code: func (f *folder) ForceRescan(file protocol.FileInfo) error {
  	file.SetMustRescan(f.shortID)
  	f.fset.Update(protocol.LocalDeviceID, []protocol.FileInfo{file})
  
  	return f.Scan([]string{file.Name})
  }
docs: // ForceRescan marks the file such that it gets rehashed on next scan and then
  // immediately executes that scan.