anchor.diff:    List<FunctionElement> functions = <FunctionElement>[];
     List<VariableElement> top_variables = <VariableElement>[];
     
  -  SourceElement(Source this.source, CompilationUnit ast);
  +  SourceElement(Source this.source, CompilationUnit this.ast);
     
   }
   
  
positive.code:     if (!analysis.containsSource(source)) {
        CompilationUnit unit = engine.getCompilationUnit(source); 
        element = new SourceElement(source, unit);
        this.visitCompilationUnit(unit);
      } else {
        element = analysis.getSource(source);
  
negative.code:   }
    
    visitImportDirective(ImportDirective node) {
      Source source = engine.getSource(this.source, node);
      ElementGenerator generator = new ElementGenerator(engine, source, analysis);
      element.addImport(source);
      super.visitImportDirective(node);
    }
  }