@Nullable
  private IdFilter extractFileEnumeration(@NotNull GlobalSearchScope scope) {
    VirtualFileEnumeration hint = VirtualFileEnumeration.extract(scope);
    if (hint != null) {
      return new IdFilter() {
        @Override
        public boolean containsFileId(int id) {
          return hint.contains(id);
        }

        @Override
        public String toString() {
          return "IdFilter of " + scope;
        }
      };
    }
    Project project = scope.getProject();
    if (project == null) return null;
    // todo support project only content scope
    return projectIndexableFiles(project);
  }
@Nullable
  private IdFilter extractFileEnumeration(@NotNull GlobalSearchScope scope)