anchor.diff:  
         // Delete the files
         changeSet = new ChangeSet();
  -      sourcesList.forEach((s) => changeSet.removedSource(s));
  +      sourcesList.forEach((s) {
  +        changeSet.changedContent(s, null);
  +        changeSet.removedSource(s);
  +      });
  +      // Remove sources implicitly created by imports of non-existing files
  +      changeSet.removedContainer(new _SourceContainer(pathPrefix));
         // _resolver.clear();
         _context.applyChanges(changeSet);
         _ensureAnalysisDone(_context, _MAX_ANALYSIS_DURATION);
  
positive.code:     //   print (folder);
      //   return _resolver;
      // };
      
      _context = builder.buildContext(_sourceDirectory.path);
  
  
  
negative.code:   }
  }
  
  class _SourceContainer implements SourceContainer {
    final String pathPrefix;
  
    _SourceContainer(this.pathPrefix);
  
    @override
    bool contains(Source source) => source.fullName.startsWith(pathPrefix);
  }
  
  class _Error {
    static final _HAS_FIXES_WHITELIST = [
      HintCode.UNUSED_IMPORT,
  