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 +268,57 @@ 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_withDoubleDashFlag_Control() {
+	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", "--", "x", "--generate-shell-completion"}
+
+	_ = cmd.Run(context.Background(), os.Args)
+	// Output:
+}
+
 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
 	}
@@ -489,11 +491,11 @@ 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.
+	for i, arg := range arguments {
+		// If there is "--" which doesn't go right before
+		// "--generate-shell-completion", shell completion is disabled.
 		// https://unix.stackexchange.com/a/11382
-		if arg == "--" {
+		if arg == "--" && i != len(arguments)-2 {
 			return false, arguments[:pos]
 		}
 	}

help_test.go

@@ -1270,6 +1270,28 @@ func TestDefaultCompleteWithFlags(t *testing.T) {
 			},
 			argv:     []string{"cmd", "--e", "--", completionFlag},
 			env:      map[string]string{"SHELL": "bash"},
+			expected: "--excitement\n--hat-shape\n",
+		},
+		{
+			name: "double-dash-in-the-middle",
+			cmd: &Command{
+				Flags: []Flag{
+					&BoolFlag{Name: "excitement"},
+					&StringFlag{Name: "hat-shape"},
+				},
+				parent: &Command{
+					Name: "cmd",
+					Flags: []Flag{
+						&BoolFlag{Name: "happiness"},
+						&Int64Flag{Name: "everybody-jump-on"},
+					},
+					Commands: []*Command{
+						{Name: "putz"},
+					},
+				},
+			},
+			argv:     []string{"cmd", "--", "--e"},
+			env:      map[string]string{"SHELL": "bash"},
 			expected: "",
 		},
 		{
@@ -1825,6 +1847,15 @@ func Test_checkShellCompleteFlag(t *testing.T) {
 			wantShellCompletion: false,
 			wantArgs:            []string{"--", "foo"},
 		},
+		{
+			name:      "double dash is just before --generate-shell-completion",
+			arguments: []string{"foo", "--", completionFlag},
+			cmd: &Command{
+				EnableShellCompletion: true,
+			},
+			wantShellCompletion: true,
+			wantArgs:            []string{"foo", "--"},
+		},
 		{
 			name:      "shell completion",
 			arguments: []string{"foo", completionFlag},