feat: Add tab completion library

app.go

@@ -50,8 +50,6 @@ type App struct {
 	// Set when the app is run via RunAsSubcommand; the version flag belongs to
 	// the top-level app only
 	runningAsSubcommand bool
-	// An action to execute when the bash-completion flag is set
-	BashComplete BashCompleteFunc
 	// An action to execute before any subcommands are run, but after the context is ready
 	// If a non-nil error is returned, no subcommands are run
 	Before BeforeFunc
@@ -128,16 +126,15 @@ func compileTime() time.Time {
 // Usage, Version and Action.
 func NewApp() *App {
 	return &App{
-		Name:         filepath.Base(os.Args[0]),
-		HelpName:     filepath.Base(os.Args[0]),
-		Usage:        "A new cli application",
-		UsageText:    "",
-		Version:      "0.0.0",
-		BashComplete: DefaultAppComplete,
-		Action:       helpCommand.Action,
-		Compiled:     compileTime(),
-		Writer:       os.Stdout,
-		HelpWriter:   os.Stdout,
+		Name:       filepath.Base(os.Args[0]),
+		HelpName:   filepath.Base(os.Args[0]),
+		Usage:      "A new cli application",
+		UsageText:  "",
+		Version:    "0.0.0",
+		Action:     helpCommand.Action,
+		Compiled:   compileTime(),
+		Writer:     os.Stdout,
+		HelpWriter: os.Stdout,
 	}
 }
 
@@ -190,13 +187,13 @@ func (a *App) Setup() {
 func (a *App) Run(arguments []string) (err error) {
 	a.Setup()
 
-	// handle the completion flag separately from the flagset since
-	// completion could be attempted after a flag, but before its value was put
-	// on the command line. this causes the flagset to interpret the completion
-	// flag name as the value of the flag before it which is undesirable
-	// note that we can only do this because the shell autocomplete function
-	// always appends the completion flag at the end of the command
-	shellComplete, arguments := checkShellCompleteFlag(a, arguments)
+	// Answer shell-completion requests: when completion is enabled and the
+	// process was spawned by the shell for completion (COMP_LINE is set),
+	// emit predictions and return without running the command.
+	if a.EnableBashCompletion && os.Getenv("COMP_LINE") != "" {
+		a.runShellCompletion()
+		return nil
+	}
 
 	// parse flags
 	flags := a.resolveFlags()
@@ -213,11 +210,6 @@ func (a *App) Run(arguments []string) (err error) {
 		fmt.Fprintln(a.Writer, nerr)
 		return nerr
 	}
-	context.shellComplete = shellComplete
-
-	if checkCompletions(context) {
-		return nil
-	}
 
 	if err != nil {
 		if onUsageError := a.resolveOnUsageError(); onUsageError != nil {
@@ -330,10 +322,6 @@ func (a *App) RunAsSubcommand(ctx *Context) (err error) {
 		return nerr
 	}
 
-	if checkCompletions(context) {
-		return nil
-	}
-
 	if err != nil {
 		if onUsageError := a.resolveOnUsageError(); onUsageError != nil {
 			err = onUsageError(context, err, true)

app_test.go

@@ -11,6 +11,8 @@ import (
 	"reflect"
 	"strings"
 	"testing"
+
+	"github.com/posener/complete"
 )
 
 var (
@@ -27,7 +29,7 @@ func init() {
 }
 
 type opCounts struct {
-	Total, BashComplete, OnUsageError, Before, CommandNotFound, Action, After, SubCommand int
+	Total, OnUsageError, Before, CommandNotFound, Action, After, SubCommand int
 }
 
 func ExampleApp_Run() {
@@ -228,43 +230,6 @@ func ExampleApp_Run_subcommandNoAction() {
 	//   --help, -h  show help
 }
 
-func ExampleApp_Run_bashComplete() {
-	// set args for examples sake
-	os.Args = []string{"greet", "--generate-bash-completion"}
-
-	app := NewApp()
-	app.Name = "greet"
-	app.EnableBashCompletion = true
-	app.Commands = []Command{
-		{
-			Name:        "describeit",
-			Aliases:     []string{"d"},
-			Usage:       "use it to see a description",
-			Description: "This is how we describe describeit the function",
-			Action: func(c *Context) error {
-				fmt.Printf("i like to describe things")
-				return nil
-			},
-		}, {
-			Name:        "next",
-			Usage:       "next example",
-			Description: "more stuff to see when generating bash completion",
-			Action: func(c *Context) error {
-				fmt.Printf("the next example")
-				return nil
-			},
-		},
-	}
-
-	app.Run(os.Args)
-	// Output:
-	// describeit
-	// d
-	// next
-	// help
-	// h
-}
-
 func TestApp_Run(t *testing.T) {
 	s := ""
 
@@ -884,12 +849,6 @@ func TestApp_OrderOfOperations(t *testing.T) {
 	resetCounts := func() { counts = &opCounts{} }
 
 	app := NewApp()
-	app.EnableBashCompletion = true
-	app.BashComplete = func(c *Context) {
-		counts.Total++
-		counts.BashComplete = counts.Total
-	}
-
 	app.OnUsageError = func(c *Context, err error, isSubcommand bool) error {
 		counts.Total++
 		counts.OnUsageError = counts.Total
@@ -950,12 +909,6 @@ func TestApp_OrderOfOperations(t *testing.T) {
 
 	resetCounts()
 
-	_ = app.Run([]string{"command", "--generate-bash-completion"})
-	expect(t, counts.BashComplete, 1)
-	expect(t, counts.Total, 1)
-
-	resetCounts()
-
 	oldOnUsageError := app.OnUsageError
 	app.OnUsageError = nil
 	_ = app.Run([]string{"command", "--nope"})
@@ -1596,6 +1549,10 @@ func (c *customBoolFlag) Apply(set *flag.FlagSet) {
 	set.String(c.Nombre, c.Nombre, "")
 }
 
+func (c *customBoolFlag) GetCompleter() complete.Predictor {
+	return complete.PredictNothing
+}
+
 func TestCustomFlagsUnused(t *testing.T) {
 	app := NewApp()
 	app.Flags = []Flag{&customBoolFlag{"custom"}}
@@ -1650,47 +1607,3 @@ func TestHandleAction_WithUnknownPanic(t *testing.T) {
 	}
 	app.Action(NewContext(app, fs, nil))
 }
-
-func TestShellCompletionForIncompleteFlags(t *testing.T) {
-	app := NewApp()
-	app.Flags = []Flag{
-		IntFlag{
-			Name: "test-completion",
-		},
-	}
-	app.EnableBashCompletion = true
-	app.BashComplete = func(ctx *Context) {
-		for _, command := range ctx.App.Commands {
-			if command.Hidden {
-				continue
-			}
-
-			for _, name := range command.Names() {
-				fmt.Fprintln(ctx.App.Writer, name)
-			}
-		}
-
-		for _, flag := range ctx.App.Flags {
-			for _, name := range strings.Split(flag.GetName(), ",") {
-				if name == BashCompletionFlag.GetName() {
-					continue
-				}
-
-				switch name = strings.TrimSpace(name); len(name) {
-				case 0:
-				case 1:
-					fmt.Fprintln(ctx.App.Writer, "-"+name)
-				default:
-					fmt.Fprintln(ctx.App.Writer, "--"+name)
-				}
-			}
-		}
-	}
-	app.Action = func(ctx *Context) error {
-		return fmt.Errorf("should not get here")
-	}
-	err := app.Run([]string{"", "--test-completion", "--" + BashCompletionFlag.GetName()})
-	if err != nil {
-		t.Errorf("app should not return an error: %s", err)
-	}
-}

cli.go

@@ -1,21 +1,23 @@
 // Package cli provides a minimal framework for creating and organizing command line
 // Go applications. cli is designed to be easy to understand and write, the most simple
 // cli application can be written as follows:
-//   func main() {
-//     cli.NewApp().Run(os.Args)
-//   }
+//
+//	func main() {
+//	  cli.NewApp().Run(os.Args)
+//	}
 //
 // Of course this application does not do much, so let's make this an actual application:
-//   func main() {
-//     app := cli.NewApp()
-//     app.Name = "greet"
-//     app.Usage = "say a greeting"
-//     app.Action = func(c *cli.Context) error {
-//       println("Greetings")
-//     }
 //
-//     app.Run(os.Args)
-//   }
+//	func main() {
+//	  app := cli.NewApp()
+//	  app.Name = "greet"
+//	  app.Usage = "say a greeting"
+//	  app.Action = func(c *cli.Context) error {
+//	    println("Greetings")
+//	  }
+//
+//	  app.Run(os.Args)
+//	}
 package cli
 
-//go:generate python ./generate-flag-types cli -i flag-types.json -o flag_generated.go
+//go:generate python3 ./generate-flag-types.py cli -i flag-types.json -o flag_generated.go

command.go

@@ -6,6 +6,8 @@ import (
 	"slices"
 	"sort"
 	"strings"
+
+	"github.com/posener/complete"
 )
 
 // Command is a subcommand for a cli.App.
@@ -26,8 +28,9 @@ type Command struct {
 	ArgsUsage string
 	// The category the command is part of
 	Category string
-	// The function to call when checking for bash command completions
-	BashComplete BashCompleteFunc
+	// Completer predicts this command's positional arguments during shell
+	// completion.
+	Completer complete.Predictor
 	// An action to execute before any sub-subcommands are run, but after the context is ready
 	// If a non-nil error is returned, no sub-subcommands are run
 	Before BeforeFunc
@@ -187,9 +190,6 @@ func (c Command) Run(ctx *Context) (err error) {
 
 	context := NewContext(ctx.App, set, ctx)
 	context.Command = c
-	if checkCommandCompletions(context, c.Name) {
-		return nil
-	}
 
 	if err != nil {
 		if onUsageError := c.resolveOnUsageError(context); onUsageError != nil {
@@ -325,12 +325,6 @@ func (c Command) startApp(ctx *Context) error {
 
 	sort.Sort(app.categories)
 
-	// bash completion
-	app.EnableBashCompletion = ctx.App.EnableBashCompletion
-	if c.BashComplete != nil {
-		app.BashComplete = c.BashComplete
-	}
-
 	// set the actions
 	app.Before = c.resolveBefore(ctx)
 	app.After = c.resolveAfter(ctx)