Detect transformer dependency cycles in packages using barback transformers.

sdk/lib/_internal/pub/lib/src/solver/version_solver.dart

Index: sdk/lib/_internal/pub/lib/src/solver/version_solver.dart
diff --git a/sdk/lib/_internal/pub/lib/src/solver/version_solver.dart b/sdk/lib/_internal/pub/lib/src/solver/version_solver.dart
index eb2fc63af90de8127d7e1bafd3004e8cda641a13..09d5fbf22fcbbed627df7da8e73121a58b2dcd6b 100644
--- a/sdk/lib/_internal/pub/lib/src/solver/version_solver.dart
+++ b/sdk/lib/_internal/pub/lib/src/solver/version_solver.dart
@@ -187,8 +187,7 @@ abstract class SolveFailure implements ApplicationException {
       map[dep.depender] = dep.dep;
     }
 
-    var names = map.keys.toList();
-    names.sort();
+    var names = ordered(map.keys);
 
     buffer.writeAll(names.map(
         (name) => "- '$name' ${_describeDependency(map[name])}"), '\n');