Make "pub update" update all packages.

utils/pub/entrypoint.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('entrypoint');
 
 #import('io.dart');
 #import('lock_file.dart');
 #import('package.dart');
 #import('root_source.dart');
@@ skipping 84 matching lines @@
       }
     }).chain((_) => id.resolved);
 
     _installs[id] = future;
 
     return future;
   }
 
   /**
    * Installs all dependencies of the [root] package to its "packages"
-   * directory. Returns a [Future] that completes when all dependencies are
-   * installed.
+   * directory, respecting the [LockFile] if present. Returns a [Future] that
+   * completes when all dependencies are installed.
    */
   Future installDependencies() {
-    return _getResolvedDependencies().chain((packageVersions) {
-      return Futures.wait(packageVersions.map((id) {
-        if (id.source is RootSource) return new Future.immediate(id);
-        return install(id);
-      }));
-    }).chain(_saveLockFile);
+    return _loadLockFile()
+      .chain((lockFile) => resolveVersions(cache.sources, root, lockFile))
+      .chain(_installDependencies);
   }
 
   /**
-   * Gets a list of all the [PackageId]s that this entrypoint transitively
-   * depends on. The concrete versions of these ids are given by the
-   * [VersionSolver] and the `pubspec.lock` file, if it exists.
+   * Installs the latest available versions of all dependencies of the [root]
+   * package to its "package" directory, writing a new [LockFile]. Returns a
+   * [Future] that completes when all dependencies are installed.
    */
-  Future<List<PackageId>> _getResolvedDependencies() {
-    return _loadLockFile().chain((lockFile) =>
-        resolveVersions(cache.sources, root, lockFile));
+  Future updateDependencies() {
+    return resolveVersions(cache.sources, root, new LockFile.empty()).
+      chain(_installDependencies);
   }
 
   /**
+   * Installs all dependencies listed in [packageVersions] and writes a
+   * [LockFile].
+   */
+  Future _installDependencies(List<PackageId> packageVersions) {
+    return Futures.wait(packageVersions.map((id) {
+      if (id.source is RootSource) return new Future.immediate(id);
+      return install(id);
+    })).chain(_saveLockFile);
+  }
+
+  /**
    * Loads the list of concrete package versions from the `pubspec.lock`, if it
    * exists. If it doesn't, this completes to an empty [LockFile].
    *
    * If there's an error reading the `pubspec.lock` file, this will print a
    * warning message and act as though the file doesn't exist.
    */
   Future<LockFile> _loadLockFile() {
     var completer = new Completer<LockFile>();
     var lockFilePath = join(root.dir, 'pubspec.lock');
     var future = readTextFile(lockFilePath);
@@ skipping 21 matching lines @@
    */
   Future _saveLockFile(List<PackageId> packageIds) {
     var lockFile = new LockFile.empty();
     for (var id in packageIds) {
       if (id.source is! RootSource) lockFile.packages[id.name] = id;
     }
 
     return writeTextFile(join(root.dir, 'pubspec.lock'), lockFile.serialize());
   }
 }