Make it strong mode clean.

lib/src/parser.dart

 // Copyright (c) 2013, 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 'arg_parser.dart';
 import 'arg_results.dart';
 import 'option.dart';
 
 final _SOLO_OPT = new RegExp(r'^-([a-zA-Z0-9])$');
 final _ABBR_OPT = new RegExp(r'^-([a-zA-Z0-9]+)(.*)$');
@@ skipping 17 matching lines @@
 
   /// The arguments being parsed.
   final List<String> args;
 
   /// The remaining non-option, non-command arguments.
   final rest = <String>[];
 
   /// The accumulated parsed options.
   final Map<String, dynamic> results = <String, dynamic>{};
 
-  Parser(this.commandName, this.grammar, this.args, this.parent, rest) {
+  Parser(this.commandName, this.grammar, this.args,
+      [this.parent, List<String> rest]) {
     if (rest != null) this.rest.addAll(rest);

[nweiz, 2016/03/02 23:58:54]

This addAll thing seems weird. Maybe change to "rest = rest ?? <String>[]".

[Bob Nystrom, 2016/03/03 00:19:08]

It is a bit weird, but if I recall, it needs to copy the list that gets passed
to it anyway, so this accomplishes that too.

   }
 
   /// The current argument being parsed.
   String get current => args[0];
 
   /// Parses the arguments. This can only be called once.
   ArgResults parse() {
     var arguments = args.toList();
     var commandResults = null;
 
@@ skipping 228 matching lines @@
   }
 
   /// Validates that [value] is allowed as a value of [option].
   void _validateAllowed(Option option, String value) {
     if (option.allowed == null) return;
 
     validate(option.allowed.contains(value),
         '"$value" is not an allowed value for option "${option.name}".');
   }
 }