error[internal]: left behind trailing whitespace, preventing all formatting

[Paladynee]

fn rustfmt_internal_error() {
    if true 
    // comment
        || false
    {}
}

error[internal]: left behind trailing whitespace
   --> \\?\C:\Users\eurydice\Desktop\folders\osumapchecker\src\test.rs:108:108:12
    |
108 |     if true
    |            ^
    |

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

There must be a space after true, and the comment needs to be on a newline.

I discovered this while writing the safety document on an unsafe function called on || control flow:

fn r#match(&mut self, expected: u8) -> bool {
    if self.is_at_end() 
        // Safety: control flow of the `||` operator guarantees that we are not at the end
        || unsafe { *self.source.get_unchecked(self.index) } != expected
    {
        false
    } else {
        self.index += 1;
        true
    }
}

so it is pretty elementary.

[ytmimi]

rustfmt doesn't handle comments between binary operators well, and won't format binary expression that contain comments (See #3591). The left behind trailing whitespace message you're seeing means there's trailing whitespace in the source code that rustfmt can't remove.