`error[internal]: left behind trailing whitespace` in file with long string line

[VojtaStanek]

In my own code I have ran into following bug.

Reproduction:

impl Foo {
    fn execute() -> () {
        func()
            .cond_where(
                {
                    let _ = ();
                
                    ()
                }
            )
            .map({
                func(
                    "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
                );
            });
    }
}

note there are whitespaces left on line 7.

Rustfmt exits with:

error[internal]: left behind trailing whitespace
 --> /playground/src/main.rs:7:7:1
  |
7 |                 
  | ^^^^^^^^^^^^^^^^
  |

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

Tested with 1.8.0-stable (2025-11-07 ed61e7d7e2) on rust playground.

Playground link: https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=ad4bcc62a9593ffd9998f1977aac0c83