Formatting introduces syntax error in a rare edge case

[Bubbler-4]

Small example:

fn main() {
    let v = vec![1, 2, 3];
    let a = v.into_iter().fold(0, |w, x|
        match x { _ => x } | w
    );
}

After one round-trip (syn::parse_file followed by prettyplease::unparse), the code becomes:

fn main() {
    let v = vec![1, 2, 3];
    let a = v
        .into_iter()
        .fold(
            0,
            |w, x| {
                match x {
                    _ => x,
                } | w
            },
        );
}

Note the extra {} around the body of the |w, x| closure. This change makes rustc complain:

error: expected one of `:`, `@`, or `|`, found `}`
  --> src/bin/temp.rs:11:13
   |
10 |                 } | w
   |                      - expected one of `:`, `@`, or `|`
11 |             },
   |             ^ unexpected token
   |
help: parentheses are required to parse this as an expression
   |
8  ~                 (match x {
9  |                     _ => x,
10 ~                 }) | w
   |

[dtolnay]

Good catch. Fixed in prettyplease 0.2.8.