cli: show help for empty root command (#6636)

vlib/cli/command.v

@@ -185,6 +185,12 @@ fn (mut cmd Command) parse_commands() {
 			}
 		}
 	}
+	if cmd.is_root() && int(cmd.execute) == 0 {
+		if !cmd.disable_help {
+			cmd.execute_help()
+			return
+		}
+	}
 	// if no further command was found, execute current command
 	if cmd.required_args > 0 {
 		if cmd.required_args > cmd.args.len {

vlib/v/tests/inout/cli_command_no_execute.vv

@@ -1,7 +1,11 @@
-import os
 import cli {Command}
 
 fn main() {
-	mut cmd := Command {}                                                       
-	cmd.parse(os.args)
+	mut cmd := Command {
+		name: 'cmd'
+	}
+	cmd.add_command({
+		name: 'foo'
+	})
+	cmd.parse(['', 'cmd', 'foo'])
 }

vlib/v/tests/inout/cli_root_default_help.out

@@ -0,0 +1,7 @@
+Usage:  [flags] [commands]
+
+Flags:
+  -help               Prints help information.
+
+Commands:
+  help                Prints help information.

vlib/v/tests/inout/cli_root_default_help.vv

@@ -0,0 +1,7 @@
+import cli {Command}
+import os
+
+fn main() {
+	mut cmd := Command {}
+	cmd.parse(os.args)
+}