Install before starting the server if the lockfile is out of date.

sdk/lib/_internal/pub/lib/src/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 pub.entrypoint;
 
 import 'dart:async';
 
 import 'package:path/path.dart' as path;
 
@@ skipping 136 matching lines @@
   }
 
   /// Loads the list of concrete package versions from the `pubspec.lock`, if it
   /// exists. If it doesn't, this completes to an empty [LockFile].
   LockFile loadLockFile() {
     var lockFilePath = path.join(root.dir, 'pubspec.lock');
     if (!entryExists(lockFilePath)) return new LockFile.empty();
     return new LockFile.load(lockFilePath, cache.sources);
   }
 
+  /// Determines whether or not the lockfile is out of date with respect to the
+  /// pubspec.
+  ///
+  /// This will be `true` if there is no lockfile at all, or if the pubspec
+  /// contains dependencies that are not in the lockfile or that don't match
+  /// what's in there.

[nweiz, 2013/07/30 19:34:36]

Doesn't this return `false` in those cases?

[Bob Nystrom, 2013/07/30 21:35:32]

Fixed. Originally wrote the method to be isLockFileOutOfDate() and forgot to
update the docs.

+  bool isLockFileUpToDate() {
+    var lockFile = loadLockFile();
+
+    checkDependency(package) {
+      var locked = lockFile.packages[package.name];
+      if (locked == null) return false;
+
+      if (package.source != locked.source) return false;
+      if (!package.constraint.allows(locked.version)) return false;
+
+      var source = cache.sources[package.source];
+      if (!source.descriptionsEqual(package.description,
+                                    locked.description)) return false;

[nweiz, 2013/07/30 19:34:36]

Style nit: I think if the if clause goes over one line, the return should be on
its own line in a block.

[Bob Nystrom, 2013/07/30 21:35:32]

Done.

+
+      return true;
+    }
+
+    if (!root.dependencies.every(checkDependency)) return false;
+    if (!root.devDependencies.every(checkDependency)) return false;
+
+    return true;
+  }
+
   /// Saves a list of concrete package versions to the `pubspec.lock` file.
   void _saveLockFile(List<PackageId> packageIds) {
     var lockFile = new LockFile.empty();
     for (var id in packageIds) {
       if (!id.isRoot) lockFile.packages[id.name] = id;
     }
 
     var lockFilePath = path.join(root.dir, 'pubspec.lock');
     writeTextFile(lockFilePath, lockFile.serialize());
   }
@@ skipping 91 matching lines @@
         // Skip directories and broken symlinks.
         if (!fileExists(file)) return false;
 
         var relative = path.relative(file, from: beneath);
         if (_BLACKLISTED_FILES.contains(path.basename(relative))) return false;
         return !path.split(relative).any(_BLACKLISTED_DIRS.contains);
       }).toList();
     });
   }
 }