Highlight "types differ in mutability" errors if a variable type is not manually declared

[lancelote]

Environment

• IntelliJ Rust plugin version: 0.2.112.2801-193-nightly
• Rust toolchain version: 1.39.0 (4560ea788 2019-11-04) x86_64-apple-darwin
• IDE name and version: CLion 2019.3 (CL-193.5233.103)
• Operating system: macOS 10.15

Problem description

Passing an immutable reference to a function expecting a mutable is not highlighted as an error if the variable type is not explicitly declared.

Steps to reproduce

Standalone example:

use std::collections::HashMap;

fn fib_dyn(n: u64, map: &mut HashMap<u64, u64>) -> u64 {
    match n {
        0 | 1 => 1,
        n => {
            if map.contains_key(&n) {
                *map.get(&n).unwrap()
            } else {
                let val = fib_dyn(n - 1, map) + fib_dyn(n - 2, map);
                map.insert(n, val);
                val
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn fib_5() {
        let mut map = HashMap::new();
        assert_eq!(fib_dyn(5, &map), 8);
    }
}

Build fails with

error[E0308]: mismatched types
  --> src/chapter1/dynamic_fibonacci.rs:25:31
   |
25 |         assert_eq!(fib_dyn(5, &map), 8);
   |                               ^^^^ types differ in mutability
   |
   = note: expected type `&mut std::collections::HashMap<u64, u64>`
              found type `&std::collections::HashMap<_, _>`

map type is reported as HashMap<?, ?>, no error is highlighted

If I do specify the type