code: func (s ShortFuncFormatter) Format(w io.Writer, entry zapcore.Entry, fields []zapcore.Field) {
  	f := runtime.FuncForPC(entry.Caller.PC)
  	if f == nil {
  		fmt.Fprintf(w, s.FormatVerb, "(unknown)")
  		return
  	}
  
  	fname := f.Name()
  	funcIdx := strings.LastIndex(fname, ".")
  	fmt.Fprintf(w, s.FormatVerb, fname[funcIdx+1:])
  }
docs: // Format writes the calling function name to the provided writer. The name is obtained from
  // the runtime and the package and line numbers are discarded.