feat(cmd): Add --completion flag

cmd/cmd.go

@@ -20,6 +20,8 @@ func New() *cobra.Command {
 		DisableAutoGenTag: true,
 	}
 
+	registerCompletionFlag(cmd)
+
 	cmd.PersistentFlags().String("config", "", `Config file (default ".changelog-generator.yaml")`)
 	_ = cmd.RegisterFlagCompletionFunc("config", func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
 		return []string{"yaml"}, cobra.ShellCompDirectiveFilterFileExt
@@ -29,6 +31,14 @@ func New() *cobra.Command {
 }
 
 func run(cmd *cobra.Command, args []string) error {
+	completionFlag, err := cmd.Flags().GetString(CompletionFlag)
+	if err != nil {
+		return err
+	}
+	if completionFlag != "" {
+		return completion(cmd, args)
+	}
+
 	conf, err := config.Load(cmd)
 	if err != nil {
 		return err

cmd/completion.go

@@ -0,0 +1,51 @@
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+const CompletionFlag = "completion"
+
+func registerCompletionFlag(cmd *cobra.Command) {
+	cmd.Flags().String(CompletionFlag, "", "Output command-line completion code for the specified shell. Can be 'bash', 'zsh', 'fish', or 'powershell'.")
+	err := cmd.RegisterFlagCompletionFunc(
+		CompletionFlag,
+		func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+			return []string{"bash", "zsh", "fish", "powershell"}, cobra.ShellCompDirectiveNoFileComp
+		},
+	)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func completion(cmd *cobra.Command, args []string) error {
+	completionFlag, err := cmd.Flags().GetString(CompletionFlag)
+	if err != nil {
+		panic(err)
+	}
+
+	switch completionFlag {
+	case "bash":
+		if err := cmd.Root().GenBashCompletion(cmd.OutOrStdout()); err != nil {
+			return err
+		}
+	case "zsh":
+		if err := cmd.Root().GenZshCompletion(cmd.OutOrStdout()); err != nil {
+			return err
+		}
+	case "fish":
+		if err := cmd.Root().GenFishCompletion(cmd.OutOrStdout(), true); err != nil {
+			return err
+		}
+	case "powershell":
+		if err := cmd.Root().GenPowerShellCompletionWithDesc(cmd.OutOrStdout()); err != nil {
+			return err
+		}
+	default:
+		return fmt.Errorf("%v: invalid shell", completionFlag)
+	}
+	return nil
+}

docs/changelog-generator.md

@@ -9,7 +9,8 @@ changelog-generator [flags]
 ### Options
 
 ```
-      --config string   Config file (default ".changelog-generator.yaml")
-  -h, --help            help for changelog-generator
+      --completion string   Output command-line completion code for the specified shell. Can be 'bash', 'zsh', 'fish', or 'powershell'.
+      --config string       Config file (default ".changelog-generator.yaml")
+  -h, --help                help for changelog-generator
 ```