Add a ShowSubcommandHelpAndExit()

[bodgit]

Checklist

• Are you running the latest v2 release? The list of releases is here.
• Did you check the manual for your release? The v2 manual is here
• Did you perform a search about this feature? Here's the Github guide about searching.

What problem does this solve?

There is a ShowAppHelpAndExit() and a ShowCommandHelpAndExit() but there's currently no ShowSubcommandHelpAndExit().

Solution description

I usually use at the top of my command actions something like this:

if c.NArg() < 2 {
        cli.ShowCommandHelpAndExit(c, c.Command.FullName(), 1)
}

So if someone doesn't supply the correct number of positional arguments they get the help and it exits with a non-zero code.

I tried to use sub-commands for the first time and found I can't do this.

Describe alternatives you've considered

I've tried implementing as:

if c.NArg() < 2 {
        cli.ShowSubcommandHelp(c)
        return cli.NewExitError(nil, 1)
}

but that doesn't work very well.

[coilysiren]

@bodgit what about your alternative doesn't work very well?

[stale]

This issue or PR has been automatically marked as stale because it has not had recent activity. Please add a comment bumping this if you're still interested in it's resolution! Thanks for your help, please let us know if you need anything else.

[stale]

Closing this as it has become stale.

[meatballhat]

Actually closed via #1183