Bad diagnostics span for unmatched angle brackets of generic args

[hkmatsumoto]

Given the following code: Playground link

use std::sync::{Arc, Mutex};

pub struct Foo {
    a: Mutex<usize>,
    b: Arc<Mutex<usize>, // an not-ok line
    c: Arc<Mutex<usize>>, // an ok line
}

The current output is:

error: expected one of `>`, a const expression, lifetime, or type, found `}`
 --> src/lib.rs:7:1
  |
6 |     c: Arc<Mutex<usize>>, // an ok line
  |                          - expected one of `>`, a const expression, lifetime, or type
7 | }
  | ^ unexpected token

Ideally the output should look like:

error: expected one of `>`, a const expression, lifetime, or type, found `}`
 --> src/lib.rs:6:1
  |
5 |     b: Arc<Mutex<usize>, // an not-ok line
  |                         - expected one of `>`, a const expression, lifetime, or type
6 | }
  | ^ unexpected token