Delve程式碼分析筆記（4）——構建command tree

這是一個建立於 的文章，其中的資訊可能已經有所發展或是發生改變。

Delve使用cobra來構造command tree。先看root command，也就是dlv：

func New() *cobra.Command {    ......    // Main dlv root command.    RootCommand = &cobra.Command{        Use:   "dlv",        Short: "Delve is a debugger for the Go programming language.",        Long:  dlvCommandLongDesc,    }    RootCommand.PersistentFlags().StringVarP(&Addr, "listen", "l", "localhost:0", "Debugging server listen address.")    RootCommand.PersistentFlags().BoolVarP(&Log, "log", "", false, "Enable debugging server logging.")    RootCommand.PersistentFlags().BoolVarP(&Headless, "headless", "", false, "Run debug server only, in headless mode.")    RootCommand.PersistentFlags().BoolVarP(&AcceptMulti, "accept-multiclient", "", false, "Allows a headless server to accept multiple client connections. Note that the server API is not reentrant and clients will have to coordinate")    RootCommand.PersistentFlags().IntVar(&ApiVersion, "api-version", 1, "Selects API version when headless")    RootCommand.PersistentFlags().StringVar(&InitFile, "init", "", "Init file, executed by the terminal client.")    RootCommand.PersistentFlags().StringVar(&BuildFlags, "build-flags", buildFlagsDefault, "Build flags, to be passed to the compiler.")    ......}

因為dlv command沒有實現run函數，所以單獨運行dlv命令只會列印cobra幫忙產生的預設輸出：

# dlvDelve is a source level debugger for Go programs.......Usage:  dlv [command]Available Commands:  version     Prints version.  ......Flags:      --accept-multiclient[=false]: Allows a headless server to accept multiple client connections. Note that the server API is not reentrant and clients will have to coordinate    ......

依次為Long description，Usage，Available Commands等等。

再以trace subcommand為例，看如何把subcommand加到root command裡：

......// 'trace' subcommand.traceCommand := &cobra.Command{    Use:   "trace [package] regexp",    Short: "Compile and begin tracing program.",    Long:  "Trace program execution. Will set a tracepoint on every function matching the provided regular expression and output information when tracepoint is hit.",    Run:   traceCmd,}traceCommand.Flags().IntVarP(&traceAttachPid, "pid", "p", 0, "Pid to attach to.")traceCommand.Flags().IntVarP(&traceStackDepth, "stack", "s", 0, "Show stack trace with given depth.")RootCommand.AddCommand(traceCommand)......

Cobra提供兩種flags：
a）Persistent Flags：對當前命令及其子命令都有效；
b）Local Flags：只對當前命令有效。