code: func (d *deployerImpl) isPresentInSite(ctx context.Context, subdir string, f pkg.FileInfo, followSymlinks bool) bool {
  	absPath, err := d.fs.RootRelToAbs(filepath.Join(subdir, filepath.FromSlash(f.Name)))
  	if err != nil {
  		panic(err) // should not happen for files present in installed packages
  	}
  
  	stat := d.fs.Lstat
  	if followSymlinks {
  		stat = d.fs.Stat
  	}
  
  	// TODO(vadimsh): Use result of this call to check the correctness of file
  	// mode of the deployed file. Also use ModTime to detect modifications to the
  	// file content in higher paranoia modes.
  	switch _, err = stat(ctx, absPath); {
  	case err == nil:
  		return true
  	case os.IsNotExist(err):
  		return false
  	default:
  		logging.Warningf(ctx, "Failed to check presence of %q, assuming it needs repair: %s", f.Name, err)
  		return false
  	}
  }
docs: // isPresentInSite checks whether the given file is installed in the site root.
  //
  // Optionally follows symlinks.
  //
  // If the file can't be checked for some reason, logs the error and returns
  // false.