Return wrapped error with "%w" verb instead of "%s"

[code19m]

func parseFile(path string, cfg interface{}) error {
	// open the configuration file
	f, err := os.OpenFile(path, os.O_RDONLY|os.O_SYNC, 0)
	if err != nil {
		return err
	}
	defer f.Close()

	// parse the file depending on the file type
	switch ext := strings.ToLower(filepath.Ext(path)); ext {
	case ".yaml", ".yml":
		err = ParseYAML(f, cfg)
	case ".json":
		err = ParseJSON(f, cfg)
	case ".toml":
		err = ParseTOML(f, cfg)
	case ".edn":
		err = parseEDN(f, cfg)
	case ".env":
		err = parseENV(f, cfg)
	default:
		return fmt.Errorf("file format '%s' doesn't supported by the parser", ext)
	}
	if err != nil {
		return fmt.Errorf("config file parsing error: %s", err.Error())
	}
	return nil
}

In this function, it would be better to return an error with the "%w" verb instead of "%s". In that case, when using cleanenv.ReadConfig, the returned error can be checked with the errors.Is(err, io.EOF) function.
Let's say I want to allow the user to leave the config file empty so that default values will be taken. But for this, I am now forced to check it with function like this:

func isEOFerr(err error) bool {
	return strings.HasSuffix(err.Error(), io.EOF.Error())
}