Formatter takes two runs to fully format comment after match arm

Input

fn main() {
    match 1 {
        _ => {},
        // hello!
    }
}

Output

fn main() {
    match 1 {
        _ => {}
        // hello!
    }
}

Expected output

fn main() {
    match 1 {
        _ => {} // hello!
    }
}

You get the expected output if you run it a second time. This means that the formatter needs multiple runs to fully finish formatting the code. That does not seem right. I want to be able to trust the formatter in that it will do it all in one run so that I never get into the habit of running it twice each time just to be 100% sure. Therefore I report this as a bug.

Meta

• rustfmt version: rustfmt 1.4.30-stable (8c6769d 2021-01-18)
• From where did you install rustfmt?: rustup

Start by reproducing the supplied Rust match-arm example with the listed rustfmt version, then trace the formatter's handling of comments after match arms. Done means one formatting run produces the expected output and a regression test covers the example.