Use Cobra for shell completion

cmd/config/completion/completion.go

@@ -0,0 +1,33 @@
+// Copyright 2020 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package completion
+
+import (
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+func NewCommand() *cobra.Command {
+	return &cobra.Command{
+		Use:                   "completion [bash|zsh|fish|powershell]",
+		Short:                 "Generate shell completion script",
+		Long:                  "Generate shell completion.",
+		DisableFlagsInUseLine: true,
+		ValidArgs:             []string{"bash", "zsh", "fish", "powershell"},
+		Args:                  cobra.ExactValidArgs(1),
+		Run: func(cmd *cobra.Command, args []string) {
+			switch args[0] {
+			case "bash":
+				cmd.Root().GenBashCompletion(os.Stdout)
+			case "zsh":
+				cmd.Root().GenZshCompletion(os.Stdout)
+			case "fish":
+				cmd.Root().GenFishCompletion(os.Stdout, true)
+			case "powershell":
+				cmd.Root().GenPowerShellCompletion(os.Stdout)
+			}
+		},
+	}
+}