"pub cache repair" prints a more detailed summary.

lib/src/source/cached.dart

 // Copyright (c) 2014, 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.source.cached;
 
 import 'dart:async';
 
 import 'package:path/path.dart' as path;
 
@@ skipping 49 matching lines @@
 
   /// Downloads the package identified by [id] to the system cache.
   Future<Package> downloadToSystemCache(PackageId id);
 
   /// Returns the [Package]s that have been downloaded to the system cache.
   List<Package> getCachedPackages();
 
   /// Reinstalls all packages that have been previously installed into the
   /// system cache by this source.
   ///
-  /// Returns a [Pair] whose first element is the number of packages
-  /// successfully repaired and the second is the number of failures.
-  Future<Pair<int, int>> repairCachedPackages();
+  /// Returns a [Pair] whose first element is the packages that were
+  /// successfully repaired and the second is the packages that failed to be
+  /// repaired.
+  Future<Pair<List<PackageId>, List<PackageId>>> repairCachedPackages();
 }