Semicolon insertion breaks on complex function declaration

Given this code,

```rust
fn difference(counts: &HashMap<(char, char), u64>, last: char) -> u64 {
    // ...
}
```

try to turn the function into a closure. You'll get:

```rust
let difference = (counts: &HashMap<(char, char);, u64>, last: char) -> u64 {
```

Probably unactionable given the incorrect code, though.