Very cool. TBH, Rust's match arm delimiter story is a bit weird. Sometimes you need to put a ",", sometimes you don't. And macro rules macros have ";" instead of ",".
> Sometimes you need to put a ",", sometimes you don't
The rule is pretty simple: if you have curly braces you don't need a comma (and rustfmt will drop it), if you don't have curly braces you need a comma.