Improve unrecognised subcommand handling (#90)

args.go

@@ -26,6 +26,15 @@ func AnyArgs() ArgValidator {
 func NoArgs() ArgValidator {
 	return func(cmd *Command, args []string) error {
 		if len(args) > 0 {
+			if len(cmd.subcommands) > 0 {
+				// Maybe it's a typo of a subcommand
+				return fmt.Errorf(
+					"unknown subcommand %q for command %q, available subcommands: %v",
+					args[0],
+					cmd.name,
+					cmd.subcommandNames(),
+				)
+			}
 			return fmt.Errorf("command %s accepts no arguments but got %v", cmd.name, args)
 		}
 		return nil

args_test.go

@@ -58,6 +58,27 @@ func TestArgValidators(t *testing.T) {
 			wantErr: true,
 			errMsg:  "command test accepts no arguments but got [some args here]",
 		},
+		{
+			name: "noargs subcommand",
+			options: []cli.Option{
+				cli.Args([]string{"subb", "args", "here"}), // Note: subb is typo of sub
+				cli.Run(func(cmd *cli.Command, args []string) error {
+					fmt.Fprintln(cmd.Stdout(), "Hello from noargs")
+					return nil
+				}),
+				cli.Allow(cli.NoArgs()),
+				cli.SubCommands(
+					func() (*cli.Command, error) {
+						return cli.New(
+							"sub",
+							cli.Run(func(cmd *cli.Command, args []string) error { return nil }),
+						)
+					},
+				),
+			},
+			wantErr: true,
+			errMsg:  `unknown subcommand "subb" for command "test", available subcommands: [sub]`,
+		},
 		{
 			name: "minargs pass",
 			options: []cli.Option{

command.go

@@ -333,6 +333,15 @@ func (c *Command) hasShortFlag(name string) bool {
 	return flag.DefaultValueNoArg != ""
 }
 
+// subcommandNames returns a list of all the names of the current command's registered subcommands.
+func (c *Command) subcommandNames() []string {
+	names := make([]string, 0, len(c.subcommands))
+	for _, sub := range c.subcommands {
+		names = append(names, sub.name)
+	}
+	return names
+}
+
 // findRequestedCommand uses the raw arguments and the command tree to determine what
 // (if any) subcommand is being requested and return that command along with the arguments
 // that were meant for it.