"error[internal]: left behind trailing whitespace" with long macro inside closure

[kryptan]

Code:

fn main() {
    true.then(|| { 
        println! { "{}",
                                                                                                    0
        };
    });
}

Error:

error[internal]: left behind trailing whitespace
 --> /playground/src/main.rs:2:2:19
  |
2 |     true.then(|| { 
  |                   ^
  |

warning: rustfmt has failed to format. See previous 1 errors.

Playground link

There are a lot of issues with "left behind trailing whitespace" but I couldn't find any sufficiently similar to this one.

---

Tested on:
1.89 stable
1.91.0-nightly (2025-09-11)