Auto-reinstall broken packages in the system cache.

utils/pub/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 source;
 
 import 'dart:async';
 import 'io.dart';
 import 'package.dart';
 import 'pubspec.dart';
@@ skipping 90 matching lines @@
   }
 
   /// Installs the package identified by [id] to the system cache. This is only
   /// called for sources with [shouldCache] set to true.
   ///
   /// By default, this uses [systemCacheDirectory] and [install].
   Future<Package> installToSystemCache(PackageId id) {
     var path;
     return systemCacheDirectory(id).then((p) {
       path = p;
-      if (dirExists(path)) return true;
+
+      // See if it's already cached.
+      if (!dirExists(path)) return false;
+
+      return _isCachedPackageCorrupted(path).then((isCorrupted) {
+        if (!isCorrupted) return true;
+
+        // Busted, so wipe out the package and reinstall.
+        return deleteDir(path).then((_) => false);
+      });
+    }).then((isInstalled) {
+      if (isInstalled) return true;
       ensureDir(dirname(path));
       return install(id, path);
     }).then((found) {
       if (!found) throw 'Package $id not found.';
       return new Package.load(id.name, path, systemCache.sources);
     });
   }
 
+  /// Since pub generates symlinks that point into the system cache (in
+  /// particular, targeting the "lib" directories of cached packages), it's
+  /// possible to accidentally break cached packages if something traverses
+  /// that symlink.
+  ///
+  /// This tries to determine if the cached package at [packageDir] has been
+  /// corrupted. The heuristics are it is corrupted if any of the following are
+  /// true:
+  ///
+  ///   * It has an empty "lib" directory.
+  ///   * It has no pubspec.
+  Future<bool> _isCachedPackageCorrupted(String packageDir) {
+    return defer(() {
+      if (!fileExists(join(packageDir, "pubspec.yaml"))) return true;
+
+      var libDir = join(packageDir, "lib");
+      if (dirExists(libDir)) {
+        return listDir(libDir).then((contents) => contents.length == 0);
+      }
+
+      // If we got here, it's OK.
+      return false;
+    });
+  }
+
   /// Returns the directory in the system cache that the package identified by
   /// [id] should be installed to. This should return a path to a subdirectory
   /// of [systemCacheRoot].
   ///
   /// This doesn't need to be implemented if [shouldCache] is false.
   Future<String> systemCacheDirectory(PackageId id) {
     return new Future.immediateError(
         "systemCacheDirectory() must be implemented if shouldCache is true.");
   }
 
@@ skipping 33 matching lines @@
   /// according to [validateDescription], although it must still be serializable
   /// to JSON and YAML. It must also be equal to [id] according to
   /// [descriptionsEqual].
   ///
   /// By default, this just returns [id].
   Future<PackageId> resolveId(PackageId id) => new Future.immediate(id);
 
   /// Returns the source's name.
   String toString() => name;
 }