use crate::store_impl::packed; impl AsRef<[u8]> for packed::Buffer {    fn as_ref(&self) -> &[u8] {        &self.data.as_ref()[self.offset..]    }} impl AsRef<[u8]> for packed::Backing {    fn as_ref(&self) -> &[u8] {        match self {            packed::Backing::InMemory(data) => data,            packed::Backing::Mapped(map) => map,        }    }} ///pub mod open {    use std::path::PathBuf;     use memmap2::Mmap;     use crate::store_impl::packed;     /// Initialization    impl packed::Buffer {        /// Open the file at `path` and map it into memory if the file size is larger than `use_memory_map_if_larger_than_bytes`.        ///        /// In order to allow fast lookups and optimizations, the contents of the packed refs must be sorted.        /// If that's not the case, they will be sorted on the fly with the data being written into a memory buffer.        pub fn open(path: impl Into<PathBuf>, use_memory_map_if_larger_than_bytes: u64) -> Result<Self, Error> {            let path = path.into();            let (backing, offset) = {                let backing = if std::fs::metadata(&path)?.len() <= use_memory_map_if_larger_than_bytes {                    packed::Backing::InMemory(std::fs::read(&path)?)                } else {                    packed::Backing::Mapped(                        // SAFETY: we have to take the risk of somebody changing the file underneath. Git never writes into the same file.                        #[allow(unsafe_code)]                        unsafe {                            Mmap::map(&std::fs::File::open(&path)?)?                        },                    )                };                 let (offset, sorted) = {                    let data = backing.as_ref();                    if *data.first().unwrap_or(&b' ') == b'#' {                        let (records, header) = packed::decode::header::<()>(data).map_err(|_| Error::HeaderParsing)?;                        let offset = records.as_ptr() as usize - data.as_ptr() as usize;                        (offset, header.sorted)                    } else {                        (0, false)                    }                };                 if !sorted {                    // this implementation is likely slower than what git does, but it's less code, too.                    let mut entries = packed::Iter::new(&backing.as_ref()[offset..])?.collect::<Result<Vec<_>, _>>()?;                    entries.sort_by_key(|e| e.name.as_bstr());                    let mut serialized = Vec::<u8>::new();                    for entry in entries {                        serialized.extend_from_slice(entry.target);                        serialized.push(b' ');                        serialized.extend_from_slice(entry.name.as_bstr());                        serialized.push(b'\n');                        if let Some(object) = entry.object {                            serialized.push(b'^');                            serialized.extend_from_slice(object);                            serialized.push(b'\n');                        }                    }                    (Backing::InMemory(serialized), 0)                } else {                    (backing, offset)                }            };            Ok(packed::Buffer {                offset,                data: backing,                path,            })        }    }     mod error {        use crate::packed;         /// The error returned by [`open()`][super::packed::Buffer::open()].        #[derive(Debug, thiserror::Error)]        #[allow(missing_docs)]        pub enum Error {            #[error("The packed-refs file did not have a header or wasn't sorted and could not be iterated")]            Iter(#[from] packed::iter::Error),            #[error("The header could not be parsed, even though first line started with '#'")]            HeaderParsing,            #[error("The buffer could not be opened or read")]            Io(#[from] std::io::Error),        }    }    pub use error::Error;     use crate::packed::Backing;}