comment in const generic default causes line duplication

[oli-obk]

type Foo = impl Send;
struct Struct<
    const C: usize = {
        let _: Foo = ();
        //~^ ERROR: mismatched types
        0
    },
>;

gets formatted to

type Foo = impl Send;
struct Struct<
    const C: usize = {
        let _: Foo = ();
        //~^ ERROR: mismatched types
        0
    },
>
;
//~^ ERROR: mismatched types
0
},
>;

Without the comment, the formatting doesn't change.