[3.1] Derive parsing FromStr args into a vector regression from 3.0

[ufoscout]

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

Rust Version

rustc 1.59.0 (9d1b2106e 2022-02-23)

Clap Version

3.1.2

Minimal reproducible code

use clap::Parser;
use std::str::FromStr;

#[derive(Debug, PartialEq)]
pub enum MyType {
    A,
    B,
}

impl FromStr for MyType {
    type Err = String;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s.to_lowercase().as_str() {
            "a" => Ok(MyType::A),
            "b" => Ok(MyType::B),
            _ => Err("".to_owned()),
        }
    }
}

#[derive(Parser)]
pub struct Config {
    #[clap(long, default_value = "a,b,a", value_delimiter = ',')]
    pub values: Vec<MyType>,
}

// These two tests pass in 3.0 but fail in 3.1

#[test]
fn shuold_build_a_vec_of_types() {
    let args: Vec<std::ffi::OsString> = vec!["".into()];
    let config = Config::parse_from(args);
    assert_eq!(vec![MyType::A, MyType::B, MyType::A], config.values);
}

#[test]
fn shuold_build_a_vec_of_types_from_default_value() {
    let args: Vec<std::ffi::OsString> = vec!["".into(), "--values=a,b".into()];
    let config = Config::parse_from(args);
    assert_eq!(vec![MyType::A, MyType::B], config.values);
}

Steps to reproduce the bug with the above code

Executes the two tests provided in the minimal reproducible code; they both fail in 3.1 but pass in 3.0

Actual Behaviour

A validation error is thrown when the configuration is built.

Expected Behaviour

The configuration is valid in 3.0 and should be valid in 3.1 too.

Additional Context

No response

Debug Output

No response

[epage]

The error message

thread 'main' panicked at 'Argument values's default_value=a,b,a failed validation: ', /home/epage/src/personal/clap/src/build/debug_asserts.rs:690:21
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

This regression was introduced in #3423 because delimited values were not taken into account.

To fix this, we need to take delimited values into account and add tests for this case (ideally at the builder level).

[epage]

v3.1.3 is now released with a fix for this.