Add support for separators.

lib/src/usage.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.
 
 library args.src.usage;
 
 import 'dart:math';
 
 import '../args.dart';
 
@@ skipping 44 matching lines @@
 
   Usage(this.args);
 
   /// Generates a string displaying usage information for the defined options.
   /// This is basically the help text shown on the command line.
   String generate() {
     buffer = new StringBuffer();
 
     calculateColumnWidths();
 
-    args.options.forEach((name, option) {
-      if (option.hide) return;
+    for (var optionOrSeparator in args.optionsAndSeparators) {
+      if (optionOrSeparator is String) {
+        // Ensure that there's always a blank line before a separator.
+        if (buffer.isNotEmpty) buffer.write("\n\n");
+        buffer.write(optionOrSeparator);
+        newlinesNeeded = 1;
+        continue;
+      }
+
+      var option = optionOrSeparator;

[Bob Nystrom, 2015/05/21 16:43:16]

Do you need an "as Option" here?

[nweiz, 2015/05/21 19:22:27]

The analyzer infers it as dynamic, so it doesn't produce any warnings. That also
means it won't warn about misuse, though; would you prefer that I add it?

[Bob Nystrom, 2015/05/21 19:42:27]

Yeah, I think so.

[nweiz, 2015/05/21 19:52:37]

Done.

+      if (option.hide) continue;
 
       write(0, getAbbreviation(option));
       write(1, getLongOption(option));
 
       if (option.help != null) write(2, option.help);
 
       if (option.allowedHelp != null) {
         var allowedNames = option.allowedHelp.keys.toList(growable: false);
         allowedNames.sort();
         newline();
@@ skipping 10 matching lines @@
         } else if (!option.isFlag) {
           write(2, '(defaults to "${option.defaultValue}")');
         }
       }
 
       // If any given option displays more than one line of text on the right
       // column (i.e. help, default value, allowed options, etc.) then put a
       // blank line after it. This gives space where it's useful while still
       // keeping simple one-line options clumped together.
       if (numHelpLines > 1) newline();
-    });
+    }
 
     return buffer.toString();
   }
 
   String getAbbreviation(Option option) {
     if (option.abbreviation != null) {
       return '-${option.abbreviation}, ';
     } else {
       return '';
     }
@@ skipping 126 matching lines @@
 String padRight(String source, int length) {
   final result = new StringBuffer();
   result.write(source);
 
   while (result.length < length) {
     result.write(' ');
   }
 
   return result.toString();
 }