How to use Option<Args> with #[command(flatten)]?

[LazyMechanic]

How can I get this behavior:

use clap::{Args, Parser};

#[test]
fn test() {
    #[derive(Parser, Debug, Eq, PartialEq)]
    pub struct CliArgs {
        #[command(flatten)]
        pub opt_args: Option<OptArgs>,
    }

    #[derive(Args, Debug, Eq, PartialEq)]
    pub struct OptArgs {
        pub arg1: i32,
        pub arg2: i32,
    }

    let result = CliArgs::try_parse_from([""]);
    assert!(result.is_ok());
    assert_eq!(result.unwrap(), CliArgs { opt_args: None });

    let result = CliArgs::try_parse_from(["--arg1=1"]);
    assert!(result.is_err());

    let result = CliArgs::try_parse_from(["--arg2=1"]);
    assert!(result.is_err());

    let result = CliArgs::try_parse_from(["--arg1=1", "--arg2=2"]);
    assert!(result.is_ok());
    assert_eq!(result.unwrap(), CliArgs { opt_args: Some(OptArgs { arg1: 1, arg2: 2 }) });
}

[epage]

To double check my understanding, what you are wanting is

• OptArgs is optional
• If OptArgs is present, every arg in the group must be present

Is that correct?

[LazyMechanic]

Yes. Only if both parameters (arg1 and arg2) are present, opt_args should be instantiated (Some(...)). If only one of the parameters (arg1 or arg2) is present, an error should occur.

# ok
> my_app

# ok
> my_app --arg1=... --arg2=...

# not ok
> my_app --arg1=...

Real project is more complex and flattening is multilevel (option params in option params in ...), but I need understand how to make basis.

Now I use 2 different types: CliArgs that contains all params on one level and Config that is complex structure with multiple levels of nested structs and manually convert CliArgs -> Config. I want to use the only one type.

[epage]

We don't have a built-in concept of "this entire ArgGroup is required". For now, you could specify that each argument requires the other arguments. You'll also need to set required = true because OptArgs doesn't know its being used in this way.