"left behind trailing whitespace" in long patterns

Code like this:

fn put_telescope_synctocoordinates(
    PutTelescopeSynctocoordinatesPathParams {
                    
                        device_number,
                    
                }: PutTelescopeSynctocoordinatesPathParams,
) {
}

triggers "left behind trailing whitespace".

I suppose it's because rustfmt tries to put entire param - both pattern and type - on the same line, fails in doing so as that exceeds the max width, and gives up. Instead, it should probably fallback to something like

fn put_telescope_synctocoordinates(
    PutTelescopeSynctocoordinatesPathParams {
      device_number,
    }: PutTelescopeSynctocoordinatesPathParams,
) {
}

Start by reproducing the reported formatting with the long Rust function parameter pattern and the repository's maximum-width settings. Trace the formatter path for long destructuring patterns, add a regression test for the example, and verify that formatting produces the intended indentation without trailing whitespace.