anchor.diff:    @override
     Source resolveAbsolute(Uri _ignore, [Uri uri]) {
       uri ??= _ignore;
  -    return _sourceCache.putIfAbsent(uri, () {
  -      if (uri.scheme != 'package') {
  -        return null;
  -      }
  -
  -      Source basicResolverSource = _normalUriResolver.resolveAbsolute(uri);
  -      if (basicResolverSource != null && basicResolverSource.exists()) {
  -        return basicResolverSource;
  -      }
  -
  -      String uriPath = uri.path;
  -      int slash = uriPath.indexOf('/');
  -
  -      // If the path either starts with a slash or has no slash, it is invalid.
  -      if (slash < 1) {
  -        return null;
  -      }
  -
  -      String packageName = uriPath.substring(0, slash);
  -      String fileUriPart = uriPath.substring(slash + 1);
  -      String filePath = fileUriPart.replaceAll('/', _context.separator);
  -
  -      File file = _workspace.builtFile(
  -          _workspace.builtPackageSourcePath(filePath), packageName);
  -      if (file != null && file.exists) {
  -        return file.createSource(uri);
  -      }
  +    if (uri.scheme != 'package') {
  +      return null;
  +    }
  +
  +    Source basicResolverSource = _normalUriResolver.resolveAbsolute(uri);
  +    if (basicResolverSource != null && basicResolverSource.exists()) {
         return basicResolverSource;
  -    });
  +    }
  +
  +    String uriPath = uri.path;
  +    int slash = uriPath.indexOf('/');
  +
  +    // If the path either starts with a slash or has no slash, it is invalid.
  +    if (slash < 1) {
  +      return null;
  +    }
  +
  +    String packageName = uriPath.substring(0, slash);
  +    String fileUriPart = uriPath.substring(slash + 1);
  +    String filePath = fileUriPart.replaceAll('/', _context.separator);
  +
  +    File file = _workspace.builtFile(
  +        _workspace.builtPackageSourcePath(filePath), packageName);
  +    if (file != null && file.exists) {
  +      return file.createSource(uri);
  +    }
  +    return basicResolverSource;
     }
   
     @override
  
positive.code:   final UriResolver _normalUriResolver;
    final path.Context _context;
  
    /**
     * The cache of absolute [Uri]s to [Source]s mappings.
     */
    final Map<Uri, Source> _sourceCache = HashMap<Uri, Source>();
  
    PackageBuildPackageUriResolver(
        PackageBuildWorkspace workspace, this._normalUriResolver)
        : _workspace = workspace,
  
negative.code: // 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:core';
  
  import 'package:analyzer/file_system/file_system.dart';
  