pkg/completion: add common completion command

Add the completion command to pkg/completion, this would allow podman,
buildah and skopeo to use the same command instead of having to
duplicate the logic.

The code is mostly copied from podman/cmd/podman/completion. I have
modified it a little to make it more generic.

Signed-off-by: Paul Holzinger <[email protected]>

Author: Luap99

pkg/completion/command.go

@@ -0,0 +1,96 @@
+package completion
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+const (
+	completionDescription = `Generate shell autocompletions.
+  Valid arguments are bash, zsh, fish and powershell.`
+
+	bash       = "bash"
+	zsh        = "zsh"
+	fish       = "fish"
+	powershell = "powershell"
+)
+
+var (
+	file   string
+	noDesc bool
+	shells = []string{bash, zsh, fish, powershell}
+)
+
+// AddCompletionCommand adds the completion command to the given command which should be the root command.
+// This command can be used the generate the cobra shell completion scripts for bash, zsh, fish and powershell.
+func AddCompletionCommand(rootCmd *cobra.Command) {
+	completionCmd := &cobra.Command{
+		Use:       fmt.Sprintf("completion [options] {%s}", strings.Join(shells, "|")),
+		Short:     "Generate shell autocompletions",
+		Long:      completionDescription,
+		ValidArgs: shells,
+		Args:      cobra.ExactValidArgs(1),
+		RunE:      completion,
+		Example: fmt.Sprintf(`%[1]s completion bash
+  %[1]s completion zsh -f _%[1]s
+  %[1]s completion fish --no-desc`, rootCmd.Name()),
+		// don't show this command to users
+		Hidden: true,
+	}
+
+	flags := completionCmd.Flags()
+	fileFlagName := "file"
+	flags.StringVarP(&file, fileFlagName, "f", "", "Output the completion to file rather than stdout.")
+	_ = completionCmd.RegisterFlagCompletionFunc(fileFlagName, AutocompleteDefault)
+
+	flags.BoolVar(&noDesc, "no-desc", false, "Don't include descriptions in the completion output.")
+
+	rootCmd.AddCommand(completionCmd)
+}
+
+func completion(cmd *cobra.Command, args []string) error {
+	var w io.Writer
+
+	if file != "" {
+		file, err := os.Create(file)
+		if err != nil {
+			return err
+		}
+		defer file.Close()
+		w = file
+	} else {
+		w = os.Stdout
+	}
+
+	var err error
+	switch args[0] {
+	case bash:
+		err = cmd.Root().GenBashCompletionV2(w, !noDesc)
+	case zsh:
+		if noDesc {
+			err = cmd.Root().GenZshCompletionNoDesc(w)
+		} else {
+			err = cmd.Root().GenZshCompletion(w)
+		}
+	case fish:
+		err = cmd.Root().GenFishCompletion(w, !noDesc)
+	case powershell:
+		if noDesc {
+			err = cmd.Root().GenPowerShellCompletion(w)
+		} else {
+			err = cmd.Root().GenPowerShellCompletionWithDesc(w)
+		}
+	}
+	if err != nil {
+		return err
+	}
+
+	_, err = io.WriteString(w, fmt.Sprintf(
+		"# This file is generated with %q; DO NOT EDIT!\n", cmd.CommandPath(),
+	))
+	return err
+}