fix completion of "--"

Use https://cli.urfave.org/v3/examples/completions/shell-completions as a
reference for completions.

The previous version completed "-" -> "--" -> "--help,", but the added comma was
incorrect, as no such flag exists and the tool does not accept it. A similar
issue occurred with "--version", which was shown as "--version,".

The root cause was that completion was explicitly disabled for this case:

$ greet -- --generate-shell-completion

As a result, it printed the default help message:

> NAME:
>    greet - A new cli application
>
> USAGE:
>    greet [global options] [command [command options]]
>
> COMMANDS:
>    add, a       add a task to the list
>    complete, c  complete a task on the list
>    template, t  options for task templates
>    help, h      Shows a list of commands or help for one command
>
> GLOBAL OPTIONS:
>    --help, -h  show help

Bash used "--help," as a flag suggestion, which was incorrect.

In this commit, completion is enabled for the "-- --generate-shell-completion"
case, and a test is added to verify correct behavior.

With this change, both "-" and "--" now complete to "--help", which is correct.

Author: starius

examples_test.go

@@ -268,6 +268,33 @@ func ExampleCommand_Run_shellComplete_bash_withShortFlag() {
 	// --help
 }
 
+func ExampleCommand_Run_shellComplete_bash_withDoubleDashFlag() {
+	cmd := &cli.Command{
+		Name:                  "greet",
+		EnableShellCompletion: true,
+		Flags: []cli.Flag{
+			&cli.Int64Flag{
+				Name:    "other",
+				Aliases: []string{"o"},
+			},
+			&cli.StringFlag{
+				Name:    "xyz",
+				Aliases: []string{"x"},
+			},
+		},
+	}
+
+	// Simulate a bash environment and command line arguments
+	os.Setenv("SHELL", "bash")
+	os.Args = []string{"greet", "--", "--generate-shell-completion"}
+
+	_ = cmd.Run(context.Background(), os.Args)
+	// Output:
+	// --other
+	// --xyz
+	// --help
+}
+
 func ExampleCommand_Run_shellComplete_bash_withLongFlag() {
 	cmd := &cli.Command{
 		Name:                  "greet",

help.go

@@ -251,16 +251,18 @@ func DefaultCompleteWithFlags(ctx context.Context, cmd *Command) {
 		tracef("running default complete with os.Args flags[%v]", args)
 	}
 	argsLen := len(args)
-	lastArg := ""
+	var lastArg, veryLastArg string
 	// parent command will have --generate-shell-completion so we need
 	// to account for that
 	if argsLen > 1 {
 		lastArg = args[argsLen-2]
+		veryLastArg = args[argsLen-1]
 	} else if argsLen > 0 {
 		lastArg = args[argsLen-1]
+		veryLastArg = args[argsLen-1]
 	}
 
-	if lastArg == "--" {
+	if lastArg == "--" && veryLastArg != completionFlag {
 		tracef("No completions due to termination")
 		return
 	}
@@ -489,15 +491,6 @@ func checkShellCompleteFlag(c *Command, arguments []string) (bool, []string) {
 		return false, arguments
 	}
 
-	for _, arg := range arguments {
-		// If arguments include "--", shell completion is disabled
-		// because after "--" only positional arguments are accepted.
-		// https://unix.stackexchange.com/a/11382
-		if arg == "--" {
-			return false, arguments[:pos]
-		}
-	}
-
 	return true, arguments[:pos]
 }
 

help_test.go

@@ -1270,7 +1270,7 @@ func TestDefaultCompleteWithFlags(t *testing.T) {
 			},
 			argv:     []string{"cmd", "--e", "--", completionFlag},
 			env:      map[string]string{"SHELL": "bash"},
-			expected: "",
+			expected: "--excitement\n--hat-shape\n",
 		},
 		{
 			name: "typical-command-suggestion",
@@ -1822,7 +1822,7 @@ func Test_checkShellCompleteFlag(t *testing.T) {
 			cmd: &Command{
 				EnableShellCompletion: true,
 			},
-			wantShellCompletion: false,
+			wantShellCompletion: true,
 			wantArgs:            []string{"--", "foo"},
 		},
 		{