range method not found in _AnonymousValueParser(usize)

[pkolaczk]

Please complete the following tasks

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

Rust Version

rustc 1.64.0 (a55dd71d5 2022-09-19)

Clap Version

4.0.0-rc2

Minimal reproducible code

#[derive(clap::Parser, Debug, Default)]
#[command(disable_version_flag = true)]
struct MyApp {
    #[arg(value_parser = clap::value_parser!(usize).range(1..))]
    pub foo: Option<usize>
}

fn main() {
}

Steps to reproduce the bug with the above code

cargo check

Actual Behaviour

error[E0599]: no method named `range` found for struct `_AnonymousValueParser` in the current scope
 --> src/test.rs:4:53
  |
4 |     #[arg(value_parser = clap::value_parser!(usize).range(1..))]
  |                                                     ^^^^^ method not found in `_AnonymousValueParser`

Expected Behaviour

Should compile fine

Additional Context

If I replace the usize type in value_parser! with u64, then it compiles fine, however I'm not sure if this is correct, because that's a different type than the type used in the field.

Debug Output

No response

[anshulrgoyal]

@pkolaczk clap::value_parser! returns RangedU64ValueParser for u64 therefore range function is available, but usize returns _AnonymousValueParser hence the compilation error.

If there is an implementation for usize then it will work.

impl ValueParserFactory for usize {
    type Parser = RangedU64ValueParser<usize>;
    fn value_parser() -> Self::Parser {
        RangedU64ValueParser::<usize>::new()
    }
}

[pkolaczk]

Such implementation can be added only by clap. I cannot add it by myself, because of foreign-crate restriction.

[anshulrgoyal]

@pkolaczk I was suggesting adding the implementation in clap only. I don't know the reason it is not already present.

[epage]

I wish I could more generically implement this...

clap does use try_into to go from u64 to T (usize in this case). My main question is if converting from u64 to usize is "good enough" or if we should have usize-native value parser.

[epage]

btw #3895 and #4034 are related PRs