Possible values from Vec of strings

[thewh1teagle]

I'm using clap with derive macros,
and I would like to have an string argument with possible string values returned from a function.
The use cases are:

1. Parsing JSON file (maybe at compile time)

fn possible_values() -> Vec<String> {
  let content = include_str!("...");
  let data = serde_json::from_str(content);
  let languages = ...;
  languages // return list of languages
} 

2. Simply having possible string values such as selecting file format (txt, csv, etc)

[epage]

For the first, because of https://docs.rs/clap/latest/clap/builder/struct.ValueParser.html#impl-From%3CVec%3CP%3E%3E-for-ValueParser you should be able to do

    #[arg(value_parser = possible_values()]
    arg: String,

If not, you can construct https://docs.rs/clap/latest/clap/builder/struct.PossibleValuesParser.html#impl-From%3CI%3E-for-PossibleValuesParser directly

The same is true for string literals. If you want to adapt those string literals into another type, you can use https://docs.rs/clap/latest/clap/builder/trait.TypedValueParser.html#method.map or https://docs.rs/clap/latest/clap/builder/struct.EnumValueParser.html

[thewh1teagle]

I had to add string feature to clap and then it worked like so:

struct Args {
    /// Language
    #[arg(short, long, value_parser = get_possible_languages())]
    language: Option<String>
}

fn get_possible_languages() -> Vec<String> { ... }

The only issue with that is that --help shows the whole language options (more than 100) and I'm not sure if there's and elegant way to handle that better instead of showing so many options for single argument always in --help.

Regarding string literals, not sure how to use it.

I imagine something like that

struct Args {
    /// Format
    #[arg(short, long, default_value = "srt", value_parser = &["srt", "vtt", "txt"])]
    // TODO: use possible values. confusing crate!
    format: String
}

[epage]

The only issue with that is that --help shows the whole language options (more than 100) and I'm not sure if there's and elegant way to handle that better instead of showing so many options for single argument always in --help.

You could set hide_possible_values = true if its too much for your --help output.

I imagine something like that

Without the &. We have an example of it on the builder function that that attribute maps to.