Adds Zsh completion (finishes issue #130) (#132)

docs/cmd/kn.md

@@ -20,7 +20,7 @@ Eventing: Manage event subscriptions and channels. Connect up event sources.
 
 ### SEE ALSO
 
-* [kn completion](kn_completion.md)	 - Output bash completion code
+* [kn completion](kn_completion.md)	 - Output shell completion code (default Bash)
 * [kn revision](kn_revision.md)	 - Revision command group
 * [kn service](kn_service.md)	 - Service command group
 * [kn version](kn_version.md)	 - Prints the client version

docs/cmd/kn_completion.md

@@ -1,10 +1,10 @@
 ## kn completion
 
-Output bash completion code
+Output shell completion code (default Bash)
 
 ### Synopsis
 
-Output bash completion code
+Output shell completion code (default Bash)
 
 ```
 kn completion [flags]
@@ -14,6 +14,7 @@ kn completion [flags]
 
 ```
   -h, --help   help for completion
+      --zsh    Generates completion code for Zsh shell.
 ```
 
 ### Options inherited from parent commands

pkg/kn/commands/completion.go

@@ -6,15 +6,25 @@ import (
 	"github.com/spf13/cobra"
 )
 
+type CompletionFlags struct {
+	Zsh bool
+}
+
 func NewCompletionCommand(p *KnParams) *cobra.Command {
+	var completionFlags CompletionFlags
+
 	completionCmd := &cobra.Command{
 		Use:   "completion",
-		Short: "Output bash completion code",
-		Run:   completionAction,
+		Short: "Output shell completion code (default Bash)",
+		Run: func(cmd *cobra.Command, args []string) {
+			if completionFlags.Zsh {
+				cmd.Root().GenZshCompletion(os.Stdout)
+			} else {
+				cmd.Root().GenBashCompletion(os.Stdout)
+			}
+		},
 	}
-	return completionCmd
-}
 
-func completionAction(cmd *cobra.Command, args []string) {
-	cmd.Root().GenBashCompletion(os.Stdout)
+	completionCmd.Flags().BoolVar(&completionFlags.Zsh, "zsh", false, "Generates completion code for Zsh shell.")
+	return completionCmd
 }