multiple args not working with clap derive on Vec<Foo> type

[tdudz]

Please complete the following tasks

• I have searched the discussions
• I have searched the existing issues

Rust Version

1.57.0

Clap Version

3.0.6

Minimal reproducible code

#[derive(Parser)]
struct Args {
    #[clap(long, short)]
    foo: Foo,
    #[clap(long, short)]
    bars: Vec<Bar>,
}

fn main() {
    let args = Args::parse();
}

Steps to reproduce the bug with the above code

cargo run -f foo1 -b bar1 bar2

Actual Behaviour

error: Found argument 'bar2' which wasn't expected, or isn't valid in this context

Expected Behaviour

it should parse bar1 and bar2 and place them into a Vec<Bar>

Additional Context

No response

Debug Output

No response

[epage]

In clap 3, we changed Vec from multiple to multiple_occurrences. This is called out in the CHANGELOG's breaking changes since structopt. This was planned in #1772.

For reference, we also have #3248 for this.