All commands are always optional when using hosting

[altafard]

In the example bellow I was expecting that running cli without specifying a subcommand would fail with the error "Required command was not provided." as it happens without using the host

var root = new Command("cli")
{
    Subcommands = { new Command("cmd") }
};

var configuration = new CommandLineConfiguration(root).UseHost(
   _ => Host.CreateDefaultBuilder(),
   cfg => cfg.UseInvocationLifetime());

await configuration.InvokeAsync(args);

However, it works fine and no errors pop up. It seems that UseHost calls HostingAction.SetHandlers extensions on the root command and it sets actions to all commands in the chain. As a result, this validation never sets the error.

command-line-api/src/System.CommandLine/Parsing/CommandResult.cs

Lines 46 to 55 in b7f0d1c

	/// <param name="completeValidation">Only the inner most command goes through complete validation.</param>
	internal void Validate(bool completeValidation)
	{
	if (completeValidation)
	{
	if (Command.Action is null && Command.HasSubcommands)
	{
	SymbolResultTree.InsertFirstError(
	new ParseError(LocalizationResources.RequiredCommandWasNotProvided(), this));
	}

Was it made intentionally? As a workaround I can use Validators and check that there are tokens provided in the arguments list, but it would be nice to keep the same behaviour as it works without using a host.