fix shell autocomplete evaluation

pkg/app/run_test.go

@@ -97,6 +97,35 @@ _fastly_bash_autocomplete() {
     return 0
 }
 complete -F _fastly_bash_autocomplete fastly
+`,
+		},
+		{
+			Name: "shell evaluate completion options",
+			Args: args("--completion-bash"),
+			WantOutput: `help
+acl
+acl-entry
+auth-token
+backend
+compute
+configure
+dictionary
+dictionaryitem
+domain
+healthcheck
+ip-list
+logging
+logs
+pops
+purge
+service
+service-version
+stats
+update
+user
+vcl
+version
+whoami
 `,
 		},
 	}

pkg/app/usage.go

@@ -341,7 +341,7 @@ func processCommandInput(
 	// error on things not already caught by ParseContext().
 	noargs := len(opts.Args) == 0
 	ctx, err := app.ParseContext(opts.Args)
-	if err != nil || noargs {
+	if err != nil && !cmd.IsCompletion(opts.Args) || noargs {
 		if noargs {
 			err = fmt.Errorf("command not specified")
 		}
@@ -359,7 +359,7 @@ func processCommandInput(
 	// completion flag, as that depends on kingpin.Parse() being called, and so
 	// the ctx is otherwise empty.
 	var found bool
-	if !cmd.IsHelpOnly(opts.Args) && !cmd.IsHelpFlagOnly(opts.Args) && !cmd.IsCompletion(opts.Args) {
+	if !cmd.IsHelpOnly(opts.Args) && !cmd.IsHelpFlagOnly(opts.Args) && !cmd.IsCompletion(opts.Args) && !cmd.IsCompletionScript(opts.Args) {
 		command, found = cmd.Select(ctx.SelectedCommand.FullCommand(), commands)
 		if !found {
 			return command, cmdName, help(vars, err)
@@ -385,7 +385,11 @@ func processCommandInput(
 	// command that we can safely append to the arguments and not have to worry
 	// about it getting removed accidentally in the future as we now have a test
 	// to validate the shell autocomplete behaviours.
-	if cmd.IsCompletion(opts.Args) {
+	//
+	// Lastly, we don't want to append our hidden shellcomplete command if the
+	// caller passes --completion-bash because adding a command to the arguments
+	// list would prevent the user's shell autocomplete logic to break.
+	if cmd.IsCompletionScript(opts.Args) {
 		opts.Args = append(opts.Args, "shellcomplete")
 	}
 
@@ -399,7 +403,7 @@ func processCommandInput(
 
 	// Kingpin generates shell completion as a side-effect of kingpin.Parse() so
 	// we allow it to call os.Exit, only if a completion flag is present.
-	if cmd.IsCompletion(opts.Args) {
+	if cmd.IsCompletion(opts.Args) || cmd.IsCompletionScript(opts.Args) {
 		app.Terminate(os.Exit)
 		return command, "shell-autocomplete", nil
 	}

pkg/cmd/flags.go

@@ -18,7 +18,8 @@ import (
 )
 
 var (
-	completionRegExp = regexp.MustCompile("completion-(?:script-)?(?:bash|zsh)$")
+	completionRegExp       = regexp.MustCompile("completion-bash$")
+	completionScriptRegExp = regexp.MustCompile("completion-script-(?:bash|zsh)$")
 )
 
 // RegisterServiceIDFlag defines a --service-id flag that will attempt to
@@ -195,8 +196,21 @@ func ContextHasHelpFlag(ctx *kingpin.ParseContext) bool {
 	return ok
 }
 
+// IsCompletionScript determines whether the supplied command arguments are for
+// shell completion output that is then eval()'ed by the user's shell.
+func IsCompletionScript(args []string) bool {
+	var found bool
+	for _, arg := range args {
+		if completionScriptRegExp.MatchString(arg) {
+			found = true
+		}
+	}
+	return found
+}
+
 // IsCompletion determines whether the supplied command arguments are for
-// bash/zsh completion output.
+// shell completion (i.e. --completion-bash) that should produce output that
+// the user's shell can utilise for handling autocomplete behaviour.
 func IsCompletion(args []string) bool {
 	var found bool
 	for _, arg := range args {