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    use std::cmp::Ordering;

    /// The possible kinds of code source.
    #[derive(Debug, Clone, PartialEq, Eq, Hash)]
    pub enum SourceKind {
        /// A git repository.
        Git(GitReference),
        /// A local path.
        Path,
        /// A remote registry.
        Registry,
        /// A sparse registry.
        SparseRegistry,
        /// A local filesystem-based registry.
        LocalRegistry,
        /// A directory-based registry.
        Directory,
    }

    impl SourceKind {
        pub fn protocol(&self) -> Option<&str> {
            match self {
                SourceKind::Path => Some("path"),
                SourceKind::Git(_) => Some("git"),
                SourceKind::Registry => Some("registry"),
                // Sparse registry URL already includes the `sparse+` prefix, see `SourceId::new`
                SourceKind::SparseRegistry => None,
                SourceKind::LocalRegistry => Some("local-registry"),
                SourceKind::Directory => Some("directory"),
            }
        }
    }

    /// Note that this is specifically not derived on `SourceKind` although the
    /// implementation here is very similar to what it might look like if it were
    /// otherwise derived.
    ///
    /// The reason for this is somewhat obtuse. First of all the hash value of
    /// `SourceKind` makes its way into `~/.cargo/registry/index/github.com-XXXX`
    /// which means that changes to the hash means that all Rust users need to
    /// redownload the crates.io index and all their crates. If possible we strive
    /// to not change this to make this redownloading behavior happen as little as
    /// possible. How is this connected to `Ord` you might ask? That's a good
    /// question!
    ///
    /// Since the beginning of time `SourceKind` has had `#[derive(Hash)]`. It for
    /// the longest time *also* derived the `Ord` and `PartialOrd` traits. In #8522,
    /// however, the implementation of `Ord` changed. This handwritten implementation
    /// forgot to sync itself with the originally derived implementation, namely
    /// placing git dependencies as sorted after all other dependencies instead of
    /// first as before.
    ///
    /// This regression in #8522 (Rust 1.47) went unnoticed. When we switched back
    /// to a derived implementation in #9133 (Rust 1.52 beta) we only then ironically
    /// saw an issue (#9334). In #9334 it was observed that stable Rust at the time
    /// (1.51) was sorting git dependencies last, whereas Rust 1.52 beta would sort
    /// git dependencies first. This is because the `PartialOrd` implementation in
    /// 1.51 used #8522, the buggy implementation, which put git deps last. In 1.52
    /// it was (unknowingly) restored to the pre-1.47 behavior with git dependencies
    /// first.
    ///
    /// Because the breakage was only witnessed after the original breakage, this
    /// trait implementation is preserving the "broken" behavior. Put a different way:
    ///
    /// * Rust pre-1.47 sorted git deps first.
    /// * Rust 1.47 to Rust 1.51 sorted git deps last, a breaking change (#8522) that
    ///   was never noticed.
    /// * Rust 1.52 restored the pre-1.47 behavior (#9133, without knowing it did
    ///   so), and breakage was witnessed by actual users due to difference with
    ///   1.51.
    /// * Rust 1.52 (the source as it lives now) was fixed to match the 1.47-1.51
    ///   behavior (#9383), which is now considered intentionally breaking from the
    ///   pre-1.47 behavior.
    ///
    /// Note that this was all discovered when Rust 1.53 was in nightly and 1.52 was
    /// in beta. #9133 was in both beta and nightly at the time of discovery. For
    /// 1.52 #9383 reverted #9133, meaning 1.52 is the same as 1.51. On nightly
    /// (1.53) #9397 was created to fix the regression introduced by #9133 relative
    /// to the current stable (1.51).
    ///
    /// That's all a long winded way of saying "it's weird that git deps hash first
    /// and are sorted last, but it's the way it is right now". The author of this
    /// comment chose to handwrite the `Ord` implementation instead of the `Hash`
    /// implementation, but it's only required that at most one of them is
    /// hand-written because the other can be derived. Perhaps one day in
    /// the future someone can figure out how to remove this behavior.
    impl Ord for SourceKind {
        fn cmp(&self, other: &SourceKind) -> Ordering {
            match (self, other) {
                (SourceKind::Path, SourceKind::Path) => Ordering::Equal,
                (SourceKind::Path, _) => Ordering::Less,
                (_, SourceKind::Path) => Ordering::Greater,

                (SourceKind::Registry, SourceKind::Registry) => Ordering::Equal,
                (SourceKind::Registry, _) => Ordering::Less,
                (_, SourceKind::Registry) => Ordering::Greater,

                (SourceKind::SparseRegistry, SourceKind::SparseRegistry) => Ordering::Equal,
                (SourceKind::SparseRegistry, _) => Ordering::Less,
                (_, SourceKind::SparseRegistry) => Ordering::Greater,

                (SourceKind::LocalRegistry, SourceKind::LocalRegistry) => Ordering::Equal,
                (SourceKind::LocalRegistry, _) => Ordering::Less,
                (_, SourceKind::LocalRegistry) => Ordering::Greater,

                (SourceKind::Directory, SourceKind::Directory) => Ordering::Equal,
                (SourceKind::Directory, _) => Ordering::Less,
                (_, SourceKind::Directory) => Ordering::Greater,

                (SourceKind::Git(a), SourceKind::Git(b)) => a.cmp(b),
            }
        }
    }

    /// Forwards to `Ord`
    impl PartialOrd for SourceKind {
        fn partial_cmp(&self, other: &SourceKind) -> Option<Ordering> {
            Some(self.cmp(other))
        }
    }

    /// Information to find a specific commit in a Git repository.
    #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
    pub enum GitReference {
        /// From a tag.
        Tag(String),
        /// From a branch.
        Branch(String),
        /// From a specific revision. Can be a commit hash (either short or full),
        /// or a named reference like `refs/pull/493/head`.
        Rev(String),
        /// The default branch of the repository, the reference named `HEAD`.
        DefaultBranch,
    }

    impl GitReference {
        pub fn from_query(
            query_pairs: impl Iterator<Item = (impl AsRef<str>, impl AsRef<str>)>,
        ) -> Self {
            let mut reference = GitReference::DefaultBranch;
            for (k, v) in query_pairs {
                let v = v.as_ref();
                match k.as_ref() {
                    // Map older 'ref' to branch.
                    "branch" | "ref" => reference = GitReference::Branch(v.to_owned()),

                    "rev" => reference = GitReference::Rev(v.to_owned()),
                    "tag" => reference = GitReference::Tag(v.to_owned()),
                    _ => {}
                }
            }
            reference
        }

        /// Returns a `Display`able view of this git reference, or None if using
        /// the head of the default branch
        pub fn pretty_ref(&self, url_encoded: bool) -> Option<PrettyRef<'_>> {
            match self {
                GitReference::DefaultBranch => None,
                _ => Some(PrettyRef {
                    inner: self,
                    url_encoded,
                }),
            }
        }
    }

    /// A git reference that can be `Display`ed
    pub struct PrettyRef<'a> {
        inner: &'a GitReference,
        url_encoded: bool,
    }

    impl<'a> std::fmt::Display for PrettyRef<'a> {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            let value: &str;
            match self.inner {
                GitReference::Branch(s) => {
                    write!(f, "branch=")?;
                    value = s;
                }
                GitReference::Tag(s) => {
                    write!(f, "tag=")?;
                    value = s;
                }
                GitReference::Rev(s) => {
                    write!(f, "rev=")?;
                    value = s;
                }
                GitReference::DefaultBranch => unreachable!(),
            }
            if self.url_encoded {
                for value in url::form_urlencoded::byte_serialize(value.as_bytes()) {
                    write!(f, "{value}")?;
                }
            } else {
                write!(f, "{value}")?;
            }
            Ok(())
        }
    }