the next asset
       // (chronologically) to the next phase. Pump the event queue first to give
       // [_next] a chance to handle the removal of its input before getting a
       // new input.
-      if (wasFirst) newFuture(() => _next.addInput(assets.first));
+      if (wasFirst) {
+        newFuture(() => _next.addInput(assets.first));
+      }
 
       // If there's still a collision, report it. This lets the user know
       // if they've successfully resolved the collision or not.
       if (assets.length > 1) {
         // Pump the event queue to ensure that the removal of the input triggers
         // a new build to which we can attach the error.
-        newFuture(() =>
-            cascade.reportError(new AssetCollisionException(output.id)));
+        newFuture(() => cascade.reportError(new AssetCollisionException(
+            assets.where((asset) => asset.transform != null)
+                .map((asset) => asset.transform.info),
+            output.id)));
       }
     });
   }
 }