use crate::{ObjectId, SIZE_OF_SHA1_DIGEST};use std::{convert::TryInto, fmt}; /// A borrowed reference to a hash identifying objects.////// # Future Proofing////// In case we wish to support multiple hashes with the same length we cannot discriminate/// using the slice length anymore. To make that work, we will use the high bits of the/// internal `bytes` slice length (a fat pointer, pointing to data and its length in bytes)/// to encode additinoal information. Before accessing or returning the bytes, a new adjusted/// slice will be constructed, while the high bits will be used to help resolving the/// hash `[`kind()`][oid::kind()]`./// We expect to have quite a few bits available for such 'conflict resolution' as most hashes aren't longer/// than 64 bytes.#[derive(PartialEq, Eq, Hash, Ord, PartialOrd)]#[repr(transparent)]#[allow(non_camel_case_types)]#[cfg_attr(feature = "serde1", derive(serde::Serialize))]pub struct oid {    bytes: [u8],} impl std::fmt::Debug for oid {    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {        match self.kind() {            crate::Kind::Sha1 => f.write_str("Sha1(")?,        }        for b in self.as_bytes() {            write!(f, "{:02x}", b)?;        }        f.write_str(")")    }} use quick_error::quick_error; quick_error! {    #[derive(Debug)]    pub enum Error {        InvalidByteSliceLength(length: usize) {            display("Cannot instantiate git hash from a digest of length {}", length)        }    }} /// Conversionimpl oid {    /// Try to create a shared object id from a slice of bytes representing a hash `digest`    pub fn try_from(digest: &[u8]) -> Result<&Self, Error> {        match digest.len() {            20 => Ok(                #[allow(unsafe_code)]                unsafe {                    &*(digest as *const [u8] as *const oid)                },            ),            len => Err(Error::InvalidByteSliceLength(len)),        }    }     /// Only from code that statically assures correct sizes using array conversions    fn from(value: &[u8]) -> &Self {        #[allow(unsafe_code)]        unsafe {            &*(value as *const [u8] as *const oid)        }    }} /// Accessimpl oid {    /// The kind of hash used for this Digest    pub fn kind(&self) -> crate::Kind {        match self.bytes.len() {            20 => crate::Kind::Sha1,            _ => unreachable!("creating this instance is checked and fails on unknown lengths"),        }    }     /// The first byte of the hash, commonly used to partition a set of `Id`s    pub fn first_byte(&self) -> u8 {        self.bytes[0]    }     #[inline]    /// Interpret this object id as raw byte slice.    pub fn as_bytes(&self) -> &[u8] {        &self.bytes    }} /// Sha1 specific methodsimpl oid {    /// Returns an array with a hexadecimal encoded version of the Sha1 hash this `Id` represents.    ///    /// **Panics** if this is not a Sha1 hash, as identifiable by [`ObjectId::kind()`].    pub fn to_sha1_hex(&self) -> [u8; SIZE_OF_SHA1_DIGEST * 2] {        let mut buf = [0u8; SIZE_OF_SHA1_DIGEST * 2];        hex::encode_to_slice(&self.bytes, &mut buf).expect("to count correctly");        buf    }     /// Returns the bytes making up the Sha1.    ///    /// **Panics** if this is not a Sha1 hash, as identifiable by [`ObjectId::kind()`].    pub fn sha1(&self) -> &[u8; SIZE_OF_SHA1_DIGEST] {        self.bytes.try_into().expect("correctly sized slice")    }     /// Returns a Sha1 digest with all bytes being initialized to zero.    pub fn null_sha1() -> &'static Self {        oid::from([0u8; SIZE_OF_SHA1_DIGEST].as_ref())    }} impl AsRef<oid> for &oid {    fn as_ref(&self) -> &oid {        self    }} impl ToOwned for oid {    type Owned = crate::ObjectId;     fn to_owned(&self) -> Self::Owned {        match self.kind() {            crate::Kind::Sha1 => crate::ObjectId::Sha1(self.bytes.try_into().expect("no bug in hash detection")),        }    }} impl<'a> From<&'a [u8; SIZE_OF_SHA1_DIGEST]> for &'a oid {    fn from(v: &'a [u8; SIZE_OF_SHA1_DIGEST]) -> Self {        oid::from(v.as_ref())    }} impl fmt::Display for &oid {    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {        for b in self.as_bytes() {            write!(f, "{:02x}", b)?;        }        Ok(())    }} impl PartialEq<crate::ObjectId> for &oid {    fn eq(&self, other: &ObjectId) -> bool {        *self == other.as_ref()    }} /// Manually created from a version that uses a slice, and we forcefully try to convert it into a borrowed array of the desired size/// Could be improved by fitting this into serde/// Unfortunately the serde::Deserialize derive wouldn't work for borrowed arrays.#[cfg(feature = "serde1")]impl<'de: 'a, 'a> serde::Deserialize<'de> for &'a oid {    fn deserialize<D>(deserializer: D) -> Result<Self, <D as serde::Deserializer<'de>>::Error>    where        D: serde::Deserializer<'de>,    {        struct __Visitor<'de: 'a, 'a> {            marker: std::marker::PhantomData<&'a oid>,            lifetime: std::marker::PhantomData<&'de ()>,        }        impl<'de: 'a, 'a> serde::de::Visitor<'de> for __Visitor<'de, 'a> {            type Value = &'a oid;            fn expecting(&self, __formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {                std::fmt::Formatter::write_str(__formatter, "tuple struct Digest")            }            #[inline]            fn visit_newtype_struct<__E>(self, __e: __E) -> std::result::Result<Self::Value, __E::Error>            where                __E: serde::Deserializer<'de>,            {                let __field0: &'a [u8] = match <&'a [u8] as serde::Deserialize>::deserialize(__e) {                    Ok(__val) => __val,                    Err(__err) => {                        return Err(__err);                    }                };                Ok(oid::try_from(__field0).expect("exactly 20 bytes"))            }            #[inline]            fn visit_seq<__A>(self, mut __seq: __A) -> std::result::Result<Self::Value, __A::Error>            where                __A: serde::de::SeqAccess<'de>,            {                let __field0 = match match serde::de::SeqAccess::next_element::<&'a [u8]>(&mut __seq) {                    Ok(__val) => __val,                    Err(__err) => {                        return Err(__err);                    }                } {                    Some(__value) => __value,                    None => {                        return Err(serde::de::Error::invalid_length(                            0usize,                            &"tuple struct Digest with 1 element",                        ));                    }                };                Ok(oid::try_from(__field0).expect("exactly 20 bytes"))            }        }        serde::Deserializer::deserialize_newtype_struct(            deserializer,            "Digest",            __Visitor {                marker: std::marker::PhantomData::<&'a oid>,                lifetime: std::marker::PhantomData,            },        )    }}