A custom flag.FlagSet returns a distinguished error, ErrHelp, when it sees the -help flag.

Where the code is written

• https://github.com/golang/go/blob/master/src/flag/flag.go#L926

if name == "help" || name == "h" { // special case for nice help message.
	f.usage()
	return false, ErrHelp
}

But, If the program is called with the wrong argument, I think that you should return explanation of usage and error.

Therefore, if you pass arguments that only "help" or "h", I think that f.usage () will be executed and (true, nil) will be returned.

I would like to know why it is implemented like this.