Make a bunch of stuff in pub synchronous.

utils/pub/git_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 git_source;
 
 import 'dart:async';
 import 'git.dart' as git;
 import 'io.dart';
 import 'package.dart';
@@ skipping 24 matching lines @@
   Future<Package> installToSystemCache(PackageId id) {
     var revisionCachePath;
 
     return git.isInstalled.then((installed) {
       if (!installed) {
         throw new Exception(
             "Cannot install '${id.name}' from Git (${_getUrl(id)}).\n"
             "Please ensure Git is correctly installed.");
       }
 
-      return ensureDir(join(systemCacheRoot, 'cache'));
-    }).then((_) => _ensureRepoCache(id))
-      .then((_) => _revisionCachePath(id))
+      ensureDir(join(systemCacheRoot, 'cache'));
+      return _ensureRepoCache(id);
+    }).then((_) => _revisionCachePath(id))
       .then((path) {
       revisionCachePath = path;
-      return exists(revisionCachePath);
-    }).then((exists) {
-      if (exists) return;
+      if (entryExists(revisionCachePath)) return;
       return _clone(_repoCachePath(id), revisionCachePath, mirror: false);
     }).then((_) {
       var ref = _getEffectiveRef(id);
       if (ref == 'HEAD') return;
       return _checkOut(revisionCachePath, ref);
     }).then((_) {
-      return Package.load(id.name, revisionCachePath, systemCache.sources);
+      return new Package(id.name, revisionCachePath, systemCache.sources);
     });
   }
 
   /// Ensures [description] is a Git URL.
   void validateDescription(description, {bool fromLockFile: false}) {
     // A single string is assumed to be a Git URL.
     if (description is String) return;
     if (description is! Map || !description.containsKey('url')) {
       throw new FormatException("The description must be a Git URL or a map "
           "with a 'url' key.");
@@ skipping 27 matching lines @@
       description['resolved-ref'] = revision;
       return new PackageId(id.name, this, id.version, description);
     });
   }
 
   /// Ensure that the canonical clone of the repository referred to by [id] (the
   /// one in `<system cache>/git/cache`) exists and is up-to-date. Returns a
   /// future that completes once this is finished and throws an exception if it
   /// fails.
   Future _ensureRepoCache(PackageId id) {
-    var path = _repoCachePath(id);
-    return exists(path).then((exists) {
-      if (!exists) return _clone(_getUrl(id), path, mirror: true);
-
+    // Make sure all errors propagate through future.
+    return defer(() {
+      var path = _repoCachePath(id);
+      if (!entryExists(path)) return _clone(_getUrl(id), path, mirror: true);
       return git.run(["fetch"], workingDir: path).then((result) => null);
     });
   }
 
   /// Returns a future that completes to the revision hash of [id].
   Future<String> _revisionAt(PackageId id) {
     return git.run(["rev-parse", _getEffectiveRef(id)],
         workingDir: _repoCachePath(id)).then((result) => result[0]);
   }
 
   /// Returns the path to the revision-specific cache of [id].
   Future<String> _revisionCachePath(PackageId id) {
     return _revisionAt(id).then((rev) {
       var revisionCacheName = '${id.name}-$rev';
       return join(systemCacheRoot, revisionCacheName);
     });
   }
 
   /// Clones the repo at the URI [from] to the path [to] on the local
   /// filesystem.
   ///
   /// If [mirror] is true, create a bare, mirrored clone. This doesn't check out
   /// the working tree, but instead makes the repository a local mirror of the
   /// remote repository. See the manpage for `git clone` for more information.
   Future _clone(String from, String to, {bool mirror: false}) {
-    // Git on Windows does not seem to automatically create the destination
-    // directory.
-    return ensureDir(to).then((_) {
+    // Make sure exceptions propagate through future.
+    return defer(() {
+      // Git on Windows does not seem to automatically create the destination
+      // directory.
+      ensureDir(to);
       var args = ["clone", from, to];
       if (mirror) args.insertRange(1, 1, "--mirror");
       return git.run(args);
     }).then((result) => null);
   }
 
   /// Checks out the reference [ref] in [repoPath].
   Future _checkOut(String repoPath, String ref) {
     return git.run(["checkout", ref], workingDir: repoPath).then(
         (result) => null);
@@ skipping 42 matching lines @@
     return description['ref'];
   }
 
   /// Returns [description] if it's a description, or [PackageId.description] if
   /// it's a [PackageId].
   _getDescription(description) {
     if (description is PackageId) return description.description;
     return description;
   }
 }