Export `Optionality` markers

[zmbush]

In order to support custom implementations of YarnFnParam, Optional and Required need to be exported.

This exports yarnspinner_core::yarn_fn::optionality as yarnspinner_core::prelude::optionality and seals the AllowedOptionalityChain trait so it cannot be implemented.

[janhohenheim]

Huh, I was even considering explicitly sealing YarnFnParam. I'm curious, why do you need a custom YarnFnParam implementation?

[bash]

@janhohenheim If you decide to merge this then I intend to do a follow-up PR to change Optionality to be an enum / associated const. I think that would make for a nicer public API than the current approach :)

@zmbush Would you be okay with me pushing that change onto this PR?

[zmbush]

It's nice to have for convenience. I have a bunch of types that I use as command arguments, and instead of taking them as Strings, it's nice to be able to do something like:

    #[yarn_command(dialog_runner)]
    fn set_background(
        In((new_bg, mode)): In<(Location, ShowOption)>,
        ...
    ) { 
        ...
    }

instead of

    #[yarn_command(dialog_runner)]
    fn set_background(
        In((new_bg, mode)): In<(String, String)>,
        ...
    ) { 
        let new_bg: Location = new_bg.parse().unwrap();
        let mode: ShowOption = mode.parse().unwrap();
        ...
    }

[zmbush]

@zmbush Would you be okay with me pushing that change onto this PR?

@bash Yeah, go ahead!

[janhohenheim]

@zmbush I see! I was thinking about making automatic parsing a feature as well, so this workaround is completely valid. I'll merge @bash's counteroffer when it's ready :)

Btw, what's that #[yarn_command(dialog_runner)]? It looks nifty. I assume it expands to something like this?

fn register_set_background(mut dialog_runner: Query<&mut DialogueRunner, Added<DialogueRunner>>) {
  for mut dialog_runner in dialog_runner.iter_mut() {
    dialog_runner.commands_mut().add_command("set_background", set_background);
  }
}

[zmbush]

@janhohenheim Yeah, that's essentially what it does. It actually started as a way to generate ysls.json files for commands so that the language server would be able to detect them. I can try to upstream it if you're interested. (This is how the current version is used: https://gist.github.com/zmbush/f23752ac3453e9ff7d3173ca8e11f898#file-yarn_command_demo-rs)

[janhohenheim]

Yeah, generating ysls.json is also on my to do list 😅 I'll look into it once Yarn Spinner V3 launches at the latest because I'll need to port a whole bunch of stuff by then anyways. It should be possible to generate it without macros because we have runtime info on both the function name and its signature (well, other than the parameter names, but that's not important for the language server).

The macro looks nice! I wouldn't upstream it since I prefer to expose exactly one way to configure stuff, but I am tempted to replicate it for my own project :D

BTW, please ping me if you publish anything using the crate, I'd love to see what cool stuff people create with it :)

[bash]

change Optionality to be an enum / associated const

Never mind, associated consts and where clauses do not like each other :/

[janhohenheim]

@zmbush I assume sealing Optionality does not break your workflow?

[zmbush]

@janhohenheim / @bash Sealing Optionality still works for my uses.