Fix a lockfile freshness checking bug.

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.
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:barback/barback.dart';
 import 'package:package_config/packages_file.dart' as packages_file;
 import 'package:path/path.dart' as p;
 import 'package:pub_semver/pub_semver.dart';
 
 import 'barback/asset_environment.dart';
+import 'exceptions.dart';
 import 'io.dart';
 import 'lock_file.dart';
 import 'log.dart' as log;
 import 'package.dart';
 import 'package_graph.dart';
 import 'sdk.dart' as sdk;
 import 'solver/version_solver.dart';
 import 'source/cached.dart';
 import 'source/unknown.dart';
 import 'system_cache.dart';
@@ skipping 480 matching lines @@
   /// not in the lockfile or that don't match what's in there.
   bool _isLockFileUpToDate() {
     if (!root.immediateDependencies.every(_isDependencyUpToDate)) return false;
 
     var overrides = root.dependencyOverrides.map((dep) => dep.name).toSet();
 
     // Check that uncached dependencies' pubspecs are also still satisfied,
     // since they're mutable and may have changed since the last get.
     return lockFile.packages.values.every((id) {
       var source = cache.sources[id.name];
-      if (source is! CachedSource) return true;
+      if (source is CachedSource) return true;
 
-      return cache.sources.load(id).dependencies.every((dep) =>
-          overrides.contains(dep.name) || _isDependencyUpToDate(dep));
+      try {
+        return cache.sources.load(id).dependencies.every((dep) =>
+            overrides.contains(dep.name) || _isDependencyUpToDate(dep));
+      } on FileException {
+        // If we can't load the pubpsec, the user needs to re-run "pub get".
+        return false;
+      }
     });
   }
 
   /// Returns whether the locked version of [dep] matches the dependency.
   bool _isDependencyUpToDate(PackageDep dep) {
     var locked = lockFile.packages[dep.name];
     if (locked == null) return false;
 
     if (dep.source != locked.source) return false;
 
@@ skipping 136 matching lines @@
   /// If [packageSymlinks] is true, creates a symlink to the "packages"
   /// directory in [dir].
   ///
   /// Otherwise, deletes a "packages" directories in [dir] if one exists.
   void _linkOrDeleteSecondaryPackageDir(String dir) {
     var symlink = p.join(dir, 'packages');
     if (entryExists(symlink)) deleteEntry(symlink);
     if (_packageSymlinks) createSymlink(packagesDir, symlink, relative: true);
   }
 }