Configurable version in usage output

[daenney]

Right now, this library will always output the result of Version() at the start of the usage output:

go-arg/usage.go

Lines 84 to 86 in 74af96c

	if p.version != "" {
	fmt.Fprintln(w, p.version)
	}

From my own observations, doing this is fairly uncommon amongst the CLI utilities installed on my system, especially for those that provide a dedicated flag to retrieve the version. To me personally it also feels a little out of place. If I were going to include the version information in usage output I would probably do it in the epilogue, not in the prologue.

Would you accept a PR which makes this configurable? Something like a func (args) VersionInHelp() bool {} that could return false causing the Version() to not be emitted, or a flag on Config?

[alexflint]

Hey @daenney - why not just have your Version() function return the empty string when you don't want to print a version?

[daenney]

I mean, I still want to print a version. Just not where the current version is being outputted in --help. I'd also still like --version to work, which also seems to require a Version() if I understand it correctly?

[alexflint]

Got it. That's reasonable. I think the best solution would be the ability to specify a custom template for help output, as discussed in a previous issue on the topic. In the absence of that, a workaround would be to omit the Version() function from your argument struct and handle ErrVersion explicitly like this:

var args struct {
  ...
}
p, err := arg.NewParser(&args)
err = p.Parse(os.Args())
if err == arg.ErrVersion {
  fmt.Println("Version: 1.2.3")
  os.Exit(1)
}

This still wouldn't solve your use-case of putting the version string at the bottom...

[daenney]

Ah, I suppose that would work. Thanks for the pointer. Being able to supply a template to customise the usage output sounds useful. I might look into that over the weekend.

[alexflint]

Will add this in upcoming v2 of this library