Support for adding a validator on a #[derive(Args)] struct

[nipunn1313]

Please complete the following tasks

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

Clap Version

3.1.3

Describe your use case

Given something like this (toy example)

#[derive(clap::Args)]
struct NameSelector {
    /// One or more names
    names: Vec<String>,
}

It might be nice to be able to achieve something similar to the Arg validator , but for the whole struct.

May be particularly useful if NameSelector grows more complex and/or reused in multiple CLI commands.

Describe the solution you'd like

// proposed idea

#[derive(clap::Args)]
#[clap(validator(name_validator))]
struct NameSelector {
    /// One or more names
    names: Vec<String>,
}

fn name_validator(v: &NameSelector) -> Result<(), String> {
    if v.names.contains("Hitler") {
        return Err("We don't like Hitler");
    }
    Ok(())
}

Alternatives, if applicable

Alternate interface could be a trait that you impl on NameSelector - but that doesn't seem in the spirit of the existing validator implementation.

Additional Context

No response

[epage]

We are looking at generalizing our validation logic so that its both optional and so users can provide their own. We are tracking this work in #3008 though it will be working at the builder level rather than at the derive level.

[nipunn1313]

Cool. Thanks for the explanation. #3008 sounds challenging, but great. Looking forward to it.