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    use crate::core::PackageId;
    use crate::sources::registry::CRATES_IO_HTTP_INDEX;
    use crate::sources::{DirectorySource, CRATES_IO_DOMAIN, CRATES_IO_INDEX, CRATES_IO_REGISTRY};
    use crate::sources::{GitSource, PathSource, RegistrySource};
    use crate::util::{config, CanonicalUrl, CargoResult, Config, IntoUrl};
    use log::trace;
    use serde::de;
    use serde::ser;
    use std::cmp::{self, Ordering};
    use std::collections::HashSet;
    use std::fmt::{self, Formatter};
    use std::hash::{self, Hash};
    use std::path::{Path, PathBuf};
    use std::ptr;
    use std::sync::Mutex;
    use url::Url;

    lazy_static::lazy_static! {
        static ref SOURCE_ID_CACHE: Mutex<HashSet<&'static SourceIdInner>> = Default::default();
    }

    /// Unique identifier for a source of packages.
    #[derive(Clone, Copy, Eq, Debug)]
    pub struct SourceId {
        inner: &'static SourceIdInner,
    }

    #[derive(Eq, Clone, Debug)]
    struct SourceIdInner {
        /// The source URL.
        url: Url,
        /// The canonical version of the above url
        canonical_url: CanonicalUrl,
        /// The source kind.
        kind: SourceKind,
        /// For example, the exact Git revision of the specified branch for a Git Source.
        precise: Option<String>,
        /// Name of the registry source for alternative registries
        /// WARNING: this is not always set for alt-registries when the name is
        /// not known.
        name: Option<String>,
        /// Name of the alt registry in the `[registries]` table.
        /// WARNING: this is not always set for alt-registries when the name is
        /// not known.
        alt_registry_key: Option<String>,
    }

    /// The possible kinds of code source. Along with `SourceIdInner`, this fully defines the
    /// source.
    #[derive(Debug, Clone, PartialEq, Eq, Hash)]
    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,
    }

    /// 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.
        Rev(String),
        /// The default branch of the repository, the reference named `HEAD`.
        DefaultBranch,
    }

    impl SourceId {
        /// Creates a `SourceId` object from the kind and URL.
        ///
        /// The canonical url will be calculated, but the precise field will not
        fn new(kind: SourceKind, url: Url, name: Option<&str>) -> CargoResult<SourceId> {
            if kind == SourceKind::SparseRegistry {
                // Sparse URLs are different because they store the kind prefix (sparse+)
                // in the URL. This is because the prefix is necessary to differentiate
                // from regular registries (git-based). The sparse+ prefix is included
                // everywhere, including user-facing locations such as the `config.toml`
                // file that defines the registry, or whenever Cargo displays it to the user.
                assert!(url.as_str().starts_with("sparse+"));
            }
            let source_id = SourceId::wrap(SourceIdInner {
                kind,
                canonical_url: CanonicalUrl::new(&url)?,
                url,
                precise: None,
                name: name.map(|n| n.into()),
                alt_registry_key: None,
            });
            Ok(source_id)
        }

        fn wrap(inner: SourceIdInner) -> SourceId {
            let mut cache = SOURCE_ID_CACHE.lock().unwrap();
            let inner = cache.get(&inner).cloned().unwrap_or_else(|| {
                let inner = Box::leak(Box::new(inner));
                cache.insert(inner);
                inner
            });
            SourceId { inner }
        }

        fn remote_source_kind(url: &Url) -> SourceKind {
            if url.as_str().starts_with("sparse+") {
                SourceKind::SparseRegistry
            } else {
                SourceKind::Registry
            }
        }

        /// Parses a source URL and returns the corresponding ID.
        ///
        /// ## Example
        ///
        /// ```
        /// use cargo::core::SourceId;
        /// SourceId::from_url("git+https://github.com/alexcrichton/\
        ///                     libssh2-static-sys#80e71a3021618eb05\
        ///                     656c58fb7c5ef5f12bc747f");
        /// ```
        pub fn from_url(string: &str) -> CargoResult<SourceId> {
            let mut parts = string.splitn(2, '+');
            let kind = parts.next().unwrap();
            let url = parts
                .next()
                .ok_or_else(|| anyhow::format_err!("invalid source `{}`", string))?;

            match kind {
                "git" => {
                    let mut url = url.into_url()?;
                    let mut reference = GitReference::DefaultBranch;
                    for (k, v) in url.query_pairs() {
                        match &k[..] {
                            // Map older 'ref' to branch.
                            "branch" | "ref" => reference = GitReference::Branch(v.into_owned()),

                            "rev" => reference = GitReference::Rev(v.into_owned()),
                            "tag" => reference = GitReference::Tag(v.into_owned()),
                            _ => {}
                        }
                    }
                    let precise = url.fragment().map(|s| s.to_owned());
                    url.set_fragment(None);
                    url.set_query(None);
                    Ok(SourceId::for_git(&url, reference)?.with_precise(precise))
                }
                "registry" => {
                    let url = url.into_url()?;
                    Ok(SourceId::new(SourceKind::Registry, url, None)?
                        .with_precise(Some("locked".to_string())))
                }
                "sparse" => {
                    let url = string.into_url()?;
                    Ok(SourceId::new(SourceKind::SparseRegistry, url, None)?
                        .with_precise(Some("locked".to_string())))
                }
                "path" => {
                    let url = url.into_url()?;
                    SourceId::new(SourceKind::Path, url, None)
                }
                kind => Err(anyhow::format_err!("unsupported source protocol: {}", kind)),
            }
        }

        /// A view of the `SourceId` that can be `Display`ed as a URL.
        pub fn as_url(&self) -> SourceIdAsUrl<'_> {
            SourceIdAsUrl {
                inner: &*self.inner,
            }
        }

        /// Creates a `SourceId` from a filesystem path.
        ///
        /// `path`: an absolute path.
        pub fn for_path(path: &Path) -> CargoResult<SourceId> {
            let url = path.into_url()?;
            SourceId::new(SourceKind::Path, url, None)
        }

        /// Creates a `SourceId` from a Git reference.
        pub fn for_git(url: &Url, reference: GitReference) -> CargoResult<SourceId> {
            SourceId::new(SourceKind::Git(reference), url.clone(), None)
        }

        /// Creates a SourceId from a remote registry URL when the registry name
        /// cannot be determined, e.g. a user passes `--index` directly from CLI.
        ///
        /// Use [`SourceId::for_alt_registry`] if a name can provided, which
        /// generates better messages for cargo.
        pub fn for_registry(url: &Url) -> CargoResult<SourceId> {
            let kind = Self::remote_source_kind(url);
            SourceId::new(kind, url.to_owned(), None)
        }

        /// Creates a `SourceId` from a remote registry URL with given name.
        pub fn for_alt_registry(url: &Url, name: &str) -> CargoResult<SourceId> {
            let kind = Self::remote_source_kind(url);
            SourceId::new(kind, url.to_owned(), Some(name))
        }

        /// Creates a SourceId from a local registry path.
        pub fn for_local_registry(path: &Path) -> CargoResult<SourceId> {
            let url = path.into_url()?;
            SourceId::new(SourceKind::LocalRegistry, url, None)
        }

        /// Creates a `SourceId` from a directory path.
        pub fn for_directory(path: &Path) -> CargoResult<SourceId> {
            let url = path.into_url()?;
            SourceId::new(SourceKind::Directory, url, None)
        }

        /// Returns the `SourceId` corresponding to the main repository.
        ///
        /// This is the main cargo registry by default, but it can be overridden in
        /// a `.cargo/config.toml`.
        pub fn crates_io(config: &Config) -> CargoResult<SourceId> {
            config.crates_io_source_id(|| {
                config.check_registry_index_not_set()?;
                let url = CRATES_IO_INDEX.into_url().unwrap();
                SourceId::new(SourceKind::Registry, url, Some(CRATES_IO_REGISTRY))
            })
        }

        /// Returns the `SourceId` corresponding to the main repository, using the
        /// sparse HTTP index if allowed.
        pub fn crates_io_maybe_sparse_http(config: &Config) -> CargoResult<SourceId> {
            if Self::crates_io_is_sparse(config)? {
                config.check_registry_index_not_set()?;
                let url = CRATES_IO_HTTP_INDEX.into_url().unwrap();
                SourceId::new(SourceKind::SparseRegistry, url, Some(CRATES_IO_REGISTRY))
            } else {
                Self::crates_io(config)
            }
        }

        /// Returns whether to access crates.io over the sparse protocol.
        pub fn crates_io_is_sparse(config: &Config) -> CargoResult<bool> {
            let proto: Option<config::Value<String>> = config.get("registries.crates-io.protocol")?;
            let is_sparse = match proto.as_ref().map(|v| v.val.as_str()) {
                Some("sparse") => true,
                Some("git") => false,
                Some(unknown) => anyhow::bail!(
                    "unsupported registry protocol `{unknown}` (defined in {})",
                    proto.as_ref().unwrap().definition
                ),
                None => true,
            };
            Ok(is_sparse)
        }

        /// Gets the `SourceId` associated with given name of the remote registry.
        pub fn alt_registry(config: &Config, key: &str) -> CargoResult<SourceId> {
            if key == CRATES_IO_REGISTRY {
                return Self::crates_io(config);
            }
            let url = config.get_registry_index(key)?;
            let kind = Self::remote_source_kind(&url);
            Ok(SourceId::wrap(SourceIdInner {
                kind,
                canonical_url: CanonicalUrl::new(&url)?,
                url,
                precise: None,
                name: Some(key.to_string()),
                alt_registry_key: Some(key.to_string()),
            }))
        }

        /// Gets this source URL.
        pub fn url(&self) -> &Url {
            &self.inner.url
        }

        /// Gets the canonical URL of this source, used for internal comparison
        /// purposes.
        pub fn canonical_url(&self) -> &CanonicalUrl {
            &self.inner.canonical_url
        }

        pub fn display_index(self) -> String {
            if self.is_crates_io() {
                format!("{} index", CRATES_IO_DOMAIN)
            } else {
                format!("`{}` index", self.display_registry_name())
            }
        }

        pub fn display_registry_name(self) -> String {
            if self.is_crates_io() {
                CRATES_IO_REGISTRY.to_string()
            } else if let Some(name) = &self.inner.name {
                name.clone()
            } else if self.precise().is_some() {
                // We remove `precise` here to retrieve an permissive version of
                // `SourceIdInner`, which may contain the registry name.
                self.with_precise(None).display_registry_name()
            } else {
                url_display(self.url())
            }
        }

        /// Gets the name of the remote registry as defined in the `[registries]` table.
        /// WARNING: alt registries that come from Cargo.lock, or --index will
        /// not have a name.
        pub fn alt_registry_key(&self) -> Option<&str> {
            self.inner.alt_registry_key.as_deref()
        }

        /// Returns `true` if this source is from a filesystem path.
        pub fn is_path(self) -> bool {
            self.inner.kind == SourceKind::Path
        }

        /// Returns the local path if this is a path dependency.
        pub fn local_path(self) -> Option<PathBuf> {
            if self.inner.kind != SourceKind::Path {
                return None;
            }

            Some(self.inner.url.to_file_path().unwrap())
        }

        /// Returns `true` if this source is from a registry (either local or not).
        pub fn is_registry(self) -> bool {
            matches!(
                self.inner.kind,
                SourceKind::Registry | SourceKind::SparseRegistry | SourceKind::LocalRegistry
            )
        }

        /// Returns `true` if this source is from a sparse registry.
        pub fn is_sparse(self) -> bool {
            matches!(self.inner.kind, SourceKind::SparseRegistry)
        }

        /// Returns `true` if this source is a "remote" registry.
        ///
        /// "remote" may also mean a file URL to a git index, so it is not
        /// necessarily "remote". This just means it is not `local-registry`.
        pub fn is_remote_registry(self) -> bool {
            matches!(
                self.inner.kind,
                SourceKind::Registry | SourceKind::SparseRegistry
            )
        }

        /// Returns `true` if this source from a Git repository.
        pub fn is_git(self) -> bool {
            matches!(self.inner.kind, SourceKind::Git(_))
        }

        /// Creates an implementation of `Source` corresponding to this ID.
        pub fn load<'a>(
            self,
            config: &'a Config,
            yanked_whitelist: &HashSet<PackageId>,
        ) -> CargoResult<Box<dyn super::Source + 'a>> {
            trace!("loading SourceId; {}", self);
            match self.inner.kind {
                SourceKind::Git(..) => Ok(Box::new(GitSource::new(self, config)?)),
                SourceKind::Path => {
                    let path = match self.inner.url.to_file_path() {
                        Ok(p) => p,
                        Err(()) => panic!("path sources cannot be remote"),
                    };
                    Ok(Box::new(PathSource::new(&path, self, config)))
                }
                SourceKind::Registry | SourceKind::SparseRegistry => Ok(Box::new(
                    RegistrySource::remote(self, yanked_whitelist, config)?,
                )),
                SourceKind::LocalRegistry => {
                    let path = match self.inner.url.to_file_path() {
                        Ok(p) => p,
                        Err(()) => panic!("path sources cannot be remote"),
                    };
                    Ok(Box::new(RegistrySource::local(
                        self,
                        &path,
                        yanked_whitelist,
                        config,
                    )))
                }
                SourceKind::Directory => {
                    let path = match self.inner.url.to_file_path() {
                        Ok(p) => p,
                        Err(()) => panic!("path sources cannot be remote"),
                    };
                    Ok(Box::new(DirectorySource::new(&path, self, config)))
                }
            }
        }

        /// Gets the value of the precise field.
        pub fn precise(self) -> Option<&'static str> {
            self.inner.precise.as_deref()
        }

        /// Gets the Git reference if this is a git source, otherwise `None`.
        pub fn git_reference(self) -> Option<&'static GitReference> {
            match self.inner.kind {
                SourceKind::Git(ref s) => Some(s),
                _ => None,
            }
        }

        /// Creates a new `SourceId` from this source with the given `precise`.
        pub fn with_precise(self, v: Option<String>) -> SourceId {
            SourceId::wrap(SourceIdInner {
                precise: v,
                ..(*self.inner).clone()
            })
        }

        /// Returns `true` if the remote registry is the standard <https://crates.io>.
        pub fn is_crates_io(self) -> bool {
            match self.inner.kind {
                SourceKind::Registry | SourceKind::SparseRegistry => {}
                _ => return false,
            }
            let url = self.inner.url.as_str();
            url == CRATES_IO_INDEX || url == CRATES_IO_HTTP_INDEX || is_overridden_crates_io_url(url)
        }

        /// Hashes `self`.
        ///
        /// For paths, remove the workspace prefix so the same source will give the
        /// same hash in different locations.
        pub fn stable_hash<S: hash::Hasher>(self, workspace: &Path, into: &mut S) {
            if self.is_path() {
                if let Ok(p) = self
                    .inner
                    .url
                    .to_file_path()
                    .unwrap()
                    .strip_prefix(workspace)
                {
                    self.inner.kind.hash(into);
                    p.to_str().unwrap().hash(into);
                    return;
                }
            }
            self.hash(into)
        }

        pub fn full_eq(self, other: SourceId) -> bool {
            ptr::eq(self.inner, other.inner)
        }

        pub fn full_hash<S: hash::Hasher>(self, into: &mut S) {
            ptr::NonNull::from(self.inner).hash(into)
        }
    }

    impl PartialEq for SourceId {
        fn eq(&self, other: &SourceId) -> bool {
            self.cmp(other) == Ordering::Equal
        }
    }

    impl PartialOrd for SourceId {
        fn partial_cmp(&self, other: &SourceId) -> Option<Ordering> {
            Some(self.cmp(other))
        }
    }

    // Custom comparison defined as canonical URL equality for git sources and URL
    // equality for other sources, ignoring the `precise` and `name` fields.
    impl Ord for SourceId {
        fn cmp(&self, other: &SourceId) -> Ordering {
            // If our interior pointers are to the exact same `SourceIdInner` then
            // we're guaranteed to be equal.
            if ptr::eq(self.inner, other.inner) {
                return Ordering::Equal;
            }

            // Sort first based on `kind`, deferring to the URL comparison below if
            // the kinds are equal.
            match self.inner.kind.cmp(&other.inner.kind) {
                Ordering::Equal => {}
                other => return other,
            }

            // If the `kind` and the `url` are equal, then for git sources we also
            // ensure that the canonical urls are equal.
            match (&self.inner.kind, &other.inner.kind) {
                (SourceKind::Git(_), SourceKind::Git(_)) => {
                    self.inner.canonical_url.cmp(&other.inner.canonical_url)
                }
                _ => self.inner.url.cmp(&other.inner.url),
            }
        }
    }

    impl ser::Serialize for SourceId {
        fn serialize<S>(&self, s: S) -> Result<S::Ok, S::Error>
        where
            S: ser::Serializer,
        {
            if self.is_path() {
                None::<String>.serialize(s)
            } else {
                s.collect_str(&self.as_url())
            }
        }
    }

    impl<'de> de::Deserialize<'de> for SourceId {
        fn deserialize<D>(d: D) -> Result<SourceId, D::Error>
        where
            D: de::Deserializer<'de>,
        {
            let string = String::deserialize(d)?;
            SourceId::from_url(&string).map_err(de::Error::custom)
        }
    }

    fn url_display(url: &Url) -> String {
        if url.scheme() == "file" {
            if let Ok(path) = url.to_file_path() {
                if let Some(path_str) = path.to_str() {
                    return path_str.to_string();
                }
            }
        }

        url.as_str().to_string()
    }

    impl fmt::Display for SourceId {
        fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
            match self.inner.kind {
                SourceKind::Git(ref reference) => {
                    // Don't replace the URL display for git references,
                    // because those are kind of expected to be URLs.
                    write!(f, "{}", self.inner.url)?;
                    if let Some(pretty) = reference.pretty_ref() {
                        write!(f, "?{}", pretty)?;
                    }

                    if let Some(ref s) = self.inner.precise {
                        let len = cmp::min(s.len(), 8);
                        write!(f, "#{}", &s[..len])?;
                    }
                    Ok(())
                }
                SourceKind::Path => write!(f, "{}", url_display(&self.inner.url)),
                SourceKind::Registry | SourceKind::SparseRegistry => {
                    write!(f, "registry `{}`", self.display_registry_name())
                }
                SourceKind::LocalRegistry => write!(f, "registry `{}`", url_display(&self.inner.url)),
                SourceKind::Directory => write!(f, "dir {}", url_display(&self.inner.url)),
            }
        }
    }

    // The hash of SourceId is used in the name of some Cargo folders, so shouldn't
    // vary. `as_str` gives the serialisation of a url (which has a spec) and so
    // insulates against possible changes in how the url crate does hashing.
    impl Hash for SourceId {
        fn hash<S: hash::Hasher>(&self, into: &mut S) {
            self.inner.kind.hash(into);
            match self.inner.kind {
                SourceKind::Git(_) => self.inner.canonical_url.hash(into),
                _ => self.inner.url.as_str().hash(into),
            }
        }
    }

    impl Hash for SourceIdInner {
        /// The hash of `SourceIdInner` is used to retrieve its interned value. We
        /// only care about fields that make `SourceIdInner` unique, which are:
        ///
        /// - `kind`
        /// - `precise`
        /// - `canonical_url`
        fn hash<S: hash::Hasher>(&self, into: &mut S) {
            self.kind.hash(into);
            self.precise.hash(into);
            self.canonical_url.hash(into);
        }
    }

    impl PartialEq for SourceIdInner {
        /// This implementation must be synced with [`SourceIdInner::hash`].
        fn eq(&self, other: &Self) -> bool {
            self.kind == other.kind
                && self.precise == other.precise
                && self.canonical_url == other.canonical_url
        }
    }

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

    // 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),
            }
        }
    }

    /// A `Display`able view into a `SourceId` that will write it as a url
    pub struct SourceIdAsUrl<'a> {
        inner: &'a SourceIdInner,
    }

    impl<'a> fmt::Display for SourceIdAsUrl<'a> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            match *self.inner {
                SourceIdInner {
                    kind: SourceKind::Path,
                    ref url,
                    ..
                } => write!(f, "path+{}", url),
                SourceIdInner {
                    kind: SourceKind::Git(ref reference),
                    ref url,
                    ref precise,
                    ..
                } => {
                    write!(f, "git+{}", url)?;
                    if let Some(pretty) = reference.pretty_ref() {
                        write!(f, "?{}", pretty)?;
                    }
                    if let Some(precise) = precise.as_ref() {
                        write!(f, "#{}", precise)?;
                    }
                    Ok(())
                }
                SourceIdInner {
                    kind: SourceKind::Registry,
                    ref url,
                    ..
                } => {
                    write!(f, "registry+{url}")
                }
                SourceIdInner {
                    kind: SourceKind::SparseRegistry,
                    ref url,
                    ..
                } => {
                    // Sparse registry URL already includes the `sparse+` prefix
                    write!(f, "{url}")
                }
                SourceIdInner {
                    kind: SourceKind::LocalRegistry,
                    ref url,
                    ..
                } => write!(f, "local-registry+{}", url),
                SourceIdInner {
                    kind: SourceKind::Directory,
                    ref url,
                    ..
                } => write!(f, "directory+{}", url),
            }
        }
    }

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

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

    impl<'a> fmt::Display for PrettyRef<'a> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            match *self.inner {
                GitReference::Branch(ref b) => write!(f, "branch={}", b),
                GitReference::Tag(ref s) => write!(f, "tag={}", s),
                GitReference::Rev(ref s) => write!(f, "rev={}", s),
                GitReference::DefaultBranch => unreachable!(),
            }
        }
    }

    #[cfg(test)]
    mod tests {
        use super::{GitReference, SourceId, SourceKind};
        use crate::util::{Config, IntoUrl};

        #[test]
        fn github_sources_equal() {
            let loc = "https://github.com/foo/bar".into_url().unwrap();
            let default = SourceKind::Git(GitReference::DefaultBranch);
            let s1 = SourceId::new(default.clone(), loc, None).unwrap();

            let loc = "git://github.com/foo/bar".into_url().unwrap();
            let s2 = SourceId::new(default, loc.clone(), None).unwrap();

            assert_eq!(s1, s2);

            let foo = SourceKind::Git(GitReference::Branch("foo".to_string()));
            let s3 = SourceId::new(foo, loc, None).unwrap();
            assert_ne!(s1, s3);
        }

        // This is a test that the hash of the `SourceId` for crates.io is a well-known
        // value.
        //
        // Note that the hash value matches what the crates.io source id has hashed
        // since long before Rust 1.30. We strive to keep this value the same across
        // versions of Cargo because changing it means that users will need to
        // redownload the index and all crates they use when using a new Cargo version.
        //
        // This isn't to say that this hash can *never* change, only that when changing
        // this it should be explicitly done. If this hash changes accidentally and
        // you're able to restore the hash to its original value, please do so!
        // Otherwise please just leave a comment in your PR as to why the hash value is
        // changing and why the old value can't be easily preserved.
        //
        // The hash value depends on endianness and bit-width, so we only run this test on
        // little-endian 64-bit CPUs (such as x86-64 and ARM64) where it matches the
        // well-known value.
        #[test]
        #[cfg(all(target_endian = "little", target_pointer_width = "64"))]
        fn test_cratesio_hash() {
            let config = Config::default().unwrap();
            let crates_io = SourceId::crates_io(&config).unwrap();
            assert_eq!(crate::util::hex::short_hash(&crates_io), "1ecc6299db9ec823");
        }

        // See the comment in `test_cratesio_hash`.
        //
        // Only test on non-Windows as paths on Windows will get different hashes.
        #[test]
        #[cfg(all(target_endian = "little", target_pointer_width = "64", not(windows)))]
        fn test_stable_hash() {
            use std::hash::Hasher;
            use std::path::Path;

            let gen_hash = |source_id: SourceId| {
                let mut hasher = std::collections::hash_map::DefaultHasher::new();
                source_id.stable_hash(Path::new("/tmp/ws"), &mut hasher);
                hasher.finish()
            };

            let url = "https://my-crates.io".into_url().unwrap();
            let source_id = SourceId::for_registry(&url).unwrap();
            assert_eq!(gen_hash(source_id), 18108075011063494626);
            assert_eq!(crate::util::hex::short_hash(&source_id), "fb60813d6cb8df79");

            let url = "https://your-crates.io".into_url().unwrap();
            let source_id = SourceId::for_alt_registry(&url, "alt").unwrap();
            assert_eq!(gen_hash(source_id), 12862859764592646184);
            assert_eq!(crate::util::hex::short_hash(&source_id), "09c10fd0cbd74bce");

            let url = "sparse+https://my-crates.io".into_url().unwrap();
            let source_id = SourceId::for_registry(&url).unwrap();
            assert_eq!(gen_hash(source_id), 8763561830438022424);
            assert_eq!(crate::util::hex::short_hash(&source_id), "d1ea0d96f6f759b5");

            let url = "sparse+https://your-crates.io".into_url().unwrap();
            let source_id = SourceId::for_alt_registry(&url, "alt").unwrap();
            assert_eq!(gen_hash(source_id), 5159702466575482972);
            assert_eq!(crate::util::hex::short_hash(&source_id), "135d23074253cb78");

            let url = "file:///tmp/ws/crate".into_url().unwrap();
            let source_id = SourceId::for_git(&url, GitReference::DefaultBranch).unwrap();
            assert_eq!(gen_hash(source_id), 15332537265078583985);
            assert_eq!(crate::util::hex::short_hash(&source_id), "73a808694abda756");

            let path = Path::new("/tmp/ws/crate");

            let source_id = SourceId::for_local_registry(path).unwrap();
            assert_eq!(gen_hash(source_id), 18446533307730842837);
            assert_eq!(crate::util::hex::short_hash(&source_id), "52a84cc73f6fd48b");

            let source_id = SourceId::for_path(path).unwrap();
            assert_eq!(gen_hash(source_id), 8764714075439899829);
            assert_eq!(crate::util::hex::short_hash(&source_id), "e1ddd48578620fc1");

            let source_id = SourceId::for_directory(path).unwrap();
            assert_eq!(gen_hash(source_id), 17459999773908528552);
            assert_eq!(crate::util::hex::short_hash(&source_id), "6568fe2c2fab5bfe");
        }

        #[test]
        fn serde_roundtrip() {
            let url = "sparse+https://my-crates.io/".into_url().unwrap();
            let source_id = SourceId::for_registry(&url).unwrap();
            let formatted = format!("{}", source_id.as_url());
            let deserialized = SourceId::from_url(&formatted).unwrap();
            assert_eq!(formatted, "sparse+https://my-crates.io/");
            assert_eq!(source_id, deserialized);
        }
    }

    /// Check if `url` equals to the overridden crates.io URL.
    // ALLOWED: For testing Cargo itself only.
    #[allow(clippy::disallowed_methods)]
    fn is_overridden_crates_io_url(url: &str) -> bool {
        std::env::var("__CARGO_TEST_CRATES_IO_URL_DO_NOT_USE_THIS").map_or(false, |v| v == url)
    }