Case splitting

Sum types allow for a very nice feature called case splitting. Suppose you have x : Result<Option<T>, E> and the following code fragment:

match x {
}

Then you press the case split hotkey, and IDE fills the cases for x:

match x {
    Ok(res) => todo!(),
    Err(err) => todo!(),
}

Then you place the cursor at res and do case splitting again. The IDE fills cases for res:

match x {
    Ok(Some(val)) => todo!(),
    Ok(None) => todo!(),
    Err(err) => todo!(),
}