Support subcommands in pub and pub help.

sdk/lib/_internal/pub/lib/src/command/help.dart

Index: sdk/lib/_internal/pub/lib/src/command/help.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/help.dart b/sdk/lib/_internal/pub/lib/src/command/help.dart
index 91181754d3420882f9a398b0e5007598b224929c..d4dec41c8b9f3cdfba9925c7f0af6fea5e53230f 100644
--- a/sdk/lib/_internal/pub/lib/src/command/help.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/help.dart
@@ -19,18 +19,47 @@ class HelpCommand extends PubCommand {
   bool get takesArguments => true;
 
   Future onRun() {
+    // Show the default help if no command was specified.
     if (commandOptions.rest.isEmpty) {
       PubCommand.printGlobalUsage();
-    } else {
-      var name = commandOptions.rest[0];
-      var command = PubCommand.commands[name];
-      if (command == null) {
-        log.error('Could not find a command named "$name".');
-        log.error('Run "pub help" to see available commands.');
-        return flushThenExit(exit_codes.USAGE);
+      return null;
+    }
+
+    // Walk the command tree to show help for the selected command or
+    // subcommand.
+    var commands = PubCommand.mainCommands;
+    var command = null;
+    var commandString = "pub";
+
+    _usageError(message) {

[nweiz, 2014/01/31 21:42:06]

You've defined this same function here and in pub.dart. Maybe
[PubCommand.listCommands] should be private and this should be
[PubCommand.usageError]?

[Bob Nystrom, 2014/02/01 01:49:32]

OK, done. This triggered a cascade of changes. To make usageError more usage, I
made it throw. In order for that to work in bin/pub.dart, I had to move the
error-handling in there to ensure it catches the UsageException.

+      var buffer = new StringBuffer();
+      buffer.writeln(message);
+      PubCommand.listCommands(commands, buffer, isSubcommand: command != null);
+      log.error(buffer);
+      return flushThenExit(exit_codes.USAGE);
+    }
+
+    for (var name in commandOptions.rest) {
+      if (commands.isEmpty) {
+        return _usageError(
+            'Command "$commandString" does not expect a subcommand.');
       }
 
-      command.printUsage();
+      if (commands[name] == null) {
+        if (command == null) {
+          return _usageError('Could not find a command named "$name".');

[nweiz, 2014/01/31 21:42:06]

Same issue with "find" as before.

[Bob Nystrom, 2014/02/01 01:49:32]

Same explanation as before. :)

+        }
+
+        return _usageError('Could not find a subcommand named "$name" '
+                           'for "$commandString".');
+      }
+
+      command = commands[name];
+      commands = command.subcommands;
+      commandString += " $name";
     }
+
+    command.printUsage();
+    return null;
   }
 }