Add an explicit distinction between a command's description and summary.

lib/command_runner.dart

 // Copyright (c) 2014, 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:async';
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'src/arg_parser.dart';
 import 'src/arg_results.dart';
@@ skipping 172 matching lines @@
 /// A command is known as a "leaf command" if it has no subcommands and is meant
 /// to be run. Leaf commands must override [run].
 ///
 /// A command with subcommands is known as a "branch command" and cannot be run
 /// itself. It should call [addSubcommand] (often from the constructor) to
 /// register subcommands.
 abstract class Command {
   /// The name of this command.
   String get name;
 
-  /// A short description of this command.
+  /// A description of this command, included in [usage].
   String get description;
 
+  /// A short description of this command, included in [parent]'s
+  /// [CommandRunner.usage].
+  ///
+  /// This defaults to the first line of [description].
+  String get summary => description.split("\n").first;
+
   /// A single-line template for how to invoke this command (e.g. `"pub get
   /// [package]"`).
   String get invocation {
     var parents = [name];
     for (var command = parent; command != null; command = command.parent) {
       parents.add(command.name);
     }
     parents.add(runner.executableName);
 
     var invocation = parents.reversed.join(" ");
@@ skipping 158 matching lines @@
   var visible = names.where((name) => !commands[name].hidden);
   if (visible.isNotEmpty) names = visible;
 
   // Show the commands alphabetically.
   names = names.toList()..sort();
   var length = names.map((name) => name.length).reduce(math.max);
 
   var buffer =
       new StringBuffer('Available ${isSubcommand ? "sub" : ""}commands:');
   for (var name in names) {
-    var lines = commands[name].description.split("\n");
+    var lines = commands[name].summary.split("\n");
     buffer.writeln();
     buffer.write('  ${padRight(name, length)}   ${lines.first}');
 
     for (var line in lines.skip(1)) {
       buffer.writeln();
       buffer.write(' ' * (length + 5));
       buffer.write(line);
     }
   }
 
   return buffer.toString();
 }