add command to generate shell completion scripts

PENDING.md

@@ -61,6 +61,7 @@ FEATURES
   * [\#3198](https://github.com/cosmos/cosmos-sdk/issues/3198) New `multisign` command to generate multisig signatures.
   * [\#3198](https://github.com/cosmos/cosmos-sdk/issues/3198) New `sign --multisig` flag to enable multisig mode.
   * [\#2715](https://github.com/cosmos/cosmos-sdk/issues/2715) Reintroduce gaia server's insecure mode.
+  * [\#3334](https://github.com/cosmos/cosmos-sdk/pull/3334) New `gaiad completion` and `gaiacli completion` to generate Bash/Zsh completion scripts.
 
 * Gaia
   * [\#2182] [x/staking] Added querier for querying a single redelegation

cmd/gaia/cmd/gaiacli/main.go

@@ -19,6 +19,7 @@ import (
 	"github.com/cosmos/cosmos-sdk/client/rpc"
 	"github.com/cosmos/cosmos-sdk/client/tx"
 	"github.com/cosmos/cosmos-sdk/cmd/gaia/app"
+	"github.com/cosmos/cosmos-sdk/server"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/cosmos/cosmos-sdk/version"
 
@@ -93,6 +94,7 @@ func main() {
 		keys.Commands(),
 		client.LineBreak,
 		version.VersionCmd,
+		server.NewCompletionCmd(rootCmd, true),
 	)
 
 	// Add flags and prefix all env exposed with GA

cmd/gaia/cmd/gaiad/main.go

@@ -42,6 +42,7 @@ func main() {
 	rootCmd.AddCommand(gaiaInit.TestnetFilesCmd(ctx, cdc))
 	rootCmd.AddCommand(gaiaInit.GenTxCmd(ctx, cdc))
 	rootCmd.AddCommand(gaiaInit.AddGenesisAccountCmd(ctx, cdc))
+	rootCmd.AddCommand(server.NewCompletionCmd(rootCmd, true))
 
 	server.AddCommands(ctx, cdc, rootCmd, newApp, exportAppStateAndTMValidators)
 

server/util.go

@@ -233,6 +233,38 @@ func UpgradeOldPrivValFile(config *cfg.Config) {
 	}
 }
 
+// NewCompletionCmd builds a cobra.Command that generate bash completion
+// scripts for the given root command. If hidden is true, the command
+// will not show up in the root command's list of available commands.
+func NewCompletionCmd(rootCmd *cobra.Command, hidden bool) *cobra.Command {
+	flagZsh := "zsh"
+	cmd := &cobra.Command{
+		Use:   "completion",
+		Short: "Generate Bash/Zsh completion script to STDOUT",
+		Long: `To load completion script run
+
+. <(completion_script)
+
+To configure your bash shell to load completions for each session add to your bashrc
+
+# ~/.bashrc or ~/.profile
+. <(completion_script)
+`,
+		RunE: func(_ *cobra.Command, _ []string) error {
+			if viper.GetBool(flagZsh) {
+				return rootCmd.GenZshCompletion(os.Stdout)
+			}
+			return rootCmd.GenBashCompletion(os.Stdout)
+		},
+		Hidden: hidden,
+		Args:   cobra.NoArgs,
+	}
+
+	cmd.Flags().Bool(flagZsh, false, "Generate Zsh completion script")
+
+	return cmd
+}
+
 func skipInterface(iface net.Interface) bool {
 	if iface.Flags&net.FlagUp == 0 {
 		return true // interface down