Can't specify multiple vector elements using env vars

[johananl]

Please complete the following tasks

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

Rust Version

rustc 1.70.0 (90c541806 2023-05-31)

Clap Version

4.3.11

Minimal reproducible code

use clap::Parser;

#[derive(Parser)]
struct Cli {
    #[arg(short, env)]
    foo: Vec<i32>,
}

fn main() {
    let cli = Cli::parse();
    println!("{:?}", cli.foo);
}

Steps to reproduce the bug with the above code

cargo run -- -f 1 -f 2

Output: [1, 2]

FOO=1 cargo run

Output: [1]

FOO="1 2" cargo run

Output: error: invalid value '1 2' for '-f <FOO>': invalid digit found in string

FOO="1,2" cargo run

Output: error: invalid value '1,2' for '-f <FOO>': invalid digit found in string

FOO="1, 2" cargo run

Output: error: invalid value '1, 2' for '-f <FOO>': invalid digit found in string

FOO="[1, 2]" cargo run

Output: error: invalid value '[1, 2]' for '-f <FOO>': invalid digit found in string

Actual Behaviour

When using env on a vector field, multiple values can be passed by specifying the argument multiple times on the CLI, however the same can't be done when using env vars (because the OS doesn't support specifying the same env var twice).

Expected Behaviour

I think it makes sense to have consistency between CLI args and env vars when using the env option even when the field is a vector. If that's not possible, the user should probably know about the expected behavior or limitation.

Potential solutions I can think of:

1. Parse env var values when using env on vector fields and split the string into vector elements. Something like FOO="[1, 2]" can likely be used.
2. Document the fact that when using env on vector fields, only one value can be specified.
3. Disallow env on vector fields.

Additional Context

No response

Debug Output

No response

[epage]

You can use value_delimiter to split the env variable though that also means that CLI values will also be split

[johananl]

Thanks @epage. I wonder if there is a way to reconcile the behavior of CLI args and env vars for vector values, as well as whether it would make sense to do so. The problem of course isn't in clap itself, it's the fact that at the OS level it's meaningless to specify the same env var twice.