If rustfmt decides to indent after the => in a match (because the line ran too long) it also adds a {} and an extra line (for the }) even if the contents of the match arm fit onto a single line.

In the example at rust-bitcoin/rust-bitcoin#959 (comment) rustfmt generated

Error::SerializationError => { "can not serialize the spending transaction in Transaction::verify()" }, 

when it arguably could have (optionally) just stuck with

Error::SerializationError => "can not serialize the spending transaction in Transaction::verify()", 

unlike ifs (and the C world) you can't get screwed by the lack of {} here - if you end up with two statements back-to-back its a compile error rather than incorrect logic.

Thanks!