code: func (m *metadataTracker) addFile(dev protocol.DeviceID, f FileIntf) {
  	m.mut.Lock()
  	defer m.mut.Unlock()
  
  	m.dirty = true
  
  	m.updateSeqLocked(dev, f)
  
  	if f.IsInvalid() && f.FileLocalFlags() == 0 {
  		// This is a remote invalid file; it does not count.
  		return
  	}
  
  	if flags := f.FileLocalFlags(); flags == 0 {
  		// Account regular files in the zero-flags bucket.
  		m.addFileLocked(dev, 0, f)
  	} else {
  		// Account in flag specific buckets.
  		eachFlagBit(flags, func(flag uint32) {
  			m.addFileLocked(dev, flag, f)
  		})
  	}
  }
docs: // addFile adds a file to the counts, adjusting the sequence number as
  // appropriate