error[internal]: left behind trailing whitespace

this code:

mod phase {
    pub trait Phase {
        const RUN: &'static str;
        const FAIL: &'static str;

        fn to_style(&self, template: &str);
    }

    pub struct Updating {}

    impl Phase for Updating {
        const RUN: &'static str = "";
        const FAIL: &'static str = "";
            
        #[rustfmt::skip]
        fn to_style(&self, template: &str) {}
    }
}

fn main() {}

produces this error:

error[internal]: left behind trailing whitespace
  --> /tmp/arif/src/main.rs:14:14:1
   |
14 |             
   | ^^^^^^^^^^^^
   |

Start by running the Rust code reproducer from the issue and inspect how rustfmt handles the #[rustfmt::skip] function and the whitespace in /tmp/arif/src/main.rs. Trace the path that reports “left behind trailing whitespace”; done means the reproducer no longer produces this internal error while preserving the intended formatting behavior.