expose HelpOption and HelpAction, move help configuration to the action

[adamsitnik]

We now have two ways of configuring help:

Before parsing:

command.Options.Add(new HelpOption()
{
    Action = new HelpAction()
    {
        Builder = helpBuilder
    }
});

Or after:

ParseResult parseResult = rootCommand.Parse("-h");

if (parseResult.Action is HelpAction helpAction)
{ 
    helpAction.Builder.CustomizeSymbol(subcommand, secondColumnText: "The custom command description");
    helpAction.Builder.CustomizeSymbol(option, secondColumnText: "The custom option description");
    helpAction.Builder.CustomizeSymbol(argument, secondColumnText: "The custom argument description");
}

parseResult.Invoke(console);

[jonsequitur]

Do you want to introduce something like HelpOption.DefaultAliases and use it here for discoverability, etc.?

[adamsitnik]

How would it be used by the end users? Currently to get the default aliases they can just do new HelpOption().Aliases

[adamsitnik]

IIRC Krzysztof or Jeremy started this discussion and the context was that it was not clear what aliases the HelpOption will use when created and added to the Command.

In #2107 I've made the config mutable and simply added xml docs to the HelpOption ctor:

command-line-api/src/System.CommandLine/Help/HelpOption.cs

Lines 8 to 18 in 2dd5b76

	/// <summary>
	/// When added to a <see cref="Command"/>, it configures the application to show help when one of the following options are specified on the command line:
	/// <code>
	/// -h
	/// /h
	/// --help
	/// -?
	/// /?
	/// </code>
	/// </summary>
	public HelpOption() : this("--help", new[] { "-h", "/h", "-?", "/?" })

I am expecting that this is going to solve the problem

[KalleOlaviNiemitalo]

If I wanted to specify the list of aliases of HelpOption (omitting "/h"), and set the maximum width, then what would be the most straightforward way to do both using this API? It seems UseHelp allows either of those customizations but not both. Should I avoid UseHelp altogether, and construct the HelpOption and HelpAction explicitly?

[adamsitnik]

If I wanted to specify the list of aliases of HelpOption (omitting "/h"), and set the maximum width

Currently it would be:

new HelpOption("--help", "-h")
{
    Action = new HelpAction()
    {
        Builder = new HelpBuilder($width)
    }
}

FWIW we are not done with our work on help customization. Most probably I won't have the time to work on it before we release a new preview package (beginning of April), I am afraid it will have to wait until June.