Detect transformer dependency cycles in packages using barback transformers.

sdk/lib/_internal/pub/lib/src/directory_tree.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.
 
 /// A simple library for rendering a list of files as a directory tree.
 library pub.directory_tree;
 
 import 'package:path/path.dart' as path;
 
+import 'utils.dart';
+
 /// Draws a directory tree for the given list of files. Given a list of files
 /// like:
 ///
 ///     TODO
 ///     example/console_example.dart
 ///     example/main.dart
 ///     example/web copy/web_example.dart
 ///     test/absolute_test.dart
 ///     test/basename_test.dart
 ///     test/dirname_test.dart
@@ skipping 74 matching lines @@
   if (isLast) return "    ";
   return "|   ";
 }
 
 void _draw(StringBuffer buffer, String prefix, bool isLast,
                  String name, Map children) {
   // Don't draw a line for the root node.
   if (name != null) _drawLine(buffer, prefix, isLast, name);
 
   // Recurse to the children.
-  var childNames = new List.from(children.keys);
-  childNames.sort();
+  var childNames = ordered(children.keys);
 
   _drawChild(bool isLastChild, String child) {
     var childPrefix = _getPrefix(name == null, isLast);
     _draw(buffer, '$prefix$childPrefix', isLastChild, child, children[child]);
   }
 
   if (name == null || childNames.length <= 10) {
     // Not too many, so show all the children.
     for (var i = 0; i < childNames.length; i++) {
       _drawChild(i == childNames.length - 1, childNames[i]);
     }
   } else {
     // Show the first few.
     _drawChild(false, childNames[0]);
     _drawChild(false, childNames[1]);
     _drawChild(false, childNames[2]);
 
     // Elide the middle ones.
     buffer.write(prefix);
     buffer.write(_getPrefix(name == null, isLast));
     buffer.writeln('| (${childNames.length - 6} more...)');
 
     // Show the last few.
     _drawChild(false, childNames[childNames.length - 3]);
     _drawChild(false, childNames[childNames.length - 2]);
     _drawChild(true, childNames[childNames.length - 1]);
   }
 }