bool flags accept a value but do not mention taking arguments in --help output

[alimpfard]

Given a bool flag like

command.PersistentFlags().BoolVarP(&opts.Frobnicate, "frobnicate", "", true, "Frobnicate the output")

--help lists:

--frobnicate                           Frobnicate the output (default true)

but the parser accepts --frobnicate false, expected behaviour is to either disallow --frobnicate false or mention the optional argument in --help like

--frobnicate [bool]                           Frobnicate the output (default true)

[jpmcb]

If you're looking for a single "switch" flag, you'll want something like this:

var bark bool

...

// use false, the "empty" value for a bool, as the default
rootCmd.PersistentFlags().BoolVarP(&bark, "woof", "", false, "prints out bark")

...

// In your command logic, use that variable
if bark {
    println("woof!")
}

Running this program looks like:

$ ./testing-app --help

...

Flags:
  -h, --help            help for testing-app
      --woof            prints out bark

$ ./testing-app
$ ./testing-app --woof
woof!
$

[alimpfard]

I am not looking for a switch flag, rather that (in your example), ./testing-app --woof=false is considered valid, yet the --help output does not mention it.

[jpmcb]

A bool flag is a switch flag.

--woof=false, --woof=true, and --woof are all valid inputs. This is intended behavior so that a user may provide the flag by itself or with a input boolean.

Are you expecting that the default template for bool flags should mention that it's expecting a bool? Or am I missing something here?

[alimpfard]

I expect the --help output to tell me that --woof accepts an optional boolean argument (as it does).
To speak in...say, getopt terms, that's the difference between option.has_arg == true and option.has_arg == false; for instance:

$ man --ascii=true
man: option '--ascii' doesn't allow an argument

ofc, I'm not asking for removal of --bool-flag=false, I'm just asking the --help output to list its optional argument.

[jpmcb]

I'm just asking the --help output to list its optional argument.

I think that's fair! Re-opening and we can get some community feedback

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[mid-kid]

bump. This issue bit me today, as I expected it to function as --bool-flag false instead of --bool-flag=false, given that all other flag arguments are passed without the =, and I think not mentioning something along the lines of --bool-flag[=VALUE] in the help output isn't a very good user experience, especially since some programs prefer --[no-]bool-flag or other schemes for controlling flags.