use std::borrow::Cow; use nom::{    branch::alt,    bytes::{complete::is_not, complete::tag},    combinator::{all_consuming, opt},    error::context,    error::{ContextError, ParseError},    multi::many0,    IResult,};use smallvec::SmallVec; use crate::{    immutable::{parse, parse::NL, Commit},    BStr, ByteSlice,}; pub fn message<'a, E: ParseError<&'a [u8]> + ContextError<&'a [u8]>>(i: &'a [u8]) -> IResult<&'a [u8], &'a BStr, E> {    if i.is_empty() {        // newline + [message]        return Err(nom::Err::Error(E::add_context(            i,            "newline + <message>",            E::from_error_kind(i, nom::error::ErrorKind::Eof),        )));    }    let (i, _) = context("a newline separates headers from the message", tag(NL))(i)?;    Ok((&[], i.as_bstr()))} pub fn commit<'a, E: ParseError<&'a [u8]> + ContextError<&'a [u8]>>(i: &'a [u8]) -> IResult<&'a [u8], Commit<'_>, E> {    let (i, tree) = context("tree <40 lowercase hex char>", |i| {        parse::header_field(i, b"tree", parse::hex_hash)    })(i)?;    let (i, parents) = context(        "zero or more 'parent <40 lowercase hex char>'",        many0(|i| parse::header_field(i, b"parent", parse::hex_hash)),    )(i)?;    let (i, author) = context("author <signature>", |i| {        parse::header_field(i, b"author", parse::signature)    })(i)?;    let (i, committer) = context("committer <signature>", |i| {        parse::header_field(i, b"committer", parse::signature)    })(i)?;    let (i, encoding) = context(        "encoding <encoding>",        opt(|i| parse::header_field(i, b"encoding", is_not(NL))),    )(i)?;    let (i, extra_headers) = context(        "<field> <single-line|multi-line>",        many0(alt((            |i| parse::any_header_field_multi_line(i).map(|(i, (k, o))| (i, (k.as_bstr(), Cow::Owned(o)))),            |i| {                parse::any_header_field(i, is_not(NL)).map(|(i, (k, o))| (i, (k.as_bstr(), Cow::Borrowed(o.as_bstr()))))            },        ))),    )(i)?;    let (i, message) = all_consuming(message)(i)?;     Ok((        i,        Commit {            tree,            parents: SmallVec::from(parents),            author,            committer,            encoding: encoding.map(ByteSlice::as_bstr),            message,            extra_headers,        },    ))}