impl StructOpt for Box<impl StructOpt>

[CreepySkeleton]

Closes #304

This PR makes is_subcommand, from_subcommand, and augment_clap part of the StructOpt trait (marking them as doc(hidden). I believe this is justifiable change because:

• The change is 100% backward compatible.
• These methods won't ever collide with user's methods.
• This way we could add more impls in future with ease.
• The change is fairly small and straightforward.

[TeXitoi]

The methods should just be declared, not implented with unimplemented!()

[CreepySkeleton]

The trick here is - what if someone wants not derive but implement StructOpt manually? A user would want to implement only clap and from_matches, they should know nothing about these hidden methods.

[TeXitoi]

But if they implement it manually, they expect it to work with generated ones, and that's not the case.

OTOH, adding new interface is a breaking change.

I don't know... I'll think a bit about it, will comeback later.

[TeXitoi]

If you're OK with the drawbacks I've shown, I'm OK to merge this as is.

[CreepySkeleton]

Yes, I'm fine with that. It's hard to imagine someone out there was trying to implement StructOpt manually anyway :)

[TeXitoi]

v0.3.6 published

[bkchr]

We implemented StructOpt on our own ^^

[bkchr]

https://github.com/paritytech/substrate/blob/master/client/cli/src/params.rs#L957 for reference is someone is interested

[CreepySkeleton]

@bkchr OK, I have an idea on how to make this work without adding new methods to the StructOpt trait

[bkchr]

Don't worry. I just wanted to comment here. I already have a patch for us to fix the problem. I also find it much better to have the method defined in the trait :)

[bkchr]

Okay, you already yanked it ^^

[CreepySkeleton]

Okay, you already yanked it ^^

It was yanked for other reasons #315

[CreepySkeleton]

Also, @bkchr , why don't you just derive it there?

#[derive(Clone, Debug, Default, StructOpt)]
#[structopt(no_version)]
pub struct NoCustom {}

As far as I can see, it would generate the same code (I mean, the code working the same way) as you have written manually.

I hope you understand that augment_clap is entirely private API, it's subject to change without notice. Don't do that:

impl AugmentClap for NoCustom {
	fn augment_clap<'a, 'b>(app: App<'a, 'b>) -> App<'a, 'b> {
		app
	}
}

If you need to do something that's not covered by the public API, please, open an issue here and we will deal with that.

[bkchr]

Good question why I not used derive(StructOpt). I don't really remember. Regarding the augment_clap function, you are right. At the time I was writing this code, StructOpt seemed to sleep a little bit :)
I make myself some note to revisit the code and make an issue for the features we need.

Basically we want to support adding extensions to the cli interface, that the users can define.

[cecton]

[edit: deleted an created a separate issue]