Barback transforms now pass through the primary input by default.

pkg/barback/test/package_graph/add_remove_transform_test.dart

Index: pkg/barback/test/package_graph/add_remove_transform_test.dart
diff --git a/pkg/barback/test/package_graph/add_remove_transform_test.dart b/pkg/barback/test/package_graph/add_remove_transform_test.dart
index ac0076cd8f1f6df3d82c75db435a69a8fc121cf8..bcb5d29a24e159b580a385bb06fb785bdcadf7ab 100644
--- a/pkg/barback/test/package_graph/add_remove_transform_test.dart
+++ b/pkg/barback/test/package_graph/add_remove_transform_test.dart
@@ -20,7 +20,6 @@ main() {
 
     updateTransformers("app", [[new RewriteTransformer("blub", "blab")]]);
     expectAsset("app|foo.blab", "foo.blab");
-    expectNoAsset("app|foo.blub");

[Bob Nystrom, 2014/02/26 01:09:15]

How about changing these to positive expectations instead of deleting them?

[nweiz, 2014/02/26 19:37:14]

They're not really relevant to the tests they're in. The negative assertions
were relevant, in that they were another way of saying "the transformer we
expected to run did", but the positive assertions would just be duplicating the
explicit pass-through tests.

     buildShouldSucceed();
   });
 
@@ -43,12 +42,10 @@ main() {
 
     updateSources(["app|foo.blub"]);
     expectAsset("app|foo.blab", "foo.blab");
-    expectNoAsset("app|foo.blub");
     buildShouldSucceed();
 
     updateTransformers("app", [[rewrite]]);
     expectAsset("app|foo.blab", "foo.blab");
-    expectNoAsset("app|foo.blub");
     buildShouldSucceed();
 
     expect(rewrite.numRuns, completion(equals(1)));
@@ -61,7 +58,6 @@ main() {
 
     updateSources(["app|foo.txt"]);
     expectAsset("app|foo.blab", "foo.blub.blab");
-    expectNoAsset("app|foo.blub");
     buildShouldSucceed();
 
     updateTransformers("app", [[rewrite2], [rewrite1]]);
@@ -94,7 +90,6 @@ main() {
 
     updateSources(["app|foo.blub"]);
     expectAsset("app|foo.blab", "foo.blab");
-    expectNoAsset("app|foo.blub");
     buildShouldSucceed();
 
     updateTransformers("app", []);
@@ -192,22 +187,6 @@ main() {
     buildShouldSucceed();
   });
 
-  test("a new transformer can see pass-through assets", () {
-    var rewrite = new RewriteTransformer("zip", "zap");
-    initGraph(["app|foo.blub"], {"app": [[rewrite]]});
-
-    updateSources(["app|foo.blub"]);
-    buildShouldSucceed();
-
-    updateTransformers("app", [
-      [rewrite],
-      [new RewriteTransformer("blub", "blab")]
-    ]);
-    expectAsset("app|foo.blab", "foo.blab");
-    expectNoAsset("app|foo.blub");
-    buildShouldSucceed();
-  });
-
   test("a cross-package transform sees a new transformer in a new phase", () {
     var rewrite = new RewriteTransformer("inc", "inc");
     initGraph({
@@ -253,6 +232,105 @@ main() {
     buildShouldSucceed();
   });
 
+  group("pass-through", () {
+    test("a new transformer can see pass-through assets", () {
+      var rewrite = new RewriteTransformer("zip", "zap");
+      initGraph(["app|foo.blub"], {"app": [[rewrite]]});
+
+      updateSources(["app|foo.blub"]);
+      buildShouldSucceed();
+
+      updateTransformers("app", [
+        [rewrite],
+        [new RewriteTransformer("blub", "blab")]
+      ]);
+      expectAsset("app|foo.blab", "foo.blab");
+      buildShouldSucceed();
+    });
+
+    test("a new transformer can overwrite an old asset", () {
+      var rewrite = new RewriteTransformer("zip", "zap");
+      initGraph(["app|foo.txt"], {"app": [[rewrite]]});
+
+      updateSources(["app|foo.txt"]);
+      expectAsset("app|foo.txt", "foo");
+      buildShouldSucceed();
+
+      updateTransformers("app", [
+        [rewrite, new RewriteTransformer("txt", "txt")]

[Bob Nystrom, 2014/02/26 01:09:15]

I'm not clear on what's going on here. Are you trying to show that a new
transformer will see an asset previously passed-through by an existing
transformer?

If so, shouldn't it be in a later phase?

[nweiz, 2014/02/26 19:37:14]

I'm asserting that a transform that's added to an existing phase can overwrite
an existing asset in that phase.

[Bob Nystrom, 2014/02/26 20:28:50]

OK, add some docs to clarify.

[nweiz, 2014/02/27 21:04:20]

Done.

+      ]);
+      expectAsset("app|foo.txt", "foo.txt");
+      buildShouldSucceed();
+    });
+
+    test("passes an asset through when an overwriting transform is removed",
+        () {
+      initGraph(["app|foo.txt"], {
+        "app": [[new RewriteTransformer("txt", "txt")]]
+      });
+
+      updateSources(["app|foo.txt"]);
+      expectAsset("app|foo.txt", "foo.txt");
+      buildShouldSucceed();
+
+      updateTransformers("app", [[]]);
+      expectAsset("app|foo.txt", "foo");
+      buildShouldSucceed();
+    });
+
+    test("passes an asset through when its overwriting transform is removed "
+        "during apply", () {
+      var rewrite = new RewriteTransformer("txt", "txt");
+      initGraph(["app|foo.txt"], {"app": [[rewrite]]});
+
+      rewrite.pauseApply();
+      updateSources(["app|foo.txt"]);
+      expectAssetDoesNotComplete("app|foo.txt");
+
+      updateTransformers("app", [[]]);
+      rewrite.resumeApply();
+      expectAsset("app|foo.txt", "foo");
+      buildShouldSucceed();
+    });
+
+    test("doesn't pass an asset through when its overwriting transform is "
+        "removed during apply if another transform overwrites it", () {
+      var rewrite1 = new RewriteTransformer("txt", "txt");
+      var rewrite2 = new RewriteTransformer("txt", "txt");
+      initGraph(["app|foo.txt"], {"app": [[rewrite1, rewrite2]]});
+
+      rewrite1.pauseApply();
+      updateSources(["app|foo.txt"]);
+      expectAssetDoesNotComplete("app|foo.txt");
+      // Ensure we're waiting on [rewrite1.apply]
+      schedule(pumpEventQueue);
+
+      updateTransformers("app", [[rewrite2]]);
+      rewrite1.resumeApply();
+      expectAsset("app|foo.txt", "foo.txt");
+      buildShouldSucceed();
+    });
+
+    test("doesn't pass an asset through when one overwriting transform is "
+        "removed if another transform still overwrites it", () {
+      var rewrite = new RewriteTransformer("txt", "txt");
+      initGraph(["app|foo.txt"], {"app": [[
+        rewrite,
+        new RewriteTransformer("txt", "txt")
+      ]]});
+
+      updateSources(["app|foo.txt"]);
+      // This could be either the output of [CheckContentTransformer] or
+      // [RewriteTransformer], depending which completes first.
+      expectAsset("app|foo.txt", anything);
+      buildShouldFail([isAssetCollisionException("app|foo.txt")]);
+
+      updateTransformers("app", [[rewrite]]);
+      expectAsset("app|foo.txt", "foo.txt");
+      buildShouldSucceed();
+    });
+  });
+
   // Regression test.
   test("a phase is added, then an input is removed and re-added", () {
     var rewrite = new RewriteTransformer("txt", "mid");