Refactor Source and SourceRegistry.

lib/src/lock_file.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:collection';
 
 import 'package:path/path.dart' as p;
 import 'package:package_config/packages_file.dart' as packages_file;
 import 'package:pub_semver/pub_semver.dart';
 import 'package:source_span/source_span.dart';
 import 'package:yaml/yaml.dart';
 
 import 'io.dart';
 import 'package.dart';
 import 'source_registry.dart';
+import 'system_cache.dart';
 import 'utils.dart';
 
 /// A parsed and validated `pubspec.lock` file.
 class LockFile {
   /// The source registry with which the lock file's IDs are interpreted.
   final SourceRegistry _sources;
 
   /// The packages this lockfile pins.
   final Map<String, PackageId> packages;
 
@@ skipping 142 matching lines @@
 
     var packages = new Map.from(this.packages);
     packages.remove(name);
     return new LockFile._(packages, sdkConstraint, _sources);
   }
 
   /// Returns the contents of the `.packages` file generated from this lockfile.
   ///
   /// If [entrypoint] is passed, a relative entry is added for its "lib/"
   /// directory.
-  String packagesFile([String entrypoint]) {
+  String packagesFile(SystemCache cache, [String entrypoint]) {
     var header = "Generated by pub on ${new DateTime.now()}.";
 
     var map = new Map.fromIterable(ordered(packages.keys), value: (name) {
       var id = packages[name];
-      var source = _sources[id.source];
+      var source = cache.source(id.source);
       return p.toUri(p.join(source.getDirectory(id), "lib"));
     });
 
     if (entrypoint != null) map[entrypoint] = Uri.parse("lib/");
 
     var text = new StringBuffer();
     packages_file.write(text, map, comment: header);
     return text.toString();
   }
 
@@ skipping 16 matching lines @@
     });
 
     var data = {'sdk': sdkConstraint.toString(), 'packages': packageMap};
     return """
 # Generated by pub
 # See http://pub.dartlang.org/doc/glossary.html#lockfile
 ${yamlToString(data)}
 """;
   }
 }