Make a bunch of stuff in pub synchronous.

utils/pub/pub.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.
 
 /// The main entrypoint for the pub command line application.
 library pub;
 
 import 'dart:async';
 import '../../pkg/args/lib/args.dart';
 import '../../pkg/path/lib/path.dart' as path;
@@ skipping 220 matching lines @@
       }
 
       exit(_chooseExitCode(error));
     }
 
     var future = new Future.immediate(null);
     if (requiresEntrypoint) {
       // TODO(rnystrom): Will eventually need better logic to walk up
       // subdirectories until we hit one that looks package-like. For now, just
       // assume the cwd is it.
-      future = Entrypoint.load(path.current, cache);
+      future = defer(() => new Entrypoint(path.current, cache));

[nweiz, 2013/02/01 02:05:55]

I think this slightly arcane control flow is an artifact of pre-libv2 APIs.
Suggest:

    defer(() {
      if (requiresEntrypoint) {
        // TODO(rnystrom): Will eventually need better logic to walk up
        // subdirectories until we hit one that looks package-like. For now,
        // just assume the cwd is it.
        this.entrypoint = Entrypoint.load(path.current, cache);
      }
      try {
        var commandFuture = onRun();
        if (commandFuture == null) return true;

        return commandFuture;
      } catch (error, trace) {
        handleError(error, trace);
      }
    }).then((_) => cache_.deleteTempDir()).catchError((asyncError) {
      var e = asyncError.error;
      if (e is PubspecNotFoundException && e.name == null) {
        e = 'Could not find a file named "pubspec.yaml" in the directory '
          '${path.current}.';
      } else if (e is PubspecHasNoNameException && e.name == null) {
        e = 'pubspec.yaml is missing the required "name" field (e.g. "name: '
          '${basename(path.current)}").';
      }

      handleError(e, asyncError.stackTrace);
    }).then((_) {
      // Explicitly exit on success to ensure that any dangling dart:io handles
      // don't cause the process to never terminate.
      exit(0);
    });

[Bob Nystrom, 2013/02/01 23:17:21]

Beautiful. Tweaked it a bit more, but that's great.

     }
 
     future = future.then((entrypoint) {
       this.entrypoint = entrypoint;
       try {
         var commandFuture = onRun();
         if (commandFuture == null) return true;
 
         return commandFuture;
       } catch (error, trace) {
@@ skipping 47 matching lines @@
     if (exception is HttpException || exception is HttpParserException ||
         exception is SocketIOException || exception is PubHttpException) {
       return exit_codes.UNAVAILABLE;
     } else if (exception is FormatException) {
       return exit_codes.DATA;
     } else {
       return 1;
     }
   }
 }