pub enum InnerStream {
    Root,
    Transaction { v: Vec<u32>, parent: Box<InnerStream> },
}

impl InnerStream {
    pub fn rollback(self) -> InnerStream {
        match self {
            InnerStream::Transaction { v: _v, parent } => {
                match *parent {
                    InnerStream::Root => InnerStream::Root,
                    InnerStream::Transaction { v, parent: parent_parent } =>
                        InnerStream::Transaction { v, parent: parent_parent }
                }
            },
            InnerStream::Root { .. } => panic!("Cannot rollback root stream."),
        }
    }
}

error[E0382]: use of collaterally moved value: `(parent as InnerStream::Transaction).parent`
  --> src/main.rs:12:59
   |
12 |                     InnerStream::Transaction { v, parent: parent_parent } =>
   |                                                -          ^^^^^^^^^^^^^ value used here after move
   |                                                |
   |                                                value moved here
   |
   = note: move occurs because the value has type `std::vec::Vec<u32>`, which does not implement the `Copy` trait

error: aborting due to previous error