Handle circular dependencies on the root package when checking SDK constraints.

utils/tests/pub/sdk_constraint_test.dart

 // Copyright (c) 2012, 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 check_sdk_test;
 
 import "test_pub.dart";
 import "../../../pkg/unittest/lib/unittest.dart";
 
 main() {
@@ skipping 99 matching lines @@
       schedulePub(args: [command],
           error:
             """
             Some packages are not compatible with your SDK version 0.1.2+3:
             - 'bar' requires <0.1.1
 
             You may be able to resolve this by upgrading to the latest Dart SDK
             or adding a version constraint to use an older version of a package.
             """);
     });
+
+    integration("handles a circular dependency on the root package", () {
+      // Using an SDK source, but this should be true of all sources.
+      dir(sdkPath, [
+        dir("pkg", [
+          dir("foo", [
+            libPubspec("foo", "0.0.1", sdk: ">3.0.0", deps: [
+              {"sdk": "myapp"}
+            ]),
+            libDir("foo")
+          ])
+        ])
+      ]).scheduleCreate();
+
+      dir(appPath, [
+        pubspec({
+          "name": "myapp",
+          "dependencies": {
+            "foo": { "sdk": "foo" }
+          },
+          "environment": {"sdk": ">2.0.0"}
+        })
+      ]).scheduleCreate();
+
+      schedulePub(args: [command],
+          error:
+            """
+            Some packages are not compatible with your SDK version 0.1.2+3:
+            - 'myapp' requires >2.0.0
+            - 'foo' requires >3.0.0
+
+            You may be able to resolve this by upgrading to the latest Dart SDK
+            or adding a version constraint to use an older version of a package.
+            """);
+    });
   }
 }