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    //! See [GitSource].

    use crate::core::global_cache_tracker;
    use crate::core::GitReference;
    use crate::core::SourceId;
    use crate::core::{Dependency, Package, PackageId};
    use crate::sources::git::utils::GitRemote;
    use crate::sources::source::MaybePackage;
    use crate::sources::source::QueryKind;
    use crate::sources::source::Source;
    use crate::sources::IndexSummary;
    use crate::sources::PathSource;
    use crate::util::cache_lock::CacheLockMode;
    use crate::util::errors::CargoResult;
    use crate::util::hex::short_hash;
    use crate::util::interning::InternedString;
    use crate::util::GlobalContext;
    use anyhow::Context as _;
    use cargo_util::paths::exclude_from_backups_and_indexing;
    use std::fmt::{self, Debug, Formatter};
    use std::task::Poll;
    use tracing::trace;
    use url::Url;

    /// `GitSource` contains one or more packages gathering from a Git repository.
    /// Under the hood it uses [`PathSource`] to discover packages inside the
    /// repository.
    ///
    /// ## Filesystem layout
    ///
    /// During a successful `GitSource` download, at least two Git repositories are
    /// created: one is the shared Git database of this remote, and the other is the
    /// Git checkout to a specific revision, which contains the actual files to be
    /// compiled. Multiple checkouts can be cloned from a single Git database.
    ///
    /// Those repositories are located at Cargo's Git cache directory
    /// `$CARGO_HOME/git`. The file tree of the cache directory roughly looks like:
    ///
    /// ```text
    /// $CARGO_HOME/git/
    /// ├── checkouts/
    /// │  ├── gimli-a0d193bd15a5ed96/
    /// │  │  ├── 8e73ef0/     # Git short ID for a certain revision
    /// │  │  ├── a2a4b78/
    /// │  │  └── e33d1ac/
    /// │  ├── log-c58e1db3de7c154d-shallow/
    /// │  │  └── 11eda98/
    /// └── db/
    ///    ├── gimli-a0d193bd15a5ed96/
    ///    └── log-c58e1db3de7c154d-shallow/
    /// ```
    ///
    /// For more on Git cache directory, see ["Cargo Home"] in The Cargo Book.
    ///
    /// For more on the directory format `<pkg>-<hash>[-shallow]`, see [`ident`]
    /// and [`ident_shallow`].
    ///
    /// ## Locked to a revision
    ///
    /// Once a `GitSource` is fetched, it will resolve to a specific commit revision.
    /// This is often mentioned as "locked revision" (`locked_rev`) throughout the
    /// codebase. The revision is written into `Cargo.lock`. This is essential since
    /// we want to ensure a package can compiles with the same set of files when
    /// a `Cargo.lock` is present. With the `locked_rev` provided, `GitSource` can
    /// precisely fetch the same revision from the Git repository.
    ///
    /// ["Cargo Home"]: https://doc.rust-lang.org/nightly/cargo/guide/cargo-home.html#directories
    pub struct GitSource<'gctx> {
        /// The git remote which we're going to fetch from.
        remote: GitRemote,
        /// The revision which a git source is locked to.
        ///
        /// Expected to always be [`Revision::Locked`] after the Git repository is fetched.
        locked_rev: Revision,
        /// The unique identifier of this source.
        source_id: SourceId,
        /// The underlying path source to discover packages inside the Git repository.
        ///
        /// This gets set to `Some` after the git repo has been checked out
        /// (automatically handled via [`GitSource::block_until_ready`]).
        path_source: Option<PathSource<'gctx>>,
        /// A short string that uniquely identifies the version of the checkout.
        ///
        /// This is typically a 7-character string of the OID hash, automatically
        /// increasing in size if it is ambiguous.
        ///
        /// This is set to `Some` after the git repo has been checked out
        /// (automatically handled via [`GitSource::block_until_ready`]).
        short_id: Option<InternedString>,
        /// The identifier of this source for Cargo's Git cache directory.
        /// See [`ident`] for more.
        ident: InternedString,
        gctx: &'gctx GlobalContext,
        /// Disables status messages.
        quiet: bool,
    }

    impl<'gctx> GitSource<'gctx> {
        /// Creates a git source for the given [`SourceId`].
        pub fn new(source_id: SourceId, gctx: &'gctx GlobalContext) -> CargoResult<GitSource<'gctx>> {
            assert!(source_id.is_git(), "id is not git, id={}", source_id);

            let remote = GitRemote::new(source_id.url());
            // Fallback to git ref from mainfest if there is no locked revision.
            let locked_rev = source_id
                .precise_git_fragment()
                .map(|s| Revision::new(s.into()))
                .unwrap_or_else(|| source_id.git_reference().unwrap().clone().into());

            let ident = ident_shallow(
                &source_id,
                gctx.cli_unstable()
                    .git
                    .map_or(false, |features| features.shallow_deps),
            );

            let source = GitSource {
                remote,
                locked_rev,
                source_id,
                path_source: None,
                short_id: None,
                ident: ident.into(),
                gctx,
                quiet: false,
            };

            Ok(source)
        }

        /// Gets the remote repository URL.
        pub fn url(&self) -> &Url {
            self.remote.url()
        }

        /// Returns the packages discovered by this source. It may fetch the Git
        /// repository as well as walk the filesystem if package information
        /// haven't yet updated.
        pub fn read_packages(&mut self) -> CargoResult<Vec<Package>> {
            if self.path_source.is_none() {
                self.invalidate_cache();
                self.block_until_ready()?;
            }
            self.path_source.as_mut().unwrap().read_packages()
        }

        fn mark_used(&self, size: Option<u64>) -> CargoResult<()> {
            self.gctx
                .deferred_global_last_use()?
                .mark_git_checkout_used(global_cache_tracker::GitCheckout {
                    encoded_git_name: self.ident,
                    short_name: self.short_id.expect("update before download"),
                    size,
                });
            Ok(())
        }
    }

    /// Indicates a [Git revision] that might be locked or deferred to be resolved.
    ///
    /// [Git revision]: https://git-scm.com/docs/revisions
    #[derive(Clone, Debug)]
    enum Revision {
        /// A [Git reference] that would trigger extra fetches when being resolved.
        ///
        /// [Git reference]: https://git-scm.com/book/en/v2/Git-Internals-Git-References
        Deferred(GitReference),
        /// A locked revision of the actual Git commit object ID.
        Locked(git2::Oid),
    }

    impl Revision {
        fn new(rev: &str) -> Revision {
            let oid = git2::Oid::from_str(rev).ok();
            match oid {
                // Git object ID is supposed to be a hex string of 20 (SHA1) or 32 (SHA256) bytes.
                // Its length must be double to the underlying bytes (40 or 64),
                // otherwise libgit2 would happily zero-pad the returned oid.
                // See rust-lang/cargo#13188
                Some(oid) if oid.as_bytes().len() * 2 == rev.len() => Revision::Locked(oid),
                _ => Revision::Deferred(GitReference::Rev(rev.to_string())),
            }
        }
    }

    impl From<GitReference> for Revision {
        fn from(value: GitReference) -> Self {
            Revision::Deferred(value)
        }
    }

    impl From<Revision> for GitReference {
        fn from(value: Revision) -> Self {
            match value {
                Revision::Deferred(git_ref) => git_ref,
                Revision::Locked(oid) => GitReference::Rev(oid.to_string()),
            }
        }
    }

    /// Create an identifier from a URL,
    /// essentially turning `proto://host/path/repo` into `repo-<hash-of-url>`.
    fn ident(id: &SourceId) -> String {
        let ident = id
            .canonical_url()
            .raw_canonicalized_url()
            .path_segments()
            .and_then(|s| s.rev().next())
            .unwrap_or("");

        let ident = if ident.is_empty() { "_empty" } else { ident };

        format!("{}-{}", ident, short_hash(id.canonical_url()))
    }

    /// Like [`ident()`], but appends `-shallow` to it, turning
    /// `proto://host/path/repo` into `repo-<hash-of-url>-shallow`.
    ///
    /// It's important to separate shallow from non-shallow clones for reasons of
    /// backwards compatibility --- older cargo's aren't necessarily handling
    /// shallow clones correctly.
    fn ident_shallow(id: &SourceId, is_shallow: bool) -> String {
        let mut ident = ident(id);
        if is_shallow {
            ident.push_str("-shallow");
        }
        ident
    }

    impl<'gctx> Debug for GitSource<'gctx> {
        fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
            write!(f, "git repo at {}", self.remote.url())?;

            // TODO(-Znext-lockfile-bump): set it to true when the default is
            // lockfile v4, because we want Source ID serialization to be
            // consistent with lockfile.
            match &self.locked_rev {
                Revision::Deferred(git_ref) => match git_ref.pretty_ref(false) {
                    Some(s) => write!(f, " ({})", s),
                    None => Ok(()),
                },
                Revision::Locked(oid) => write!(f, " ({oid})"),
            }
        }
    }

    impl<'gctx> Source for GitSource<'gctx> {
        fn query(
            &mut self,
            dep: &Dependency,
            kind: QueryKind,
            f: &mut dyn FnMut(IndexSummary),
        ) -> Poll<CargoResult<()>> {
            if let Some(src) = self.path_source.as_mut() {
                src.query(dep, kind, f)
            } else {
                Poll::Pending
            }
        }

        fn supports_checksums(&self) -> bool {
            false
        }

        fn requires_precise(&self) -> bool {
            true
        }

        fn source_id(&self) -> SourceId {
            self.source_id
        }

        fn block_until_ready(&mut self) -> CargoResult<()> {
            if self.path_source.is_some() {
                self.mark_used(None)?;
                return Ok(());
            }

            let git_fs = self.gctx.git_path();
            // Ignore errors creating it, in case this is a read-only filesystem:
            // perhaps the later operations can succeed anyhow.
            let _ = git_fs.create_dir();
            let git_path = self
                .gctx
                .assert_package_cache_locked(CacheLockMode::DownloadExclusive, &git_fs);

            // Before getting a checkout, make sure that `<cargo_home>/git` is
            // marked as excluded from indexing and backups. Older versions of Cargo
            // didn't do this, so we do it here regardless of whether `<cargo_home>`
            // exists.
            //
            // This does not use `create_dir_all_excluded_from_backups_atomic` for
            // the same reason: we want to exclude it even if the directory already
            // exists.
            exclude_from_backups_and_indexing(&git_path);

            let db_path = self.gctx.git_db_path().join(&self.ident);
            let db_path = db_path.into_path_unlocked();

            let db = self.remote.db_at(&db_path).ok();

            let (db, actual_rev) = match (&self.locked_rev, db) {
                // If we have a locked revision, and we have a preexisting database
                // which has that revision, then no update needs to happen.
                (Revision::Locked(oid), Some(db)) if db.contains(*oid) => (db, *oid),

                // If we're in offline mode, we're not locked, and we have a
                // database, then try to resolve our reference with the preexisting
                // repository.
                (Revision::Deferred(git_ref), Some(db)) if self.gctx.offline() => {
                    let rev = db.resolve(&git_ref).with_context(|| {
                        "failed to lookup reference in preexisting repository, and \
                             can't check for updates in offline mode (--offline)"
                    })?;
                    (db, rev)
                }

                // ... otherwise we use this state to update the git database. Note
                // that we still check for being offline here, for example in the
                // situation that we have a locked revision but the database
                // doesn't have it.
                (locked_rev, db) => {
                    if self.gctx.offline() {
                        anyhow::bail!(
                            "can't checkout from '{}': you are in the offline mode (--offline)",
                            self.remote.url()
                        );
                    }

                    if !self.quiet {
                        self.gctx.shell().status(
                            "Updating",
                            format!("git repository `{}`", self.remote.url()),
                        )?;
                    }

                    trace!("updating git source `{:?}`", self.remote);

                    let locked_rev = locked_rev.clone().into();
                    self.remote.checkout(&db_path, db, &locked_rev, self.gctx)?
                }
            };

            // Don’t use the full hash, in order to contribute less to reaching the
            // path length limit on Windows. See
            // <https://github.com/servo/servo/pull/14397>.
            let short_id = db.to_short_id(actual_rev)?;

            // Check out `actual_rev` from the database to a scoped location on the
            // filesystem. This will use hard links and such to ideally make the
            // checkout operation here pretty fast.
            let checkout_path = self
                .gctx
                .git_checkouts_path()
                .join(&self.ident)
                .join(short_id.as_str());
            let checkout_path = checkout_path.into_path_unlocked();
            db.copy_to(actual_rev, &checkout_path, self.gctx)?;

            let source_id = self
                .source_id
                .with_git_precise(Some(actual_rev.to_string()));
            let path_source = PathSource::new_recursive(&checkout_path, source_id, self.gctx);

            self.path_source = Some(path_source);
            self.short_id = Some(short_id.as_str().into());
            self.locked_rev = Revision::Locked(actual_rev);
            self.path_source.as_mut().unwrap().update()?;

            // Hopefully this shouldn't incur too much of a performance hit since
            // most of this should already be in cache since it was just
            // extracted.
            let size = global_cache_tracker::du_git_checkout(&checkout_path)?;
            self.mark_used(Some(size))?;
            Ok(())
        }

        fn download(&mut self, id: PackageId) -> CargoResult<MaybePackage> {
            trace!(
                "getting packages for package ID `{}` from `{:?}`",
                id,
                self.remote
            );
            self.mark_used(None)?;
            self.path_source
                .as_mut()
                .expect("BUG: `update()` must be called before `get()`")
                .download(id)
        }

        fn finish_download(&mut self, _id: PackageId, _data: Vec<u8>) -> CargoResult<Package> {
            panic!("no download should have started")
        }

        fn fingerprint(&self, _pkg: &Package) -> CargoResult<String> {
            match &self.locked_rev {
                Revision::Locked(oid) => Ok(oid.to_string()),
                _ => unreachable!("locked_rev must be resolved when computing fingerprint"),
            }
        }

        fn describe(&self) -> String {
            format!("Git repository {}", self.source_id)
        }

        fn add_to_yanked_whitelist(&mut self, _pkgs: &[PackageId]) {}

        fn is_yanked(&mut self, _pkg: PackageId) -> Poll<CargoResult<bool>> {
            Poll::Ready(Ok(false))
        }

        fn invalidate_cache(&mut self) {}

        fn set_quiet(&mut self, quiet: bool) {
            self.quiet = quiet;
        }
    }

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

        #[test]
        pub fn test_url_to_path_ident_with_path() {
            let ident = ident(&src("https://github.com/carlhuda/cargo"));
            assert!(ident.starts_with("cargo-"));
        }

        #[test]
        pub fn test_url_to_path_ident_without_path() {
            let ident = ident(&src("https://github.com"));
            assert!(ident.starts_with("_empty-"));
        }

        #[test]
        fn test_canonicalize_idents_by_stripping_trailing_url_slash() {
            let ident1 = ident(&src("https://github.com/PistonDevelopers/piston/"));
            let ident2 = ident(&src("https://github.com/PistonDevelopers/piston"));
            assert_eq!(ident1, ident2);
        }

        #[test]
        fn test_canonicalize_idents_by_lowercasing_github_urls() {
            let ident1 = ident(&src("https://github.com/PistonDevelopers/piston"));
            let ident2 = ident(&src("https://github.com/pistondevelopers/piston"));
            assert_eq!(ident1, ident2);
        }

        #[test]
        fn test_canonicalize_idents_by_stripping_dot_git() {
            let ident1 = ident(&src("https://github.com/PistonDevelopers/piston"));
            let ident2 = ident(&src("https://github.com/PistonDevelopers/piston.git"));
            assert_eq!(ident1, ident2);
        }

        #[test]
        fn test_canonicalize_idents_different_protocols() {
            let ident1 = ident(&src("https://github.com/PistonDevelopers/piston"));
            let ident2 = ident(&src("git://github.com/PistonDevelopers/piston"));
            assert_eq!(ident1, ident2);
        }

        fn src(s: &str) -> SourceId {
            SourceId::for_git(&s.into_url().unwrap(), GitReference::DefaultBranch).unwrap()
        }
    }