Provide a cli option to enable and disable completion command

Signed-off-by: Adrian Orive <adrian.orive.oneca@gmail.com>

cmd/main.go

@@ -27,6 +27,7 @@ import (
 
 func main() {
 	c, err := cli.New(
+		cli.WithCommandName("kubebuilder"),
 		cli.WithPlugins(
 			&pluginv2.Plugin{},
 			&pluginv3.Plugin{},
@@ -35,9 +36,9 @@ func main() {
 			&pluginv2.Plugin{},
 		),
 		cli.WithExtraCommands(
-			newCompletionCmd(),
 			version.NewCmd(),
 		),
+		cli.WithCompletion,
 	)
 	if err != nil {
 		log.Fatal(err)

docs/book/src/reference/completion.md

@@ -1,5 +1,5 @@
 # Enabling shell autocompletion
-The Kubebuilder completion script for Bash can be generated with the command `kubebuilder completion bash` as the Kubebuilder completion script for Zsh can be generated with the command `kubebuilder completion zsh`. 
+The Kubebuilder completion script can be generated with the command `kubebuilder completion [bash|zsh|fish|powershell]`. 
 Note that sourcing the completion script in your shell enables Kubebuilder autocompletion. 
 
 <aside class="note">

pkg/cli/cli.go

@@ -66,6 +66,9 @@ type cli struct {
 	// Whether the command is requesting help.
 	doGenericHelp bool
 
+	// Whether to add a completion command to the cli
+	completionCommand bool
+
 	// Plugins injected by options.
 	pluginsFromOptions map[string][]plugin.Base
 	// Default plugins injected by options. Only one plugin per project version
@@ -173,6 +176,12 @@ func WithExtraCommands(cmds ...*cobra.Command) Option {
 	}
 }
 
+// WithCompletion is an Option that adds the completion subcommand.
+func WithCompletion(c *cli) error {
+	c.completionCommand = true
+	return nil
+}
+
 // initialize initializes the cli.
 func (c *cli) initialize() error {
 	// Initialize cli with globally-relevant flags or flags that determine
@@ -345,6 +354,12 @@ func (c cli) buildRootCmd() *cobra.Command {
 		rootCmd.AddCommand(alphaCmd)
 	}
 
+	// kubebuilder completion
+	// Only add completion if requested
+	if c.completionCommand {
+		rootCmd.AddCommand(c.newCompletionCmd())
+	}
+
 	// kubebuilder create
 	createCmd := c.newCreateCmd()
 	// kubebuilder create api

pkg/cli/completion.go

@@ -0,0 +1,87 @@
+/*
+Copyright 2020 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cli
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+// TODO: support fish code completion
+//  At the time this comment is written, the imported spf13.cobra version does not support fish completion.
+//  However, fish completion has been added to new spf13.cobra versions. When a new spf13.cobra version that
+//  supports it is used, the changes indicated with `NOTE(fish)` should be applied to support it.
+
+func (c *cli) newCompletionCmd() *cobra.Command {
+	return &cobra.Command{
+		Use:                   "completion [bash|zsh|powershell]", // NOTE(fish): add fish
+		DisableFlagsInUseLine: true,
+		ValidArgs:             []string{"bash", "zsh", "powershell"}, // NOTE(fish): add fish
+		Args:                  cobra.ExactValidArgs(1),
+		Short:                 "Generate completion script",
+		Long: fmt.Sprintf(`To load completions:
+
+Bash:
+
+$ source <(%[1]s completion bash)
+
+# To load completions for each session, execute once:
+Linux:
+  $ %[1]s completion bash > /etc/bash_completion.d/%[1]s
+MacOS:
+  $ %[1]s completion bash > /usr/local/etc/bash_completion.d/%[1]s
+
+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:
+$ %[1]s completion zsh > "${fpath[1]}/_%[1]s"
+
+# You will need to start a new shell for this setup to take effect.
+`, c.commandName),
+		/* NOTE(fish): add the following description to Long
+		   `
+		   Fish:
+
+		   $ %[1]s completion fish | source
+
+		   # To load completions for each session, execute once:
+		   $ %[1]s completion fish > ~/.config/fish/completions/%[1]s.fish
+		   `
+		*/
+		RunE: func(cmd *cobra.Command, args []string) (err error) {
+			switch args[0] {
+			case "bash":
+				err = cmd.Root().GenBashCompletion(os.Stdout)
+			case "zsh":
+				err = cmd.Root().GenZshCompletion(os.Stdout)
+			// NOTE(fish): uncomment the following two lines
+			//case "fish":
+			//	err = cmd.Root().GenFishCompletion(os.Stdout, true)
+			case "powershell":
+				err = cmd.Root().GenPowerShellCompletion(os.Stdout)
+			}
+			return
+		},
+	}
+}