Have Pub make use of the arg parser.

tests/lib/args/args_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('args_test');
 
 #import('../../../lib/unittest/unittest.dart');
 #import('../../../lib/args/args.dart');
 
 main() {
@@ skipping 104 matching lines @@
 
       test('are not preferred over a colliding one without', () {
         var parser = new ArgParser();
         parser.addFlag('no-strum');
         parser.addFlag('strum');
 
         var args = parser.parse(['--no-strum']);
         expect(args['no-strum'], isTrue);
         expect(args['strum'], isFalse);
       });
+
+      test('fail for non-negatable flags', () {
+        var parser = new ArgParser();
+        parser.addFlag('strum', negatable: false);
+
+        throwsBadFormat(parser, ['--no-strum']);
+      });
     });
 
     group('callbacks', () {
       test('for present flags are invoked with the value', () {
         var a;
         var parser = new ArgParser();
         parser.addFlag('a', callback: (value) => a = value);
 
         var args = parser.parse(['--a']);
         expect(a, isTrue);
@@ skipping 238 matching lines @@
 
         var results = parser.parse(['--woof', '--', '--meow']);
         expect(results['woof'], isTrue);
         expect(results['meow'], equals('kitty'));
         expect(results.rest, orderedEquals(['--meow']));
       });
     });
   });
 
   group('ArgParser.getUsage()', () {
-    test('flags show "no-" in title', () {
+    test('negatable flags show "no-" in title', () {
       var parser = new ArgParser();
       parser.addFlag('mode', help: 'The mode');
 
       validateUsage(parser,
           '''
           --[no-]mode    The mode
           ''');
     });
 
+    test('non-negatable flags don\'t show "no-" in title', () {
+      var parser = new ArgParser();
+      parser.addFlag('mode', negatable: false, help: 'The mode');
+
+      validateUsage(parser,
+          '''
+          --mode    The mode
+          ''');
+    });
+
     test('if there are no abbreviations, there is no column for them', () {
       var parser = new ArgParser();
       parser.addFlag('mode', help: 'The mode');
 
       validateUsage(parser,
           '''
           --[no-]mode    The mode
           ''');
     });
 
@@ skipping 177 matching lines @@
         throw new IllegalArgumentException(
             'Line "$line" does not have enough indentation.');
       }
 
       lines[i] = line.substring(indent);
     }
   }
 
   return Strings.join(lines, '\n');
 }