"pub get" doesn't choke on previously-cached unknown transformers.

sdk/lib/_internal/pub/test/transformer/cache_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS d.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 pub_tests;
 
+import 'package:scheduled_test/scheduled_stream.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import '../serve/utils.dart';
 
 const REPLACE_FROM_LIBRARY_TRANSFORMER = """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
@@ skipping 29 matching lines @@
       ])
     ]);
 
     builder.serve("bar", "1.2.3",
         deps: {'barback': 'any'},
         contents: [
       d.dir("lib", [
         d.file("transformer.dart", replaceTransformer("Goodbye", "See ya"))
       ])
     ]);
+
+    builder.serve("baz", "1.2.3");
   });
 
   d.dir(appPath, [
     d.pubspec({
       "name": "myapp",
       "dependencies": {
         "foo": "1.2.3",
         "bar": "1.2.3"
       },
       "transformers": ["foo"]
@@ skipping 193 matching lines @@
         "transformers": ["foo"]
       })
     ]).create();
 
     pubUpgrade();
 
     process = pubRun(args: ['myapp']);
     process.stdout.expect("See ya!");
     process.shouldExit();
   });
+
+  // Issue 21298.
+  solo_integration("doesn't recache when a transformer is removed", () {
+    setUp();
+
+    d.dir(appPath, [
+      d.pubspec({
+        "name": "myapp",
+        "dependencies": {
+          "foo": "1.2.3",
+          "bar": "1.2.3"
+        },
+        "transformers": ["foo", "bar"]
+      }),
+      d.dir("bin", [
+        d.file("myapp.dart", "main() => print('Hello!');")
+      ])
+    ]).create();
+
+    var process = pubRun(args: ['myapp']);
+    process.stdout.expect("See ya!");
+    process.shouldExit();
+
+    d.dir(appPath, [
+      d.pubspec({
+        "name": "myapp",
+        "dependencies": {
+          "foo": "1.2.3",
+          // Add a new dependency to trigger another "pub get". This works
+          // around issue 20498.
+          "baz": "1.2.3"
+        },
+        "transformers": ["foo"]
+      }),
+      d.dir("bin", [
+        d.file("myapp.dart", "main() => print('Hello!');")
+      ])
+    ]).create();
+
+    process = pubRun(args: ['myapp']);
+    process.stdout.expect("Your pubspec has changed, so we need to update your lockfile:");

[Alan Knight, 2014/10/13 23:06:42]

80 cols

[nweiz, 2014/10/13 23:09:08]

Done.

+    process.stdout.expect(consumeThrough("Goodbye!"));
+    process.shouldExit();
+
+    // "bar" should still be in the manifest, since there's no reason to
+    // recompile the cache.
+    d.dir(appPath, [
+      d.dir(".pub/transformers", [
+        d.file("manifest.txt", "0.1.2+3\nbar,foo"),
+        d.matcherFile("transformers.snapshot", isNot(isEmpty))
+      ])
+    ]).validate();
+  });
 }
 
 String replaceTransformer(String input, String output) {
   return """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
 class ReplaceTransformer extends Transformer {
   ReplaceTransformer.asPlugin();
 
   String get allowedExtensions => '.dart';
 
   Future apply(Transform transform) {
     return transform.primaryInput.readAsString().then((contents) {
       transform.addOutput(new Asset.fromString(
           transform.primaryInput.id,
           contents.replaceAll("$input", "$output")));
     });
   }
 }
 """;
 }