Check that each strings fields in a Struct are non-zero value using reflect and return error contains specific tag value

main.go

// validate ensure all required secrets are set up
func (secrets *s) validate(sub ...interface{}) error {
	// Reflect it
	v := reflect.ValueOf(*secrets)
	if len(sub) > 0 {
		// Recursive
		v = reflect.ValueOf(sub[0])
	}

	// Iterate over each fields and looks from empty string
	for i := 0; i < v.NumField(); i++ {
		switch v.Field(i).Kind() {
		case reflect.String:
			if v.Field(i).IsZero() {
				fields, ok := v.Type().FieldByName(v.Type().Field(i).Name)
				var missingField = v.Type().Field(i).Name
				if ok {
					missingField = fields.Tag.Get("mapstructure")
				}

				return fmt.Errorf("LoadConfigFromVault(): %q key is missing on Vault (using %s secrets path)", missingField, requiredSecrets)
			}
		case reflect.Struct:
			if err := secrets.validate(v.Field(i).Interface()); err != nil {
				return err
			}
		default:
			panic("missing type implementation")
		}
	}

	return nil
}