how golang wire use struct embeding?

config.go

type Config struct {
    Database string      `json:"database"`
    Mysql    MySQLConfig `json:"mysql"`
}

type MySQLConfig struct {
    Host string `json:"host"`
    Port int64  `json:"port"`
}

func NewConfig() (*Config, error) {
    fp, err := os.Open("../config/app.json")
    if err != nil {
        return nil, err
    }
    defer fp.Close()
    var cfg Config
    if err := json.NewDecoder(fp).Decode(&cfg); err != nil {
        return nil, err
    }
    return &cfg, nil
}

mysql.go

type MySQL struct {
}

func NewDB(cfg MySQLConfig) (*MySQL, error) {
    fmt.Printf("mysql config: %#vn", cfg)
    return &MySQL{}, nil
}

wire.go

func InitAPP() (*MySQL, error) {
    wire.Build(NewConfig, NewDB)
    return &MySQL{}, nil
}

error:
wire.go:10:1: inject InitAPP: no provider found for demo/demo6_cfg.MySQLConfig
needed by *demo/demo6_cfg.MySQL in provider “NewDB” (/demo6_cfg/mysql.go:10:6)
wire: demo/demo6_cfg: generate failed

what should I fix this error?