Using rustfmt 1.7.1-stable (eeb90cda 2024-09-04), In the following example:

fn main() { let x: Option<i32> = Some(10); let value = match x { Some(i) => i /* comment */, None => 0 }; println!("{}", value); }

Rustfmt adds an additional comma before the block comment, which causes the following error:

error: expected pattern, found `,` --> src/test.rs:4:36 | 4 | Some(i) => i, /* comment */, | ^ expected pattern error: aborting due to 1 previous error