Make lazy and declaring transformers work with $include/$exclude.

sdk/lib/_internal/pub/lib/src/barback/excluding_transformer.dart

Index: sdk/lib/_internal/pub/lib/src/barback/excluding_transformer.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/excluding_transformer.dart b/sdk/lib/_internal/pub/lib/src/barback/excluding_transformer.dart
index 0d9a9651cca857dd2050cb84b2ea3f25dc5c207c..9182ec6d48a3ee4efba22646dffb275a649e0619 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/excluding_transformer.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/excluding_transformer.dart
@@ -19,7 +19,15 @@ class ExcludingTransformer extends Transformer {
       Set<String> excludes) {
     if (includes == null && excludes == null) return inner;
 
-    return new ExcludingTransformer._(inner, includes, excludes);
+    if (inner is LazyTransformer) {
+      return new _LazyExcludingTransformer(
+          inner as LazyTransformer, includes, excludes);
+    } else if (inner is DeclaringTransformer) {
+      return new _DeclaringExcludingTransformer(
+          inner as DeclaringTransformer, includes, excludes);

[Bob Nystrom, 2014/05/27 17:40:19]

Based on my reading of the spec, these "as" expressions should not be necessary.
Can you file a bug for them and add a TODO?

[nweiz, 2014/05/27 20:36:50]

Done.

+    } else {
+      return new ExcludingTransformer._(inner, includes, excludes);
+    }
   }
 
   final Transformer _inner;
@@ -56,3 +64,20 @@ class ExcludingTransformer extends Transformer {
 
   String toString() => _inner.toString();
 }
+
+class _DeclaringExcludingTransformer extends ExcludingTransformer
+    implements DeclaringTransformer {
+  _DeclaringExcludingTransformer(DeclaringTransformer inner,
+        Set<String> includes, Set<String> excludes)
+      : super._(inner as Transformer, includes, excludes);

[Bob Nystrom, 2014/05/27 17:40:19]

I know we discussed this, but I can't recall the details. Does this mean
DeclaringTransformer does not implement/extend Transformer? Why not?

[nweiz, 2014/05/27 20:36:50]

I don't remember our original reason for not making DeclaringTransformer
implement Transformer. Maybe it was to make it clear what method it added? I
think right now I'd make the other choice, but that would technically be
backwards incompatible :-/.

+
+  Future declareOutputs(DeclaringTransform transform) =>
+      (_inner as DeclaringTransformer).declareOutputs(transform);
+}
+
+class _LazyExcludingTransformer extends _DeclaringExcludingTransformer
+    implements LazyTransformer {
+  _LazyExcludingTransformer(DeclaringTransformer inner,
+        Set<String> includes, Set<String> excludes)
+      : super(inner, includes, excludes);
+}