use std::{    borrow::Borrow,    convert::TryInto,    fmt,    hash::{Hash, Hasher},    ops::Deref,}; use crate::{borrowed::oid, Kind, SIZE_OF_SHA1_DIGEST}; /// An owned hash identifying objects, most commonly Sha1#[derive(PartialEq, Eq, Ord, PartialOrd, Clone, Copy)]#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]pub enum ObjectId {    /// A SHA 1 hash digest    Sha1([u8; SIZE_OF_SHA1_DIGEST]),} // False positive: https://github.com/rust-lang/rust-clippy/issues/2627// ingoring some fields while hashing is perfectly valid and just leads to// increased HashCollisions. One Sha1 being a prefix of another Sha256 is// extremly unlikely to begin with so it doesn't matter.// This implementation matches the `Hash` implementation for `oid`// and allows the usage of custom Hashers that only copy a truncated ShaHash#[allow(clippy::derive_hash_xor_eq)]impl Hash for ObjectId {    fn hash<H: Hasher>(&self, state: &mut H) {        state.write(self.as_slice())    }} #[allow(missing_docs)]pub mod decode {    use std::str::FromStr;     use crate::object_id::ObjectId;     /// An error returned by [`ObjectId::from_hex()`][crate::ObjectId::from_hex()]    #[derive(Debug, thiserror::Error)]    #[allow(missing_docs)]    pub enum Error {        #[error("A hash sized {0} hexadecimal characters is invalid")]        InvalidHexEncodingLength(usize),        #[error("Invalid character {c} at position {index}")]        Invalid { c: char, index: usize },    }     /// Hash decoding    impl ObjectId {        /// Create an instance from a `buffer` of 40 bytes encoded with hexadecimal notation.        ///        /// Such a buffer can be obtained using [`oid::write_hex_to(buffer)`][super::oid::write_hex_to()]        pub fn from_hex(buffer: &[u8]) -> Result<ObjectId, Error> {            use hex::FromHex;            match buffer.len() {                40 => Ok(ObjectId::Sha1(<[u8; 20]>::from_hex(buffer).map_err(                    |err| match err {                        hex::FromHexError::InvalidHexCharacter { c, index } => Error::Invalid { c, index },                        hex::FromHexError::OddLength | hex::FromHexError::InvalidStringLength => {                            unreachable!("BUG: This is already checked")                        }                    },                )?)),                len => Err(Error::InvalidHexEncodingLength(len)),            }        }    }     impl FromStr for ObjectId {        type Err = Error;         fn from_str(s: &str) -> Result<Self, Self::Err> {            Self::from_hex(s.as_bytes())        }    }} /// Access and conversionimpl ObjectId {    /// Returns the kind of hash used in this `Id`    #[inline]    pub fn kind(&self) -> crate::Kind {        match self {            ObjectId::Sha1(_) => crate::Kind::Sha1,        }    }    /// Return the raw byte slice representing this hash    #[inline]    pub fn as_slice(&self) -> &[u8] {        match self {            Self::Sha1(b) => b.as_ref(),        }    }    /// Return the raw mutable byte slice representing this hash    #[inline]    pub fn as_mut_slice(&mut self) -> &mut [u8] {        match self {            Self::Sha1(b) => b.as_mut(),        }    }     /// The hash of an empty tree    #[inline]    pub const fn empty_tree(hash: Kind) -> ObjectId {        match hash {            Kind::Sha1 => {                ObjectId::Sha1(*b"\x4b\x82\x5d\xc6\x42\xcb\x6e\xb9\xa0\x60\xe5\x4b\xf8\xd6\x92\x88\xfb\xee\x49\x04")            }        }    }     /// Returns true if this hash consists of all null bytes    #[inline]    pub fn is_null(&self) -> bool {        match self {            ObjectId::Sha1(digest) => &digest[..] == oid::null_sha1().as_bytes(),        }    }     /// Returns an Digest representing a hash with whose memory is zeroed.    #[inline]    pub const fn null(kind: crate::Kind) -> ObjectId {        match kind {            crate::Kind::Sha1 => Self::null_sha1(),        }    }} /// Sha1 hash specific methodsimpl ObjectId {    /// Instantiate an Digest from 20 bytes of a Sha1 digest.    #[inline]    fn new_sha1(id: [u8; SIZE_OF_SHA1_DIGEST]) -> Self {        ObjectId::Sha1(id)    }     /// Instantiate an Digest from a slice 20 borrowed bytes of a Sha1 digest.    ///    /// Panics of the slice doesn't have a length of 20.    #[inline]    pub(crate) fn from_20_bytes(b: &[u8]) -> ObjectId {        let mut id = [0; SIZE_OF_SHA1_DIGEST];        id.copy_from_slice(b);        ObjectId::Sha1(id)    }     /// Returns an Digest representing a Sha1 with whose memory is zeroed.    #[inline]    pub(crate) const fn null_sha1() -> ObjectId {        ObjectId::Sha1([0u8; 20])    }} impl std::fmt::Debug for ObjectId {    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {        match self {            ObjectId::Sha1(_hash) => f.write_str("Sha1(")?,        }        for b in self.as_bytes() {            write!(f, "{:02x}", b)?;        }        f.write_str(")")    }} impl From<[u8; SIZE_OF_SHA1_DIGEST]> for ObjectId {    fn from(v: [u8; 20]) -> Self {        Self::new_sha1(v)    }} impl From<&[u8]> for ObjectId {    fn from(v: &[u8]) -> Self {        match v.len() {            20 => Self::Sha1(v.try_into().expect("prior length validation")),            other => panic!("BUG: unsupported hash len: {}", other),        }    }} impl From<&crate::oid> for ObjectId {    fn from(v: &oid) -> Self {        match v.kind() {            crate::Kind::Sha1 => ObjectId::from_20_bytes(v.as_bytes()),        }    }} impl Deref for ObjectId {    type Target = oid;     fn deref(&self) -> &Self::Target {        self.as_ref()    }} impl AsRef<crate::oid> for ObjectId {    fn as_ref(&self) -> &oid {        oid::from_bytes_unchecked(self.as_slice())    }} impl Borrow<crate::oid> for ObjectId {    fn borrow(&self) -> &oid {        self.as_ref()    }} impl fmt::Display for ObjectId {    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {        write!(f, "{}", self.to_hex())    }} impl PartialEq<&crate::oid> for ObjectId {    fn eq(&self, other: &&oid) -> bool {        self.as_ref() == *other    }}