Add completion

Signed-off-by: KeisukeYamashita <19yamashita15@gmail.com>

cmd/completion.go

@@ -0,0 +1,53 @@
+package cmd
+
+import (
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+func newCompletionCmd() *cobra.Command {
+	return &cobra.Command{
+		Use:   "completion [bash|zsh|fish]",
+		Short: "Generate a shell completion for spin-admin",
+		Long: `To load completions:
+	Bash:
+	$ source <(spin-admin completion bash)
+	# To load completions for each session, execute once:
+	Linux:
+	  $ spin-admin completion bash > /etc/bash_completion.d/spin-admin
+	MacOS:
+	  $ spin-admin completion bash > /usr/local/etc/bash_completion.d/spin-admin
+	Zsh:
+	# If shell completion is not already enabled in your environment you will need
+	# to enable it.  You can execute the following once:
+	$ echo "autoload -U compinit; compinit" >> ~/.zshrc
+	# To load completions for each session, execute once:
+	$ spin-admin completion zsh > "${fpath[1]}/_spin-admin"
+	# You will need to start a new shell for this setup to take effect.
+	Fish:
+	$ spin-admin completion fish | source
+	# To load completions for each session, execute once:
+	$ spin-admin completion fish > ~/.config/fish/completions/spin-admin.fish
+	`,
+		DisableFlagsInUseLine: true,
+		ValidArgs:             []string{"bash", "fish", "zsh"},
+		Args:                  cobra.ExactValidArgs(1),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			var err error
+			switch args[0] {
+			case "zsh":
+				err = cmd.Root().GenZshCompletion(os.Stdout)
+			case "bash":
+				err = cmd.Root().GenBashCompletion(os.Stdout)
+			case "fish":
+				err = cmd.Root().GenFishCompletion(os.Stdout, true)
+			}
+			if err != nil {
+				return err
+			}
+
+			return nil
+		},
+	}
+}

cmd/root.go

@@ -13,6 +13,7 @@ var rootCmd = &cobra.Command{
 func init() {
 	rootCmd.AddCommand(sa.NewServiceAccountCommand())
 	rootCmd.AddCommand(newVersionCommand())
+	rootCmd.AddCommand(newCompletionCmd())
 }
 
 func Execute() error {