anchor.diff:          // Drop patch files, since we don't have their source in the compiled
           // SDK.
           if (path.endsWith('-patch')) {
  -          failed.add(uri);
             return null;
           }
           // Canonicalize path. For instance: _collection-dev => _collection_dev.
  
positive.code: 
    final String pkgRoot;
    final String sdkRoot;
    List failed = [];
  
    Resolver({packageRoot: null, sdkRoot: null})
        : pkgRoot = packageRoot,
  
negative.code:       return uri;
      }
      // We cannot deal with anything else.
      return null;
    }
  }
  