StringToSliceHookFunc adds TrimSpace to handle the problem of spaces before and after array strings

[whybangbang]

Preflight Checklist

• I have searched the issue tracker for an issue that matches the one I want to file, without success.

Problem Description

1. For example add this hook StringToSliceHookFunc(",") to viper, only handle this array string "a,b,c,d", can't handle "a, b, c, d", but in the same service, a viper will handle these two different formats
2. https://github.com/urfave/cli have resolve this problem, refer to https://github.com/urfave/cli/blob/e8abd76fa3ee5f1bacb52eab9b71dedbeab41991/flag_slice_base.go#L61

Proposed Solution

Use TrimSpace trim items in string array, and also can trim other space defined by Unicode.

func StringToSliceHookFunc(sep string) mapstructure.DecodeHookFunc {
	return func(
		f reflect.Kind,
		t reflect.Kind,
		data interface{}) (interface{}, error) {
		if f != reflect.String || t != reflect.Slice {
			return data, nil
		}

		raw := data.(string)
		if raw == "" {
			return []string{}, nil
		}

		var strs []string
		for _, s := range strings.Split(raw, sep) {
			s = strings.TrimSpace(s)
			strs = append(strs, s)
		}

		return strs, nil
	}
}

Alternatives Considered

No response

Additional Information

No response

[github-actions]

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