Beat on hosted repo support on Windows a bit more.

utils/pub/hosted_source.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('hosted_source');
 
+#import('dart:io', prefix: 'io');
 #import('dart:json');
 #import('dart:uri');
+
 #import('io.dart');
 #import('package.dart');
 #import('pubspec.dart');
 #import('source.dart');
 #import('source_registry.dart');
 #import('utils.dart');
 #import('version.dart');
 
 /**
  * A package source that installs packages from a package hosting site that
@@ skipping 44 matching lines @@
 
   /**
    * Downloads a package from the site and unpacks it.
    */
   Future<bool> install(PackageId id, String destPath) {
     var parsedDescription = _parseDescription(id.description);
     var name = parsedDescription.first;
     var url = parsedDescription.last;
 
     var fullUrl = "$url/packages/$name/versions/${id.version}.tar.gz";
+
     return Futures.wait([httpGet(fullUrl), ensureDir(destPath)]).chain((args) {
       return timeout(extractTarGz(args[0], args[1]), HTTP_TIMEOUT,
           'Timed out while fetching URL "$fullUrl".');
+    }).transformException((ex) {
+      // If the install failed, delete the directory. Prevents leaving a ghost
+      // directory in the system cache which would later make pub think the
+      // install succeeded.
+      // TODO(rnystrom): Use deleteDir() here when transformException() supports
+      // returning a future. Also remove dart:io import then.
+      new io.Directory(destPath).deleteRecursivelySync();
+
+      throw ex;
     });
   }
 
   /**
    * The system cache directory for the hosted source contains subdirectories
    * for each separate repository URL that's used on the system. Each of these
    * subdirectories then contains a subdirectory for each package installed
    * from that site.
    */
   String systemCacheDirectory(PackageId id) {
@@ skipping 44 matching lines @@
 
     var name = description["name"];
     if (name is! String) {
       throw new FormatException("The 'name' key must have a string value.");
     }
 
     var url = description.containsKey("url") ? description["url"] : defaultUrl;
     return new Pair<String, String>(name, url);
   }
 }