Can't use ValueParser to replace PossibleValues in v4

[o2sh]

Please complete the following tasks

• I have searched the discussions
• I have searched the open and rejected issues

Rust Version

1.64.0

Clap Version

4.08

Minimal reproducible code

static COLOR_RESOLUTIONS: [&str; 5] = ["16", "32", "64", "128", "256"];

#[arg(
    long,
    value_name = "VALUE",
    requires = "image",
    default_value_t = 16usize,
    // possible_values = ["16", "32", "64", "128", "256"], // Used to work before v4
    value_parser = PossibleValuesParser::new(COLOR_RESOLUTIONS) // fails
)]
pub color_resolution: usize,

$ cargo run

thread 'main' panicked at 'Mismatch between definition and access of `color_resolution`. Could not downcast to TypeId { t: 13834754221672687376 }, need to downcast to TypeId { t: 5005868189860995316 }

[epage]

For now, PossibleValuesParser only works with String though you can use TypedValueParser::map to adapt the type. In #4352, I'm adding some examples on how to do this.

[aldanor]

For now, PossibleValuesParser only works with String

Just wondering, is it planned to have it back working with other types eventually? (e.g. that implement FromStr?)

Chances are, these lines will be copied/pasted many-many times all over the place (it's just one of the most common use cases for the old possible_values):

use clap::builder::{PossibleValuesParser, TypedValueParser as _};
...
    value_parser = PossibleValuesParser::new(Foo::VARIANTS)
        .map(|s| s.parse::<Foo>().unwrap())

E.g.:

    value_parser = PossibleValuesFromStr::<Foo>::new(Foo::VARIANTS)

[epage]

Feel free to create an issue for making it more convenient.

[aldanor]

@epage An issue or a PR? If you have a particular view on what would be the most convenient option(s) I wouldn't mind contributing.

(e.g. bringing back something along the lines of possible_values_from_str = [...] as probably the most convenient thing, with the name being more explicit so as to be less confusing; or one step back, PossibleValuesFromStr as above).

[epage]

Issue first as I prefer exploring on directions there. Once we have a direction, you are welcome to get a PR going.