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

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)

Reproduce the example from the issue in the Rust Playground with rustfmt on the listed stable and nightly versions. Start by narrowing the failure around the long macro inside the closure and the reported trailing whitespace location. Done means the sample formats without the internal error while preserving valid Rust formatting.