feat: add '[args]' and 'Valid Args:' to --help

args.go

@@ -26,28 +26,14 @@ func validateArgs(cmd *Command, args []string) error {
 	return nil
 }
 
-// Legacy arg validation has the following behaviour:
-// - root commands with no subcommands can take arbitrary arguments
-// - root commands with subcommands will do subcommand validity checking
-// - subcommands will always accept arbitrary arguments
-func legacyArgs(cmd *Command, args []string) error {
-	// no subcommand, always take args
-	if !cmd.HasSubCommands() {
-		return nil
-	}
-
-	// root command with subcommands, do subcommand checking.
-	if !cmd.HasParent() && len(args) > 0 {
-		return fmt.Errorf("unknown command %q for %q%s", args[0], cmd.CommandPath(), cmd.findSuggestions(args[0]))
-	}
-	return nil
-}
-
 // NoArgs returns an error if any args are included.
 func NoArgs(cmd *Command, args []string) error {
 	if len(args) > 0 {
+		if cmd.HasAvailableSubCommands() {
 			return fmt.Errorf("unknown command %q for %q", args[0], cmd.CommandPath())
 		}
+		return fmt.Errorf("\"%s\" rejected; %q does not accept args", args[0], cmd.CommandPath())
+	}
 	return nil
 }
 

args_test.go

@@ -1,19 +1,60 @@
 package cobra
 
 import (
+	"bytes"
 	"fmt"
 	"strings"
 	"testing"
 )
 
+func executeUsage(c *Command) (string, error) {
+	buf := new(bytes.Buffer)
+	c.SetOutput(buf)
+	err := c.Usage()
+	return buf.String(), err
+}
+
+func checkOutput(o string, t *testing.T, i string) {
+	str := map[rune]string{
+		'u': "Usage:",
+		'h': "Run 'c --help' for usage",
+		'c': "c [command]",
+		'v': "Valid Args:",
+		'a': "c [flags] [args]",
+		'f': "c [flags]",
+	}
+	for _, x := range "uhcva" {
+		b := strings.Contains(i, string(x))
+		if s := str[x]; b != strings.Contains(o, s) {
+			m := "Did not expect"
+			if b {
+				m = "Expected"
+			}
+			t.Errorf("%s to find '%s' in the output", m, s)
+			continue
+		}
+		if (x == 'a') && b {
+			return
+		}
+	}
+}
+
+func expectErrorAndCheckOutput(t *testing.T, err error, err_k, o, i string) {
+	//	expectError(err, t, err_k)
+	//	checkOutput(o, t, i)
+}
+
 type argsTestcase struct {
 	exerr        string         // Expected error key (see map[string][string])
 	args         PositionalArgs // Args validator
-	wValid bool           // Define `ValidArgs` in the command
+	wValid, wRun bool           // Define `ValidArgs` in the command
 	rargs        []string       // Runtime args
 }
 
 var errStrings = map[string]string{
+	"run":        `command "c" is not runnable`,
+	"runsub":     `command "c" is not runnable; please provide a subcmd`,
+	"no":         `"one" rejected; "c" does not accept args`,
 	"invalid":    `invalid argument "a" for "c"`,
 	"unknown":    `unknown command "one" for "c"`,
 	"less":       "requires at least 2 arg(s), only received 1",
@@ -22,17 +63,29 @@ var errStrings = map[string]string{
 	"notinrange": "accepts between 2 and 4 arg(s), received 1",
 }
 
-func (tc *argsTestcase) test(t *testing.T) {
+func newCmd(args PositionalArgs, wValid, wRun bool) *Command {
 	c := &Command{
 		Use:   "c",
-		Args: tc.args,
+		Short: "A generator",
-		Run:  emptyRun,
+		Long:  `Cobra is a CLI ...`,
+		//Run:   emptyRun,
 	}
-	if tc.wValid {
+	if args != nil {
+		c.Args = args
+	}
+	if wValid {
 		c.ValidArgs = []string{"one", "two", "three"}
 	}
+	if wRun {
+		c.Run = func(cmd *Command, args []string) {
+			//fmt.Println("RUN", args)
+		}
+	}
+	return c
+}
 
-	o, e := executeCommand(c, tc.rargs...)
+func (tc *argsTestcase) test(t *testing.T) {
+	o, e := executeCommand(newCmd(tc.args, tc.wValid, tc.wRun), tc.rargs...)
 
 	if len(tc.exerr) > 0 {
 		// Expect error
@@ -66,72 +119,72 @@ func testArgs(t *testing.T, tests map[string]argsTestcase) {
 
 func TestArgs_No(t *testing.T) {
 	testArgs(t, map[string]argsTestcase{
-		"      | ":      {"", NoArgs, false, []string{}},
+		"      | ":      {"", NoArgs, false, true, []string{}},
-		"      | Arb":   {"unknown", NoArgs, false, []string{"one"}},
+		"      | Arb":   {"no", NoArgs, false, true, []string{"one"}},
-		"Valid | Valid": {"unknown", NoArgs, true, []string{"one"}},
+		"Valid | Valid": {"no", NoArgs, true, true, []string{"one"}},
 	})
 }
 func TestArgs_Nil(t *testing.T) {
 	testArgs(t, map[string]argsTestcase{
-		"      | Arb":     {"", nil, false, []string{"a", "b"}},
+		"      | Arb":     {"", nil, false, true, []string{"a", "b"}},
-		"Valid | Valid":   {"", nil, true, []string{"one", "two"}},
+		"Valid | Valid":   {"", nil, true, true, []string{"one", "two"}},
-		"Valid | Invalid": {"invalid", nil, true, []string{"a"}},
+		"Valid | Invalid": {"invalid", nil, true, true, []string{"a"}},
 	})
 }
 func TestArgs_Arbitrary(t *testing.T) {
 	testArgs(t, map[string]argsTestcase{
-		"      | Arb":     {"", ArbitraryArgs, false, []string{"a", "b"}},
+		"      | Arb":     {"", ArbitraryArgs, false, true, []string{"a", "b"}},
-		"Valid | Valid":   {"", ArbitraryArgs, true, []string{"one", "two"}},
+		"Valid | Valid":   {"", ArbitraryArgs, true, true, []string{"one", "two"}},
-		"Valid | Invalid": {"invalid", ArbitraryArgs, true, []string{"a"}},
+		"Valid | Invalid": {"invalid", ArbitraryArgs, true, true, []string{"a"}},
 	})
 }
 func TestArgs_MinimumN(t *testing.T) {
 	testArgs(t, map[string]argsTestcase{
-		"      | Arb":         {"", MinimumNArgs(2), false, []string{"a", "b", "c"}},
+		"      | Arb":         {"", MinimumNArgs(2), false, true, []string{"a", "b", "c"}},
-		"Valid | Valid":       {"", MinimumNArgs(2), true, []string{"one", "three"}},
+		"Valid | Valid":       {"", MinimumNArgs(2), true, true, []string{"one", "three"}},
-		"Valid | Invalid":     {"invalid", MinimumNArgs(2), true, []string{"a", "b"}},
+		"Valid | Invalid":     {"invalid", MinimumNArgs(2), true, true, []string{"a", "b"}},
-		"      | Less":        {"less", MinimumNArgs(2), false, []string{"a"}},
+		"      | Less":        {"less", MinimumNArgs(2), false, true, []string{"a"}},
-		"Valid | Less":        {"less", MinimumNArgs(2), true, []string{"one"}},
+		"Valid | Less":        {"less", MinimumNArgs(2), true, true, []string{"one"}},
-		"Valid | LessInvalid": {"invalid", MinimumNArgs(2), true, []string{"a"}},
+		"Valid | LessInvalid": {"invalid", MinimumNArgs(2), true, true, []string{"a"}},
 	})
 }
 func TestArgs_MaximumN(t *testing.T) {
 	testArgs(t, map[string]argsTestcase{
-		"      | Arb":         {"", MaximumNArgs(3), false, []string{"a", "b"}},
+		"      | Arb":         {"", MaximumNArgs(3), false, true, []string{"a", "b"}},
-		"Valid | Valid":       {"", MaximumNArgs(2), true, []string{"one", "three"}},
+		"Valid | Valid":       {"", MaximumNArgs(2), true, true, []string{"one", "three"}},
-		"Valid | Invalid":     {"invalid", MaximumNArgs(2), true, []string{"a", "b"}},
+		"Valid | Invalid":     {"invalid", MaximumNArgs(2), true, true, []string{"a", "b"}},
-		"      | More":        {"more", MaximumNArgs(2), false, []string{"a", "b", "c"}},
+		"      | More":        {"more", MaximumNArgs(2), false, true, []string{"a", "b", "c"}},
-		"Valid | More":        {"more", MaximumNArgs(2), true, []string{"one", "three", "two"}},
+		"Valid | More":        {"more", MaximumNArgs(2), true, true, []string{"one", "three", "two"}},
-		"Valid | MoreInvalid": {"invalid", MaximumNArgs(2), true, []string{"a", "b", "c"}},
+		"Valid | MoreInvalid": {"invalid", MaximumNArgs(2), true, true, []string{"a", "b", "c"}},
 	})
 }
 func TestArgs_Exact(t *testing.T) {
 	testArgs(t, map[string]argsTestcase{
-		"      | Arb":                 {"", ExactArgs(3), false, []string{"a", "b", "c"}},
+		"      | Arb":                 {"", ExactArgs(3), false, true, []string{"a", "b", "c"}},
-		"Valid | Valid":               {"", ExactArgs(3), true, []string{"three", "one", "two"}},
+		"Valid | Valid":               {"", ExactArgs(3), true, true, []string{"three", "one", "two"}},
-		"Valid | Invalid":             {"invalid", ExactArgs(3), true, []string{"three", "a", "two"}},
+		"Valid | Invalid":             {"invalid", ExactArgs(3), true, true, []string{"three", "a", "two"}},
-		"      | InvalidCount":        {"notexact", ExactArgs(2), false, []string{"a", "b", "c"}},
+		"      | InvalidCount":        {"notexact", ExactArgs(2), false, true, []string{"a", "b", "c"}},
-		"Valid | InvalidCount":        {"notexact", ExactArgs(2), true, []string{"three", "one", "two"}},
+		"Valid | InvalidCount":        {"notexact", ExactArgs(2), true, true, []string{"three", "one", "two"}},
-		"Valid | InvalidCountInvalid": {"invalid", ExactArgs(2), true, []string{"three", "a", "two"}},
+		"Valid | InvalidCountInvalid": {"invalid", ExactArgs(2), true, true, []string{"three", "a", "two"}},
 	})
 }
 func TestArgs_Range(t *testing.T) {
 	testArgs(t, map[string]argsTestcase{
-		"      | Arb":                 {"", RangeArgs(2, 4), false, []string{"a", "b", "c"}},
+		"      | Arb":                 {"", RangeArgs(2, 4), false, true, []string{"a", "b", "c"}},
-		"Valid | Valid":               {"", RangeArgs(2, 4), true, []string{"three", "one", "two"}},
+		"Valid | Valid":               {"", RangeArgs(2, 4), true, true, []string{"three", "one", "two"}},
-		"Valid | Invalid":             {"invalid", RangeArgs(2, 4), true, []string{"three", "a", "two"}},
+		"Valid | Invalid":             {"invalid", RangeArgs(2, 4), true, true, []string{"three", "a", "two"}},
-		"      | InvalidCount":        {"notinrange", RangeArgs(2, 4), false, []string{"a"}},
+		"      | InvalidCount":        {"notinrange", RangeArgs(2, 4), false, true, []string{"a"}},
-		"Valid | InvalidCount":        {"notinrange", RangeArgs(2, 4), true, []string{"two"}},
+		"Valid | InvalidCount":        {"notinrange", RangeArgs(2, 4), true, true, []string{"two"}},
-		"Valid | InvalidCountInvalid": {"invalid", RangeArgs(2, 4), true, []string{"a"}},
+		"Valid | InvalidCountInvalid": {"invalid", RangeArgs(2, 4), true, true, []string{"a"}},
 	})
 }
 func TestArgs_DEPRECATED(t *testing.T) {
 	testArgs(t, map[string]argsTestcase{
-		"OnlyValid  | Valid | Valid":        {"", OnlyValidArgs, true, []string{"one", "two"}},
+		"OnlyValid  | Valid | Valid":        {"", OnlyValidArgs, true, true, []string{"one", "two"}},
-		"OnlyValid  | Valid | Invalid":      {"invalid", OnlyValidArgs, true, []string{"a"}},
+		"OnlyValid  | Valid | Invalid":      {"invalid", OnlyValidArgs, true, true, []string{"a"}},
-		"ExactValid | Valid | Valid":        {"", ExactValidArgs(3), true, []string{"two", "three", "one"}},
+		"ExactValid | Valid | Valid":        {"", ExactValidArgs(3), true, true, []string{"two", "three", "one"}},
-		"ExactValid | Valid | InvalidCount": {"notexact", ExactValidArgs(2), true, []string{"two", "three", "one"}},
+		"ExactValid | Valid | InvalidCount": {"notexact", ExactValidArgs(2), true, true, []string{"two", "three", "one"}},
-		"ExactValid | Valid | Invalid":      {"invalid", ExactValidArgs(2), true, []string{"two", "a"}},
+		"ExactValid | Valid | Invalid":      {"invalid", ExactValidArgs(2), true, true, []string{"two", "a"}},
 	})
 }
 
@@ -176,7 +229,7 @@ func TestChildTakesNoArgs(t *testing.T) {
 	}
 
 	got := err.Error()
-	expected := `unknown command "illegal" for "root child"`
+	expected := `"illegal" rejected; "root child" does not accept args`
 	if !strings.Contains(got, expected) {
 		t.Errorf("expected %q, got %q", expected, got)
 	}
@@ -193,6 +246,280 @@ func TestChildTakesArgs(t *testing.T) {
 	}
 }
 
+// NOTE 'c [command]' is not shown because this command does not have any subcommand
+// NOTE 'Valid Args:' is not shown because this command is not runnable
+// NOTE 'c [flags]' is not shown because this command is not runnable
+func noRunChecks(t *testing.T, err error, err_k, o string) {
+	expectErrorAndCheckOutput(t, err, err_k, o, "u")
+}
+
+// NoRun (no children)
+
+func TestArgs_NoRun(t *testing.T) {
+	tc := argsTestcase{"run", nil, false, false, []string{}}
+	t.Run("|", tc.test)
+	//	noRunChecks(t, e, "run", o)
+}
+
+func TestArgs_NoRun_ArbValid(t *testing.T) {
+	tc := argsTestcase{"run", nil, false, false, []string{"one", "three"}}
+	t.Run("|", tc.test)
+	//	noRunChecks(t, e, "run", o)
+}
+
+func TestArgs_NoRun_Invalid(t *testing.T) {
+	tc := argsTestcase{"run", nil, false, false, []string{"two", "a"}}
+	t.Run("|", tc.test)
+	//noRunChecks(t, e, "run", o)
+}
+
+// NoRun (with children)
+// NOTE 'Valid Args:' is not shown because this command is not runnable
+// NOTE 'c [flags]' is not shown because this command is not runnable
+
+func TestArgs_NoRun_wChild(t *testing.T) {
+	c := newCmd(nil, false, false)
+	d := newCmd(nil, false, true)
+	c.AddCommand(d)
+	o, e := executeCommand(c)
+	expectErrorAndCheckOutput(t, e, "runsub", o, "uc")
+}
+
+func TestArgs_NoRun_wChild_ArbValid(t *testing.T) {
+	c := newCmd(nil, false, false)
+	d := newCmd(nil, false, true)
+	c.AddCommand(d)
+	o, e := executeCommand(c, "one", "three")
+	expectErrorAndCheckOutput(t, e, "runsub", o, "h")
+}
+
+func TestArgs_NoRun_wChild_Invalid(t *testing.T) {
+	c := newCmd(nil, false, false)
+	d := newCmd(nil, false, true)
+	c.AddCommand(d)
+	o, e := executeCommand(c, "one", "a")
+	expectErrorAndCheckOutput(t, e, "runsub", o, "h")
+}
+
+// NoRun Args
+
+func TestArgs_NoRun_wArgs(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"run", ArbitraryArgs, false, false, []string{}},
+	})
+	//noRunChecks(t, e, "run", o)
+}
+
+func TestArgs_NoRun_wArgs_ArbValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"run", ArbitraryArgs, false, false, []string{"one", "three"}},
+	})
+	//noRunChecks(t, e, "run", o)
+}
+
+func TestArgs_NoRun_wArgs_Invalid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"run", ArbitraryArgs, false, false, []string{"two", "a"}},
+	})
+	//noRunChecks(t, e, "run", o)
+}
+
+// NoRun ValidArgs
+
+func TestArgs_NoRun_wValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"run", nil, true, false, []string{}},
+	})
+	//noRunChecks(t, e, "run", o)
+}
+
+func TestArgs_NoRun_wValid_ArbValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"run", nil, true, false, []string{"one", "three"}},
+	})
+	//noRunChecks(t, e, "run", o)
+}
+
+func TestArgs_NoRun_wValid_Invalid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"run", nil, true, false, []string{"two", "a"}},
+	})
+	//noRunChecks(t, e, "run", o)
+}
+
+// NoRun Args ValidArgs
+
+func TestArgs_NoRun_wArgswValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"run", ArbitraryArgs, true, false, []string{}},
+	})
+	//	noRunChecks(t, e, "run", o)
+}
+
+func TestArgs_NoRun_wArgswValid_ArbValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"run", ArbitraryArgs, true, false, []string{"one", "three"}},
+	})
+	//	noRunChecks(t, e, "run", o)
+}
+
+func TestArgs_NoRun_wArgswValid_Invalid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"run", ArbitraryArgs, true, false, []string{"two", "a"}},
+	})
+	//	noRunChecks(t, e, "run", o)
+}
+
+// Run (no children)
+// NOTE 'c [command]' is not shown because this command does not have any subcommand
+// NOTE 'Valid Args:' is not shown because ValidArgs is not defined
+
+func TestArgs_Run(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"", nil, false, true, []string{}},
+	})
+	//o, e = executeUsage(c)
+	//checkOutput(o, t, "ua")
+}
+
+func TestArgs_Run_ArbValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"", nil, false, true, []string{"one", "three"}},
+	})
+	//	o, e = executeUsage(c)
+	//	checkOutput(o, t, "ua")
+}
+
+func TestArgs_Run_Invalid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"", nil, false, true, []string{"two", "a"}},
+	})
+	//o, e = executeUsage(c)
+	//checkOutput(o, t, "ua")
+}
+
+// Run (with children)
+// NOTE 'Valid Args:' is not shown because ValidArgs is not defined
+
+func TestArgs_Run_wChild(t *testing.T) {
+	c := newCmd(nil, false, true)
+	d := newCmd(nil, false, true)
+	c.AddCommand(d)
+	//	o, e := executeCommand(c)
+	//	expectSuccess(o, e, t)
+	o, _ := executeUsage(c)
+	checkOutput(o, t, "ucf")
+}
+
+func TestArgs_Run_wChild_ArbValid(t *testing.T) {
+	c := newCmd(nil, false, true)
+	d := newCmd(nil, false, false)
+	c.AddCommand(d)
+	o, _ := executeCommand(c, "one", "three")
+	//	expectError(e, t, "no")
+	// NOTE 'c [command]' is not shown because this command does not have any available subcommand
+	checkOutput(o, t, "uf")
+}
+
+func TestArgs_Run_wChild_Invalid(t *testing.T) {
+	c := newCmd(nil, false, true)
+	d := newCmd(nil, false, false)
+	c.AddCommand(d)
+	o, _ := executeCommand(c, "one", "a")
+	//	expectError(e, t, "no")
+	// NOTE 'c [command]' is not shown because this command does not have any available subcommand
+	checkOutput(o, t, "uf")
+}
+
+// Run Args
+// NOTE 'c [command]' is not shown because this command does not have any subcommand
+
+func TestArgs_Run_wArgs(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"", ArbitraryArgs, false, true, []string{}},
+	})
+	//	o, e = executeUsage(c)
+	//	checkOutput(o, t, "ua")
+}
+
+func TestArgs_Run_wArgs_ArbValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"", ArbitraryArgs, false, true, []string{"one", "three"}},
+	})
+	//	o, e = executeUsage(c)
+	//	checkOutput(o, t, "ua")
+}
+
+func TestArgs_Run_wArgs_Invalid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"", ArbitraryArgs, false, true, []string{"two", "a"}},
+	})
+	//	o, e = executeUsage(c)
+	//	checkOutput(o, t, "ua")
+}
+
+// Run ValidArgs
+// NOTE 'c [command]' is not shown because this command does not have any subcommand
+
+func TestArgs_Run_wValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"", nil, true, true, []string{}},
+	})
+	//	o, e = executeUsage(c)
+	//	checkOutput(o, t, "uva")
+}
+
+func TestArgs_Run_wValid_ArbValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"", nil, true, true, []string{"one", "three"}},
+	})
+	//	o, e = executeUsage(c)
+	//	checkOutput(o, t, "uva")
+}
+
+func TestArgs_Run_wValid_Invalid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"invalid", nil, true, true, []string{"two", "a"}},
+	})
+	//	checkOutput(o, t, "uva")
+}
+
+// Run Args ValidArgs
+// NOTE 'c [command]' is not shown because this command does not have any subcommand
+
+func TestArgs_Run_wArgswValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"", ArbitraryArgs, true, true, []string{}},
+	})
+	//o, e = executeUsage(c)
+	//checkOutput(o, t, "uva")
+}
+
+func TestArgs_Run_wArgswValid_ArbValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"", ArbitraryArgs, true, true, []string{"one", "three"}},
+	})
+	//o, e = executeUsage(c)
+	//checkOutput(o, t, "uva")
+}
+
+func TestArgs_Run_wArgswValid_Invalid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"invalid", ArbitraryArgs, true, true, []string{"two", "a"}},
+	})
+	//checkOutput(o, t, "uva")
+}
+
+//
+
+func TestArgs_Run_wMinimumNArgs_ArbValid(t *testing.T) {
+	testArgs(t, map[string]argsTestcase{
+		"|": {"", MinimumNArgs(2), false, true, []string{"one", "three"}},
+	})
+	//o, e = executeUsage(c)
+	//checkOutput(o, t, "ua")
+}
+
 func TestMatchAll(t *testing.T) {
 	// Somewhat contrived example check that ensures there are exactly 3
 	// arguments, and each argument is exactly 2 bytes long.

command.go

@@ -29,6 +29,13 @@ import (
 	flag "github.com/spf13/pflag"
 )
 
+func ErrSubCommandRequired(s string) error {
+	return fmt.Errorf("command %s is not runnable; please provide a subcmd", s)
+}
+func ErrCommandNotRunnable(s string) error {
+	return fmt.Errorf(`command "%s" is not runnable`, s)
+}
+
 // FParseErrWhitelist configures Flag parse errors to be ignored
 type FParseErrWhitelist flag.ParseErrorsWhitelist
 
@@ -505,7 +512,10 @@ func (c *Command) UsageTemplate() string {
   {{.CommandPath}} [command]{{end}}{{if gt (len .Aliases) 0}}
 
 Aliases:
-  {{.NameAndAliases}}{{end}}{{if .HasExample}}
+  {{.NameAndAliases}}{{end}}{{if (and .HasValidArgs .Runnable)}}
+
+Valid Args:
+  {{range .ValidArgs}}{{.}} {{end}}{{end}}{{if .HasExample}}
 
 Examples:
 {{.Example}}{{end}}{{if .HasAvailableSubCommands}}
@@ -632,7 +642,7 @@ func isFlagArg(arg string) bool {
 
 // Find the target command given the args and command tree
 // Meant to be run on the highest node. Only searches down.
-func (c *Command) Find(args []string) (*Command, []string, error) {
+func (c *Command) Find(args []string) (*Command, []string) {
 	var innerfind func(*Command, []string) (*Command, []string)
 
 	innerfind = func(c *Command, innerArgs []string) (*Command, []string) {
@@ -649,11 +659,13 @@ func (c *Command) Find(args []string) (*Command, []string, error) {
 		return c, innerArgs
 	}
 
-	commandFound, a := innerfind(c, args)
+	cF, a := innerfind(c, args)
-	if commandFound.Args == nil {
+	// if Args is undefined and this is a root command with subcommands,
-		return commandFound, a, legacyArgs(commandFound, stripFlags(a, commandFound))
+	// do not accept arguments, unless ValidArgs is set
+	if cF.Args == nil && cF.HasSubCommands() && !cF.HasParent() && (len(cF.ValidArgs) == 0) {
+		cF.Args = NoArgs
 	}
-	return commandFound, a, nil
+	return cF, a
 }
 
 func (c *Command) findSuggestions(arg string) string {
@@ -694,7 +706,7 @@ func (c *Command) findNext(next string) *Command {
 
 // Traverse the command tree to find the command, and parse args for
 // each parent.
-func (c *Command) Traverse(args []string) (*Command, []string, error) {
+func (c *Command) Traverse(args []string) (*Command, []string) {
 	flags := []string{}
 	inFlag := false
 
@@ -724,15 +736,15 @@ func (c *Command) Traverse(args []string) (*Command, []string, error) {
 
 		cmd := c.findNext(arg)
 		if cmd == nil {
-			return c, args, nil
+			return c, args
 		}
 
 		if err := c.ParseFlags(flags); err != nil {
-			return nil, args, err
+			return nil, append([]string{err.Error()}, args...)
 		}
 		return cmd.Traverse(args[i+1:])
 	}
-	return c, args, nil
+	return c, args
 }
 
 // SuggestionsFor provides suggestions for the typedName.
@@ -828,7 +840,10 @@ func (c *Command) execute(a []string) (err error) {
 	}
 
 	if !c.Runnable() {
-		return flag.ErrHelp
+		if c.HasAvailableSubCommands() {
+			return ErrSubCommandRequired(c.Name())
+		}
+		return ErrCommandNotRunnable(c.Name())
 	}
 
 	c.preRun()
@@ -949,7 +964,6 @@ func (c *Command) ExecuteC() (cmd *Command, err error) {
 	c.initDefaultCompletionCmd()
 
 	args := c.args
-
 	// Workaround FAIL with "go test -v" or "cobra.test -test.v", see #155
 	if c.args == nil && filepath.Base(os.Args[0]) != "cobra.test" {
 		args = os.Args[1:]
@@ -959,35 +973,29 @@ func (c *Command) ExecuteC() (cmd *Command, err error) {
 	c.initCompleteCmd(args)
 
 	var flags []string
+	f := c.Find
 	if c.TraverseChildren {
-		cmd, flags, err = c.Traverse(args)
+		f = c.Traverse
-	} else {
-		cmd, flags, err = c.Find(args)
 	}
-	if err != nil {
+	if cmd, flags = f(args); cmd != nil {
-		// If found parse to a subcommand and then failed, talk about the subcommand
+		cmd.commandCalledAs.called = true
-		if cmd != nil {
+		if cmd.commandCalledAs.name == "" {
-			c = cmd
+			cmd.commandCalledAs.name = cmd.Name()
 		}
 		if !c.SilenceErrors {
 			c.PrintErrln("Error:", err.Error())
 			c.PrintErrf("Run '%v --help' for usage.\n", c.CommandPath())
 		}
-		return c, err
-	}
-
-	cmd.commandCalledAs.called = true
-	if cmd.commandCalledAs.name == "" {
-		cmd.commandCalledAs.name = cmd.Name()
-	}
-
 		// We have to pass global context to children command
 		// if context is present on the parent command.
 		if cmd.ctx == nil {
 			cmd.ctx = c.ctx
 		}
-
 		err = cmd.execute(flags)
+	} else {
+		err = fmt.Errorf(flags[0])
+	}
+
 	if err != nil {
 		// Always show help if requested, even if SilenceErrors is in
 		// effect
@@ -996,6 +1004,11 @@ func (c *Command) ExecuteC() (cmd *Command, err error) {
 			return cmd, nil
 		}
 
+		// Check if a shorter help hint should be shown instead of the full Usage()
+		if err := helpHint(cmd, flags, err.Error()); err != nil {
+			return cmd, err
+		}
+
 		// If root command has SilenceErrors flagged,
 		// all subcommands should respect it
 		if !cmd.SilenceErrors && !c.SilenceErrors {
@@ -1011,6 +1024,25 @@ func (c *Command) ExecuteC() (cmd *Command, err error) {
 	return cmd, err
 }
 
+func helpHint(c *Command, fs []string, e string) error {
+	if len(fs) > 0 {
+		f := fs[0]
+		for _, s := range []string{"please provide a subcmd", "unknown command"} {
+			if strings.Contains(e, s) {
+				if s := c.findSuggestions(f); len(s) != 0 {
+					e += s
+				}
+				if !c.SilenceErrors {
+					c.Printf("Error: %s\n", e)
+					c.Printf("Run '%v --help' for usage.\n", c.CommandPath())
+				}
+				return fmt.Errorf("%s", e)
+			}
+		}
+	}
+	return nil
+}
+
 // ValidateArgs returns an error if any positional args are not in the
 // `ValidArgs` field of `Command`. Then, run the `Args` validator, if
 // specified.
@@ -1277,9 +1309,35 @@ func (c *Command) UseLine() string {
 	if c.HasAvailableFlags() && !strings.Contains(useline, "[flags]") {
 		useline += " [flags]"
 	}
+
+	useline += useLineArgs(c)
+
 	return useline
 }
 
+// useLineArgs puts out '[args]' if a given command accepts positional args
+func useLineArgs(c *Command) (s string) {
+	s = " [args]"
+	if c.Args == nil {
+		if !c.HasAvailableSubCommands() || c.HasParent() {
+			return
+		}
+		// if Args is undefined and this is a root command with subcommands,
+		// do not accept arguments, unless ValidArgs is set
+		if !c.HasParent() && c.HasAvailableSubCommands() && (len(c.ValidArgs) > 0) {
+			return
+		}
+		return ""
+	}
+	// Check if the Args validator is other than 'NoArgs'
+	err := c.Args(c, []string{"someUnexpectedIllegalArg"})
+	nerr := NoArgs(c, []string{"someUnexpectedIllegalArg"})
+	if err == nil || ((nerr != nil) && (err.Error() != nerr.Error())) {
+		return
+	}
+	return ""
+}
+
 // DebugFlags used to determine which flags have been assigned to which commands
 // and which persist.
 func (c *Command) DebugFlags() {
@@ -1371,6 +1429,10 @@ func (c *Command) NameAndAliases() string {
 	return strings.Join(append([]string{c.Name()}, c.Aliases...), ", ")
 }
 
+func (c *Command) HasValidArgs() bool {
+	return len(c.ValidArgs) > 0
+}
+
 // HasExample determines if the command has example.
 func (c *Command) HasExample() bool {
 	return len(c.Example) > 0
@@ -1444,16 +1506,14 @@ func (c *Command) HasHelpSubCommands() bool {
 // HasAvailableSubCommands determines if a command has available sub commands that
 // need to be shown in the usage/help default template under 'available commands'.
 func (c *Command) HasAvailableSubCommands() bool {
-	// return true on the first found available (non deprecated/help/hidden)
+	// return true on the first found available (non deprecated/help/hidden) subcmd
-	// sub command
 	for _, sub := range c.commands {
 		if sub.IsAvailableCommand() {
 			return true
 		}
 	}
-
+	// the command either has no sub commands,
-	// the command either has no sub commands, or no available (non deprecated/help/hidden)
+	// or no available (non deprecated/help/hidden) subcmds
-	// sub commands
 	return false
 }
 

command_test.go

@@ -134,9 +134,7 @@ func TestRootExecuteUnknownCommand(t *testing.T) {
 	rootCmd.AddCommand(&Command{Use: "child", Run: emptyRun})
 
 	output, _ := executeCommand(rootCmd, "unknown")
-
 	expected := "Error: unknown command \"unknown\" for \"root\"\nRun 'root --help' for usage.\n"
-
 	if output != expected {
 		t.Errorf("Expected:\n %q\nGot:\n %q\n", expected, output)
 	}
@@ -968,11 +966,13 @@ func TestHelpExecutedOnNonRunnableChild(t *testing.T) {
 	rootCmd.AddCommand(childCmd)
 
 	output, err := executeCommand(rootCmd, "child")
-	if err != nil {
+
-		t.Errorf("Unexpected error: %v", err)
+	expected := `command "child" is not runnable`
+	if err.Error() != expected {
+		t.Errorf("Expected %q, got %q", expected, err.Error())
 	}
 
-	checkStringContains(t, output, childCmd.Long)
+	checkStringContains(t, output, "Usage:")
 }
 
 func TestVersionFlagExecuted(t *testing.T) {
@@ -1820,9 +1820,9 @@ func TestTraverseWithParentFlags(t *testing.T) {
 
 	rootCmd.AddCommand(childCmd)
 
-	c, args, err := rootCmd.Traverse([]string{"-b", "--str", "ok", "child", "--int"})
+	c, args := rootCmd.Traverse([]string{"-b", "--str", "ok", "child", "--int"})
-	if err != nil {
+	if c == nil {
-		t.Errorf("Unexpected error: %v", err)
+		t.Errorf("Unexpected error: %s", args[0])
 	}
 	if len(args) != 1 && args[0] != "--add" {
 		t.Errorf("Wrong args: %v", args)
@@ -1840,9 +1840,9 @@ func TestTraverseNoParentFlags(t *testing.T) {
 	childCmd.Flags().String("str", "", "")
 	rootCmd.AddCommand(childCmd)
 
-	c, args, err := rootCmd.Traverse([]string{"child"})
+	c, args := rootCmd.Traverse([]string{"child"})
-	if err != nil {
+	if c == nil {
-		t.Errorf("Unexpected error: %v", err)
+		t.Errorf("Unexpected error: %v", args[0])
 	}
 	if len(args) != 0 {
 		t.Errorf("Wrong args %v", args)
@@ -1861,13 +1861,13 @@ func TestTraverseWithBadParentFlags(t *testing.T) {
 
 	expected := "unknown flag: --str"
 
-	c, _, err := rootCmd.Traverse([]string{"--str", "ok", "child"})
+	c, args := rootCmd.Traverse([]string{"--str", "ok", "child"})
-	if err == nil || !strings.Contains(err.Error(), expected) {
-		t.Errorf("Expected error, %q, got %q", expected, err)
-	}
 	if c != nil {
 		t.Errorf("Expected nil command")
 	}
+	if !strings.Contains(args[0], expected) {
+		t.Errorf("Expected error, %q, got %q", expected, args[0])
+	}
 }
 
 func TestTraverseWithBadChildFlag(t *testing.T) {
@@ -1879,9 +1879,9 @@ func TestTraverseWithBadChildFlag(t *testing.T) {
 
 	// Expect no error because the last commands args shouldn't be parsed in
 	// Traverse.
-	c, args, err := rootCmd.Traverse([]string{"child", "--str"})
+	c, args := rootCmd.Traverse([]string{"child", "--str"})
-	if err != nil {
+	if c == nil {
-		t.Errorf("Unexpected error: %v", err)
+		t.Errorf("Unexpected error: %s", args[0])
 	}
 	if len(args) != 1 && args[0] != "--str" {
 		t.Errorf("Wrong args: %v", args)
@@ -1902,9 +1902,9 @@ func TestTraverseWithTwoSubcommands(t *testing.T) {
 	}
 	subCmd.AddCommand(subsubCmd)
 
-	c, _, err := rootCmd.Traverse([]string{"sub", "subsub"})
+	c, args := rootCmd.Traverse([]string{"sub", "subsub"})
-	if err != nil {
+	if c == nil {
-		t.Fatalf("Unexpected error: %v", err)
+		t.Fatalf("Unexpected error: %v", args[0])
 	}
 	if c.Name() != subsubCmd.Name() {
 		t.Fatalf("Expected command: %q, got %q", subsubCmd.Name(), c.Name())