Adds check for `AsExpression`s (Fix #145).

tool/rule.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:io';
 
 import 'package:args/args.dart';
 
 String capitalize(String s) => s.substring(0, 1).toUpperCase() + s.substring(1);
 
@@ skipping 46 matching lines @@
     }
   }
 
   var libName = options['library'];
 
   if (libName == null) {
     printUsage(parser);
     return;
   }
 
-  // Generate rule stub
+  // Generate rule stub.
   generateStub(libName, outDir: outDir);
 
-  // Generate test stub
+  // Generate test stub.
   generateTest(libName, outDir: outDir);
+
+  // Update rule registry.
+  updateRuleRegistry(libName);
 }
 
 void printUsage(ArgParser parser, [String error]) {
   var message = error ?? 'Generates rule stubs.';
 
   stdout.write('''$message
 Usage: rule
 ${parser.usage}
 ''');
 }
@@ skipping 47 matching lines @@
 
 
 }
 """;
 
 String _generateTest(String libName, String className) => '''
 // Copyright (c) 2015, 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.
 
+// test w/ `dart test/util/solo_test.dart $libName`
+
 ''';
 
-void addToRuleIndex(String libName, String className) {
+void updateRuleRegistry(String libName) {
   //TODO: find right place to insert into imports and ruleMap
+  print("Don't forget to update lib/rules.dart with a line like:");
+  print("  ..register(new ${toClassName(libName)}())");
+  print("Then run your test like so:");
+  print("  dart test/util/solo_test.dart $libName");
 }