Preserve laziness in declaring transformers.

pkg/barback/lib/src/transform_node.dart

Index: pkg/barback/lib/src/transform_node.dart
diff --git a/pkg/barback/lib/src/transform_node.dart b/pkg/barback/lib/src/transform_node.dart
index ecd8d8f677f6b481fc6ca1b586bab96a51542974..ee56ffd46600f56c02c18edbe71a89cc770e5ab4 100644
--- a/pkg/barback/lib/src/transform_node.dart
+++ b/pkg/barback/lib/src/transform_node.dart
@@ -114,12 +114,16 @@ class TransformNode {
   /// [declareOutputs] has been run successfully.
   Set<AssetId> _declaredOutputs;
 
-  TransformNode(this.phase, Transformer transformer, this.primary,
+  TransformNode(this.phase, Transformer transformer, AssetNode primary,
       this._location)
       : transformer = transformer,
-        _isLazy = transformer is LazyTransformer {
+        primary = primary,
+        _isLazy = transformer is LazyTransformer ||
+            (transformer is DeclaringTransformer && primary.isLazy) {

[Bob Nystrom, 2014/04/10 20:45:34]

Laziness propagates downwards from previous lazy transformers?

If so, this should be documented at _isLazy's declaration.

[nweiz, 2014/04/10 20:54:53]

Done.

     _onLogPool.add(_onLogController.stream);
 
+    if (!_isLazy) primary.force();
+
     _primarySubscription = primary.onStateChange.listen((state) {
       if (state.isRemoved) {
         remove();
@@ -167,6 +171,7 @@ class TransformNode {
     // TODO(nweiz): we might want to have a timeout after which, if the
     // transform's outputs have gone unused, we switch it back to lazy mode.
     if (!_isLazy) return;
+    primary.force();
     _isLazy = false;
     _dirty();
   }
@@ -253,7 +258,7 @@ class TransformNode {
       if (!_declaredOutputs.contains(primary.id)) _emitPassThrough();
 
       for (var id in _declaredOutputs) {
-        var controller = transformer is LazyTransformer
+        var controller = _isLazy
             ? new AssetNodeController.lazy(id, force, this)
             : new AssetNodeController(id, this);
         _outputControllers[id] = controller;