Syntax error in patterns should elide missing field errors

[estebank]

The following code

struct S {
    a: usize,
    b: usize,
}

fn main() {
    let s = S { a: 4, b: 2 };
    let S {a , ref b: _ } = s;
}

produces the following error:

error: expected `,`
 --> src/main.rs:8:20
  |
8 |     let S {a , ref b: _ } = s;
  |                    ^

error[E0027]: pattern does not mention fields `a`, `b`
 --> src/main.rs:8:9
  |
8 |     let S {a , ref b: _ } = s;
  |         ^^^^^^^^^^^^^^^^^ missing fields `a`, `b`

It shouldn't complain about the missing fields.