Add zsh completion

Fixes GoogleContainerTools#1012

cmd/skaffold/app/cmd/completion.go

@@ -24,30 +24,46 @@ import (
 	"github.com/spf13/cobra"
 )
 
-// completionCmd represents the completion command
+const longDescription = `
+	Outputs skaffold shell completion for the given shell (bash or zsh)
+
+	This depends on the bash-completion binary.  Example installation instructions:
+	OS X:
+		$ brew install bash-completion
+		$ source $(brew --prefix)/etc/bash_completion
+		$ skaffold completion bash > ~/.skaffold-completion  # for bash users
+		$ skaffold completion zsh > ~/.skaffold-completion   # for zsh users
+		$ source ~/.skaffold-completion
+	Ubuntu:
+		$ apt-get install bash-completion
+		$ source /etc/bash-completion
+		$ source <(skaffold completion bash) # for bash users
+		$ source <(skaffold completion zsh)  # for zsh users
+
+	Additionally, you may want to output the completion to a file and source in your .bashrc
+`
+
 var completionCmd = &cobra.Command{
-	// Only bash is supported for now. However, having args after
-	// "completion" will help when supporting multiple shells
-	Use: "completion bash",
+	Use: "completion SHELL",
 	Args: func(cmd *cobra.Command, args []string) error {
 		if len(args) != 1 {
 			return fmt.Errorf("requires 1 arg, found %d", len(args))
 		}
 		return cobra.OnlyValidArgs(cmd, args)
 	},
-	ValidArgs: []string{"bash"},
-	Short:     "Output command completion script for the bash shell",
-	Long: `To enable command completion run
-
-eval "$(skaffold completion bash)"
-
-To configure bash shell completion for all your sessions, add the following to your
-~/.bashrc or ~/.bash_profile:
+	ValidArgs: []string{"bash", "zsh"},
+	Short:     "Output skaffold shell completion for the given shell (bash or zsh)",
+	Long:      longDescription,
+	Run:       completion,
+}
 
-eval "$(skaffold completion bash)"`,
-	Run: func(cmd *cobra.Command, args []string) {
+func completion(_cmd *cobra.Command, args []string) {
+	switch args[0] {
+	case "bash":
 		rootCmd.GenBashCompletion(os.Stdout)
-	},
+	case "zsh":
+		rootCmd.GenZshCompletion(os.Stdout)
+	}
 }
 
 // NewCmdCompletion returns the cobra command that outputs shell completion code

docs/content/en/docs/references/cli/_index.md

@@ -91,11 +91,11 @@ Env vars:
 
 ### skaffold completion
 
-Output command completion script for the bash shell
+Output skaffold shell completion for the given shell (bash or zsh)
 
 ```
 Usage:
-  skaffold completion bash [flags]
+  skaffold completion SHELL [flags]
 
 Global Flags:
   -v, --verbosity string   Log level (debug, info, warn, error, fatal, panic) (default "warning")