grit_lib/refs/

mod.rs

//! Reference storage — files backend + reftable backend.
//!
//! Git stores references as text files under `<git-dir>/refs/` (and
//! `<git-dir>/packed-refs` for the packed backend).  Each loose ref file
//! contains either:
//!
//! - A 40-character hex SHA-1 followed by a newline, **or**
//! - The string `"ref: <target>\n"` for symbolic refs.
//!
//! `HEAD` is a special case: it is normally a symbolic ref but may also be
//! detached (pointing directly at a commit hash).
//!
//! When `extensions.refStorage = reftable`, the reftable backend is used
//! instead.  The public API is the same; dispatch is handled internally.
//!
//! Library guide: [mod](https://grit-scm.com/docs/library/refs)
//!
//! ```rust
//! use grit_lib::repo::{InitOptions, Repository};
//! # fn main() -> grit_lib::error::Result<()> {
//! let dir = tempfile::tempdir()?;
//! let _repo = Repository::init(dir.path(), &InitOptions::default())?;
//! assert!(_repo.refs().read_raw("HEAD")?.is_some());
//!
//! # Ok(())
//! # }
//! ```

pub mod handle;
pub mod listing;
pub mod query_reachability;
pub mod shorten;
pub mod store;
pub mod version_sort;

pub use shorten::{
    expand_ref_dwim_full_name, peel_symref_to_terminal_ref, shorten_unambiguous,
    warn_ambiguous_refs_from_config,
};

mod domain_reexports;
mod on_store;
pub use domain_reexports::*;
pub use handle::References;
pub use on_store::update_branch_for_commit_on_store;
pub(crate) use on_store::{
    append_reflog_on_store, delete_ref_on_store, update_detached_head_for_commit_on_store,
    write_symbolic_ref_on_store,
};

/// In-process ref-transaction and loose-object prune helpers.
pub mod gc {
    pub use crate::gc::*;
}

use std::collections::{BTreeSet, HashMap, HashSet};
use std::fs;
use std::io;
use std::ops::ControlFlow;
use std::path::{Path, PathBuf};
use store::{
    open_ref_store, Expected, RawRef as StoreRawRef, RefCaseOnlyRename, RefEntry, RefReflogRename,
    RefStorageFormat, RefStore, RefTransaction, RefUpdate, RefUpdateFlags, ReflogUpdate,
};

use crate::check_ref_format::{check_refname_format, RefNameOptions};
use crate::config::ConfigSet;
use crate::error::{Error, RefLockError, Result};
use crate::ident::Signature;
use crate::objects::{HashAlgo, ObjectId};
use crate::pack;
use store::format_reflog_identity;

/// Maximum symbolic ref hops when resolving a ref (Git `SYMREF_MAXDEPTH`).
pub const SYMREF_MAXDEPTH: usize = 5;

fn map_public_ref_store_error(err: Error, refname: &str) -> Error {
    match err {
        Error::RefStore(store::RefStoreError::SymrefLoop) => {
            Error::InvalidRef(format!("ref symlink too deep: {refname}"))
        }
        other => other,
    }
}

/// Loose-files checks shared by legacy [`write_ref_at_storage`] and RefStore-backed writes.
///
/// Only meaningful for the files backend; callers check the store format first.
fn files_legacy_write_precheck(git_dir: &Path, refname: &str) -> Result<()> {
    let storage_dir = ref_storage_dir(git_dir, refname);
    let stor = crate::ref_namespace::storage_ref_name(refname);
    let path = storage_dir.join(stor);
    remove_empty_ref_directory(&path);
    if fs::symlink_metadata(&path)
        .map(|m| m.file_type().is_dir())
        .unwrap_or(false)
    {
        let display = ref_path_for_display(&path);
        return Err(crate::error::RefLockError::DirectoryInTheWay {
            refname: refname.to_owned(),
            path: display,
        }
        .into());
    }
    if path.is_file() && matches!(read_ref_file(&path), Err(Error::InvalidRef(_))) {
        return Err(Error::InvalidRef(format!(
            "cannot update ref '{refname}': reference broken"
        )));
    }
    Ok(())
}

fn legacy_ref_update_flags(refname: &str) -> RefUpdateFlags {
    let mut flags = RefUpdateFlags::default();
    // Direct updates to `HEAD` detach or reattach the worktree HEAD file; do not peel symrefs.
    if refname == "HEAD" {
        flags.no_deref = true;
    }
    flags
}

pub(crate) fn commit_store_update(git_dir: &Path, update: RefUpdate) -> Result<()> {
    let store = open_ref_store(git_dir)?;
    commit_ref_update_on_store(store.as_ref(), update)
}

/// Apply one ref update through an already-selected [`RefStore`] (for example the store on
/// [`crate::repo::Repository`] after [`crate::repo::Repository::with_ref_store`]).
///
/// # Errors
///
/// Propagates validation, compare-and-swap, and backend errors.
pub fn commit_ref_update_on_store(store: &dyn RefStore, update: RefUpdate) -> Result<()> {
    if let Some(ref log) = update.reflog {
        validate_reflog_update(log)?;
    }
    let refname = update.name.clone();
    let txn = RefTransaction::new()
        .update(update)
        .map_err(crate::error::Error::from)?;
    let prepared = store
        .prepare(txn)
        .map_err(|e| map_public_ref_store_error(Error::from(e), &refname))?;
    prepared
        .commit()
        .map_err(|e| map_public_ref_store_error(Error::from(e), &refname))
}

/// Point `refname` at `oid` using `store`, optionally running loose-files prechecks when
/// `store` uses the files backend under `git_dir`.
///
/// # Errors
///
/// Same as [`write_ref`], except updates go through `store` instead of reopening storage from
/// `git_dir`.
pub fn update_direct_ref_on_store(
    store: &dyn RefStore,
    git_dir: &Path,
    refname: &str,
    oid: &ObjectId,
) -> Result<()> {
    store_write_value_on_store(
        store,
        git_dir,
        refname,
        Some(StoreRawRef::Direct(*oid)),
        Expected::Any,
        None,
    )
}

pub(crate) fn store_write_value_on_store(
    store: &dyn RefStore,
    git_dir: &Path,
    refname: &str,
    new_value: Option<StoreRawRef>,
    expected: Expected,
    reflog: Option<ReflogUpdate>,
) -> Result<()> {
    ensure_refname_safe_for_storage(refname)?;
    if new_value.is_some() && store.format() == RefStorageFormat::Files {
        files_legacy_write_precheck(git_dir, refname)?;
    }
    commit_ref_update_on_store(
        store,
        RefUpdate {
            name: refname.to_owned(),
            new_value,
            expected,
            reflog,
            flags: legacy_ref_update_flags(refname),
        },
    )
}

/// Apply several ref updates in one [`RefStore::prepare`] / commit (all-or-nothing).
///
/// Used by batch ref paths (`fetch`, `push`, `receive-pack`, [`crate::gc::update_refs`]).
///
/// # Errors
///
/// Returns [`crate::refs::store::RefStoreError`] for duplicate names, CAS failures,
/// lock conflicts, and namespace conflicts. Propagates I/O and corrupt-store failures.
pub fn commit_ref_store_batch(git_dir: &Path, updates: &[RefUpdate]) -> Result<()> {
    if updates.is_empty() {
        return Ok(());
    }
    let store = open_ref_store(git_dir)?;
    commit_ref_updates_on_store(store.as_ref(), updates, &[])
}

/// Apply several ref updates atomically through an existing [`RefStore`].
///
/// # Errors
///
/// Propagates validation, compare-and-swap, and backend errors from [`RefStore::prepare`].
pub fn commit_ref_updates_on_store(
    store: &dyn RefStore,
    updates: &[RefUpdate],
    reflog_renames: &[RefReflogRename],
) -> Result<()> {
    commit_ref_batch_on_store(store, updates, reflog_renames, &[])
}

/// Apply ref updates, reflog renames, and optional case-only ref renames atomically.
///
/// # Errors
///
/// Propagates validation, compare-and-swap, and backend errors from [`RefStore::prepare`].
pub fn commit_ref_batch_on_store(
    store: &dyn RefStore,
    updates: &[RefUpdate],
    reflog_renames: &[RefReflogRename],
    case_only_renames: &[RefCaseOnlyRename],
) -> Result<()> {
    if updates.is_empty() && reflog_renames.is_empty() && case_only_renames.is_empty() {
        return Ok(());
    }
    commit_owned_ref_batch_on_store(
        store,
        updates.to_vec(),
        reflog_renames.to_vec(),
        case_only_renames.to_vec(),
    )
}

/// [`commit_ref_updates_on_store`] taking ownership of `updates`, so a large batch is not copied.
///
/// # Errors
///
/// Same as [`commit_ref_updates_on_store`].
pub(crate) fn commit_owned_ref_updates_on_store(
    store: &dyn RefStore,
    updates: Vec<RefUpdate>,
) -> Result<()> {
    if updates.is_empty() {
        return Ok(());
    }
    commit_owned_ref_batch_on_store(store, updates, Vec::new(), Vec::new())
}

fn commit_owned_ref_batch_on_store(
    store: &dyn RefStore,
    updates: Vec<RefUpdate>,
    reflog_renames: Vec<RefReflogRename>,
    case_only_renames: Vec<RefCaseOnlyRename>,
) -> Result<()> {
    for update in &updates {
        if let Some(ref log) = update.reflog {
            validate_reflog_update(log)?;
        }
    }
    for rename in &reflog_renames {
        validate_reflog_update(&rename.append)?;
    }
    let label = updates
        .first()
        .map(|u| u.name.clone())
        .or_else(|| reflog_renames.first().map(|r| r.from.clone()))
        .or_else(|| case_only_renames.first().map(|r| r.from.clone()))
        .unwrap_or_else(|| "refs".to_owned());
    let mut txn = RefTransaction::from_updates(updates).map_err(|e| {
        let name = match &e {
            store::RefStoreError::DuplicateUpdate { name } => name.clone(),
            _ => label.clone(),
        };
        map_public_ref_store_error(Error::from(e), &name)
    })?;
    for rename in reflog_renames {
        txn = txn.with_reflog_rename(rename);
    }
    for rename in case_only_renames {
        txn = txn.with_case_only_rename(rename);
    }
    let prepared = store
        .prepare(txn)
        .map_err(|e| map_public_ref_store_error(Error::from(e), &label))?;
    prepared
        .commit()
        .map_err(|e| map_public_ref_store_error(Error::from(e), &label))
}

fn store_write_value(
    git_dir: &Path,
    refname: &str,
    new_value: Option<StoreRawRef>,
    expected: Expected,
    reflog: Option<ReflogUpdate>,
) -> Result<()> {
    let store = open_ref_store(git_dir)?;
    store_write_value_on_store(
        store.as_ref(),
        git_dir,
        refname,
        new_value,
        expected,
        reflog,
    )
}

fn collect_resolved_refs(store: &dyn RefStore, prefix: &str) -> Result<Vec<(String, ObjectId)>> {
    collect_resolved_ref_entries(store, |f| store.for_each_ref(prefix, f))
}

/// Resolve each entry `for_each` yields to an object id through `store`.
fn collect_resolved_ref_entries(
    store: &dyn RefStore,
    for_each: impl FnOnce(&mut dyn FnMut(&RefEntry) -> ControlFlow<()>) -> Result<()>,
) -> Result<Vec<(String, ObjectId)>> {
    let mut results = Vec::new();
    for_each(&mut |entry: &RefEntry| {
        let oid = entry
            .peeled
            .or_else(|| match &entry.value {
                StoreRawRef::Direct(oid) => Some(*oid),
                StoreRawRef::Symbolic(target) => store.resolve(target).ok(),
            })
            .or_else(|| store.resolve(&entry.name).ok());
        if let Some(oid) = oid {
            results.push((entry.name.clone(), oid));
        }
        ControlFlow::Continue(())
    })?;
    Ok(results)
}

/// A symbolic or direct reference.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Ref {
    /// Direct reference: stores an [`ObjectId`].
    Direct(ObjectId),
    /// Symbolic reference: stores the name of the target ref.
    Symbolic(String),
}

/// Read a single reference file from `path`.
///
/// # Errors
///
/// - [`Error::InvalidRef`] if the file content is not a valid ref.
/// - [`Error::Io`] on filesystem errors.
pub fn read_ref_file(path: &Path) -> Result<Ref> {
    if let Ok(target) = fs::read_link(path) {
        return Ok(Ref::Symbolic(target.to_string_lossy().into_owned()));
    }

    let content = match fs::read_to_string(path) {
        Ok(c) => c,
        // `refs/heads/master` can be a directory when a branch named `master/...` exists, and a
        // probe like `refs/remotes/v1` can hit ENOTDIR when `refs/remotes` is a file. Treat both
        // like a missing loose ref so optional DWIM candidates fall through cleanly.
        Err(e)
            if e.kind() == io::ErrorKind::IsADirectory
                || e.kind() == io::ErrorKind::NotADirectory
                || e.raw_os_error() == Some(libc::EISDIR)
                || e.raw_os_error() == Some(libc::ENOTDIR) =>
        {
            return Err(Error::Io(io::Error::new(io::ErrorKind::NotFound, e)));
        }
        Err(e) => return Err(Error::Io(e)),
    };
    let content = content.trim_end_matches('\n');
    parse_ref_content(content)
}

/// Parse the content of a ref file (without trailing newline).
pub(crate) fn parse_ref_content(content: &str) -> Result<Ref> {
    if let Some(target) = content.strip_prefix("ref: ") {
        Ok(Ref::Symbolic(target.trim().to_owned()))
    } else if let Some(token) = content.split_whitespace().next() {
        if ObjectId::is_full_hex(token) {
            let oid: ObjectId = token.parse()?;
            Ok(Ref::Direct(oid))
        } else if content == "unknown-oid" {
            const PLACEHOLDER: &[u8; 20] = b"GritUnknownOidPlc!X!";
            let oid = ObjectId::from_bytes(PLACEHOLDER)?;
            Ok(Ref::Direct(oid))
        } else {
            Err(Error::InvalidRef(content.to_owned()))
        }
    } else {
        Err(Error::InvalidRef(content.to_owned()))
    }
}

/// Resolve a reference to its target [`ObjectId`], following symbolic refs.
///
/// Dispatches to the reftable backend when `extensions.refStorage = reftable`.
///
/// # Parameters
///
/// - `git_dir` — path to the git directory.
/// - `refname` — reference name (e.g. `"HEAD"`, `"refs/heads/main"`).
///
/// # Errors
///
/// - [`Error::RefStore`] with [`RefStoreError::NotFound`](store::RefStoreError::NotFound) if
///   `refname`, or the target at the end of its symbolic chain, does not exist.
/// - [`Error::InvalidRef`] if the ref is malformed or forms a cycle.
pub fn resolve_ref(git_dir: &Path, refname: &str) -> Result<ObjectId> {
    open_ref_store(git_dir)?
        .resolve(refname)
        .map_err(|err| map_public_ref_store_error(err, refname))
}

/// Determine the common git directory for worktree-aware ref resolution.
///
/// If `<git_dir>/commondir` exists, its contents point to the shared
/// git directory. Returns `None` when git_dir is already the common dir.
pub fn common_dir(git_dir: &Path) -> Option<PathBuf> {
    let commondir_file = git_dir.join("commondir");
    if !commondir_file.is_file() {
        return None;
    }
    let raw = fs::read_to_string(commondir_file).ok()?;
    let rel = raw.trim();
    // Match Git: `commondir` may be relative to this gitdir or an absolute path (see
    // `git worktree add` and `refs/files-backend.c`).
    let path = if Path::new(rel).is_absolute() {
        PathBuf::from(rel)
    } else {
        git_dir.join(rel)
    };
    path.canonicalize().ok()
}

/// Outcome of a single storage-level ref lookup (Git `refs_read_raw_ref` style).
///
/// This checks whether a ref **name** exists in the ref store without applying
/// DWIM rules. A symbolic ref is considered to exist if its ref file (or
/// reftable record) is present, even when the target is missing.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RawRefLookup {
    /// A loose ref file, packed ref line, or reftable record exists for this name.
    Exists,
    /// No ref is recorded under this exact name.
    NotFound,
    /// A path component exists as a directory where a ref file was expected (e.g. `refs/heads`).
    IsDirectory,
}

/// Return whether `refname` exists as a ref in the repository's ref storage.
///
/// This matches `git refs exists` / `git show-ref --exists`: no DWIM, no
/// resolution of symbolic targets. Dispatches to the reftable backend when
/// configured.
///
/// # Parameters
///
/// - `git_dir` — path to the git directory (worktree gitdir or bare `.git`).
/// - `refname` — full ref name (e.g. `HEAD`, `refs/heads/main`, `CHERRY_PICK_HEAD`).
///
/// # Errors
///
/// Propagates I/O and reftable errors other than "not found".
pub fn read_raw_ref(git_dir: &Path, refname: &str) -> Result<RawRefLookup> {
    let store = open_ref_store(git_dir)?;
    match store.read_raw(refname)? {
        Some(_) => Ok(RawRefLookup::Exists),
        None => {
            let (storage_dir, stor_name) =
                crate::worktree_ref::resolve_ref_storage(git_dir, refname);
            let path = storage_dir.join(&stor_name);
            if fs::symlink_metadata(&path)
                .map(|m| m.is_dir())
                .unwrap_or(false)
            {
                Ok(RawRefLookup::IsDirectory)
            } else {
                Ok(RawRefLookup::NotFound)
            }
        }
    }
}

/// Lock file path for a loose ref file (`<refpath>.lock`), matching Git's naming for nested refs.
#[must_use]
pub fn lock_path_for_ref(path: &Path) -> PathBuf {
    let mut s = path.as_os_str().to_owned();
    s.push(".lock");
    PathBuf::from(s)
}

/// First packed ref name strictly under `refname/` (sorted `packed-refs` prefix scan).
fn first_packed_descendant_ref(store: &Path, refname: &str) -> Result<Option<String>> {
    let leaf_dir = format!("{refname}/");
    let map = read_packed_refs_map_for_prefix(store, refname)?;
    let sorted: BTreeSet<String> = map.keys().cloned().collect();
    Ok(sorted
        .range(leaf_dir.clone()..)
        .next()
        .filter(|name| name.starts_with(&leaf_dir))
        .cloned())
}

fn packed_ref_name_exists(git_dir: &Path, refname: &str) -> Result<bool> {
    Ok(lookup_packed_ref(git_dir, refname)?.is_some())
}

/// Whether any name in `sorted_packed` namespace-conflicts with `candidate`.
///
/// Uses prefix walks and one sorted range probe — `O(log n)` in the number of
/// packed refs — instead of scanning every packed name.
pub(crate) fn packed_refname_namespace_conflict(
    sorted_packed: &BTreeSet<String>,
    candidate: &str,
) -> bool {
    let segments: Vec<&str> = candidate.split('/').filter(|s| !s.is_empty()).collect();
    if segments.len() > 1 {
        let mut dirname = String::new();
        for part in &segments[..segments.len() - 1] {
            if !dirname.is_empty() {
                dirname.push('/');
            }
            dirname.push_str(part);
            if sorted_packed.contains(&dirname) {
                return true;
            }
        }
    }

    let leaf_dir = format!("{candidate}/");
    if let Some(existing) = sorted_packed.range(leaf_dir.clone()..).next() {
        if existing.starts_with(&leaf_dir) {
            return true;
        }
    }
    false
}

fn packed_ref_namespace_conflict(git_dir: &Path, refname: &str) -> Result<bool> {
    Ok(PackedRefs::load(git_dir)?.has_namespace_conflict(refname))
}

/// Returns true if `packed-refs` in the ref storage directory for `refname` contains that name.
///
/// Used to mirror Git's `is_packed_transaction_needed` behaviour: deleting a ref may open a nested
/// packed-refs transaction whose abort runs the `reference-transaction` hook in the `aborted`
/// state between `preparing` and `prepared` on the main transaction.
///
/// Returns `false` for reftable repositories and for `HEAD` (packed-refs does not store `HEAD`).
///
/// # Errors
///
/// Propagates I/O errors reading `packed-refs`.
pub fn packed_refs_entry_exists(git_dir: &Path, refname: &str) -> Result<bool> {
    if refname == "HEAD" {
        return Ok(false);
    }
    if open_ref_store(git_dir)?.format() != RefStorageFormat::Files {
        return Ok(false);
    }
    let storage_dir = ref_storage_dir(git_dir, refname);
    packed_ref_name_exists(&storage_dir, refname)
}

/// Why a reference name cannot be created (Git `refs_verify_refname_available` style).
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum RefnameUnavailable {
    /// An ancestor ref already exists in the store (e.g. `refs/foo` blocks `refs/foo/bar`).
    AncestorExists {
        /// Existing ref that blocks creation.
        blocking: String,
        /// Ref the caller tried to create.
        new_ref: String,
    },
    /// A descendant ref already exists (e.g. `refs/foo/bar` blocks `refs/foo`).
    DescendantExists {
        /// Existing ref under `new_ref/`.
        blocking: String,
        /// Ref the caller tried to create.
        new_ref: String,
    },
    /// Two refnames in the same batch are mutually incompatible (parent vs child).
    SameBatch {
        /// Ref being validated (Git prints this first).
        refname: String,
        /// Other ref in the batch (parent dirname or descendant name).
        other: String,
    },
}

impl RefnameUnavailable {
    /// Suffix after `cannot lock ref '<display_ref>': ` for stderr (no trailing newline).
    #[must_use]
    pub fn lock_message_suffix(&self) -> String {
        match self {
            RefnameUnavailable::AncestorExists { blocking, new_ref } => {
                format!("'{blocking}' exists; cannot create '{new_ref}'")
            }
            RefnameUnavailable::DescendantExists { blocking, new_ref } => {
                format!("'{blocking}' exists; cannot create '{new_ref}'")
            }
            RefnameUnavailable::SameBatch { refname, other } => {
                format!("cannot process '{refname}' and '{other}' at the same time")
            }
        }
    }
}

fn find_descendant_in_sorted_extras(
    dirname_with_slash: &str,
    extras: &BTreeSet<String>,
) -> Option<String> {
    let start = extras
        .range(dirname_with_slash.to_string()..)
        .next()
        .cloned()?;
    if start.starts_with(dirname_with_slash) {
        Some(start)
    } else {
        None
    }
}

/// Whether a network-advertised ref name is safe to accept during fetch.
///
/// Delegates to [`crate::check_ref_format::is_valid_fetch_advertised_ref`].
#[must_use]
pub fn is_valid_fetch_advertised_ref(name: &str) -> bool {
    crate::check_ref_format::is_valid_fetch_advertised_ref(name)
}

/// Whether a name from a protocol-v2 `ls-refs` response should be kept.
///
/// `HEAD` is valid without a `refs/` prefix; every other name must pass
/// [`is_valid_fetch_advertised_ref`].
#[must_use]
pub fn is_valid_ls_refs_advertised_name(name: &str) -> bool {
    name == "HEAD" || is_valid_fetch_advertised_ref(name)
}

/// Whether a ref name is safe to store under the ref backend (post-refspec mapping).
#[must_use]
pub fn is_valid_storable_ref_name(name: &str) -> bool {
    is_valid_fetch_advertised_ref(name)
}

/// Whether a symref target from a ref advertisement is safe to record.
#[must_use]
pub fn is_valid_advertised_symref_target(name: &str) -> bool {
    crate::check_ref_format::is_valid_advertised_symref_target(name)
}

/// Verify that `refname` can be created without directory/file conflicts with the ref store
/// and with other refnames queued in the same transaction (`extras`).
///
/// `skip` names are ignored when checking the filesystem (updates that delete or replace
/// those refs in the same batch). Matches Git's `refs_verify_refname_available`.
///
/// # Parameters
///
/// - `git_dir` — repository git directory.
/// - `refname` — full ref name to create.
/// - `extras` — other refnames touched in the same stdin batch / transaction (sorted set).
/// - `skip` — refnames that may be deleted or updated away in the same batch.
pub fn verify_refname_available_for_create(
    git_dir: &Path,
    refname: &str,
    extras: &BTreeSet<String>,
    skip: &HashSet<String>,
) -> std::result::Result<(), RefnameUnavailable> {
    // `Repository::git_dir` may be a relative path (e.g. `.git`); resolve so lookups match the
    // on-disk ref store regardless of process cwd (test harness runs from `trash/.git/...`).
    let git_dir = fs::canonicalize(git_dir).unwrap_or_else(|_| git_dir.to_path_buf());
    let mut seen_dirnames: HashSet<String> = HashSet::new();
    let segments: Vec<&str> = refname.split('/').filter(|s| !s.is_empty()).collect();
    if segments.len() <= 1 {
        // No slash-separated parent prefixes (e.g. `HEAD`).
    } else {
        let mut dirname = String::new();
        for part in &segments[..segments.len() - 1] {
            if !dirname.is_empty() {
                dirname.push('/');
            }
            dirname.push_str(part);

            if !seen_dirnames.insert(dirname.clone()) {
                continue;
            }

            if skip.contains(&dirname) {
                continue;
            }

            match read_raw_ref(&git_dir, &dirname) {
                Ok(RawRefLookup::Exists) => {
                    return Err(RefnameUnavailable::AncestorExists {
                        blocking: dirname.clone(),
                        new_ref: refname.to_owned(),
                    });
                }
                // A directory at `refs/prefix` is normal when storing `refs/prefix/child`; only a
                // real ref (loose file or packed line) blocks creating `refs/prefix/...`.
                Ok(RawRefLookup::NotFound | RawRefLookup::IsDirectory) => {}
                Err(_) => {}
            }

            if extras.contains(&dirname) {
                return Err(RefnameUnavailable::SameBatch {
                    refname: refname.to_owned(),
                    other: dirname.clone(),
                });
            }
        }
    }

    let mut leaf_dir = String::with_capacity(refname.len() + 1);
    leaf_dir.push_str(refname);
    leaf_dir.push('/');

    // Loose descendants can only exist inside a `<refname>/` directory; packed
    // and stray-file descendants are checked separately below. Skipping the
    // listing when no such directory exists keeps batch creates linear: listing
    // a missing directory walks its parent, so a clone writing N tags would
    // otherwise read every sibling ref N times.
    let packed_dir = common_dir(&git_dir).unwrap_or_else(|| git_dir.clone());
    let may_have_loose_descendants = packed_dir.join("reftable").is_dir()
        || git_dir.join(refname).is_dir()
        || packed_dir.join(refname).is_dir();
    let under = if may_have_loose_descendants {
        list_refs(&git_dir, &leaf_dir).unwrap_or_default()
    } else {
        Vec::new()
    };
    if under.is_empty() {
        if let Ok(Some(name)) = first_packed_descendant_ref(&packed_dir, refname) {
            if !skip.contains(&name) {
                return Err(RefnameUnavailable::DescendantExists {
                    blocking: name,
                    new_ref: refname.to_owned(),
                });
            }
        }
        if packed_dir != git_dir {
            if let Ok(Some(name)) = first_packed_descendant_ref(&git_dir, refname) {
                if !skip.contains(&name) {
                    return Err(RefnameUnavailable::DescendantExists {
                        blocking: name,
                        new_ref: refname.to_owned(),
                    });
                }
            }
        }
    }
    if under.is_empty()
        && fs::symlink_metadata(git_dir.join(refname))
            .map(|m| m.is_dir())
            .unwrap_or(false)
    {
        let mut blocking: Option<String> = None;
        let dir_path = git_dir.join(refname);
        if let Ok(read) = fs::read_dir(&dir_path) {
            for entry in read.flatten() {
                let path = entry.path();
                let Ok(meta) = fs::metadata(&path) else {
                    continue;
                };
                if !meta.is_file() {
                    continue;
                }
                let name = entry.file_name().to_string_lossy().into_owned();
                let full = format!("{refname}/{name}");
                blocking = Some(full);
                break;
            }
        }
        if let Some(b) = blocking {
            if !skip.contains(&b) {
                return Err(RefnameUnavailable::DescendantExists {
                    blocking: b,
                    new_ref: refname.to_owned(),
                });
            }
        }
    }

    for (existing, _) in under {
        if skip.contains(&existing) {
            continue;
        }
        return Err(RefnameUnavailable::DescendantExists {
            blocking: existing,
            new_ref: refname.to_owned(),
        });
    }

    if let Some(extra) = find_descendant_in_sorted_extras(&leaf_dir, extras) {
        if !skip.contains(&extra) {
            return Err(RefnameUnavailable::SameBatch {
                refname: refname.to_owned(),
                other: extra,
            });
        }
    }

    Ok(())
}

/// One ref create/update/delete in a batch transaction (see [`crate::gc::update_refs`]).
#[derive(Clone, Debug)]
pub struct RefBatchItem {
    /// Full ref name (e.g. `refs/heads/main`).
    pub name: String,
    /// New oid to write, or `None` to delete the ref.
    pub new_oid: Option<ObjectId>,
}

/// Verify that every *new* ref in a batch can be created without D/F or namespace
/// conflicts with the existing store or other items in the batch.
///
/// Matches Git's pre-lock `refs_verify_refnames_available` checks with an empty
/// `skip` list (refs scheduled for deletion in the same batch do not suppress
/// ancestor/descendant conflicts — see t1404 D/F batch tests).
///
/// # Errors
///
/// Returns [`RefnameUnavailable`] describing the first conflict.
pub fn verify_ref_transaction_batch(
    git_dir: &Path,
    items: &[RefBatchItem],
) -> std::result::Result<(), RefnameUnavailable> {
    if let Some((parent, child)) =
        batch_refname_prefix_conflict(items.iter().map(|i| i.name.as_str()))
    {
        return Err(RefnameUnavailable::SameBatch {
            refname: child,
            other: parent,
        });
    }

    if crate::ref_storage::detect_format(git_dir).is_ok_and(|f| f.is_reftable()) {
        return crate::reftable::verify_ref_transaction_batch_reftable(git_dir, items);
    }

    let extras: BTreeSet<String> = items.iter().map(|i| i.name.clone()).collect();
    let empty_skip = HashSet::new();
    for item in items {
        let Some(_oid) = item.new_oid else {
            continue;
        };
        if resolve_ref(git_dir, &item.name).is_ok() {
            continue;
        }
        verify_refname_available_for_create(git_dir, &item.name, &extras, &empty_skip)?;
    }
    Ok(())
}

/// First strict prefix conflict in a batch, if any (sorted adjacent scan).
pub(crate) fn batch_refname_prefix_conflict<'a>(
    names: impl Iterator<Item = &'a str>,
) -> Option<(String, String)> {
    let mut sorted: Vec<&str> = names.collect();
    sorted.sort_unstable();
    for pair in sorted.windows(2) {
        let (a, b) = (pair[0], pair[1]);
        if refname_is_strict_prefix(a, b) {
            return Some((a.to_owned(), b.to_owned()));
        }
        if refname_is_strict_prefix(b, a) {
            return Some((b.to_owned(), a.to_owned()));
        }
    }
    None
}

fn refname_is_strict_prefix(parent: &str, child: &str) -> bool {
    child.len() > parent.len()
        && child.as_bytes().get(parent.len()) == Some(&b'/')
        && child.starts_with(parent)
}

fn packed_refs_unexpected_line(path: &Path, line: impl Into<String>) -> Error {
    Error::PackedRefsUnexpectedLine {
        path: path.display().to_string(),
        line: line.into(),
    }
}

fn packed_refs_unterminated_line(path: &Path, line: impl Into<String>) -> Error {
    Error::PackedRefsUnexpectedLine {
        path: path.display().to_string(),
        line: line.into(),
    }
}

/// Validate a `^<peeled-oid>` line and return the peeled id.
fn parse_packed_ref_peel_line(path: &Path, line: &str, expect_peel: bool) -> Result<ObjectId> {
    if !expect_peel {
        return Err(packed_refs_unexpected_line(path, line));
    }
    line.strip_prefix('^')
        .and_then(|inner| ObjectId::from_hex(inner).ok())
        .ok_or_else(|| packed_refs_unexpected_line(path, line))
}

/// Id-prefix length and id of a record line: 40 or 64 hex digits followed by a space.
fn packed_line_oid(line: &str) -> Option<(usize, ObjectId)> {
    let bytes = line.as_bytes();
    let hex_len = [HashAlgo::Sha1.hex_len(), HashAlgo::Sha256.hex_len()]
        .into_iter()
        .find(|&len| bytes.get(len) == Some(&b' '))?;
    // Byte `hex_len` is an ASCII space, so the slice ends on a char boundary.
    let oid = ObjectId::from_hex(&line[..hex_len]).ok()?;
    Some((hex_len, oid))
}

fn packed_ref_data_line_refname(line: &str) -> Option<&str> {
    let bytes = line.as_bytes();
    let mut j = 0usize;
    while j < bytes.len() && bytes[j].is_ascii_hexdigit() {
        j += 1;
    }
    if !ObjectId::is_hex_len(j) || j + 1 >= bytes.len() || bytes[j] != b' ' {
        return None;
    }
    let refname = &line[j + 1..];
    if refname.is_empty() || refname.as_bytes().iter().any(|b| b.is_ascii_whitespace()) {
        return None;
    }
    Some(refname)
}

fn parse_packed_ref_data_line(
    path: &Path,
    line: &str,
    ref_opts: &RefNameOptions,
) -> Result<(String, ObjectId)> {
    let (refname, oid) = parse_packed_ref_data_line_borrowed(path, line, ref_opts)?;
    Ok((refname.to_owned(), oid))
}

fn parse_packed_ref_data_line_borrowed<'a>(
    path: &Path,
    line: &'a str,
    ref_opts: &RefNameOptions,
) -> Result<(&'a str, ObjectId)> {
    let Some((hex_len, oid)) = packed_line_oid(line) else {
        return Err(packed_refs_unexpected_line(path, line));
    };
    let refname = &line[hex_len + 1..];
    if refname.is_empty() || refname.as_bytes().iter().any(|b| b.is_ascii_whitespace()) {
        return Err(packed_refs_unexpected_line(path, line));
    }
    if check_refname_format(refname, ref_opts).is_err() {
        return Err(packed_refs_unexpected_line(path, line));
    }
    Ok((refname, oid))
}

/// Parse `packed-refs` bytes the way Git reads them for ref listing (strict).
/// In-memory view of a `packed-refs` file for indexed lookup without a full parse.
#[derive(Debug, Clone)]
pub(crate) struct PackedRefsFileView {
    data: std::sync::Arc<crate::pack_map::PackData>,
    /// The header declares the `sorted` trait, so lookups and prefix scans binary-search the
    /// bytes in place. Like Git, the claim is trusted; `fsck` reports a file that breaks it.
    sorted: bool,
    /// Hex length of the repository's object ids; the refname starts one byte after it.
    hex_len: usize,
    /// Offset just past the first line when it is a comment (the header), else 0.
    body_start: usize,
    /// Which records the header promises a peel line for.
    peel_trait: PackedPeelTrait,
}

impl PackedRefsFileView {
    /// [`Self::from_data`] over an owned buffer.
    #[cfg(test)]
    fn from_bytes(path: &Path, data: Vec<u8>, hash_algo: crate::objects::HashAlgo) -> Result<Self> {
        Self::from_data(path, crate::pack_map::PackData::from_owned(data), hash_algo)
    }

    /// View `data`, the (possibly memory-mapped) bytes of `path`, for a repository using
    /// `hash_algo`.
    ///
    /// Checks only what Git checks before any lookup: a final newline, a last line (after
    /// the header) long enough to hold an object id, and here also a UTF-8 header. Opening
    /// reads the header and the last line, nothing in between; each scan and lookup parses
    /// the lines it reaches. Records are the lines with an id-sized prefix, a space and a
    /// name.
    fn from_data(
        path: &Path,
        data: std::sync::Arc<crate::pack_map::PackData>,
        hash_algo: crate::objects::HashAlgo,
    ) -> Result<Self> {
        let hex_len = hash_algo.hex_len();
        if data.is_empty() {
            return Ok(Self {
                data,
                sorted: false,
                hex_len,
                body_start: 0,
                peel_trait: PackedPeelTrait::None,
            });
        }
        if !data.ends_with(b"\n") {
            let tail = std::str::from_utf8(&data)
                .map(|s| s.rsplit('\n').next().unwrap_or(s))
                .unwrap_or("<invalid utf-8>");
            return Err(packed_refs_unterminated_line(path, tail));
        }
        // Only the header (the leading comment lines) is decoded up front; scans and lookups
        // check the encoding of the lines they parse.
        let text = std::str::from_utf8(&data[..packed_refs_leading_comments_end(&data)])
            .map_err(|_| packed_refs_unexpected_line(path, "<invalid utf-8>"))?;
        // Ranged scans never reach the end of a sorted file, so check the last line up front, as
        // Git does: past the header, it must be long enough to hold an object id.
        let body_start = if data.starts_with(b"#") {
            memchr::memchr(b'\n', &data).map_or(data.len(), |nl| nl + 1)
        } else {
            0
        };
        let body = &data[body_start..];
        if let Some(rest) = body.strip_suffix(b"\n") {
            let last_line = memchr::memrchr(b'\n', rest).map_or(rest, |nl| &rest[nl + 1..]);
            if last_line.len() < hex_len + 1 {
                return Err(packed_refs_unexpected_line(
                    path,
                    String::from_utf8_lossy(last_line),
                ));
            }
        }
        Ok(Self {
            sorted: packed_refs_file_declares_sorted(text),
            hex_len,
            body_start,
            peel_trait: packed_refs_peel_trait(text),
            data,
        })
    }

    /// The name of the record at `line_start`: everything after `<hex id> `.
    fn record_name(&self, line_start: usize) -> &[u8] {
        let end = packed_line_end(&self.data, line_start);
        &self.data[line_start + self.hex_len + 1..end]
    }

    fn record_cmp(&self, line_start: usize, name: &str) -> std::cmp::Ordering {
        self.record_name(line_start).cmp(name.as_bytes())
    }

    /// Start of the first record beginning at or after the line start `from` and before
    /// `limit`.
    fn next_record(&self, from: usize, limit: usize) -> Option<usize> {
        let hex_len = self.hex_len;
        let mut start = from;
        while start < limit {
            let rest = &self.data[start..];
            // A peel line (`^`, an id, a newline) needs no search: any line starting inside
            // it ends at that newline, too short to be a record.
            if rest[0] == b'^' && rest.get(hex_len + 1) == Some(&b'\n') {
                start += hex_len + 2;
                continue;
            }
            let end = memchr::memchr(b'\n', rest).unwrap_or(rest.len());
            if packed_line_is_record(&rest[..end], hex_len) {
                return Some(start);
            }
            start += end + 1;
        }
        None
    }

    /// Start of the last record beginning before the line start `before`.
    fn prev_record(&self, before: usize) -> Option<usize> {
        let mut end = before;
        while end > 0 {
            let line_end = end - 1;
            let start = memchr::memrchr(b'\n', &self.data[..line_end]).map_or(0, |nl| nl + 1);
            if packed_line_is_record(&self.data[start..line_end], self.hex_len) {
                return Some(start);
            }
            end = start;
        }
        None
    }

    /// Starts of every record, in file order.
    fn records(&self) -> impl Iterator<Item = usize> + '_ {
        let len = self.data.len();
        std::iter::successors(self.next_record(0, len), move |&start| {
            self.next_record(packed_line_end(&self.data, start) + 1, len)
        })
    }

    /// Binary search of a sorted file for `name`: `Ok` with the start of a record named
    /// `name`, else `Err` with the start of the first record after every record found
    /// smaller (the file length when there is none).
    ///
    /// Each probe takes the first record starting on or after the line holding the midpoint,
    /// so the search only reads the lines it probes. In a file whose records really are in
    /// order the answer is exact; otherwise it is whatever the probes lead to, as in Git.
    fn search(&self, name: &str) -> std::result::Result<usize, usize> {
        let len = self.data.len();
        let mut lo = self.body_start;
        let mut hi = len;
        while lo < hi {
            let mid = lo + (hi - lo) / 2;
            let line = memchr::memrchr(b'\n', &self.data[lo..mid]).map_or(lo, |nl| lo + nl + 1);
            let Some(record) = self.next_record(line, hi) else {
                hi = line;
                continue;
            };
            match self.record_cmp(record, name) {
                std::cmp::Ordering::Less => lo = packed_line_end(&self.data, record) + 1,
                std::cmp::Ordering::Greater => hi = record,
                std::cmp::Ordering::Equal => return Ok(record),
            }
        }
        Err(self.next_record(lo, len).unwrap_or(len))
    }

    /// Start of the first record of a sorted file not less than `name` (or the file length).
    fn lower_bound(&self, name: &str) -> usize {
        let (Ok(start) | Err(start)) = self.search(name);
        start
    }

    /// Object id stored for `refname`, and optional peeled tag target from the following `^` line.
    fn lookup_entry(
        &self,
        path: &Path,
        refname: &str,
    ) -> Result<Option<(ObjectId, Option<ObjectId>)>> {
        let ref_opts = RefNameOptions {
            allow_onelevel: false,
            refspec_pattern: false,
            normalize: false,
        };
        let line_start = if self.sorted {
            self.search(refname).ok()
        } else {
            self.records()
                .find(|&start| self.record_cmp(start, refname).is_eq())
        };
        let Some(start) = line_start else {
            return Ok(None);
        };
        let (name, oid) = parse_packed_line_at(path, &self.data, start, &ref_opts)?;
        debug_assert_eq!(name, refname);
        let line_end = packed_line_end(&self.data, start);
        if line_end + 1 < self.data.len() && self.data[line_end + 1] == b'^' {
            let peel_line = packed_line_as_str(&self.data, line_end + 1);
            parse_packed_ref_peel_line(path, peel_line, true)?;
        }
        let peel = peel_oid_following_line(&self.data, start);
        Ok(Some((oid, peel)))
    }

    fn lookup_oid(&self, path: &Path, refname: &str) -> Result<Option<ObjectId>> {
        Ok(self.lookup_entry(path, refname)?.map(|(oid, _)| oid))
    }

    /// Smallest packed ref strictly under `refname/`, with its object id.
    ///
    /// A sorted file only parses the records sharing `refname` as a prefix.
    pub(crate) fn first_descendant(
        &self,
        path: &Path,
        refname: &str,
    ) -> Result<Option<(String, ObjectId)>> {
        let leaf_dir = format!("{refname}/");
        Ok(self
            .map_for_prefix(path, Some(refname))?
            .into_iter()
            .filter(|(name, _)| name.starts_with(&leaf_dir))
            .min_by(|a, b| a.0.cmp(&b.0)))
    }

    /// Refs whose names start with `prefix` (all refs for `None`).
    ///
    /// Every line the scan covers is parsed strictly, peel and comment lines included. In a
    /// sorted file a prefix scan covers the binary-searched range of matching records plus
    /// whatever lies between them and the records on either side, so a corrupt line
    /// in or next to the range is reported rather than skipped. Like Git, it does not read
    /// records further away. Scans without a prefix, of all of `refs/`, or of an unsorted
    /// file cover the whole file.
    fn map_for_prefix(
        &self,
        path: &Path,
        prefix: Option<&str>,
    ) -> Result<HashMap<String, ObjectId>> {
        self.map_for_prefix_filtered(path, prefix, None)
    }

    /// [`Self::map_for_prefix`], leaving out the records `keep` rejects. Rejected records are
    /// still parsed strictly; they are only spared the allocation.
    fn map_for_prefix_filtered(
        &self,
        path: &Path,
        prefix: Option<&str>,
        keep: Option<PackedRecordFilter<'_>>,
    ) -> Result<HashMap<String, ObjectId>> {
        let prefix_trim = prefix.map(|p| p.trim_end_matches('/'));
        let range_prefix = prefix_trim.filter(|p| self.sorted && !p.is_empty() && *p != "refs");
        let (begin, end) = match range_prefix {
            Some(prefix) => {
                let first = self.lower_bound(prefix);
                // In a file whose records are out of order the bounds can cross.
                let end = list_prefix_upper_bound(prefix)
                    .map_or(self.data.len(), |upper| self.lower_bound(&upper))
                    .max(first);
                // Start after the record before the range and its peel line (which belongs to
                // that record), so anything else up to the first record in range is checked.
                let begin = self.prev_record(first).map_or(0, |prev| {
                    let after = packed_line_end(&self.data, prev) + 1;
                    if self.data.get(after) == Some(&b'^') {
                        packed_line_end(&self.data, after) + 1
                    } else {
                        after
                    }
                });
                (begin, end)
            }
            None => (0, self.data.len()),
        };
        // Both bounds are line starts or the end of the file, so the region is whole lines.
        let region = std::str::from_utf8(&self.data[begin..end])
            .map_err(|_| packed_refs_unexpected_line(path, "<invalid utf-8>"))?;
        parse_packed_refs_region(path, region, prefix_trim, keep, self.peel_trait)
    }
}

/// What a `packed-refs` record tells about the object its ref names, given the file's
/// `peeled` / `fully-peeled` header traits.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) enum PackedPeel {
    /// The ref names an annotated tag that peels to this object.
    Peeled(ObjectId),
    /// The ref is known not to name an annotated tag.
    NotTag,
    /// The file does not say; the object must be read to peel it.
    Unknown,
}

/// Decides, from its storage name, object id and [`PackedPeel`], whether a `packed-refs`
/// record is listed.
pub(crate) type PackedRecordFilter<'a> = &'a dyn Fn(&str, &ObjectId, PackedPeel) -> bool;

/// Strictly parse the `packed-refs` lines of `region`, keeping refs that match `prefix`.
///
/// `region` starts at the beginning of the file or of a line that is not a peel line, and ends
/// at the end of the file or just before a ref line, so peel lines stay attached to their ref.
fn parse_packed_refs_region(
    path: &Path,
    region: &str,
    prefix: Option<&str>,
    keep: Option<PackedRecordFilter<'_>>,
    peel_trait: PackedPeelTrait,
) -> Result<HashMap<String, ObjectId>> {
    let ref_opts = RefNameOptions {
        allow_onelevel: false,
        refspec_pattern: false,
        normalize: false,
    };
    let mut map = HashMap::new();
    // With a filter, a record is decided once its peel line (if any) has been seen.
    let mut pending: Option<(&str, ObjectId, Option<ObjectId>)> = None;
    let flush = |map: &mut HashMap<String, ObjectId>,
                 pending: &mut Option<(&str, ObjectId, Option<ObjectId>)>| {
        let (Some(keep), Some((refname, oid, peeled))) = (keep, pending.take()) else {
            return;
        };
        let peel = if peel_trait.covers(refname) {
            peeled.map_or(PackedPeel::NotTag, PackedPeel::Peeled)
        } else {
            PackedPeel::Unknown
        };
        if keep(refname, &oid, peel) {
            map.insert(refname.to_owned(), oid);
        }
    };
    let mut expect_peel = false;
    let mut lines = region.split('\n').peekable();
    while let Some(line) = lines.next() {
        if line.is_empty() {
            if lines.peek().is_some() {
                return Err(packed_refs_unexpected_line(path, line));
            }
            break;
        }
        if line.starts_with('#') {
            flush(&mut map, &mut pending);
            expect_peel = false;
            continue;
        }
        if line.starts_with('^') {
            let peel = parse_packed_ref_peel_line(path, line, expect_peel)?;
            if let Some((_, _, peeled)) = pending.as_mut() {
                *peeled = Some(peel);
            }
            expect_peel = false;
            continue;
        }
        flush(&mut map, &mut pending);
        let (refname, oid) = parse_packed_ref_data_line_borrowed(path, line, &ref_opts)?;
        if prefix.is_none_or(|p| ref_name_matches_list_prefix(refname, p)) {
            if keep.is_some() {
                pending = Some((refname, oid, None));
            } else {
                map.insert(refname.to_owned(), oid);
            }
        }
        expect_peel = true;
    }
    flush(&mut map, &mut pending);
    Ok(map)
}

fn read_packed_refs_file_view(store: &Path) -> Result<Option<PackedRefsFileView>> {
    let packed_path = store::paths::packed_refs_path(store);
    // Writers publish `packed-refs` by renaming a new file over it, never by rewriting it in
    // place, so a large file can be mapped like a pack instead of copied.
    let data = match crate::pack_map::PackData::open_with_min_len(&packed_path, 0) {
        Ok(d) => d,
        Err(Error::Io(e)) if e.kind() == io::ErrorKind::NotFound => return Ok(None),
        Err(e) => return Err(e),
    };
    let hash_algo = crate::repo::read_repository_format_from_git_dir(store)
        .map(|format| format.hash_algo())
        .unwrap_or(crate::objects::HashAlgo::Sha1);
    Ok(Some(PackedRefsFileView::from_data(
        &packed_path,
        data,
        hash_algo,
    )?))
}

/// Whether `line` (without its newline) is shaped like a record: `hex_len` bytes, a space and
/// a non-empty name. Other lines are left for the strict parse.
fn packed_line_is_record(line: &[u8], hex_len: usize) -> bool {
    line.len() > hex_len + 1 && line[hex_len] == b' ' && !matches!(line[0], b'#' | b'^')
}

fn packed_line_end(data: &[u8], line_start: usize) -> usize {
    memchr::memchr(b'\n', &data[line_start..]).map_or(data.len(), |p| line_start + p)
}

fn packed_line_as_str(data: &[u8], line_start: usize) -> &str {
    std::str::from_utf8(&data[line_start..packed_line_end(data, line_start)]).unwrap_or("")
}

fn peel_oid_following_line(data: &[u8], line_start: usize) -> Option<ObjectId> {
    let line_end = packed_line_end(data, line_start);
    if line_end >= data.len() || data[line_end] != b'\n' {
        return None;
    }
    let peel_start = line_end + 1;
    if peel_start >= data.len() || data[peel_start] != b'^' {
        return None;
    }
    let peel_end = packed_line_end(data, peel_start);
    let inner = std::str::from_utf8(&data[peel_start + 1..peel_end]).ok()?;
    ObjectId::from_hex(inner.trim()).ok()
}

fn parse_packed_line_at(
    path: &Path,
    data: &[u8],
    line_start: usize,
    ref_opts: &RefNameOptions,
) -> Result<(String, ObjectId)> {
    let line = packed_line_as_str(data, line_start);
    parse_packed_ref_data_line(path, line, ref_opts)
}

pub(crate) fn parse_packed_refs_to_map(
    path: &Path,
    data: &[u8],
) -> Result<HashMap<String, ObjectId>> {
    parse_packed_refs_to_map_with_prefix(path, data, None)
}

/// Offset just past the comment lines (`#...\n`) at the start of `data`.
fn packed_refs_leading_comments_end(data: &[u8]) -> usize {
    let mut end = 0;
    while data.get(end) == Some(&b'#') {
        match memchr::memchr(b'\n', &data[end..]) {
            Some(nl) => end += nl + 1,
            None => return data.len(),
        }
    }
    end
}

/// Whether the `packed-refs` header comment lists Git's `sorted` trait (`pack-refs --all`).
fn packed_refs_file_declares_sorted(text: &str) -> bool {
    for line in text.split('\n') {
        if line.is_empty() {
            break;
        }
        if !line.starts_with('#') {
            break;
        }
        let body = line[1..].trim();
        let Some(traits) = body.strip_prefix("pack-refs with:") else {
            continue;
        };
        return traits.split_whitespace().any(|t| t == "sorted");
    }
    false
}

fn parse_packed_refs_to_map_with_prefix(
    path: &Path,
    data: &[u8],
    prefix_filter: Option<&str>,
) -> Result<HashMap<String, ObjectId>> {
    if data.is_empty() {
        return Ok(HashMap::new());
    }
    if data.contains(&b'\r') {
        return Err(packed_refs_unexpected_line(
            path,
            "<contains carriage return>",
        ));
    }
    if !data.ends_with(b"\n") {
        let tail = std::str::from_utf8(data)
            .map(|s| s.rsplit('\n').next().unwrap_or(s))
            .unwrap_or("<invalid utf-8>");
        return Err(packed_refs_unterminated_line(path, tail));
    }
    let text = std::str::from_utf8(data)
        .map_err(|_| packed_refs_unexpected_line(path, "<invalid utf-8>"))?;

    let ref_opts = RefNameOptions {
        allow_onelevel: false,
        refspec_pattern: false,
        normalize: false,
    };

    let mut map = HashMap::new();
    let mut expect_peel = false;
    let prefix_trim = prefix_filter.map(|p| p.trim_end_matches('/'));
    let packed_sorted = packed_refs_file_declares_sorted(text);
    let prefix_upper = if packed_sorted {
        prefix_trim.and_then(list_prefix_upper_bound)
    } else {
        None
    };
    let mut lines = text.split('\n').peekable();
    while let Some(line) = lines.next() {
        if line.is_empty() {
            if lines.peek().is_some() {
                return Err(packed_refs_unexpected_line(path, line));
            }
            break;
        }
        if line.starts_with('#') {
            expect_peel = false;
            continue;
        }
        if line.starts_with('^') {
            parse_packed_ref_peel_line(path, line, expect_peel)?;
            expect_peel = false;
            continue;
        }

        if let Some(prefix) = prefix_trim {
            let Some(refname) = packed_ref_data_line_refname(line) else {
                return Err(packed_refs_unexpected_line(path, line));
            };
            if packed_sorted {
                if refname < prefix {
                    expect_peel = true;
                    continue;
                }
                if let Some(upper) = &prefix_upper {
                    if refname >= upper.as_str() {
                        break;
                    }
                }
            }
            if !ref_name_matches_list_prefix(refname, prefix) {
                expect_peel = true;
                continue;
            }
        }
        let (refname, oid) = parse_packed_ref_data_line(path, line, &ref_opts)?;
        map.insert(refname, oid);
        expect_peel = true;
    }
    Ok(map)
}

pub(crate) fn read_packed_refs_map(store: &Path) -> Result<HashMap<String, ObjectId>> {
    read_packed_refs_map_for_prefix(store, "")
}

pub(crate) fn read_packed_refs_map_for_prefix(
    store: &Path,
    prefix: &str,
) -> Result<HashMap<String, ObjectId>> {
    read_packed_refs_map_for_prefix_filtered(store, prefix, None)
}

/// [`read_packed_refs_map_for_prefix`], leaving out the records `keep` rejects.
pub(crate) fn read_packed_refs_map_for_prefix_filtered(
    store: &Path,
    prefix: &str,
    keep: Option<PackedRecordFilter<'_>>,
) -> Result<HashMap<String, ObjectId>> {
    let Some(view) = read_packed_refs_file_view(store)? else {
        return Ok(HashMap::new());
    };
    let packed_path = store::paths::packed_refs_path(store);
    let filter = if prefix.is_empty() {
        None
    } else {
        Some(prefix)
    };
    view.map_for_prefix_filtered(&packed_path, filter, keep)
}

/// What a `packed-refs` header promises about its `^` peel lines.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum PackedPeelTrait {
    /// No `peeled` trait: peel lines may be missing for any ref.
    None,
    /// `peeled`: every annotated tag under `refs/tags/` has a peel line.
    Tags,
    /// `fully-peeled`: every ref that names an annotated tag has a peel line.
    All,
}

impl PackedPeelTrait {
    /// Whether a ref named `refname` without a peel line is known not to name an annotated tag.
    fn covers(self, refname: &str) -> bool {
        match self {
            Self::None => false,
            Self::Tags => refname.starts_with("refs/tags/"),
            Self::All => true,
        }
    }
}

/// Read-only snapshot of the peel lines recorded in `packed-refs`.
///
/// Lets callers that peel many refs (log decorations, for example) skip reading tag
/// objects when `packed-refs` already records the peeled value, the same shortcut
/// Git takes when iterating packed refs.
///
/// Lookups trust the record shape found by [`PackedRefsFileView`] and skip the strict
/// per-line validation: callers pair this with a ref listing that already parsed the
/// file strictly.
pub(crate) struct PackedRefPeels {
    view: Option<PackedRefsFileView>,
    /// Record start by name for unsorted files, where binary search is not exact.
    unsorted: Option<HashMap<Box<[u8]>, usize>>,
    peel_trait: PackedPeelTrait,
    /// Start of the record after the last hit in a sorted file (or the file length), so
    /// lookups made in name order (a ref listing) are answered without a binary search.
    next: std::cell::Cell<usize>,
}

impl PackedRefPeels {
    /// Load the peel snapshot for the files ref store backing `git_dir`.
    ///
    /// A missing `packed-refs`, or a ref store that is not the files backend, yields a
    /// snapshot that knows nothing (every [`Self::peeled`] call returns `None`).
    ///
    /// # Errors
    ///
    /// Returns [`Error::Io`] when `packed-refs` exists but cannot be read, or
    /// [`Error::PackedRefsUnexpectedLine`] when it is malformed.
    pub(crate) fn load(git_dir: &Path, format: RefStorageFormat) -> Result<Self> {
        if format != RefStorageFormat::Files {
            return Ok(Self::from_view(None));
        }
        let store = common_dir(git_dir).unwrap_or_else(|| git_dir.to_path_buf());
        Ok(Self::from_view(read_packed_refs_file_view(&store)?))
    }

    /// [`Self::load`] for the refs of `store`, the ref store opened for `git_dir`.
    ///
    /// A files backend hands over the `packed-refs` view it already holds (a listing just
    /// read it), so the file is neither mapped nor indexed a second time.
    ///
    /// # Errors
    ///
    /// Same as [`Self::load`].
    pub(crate) fn for_store(store: &dyn store::RefStore, git_dir: &Path) -> Result<Self> {
        match store.as_files() {
            Some(files) => Ok(Self::from_view(files.packed_refs_view()?)),
            None => Self::load(git_dir, store.format()),
        }
    }

    fn from_view(view: Option<PackedRefsFileView>) -> Self {
        let empty = Self {
            view: None,
            unsorted: None,
            peel_trait: PackedPeelTrait::None,
            next: std::cell::Cell::new(0),
        };
        let Some(view) = view else {
            return empty;
        };
        let peel_trait = view.peel_trait;
        if peel_trait == PackedPeelTrait::None {
            return empty;
        }
        let unsorted = (!view.sorted).then(|| {
            view.records()
                .map(|start| (Box::<[u8]>::from(view.record_name(start)), start))
                .collect()
        });
        let first = view
            .next_record(view.body_start, view.data.len())
            .unwrap_or(view.data.len());
        Self {
            view: Some(view),
            unsorted,
            peel_trait,
            next: std::cell::Cell::new(first),
        }
    }

    /// Peeled value of `refname` when `packed-refs` vouches for it.
    ///
    /// `oid` is the ref's current value; packed data is only trusted when it records the
    /// same value (a loose ref overriding the packed one is not covered).
    ///
    /// # Returns
    ///
    /// - `Some(Some(peeled))`: the ref names an annotated tag that peels to `peeled`
    ///   (the innermost non-tag object).
    /// - `Some(None)`: the ref is known not to name an annotated tag.
    /// - `None`: `packed-refs` does not say; the caller must peel the object itself.
    pub(crate) fn peeled(&self, refname: &str, oid: &ObjectId) -> Option<Option<ObjectId>> {
        if !self.peel_trait.covers(refname) {
            return None;
        }
        let view = self.view.as_ref()?;
        let start = match &self.unsorted {
            Some(map) => *map.get(refname.as_bytes())?,
            None => {
                let len = view.data.len();
                let hint = self.next.get();
                let start = if hint < len && view.record_cmp(hint, refname).is_eq() {
                    hint
                } else {
                    view.search(refname).ok()?
                };
                let after = packed_line_end(&view.data, start) + 1;
                self.next.set(view.next_record(after, len).unwrap_or(len));
                start
            }
        };
        let hex = std::str::from_utf8(&view.data[start..start + view.hex_len]).ok()?;
        let packed_oid = ObjectId::from_hex(hex).ok()?;
        (packed_oid == *oid).then(|| peel_oid_following_line(&view.data, start))
    }
}

/// The peel guarantee declared by the `# pack-refs with:` header of `text`.
fn packed_refs_peel_trait(text: &str) -> PackedPeelTrait {
    let Some(header) = text.strip_prefix("# pack-refs with: ") else {
        return PackedPeelTrait::None;
    };
    let traits = header.split('\n').next().unwrap_or_default();
    let mut peel_trait = PackedPeelTrait::None;
    for t in traits.split_whitespace() {
        match t {
            "fully-peeled" => return PackedPeelTrait::All,
            "peeled" => peel_trait = PackedPeelTrait::Tags,
            _ => {}
        }
    }
    peel_trait
}

fn acquire_packed_refs_lock(
    git_dir: &Path,
    lock: &Path,
    lock_display: &Path,
) -> Result<crate::lockfile::LockFile> {
    use crate::lockfile::{LockError, LockFile, LockWait};
    let wait = LockWait::packed_refs_for_git_dir(git_dir);
    LockFile::acquire(lock, wait).map_err(|err| match err {
        LockError::Held { .. } => Error::from(RefLockError::PackedRefsLockHeld {
            lock_path: lock_display.display().to_string(),
        }),
        LockError::Io { source, .. } => Error::Io(source),
    })
}

/// Look up a refname in `packed-refs`.
pub(crate) fn lookup_packed_ref(git_dir: &Path, refname: &str) -> Result<Option<ObjectId>> {
    let Some(view) = read_packed_refs_file_view(git_dir)? else {
        return Ok(None);
    };
    let packed_path = store::paths::packed_refs_path(git_dir);
    view.lookup_oid(&packed_path, refname)
}

/// Look up a refname and optional peeled tag oid in `packed-refs`.
#[cfg(test)]
pub(crate) fn lookup_packed_ref_with_peel(
    git_dir: &Path,
    refname: &str,
) -> Result<Option<(ObjectId, Option<ObjectId>)>> {
    let Some(view) = read_packed_refs_file_view(git_dir)? else {
        return Ok(None);
    };
    let packed_path = store::paths::packed_refs_path(git_dir);
    view.lookup_entry(&packed_path, refname)
}

/// Write a symbolic ref (e.g. `NOTES_MERGE_REF` → `refs/notes/m`).
///
/// For reftable-backed repositories this dispatches to the reftable writer.
///
/// # Errors
///
/// Returns [`Error::InvalidRef`] when `refname` is not safe for ref storage (e.g. path
/// traversal under `refs/`), on a namespace conflict, or [`Error::Io`] on filesystem errors.
pub fn write_symbolic_ref(git_dir: &Path, refname: &str, target: &str) -> Result<()> {
    store_write_value(
        git_dir,
        refname,
        Some(StoreRawRef::Symbolic(target.to_owned())),
        Expected::Any,
        None,
    )
}

pub(crate) fn ensure_refname_safe_for_storage(refname: &str) -> Result<()> {
    if let Some(rest) = refname.strip_prefix("refs/") {
        if rest.is_empty() || !crate::check_ref_format::is_valid_fetch_advertised_ref(refname) {
            return Err(Error::InvalidRef(format!(
                "refusing to update ref with bad name '{refname}'"
            )));
        }
        return Ok(());
    }
    if crate::check_ref_format::refname_is_safe(refname) {
        Ok(())
    } else {
        Err(Error::InvalidRef(format!(
            "refusing to update ref with bad name '{refname}'"
        )))
    }
}

/// Write a ref, creating parent directories as needed.
///
/// Dispatches to the reftable backend when `extensions.refStorage = reftable`.
///
/// # Parameters
///
/// - `git_dir` — path to the git directory.
/// - `refname` — reference name (e.g. `"refs/heads/main"`).
/// - `oid` — the new target object ID.
///
/// # Errors
///
/// Returns [`Error::InvalidRef`] when `refname` is not safe for ref storage (e.g. path
/// traversal under `refs/`), on a namespace conflict, or [`Error::Io`] on filesystem errors.
pub fn write_ref(git_dir: &Path, refname: &str, oid: &ObjectId) -> Result<()> {
    store_write_value(
        git_dir,
        refname,
        Some(StoreRawRef::Direct(*oid)),
        Expected::Any,
        None,
    )
}

/// Per-ref update flags for [`RefUpdate`] (e.g. `REF_NO_DEREF` on `HEAD`).
#[must_use]
pub fn ref_update_flags(refname: &str) -> RefUpdateFlags {
    legacy_ref_update_flags(refname)
}

/// Create a new direct ref and its initial reflog line in one store transaction.
///
/// # Errors
///
/// Returns an error when the ref already exists, the name is invalid, or ref/reflog I/O fails.
pub fn create_ref_with_reflog(
    git_dir: &Path,
    refname: &str,
    oid: &ObjectId,
    identity: &str,
    message: &str,
) -> Result<()> {
    let config = ConfigSet::load(
        &crate::environment::Environment::empty(),
        Some(git_dir),
        true,
    )
    .unwrap_or_default();
    let store = open_ref_store(git_dir)?;
    create_ref_with_reflog_on_store(
        store.as_ref(),
        git_dir,
        &config,
        refname,
        oid,
        identity,
        message,
    )
}

/// [`create_ref_with_reflog`] through an already-open store with already-loaded `config`, so
/// a caller holding a [`crate::repo::Repository`] reuses its packed-refs and config caches.
pub(crate) fn create_ref_with_reflog_on_store(
    store: &dyn RefStore,
    git_dir: &Path,
    config: &ConfigSet,
    refname: &str,
    oid: &ObjectId,
    identity: &str,
    message: &str,
) -> Result<()> {
    let reflog =
        should_autocreate_reflog_with_config(config, git_dir, refname).then(|| ReflogUpdate {
            identity: identity.to_owned(),
            message: message.to_owned(),
            time: time::OffsetDateTime::now_utc(),
            old_oid: None,
            new_oid: None,
        });
    store_write_value_on_store(
        store,
        git_dir,
        refname,
        Some(StoreRawRef::Direct(*oid)),
        Expected::Missing,
        reflog,
    )
}

/// Write a loose ref file under `storage_dir`: the body shared by [`write_ref`]
/// and [`write_ref_cached`], run after the packed-refs namespace-conflict check.
fn write_ref_at_storage(
    git_dir: &Path,
    storage_dir: &Path,
    refname: &str,
    oid: &ObjectId,
) -> Result<()> {
    let stor = crate::ref_namespace::storage_ref_name(refname);
    let path = storage_dir.join(stor);
    // An empty directory left over from a previously deleted nested ref can sit exactly where
    // this ref file must go (e.g. `refs/e-create/foo` after `refs/e-create/foo/bar` was pruned).
    // Git removes such empty directory trees before locking the ref (see t0600 "empty directory
    // should not fool create/update"); mirror that so the rename below does not hit "Is a
    // directory". Non-empty directories (containing files or `*.lock`) are left in place so the
    // subsequent write surfaces the conflict, matching Git's behaviour.
    remove_empty_ref_directory(&path);
    // If a *non-empty* directory still sits where the ref file must go, locking cannot
    // proceed. Git reports this as a "non-empty directory ... blocking reference" rather
    // than letting the rename fail with a raw "Is a directory" I/O error (see t0600
    // "non-empty directory blocks create"). Mirror that message so callers display it
    // verbatim. This only applies to direct (non-deref) writes where `refname` is also the
    // user-visible ref; indirect symref writes are handled by the caller.
    if fs::symlink_metadata(&path)
        .map(|m| m.file_type().is_dir())
        .unwrap_or(false)
    {
        let display = ref_path_for_display(&path);
        return Err(crate::error::RefLockError::DirectoryInTheWay {
            refname: refname.to_owned(),
            path: display,
        }
        .into());
    }
    if path.is_file() && matches!(read_ref_file(&path), Err(Error::InvalidRef(_))) {
        return Err(Error::InvalidRef(format!(
            "cannot update ref '{refname}': reference broken"
        )));
    }
    if let Some(parent) = path.parent() {
        crate::git_dir::io_error::io_with_git_path(
            git_dir,
            parent,
            crate::git_dir::GitDirPathOperation::CreateDir,
            fs::create_dir_all(parent),
        )?;
    }
    let content = format!("{oid}\n");
    // Write via lock file for atomicity (`O_CREAT|O_EXCL`), with optional backoff
    // per `core.filesRefLockTimeout`. A held lock surfaces as `Error::LockHeld`.
    let lock_path = lock_path_for_ref(&path);
    use crate::lockfile::{LockError, LockFile, LockWait};
    use std::io::Write as _;
    let wait = LockWait::files_ref_lock_for_git_dir(git_dir);
    let mut lock = LockFile::acquire(&lock_path, wait).map_err(|err| match err {
        held @ LockError::Held { .. } => Error::from(held),
        LockError::Io { source, .. } => crate::git_dir::io_error::map_git_dir_io(
            git_dir,
            &lock_path,
            crate::git_dir::GitDirPathOperation::UpdateRef,
            source,
        ),
    })?;
    crate::git_dir::io_error::io_with_git_path(
        git_dir,
        &path,
        crate::git_dir::GitDirPathOperation::UpdateRef,
        lock.write_all(content.as_bytes()),
    )?;
    lock.commit_to(&path).map_err(|err| match err {
        LockError::Io { source, .. } => crate::git_dir::io_error::map_git_dir_io(
            git_dir,
            &path,
            crate::git_dir::GitDirPathOperation::UpdateRef,
            source,
        ),
        held @ LockError::Held { .. } => Error::from(held),
    })?;
    Ok(())
}

/// Like [`write_ref`], but requires `expected_old` to match the ref's current value
/// while the loose-ref lock is held (atomic CAS for concurrent updaters).
///
/// # Errors
///
/// Same as [`write_ref`], plus [`store::RefStoreError::ExpectedMismatch`] when the CAS check
/// fails under lock.
pub fn write_ref_cas(
    git_dir: &Path,
    refname: &str,
    oid: &ObjectId,
    expected_old: ObjectId,
) -> Result<()> {
    store_write_value(
        git_dir,
        refname,
        Some(StoreRawRef::Direct(*oid)),
        Expected::Oid(expected_old),
        None,
    )
}

/// Like [`delete_ref`], but requires `expected_old` to match under the ref lock.
///
/// # Errors
///
/// Same as [`delete_ref`], plus [`store::RefStoreError::ExpectedMismatch`] when the CAS check
/// fails.
pub fn delete_ref_cas(git_dir: &Path, refname: &str, expected_old: ObjectId) -> Result<()> {
    store_write_value(git_dir, refname, None, Expected::Oid(expected_old), None)
}

/// Unlink a loose ref file after `packed-refs` was updated, when the file still contains
/// `expected`. Does not modify `packed-refs` (unlike [`delete_ref`] / [`delete_ref_cas`]).
///
/// Returns `Ok(true)` when the loose file was removed, `Ok(false)` when the OID differed or the
/// file was already absent.
///
/// # Errors
///
/// Propagates I/O failures and when the ref lock is already held.
pub(crate) fn prune_loose_ref_cas(
    git_dir: &Path,
    refname: &str,
    expected: ObjectId,
) -> Result<bool> {
    ensure_refname_safe_for_storage(refname)?;
    let storage_dir = ref_storage_dir(git_dir, refname);
    let stor = crate::ref_namespace::storage_ref_name(refname);
    let path = storage_dir.join(&stor);
    let lock_path = lock_path_for_ref(&path);
    use crate::lockfile::{LockFile, LockWait};
    let wait = LockWait::files_ref_lock_for_git_dir(git_dir);
    let _lock = LockFile::acquire(&lock_path, wait)?;
    let outcome = (|| -> Result<bool> {
        if !path.is_file() {
            return Ok(true);
        }
        let Ok(Ref::Direct(oid)) = read_ref_file(&path) else {
            return Ok(false);
        };
        if oid != expected {
            return Ok(false);
        }
        remove_empty_ref_directory(&path);
        fs::remove_file(&path).map_err(Error::Io)?;
        if let Some(parent) = path.parent() {
            remove_empty_ref_directory(parent);
        }
        Ok(true)
    })();
    outcome
}

/// A one-time, in-memory snapshot of a ref store's `packed-refs` file.
///
/// Bulk ref operations — notably `fetch`'s apply phase — resolve and write
/// thousands of refs back-to-back. Going through [`resolve_ref`] / [`write_ref`]
/// for each one re-reads and re-scans the *entire* `packed-refs` file on every
/// call, making the apply O(refs × packed-refs size). On a repository with tens
/// of thousands of packed refs that dominates the whole fetch even when no
/// objects are transferred. Loading the file once into this snapshot and using
/// [`resolve_ref_cached`] / [`write_ref_cached`] makes the apply linear.
///
/// The snapshot reflects `packed-refs` at load time. [`write_ref_cached`] may
/// update the snapshot in place so later namespace checks in the same apply batch
/// see loose refs without reloading the file. Otherwise
/// treat it as read-only: stale packed data only omits refs that were loose on
/// disk (resolved outside the snapshot) to begin with.
pub struct PackedRefs {
    map: HashMap<String, ObjectId>,
    sorted_names: BTreeSet<String>,
}

fn packed_refs_from_map(map: HashMap<String, ObjectId>) -> PackedRefs {
    let sorted_names = map.keys().cloned().collect();
    PackedRefs { map, sorted_names }
}

impl PackedRefs {
    /// Load the `packed-refs` snapshot for the ref store backing `git_dir` (the
    /// shared common dir for linked worktrees). A missing file yields an empty
    /// snapshot; reftable repositories also yield an empty snapshot.
    ///
    /// # Errors
    ///
    /// Returns [`Error::Io`] if `packed-refs` exists but cannot be read, or
    /// [`Error::PackedRefsUnexpectedLine`] when the file contains lines Git would reject.
    pub fn load(git_dir: &Path) -> Result<Self> {
        let store = common_dir(git_dir).unwrap_or_else(|| git_dir.to_path_buf());
        let map = read_packed_refs_map(&store)?;
        Ok(packed_refs_from_map(map))
    }

    /// The packed value recorded for `refname`, if any.
    #[must_use]
    pub fn get(&self, refname: &str) -> Option<ObjectId> {
        self.map.get(refname).copied()
    }

    /// Whether any packed ref name conflicts with `refname` as a path prefix
    /// (e.g. an existing `refs/heads/x` blocks creating `refs/heads/x/y`).
    /// Mirrors the internal `packed_ref_namespace_conflict` helper against the snapshot.
    #[must_use]
    pub fn has_namespace_conflict(&self, refname: &str) -> bool {
        packed_refname_namespace_conflict(&self.sorted_names, refname)
    }

    /// Record a ref written as loose during a cached apply batch so later
    /// namespace checks in the same batch see it without reloading `packed-refs`.
    pub(crate) fn record_loose_write(&mut self, refname: &str, oid: ObjectId) {
        self.map.insert(refname.to_owned(), oid);
        self.sorted_names.insert(refname.to_owned());
    }
}

/// Resolve `refname` to its current object id using a preloaded [`PackedRefs`]
/// snapshot instead of re-reading `packed-refs`. Loose refs win over packed
/// (matching [`resolve_ref`]); a symbolic loose ref falls back to the full
/// [`resolve_ref`] resolver (rare for the tracking/tag refs this is used for).
/// Returns `Ok(None)` when the ref does not exist.
///
/// # Errors
///
/// Returns an error on ref-file I/O failures other than "not found".
pub fn resolve_ref_cached(
    git_dir: &Path,
    refname: &str,
    packed: &PackedRefs,
) -> Result<Option<ObjectId>> {
    if open_ref_store(git_dir)?.format() != RefStorageFormat::Files {
        return Ok(resolve_ref(git_dir, refname).ok());
    }
    resolve_files_ref_cached(git_dir, refname, packed)
}

fn resolve_files_ref_cached(
    git_dir: &Path,
    refname: &str,
    packed: &PackedRefs,
) -> Result<Option<ObjectId>> {
    let (store, stor_name) = crate::worktree_ref::resolve_ref_storage(git_dir, refname);
    let storage_owned = crate::ref_namespace::storage_ref_name(&stor_name);
    let try_names: Vec<&str> = if storage_owned != stor_name {
        vec![storage_owned.as_str(), stor_name.as_str()]
    } else {
        vec![stor_name.as_str()]
    };

    for name in &try_names {
        let path = store.join(name);
        match read_ref_file(&path) {
            Ok(Ref::Direct(oid)) => return Ok(Some(oid)),
            Ok(Ref::Symbolic(target)) => return Ok(resolve_ref(git_dir, &target).ok()),
            Err(Error::Io(ref e)) if e.kind() == io::ErrorKind::NotFound => {}
            Err(e) => return Err(e),
        }
    }

    for name in &try_names {
        if let Some(oid) = packed.get(name) {
            return Ok(Some(oid));
        }
    }
    Ok(None)
}

/// Like [`write_ref`], but checks the packed-refs namespace conflict against a
/// preloaded [`PackedRefs`] snapshot instead of re-reading `packed-refs` on
/// every call. Behaves identically to [`write_ref`] otherwise.
///
/// # Errors
///
/// Returns [`Error::InvalidRef`] when `refname` is not safe for ref storage, on a namespace
/// conflict, or [`Error::Io`] / [`Error::Message`] on filesystem errors.
pub fn write_ref_cached(
    git_dir: &Path,
    refname: &str,
    oid: &ObjectId,
    packed: &mut PackedRefs,
) -> Result<()> {
    if open_ref_store(git_dir)?.format() != RefStorageFormat::Files {
        return write_ref(git_dir, refname, oid);
    }
    ensure_refname_safe_for_storage(refname)?;
    if packed.has_namespace_conflict(refname) {
        return Err(Error::InvalidRef(format!(
            "cannot update ref '{refname}': reference namespace conflict"
        )));
    }
    let storage_dir = ref_storage_dir(git_dir, refname);
    write_ref_at_storage(git_dir, &storage_dir, refname, oid)?;
    packed.record_loose_write(refname, *oid);
    Ok(())
}

/// Render a ref-store path for user-facing diagnostics the way Git does: relative to the
/// current working directory when possible (e.g. `.git/refs/foo/bar`), otherwise the full
/// path. Git builds these paths relative to the worktree root, so under the normal in-tree
/// case this yields the `.git/...` form that the upstream tests expect.
fn ref_path_for_display(path: &Path) -> String {
    let cwd = crate::environment::Environment::empty().cwd.clone();
    if let Ok(rel) = path.strip_prefix(&cwd) {
        return rel.to_string_lossy().into_owned();
    }
    // On platforms where the cwd and the (canonicalized) ref path disagree only by a
    // symlinked prefix (e.g. macOS `/tmp` -> `/private/tmp`), retry with both sides
    // canonicalized so the relative form is still recovered.
    if let (Ok(cwd_c), Ok(path_c)) = (cwd.canonicalize(), path.canonicalize()) {
        if let Ok(rel) = path_c.strip_prefix(&cwd_c) {
            return rel.to_string_lossy().into_owned();
        }
    }
    path.to_string_lossy().into_owned()
}

/// Remove the directory at `path` if it is an empty directory tree (contains only empty
/// directories, no regular files or lock files). Best-effort: returns silently on any error or
/// if `path` is not a directory. Mirrors Git's `remove_empty_directories`
/// (`remove_dir_recursively(REMOVE_DIR_EMPTY_ONLY)`), used to clear stale directories that sit
/// where a ref file must be created or deleted.
pub(crate) fn remove_empty_ref_directory(path: &Path) {
    match fs::symlink_metadata(path) {
        Ok(meta) if meta.file_type().is_dir() => {}
        _ => return,
    }
    // `remove_dir_all` would also delete files; we only want to remove trees that are entirely
    // empty of files. `fs::remove_dir` fails (non-empty) unless we recurse, so walk first.
    if dir_tree_has_files(path) {
        return;
    }
    let _ = remove_dir_tree(path);
}

/// Return true if the directory tree rooted at `dir` contains any non-directory entry.
fn dir_tree_has_files(dir: &Path) -> bool {
    let Ok(entries) = fs::read_dir(dir) else {
        // Unreadable: treat conservatively as "has files" so we do not delete it.
        return true;
    };
    for entry in entries.flatten() {
        match entry.file_type() {
            Ok(ft) if ft.is_dir() => {
                if dir_tree_has_files(&entry.path()) {
                    return true;
                }
            }
            Ok(_) => return true, // a file, symlink, or `*.lock`
            Err(_) => return true,
        }
    }
    false
}

/// Walk upward from `ref_path`'s parent, removing empty directories until `refs/`.
pub(crate) fn prune_empty_loose_ref_parents(storage_dir: &Path, ref_path: &Path) {
    if let Some(dir) = ref_path.parent() {
        prune_empty_ref_dirs(storage_dir, dir);
    }
}

/// Remove `dir` and then its parents while they hold no files, stopping at `refs/`.
pub(crate) fn prune_empty_ref_dirs(storage_dir: &Path, dir: &Path) {
    let refs_root = storage_dir.join("refs");
    let mut current = Some(dir);
    while let Some(dir) = current {
        if dir == refs_root.as_path() || !dir.starts_with(&refs_root) {
            break;
        }
        if dir_tree_has_files(dir) {
            break;
        }
        if fs::remove_dir(dir).is_err() {
            break;
        }
        current = dir.parent();
    }
}

/// Recursively remove an empty directory tree (assumes [`dir_tree_has_files`] returned false).
fn remove_dir_tree(dir: &Path) -> io::Result<()> {
    for entry in fs::read_dir(dir)? {
        let entry = entry?;
        if entry.file_type()?.is_dir() {
            remove_dir_tree(&entry.path())?;
        }
    }
    fs::remove_dir(dir)
}

/// Delete a ref.
///
/// Dispatches to the reftable backend when `extensions.refStorage = reftable`.
///
/// # Errors
///
/// Returns [`RefStoreError::NotFound`](store::RefStoreError::NotFound) (inside
/// [`Error::RefStore`]) when `refname` does not exist, [`Error::InvalidRef`] when it is not
/// safe for ref storage, or [`Error::Io`] for filesystem failures.
pub fn delete_ref(git_dir: &Path, refname: &str) -> Result<()> {
    if matches!(read_raw_ref(git_dir, refname)?, RawRefLookup::NotFound) {
        return Err(store::RefStoreError::not_found(refname).into());
    }
    if open_ref_store(git_dir)?.format() != RefStorageFormat::Files {
        let store = open_ref_store(git_dir)?;
        let mut flags = legacy_ref_update_flags(refname);
        if refname != "HEAD" {
            if let Ok(Some(StoreRawRef::Symbolic(_))) = store.read_raw(refname) {
                flags.no_deref = true;
            }
        }
        return commit_store_update(
            git_dir,
            RefUpdate {
                name: refname.to_owned(),
                new_value: None,
                expected: Expected::Exists,
                reflog: None,
                flags,
            },
        )
        .map_err(|e| map_public_ref_store_error(e, refname));
    }
    ensure_refname_safe_for_storage(refname)?;
    let storage_dir = ref_storage_dir(git_dir, refname);
    let stor = crate::ref_namespace::storage_ref_name(refname);
    let path = storage_dir.join(&stor);
    let lock = lock_path_for_ref(&path);
    if fs::symlink_metadata(&lock).is_ok() {
        return Err(Error::from(crate::lockfile::LockError::Held { path: lock }));
    }

    // Remove the packed-refs entry *first* (acquiring the packed-refs lock). Git deletes the
    // packed version while holding the lock before unlinking the loose ref, so that a failure to
    // rewrite packed-refs (lock held, stale `packed-refs.new`, ...) leaves the reference fully
    // intact rather than dropping the loose file and exposing a stale packed value. See t0600
    // "delete fails cleanly if packed-refs file is locked / .new write fails".
    remove_packed_ref(&storage_dir, &stor)?;

    // Remove the loose ref file. An empty directory tree may occupy the ref path (a leftover
    // from a previously deleted nested ref); clear it so the delete succeeds rather than failing
    // with "Is a directory" (see t0600 "empty directory should not fool 0/1-arg delete").
    remove_empty_ref_directory(&path);
    match fs::remove_file(&path) {
        Ok(()) => {}
        Err(e) if e.kind() == io::ErrorKind::NotFound => {}
        Err(e)
            if e.kind() == io::ErrorKind::NotADirectory
                || e.raw_os_error() == Some(libc::ENOTDIR) => {}
        // The path is (still) a directory — e.g. a non-empty tree we declined to remove.
        // Treat as "loose ref not present"; the packed-refs entry was already removed above.
        Err(e)
            if e.raw_os_error() == Some(libc::EISDIR) || e.raw_os_error() == Some(libc::EPERM) => {}
        Err(e) => return Err(Error::Io(e)),
    }

    prune_empty_loose_ref_parents(&storage_dir, &path);

    let log_path = storage_dir.join("logs").join(&stor);

    // Remove the ref's reflog and clean up empty parent directories, matching Git's
    // `files_transaction_finish` (which deletes the reflog of any deleted ref and then calls
    // `try_remove_empty_parents`). Leaving the reflog behind would block a later nested ref
    // (e.g. deleting `k/l` then creating `k/l/m`, which needs `logs/refs/heads/k/l` to be a
    // directory) — see t0601 and t1410 "stale dirs do not cause d/f conflicts".
    let _ = fs::remove_file(&log_path);

    let logs_root = storage_dir.join("logs");
    let mut parent = log_path.parent();
    while let Some(p) = parent {
        if p == logs_root.as_path() || !p.starts_with(&logs_root) {
            break;
        }
        if fs::remove_dir(p).is_err() {
            break; // not empty or other error
        }
        parent = p.parent();
    }

    Ok(())
}

/// Remove a single entry from the packed-refs file, rewriting it.
pub(crate) fn remove_packed_ref(git_dir: &Path, refname: &str) -> Result<()> {
    remove_packed_refs_inner(git_dir, &|name| name == refname, false, false).map(drop)
}

pub(crate) fn remove_packed_ref_under_lock(git_dir: &Path, refname: &str) -> Result<()> {
    remove_packed_refs_inner(git_dir, &|name| name == refname, false, true).map(drop)
}

/// Remove every record named in `refnames` from `git_dir`'s packed-refs in a single rewrite,
/// with the caller already holding `packed-refs.lock`.
///
/// Returns the removed records verbatim (the ref line plus any `^` peel line, each ending in a
/// newline), so [`restore_packed_records_under_lock`] can put them back.
///
/// # Errors
///
/// Fails without touching the file when it does not parse, or when writing the replacement fails.
pub(crate) fn remove_packed_refs_under_lock(
    git_dir: &Path,
    refnames: &HashSet<String>,
) -> Result<Vec<String>> {
    if refnames.is_empty() {
        return Ok(Vec::new());
    }
    remove_packed_refs_inner(git_dir, &|name| refnames.contains(name), true, true)
}

/// Storage name of a packed record returned by [`remove_packed_refs_under_lock`].
pub(crate) fn packed_record_name(record: &str) -> &str {
    let line = record.lines().next().unwrap_or("");
    line.split_once(' ').map_or("", |(_, name)| name.trim())
}

/// Object id of a packed record returned by [`remove_packed_refs_under_lock`].
pub(crate) fn packed_record_oid(record: &str) -> Option<ObjectId> {
    let line = record.lines().next()?;
    ObjectId::from_hex(line.split_once(' ')?.0).ok()
}

/// Put `records` (as returned by [`remove_packed_refs_under_lock`]) back into `git_dir`'s
/// packed-refs, keeping the file sorted, with the caller holding `packed-refs.lock`.
///
/// # Errors
///
/// Fails without touching the file when it does not parse, or when writing the replacement fails.
pub(crate) fn restore_packed_records_under_lock(git_dir: &Path, records: &[&str]) -> Result<()> {
    if records.is_empty() {
        return Ok(());
    }
    let packed_path = store::paths::packed_refs_path(git_dir);
    let content = match fs::read(&packed_path) {
        Ok(c) => c,
        Err(e) if e.kind() == io::ErrorKind::NotFound => Vec::new(),
        Err(e) => return Err(Error::Io(e)),
    };
    parse_packed_refs_to_map(&packed_path, &content)?;
    let content = String::from_utf8(content)
        .map_err(|_| packed_refs_unexpected_line(&packed_path, "<invalid utf-8>"))?;

    let mut blocks: Vec<String> = Vec::new();
    for line in content.lines() {
        if line.starts_with('#') {
            continue;
        }
        match blocks.last_mut() {
            Some(block) if line.starts_with('^') => block.push_str(line),
            _ => blocks.push(line.to_owned()),
        }
        if let Some(block) = blocks.last_mut() {
            block.push('\n');
        }
    }
    blocks.extend(records.iter().map(|r| (*r).to_owned()));
    blocks.sort_by(|a, b| packed_record_name(a).cmp(packed_record_name(b)));

    let mut out =
        String::with_capacity(content.len() + records.iter().map(|r| r.len()).sum::<usize>());
    out.push_str(PACKED_REFS_HEADER);
    for block in &blocks {
        out.push_str(block);
    }
    replace_packed_refs_file(git_dir, &packed_path, &out, true)
}

const PACKED_REFS_HEADER: &str = "# pack-refs with: peeled fully-peeled sorted\n";

fn remove_packed_refs_inner(
    git_dir: &Path,
    remove: &dyn Fn(&str) -> bool,
    keep_removed: bool,
    lock_already_held: bool,
) -> Result<Vec<String>> {
    let mut removed: Vec<String> = Vec::new();
    let packed_path = store::paths::packed_refs_path(git_dir);
    let content = match fs::read(&packed_path) {
        Ok(c) => c,
        Err(e)
            if e.kind() == io::ErrorKind::NotFound
                || e.kind() == io::ErrorKind::NotADirectory
                || e.raw_os_error() == Some(libc::ENOTDIR) =>
        {
            return Ok(removed);
        }
        Err(e) => return Err(Error::Io(e)),
    };
    // Fail before mutating anything if the on-disk file is not readable like Git's.
    parse_packed_refs_to_map(&packed_path, &content)?;

    let content = String::from_utf8(content)
        .map_err(|_| packed_refs_unexpected_line(&packed_path, "<invalid utf-8>"))?;

    let mut out = String::with_capacity(content.len());
    let mut skip_peeled = false;
    let mut changed = false;
    // Write a fresh header (don't preserve old comment lines — real git
    // regenerates the header on every rewrite).
    let mut header_written = false;

    for line in content.lines() {
        if skip_peeled {
            if line.starts_with('^') {
                if let Some(record) = removed.last_mut().filter(|_| keep_removed) {
                    record.push_str(line);
                    record.push('\n');
                }
                changed = true;
                continue;
            }
            skip_peeled = false;
        }

        if line.starts_with('#') {
            // Skip old header lines — we'll write a fresh one
            continue;
        }
        if line.starts_with('^') {
            out.push_str(line);
            out.push('\n');
            continue;
        }

        // Write fresh header before the first data line
        if !header_written {
            out.insert_str(0, PACKED_REFS_HEADER);
            header_written = true;
        }

        let name = line.split_once(' ').map_or("", |(_, name)| name.trim());
        if remove(name) {
            if keep_removed {
                removed.push(format!("{line}\n"));
            }
            changed = true;
            skip_peeled = true;
            continue;
        }

        out.push_str(line);
        out.push('\n');
    }

    if changed {
        replace_packed_refs_file(git_dir, &packed_path, &out, lock_already_held)?;
    }

    Ok(removed)
}

/// Replace `packed_path` with `body`, taking `packed-refs.lock` unless the caller holds it.
fn replace_packed_refs_file(
    git_dir: &Path,
    packed_path: &Path,
    body: &str,
    lock_already_held: bool,
) -> Result<()> {
    // Git rewrites packed-refs under two files: it first takes the `packed-refs.lock`
    // lockfile (failing if another process holds it), then writes the new content to the
    // `packed-refs.new` tempfile and renames it over `packed-refs`. Mirror both so that
    // `update-ref -d` fails cleanly — leaving the reference intact — when either file is
    // already present (t0600 "delete fails cleanly if packed-refs file is locked / .new
    // write fails").
    let lock = lock_path_for_ref(packed_path); // packed-refs.lock
    let _packed_lock = if !lock_already_held {
        let abs_lock = fs::canonicalize(git_dir)
            .map(|d| d.join("packed-refs.lock"))
            .unwrap_or_else(|_| lock.clone());
        Some(acquire_packed_refs_lock(git_dir, &lock, &abs_lock)?)
    } else {
        None
    };

    let tmp = packed_path.with_extension("new");
    let mut created_tmp = false;
    let write_result = (|| -> Result<()> {
        // Staged packed-refs body (not a lock file); exclusive create avoids clobber.
        let mut file = std::fs::OpenOptions::new()
            .write(true)
            .create_new(true)
            .open(&tmp)
            .map_err(Error::Io)?;
        created_tmp = true;
        use std::io::Write as _;
        file.write_all(body.as_bytes()).map_err(Error::Io)?;
        drop(file);
        fs::rename(&tmp, packed_path).map_err(Error::Io)?;
        created_tmp = false; // consumed by rename
        Ok(())
    })();

    if write_result.is_err() && created_tmp {
        let _ = fs::remove_file(&tmp);
    }
    write_result
}

/// Read the symbolic ref target of `HEAD`.
///
/// Returns `None` if HEAD is detached (points directly to a commit hash).
///
/// # Errors
///
/// Returns [`Error::Io`] or [`Error::InvalidRef`] on failures.
pub fn read_head(git_dir: &Path) -> Result<Option<String>> {
    read_symbolic_ref(git_dir, "HEAD")
}

/// Read symbolic target of any ref.
///
/// Dispatches to the reftable backend when `extensions.refStorage = reftable`.
///
/// Returns `Ok(Some(target))` when `refname` exists and is symbolic,
/// `Ok(None)` when it is direct or missing.
pub fn read_symbolic_ref(git_dir: &Path, refname: &str) -> Result<Option<String>> {
    match open_ref_store(git_dir)?.read_raw(refname)? {
        Some(StoreRawRef::Symbolic(target)) => Ok(Some(target)),
        Some(StoreRawRef::Direct(_)) | None => Ok(None),
    }
}

/// Like [`read_symbolic_ref`] but uses an open [`crate::repo::Repository`] ref store (no format re-detection).
pub fn read_symbolic_ref_for_repository(
    repo: &crate::repo::Repository,
    refname: &str,
) -> Result<Option<String>> {
    match repo.refs().read_raw(refname)? {
        Some(StoreRawRef::Symbolic(target)) => Ok(Some(target)),
        Some(StoreRawRef::Direct(_)) | None => Ok(None),
    }
}

/// Core `logAllRefUpdates` modes (after config lookup), matching Git's `log_refs_config`.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum LogRefsConfig {
    /// `core.logAllRefUpdates` not set; resolved per-repo (bare vs non-bare).
    Unset,
    /// Explicitly disabled.
    None,
    /// `true` — log branch-like refs only (see [`should_autocreate_reflog`]).
    Normal,
    /// `always` — log updates to any ref.
    Always,
}

impl LogRefsConfig {
    /// Parse a `core.logAllRefUpdates` value; `None` when it is not a recognised mode.
    pub(crate) fn parse(raw: &str) -> Option<Self> {
        match raw.trim().to_ascii_lowercase().as_str() {
            "always" => Some(Self::Always),
            "1" | "true" | "yes" | "on" => Some(Self::Normal),
            "0" | "false" | "no" | "off" | "never" => Some(Self::None),
            _ => None,
        }
    }
}

/// Read `[core] logAllRefUpdates` from the repository config.
///
/// Returns [`LogRefsConfig::Unset`] when the key is absent.
pub fn read_log_refs_config(git_dir: &Path) -> LogRefsConfig {
    ConfigSet::load(
        &crate::environment::Environment::empty(),
        Some(git_dir),
        true,
    )
    .map(|cfg| cfg.log_refs_config())
    .unwrap_or(LogRefsConfig::Unset)
}

/// Effective `logAllRefUpdates` after applying Git's `LOG_REFS_UNSET` rule.
///
/// Falls back to [`LogRefsConfig::Normal`] when the config cannot be loaded.
pub fn effective_log_refs_config(git_dir: &Path) -> LogRefsConfig {
    ConfigSet::load(
        &crate::environment::Environment::empty(),
        Some(git_dir),
        true,
    )
    .map(|cfg| cfg.effective_log_refs_config())
    .unwrap_or(LogRefsConfig::Normal)
}

/// Whether a new reflog file may be auto-created for `refname` given an already-resolved
/// `core.logAllRefUpdates` mode (including command-line config).
#[must_use]
pub fn should_autocreate_reflog_for_mode(refname: &str, mode: LogRefsConfig) -> bool {
    match mode {
        LogRefsConfig::Always => true,
        LogRefsConfig::Normal => {
            refname == "HEAD"
                || refname.starts_with("refs/heads/")
                || refname.starts_with("refs/remotes/")
                || refname.starts_with("refs/notes/")
        }
        LogRefsConfig::None | LogRefsConfig::Unset => false,
    }
}

/// Whether a new reflog file may be auto-created for `refname` (Git `should_autocreate_reflog`).
#[must_use]
pub fn should_autocreate_reflog(git_dir: &Path, refname: &str) -> bool {
    should_autocreate_reflog_for_mode(refname, effective_log_refs_config(git_dir))
}

/// Like [`should_autocreate_reflog`], using an already-loaded repository config snapshot.
#[must_use]
pub fn should_autocreate_reflog_with_config(
    config: &ConfigSet,
    _git_dir: &Path,
    refname: &str,
) -> bool {
    should_autocreate_reflog_for_mode(refname, config.effective_log_refs_config())
}

/// Write a reflog entry.
///
/// Dispatches to the reftable backend when `extensions.refStorage = reftable`.
///
/// # Parameters
///
/// - `git_dir` — path to the git directory.
/// - `refname` — reference name (e.g. `"refs/heads/main"`).
/// - `old_oid` — previous OID (use `ObjectId::from_bytes(&[0;20])` for a new ref).
/// - `new_oid` — new OID.
/// - `identity` — `"Name <email> <timestamp> <tz>"` formatted string.
/// - `message` — short log message.
/// - `force_create` — if true, create the log file even when [`should_autocreate_reflog`] would not.
///
/// # Errors
///
/// Returns [`Error::Io`] on filesystem errors.
/// Remove stale reflog *files* that occupy path components which must become directories.
///
/// When a branch is deleted we keep its reflog file (so `branch -D` + later recreate can
/// retain history). If a later nested branch (e.g. `k/l/m`) needs `logs/refs/heads/k/l` to be
/// a directory, the leftover file at that path blocks `create_dir_all`. Walk from `logs_root`
/// down toward `target` and remove any regular file sitting where a directory is required, so
/// the directory can be created. Best-effort: filesystem errors are ignored (the subsequent
/// `create_dir_all` surfaces any real problem).
fn clear_conflicting_reflog_files(logs_root: &Path, target: &Path) {
    let Ok(rel) = target.strip_prefix(logs_root) else {
        return;
    };
    let mut cur = logs_root.to_path_buf();
    for component in rel.components() {
        cur.push(component);
        match fs::symlink_metadata(&cur) {
            Ok(meta) if meta.file_type().is_dir() => {}
            Ok(_) => {
                // A non-directory (stale reflog file or symlink) is in the way of a needed
                // directory. Remove it so the directory hierarchy can be created.
                let _ = fs::remove_file(&cur);
            }
            Err(_) => break, // does not exist yet (or unreadable); nothing more to clear
        }
    }
}

/// Render a reflog entry's `(old, new)` OIDs as hex, widening a null OID to the
/// width of the non-null side so the line matches the repository hash algorithm.
pub(crate) fn reflog_oid_hex_pair(old: &ObjectId, new: &ObjectId) -> (String, String) {
    let width = if !old.is_zero() {
        old.algo().hex_len()
    } else if !new.is_zero() {
        new.algo().hex_len()
    } else {
        old.algo().hex_len()
    };
    let render = |oid: &ObjectId| {
        if oid.is_zero() {
            "0".repeat(width)
        } else {
            oid.to_hex()
        }
    };
    (render(old), render(new))
}

fn map_reflog_store_validation(err: store::RefStoreError) -> Error {
    match err {
        store::RefStoreError::InvalidReflog(sig) => Error::InvalidSignature(sig),
        other => Error::from(other),
    }
}

fn validate_reflog_message(message: &str) -> Result<()> {
    store::validate_reflog_message(message).map_err(map_reflog_store_validation)
}

fn validate_reflog_identity_string(identity: &str) -> Result<()> {
    store::validate_reflog_identity_string(identity).map_err(map_reflog_store_validation)
}

/// Reject reflog metadata that would forge or corrupt a log line on either backend.
fn validate_reflog_update(log: &ReflogUpdate) -> Result<()> {
    store::validate_reflog_update(log).map_err(map_reflog_store_validation)
}

/// Append one line to the reflog for `refname` using a validated [`Signature`].
///
/// # Errors
///
/// Propagates I/O failures, invalid refname errors, and [`Error::InvalidSignature`].
pub fn append_reflog_with_signature(
    git_dir: &Path,
    refname: &str,
    old_oid: &ObjectId,
    new_oid: &ObjectId,
    identity: &Signature,
    message: &str,
    force_create: bool,
) -> Result<()> {
    identity.validate().map_err(Error::InvalidSignature)?;
    let formatted = format_reflog_identity(&identity.reflog_name_email(), identity.time);
    append_reflog_with_config(
        git_dir,
        refname,
        old_oid,
        new_oid,
        &formatted,
        message,
        force_create,
        None,
    )
}

/// Append one line to the reflog for `refname`.
///
/// Creates the reflog file when `force_create` is true or when the ref already
/// has a reflog. Identity and message are written in Git's standard reflog format.
///
/// # Errors
///
/// Propagates I/O failures and invalid refname errors.
pub fn append_reflog(
    git_dir: &Path,
    refname: &str,
    old_oid: &ObjectId,
    new_oid: &ObjectId,
    identity: &str,
    message: &str,
    force_create: bool,
) -> Result<()> {
    append_reflog_with_config(
        git_dir,
        refname,
        old_oid,
        new_oid,
        identity,
        message,
        force_create,
        None,
    )
}

/// Like [`append_reflog`], reusing `config` for reflog auto-create policy when provided.
#[allow(clippy::too_many_arguments)]
pub fn append_reflog_with_config(
    git_dir: &Path,
    refname: &str,
    old_oid: &ObjectId,
    new_oid: &ObjectId,
    identity: &str,
    message: &str,
    force_create: bool,
    config: Option<&ConfigSet>,
) -> Result<()> {
    validate_reflog_identity_string(identity)?;
    validate_reflog_message(message)?;
    test_inject_reflog_fail(refname)?;
    if open_ref_store(git_dir)?.format() != RefStorageFormat::Files {
        return crate::reftable::reftable_append_reflog(
            git_dir,
            refname,
            old_oid,
            new_oid,
            identity,
            message,
            force_create,
        );
    }
    let storage_dir = ref_storage_dir(git_dir, refname);
    let stor = crate::ref_namespace::storage_ref_name(refname);
    let log_path = storage_dir.join("logs").join(&stor);
    let may_create = force_create
        || match config {
            Some(cfg) => should_autocreate_reflog_with_config(cfg, git_dir, refname),
            None => should_autocreate_reflog(git_dir, refname),
        };
    if !may_create && !log_path.exists() {
        return Ok(());
    }
    if let Some(parent) = log_path.parent() {
        // A stale reflog *file* left behind by a deleted branch (e.g. `logs/refs/heads/k/l`)
        // can occupy a path component that must now become a directory (for `k/l/m`). Git
        // removes such leftovers while creating the reflog; mirror that so `create_dir_all`
        // does not fail with "File exists" / "Not a directory".
        let logs_root = storage_dir.join("logs");
        clear_conflicting_reflog_files(&logs_root, parent);
        crate::git_dir::io_error::io_with_git_path(
            git_dir,
            parent,
            crate::git_dir::GitDirPathOperation::CreateDir,
            fs::create_dir_all(parent),
        )?;
    }
    // A reflog records `<old> <new>` at the repository's hash width. The null
    // ("0000…") side of a ref creation/deletion is stored at SHA-1 width by
    // callers; widen it to match the non-null side so sha256 reflogs are
    // internally consistent (and re-parseable).
    let (old_hex, new_hex) = reflog_oid_hex_pair(old_oid, new_oid);
    let line = if message.is_empty() {
        format!("{old_hex} {new_hex} {identity}\n")
    } else {
        format!("{old_hex} {new_hex} {identity}\t{message}\n")
    };
    let mut file = fs::OpenOptions::new()
        .create(true)
        .append(true)
        .open(&log_path)
        .map_err(|source| {
            crate::git_dir::io_error::map_git_dir_io(
                git_dir,
                &log_path,
                crate::git_dir::GitDirPathOperation::AppendReflog,
                source,
            )
        })?;
    use io::Write;
    crate::git_dir::io_error::io_with_git_path(
        git_dir,
        &log_path,
        crate::git_dir::GitDirPathOperation::AppendReflog,
        file.write_all(line.as_bytes()),
    )?;
    Ok(())
}

fn pack_ref_include_pattern(all: bool) -> &'static [u8] {
    if all {
        b"*"
    } else {
        b"refs/tags/*"
    }
}

fn ref_matches_pack_include(refname: &str, all: bool) -> bool {
    crate::wildmatch::wildmatch(pack_ref_include_pattern(all), refname.as_bytes(), 0)
}

fn collect_loose_ref_files(
    dir: &Path,
    prefix: &str,
    out: &mut Vec<(String, PathBuf)>,
) -> Result<()> {
    let read = match fs::read_dir(dir) {
        Ok(r) => r,
        Err(e)
            if e.kind() == io::ErrorKind::NotFound
                || e.kind() == io::ErrorKind::NotADirectory
                || e.raw_os_error() == Some(libc::ENOTDIR) =>
        {
            return Ok(());
        }
        Err(e) => return Err(Error::Io(e)),
    };
    for entry in read {
        let entry = entry?;
        let name = entry.file_name().to_string_lossy().to_string();
        let refname = format!("{prefix}{name}");
        let path = entry.path();
        if path.is_dir() {
            collect_loose_ref_files(&path, &format!("{refname}/"), out)?;
        } else if path.is_file() {
            out.push((refname, path));
        }
    }
    Ok(())
}

fn load_packed_refs_with_peel(
    packed_path: &Path,
    merged: &mut HashMap<String, (ObjectId, Option<ObjectId>)>,
) -> Result<()> {
    if !packed_path.is_file() {
        return Ok(());
    }
    let data = fs::read(packed_path)?;
    parse_packed_refs_to_map(packed_path, &data)?;
    let content = String::from_utf8(data)
        .map_err(|_| packed_refs_unexpected_line(packed_path, "<invalid utf-8>"))?;
    let mut last_name: Option<String> = None;
    for line in content.lines() {
        if line.starts_with('#') {
            continue;
        }
        if let Some(hex) = line.strip_prefix('^') {
            let Ok(peel_oid) = ObjectId::from_hex(hex.trim()) else {
                continue;
            };
            if let Some(name) = &last_name {
                if let Some(entry) = merged.get_mut(name) {
                    entry.1 = Some(peel_oid);
                }
            }
            continue;
        }
        let mut parts = line.splitn(2, ' ');
        let Some(hex) = parts.next() else {
            continue;
        };
        let Some(name) = parts.next() else {
            continue;
        };
        let name = name.trim();
        let Ok(oid) = ObjectId::from_hex(hex) else {
            continue;
        };
        merged.insert(name.to_owned(), (oid, None));
        last_name = Some(name.to_owned());
    }
    Ok(())
}

/// Pack loose refs for `repo` (files `packed-refs` or reftable compaction).
pub(crate) fn pack_refs_for_repository(
    repo: &crate::repo::Repository,
    all: bool,
    dry_run: bool,
) -> Result<(PathBuf, usize, usize)> {
    let git_dir = repo.git_dir();
    if open_ref_store(git_dir)?.format() != RefStorageFormat::Files {
        return pack_refs_reftable(git_dir, dry_run);
    }
    pack_refs_files(git_dir, repo.odb(), all, dry_run)
}

fn pack_refs_reftable(git_dir: &Path, dry_run: bool) -> Result<(PathBuf, usize, usize)> {
    use crate::reftable::ReftableStack;
    let store_git_dir = common_dir(git_dir).unwrap_or_else(|| git_dir.to_path_buf());
    let rt_dir = store_git_dir.join("reftable");
    let tables_before = fs::read_to_string(rt_dir.join("tables.list"))
        .map(|s| s.lines().filter(|l| !l.is_empty()).count())
        .unwrap_or(0);
    if dry_run {
        let tables_pruned = tables_before.saturating_sub(1);
        return Ok((rt_dir, 0, tables_pruned));
    }
    let mut stack = ReftableStack::open(&store_git_dir)?;
    stack.compact()?;
    let tables_after = fs::read_to_string(rt_dir.join("tables.list"))
        .map(|s| s.lines().filter(|l| !l.is_empty()).count())
        .unwrap_or(0);
    Ok((rt_dir, 0, tables_before.saturating_sub(tables_after)))
}

fn pack_refs_files(
    git_dir: &Path,
    odb: &crate::odb::Odb,
    all: bool,
    dry_run: bool,
) -> Result<(PathBuf, usize, usize)> {
    let storage_git_dir = common_dir(git_dir).unwrap_or_else(|| git_dir.to_path_buf());
    let packed_path = store::paths::packed_refs_path(&storage_git_dir);

    let mut merged: HashMap<String, (ObjectId, Option<ObjectId>)> = HashMap::new();
    load_packed_refs_with_peel(&packed_path, &mut merged)?;

    let mut loose_files = Vec::new();
    collect_loose_ref_files(&storage_git_dir.join("refs"), "refs/", &mut loose_files)?;

    let mut packed_loose = 0usize;
    let mut to_prune: Vec<(String, ObjectId)> = Vec::new();

    for (refname, path) in loose_files {
        if crate::worktree_ref::is_per_worktree_ref(&refname) {
            continue;
        }
        if !ref_matches_pack_include(&refname, all) {
            continue;
        }
        let Ok(Ref::Direct(oid)) = read_ref_file(&path) else {
            continue;
        };
        if odb.read(&oid).is_err() {
            continue;
        }
        let peel = if refname.starts_with("refs/tags/") {
            packed_ref_peel(odb, oid)
        } else {
            None
        };
        merged.insert(refname.clone(), (oid, peel));
        to_prune.push((refname, oid));
        let _ = path;
        packed_loose += 1;
    }

    if packed_loose == 0 && merged.is_empty() {
        return Ok((packed_path, 0, 0));
    }

    if dry_run {
        return Ok((packed_path, packed_loose, to_prune.len()));
    }

    let mut names: Vec<String> = merged.keys().cloned().collect();
    names.sort();

    let mut body = String::from("# pack-refs with: peeled fully-peeled sorted\n");
    for name in &names {
        let Some((oid, peel)) = merged.get(name) else {
            continue;
        };
        body.push_str(&oid.to_hex());
        body.push(' ');
        body.push_str(name);
        body.push('\n');
        if let Some(p) = peel {
            body.push('^');
            body.push_str(&p.to_hex());
            body.push('\n');
        }
    }

    atomic_rewrite_packed_refs(&storage_git_dir, &body)?;

    #[cfg(test)]
    pack_refs_test_hooks::run_before_prune();

    let mut pruned = 0usize;
    for (refname, expected) in &to_prune {
        match prune_loose_ref_cas(git_dir, refname, *expected) {
            Ok(true) => pruned += 1,
            Ok(false) => {
                remove_packed_ref(git_dir, refname)?;
            }
            Err(e) => return Err(e),
        }
    }

    Ok((packed_path, packed_loose, pruned))
}

/// Test hook: runs once after `packed-refs` is rewritten and before loose refs are pruned.
#[cfg(test)]
mod pack_refs_test_hooks {
    use std::cell::RefCell;

    thread_local! {
        static BEFORE_PRUNE: RefCell<Option<Box<dyn Fn()>>> = const { RefCell::new(None) };
    }

    pub fn set_before_prune(f: Option<Box<dyn Fn()>>) {
        BEFORE_PRUNE.with(|c| *c.borrow_mut() = f);
    }

    pub fn run_before_prune() {
        BEFORE_PRUNE.with(|c| {
            if let Some(f) = c.borrow_mut().take() {
                f();
            }
        });
    }
}

/// Test hook: when set to a ref name, the next [`append_reflog`] for that ref fails.
///
/// Only active in debug builds; used by regression tests for commit ref/reflog atomicity.
#[cfg(test)]
mod reflog_fail_inject {
    use std::cell::RefCell;

    // hygiene: test-only reflog failure injection hook
    thread_local! {
        pub static INJECT: RefCell<Option<String>> = const { RefCell::new(None) };
    }
}

/// Test hook: fail the next reflog append for `refname` (or any ref when `None`).
#[cfg(test)]
pub fn set_test_inject_reflog_fail(refname: Option<&str>) {
    reflog_fail_inject::INJECT.with(|c| {
        *c.borrow_mut() = refname.map(str::to_owned);
    });
}

#[cfg(test)]
fn test_inject_reflog_fail(refname: &str) -> Result<()> {
    reflog_fail_inject::INJECT.with(|c| {
        if c.borrow().as_deref() == Some(refname) {
            return Err(Error::Io(std::io::Error::other("injected reflog failure")));
        }
        Ok(())
    })
}

#[cfg(not(test))]
fn test_inject_reflog_fail(_refname: &str) -> Result<()> {
    Ok(())
}

/// Move a checked-out branch to `new_oid` and append matching branch and `HEAD` reflogs.
///
/// Verifies `HEAD` is a symbolic ref to `branch_ref`, then runs a storage transaction:
/// on the files backend the branch ref lock is held from CAS through reflog writes and
/// ref commit; on reftable, branch and `HEAD` logs are written in one transaction.
/// Reflog failures before the ref commit do not advance the branch tip.
///
/// # Errors
///
/// Returns [`Error::Message`] when `HEAD` does not point at `branch_ref`,
/// [`store::RefStoreError::ExpectedMismatch`] (see [`verify_branch_commit_cas`]) when the
/// CAS check fails, or an I/O error when ref/reflog writes fail.
pub struct BranchCommitRefUpdate<'a> {
    /// Branch ref to update (e.g. `refs/heads/main`).
    pub branch_ref: &'a str,
    /// Expected current tip; `None` when the branch must not exist yet (unborn).
    pub expected_old: Option<ObjectId>,
    /// New commit OID for the branch tip.
    pub new_oid: ObjectId,
    /// Committer identity for reflog lines.
    pub identity: &'a str,
    /// Reflog message (without trailing newline).
    pub reflog_message: &'a str,
}

/// Compare expected and current branch tips for compare-and-swap ref updates.
///
/// `None` means the branch is absent (unborn) on either side.
///
/// # Errors
///
/// Returns [`Error::RefStore`] with [`store::RefStoreError::ExpectedMismatch`] when
/// `current` does not match `expected`; `expected` is [`Expected::Missing`] when the branch
/// had to be absent, and `actual` is `None` when it was.
pub fn verify_branch_commit_cas(
    expected: Option<ObjectId>,
    current: Option<ObjectId>,
    refname: &str,
) -> Result<()> {
    verify_branch_cas(expected, current, refname)
}

fn verify_branch_cas(
    expected: Option<ObjectId>,
    current: Option<ObjectId>,
    refname: &str,
) -> Result<()> {
    if expected == current {
        return Ok(());
    }
    Err(store::RefStoreError::ExpectedMismatch {
        name: refname.to_owned(),
        expected: expected.map_or(Expected::Missing, Expected::Oid),
        actual: current.map(StoreRawRef::Direct),
    }
    .into())
}

fn read_loose_or_packed_oid(git_dir: &Path, refname: &str) -> Result<Option<ObjectId>> {
    let (store, stor_name) = crate::worktree_ref::resolve_ref_storage(git_dir, refname);
    let storage_owned = crate::ref_namespace::storage_ref_name(&stor_name);
    let try_names: Vec<&str> = if storage_owned != stor_name {
        vec![storage_owned.as_str(), stor_name.as_str()]
    } else {
        vec![stor_name.as_str()]
    };
    for name in try_names {
        let path = store.join(name);
        if let Ok(Ref::Direct(oid)) = read_ref_file(&path) {
            return Ok(Some(oid));
        }
        if let Some(oid) = lookup_packed_ref(&store, name)? {
            return Ok(Some(oid));
        }
    }
    Ok(None)
}

#[cfg(test)]
mod test_pause_inject_serial {
    use std::sync::{Mutex, OnceLock};

    // hygiene: test-only pause injection serialization
    static SERIAL: OnceLock<Mutex<()>> = OnceLock::new();

    pub fn lock() -> std::sync::MutexGuard<'static, ()> {
        SERIAL
            .get_or_init(|| Mutex::new(()))
            .lock()
            .unwrap_or_else(|e| e.into_inner())
    }
}

/// Serialize tests that install global ref pause injection hooks (parallel `cargo test` safe).
#[cfg(test)]
pub fn test_pause_injection_serial_guard() -> std::sync::MutexGuard<'static, ()> {
    test_pause_inject_serial::lock()
}

#[cfg(test)]
mod branch_ref_pause_inject {
    use std::sync::{Condvar, Mutex, OnceLock};

    pub struct PauseGate {
        pub wait: Mutex<bool>,
        pub cv: Condvar,
    }

    // hygiene: test-only branch-ref commit pause injection
    static PAUSE_BEFORE_COMMIT: OnceLock<Mutex<Option<std::sync::Arc<PauseGate>>>> =
        OnceLock::new();

    pub fn pause_slot() -> &'static Mutex<Option<std::sync::Arc<PauseGate>>> {
        PAUSE_BEFORE_COMMIT.get_or_init(|| Mutex::new(None))
    }
}

/// Synchronization gate used with [`set_test_inject_branch_ref_pause_before_commit`].
#[cfg(test)]
pub type BranchRefPauseGate = std::sync::Arc<branch_ref_pause_inject::PauseGate>;

/// Test-only: pause [`update_branch_for_commit`] on the files backend after reflogs, before committing the ref.
#[cfg(test)]
pub fn set_test_inject_branch_ref_pause_before_commit(gate: Option<BranchRefPauseGate>) {
    *branch_ref_pause_inject::pause_slot()
        .lock()
        .unwrap_or_else(|e| e.into_inner()) = gate;
}

#[cfg(test)]
fn test_branch_ref_pause_before_commit() {
    let gate = branch_ref_pause_inject::pause_slot()
        .lock()
        .unwrap_or_else(|e| e.into_inner())
        .clone();
    if let Some(gate) = gate {
        let mut wait = gate.wait.lock().unwrap_or_else(|e| e.into_inner());
        *wait = true;
        gate.cv.notify_all();
        while *wait {
            wait = gate.cv.wait(wait).unwrap_or_else(|e| e.into_inner());
        }
    }
}

#[cfg(not(test))]
fn test_branch_ref_pause_before_commit() {}

#[cfg(test)]
mod ref_store_batch_pause_inject {
    use std::sync::{Condvar, Mutex, OnceLock};

    pub struct PauseGate {
        pub wait: Mutex<bool>,
        pub cv: Condvar,
    }

    // hygiene: test-only ref-store batch commit pause injection
    /// Armed pause: ref index, the repository it applies to, and the gate.
    pub type PauseSlot = Option<(usize, std::path::PathBuf, std::sync::Arc<PauseGate>)>;

    static PAUSE_AFTER_REF_WRITE: OnceLock<Mutex<PauseSlot>> = OnceLock::new();

    pub fn pause_slot() -> &'static Mutex<PauseSlot> {
        PAUSE_AFTER_REF_WRITE.get_or_init(|| Mutex::new(None))
    }
}

/// Synchronization gate used with [`set_test_inject_ref_store_batch_pause_after_apply`].
#[cfg(test)]
pub type RefStoreBatchPauseGate = std::sync::Arc<ref_store_batch_pause_inject::PauseGate>;

/// Test-only: build a pause gate for [`set_test_inject_ref_store_batch_pause_after_apply`].
#[cfg(test)]
pub fn new_ref_store_batch_pause_gate() -> RefStoreBatchPauseGate {
    std::sync::Arc::new(ref_store_batch_pause_inject::PauseGate {
        wait: std::sync::Mutex::new(false),
        cv: std::sync::Condvar::new(),
    })
}

/// Test-only: pause files ref-store batch commit after persisting the ref at `apply_index` (0-based).
///
/// Only ref stores for `git_dir` pause, so tests running in parallel against
/// other repositories are unaffected.
#[cfg(test)]
pub fn set_test_inject_ref_store_batch_pause_after_apply(
    apply_index: usize,
    git_dir: &Path,
    gate: Option<RefStoreBatchPauseGate>,
) {
    *ref_store_batch_pause_inject::pause_slot()
        .lock()
        .unwrap_or_else(|e| e.into_inner()) = gate.map(|g| (apply_index, git_dir.to_path_buf(), g));
}

#[cfg(test)]
struct RefStorePauseTestSerial {
    /// Held while one test owns ref-store batch pause injection.
    holder: Option<std::thread::ThreadId>,
}

#[cfg(test)]
static REF_STORE_PAUSE_TEST_SERIAL: std::sync::Mutex<RefStorePauseTestSerial> =
    std::sync::Mutex::new(RefStorePauseTestSerial { holder: None });

/// Serialize ref-store batch pause injection tests and clear injection on drop.
#[cfg(test)]
pub(crate) struct RefStoreBatchPauseTestScope {
    _serial: std::sync::MutexGuard<'static, RefStorePauseTestSerial>,
}

#[cfg(test)]
pub(crate) fn ref_store_batch_pause_test_scope() -> RefStoreBatchPauseTestScope {
    let mut serial = REF_STORE_PAUSE_TEST_SERIAL
        .lock()
        .unwrap_or_else(|e| e.into_inner());
    assert!(
        serial.holder.is_none(),
        "ref_store_batch_pause_test_scope must not nest"
    );
    serial.holder = Some(std::thread::current().id());
    set_test_inject_ref_store_batch_pause_after_apply(0, Path::new(""), None);
    RefStoreBatchPauseTestScope { _serial: serial }
}

#[cfg(test)]
impl Drop for RefStoreBatchPauseTestScope {
    fn drop(&mut self) {
        set_test_inject_ref_store_batch_pause_after_apply(0, Path::new(""), None);
        self._serial.holder = None;
    }
}

#[cfg(test)]
pub(crate) fn test_ref_store_batch_pause_after_ref_write(idx: usize, git_dir: &Path) {
    let slot = ref_store_batch_pause_inject::pause_slot()
        .lock()
        .unwrap_or_else(|e| e.into_inner())
        .clone();
    if let Some((target, target_dir, gate)) = slot {
        let same_repo = |a: &Path, b: &Path| {
            a == b || matches!((a.canonicalize(), b.canonicalize()), (Ok(a), Ok(b)) if a == b)
        };
        if idx != target || !same_repo(git_dir, &target_dir) {
            return;
        }
        let mut wait = gate.wait.lock().unwrap_or_else(|e| e.into_inner());
        *wait = true;
        gate.cv.notify_all();
        while *wait {
            wait = gate.cv.wait(wait).unwrap_or_else(|e| e.into_inner());
        }
    }
}

#[cfg(not(test))]
pub(crate) fn test_ref_store_batch_pause_after_ref_write(_idx: usize, _git_dir: &Path) {}

/// Loose branch ref lock held between CAS validation and the ref file commit.
///
/// Dropping without [`commit_branch_commit_ref_lock`](Self::commit) aborts the lock file.
pub struct BranchCommitRefLock {
    lock: Option<crate::lockfile::LockFile>,
    disarmed: bool,
}

impl BranchCommitRefLock {
    /// Acquire the branch ref lock and verify `expected_old` before worktree mutations.
    ///
    /// # Errors
    ///
    /// Same as [`update_branch_for_commit_with_config`], except no reflogs or ref write occur yet.
    pub fn acquire(
        git_dir: &Path,
        branch_ref: &str,
        expected_old: Option<ObjectId>,
    ) -> Result<Self> {
        ensure_refname_safe_for_storage(branch_ref)?;
        let storage_dir = ref_storage_dir(git_dir, branch_ref);
        if packed_ref_namespace_conflict(&storage_dir, branch_ref)? {
            return Err(Error::InvalidRef(format!(
                "cannot update ref '{}': reference namespace conflict",
                branch_ref
            )));
        }
        let stor = crate::ref_namespace::storage_ref_name(branch_ref);
        let path = storage_dir.join(&stor);
        remove_empty_ref_directory(&path);
        if fs::symlink_metadata(&path)
            .map(|m| m.file_type().is_dir())
            .unwrap_or(false)
        {
            let display = ref_path_for_display(&path);
            return Err(crate::error::RefLockError::DirectoryInTheWay {
                refname: branch_ref.to_owned(),
                path: display,
            }
            .into());
        }
        if let Some(parent) = path.parent() {
            crate::git_dir::io_error::io_with_git_path(
                git_dir,
                parent,
                crate::git_dir::GitDirPathOperation::CreateDir,
                fs::create_dir_all(parent),
            )?;
        }

        let lock_path = lock_path_for_ref(&path);
        use crate::lockfile::{LockError, LockFile, LockWait};
        let wait = LockWait::files_ref_lock_for_git_dir(git_dir);
        let lock = LockFile::acquire(&lock_path, wait).map_err(|err| match err {
            held @ LockError::Held { .. } => Error::from(held),
            LockError::Io { source, path } => crate::git_dir::io_error::map_git_dir_io(
                git_dir,
                path.as_path(),
                crate::git_dir::GitDirPathOperation::UpdateRef,
                source,
            ),
        })?;

        let current = read_loose_or_packed_oid(git_dir, branch_ref)?;
        verify_branch_cas(expected_old, current, branch_ref)?;

        Ok(Self {
            lock: Some(lock),
            disarmed: false,
        })
    }

    /// Append branch and `HEAD` reflog entries while holding the lock from [`Self::acquire`].
    ///
    /// Intended to run before worktree checkout so reflog I/O failures do not leave the
    /// index or working tree ahead of `HEAD`.
    ///
    /// # Errors
    ///
    /// Returns I/O or reflog failures; the ref lock is aborted and any branch reflog line
    /// written in this call is truncated.
    pub fn write_reflogs(
        &mut self,
        git_dir: &Path,
        update: &BranchCommitRefUpdate<'_>,
        reflog_old: &ObjectId,
        config: &ConfigSet,
    ) -> Result<()> {
        write_branch_commit_reflogs(git_dir, self, update, reflog_old, config)
    }

    /// Write the new OID into the held lock file and rename it over the branch ref.
    ///
    /// Call after the worktree matches `update.new_oid` when splitting reflog work from checkout.
    ///
    /// # Errors
    ///
    /// Returns I/O failures; the ref lock is aborted unless the rename succeeds.
    pub fn finish_ref_commit(
        mut self,
        git_dir: &Path,
        update: &BranchCommitRefUpdate<'_>,
    ) -> Result<()> {
        finish_branch_commit_ref_lock_files(git_dir, &mut self, update)?;
        self.disarmed = true;
        Ok(())
    }

    /// Write reflogs and commit the branch ref while holding the lock from [`Self::acquire`].
    ///
    /// # Errors
    ///
    /// Returns I/O or reflog failures; the lock is aborted unless the ref commit succeeds.
    pub fn commit(
        mut self,
        git_dir: &Path,
        update: &BranchCommitRefUpdate<'_>,
        reflog_old: &ObjectId,
        config: &ConfigSet,
    ) -> Result<()> {
        write_branch_commit_reflogs(git_dir, &mut self, update, reflog_old, config)?;
        finish_branch_commit_ref_lock_files(git_dir, &mut self, update)?;
        self.disarmed = true;
        Ok(())
    }
}

impl Drop for BranchCommitRefLock {
    fn drop(&mut self) {
        drop(self.lock.take());
    }
}

fn write_branch_commit_reflogs(
    git_dir: &Path,
    lock: &mut BranchCommitRefLock,
    update: &BranchCommitRefUpdate<'_>,
    reflog_old: &ObjectId,
    config: &ConfigSet,
) -> Result<()> {
    let mut branch_reflog_written = false;
    if should_autocreate_reflog_with_config(config, git_dir, update.branch_ref) {
        match append_reflog_with_config(
            git_dir,
            update.branch_ref,
            reflog_old,
            &update.new_oid,
            update.identity,
            update.reflog_message,
            false,
            Some(config),
        ) {
            Ok(()) => branch_reflog_written = true,
            Err(err) => {
                drop(lock.lock.take());
                return Err(err);
            }
        }
    }

    if should_autocreate_reflog_with_config(config, git_dir, "HEAD") {
        if let Err(err) = append_reflog_with_config(
            git_dir,
            "HEAD",
            reflog_old,
            &update.new_oid,
            update.identity,
            update.reflog_message,
            false,
            Some(config),
        ) {
            if branch_reflog_written {
                let _ = crate::reflog::truncate_last_reflog_line(git_dir, update.branch_ref);
            }
            drop(lock.lock.take());
            return Err(err);
        }
    }

    Ok(())
}

fn finish_branch_commit_ref_lock_files(
    git_dir: &Path,
    lock: &mut BranchCommitRefLock,
    update: &BranchCommitRefUpdate<'_>,
) -> Result<()> {
    test_branch_ref_pause_before_commit();

    let storage_dir = ref_storage_dir(git_dir, update.branch_ref);
    let stor = crate::ref_namespace::storage_ref_name(update.branch_ref);
    let path = storage_dir.join(&stor);
    let content = format!("{}\n", update.new_oid);
    use crate::lockfile::LockError;
    use std::io::Write as _;
    let mut file_lock = lock
        .lock
        .take()
        .ok_or_else(|| Error::Message("branch ref lock already released".into()))?;
    crate::git_dir::io_error::io_with_git_path(
        git_dir,
        &path,
        crate::git_dir::GitDirPathOperation::UpdateRef,
        file_lock.write_all(content.as_bytes()),
    )?;
    file_lock.commit_to(&path).map_err(|err| match err {
        LockError::Io {
            source,
            path: lock_path,
        } => crate::git_dir::io_error::map_git_dir_io(
            git_dir,
            lock_path.as_path(),
            crate::git_dir::GitDirPathOperation::UpdateRef,
            source,
        ),
        held @ LockError::Held { .. } => Error::from(held),
    })?;
    Ok(())
}

pub(crate) fn update_branch_for_commit_files(
    git_dir: &Path,
    update: &BranchCommitRefUpdate<'_>,
    reflog_old: &ObjectId,
    config: &ConfigSet,
) -> Result<()> {
    let lock = BranchCommitRefLock::acquire(git_dir, update.branch_ref, update.expected_old)?;
    lock.commit(git_dir, update, reflog_old, config)
}

/// Apply [`BranchCommitRefUpdate`]: branch CAS, ref write, branch + `HEAD` reflogs.
///
/// Opens the ref store for `git_dir`; prefer [`update_branch_for_commit_on_store`] with
/// [`crate::repo::Repository::refs`] when a repository handle is available.
pub fn update_branch_for_commit(git_dir: &Path, update: &BranchCommitRefUpdate<'_>) -> Result<()> {
    let config = ConfigSet::load(
        &crate::environment::Environment::empty(),
        Some(git_dir),
        true,
    )
    .unwrap_or_default();
    update_branch_for_commit_with_config(git_dir, update, &config)
}

/// Like [`update_branch_for_commit`], using a repository config snapshot for reflog policy.
///
/// Opens the ref store for `git_dir`; see [`update_branch_for_commit_on_store`].
pub fn update_branch_for_commit_with_config(
    git_dir: &Path,
    update: &BranchCommitRefUpdate<'_>,
    config: &ConfigSet,
) -> Result<()> {
    update_branch_for_commit_on_store(open_ref_store(git_dir)?.as_ref(), update, config)
}

/// Files-backend body of [`update_detached_head_for_commit_on_store`]; the caller has checked
/// that `HEAD` is detached.
pub(crate) fn update_detached_head_for_commit_files(
    git_dir: &Path,
    expected_old: Option<ObjectId>,
    new_oid: ObjectId,
    identity: &str,
    reflog_message: &str,
    config: &ConfigSet,
) -> Result<()> {
    let current = resolve_ref(git_dir, "HEAD").ok();
    verify_branch_cas(expected_old, current, "HEAD")?;
    let reflog_old = expected_old.unwrap_or_else(crate::diff::zero_oid);

    write_ref_cas(git_dir, "HEAD", &new_oid, reflog_old)?;
    if should_autocreate_reflog_with_config(config, git_dir, "HEAD") {
        if let Err(err) = append_reflog_with_config(
            git_dir,
            "HEAD",
            &reflog_old,
            &new_oid,
            identity,
            reflog_message,
            false,
            Some(config),
        ) {
            let _ = write_ref_cas(git_dir, "HEAD", &reflog_old, new_oid);
            return Err(err);
        }
    }
    Ok(())
}

/// Filesystem path to the reflog file for `refname` (same layout as [`append_reflog`]).
///
/// Branch and tag reflogs live under the shared [`common_dir`] when the repository uses a
/// `commondir` link (linked worktrees / `git clone --shared` member repos); `HEAD` stays under
/// `git_dir`.
#[must_use]
pub fn reflog_file_path(git_dir: &Path, refname: &str) -> PathBuf {
    let (store, stor_name) = crate::worktree_ref::resolve_ref_storage(git_dir, refname);
    store.join("logs").join(stor_name)
}

fn ref_storage_dir(git_dir: &Path, refname: &str) -> PathBuf {
    crate::worktree_ref::resolve_ref_storage(git_dir, refname).0
}

/// Normalize a ref prefix for filesystem traversal and packed-ref filtering.
///
/// Loose refs live in a directory tree mirroring ref names. A prefix like
/// `refs/remotes/origin` (no trailing slash) must map to the `origin/` directory
/// under `refs/remotes/`, not to a sibling file named `origin`. When the prefix
/// already names a **single loose ref file** (e.g. `refs/heads/main`), keep it
/// without a trailing slash so we read that file instead of a non-existent
/// directory.
fn normalize_list_refs_prefix(git_dir: &Path, prefix: &str) -> String {
    if prefix.is_empty() {
        return String::new();
    }
    if prefix.ends_with('/') {
        return prefix.to_string();
    }
    let candidate = ref_storage_dir(git_dir, prefix).join(prefix);
    if candidate.is_file() {
        prefix.to_string()
    } else {
        format!("{prefix}/")
    }
}

/// The `^` line of a `fully-peeled` `packed-refs` entry: the innermost non-tag object when `oid`
/// is an annotated tag. Lightweight refs, and tags whose chain cannot be read, get no peel line.
fn packed_ref_peel(odb: &crate::odb::Odb, oid: ObjectId) -> Option<ObjectId> {
    odb.peel_tag_target(oid).ok().flatten()
}

/// After the first clone fetch, batch remote-tracking refs into `packed-refs`
/// (Git's post-clone layout). Leaves `refs/remotes/{remote}/HEAD` as a loose
/// symbolic ref.
///
/// # Errors
///
/// Returns [`Error::Io`] on filesystem failures, or when a tag peel cannot be read.
pub fn pack_remote_tracking_refs_for_clone(git_dir: &Path, remote: &str) -> Result<()> {
    if open_ref_store(git_dir)?.format() != RefStorageFormat::Files {
        return Ok(());
    }
    let prefix = format!("refs/remotes/{remote}/");
    let head_sym = format!("refs/remotes/{remote}/HEAD");
    let mut entries = list_refs(git_dir, &prefix)?;
    entries.retain(|(name, _)| name != &head_sym);
    if entries.is_empty() {
        return Ok(());
    }
    entries.sort_by(|a, b| a.0.cmp(&b.0));

    let odb =
        crate::odb::Odb::new(&git_dir.join("objects")).with_config_git_dir(git_dir.to_path_buf());
    let mut merged: HashMap<String, (ObjectId, Option<ObjectId>)> = HashMap::new();
    let packed_path = store::paths::packed_refs_path(git_dir);
    if let Ok(data) = fs::read(&packed_path) {
        parse_packed_refs_to_map(&packed_path, &data)?;
        let content = String::from_utf8(data)
            .map_err(|_| packed_refs_unexpected_line(&packed_path, "<invalid utf-8>"))?;
        let mut last_name: Option<String> = None;
        for line in content.split('\n') {
            if line.starts_with('#') {
                continue;
            }
            if let Some(hex) = line.strip_prefix('^') {
                let Ok(peel_oid) = ObjectId::from_hex(hex.trim()) else {
                    continue;
                };
                if let Some(name) = &last_name {
                    if let Some(entry) = merged.get_mut(name) {
                        entry.1 = Some(peel_oid);
                    }
                }
                continue;
            }
            let mut parts = line.splitn(2, ' ');
            let Some(hex) = parts.next() else {
                continue;
            };
            let Some(name) = parts.next() else {
                continue;
            };
            let name = name.trim();
            let Ok(oid) = ObjectId::from_hex(hex) else {
                continue;
            };
            if name.starts_with(&prefix) {
                last_name = None;
                continue;
            }
            merged.insert(name.to_owned(), (oid, None));
            last_name = Some(name.to_owned());
        }
    }

    for (name, oid) in &entries {
        merged.insert(name.clone(), (*oid, packed_ref_peel(&odb, *oid)));
    }

    let mut names: Vec<String> = merged.keys().cloned().collect();
    names.sort();

    let mut body = String::from("# pack-refs with: peeled fully-peeled sorted\n");
    for name in &names {
        let Some((oid, peel)) = merged.get(name) else {
            continue;
        };
        body.push_str(&oid.to_hex());
        body.push(' ');
        body.push_str(name);
        body.push('\n');
        if let Some(p) = peel {
            body.push('^');
            body.push_str(&p.to_hex());
            body.push('\n');
        }
    }

    atomic_rewrite_packed_refs(git_dir, &body)?;

    for (name, _) in &entries {
        let storage_dir = ref_storage_dir(git_dir, name);
        let stor = crate::ref_namespace::storage_ref_name(name);
        let path = storage_dir.join(&stor);
        if path.is_file() {
            let _ = fs::remove_file(&path);
        }
        if let Some(parent) = path.parent() {
            remove_empty_ref_directory(parent);
        }
    }
    Ok(())
}

/// Rewrite `packed-refs` under the packed-refs lock (tempfile + rename).
fn atomic_rewrite_packed_refs(git_dir: &Path, body: &str) -> Result<()> {
    let packed_path = store::paths::packed_refs_path(git_dir);
    let lock = lock_path_for_ref(&packed_path);
    let abs_lock = fs::canonicalize(git_dir)
        .map(|d| d.join("packed-refs.lock"))
        .unwrap_or_else(|_| lock.clone());
    let _packed_lock = acquire_packed_refs_lock(git_dir, &lock, &abs_lock)?;

    let tmp = packed_path.with_extension("new");
    let mut created_tmp = false;
    let write_result = (|| -> Result<()> {
        // Staged packed-refs body (not a lock file); exclusive create avoids clobber.
        let mut file = std::fs::OpenOptions::new()
            .write(true)
            .create_new(true)
            .open(&tmp)
            .map_err(Error::Io)?;
        created_tmp = true;
        use std::io::Write as _;
        file.write_all(body.as_bytes()).map_err(Error::Io)?;
        drop(file);
        fs::rename(&tmp, &packed_path).map_err(Error::Io)?;
        created_tmp = false;
        Ok(())
    })();
    if write_result.is_err() && created_tmp {
        let _ = fs::remove_file(&tmp);
    }
    write_result
}

/// One reference line (and optional peel) for [`write_packed_refs_file`].
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct PackedRefRecord {
    /// Full ref name (for example `refs/heads/feature`).
    pub refname: String,
    /// Object id stored at this ref.
    pub oid: ObjectId,
    /// When set, emit a following `^` peeled line (annotated tags).
    pub peeled: Option<ObjectId>,
}

/// Replace `packed-refs` with `records`, sorted by ref name.
///
/// Existing loose ref files for names present in `records` are removed so the
/// packed file is authoritative (Git's `pack-refs` behaviour).
///
/// # Errors
///
/// Returns [`Error::InvalidRef`] for unsafe ref names, or [`Error::Io`] on failure.
pub fn write_packed_refs_file(git_dir: &Path, records: &[PackedRefRecord]) -> Result<()> {
    let mut sorted: Vec<&PackedRefRecord> = records.iter().collect();
    sorted.sort_by(|a, b| a.refname.cmp(&b.refname));
    for rec in &sorted {
        ensure_refname_safe_for_storage(&rec.refname)?;
    }
    let mut body = String::from("# pack-refs with: peeled fully-peeled sorted\n");
    for rec in &sorted {
        body.push_str(&rec.oid.to_hex());
        body.push(' ');
        body.push_str(&rec.refname);
        body.push('\n');
        if let Some(peeled) = rec.peeled {
            body.push('^');
            body.push_str(&peeled.to_hex());
            body.push('\n');
        }
    }
    atomic_rewrite_packed_refs(git_dir, &body)?;
    for rec in &sorted {
        let storage_dir = ref_storage_dir(git_dir, &rec.refname);
        let stor = crate::ref_namespace::storage_ref_name(&rec.refname);
        let loose = storage_dir.join(stor);
        if loose.is_file() {
            fs::remove_file(&loose).map_err(Error::Io)?;
        }
        if let Some(parent) = loose.parent() {
            remove_empty_ref_directory(parent);
        }
    }
    Ok(())
}

/// List all refs under a given prefix (e.g. `"refs/heads/"`).
///
/// Dispatches to the reftable backend when `extensions.refStorage = reftable`.
///
/// Returns a sorted list of `(refname, ObjectId)` pairs.
///
/// # Errors
///
/// Returns [`Error::Io`] on directory traversal errors.
/// List refs under `prefix` using the given repository's ref store.
pub fn list_refs_for_repository(
    repo: &crate::repo::Repository,
    prefix: &str,
) -> Result<Vec<(String, ObjectId)>> {
    let prefix_norm = normalize_list_refs_prefix(repo.git_dir(), prefix);
    list_store_refs_with_name_prefix(repo, &prefix_norm)
}

/// Refs whose names start with `prefix` (taken literally), from `repo`'s ref store.
fn list_store_refs_with_name_prefix(
    repo: &crate::repo::Repository,
    prefix: &str,
) -> Result<Vec<(String, ObjectId)>> {
    let git_dir = repo.git_dir();
    let mut results = collect_resolved_refs(repo.refs(), prefix)?;
    if crate::worktree_ref::is_linked_worktree_git_dir(git_dir) {
        results.retain(|(name, _)| crate::worktree_ref::ref_visible_from_worktree(git_dir, name));
    }
    results.sort_by(|a, b| a.0.cmp(&b.0));
    Ok(results)
}

/// [`list_refs`] for `repo`, honouring an injected ref store.
///
/// Files and reftable repositories are listed from the git directory with a throwaway store:
/// for a one-off listing of many refs that is faster and leaner than going through the
/// handle's long-lived store, which keeps a `packed-refs` snapshot. Any other store is
/// listed through [`list_refs_for_repository`].
///
/// # Errors
///
/// Propagates ref-store open/read failures.
pub(crate) fn list_refs_in(
    repo: &crate::repo::Repository,
    prefix: &str,
) -> Result<Vec<(String, ObjectId)>> {
    if repo.refs_on_disk() {
        list_refs(repo.git_dir(), prefix)
    } else {
        list_refs_for_repository(repo, prefix)
    }
}

/// [`resolve_ref`] for `repo`, honouring an injected ref store the same way [`list_refs_in`]
/// does.
///
/// # Errors
///
/// Same as [`resolve_ref`].
pub(crate) fn resolve_ref_in(repo: &crate::repo::Repository, refname: &str) -> Result<ObjectId> {
    if repo.refs_on_disk() {
        resolve_ref(repo.git_dir(), refname)
    } else {
        repo.resolve_ref_oid(refname)
    }
}

/// [`list_refs_glob`] for `repo`, honouring an injected ref store the same way
/// [`list_refs_in`] does.
///
/// # Errors
///
/// Propagates ref-store open/read failures.
pub(crate) fn list_refs_glob_in(
    repo: &crate::repo::Repository,
    pattern: &str,
) -> Result<Vec<(String, ObjectId)>> {
    if repo.refs_on_disk() {
        list_refs_glob(repo.git_dir(), pattern)
    } else {
        list_refs_glob_for_repository(repo, pattern)
    }
}

/// List resolved refs under `git_dir` whose full names start with `prefix`.
///
/// Uses the on-disk ref backend (files or reftable) and applies linked-worktree
/// visibility rules when `git_dir` is a linked worktree git directory.
///
/// # Errors
///
/// Propagates ref-store open/read failures.
pub fn list_refs(git_dir: &Path, prefix: &str) -> Result<Vec<(String, ObjectId)>> {
    let prefix_norm = normalize_list_refs_prefix(git_dir, prefix);
    let prefix = prefix_norm.as_str();
    let store = open_ref_store(git_dir)?;
    if store.format() != RefStorageFormat::Files {
        return crate::reftable::reftable_list_refs(git_dir, prefix);
    }
    let mut results = collect_resolved_refs(store.as_ref(), prefix)?;
    if crate::worktree_ref::is_linked_worktree_git_dir(git_dir) {
        results.retain(|(name, _)| crate::worktree_ref::ref_visible_from_worktree(git_dir, name));
    }
    results.sort_by(|a, b| a.0.cmp(&b.0));
    Ok(results)
}

/// [`list_refs`], except that `packed-refs` records `keep` rejects may be left out.
///
/// `keep` receives each packed record's name, object id and what the file records about
/// peeling it, before anything is allocated for the record. Loose refs, and every ref of a
/// reftable repository, are always listed, so `keep` only ever narrows the listing to a
/// subset of [`list_refs`].
///
/// # Errors
///
/// Propagates ref-store open/read failures, like [`list_refs`].
pub(crate) fn list_refs_filtering_packed(
    git_dir: &Path,
    prefix: &str,
    keep: PackedRecordFilter<'_>,
) -> Result<Vec<(String, ObjectId)>> {
    let Some(store) = store::open_files_ref_store(git_dir)? else {
        return list_refs(git_dir, prefix);
    };
    let prefix_norm = normalize_list_refs_prefix(git_dir, prefix);
    let prefix = prefix_norm.as_str();
    let mut results = collect_resolved_ref_entries(&store, |f| {
        store.for_each_ref_filtered(prefix, Some(keep), f)
    })?;
    if crate::worktree_ref::is_linked_worktree_git_dir(git_dir) {
        results.retain(|(name, _)| crate::worktree_ref::ref_visible_from_worktree(git_dir, name));
    }
    results.sort_by(|a, b| a.0.cmp(&b.0));
    Ok(results)
}

/// Resolve a ref using Git DWIM rules (`expand_ref` / `repo_dwim_ref`).
pub fn resolve_ref_dwim(git_dir: &Path, spec: &str) -> (usize, Option<ObjectId>) {
    crate::worktree_ref::resolve_ref_dwim(|candidate| resolve_ref(git_dir, candidate).ok(), spec)
}

/// List refs under `prefix` using **literal** on-disk paths (ignores `GIT_NAMESPACE`).
///
/// Used by `receive-pack` when advertising: the server must see every physical ref so refs outside
/// the active namespace can be offered as `.have` lines (matches Git `show_ref_cb`).
pub fn list_refs_physical(git_dir: &Path, prefix: &str) -> Result<Vec<(String, ObjectId)>> {
    if open_ref_store(git_dir)?.format() != RefStorageFormat::Files {
        return crate::reftable::reftable_list_refs(git_dir, prefix);
    }
    let mut by_name: HashMap<String, ObjectId> = HashMap::new();
    let stored_prefix = prefix.to_owned();

    if let Some(cdir) = common_dir(git_dir) {
        if cdir != git_dir {
            collect_packed_refs_into_map(&cdir, &stored_prefix, true, &mut by_name)?;
            let (loose_root, loose_prefix) = loose_ref_list_walk_root(&cdir, &stored_prefix);
            collect_loose_refs_into_map(
                &loose_root,
                &loose_prefix,
                &stored_prefix,
                &cdir,
                true,
                &mut by_name,
            )?;
        }
    }

    collect_packed_refs_into_map(git_dir, &stored_prefix, true, &mut by_name)?;
    let (loose_root, loose_prefix) = loose_ref_list_walk_root(git_dir, &stored_prefix);
    collect_loose_refs_into_map(
        &loose_root,
        &loose_prefix,
        &stored_prefix,
        git_dir,
        true,
        &mut by_name,
    )?;

    let mut results: Vec<(String, ObjectId)> = by_name.into_iter().collect();
    results.sort_by(|a, b| a.0.cmp(&b.0));
    Ok(results)
}

/// Collect commit OIDs from alternate repositories' refs, matching Git's
/// `git for-each-ref --format=%(objectname)` on each alternate (with optional
/// `core.alternateRefsPrefixes` arguments).
///
/// Order is preserved: alternates file order, then ref iteration order from
/// [`list_refs`] under each configured prefix (or all of `refs/` when no
/// prefixes are set). Duplicate OIDs are skipped while preserving first-seen
/// order.
pub fn collect_alternate_ref_oids(receiving_git_dir: &Path) -> Result<Vec<ObjectId>> {
    let config = ConfigSet::load(
        &crate::environment::Environment::empty(),
        Some(receiving_git_dir),
        true,
    )?;
    let objects_dir = receiving_git_dir.join("objects");
    let alternates = pack::read_alternates_recursive(&objects_dir).unwrap_or_default();
    let mut out = Vec::new();
    let mut seen = std::collections::HashSet::new();
    for alt_objects in alternates {
        let Some(alt_git_dir) = alt_objects.parent().map(PathBuf::from) else {
            continue;
        };
        if !alt_git_dir.join("refs").is_dir() {
            continue;
        }
        if let Some(prefixes) = config
            .get("core.alternaterefsprefixes")
            .or_else(|| config.get("core.alternateRefsPrefixes"))
        {
            for part in prefixes.split_whitespace() {
                if let Ok(oid) = resolve_ref(&alt_git_dir, part) {
                    if seen.insert(oid) {
                        out.push(oid);
                    }
                    continue;
                }
                for (_, oid) in list_refs(&alt_git_dir, part)? {
                    if seen.insert(oid) {
                        out.push(oid);
                    }
                }
            }
        } else {
            for (_, oid) in list_refs(&alt_git_dir, "refs/")? {
                if seen.insert(oid) {
                    out.push(oid);
                }
            }
        }
    }
    Ok(out)
}

/// List refs matching a glob pattern (e.g. `refs/heads/topic/*`) using `repo`'s ref store.
pub fn list_refs_glob_for_repository(
    repo: &crate::repo::Repository,
    pattern: &str,
) -> Result<Vec<(String, ObjectId)>> {
    // The text before a wildcard is a name prefix, not a directory (`refs/tags/v*` must
    // list `refs/tags/v1`), so it skips the directory normalization of
    // [`list_refs_for_repository`].
    let all = match pattern.find(['*', '?', '[']) {
        Some(pos) => list_store_refs_with_name_prefix(repo, &pattern[..pos])?,
        None => {
            let mut dir = pattern.trim_end_matches('/').to_owned();
            if !dir.is_empty() {
                dir.push('/');
            }
            list_refs_for_repository(repo, &dir)?
        }
    };
    Ok(all
        .into_iter()
        .filter(|(refname, _)| ref_matches_glob(refname, pattern))
        .collect())
}

/// List refs matching a glob pattern (e.g. `refs/heads/topic/*`).
pub fn list_refs_glob(git_dir: &Path, pattern: &str) -> Result<Vec<(String, ObjectId)>> {
    let glob_pos = pattern.find(['*', '?', '[']);
    let prefix_owned: String = match glob_pos {
        // Literal segment before the first wildcard (e.g. `refs/heads/b05*` → `refs/heads/b05`).
        Some(pos) => pattern[..pos].to_owned(),
        None => {
            let mut p = pattern.trim_end_matches('/').to_owned();
            if !p.is_empty() {
                p.push('/');
            }
            p
        }
    };
    let prefix = prefix_owned.as_str();
    let all = list_refs(git_dir, prefix)?;
    let mut results = Vec::new();
    for (refname, oid) in all {
        if ref_matches_glob(&refname, pattern) {
            results.push((refname, oid));
        }
    }
    Ok(results)
}

/// Check whether a ref name matches a glob pattern.
///
/// Supports `*`, `?`, and `[…]` wildcards. An exact string match is also accepted.
pub fn ref_matches_glob(refname: &str, pattern: &str) -> bool {
    // For exact matches (no glob characters), check suffix match
    if !pattern.contains('*') && !pattern.contains('?') && !pattern.contains('[') {
        return refname == pattern
            || refname.ends_with(&format!("/{pattern}"))
            || refname.starts_with(&format!("{pattern}/"));
    }
    glob_match(pattern, refname)
}

fn glob_match(pattern: &str, text: &str) -> bool {
    let pat = pattern.as_bytes();
    let txt = text.as_bytes();
    let (mut pi, mut ti) = (0, 0);
    let (mut star_pi, mut star_ti) = (usize::MAX, 0);
    while ti < txt.len() {
        if pi < pat.len() && (pat[pi] == b'?' || pat[pi] == txt[ti]) {
            pi += 1;
            ti += 1;
        } else if pi < pat.len() && pat[pi] == b'*' {
            star_pi = pi;
            star_ti = ti;
            pi += 1;
        } else if star_pi != usize::MAX {
            pi = star_pi + 1;
            star_ti += 1;
            ti = star_ti;
        } else {
            return false;
        }
    }
    while pi < pat.len() && pat[pi] == b'*' {
        pi += 1;
    }
    pi == pat.len()
}

/// OID stored directly in a loose ref file (40 hex), ignoring symbolic targets.
fn loose_ref_file_direct_oid(path: &Path) -> Option<ObjectId> {
    let content = fs::read_to_string(path).ok()?;
    let content = content.trim_end_matches('\n').trim();
    if ObjectId::is_full_hex(content) {
        content.parse().ok()
    } else {
        None
    }
}

fn collect_loose_refs_into_map(
    dir: &Path,
    prefix: &str,
    filter_prefix: &str,
    resolve_git_dir: &Path,
    physical_keys: bool,
    out: &mut HashMap<String, ObjectId>,
) -> Result<()> {
    let read = match fs::read_dir(dir) {
        Ok(r) => r,
        Err(e)
            if e.kind() == io::ErrorKind::NotFound
                || e.kind() == io::ErrorKind::NotADirectory
                || e.raw_os_error() == Some(libc::ENOTDIR) =>
        {
            return Ok(());
        }
        Err(e) => return Err(Error::Io(e)),
    };

    for entry in read {
        let entry = entry?;
        let name = entry.file_name();
        let name_str = name.to_string_lossy();
        let refname = format!("{prefix}{name_str}");
        let path = entry.path();
        let meta = match fs::metadata(&path) {
            Ok(m) => m,
            Err(_) => continue,
        };

        if meta.is_dir() {
            collect_loose_refs_into_map(
                &path,
                &format!("{refname}/"),
                filter_prefix,
                resolve_git_dir,
                physical_keys,
                out,
            )?;
        } else if meta.is_file() {
            if physical_keys {
                if let Some(oid) = loose_ref_file_direct_oid(&path) {
                    out.insert(refname, oid);
                } else if let Ok(Ref::Symbolic(target)) = read_ref_file(&path) {
                    if let Ok(oid) = resolve_ref(resolve_git_dir, target.trim()) {
                        out.insert(refname, oid);
                    }
                }
            } else {
                let logical = crate::ref_namespace::logical_ref_name_from_storage(&refname)
                    .unwrap_or_else(|| refname.clone());
                if !ref_name_matches_list_prefix(&logical, filter_prefix.trim_end_matches('/')) {
                    continue;
                }
                if let Some(oid) = loose_ref_file_direct_oid(&path) {
                    out.insert(logical, oid);
                } else if let Ok(Ref::Symbolic(target)) = read_ref_file(&path) {
                    if let Ok(oid) = resolve_ref(resolve_git_dir, target.trim()) {
                        out.insert(logical, oid);
                    }
                }
            }
        }
    }
    Ok(())
}

/// Resolve `@{-N}` syntax to the branch name (not an OID).
/// Returns the branch name of the Nth previously checked out branch.
pub fn resolve_at_n_branch(git_dir: &Path, spec: &str) -> Result<String> {
    // Parse the N from @{-N}
    let inner = spec
        .strip_prefix("@{-")
        .and_then(|s| s.strip_suffix('}'))
        .ok_or_else(|| Error::InvalidRef(format!("not an @{{-N}} ref: {spec}")))?;
    let n: usize = inner
        .parse()
        .map_err(|_| Error::InvalidRef(format!("invalid N in {spec}")))?;
    if n == 0 {
        return Err(Error::InvalidRef("@{-0} is not valid".to_string()));
    }
    let entries = crate::reflog::read_reflog(git_dir, "HEAD")?;
    let mut count = 0usize;
    for entry in entries.iter().rev() {
        let msg = &entry.message;
        if let Some(rest) = msg.strip_prefix("checkout: moving from ") {
            count += 1;
            if count == n {
                if let Some(to_pos) = rest.find(" to ") {
                    return Ok(rest[..to_pos].to_string());
                }
            }
        }
    }
    Err(Error::InvalidRef(format!(
        "{spec}: only {count} checkout(s) in reflog"
    )))
}

fn ref_name_matches_list_prefix(refname: &str, prefix: &str) -> bool {
    let prefix = prefix.trim_end_matches('/');
    if prefix.is_empty() {
        return true;
    }
    if refname.starts_with(prefix) {
        return true;
    }
    if refname == prefix {
        return true;
    }
    false
}

fn list_prefix_upper_bound(prefix: &str) -> Option<String> {
    let base = prefix.trim_end_matches('/');
    let (head, tail) = base.rsplit_once('/')?;
    let mut chars: Vec<char> = tail.chars().collect();
    while let Some(last) = chars.pop() {
        if last != '\u{10ffff}' {
            chars.push(char::from_u32(last as u32 + 1).unwrap_or(last));
            return Some(format!("{head}/{}", chars.into_iter().collect::<String>()));
        }
    }
    None
}

/// When `prefix` names a partial ref (e.g. `refs/heads/b05/` with no `b05/` directory),
/// start the walk at the parent directory (`refs/heads/`) and filter by prefix.
pub(crate) fn loose_ref_list_walk_root(git_dir: &Path, prefix: &str) -> (PathBuf, String) {
    let trimmed = prefix.trim_end_matches('/');
    if trimmed.is_empty() {
        return (git_dir.join("refs"), "refs/".to_owned());
    }
    let direct = git_dir.join(trimmed);
    if direct.is_dir() {
        return (direct, format!("{trimmed}/"));
    }
    if let Some(slash) = trimmed.rfind('/') {
        let parent = &trimmed[..slash];
        return (git_dir.join(parent), format!("{parent}/"));
    }
    (git_dir.to_path_buf(), String::new())
}

fn collect_packed_refs_into_map(
    git_dir: &Path,
    prefix: &str,
    physical_keys: bool,
    out: &mut HashMap<String, ObjectId>,
) -> Result<()> {
    let map = read_packed_refs_map_for_prefix(git_dir, prefix)?;
    for (refname, oid) in map {
        let key = if physical_keys {
            refname.clone()
        } else {
            crate::ref_namespace::logical_ref_name_from_storage(&refname).unwrap_or(refname)
        };
        out.insert(key, oid);
    }
    Ok(())
}

#[cfg(test)]
mod update_branch_for_commit_tests {
    use super::*;
    use crate::reflog::read_reflog;
    use crate::repo::init_repository;
    use std::sync::{Arc, Condvar, Mutex};
    use std::thread;
    use tempfile::TempDir;

    fn sample_oid(hex: &str) -> ObjectId {
        hex.parse().unwrap()
    }

    #[test]
    fn update_branch_for_commit_holds_lock_until_ref_commit() {
        let _pause_serial = super::test_pause_injection_serial_guard();
        let tmp = TempDir::new().unwrap();
        let repo = init_repository(
            tmp.path(),
            false,
            "main",
            None,
            crate::RefStorageFormat::Files,
        )
        .unwrap();
        let git_dir = repo.git_dir().to_path_buf();
        let oid1 = sample_oid("67bf698f3ab735e92fb011a99cff3497c44d30c1");
        let oid2 = sample_oid("1111111111111111111111111111111111111111");
        let oid3 = sample_oid("2222222222222222222222222222222222222222");
        write_ref(&git_dir, "refs/heads/main", &oid1).unwrap();

        let gate = Arc::new(branch_ref_pause_inject::PauseGate {
            wait: Mutex::new(false),
            cv: Condvar::new(),
        });
        set_test_inject_branch_ref_pause_before_commit(Some(gate.clone()));

        let git_dir_thread = git_dir.clone();
        let handle = thread::spawn(move || {
            update_branch_for_commit(
                &git_dir_thread,
                &BranchCommitRefUpdate {
                    branch_ref: "refs/heads/main",
                    expected_old: Some(oid1),
                    new_oid: oid2,
                    identity: "T <t@e.com> 1 +0000",
                    reflog_message: "commit: test",
                },
            )
        });

        let mut wait = gate.wait.lock().unwrap();
        while !*wait {
            wait = gate.cv.wait(wait).unwrap();
        }

        assert!(
            write_ref(&git_dir, "refs/heads/main", &oid3).is_err(),
            "concurrent branch update must block on the held ref lock"
        );

        *wait = false;
        gate.cv.notify_all();
        drop(wait);
        handle.join().unwrap().unwrap();
        set_test_inject_branch_ref_pause_before_commit(None);

        assert_eq!(resolve_ref(&git_dir, "refs/heads/main").unwrap(), oid2);
    }

    #[test]
    fn update_branch_for_commit_reftable_transaction_is_all_or_nothing() {
        let tmp = TempDir::new().unwrap();
        let repo = init_repository(
            tmp.path(),
            false,
            "main",
            None,
            crate::RefStorageFormat::Reftable,
        )
        .unwrap();
        let git_dir = repo.git_dir().to_path_buf();
        let new_oid = sample_oid("3333333333333333333333333333333333333333");

        crate::reftable::set_test_inject_reftable_transaction_fail(true);
        let err = update_branch_for_commit(
            &git_dir,
            &BranchCommitRefUpdate {
                branch_ref: "refs/heads/main",
                expected_old: None,
                new_oid,
                identity: "T <t@e.com> 1 +0000",
                reflog_message: "commit (initial): test",
            },
        )
        .unwrap_err();
        crate::reftable::set_test_inject_reftable_transaction_fail(false);
        assert!(!matches!(err, Error::Message(_)));

        assert!(resolve_ref(&git_dir, "refs/heads/main").is_err());
        assert!(read_reflog(&git_dir, "refs/heads/main").unwrap().is_empty());
        assert!(read_reflog(&git_dir, "HEAD").unwrap().is_empty());
    }
}

#[cfg(test)]
mod refname_available_tests {
    use super::*;
    use std::collections::{BTreeSet, HashSet};
    use tempfile::tempdir;

    #[test]
    fn verify_ref_transaction_batch_rejects_same_batch_parent_child() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/heads")).unwrap();
        let items = vec![
            RefBatchItem {
                name: "refs/heads/c".to_owned(),
                new_oid: Some(sample_oid()),
            },
            RefBatchItem {
                name: "refs/heads/c/x".to_owned(),
                new_oid: Some(sample_oid()),
            },
        ];
        let err = verify_ref_transaction_batch(git_dir, &items).unwrap_err();
        assert!(matches!(
            err,
            RefnameUnavailable::SameBatch { refname, .. } if refname == "refs/heads/c/x"
        ));
    }

    fn sample_oid() -> ObjectId {
        "67bf698f3ab735e92fb011a99cff3497c44d30c1".parse().unwrap()
    }

    #[test]
    fn loose_parent_blocks_child_create() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/1l")).unwrap();
        fs::write(
            git_dir.join("refs/1l/c"),
            "67bf698f3ab735e92fb011a99cff3497c44d30c1\n",
        )
        .unwrap();
        assert_eq!(
            read_raw_ref(git_dir, "refs/1l/c").unwrap(),
            RawRefLookup::Exists
        );
        let extras = BTreeSet::from([
            "refs/1l/b".to_string(),
            "refs/1l/c/x".to_string(),
            "refs/1l/d".to_string(),
        ]);
        let skip = HashSet::new();
        let err = verify_refname_available_for_create(git_dir, "refs/1l/c/x", &extras, &skip)
            .unwrap_err();
        assert!(matches!(
            err,
            RefnameUnavailable::AncestorExists { ref blocking, .. } if blocking == "refs/1l/c"
        ));
    }

    #[test]
    fn verify_sees_loose_ref_after_canonical_git_dir() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path().join(".git");
        fs::create_dir_all(git_dir.join("refs/1l")).unwrap();
        fs::write(
            git_dir.join("refs/1l/c"),
            "67bf698f3ab735e92fb011a99cff3497c44d30c1\n",
        )
        .unwrap();
        let skip = HashSet::new();
        let extras = BTreeSet::new();
        let err = verify_refname_available_for_create(&git_dir, "refs/1l/c/x", &extras, &skip)
            .unwrap_err();
        assert!(matches!(
            err,
            RefnameUnavailable::AncestorExists { ref blocking, .. } if blocking == "refs/1l/c"
        ));
    }

    fn refname_namespace_conflicts(existing: &str, candidate: &str) -> bool {
        if existing == candidate {
            return false;
        }
        existing
            .strip_prefix(candidate)
            .is_some_and(|rest| rest.starts_with('/'))
            || candidate
                .strip_prefix(existing)
                .is_some_and(|rest| rest.starts_with('/'))
    }

    #[test]
    fn packed_namespace_index_matches_pairwise_scan() {
        let mut sorted: BTreeSet<String> = BTreeSet::new();
        for i in 0..500 {
            sorted.insert(format!("refs/heads/b{i:05}"));
        }
        sorted.insert("refs/heads/parent".into());
        sorted.insert("refs/heads/a/b".into());
        let candidates = [
            "refs/heads/b00001",
            "refs/heads/parent/child",
            "refs/heads/new",
            "refs/heads/a",
        ];
        for candidate in candidates {
            let indexed = packed_refname_namespace_conflict(&sorted, candidate);
            let linear = sorted
                .iter()
                .any(|existing| refname_namespace_conflicts(existing, candidate));
            assert_eq!(indexed, linear, "candidate {candidate}");
        }
    }

    #[test]
    fn list_refs_glob_b05_star_matches_one_thousand_packed_refs() {
        let git_dir = Path::new("/tmp/grit-bench-refs-cache/refs-100k-packed");
        if !git_dir.is_dir() {
            return;
        }
        let listed = list_refs_glob(git_dir, "refs/heads/b05*").unwrap();
        assert_eq!(listed.len(), 1000, "expected 1k b05* refs");
        assert!(listed
            .iter()
            .all(|(name, _)| name.starts_with("refs/heads/b05")));
    }

    #[test]
    fn list_refs_finds_sibling_under_parent_directory() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/ns/p")).unwrap();
        fs::write(
            git_dir.join("refs/ns/p/x"),
            "67bf698f3ab735e92fb011a99cff3497c44d30c1\n",
        )
        .unwrap();
        let listed = list_refs(git_dir, "refs/ns/p/").unwrap();
        assert!(
            listed.iter().any(|(n, _)| n == "refs/ns/p/x"),
            "got {listed:?}"
        );
    }

    #[test]
    fn verify_blocks_parent_when_child_ref_exists() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/ns/p")).unwrap();
        fs::write(
            git_dir.join("refs/ns/p/x"),
            "67bf698f3ab735e92fb011a99cff3497c44d30c1\n",
        )
        .unwrap();
        let extras = BTreeSet::from(["refs/ns/p".to_string()]);
        let skip = HashSet::new();
        let err =
            verify_refname_available_for_create(git_dir, "refs/ns/p", &extras, &skip).unwrap_err();
        assert!(matches!(
            err,
            RefnameUnavailable::DescendantExists { ref blocking, .. }
                if blocking == "refs/ns/p/x"
        ));
    }

    #[test]
    fn verify_blocks_parent_when_only_a_packed_child_exists() {
        // No `refs/ns/q/` directory on disk, so the loose listing is skipped;
        // the packed-refs check must still find the descendant.
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs")).unwrap();
        fs::write(
            store::paths::packed_refs_path(git_dir),
            "# pack-refs with: peeled fully-peeled\n\
             67bf698f3ab735e92fb011a99cff3497c44d30c1 refs/ns/q/x\n",
        )
        .unwrap();
        let err = verify_refname_available_for_create(
            git_dir,
            "refs/ns/q",
            &BTreeSet::new(),
            &HashSet::new(),
        )
        .unwrap_err();
        assert!(matches!(
            err,
            RefnameUnavailable::DescendantExists { ref blocking, .. }
                if blocking == "refs/ns/q/x"
        ));
    }

    #[test]
    fn verify_allows_name_whose_siblings_share_a_prefix() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/tags")).unwrap();
        for name in ["v1.0.1", "v1.0-rc1"] {
            fs::write(
                git_dir.join("refs/tags").join(name),
                "67bf698f3ab735e92fb011a99cff3497c44d30c1\n",
            )
            .unwrap();
        }
        verify_refname_available_for_create(
            git_dir,
            "refs/tags/v1.0",
            &BTreeSet::new(),
            &HashSet::new(),
        )
        .expect("siblings are not descendants");
    }

    #[test]
    fn verify_blocks_parent_git_style_nested_path() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/3l/c")).unwrap();
        fs::write(
            git_dir.join("refs/3l/c/x"),
            "67bf698f3ab735e92fb011a99cff3497c44d30c1\n",
        )
        .unwrap();
        let extras = BTreeSet::from(["refs/3l/c".to_string()]);
        let skip = HashSet::new();
        let err =
            verify_refname_available_for_create(git_dir, "refs/3l/c", &extras, &skip).unwrap_err();
        assert!(matches!(
            err,
            RefnameUnavailable::DescendantExists { ref blocking, .. }
                if blocking == "refs/3l/c/x"
        ));
    }

    #[test]
    fn intermediate_directory_does_not_block_nested_create() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/ns")).unwrap();
        fs::write(
            git_dir.join("refs/ns/existing"),
            "67bf698f3ab735e92fb011a99cff3497c44d30c1\n",
        )
        .unwrap();
        assert_eq!(
            read_raw_ref(git_dir, "refs/ns").unwrap(),
            RawRefLookup::IsDirectory
        );
        let extras = BTreeSet::from(["refs/ns/newchild".to_string()]);
        let skip = HashSet::new();
        verify_refname_available_for_create(git_dir, "refs/ns/newchild", &extras, &skip).unwrap();
    }
}

#[cfg(test)]
mod ref_storage_traversal_guard_tests {
    use super::*;
    use crate::objects::ObjectId;
    use tempfile::tempdir;

    const TRAVERSAL_REF: &str = "refs/heads/../../config";

    fn bare_repo_with_config() -> (tempfile::TempDir, PathBuf) {
        let dir = tempdir().unwrap();
        let git_dir = dir.path().to_path_buf();
        fs::create_dir_all(git_dir.join("refs/heads")).unwrap();
        fs::write(
            git_dir.join("config"),
            "[core]\nrepositoryformatversion = 0\n",
        )
        .unwrap();
        (dir, git_dir)
    }

    fn sample_oid() -> ObjectId {
        "67bf698f3ab735e92fb011a99cff3497c44d30c1".parse().unwrap()
    }

    fn assert_invalid_ref_preserves_config(git_dir: &Path, result: Result<()>) {
        assert!(matches!(result, Err(Error::InvalidRef(_))));
        assert!(
            git_dir.join("config").is_file(),
            "repository config must not be touched"
        );
    }

    #[test]
    fn write_ref_rejects_traversal_refname() {
        let (_dir, git_dir) = bare_repo_with_config();
        let result = write_ref(&git_dir, TRAVERSAL_REF, &sample_oid());
        assert_invalid_ref_preserves_config(&git_dir, result);
    }

    #[test]
    fn write_ref_cached_rejects_traversal_refname() {
        let (_dir, git_dir) = bare_repo_with_config();
        let mut packed = PackedRefs::load(&git_dir).unwrap();
        let result = write_ref_cached(&git_dir, TRAVERSAL_REF, &sample_oid(), &mut packed);
        assert_invalid_ref_preserves_config(&git_dir, result);
    }

    #[test]
    fn write_symbolic_ref_rejects_traversal_refname() {
        let (_dir, git_dir) = bare_repo_with_config();
        let result = write_symbolic_ref(&git_dir, TRAVERSAL_REF, "refs/heads/main");
        assert_invalid_ref_preserves_config(&git_dir, result);
    }

    #[test]
    fn delete_ref_rejects_traversal_refname() {
        let (_dir, git_dir) = bare_repo_with_config();
        let result = delete_ref(&git_dir, TRAVERSAL_REF);
        assert_invalid_ref_preserves_config(&git_dir, result);
    }

    #[test]
    fn write_ref_rejects_illegal_branch_refname() {
        let (_dir, git_dir) = bare_repo_with_config();
        for refname in [
            "refs/heads/bad name",
            "refs/heads/x..y",
            "refs/heads/a~b",
            "refs/heads/a.lock",
        ] {
            let result = write_ref(&git_dir, refname, &sample_oid());
            assert_invalid_ref_preserves_config(&git_dir, result);
            assert!(
                !git_dir
                    .join(refname.strip_prefix("refs/").unwrap())
                    .exists(),
                "must not write loose ref for {refname}"
            );
        }
    }

    #[test]
    fn write_ref_accepts_refs_heads_head() {
        let (_dir, git_dir) = bare_repo_with_config();
        write_ref(&git_dir, "refs/heads/HEAD", &sample_oid())
            .expect("refs/heads/HEAD is valid ref syntax");
        assert!(git_dir.join("refs/heads/HEAD").is_file());
    }
}

#[cfg(test)]
mod log_refs_config_tests {
    use super::*;
    use crate::config::{ConfigFile, ConfigScope};

    fn set(text: &str) -> ConfigSet {
        let file = ConfigFile::parse(Path::new("config"), text, ConfigScope::Local).unwrap();
        let mut set = ConfigSet::new();
        set.merge(&file);
        set
    }

    #[test]
    fn parse_accepts_modes_and_bool_spellings() {
        for (raw, mode) in [
            ("always", LogRefsConfig::Always),
            (" ALWAYS ", LogRefsConfig::Always),
            ("true", LogRefsConfig::Normal),
            ("Yes", LogRefsConfig::Normal),
            ("on", LogRefsConfig::Normal),
            ("1", LogRefsConfig::Normal),
            ("false", LogRefsConfig::None),
            ("no", LogRefsConfig::None),
            ("OFF", LogRefsConfig::None),
            ("0", LogRefsConfig::None),
            ("never", LogRefsConfig::None),
        ] {
            assert_eq!(LogRefsConfig::parse(raw), Some(mode), "{raw}");
        }
        assert_eq!(LogRefsConfig::parse("sometimes"), None);
    }

    #[test]
    fn effective_mode_applies_bare_default_only_when_unset() {
        assert_eq!(set("").log_refs_config(), LogRefsConfig::Unset);
        assert_eq!(set("").effective_log_refs_config(), LogRefsConfig::Normal);
        let bare = set("[core]\n\tbare = true\n");
        assert_eq!(bare.effective_log_refs_config(), LogRefsConfig::None);
        let bogus = set("[core]\n\tbare = true\n\tlogAllRefUpdates = sometimes\n");
        assert_eq!(bogus.log_refs_config(), LogRefsConfig::Unset);
        assert_eq!(bogus.effective_log_refs_config(), LogRefsConfig::None);
        let bare_logged = set("[core]\n\tbare = true\n\tlogAllRefUpdates\n");
        assert_eq!(
            bare_logged.effective_log_refs_config(),
            LogRefsConfig::Normal
        );
        let always = set("[core]\n\tlogAllRefUpdates = always\n");
        assert_eq!(always.effective_log_refs_config(), LogRefsConfig::Always);
    }

    #[test]
    fn autocreate_with_config_matches_mode() {
        let normal = set("[core]\n\tlogAllRefUpdates = true\n");
        let git_dir = Path::new(".git");
        assert!(should_autocreate_reflog_with_config(
            &normal,
            git_dir,
            "refs/heads/main"
        ));
        assert!(!should_autocreate_reflog_with_config(
            &normal,
            git_dir,
            "refs/tags/v1"
        ));
        let none = set("[core]\n\tlogAllRefUpdates = false\n");
        assert!(!should_autocreate_reflog_with_config(
            &none, git_dir, "HEAD"
        ));
    }
}

#[cfg(test)]
mod read_raw_ref_tests {
    use super::*;
    use tempfile::tempdir;

    #[test]
    fn loose_ref_file_is_exists() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/heads")).unwrap();
        fs::write(
            git_dir.join("refs/heads/side"),
            "0000000000000000000000000000000000000000\n",
        )
        .unwrap();
        assert_eq!(
            read_raw_ref(git_dir, "refs/heads/side").unwrap(),
            RawRefLookup::Exists
        );
    }

    #[test]
    fn missing_ref_is_not_found() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/heads")).unwrap();
        assert_eq!(
            read_raw_ref(git_dir, "refs/heads/nope").unwrap(),
            RawRefLookup::NotFound
        );
    }

    #[test]
    fn directory_where_ref_expected_is_is_directory() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/heads")).unwrap();
        assert_eq!(
            read_raw_ref(git_dir, "refs/heads").unwrap(),
            RawRefLookup::IsDirectory
        );
    }

    #[test]
    fn packed_ref_name_is_exists() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        fs::write(
            store::paths::packed_refs_path(git_dir),
            "# pack-refs with: peeled fully-peeled \n\
             0000000000000000000000000000000000000000 refs/heads/packed\n",
        )
        .unwrap();
        assert_eq!(
            read_raw_ref(git_dir, "refs/heads/packed").unwrap(),
            RawRefLookup::Exists
        );
    }
}

#[cfg(test)]
mod packed_refs_parse_tests {
    use super::*;

    use tempfile::tempdir;

    #[test]
    fn parse_rejects_garbage_line() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        fs::write(
            &path,
            "# pack-refs with: peeled\n\
             0000000000000000000000000000000000000000 refs/heads/main\n\
             not a ref line\n",
        )
        .unwrap();
        let data = fs::read(&path).unwrap();
        assert!(matches!(
            parse_packed_refs_to_map(&path, &data),
            Err(Error::PackedRefsUnexpectedLine { .. })
        ));
    }

    #[test]
    fn parse_rejects_carriage_return_bytes() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        fs::write(
            &path,
            "# pack-refs with: peeled\n\
             0000000000000000000000000000000000000000 refs/heads/main\r\n",
        )
        .unwrap();
        let data = fs::read(&path).unwrap();
        assert!(matches!(
            parse_packed_refs_to_map(&path, &data),
            Err(Error::PackedRefsUnexpectedLine { .. })
        ));
    }

    #[test]
    fn prefix_filter_unsorted_packed_refs_scans_past_later_names() {
        let dir = tempdir().unwrap();
        let git_dir = dir.path();
        let oid = "1111111111111111111111111111111111111111";
        fs::write(
            store::paths::packed_refs_path(git_dir),
            format!(
                "# pack-refs with: peeled fully-peeled\n{oid} refs/heads/zzz\n{oid} refs/heads/aaa\n{oid} refs/heads/main\n"
            ),
        )
        .unwrap();
        let listed = list_refs_glob(git_dir, "refs/heads/a*").unwrap();
        assert_eq!(listed.len(), 1);
        assert_eq!(listed[0].0, "refs/heads/aaa");
    }

    #[test]
    fn parse_rejects_blank_line_and_missing_final_newline() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        fs::write(
            &path,
            "# pack-refs with: peeled\n\n\
             0000000000000000000000000000000000000000 refs/heads/main\n",
        )
        .unwrap();
        let data = fs::read(&path).unwrap();
        assert!(matches!(
            parse_packed_refs_to_map(&path, &data),
            Err(Error::PackedRefsUnexpectedLine { .. })
        ));

        fs::write(
            &path,
            "# pack-refs with: peeled\n\
             0000000000000000000000000000000000000000 refs/heads/main",
        )
        .unwrap();
        let data = fs::read(&path).unwrap();
        assert!(matches!(
            parse_packed_refs_to_map(&path, &data),
            Err(Error::PackedRefsUnexpectedLine { .. })
        ));
    }

    #[test]
    fn packed_record_filter_sees_trusted_peels_and_keeps_strictness() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        let a = "1111111111111111111111111111111111111111";
        let b = "2222222222222222222222222222222222222222";
        let peel = "3333333333333333333333333333333333333333";
        let body = |header: &str| {
            format!(
                "{header}{a} refs/heads/main\n\
                 {b} refs/heads/tagged\n\
                 ^{peel}\n\
                 {a} refs/tags/light\n\
                 {b} refs/tags/v1\n\
                 ^{peel}\n"
            )
        };
        let a: ObjectId = a.parse().unwrap();
        let b: ObjectId = b.parse().unwrap();
        let peel: ObjectId = peel.parse().unwrap();
        let cases = [
            (
                "# pack-refs with: peeled fully-peeled sorted \n",
                [
                    PackedPeel::NotTag,
                    PackedPeel::Peeled(peel),
                    PackedPeel::NotTag,
                    PackedPeel::Peeled(peel),
                ],
            ),
            (
                "# pack-refs with: peeled sorted \n",
                [
                    PackedPeel::Unknown,
                    PackedPeel::Unknown,
                    PackedPeel::NotTag,
                    PackedPeel::Peeled(peel),
                ],
            ),
            ("", [PackedPeel::Unknown; 4]),
        ];
        for (header, want) in cases {
            let data = body(header).into_bytes();
            let view = PackedRefsFileView::from_bytes(&path, data, HashAlgo::Sha1).unwrap();
            let seen = std::cell::RefCell::new(Vec::new());
            let keep = |name: &str, oid: &ObjectId, peel: PackedPeel| {
                seen.borrow_mut().push((name.to_owned(), *oid, peel));
                name.starts_with("refs/tags/")
            };
            let kept = view
                .map_for_prefix_filtered(&path, Some("refs"), Some(&keep))
                .unwrap();
            assert_eq!(
                seen.into_inner(),
                vec![
                    ("refs/heads/main".to_owned(), a, want[0]),
                    ("refs/heads/tagged".to_owned(), b, want[1]),
                    ("refs/tags/light".to_owned(), a, want[2]),
                    ("refs/tags/v1".to_owned(), b, want[3]),
                ],
                "header {header:?}"
            );
            let mut kept: Vec<_> = kept.into_iter().collect();
            kept.sort();
            assert_eq!(
                kept,
                vec![
                    ("refs/tags/light".to_owned(), a),
                    ("refs/tags/v1".to_owned(), b)
                ]
            );
            assert_eq!(
                view.map_for_prefix_filtered(&path, Some("refs"), None)
                    .unwrap(),
                view.map_for_prefix(&path, Some("refs")).unwrap()
            );
        }

        // A malformed record is an error even when the filter would drop it.
        let bad = format!("# pack-refs with: peeled fully-peeled \n{a} refs/heads/bad..name\n");
        let view = PackedRefsFileView::from_bytes(&path, bad.into_bytes(), HashAlgo::Sha1).unwrap();
        assert!(matches!(
            view.map_for_prefix_filtered(&path, None, Some(&|_: &str, _: &ObjectId, _| false)),
            Err(Error::PackedRefsUnexpectedLine { .. })
        ));
    }

    #[test]
    fn indexed_lookup_matches_full_parse_sorted_and_unsorted() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        let oid = "1111111111111111111111111111111111111111";
        let peel = "2222222222222222222222222222222222222222";
        let sorted_body = format!(
            "# pack-refs with: peeled fully-peeled sorted\n\
             {oid} refs/heads/aaa\n\
             {oid} refs/heads/main\n\
             {oid} refs/heads/zzz\n\
             {oid} refs/tags/v1\n\
             ^{peel}\n"
        );
        fs::write(&path, &sorted_body).unwrap();
        let data = fs::read(&path).unwrap();
        let view = PackedRefsFileView::from_bytes(&path, data.clone(), HashAlgo::Sha1).unwrap();
        let full = parse_packed_refs_to_map(&path, &data).unwrap();
        for (name, want) in &full {
            assert_eq!(view.lookup_oid(&path, name).unwrap(), Some(*want));
        }
        assert_eq!(
            lookup_packed_ref_with_peel(dir.path(), "refs/tags/v1")
                .unwrap()
                .map(|(o, p)| (o, p.unwrap())),
            Some((oid.parse().unwrap(), peel.parse().unwrap()))
        );

        let unsorted_body = format!(
            "# pack-refs with: peeled\n{oid} refs/heads/zzz\n{oid} refs/heads/aaa\n{oid} refs/heads/main\n"
        );
        fs::write(&path, unsorted_body).unwrap();
        let data = fs::read(&path).unwrap();
        let view = PackedRefsFileView::from_bytes(&path, data.clone(), HashAlgo::Sha1).unwrap();
        let full = parse_packed_refs_to_map(&path, &data).unwrap();
        for (name, want) in &full {
            assert_eq!(view.lookup_oid(&path, name).unwrap(), Some(*want));
        }
        assert_eq!(
            view.map_for_prefix(&path, Some("refs/heads/a")).unwrap(),
            parse_packed_refs_to_map_with_prefix(&path, &data, Some("refs/heads/a")).unwrap()
        );
    }

    #[test]
    fn sorted_prefix_without_upper_bound_filters_names() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        let oid = "1111111111111111111111111111111111111111";
        let sorted_body = format!(
            "# pack-refs with: peeled fully-peeled sorted\n\
             {oid} refs/heads/aaa\n\
             {oid} refs/heads/zzz\n\
             {oid} refs/tags/v1\n"
        );
        fs::write(&path, sorted_body).unwrap();
        let data = fs::read(&path).unwrap();
        let view = PackedRefsFileView::from_bytes(&path, data.clone(), HashAlgo::Sha1).unwrap();
        assert_eq!(
            view.map_for_prefix(&path, Some("refs/heads/a")).unwrap(),
            parse_packed_refs_to_map_with_prefix(&path, &data, Some("refs/heads/a")).unwrap()
        );
        assert!(
            !view
                .map_for_prefix(&path, Some("refs/heads/a"))
                .unwrap()
                .contains_key("refs/heads/zzz"),
            "prefix refs/heads/a must not include refs/heads/zzz"
        );
        assert_eq!(
            view.map_for_prefix(&path, Some("refs")).unwrap(),
            parse_packed_refs_to_map_with_prefix(&path, &data, Some("refs")).unwrap()
        );
    }

    #[test]
    fn sorted_prefix_scan_validates_only_its_range() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        let oid = "1111111111111111111111111111111111111111";
        let view_of =
            |body: String| PackedRefsFileView::from_bytes(&path, body.into_bytes(), HashAlgo::Sha1);

        let bad_peel_on_branch = view_of(format!(
            "# pack-refs with: peeled fully-peeled sorted\n\
             {oid} refs/heads/main\n\
             ^not-hex\n\
             {oid} refs/tags/v1\n"
        ))
        .unwrap();
        assert!(matches!(
            bad_peel_on_branch.map_for_prefix(&path, Some("refs/heads")),
            Err(Error::PackedRefsUnexpectedLine { .. })
        ));
        let tags = bad_peel_on_branch
            .map_for_prefix(&path, Some("refs/tags"))
            .unwrap();
        assert_eq!(tags.keys().collect::<Vec<_>>(), ["refs/tags/v1"]);
        assert!(bad_peel_on_branch.map_for_prefix(&path, None).is_err());

        let blank_among_tags = view_of(format!(
            "# pack-refs with: peeled fully-peeled sorted\n\
             {oid} refs/heads/main\n\
             {oid} refs/tags/v1\n\
             \n\
             {oid} refs/tags/v2\n"
        ))
        .unwrap();
        assert_eq!(
            blank_among_tags
                .map_for_prefix(&path, Some("refs/heads"))
                .unwrap()
                .len(),
            1
        );
        assert!(blank_among_tags
            .map_for_prefix(&path, Some("refs/tags"))
            .is_err());

        let no_match = blank_among_tags
            .map_for_prefix(&path, Some("refs/notes"))
            .unwrap();
        assert!(no_match.is_empty());
    }

    #[test]
    fn non_utf8_record_only_breaks_reads_that_cover_it() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        let oid = "1111111111111111111111111111111111111111";
        let mut body =
            format!("# pack-refs with: peeled fully-peeled sorted \n{oid} refs/heads/main\n")
                .into_bytes();
        body.extend_from_slice(format!("{oid} refs/tags/v1\n{oid} refs/tags/").as_bytes());
        body.extend_from_slice(b"\xff\n");
        let view = PackedRefsFileView::from_bytes(&path, body, HashAlgo::Sha1).unwrap();
        assert!(view.sorted);
        for name in ["refs/heads/main", "refs/tags/v1"] {
            assert_eq!(
                view.lookup_oid(&path, name).unwrap(),
                Some(oid.parse().unwrap())
            );
        }
        assert_eq!(view.lookup_oid(&path, "refs/tags/v2").unwrap(), None);
        let heads = view.map_for_prefix(&path, Some("refs/heads")).unwrap();
        assert_eq!(heads.keys().collect::<Vec<_>>(), ["refs/heads/main"]);
        assert!(matches!(
            view.map_for_prefix(&path, Some("refs/tags")),
            Err(Error::PackedRefsUnexpectedLine { .. })
        ));
        assert!(view.map_for_prefix(&path, None).is_err());

        let mut bad_header = b"# pack-refs with: \xff sorted \n".to_vec();
        bad_header.extend_from_slice(format!("{oid} refs/heads/main\n").as_bytes());
        assert!(matches!(
            PackedRefsFileView::from_bytes(&path, bad_header, HashAlgo::Sha1),
            Err(Error::PackedRefsUnexpectedLine { .. })
        ));
    }

    #[test]
    fn scan_of_file_without_ref_lines_still_validates_it() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        let view = PackedRefsFileView::from_bytes(
            &path,
            b"# pack-refs with: peeled fully-peeled sorted\n\
              ^1111111111111111111111111111111111111111\n"
                .to_vec(),
            HashAlgo::Sha1,
        )
        .unwrap();
        for prefix in [None, Some("refs/heads")] {
            assert!(matches!(
                view.map_for_prefix(&path, prefix),
                Err(Error::PackedRefsUnexpectedLine { .. })
            ));
        }
        let header_only = PackedRefsFileView::from_bytes(
            &path,
            b"# pack-refs with: peeled fully-peeled sorted\n".to_vec(),
            HashAlgo::Sha1,
        )
        .unwrap();
        assert!(header_only.map_for_prefix(&path, None).unwrap().is_empty());
    }

    #[test]
    fn view_checks_last_line_length_against_the_repository_hash() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        let sha1 = "1111111111111111111111111111111111111111";
        let sha256 = "2".repeat(64);
        let view =
            |body: String, algo| PackedRefsFileView::from_bytes(&path, body.into_bytes(), algo);
        let header = "# pack-refs with: peeled fully-peeled sorted\n";
        let fifty_bytes = "x".repeat(49);

        for (body, algo) in [
            (
                format!("{header}{sha1} refs/heads/main\ngarbage\n"),
                HashAlgo::Sha1,
            ),
            (
                format!("{header}{sha1} refs/heads/main\n^{}\n", &sha1[1..]),
                HashAlgo::Sha1,
            ),
            (
                format!("{header}{sha1} refs/heads/main\n#\n"),
                HashAlgo::Sha1,
            ),
            (
                format!("{header}{sha256} refs/heads/main\n{fifty_bytes}\n"),
                HashAlgo::Sha256,
            ),
            (format!("{header}{sha1} refs/heads/a\n"), HashAlgo::Sha256),
        ] {
            assert!(
                matches!(
                    view(body.clone(), algo),
                    Err(Error::PackedRefsUnexpectedLine { .. })
                ),
                "{algo:?}: {body:?}"
            );
        }
        for (body, algo) in [
            (header.to_owned(), HashAlgo::Sha1),
            (header.to_owned(), HashAlgo::Sha256),
            ("# pack-refs with: peeled\n".to_owned(), HashAlgo::Sha256),
            (
                format!("{header}{sha1} refs/heads/main\n{fifty_bytes}\n"),
                HashAlgo::Sha1,
            ),
            (
                format!("{header}{sha1} refs/heads/main\n^{sha1}\n"),
                HashAlgo::Sha1,
            ),
            (
                format!("{header}{sha256} refs/heads/main\n^{sha256}\n"),
                HashAlgo::Sha256,
            ),
        ] {
            assert!(view(body.clone(), algo).is_ok(), "{algo:?}: {body:?}");
        }
    }

    #[test]
    fn sha256_short_last_record_fails_branch_listing() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        let sha256 = "2".repeat(64);
        let body = format!(
            "# pack-refs with: peeled fully-peeled sorted\n{sha256} refs/heads/main\n{}\n",
            "x".repeat(49)
        );
        assert!(
            PackedRefsFileView::from_bytes(&path, body.into_bytes(), HashAlgo::Sha256).is_err()
        );
    }

    #[test]
    fn corrupt_line_inside_prefix_range_fails_instead_of_dropping_refs() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        let oid = "1111111111111111111111111111111111111111";
        let header = "# pack-refs with: peeled fully-peeled sorted\n";
        let view = |body: String| {
            PackedRefsFileView::from_bytes(&path, body.into_bytes(), HashAlgo::Sha1).unwrap()
        };

        let garbage_after_first_branch = view(format!(
            "{header}{oid} refs/heads/a\ngarbage line\n{oid} refs/heads/b\n{oid} refs/heads/c\n\
             {oid} refs/tags/t1\n"
        ));
        assert!(matches!(
            garbage_after_first_branch.map_for_prefix(&path, Some("refs/heads")),
            Err(Error::PackedRefsUnexpectedLine { .. })
        ));
        let tags = garbage_after_first_branch
            .map_for_prefix(&path, Some("refs/tags"))
            .unwrap();
        assert_eq!(tags.keys().collect::<Vec<_>>(), ["refs/tags/t1"]);

        let garbage_before_range = view(format!(
            "{header}{oid} refs/heads/a\ngarbage line\n{oid} refs/tags/t1\n"
        ));
        for prefix in ["refs/heads", "refs/tags", "refs/notes"] {
            assert!(
                garbage_before_range
                    .map_for_prefix(&path, Some(prefix))
                    .is_err(),
                "{prefix}"
            );
        }
        assert_eq!(
            garbage_before_range
                .map_for_prefix(&path, Some("refs/zz"))
                .unwrap()
                .len(),
            0
        );

        let peeled_tag_before_range = view(format!(
            "{header}{oid} refs/heads/a\n^{oid}\n{oid} refs/tags/t1\n"
        ));
        let orphan_peel_before_range = view(format!(
            "{header}{oid} refs/heads/a\n^{oid}\n^{oid}\n{oid} refs/tags/t1\n"
        ));
        assert!(orphan_peel_before_range
            .map_for_prefix(&path, Some("refs/tags"))
            .is_err());
        assert_eq!(
            peeled_tag_before_range
                .map_for_prefix(&path, Some("refs/tags"))
                .unwrap()
                .len(),
            1
        );
    }

    #[test]
    fn sorted_trait_is_trusted_even_when_names_are_out_of_order() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        let oid = "1111111111111111111111111111111111111111";
        let records = format!("{oid} refs/heads/b\n{oid} refs/heads/a\n{oid} refs/tags/t\n");
        let view_of = |header: &str| {
            PackedRefsFileView::from_bytes(
                &path,
                format!("{header}{records}").into_bytes(),
                HashAlgo::Sha1,
            )
            .unwrap()
        };

        let lying = view_of("# pack-refs with: peeled fully-peeled sorted\n");
        assert!(lying.sorted);
        // The search probes `refs/heads/a` first, then moves right past it.
        assert!(lying.lookup_oid(&path, "refs/heads/a").unwrap().is_some());
        assert_eq!(lying.lookup_oid(&path, "refs/heads/b").unwrap(), None);
        let heads = lying.map_for_prefix(&path, Some("refs/heads")).unwrap();
        assert_eq!(heads.len(), 2);

        let unsorted = view_of("# pack-refs with: peeled fully-peeled\n");
        assert!(!unsorted.sorted);
        for name in ["refs/heads/a", "refs/heads/b", "refs/tags/t"] {
            assert!(
                unsorted.lookup_oid(&path, name).unwrap().is_some(),
                "{name}"
            );
        }
    }

    #[test]
    fn records_are_only_record_shaped_lines() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        let view = |data: &[u8]| {
            PackedRefsFileView::from_bytes(&path, data.to_vec(), HashAlgo::Sha1).unwrap()
        };
        let hex = "1".repeat(40);
        let data = format!("# header\n{hex} x\n^peel\n\n{hex} y\n#c\nshort\n{hex}z\n{hex} z\n");
        let starts: Vec<usize> = view(data.as_bytes()).records().collect();
        assert_eq!(starts, [9, 59, 153]);
        assert_eq!(view(b"").records().count(), 0);
        let out_of_order = format!("{hex} b\n{hex} a\n");
        assert_eq!(
            view(out_of_order.as_bytes()).records().collect::<Vec<_>>(),
            [0, 43]
        );
    }

    #[test]
    fn parse_rejects_orphan_peel_and_double_space() {
        let dir = tempdir().unwrap();
        let path = store::paths::packed_refs_path(dir.path());
        fs::write(
            &path,
            "# pack-refs with: peeled\n\
             ^0000000000000000000000000000000000000000\n\
             0000000000000000000000000000000000000000 refs/heads/main\n",
        )
        .unwrap();
        let data = fs::read(&path).unwrap();
        assert!(matches!(
            parse_packed_refs_to_map(&path, &data),
            Err(Error::PackedRefsUnexpectedLine { .. })
        ));

        fs::write(
            &path,
            "# pack-refs with: peeled\n\
             0000000000000000000000000000000000000000  refs/heads/main\n",
        )
        .unwrap();
        let data = fs::read(&path).unwrap();
        assert!(matches!(
            parse_packed_refs_to_map(&path, &data),
            Err(Error::PackedRefsUnexpectedLine { .. })
        ));
    }
}

#[cfg(test)]
mod pack_refs_tests {
    use super::*;
    use crate::objects::{serialize_commit, CommitData, ObjectKind};
    use crate::repo::{init_repository, Repository};
    use std::fs;
    use std::sync::Arc;

    fn write_commit(repo: &Repository, parents: Vec<ObjectId>) -> ObjectId {
        let tree = repo.odb().write(ObjectKind::Tree, b"").expect("tree");
        let raw = serialize_commit(&CommitData {
            tree,
            parents,
            author: "T <t@example.com> 1 +0000".into(),
            committer: "T <t@example.com> 1 +0000".into(),
            author_raw: Vec::new(),
            committer_raw: Vec::new(),
            encoding: None,
            message: "m\n".into(),
            raw_message: None,
            extra_headers: Vec::new(),
        });
        repo.odb().write(ObjectKind::Commit, &raw).expect("commit")
    }

    #[test]
    fn pack_refs_skips_concurrent_loose_update() {
        let dir = tempfile::tempdir().expect("tempdir");
        let repo = init_repository(
            dir.path(),
            false,
            "main",
            None,
            crate::RefStorageFormat::Files,
        )
        .expect("init");
        let git_dir = repo.git_dir().to_path_buf();
        let c1 = write_commit(&repo, vec![]);
        let c2 = write_commit(&repo, vec![c1]);
        write_ref(&git_dir, "refs/heads/race", &c1).expect("seed loose");

        let git_dir_hook = git_dir.clone();
        let c2 = Arc::new(c2);
        let c2_hook = Arc::clone(&c2);
        pack_refs_test_hooks::set_before_prune(Some(Box::new(move || {
            write_ref(&git_dir_hook, "refs/heads/race", &c2_hook).expect("concurrent update");
        })));

        let (_path, packed, pruned) =
            pack_refs_files(&git_dir, repo.odb(), true, false).expect("pack");
        pack_refs_test_hooks::set_before_prune(None);
        assert!(packed >= 1);
        assert_eq!(pruned, 0, "stale CAS must not delete the updated loose ref");

        let resolved = resolve_ref(&git_dir, "refs/heads/race").expect("resolve");
        assert_eq!(resolved, *c2);
        let packed_body =
            fs::read_to_string(store::paths::packed_refs_path(&git_dir)).unwrap_or_default();
        assert!(
            !packed_body.contains("refs/heads/race"),
            "packed entry for concurrently updated ref must be removed"
        );
    }

    #[test]
    fn pack_refs_nested_tag_peel_line_points_at_commit() {
        let dir = tempfile::tempdir().expect("tempdir");
        let repo = init_repository(
            dir.path(),
            false,
            "main",
            None,
            crate::RefStorageFormat::Files,
        )
        .expect("init");
        let commit = write_commit(&repo, vec![]);
        let inner_tag_body = format!(
            "object {}\ntype commit\ntagger T <t@example.com> 1 +0000\n\ninner\n",
            commit.to_hex()
        );
        let inner = repo
            .odb()
            .write(ObjectKind::Tag, inner_tag_body.as_bytes())
            .expect("inner tag");
        let outer_tag_body = format!(
            "object {}\ntype tag\ntagger T <t@example.com> 2 +0000\n\nouter\n",
            inner.to_hex()
        );
        let outer = repo
            .odb()
            .write(ObjectKind::Tag, outer_tag_body.as_bytes())
            .expect("outer tag");
        write_ref(repo.git_dir(), "refs/tags/outer", &outer).expect("tag ref");

        pack_refs_files(repo.git_dir(), repo.odb(), false, false).expect("pack");
        let body =
            fs::read_to_string(store::paths::packed_refs_path(repo.git_dir())).expect("packed");
        let mut lines = body.lines();
        let tag_line = lines
            .find(|l| l.contains("refs/tags/outer"))
            .expect("tag line");
        assert!(tag_line.starts_with(&outer.to_hex()));
        let peel_line = lines.find(|l| l.starts_with('^')).expect("peel line");
        assert!(
            peel_line.contains(&commit.to_hex()),
            "peel must reach commit through nested tags, got {peel_line}"
        );
    }

    #[test]
    fn pack_refs_tree_target_tag_has_peel_line() {
        let dir = tempfile::tempdir().expect("tempdir");
        let repo = init_repository(
            dir.path(),
            false,
            "main",
            None,
            crate::RefStorageFormat::Files,
        )
        .expect("init");
        let tree = repo.odb().write(ObjectKind::Tree, b"").expect("tree");
        let tag_body = format!(
            "object {}\ntype tree\ntagger T <t@example.com> 1 +0000\n\ntree tag\n",
            tree.to_hex()
        );
        let tag = repo
            .odb()
            .write(ObjectKind::Tag, tag_body.as_bytes())
            .expect("tag");
        write_ref(repo.git_dir(), "refs/tags/tree-tag", &tag).expect("tag ref");

        pack_refs_files(repo.git_dir(), repo.odb(), true, false).expect("pack");
        let body =
            fs::read_to_string(store::paths::packed_refs_path(repo.git_dir())).expect("packed");
        assert!(body.contains("refs/tags/tree-tag"));
        assert!(
            body.contains(&format!("^{}", tree.to_hex())),
            "expected peel to tree: {body}"
        );
    }

    #[test]
    fn write_packed_refs_file_survives_publish_failure() {
        let dir = tempfile::tempdir().expect("tempdir");
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/heads")).expect("refs/heads");
        let oid = ObjectId::from_hex("0000000000000000000000000000000000000001").expect("oid");
        fs::write(git_dir.join("refs/heads/keep"), format!("{oid}\n")).expect("loose ref");
        fs::create_dir_all(store::paths::packed_refs_path(git_dir))
            .expect("block packed-refs file");
        let err = write_packed_refs_file(
            git_dir,
            &[PackedRefRecord {
                refname: "refs/heads/keep".into(),
                oid,
                peeled: None,
            }],
        )
        .expect_err("publish should fail");
        assert!(matches!(err, Error::Io(_)));
        assert!(git_dir.join("refs/heads/keep").is_file());
    }

    #[test]
    fn write_packed_refs_file_replaces_loose_and_sorts() {
        let dir = tempfile::tempdir().expect("tempdir");
        let git_dir = dir.path();
        fs::create_dir_all(git_dir.join("refs/heads")).expect("refs/heads");
        let oid_a = ObjectId::from_hex("0000000000000000000000000000000000000001").expect("oid a");
        let oid_b = ObjectId::from_hex("0000000000000000000000000000000000000002").expect("oid b");
        fs::write(git_dir.join("refs/heads/a-first"), format!("{oid_b}\n")).expect("loose ref");
        write_packed_refs_file(
            git_dir,
            &[
                PackedRefRecord {
                    refname: "refs/heads/z-last".into(),
                    oid: oid_b,
                    peeled: None,
                },
                PackedRefRecord {
                    refname: "refs/heads/a-first".into(),
                    oid: oid_a,
                    peeled: None,
                },
            ],
        )
        .expect("write packed-refs");
        assert!(!git_dir.join("refs/heads/a-first").exists());
        let body =
            fs::read_to_string(store::paths::packed_refs_path(git_dir)).expect("packed-refs");
        assert!(body.contains("refs/heads/a-first"));
        assert!(body.find("a-first").expect("a-first") < body.find("z-last").expect("z-last"));
    }
}

#[cfg(test)]
mod packed_ref_peels_tests {
    use super::*;

    fn oid(n: u8) -> ObjectId {
        ObjectId::from_bytes(&[n; 20]).expect("oid")
    }

    fn peels_for(body: &str) -> (tempfile::TempDir, PackedRefPeels) {
        let dir = tempfile::tempdir().expect("tempdir");
        fs::write(store::paths::packed_refs_path(dir.path()), body).expect("packed-refs");
        let peels = PackedRefPeels::load(dir.path(), RefStorageFormat::Files).expect("load");
        (dir, peels)
    }

    fn body(header: &str, records: &[(&str, ObjectId, Option<ObjectId>)]) -> String {
        let mut out = String::from(header);
        for (name, oid, peel) in records {
            out.push_str(&format!("{oid} {name}\n"));
            if let Some(peel) = peel {
                out.push_str(&format!("^{peel}\n"));
            }
        }
        out
    }

    #[test]
    fn fully_peeled_file_answers_for_every_ref() {
        for header in [
            "# pack-refs with: peeled fully-peeled sorted \n",
            "# pack-refs with: peeled fully-peeled \n",
        ] {
            let records = [
                ("refs/heads/main", oid(1), None),
                ("refs/remotes/origin/tag-ish", oid(2), Some(oid(3))),
                ("refs/tags/v1", oid(4), Some(oid(1))),
                ("refs/tags/light", oid(1), None),
            ];
            // A `sorted` header is trusted, so only the file without it is written out of order.
            let mut ordered = records;
            if header.contains(" sorted") {
                ordered.sort_by_key(|(name, _, _)| *name);
            } else {
                ordered.reverse();
            }
            let (_dir, peels) = peels_for(&body(header, &ordered));
            assert_eq!(peels.peeled("refs/heads/main", &oid(1)), Some(None));
            assert_eq!(
                peels.peeled("refs/remotes/origin/tag-ish", &oid(2)),
                Some(Some(oid(3)))
            );
            assert_eq!(peels.peeled("refs/tags/v1", &oid(4)), Some(Some(oid(1))));
            assert_eq!(peels.peeled("refs/tags/light", &oid(1)), Some(None));
            // A loose ref that overrides the packed value is not vouched for.
            assert_eq!(peels.peeled("refs/tags/v1", &oid(9)), None);
            assert_eq!(peels.peeled("refs/tags/missing", &oid(1)), None);
        }
    }

    #[test]
    fn peeled_trait_only_covers_tags_and_no_trait_covers_nothing() {
        let records = [
            ("refs/heads/main", oid(1), None),
            ("refs/tags/v1", oid(4), Some(oid(1))),
        ];
        let (_dir, peels) = peels_for(&body("# pack-refs with: peeled sorted\n", &records));
        assert_eq!(peels.peeled("refs/heads/main", &oid(1)), None);
        assert_eq!(peels.peeled("refs/tags/v1", &oid(4)), Some(Some(oid(1))));

        for header in [
            "",
            "# pack-refs with: sorted\n",
            "# some comment\n",
            "#pack-refs with: peeled fully-peeled\n",
            "#  pack-refs with: peeled fully-peeled\n",
        ] {
            let (_dir, peels) = peels_for(&body(header, &records));
            assert_eq!(peels.peeled("refs/heads/main", &oid(1)), None, "{header:?}");
            assert_eq!(peels.peeled("refs/tags/v1", &oid(4)), None, "{header:?}");
        }
    }

    #[test]
    fn missing_file_and_other_backends_know_nothing() {
        let dir = tempfile::tempdir().expect("tempdir");
        let peels = PackedRefPeels::load(dir.path(), RefStorageFormat::Files).expect("load");
        assert_eq!(peels.peeled("refs/heads/main", &oid(1)), None);

        let records = [("refs/heads/main", oid(1), None)];
        fs::write(
            store::paths::packed_refs_path(dir.path()),
            body("# pack-refs with: peeled fully-peeled sorted\n", &records),
        )
        .expect("packed-refs");
        let peels = PackedRefPeels::load(dir.path(), RefStorageFormat::Reftable).expect("load");
        assert_eq!(peels.peeled("refs/heads/main", &oid(1)), None);
    }

    #[test]
    fn lookups_in_any_order_agree_with_a_fresh_snapshot() {
        let records = [
            ("refs/heads/main", oid(1), None),
            ("refs/tags/a", oid(2), Some(oid(1))),
            ("refs/tags/b", oid(1), None),
            ("refs/tags/c", oid(3), Some(oid(4))),
            ("refs/tags/d", oid(5), None),
        ];
        let text = body("# pack-refs with: peeled fully-peeled sorted \n", &records);
        let (_dir, peels) = peels_for(&text);
        let fresh = |name: &str, value: &ObjectId| peels_for(&text).1.peeled(name, value);
        let queries = [
            ("refs/tags/a", oid(2)),
            ("refs/tags/b", oid(1)),
            ("refs/tags/b", oid(1)),
            ("refs/tags/bb", oid(1)),
            ("refs/tags/c", oid(3)),
            ("refs/tags/d", oid(9)),
            ("refs/tags/d", oid(5)),
            ("refs/heads/main", oid(1)),
            ("refs/tags/c", oid(3)),
            ("refs/tags/a", oid(2)),
            ("refs/tags/zzz", oid(1)),
            ("refs/tags/a", oid(2)),
            ("refs/tags/b", oid(1)),
        ];
        for (name, value) in queries {
            assert_eq!(
                peels.peeled(name, &value),
                fresh(name, &value),
                "{name} {value}"
            );
        }
        assert_eq!(peels.peeled("refs/tags/c", &oid(3)), Some(Some(oid(4))));
        assert_eq!(peels.peeled("refs/tags/d", &oid(5)), Some(None));
    }

    #[test]
    fn store_snapshot_reuses_the_files_store_view_and_follows_rewrites() {
        let dir = tempfile::tempdir().expect("tempdir");
        let path = store::paths::packed_refs_path(dir.path());
        let header = "# pack-refs with: peeled fully-peeled sorted \n";
        let records = [
            ("refs/heads/main", oid(1), None),
            ("refs/tags/v1", oid(2), Some(oid(1))),
            ("refs/tags/v2", oid(3), None),
        ];
        fs::write(&path, body(header, &records)).expect("packed-refs");
        let files = store::FilesRefStore::from_git_dir(dir.path()).expect("files store");

        let peels = PackedRefPeels::for_store(&files, dir.path()).expect("for_store");
        let loaded = PackedRefPeels::load(dir.path(), RefStorageFormat::Files).expect("load");
        for (name, value, _) in records {
            assert_eq!(
                peels.peeled(name, &value),
                loaded.peeled(name, &value),
                "{name}"
            );
        }
        assert_eq!(peels.peeled("refs/tags/v1", &oid(2)), Some(Some(oid(1))));
        let cached = files
            .packed_refs_view()
            .expect("view")
            .expect("packed-refs");
        let shared = peels.view.as_ref().expect("snapshot view");
        assert!(std::sync::Arc::ptr_eq(&cached.data, &shared.data));

        let rewritten = [
            ("refs/heads/main", oid(1), None),
            ("refs/tags/v1", oid(4), Some(oid(5))),
            ("refs/tags/v2", oid(3), None),
            ("refs/tags/v3", oid(6), Some(oid(1))),
        ];
        fs::write(&path, body(header, &rewritten)).expect("rewrite packed-refs");
        let peels = PackedRefPeels::for_store(&files, dir.path()).expect("for_store");
        assert_eq!(peels.peeled("refs/tags/v1", &oid(2)), None);
        assert_eq!(peels.peeled("refs/tags/v1", &oid(4)), Some(Some(oid(5))));
        assert_eq!(peels.peeled("refs/tags/v3", &oid(6)), Some(Some(oid(1))));

        let memory = store::MemoryRefStore::new();
        let fallback = PackedRefPeels::for_store(&memory, dir.path()).expect("fallback");
        let direct = PackedRefPeels::load(dir.path(), memory.format()).expect("load");
        for (name, value, _) in rewritten {
            assert_eq!(
                fallback.peeled(name, &value),
                direct.peeled(name, &value),
                "{name}"
            );
        }
    }

    /// View over raw bytes, without the checks [`PackedRefsFileView::from_data`] makes.
    fn raw_view(data: &[u8], hex_len: usize) -> PackedRefsFileView {
        PackedRefsFileView {
            data: crate::pack_map::PackData::from_owned(data.to_vec()),
            sorted: true,
            hex_len,
            body_start: 0,
            peel_trait: PackedPeelTrait::None,
        }
    }

    /// Reference record scan: the start of every record-shaped line, one line at a time.
    fn naive_record_starts(data: &[u8], hex_len: usize) -> Vec<usize> {
        let mut out = Vec::new();
        let mut start = 0;
        for line in data.split(|&b| b == b'\n') {
            if start >= data.len() {
                break;
            }
            if packed_line_is_record(line, hex_len) {
                out.push(start);
            }
            start += line.len() + 1;
        }
        out
    }

    fn assert_record_walks_match(data: &[u8], hex_len: usize) {
        let view = raw_view(data, hex_len);
        let want = naive_record_starts(data, hex_len);
        assert_eq!(
            view.records().collect::<Vec<_>>(),
            want,
            "{:?} hex_len={hex_len}",
            String::from_utf8_lossy(data)
        );
        let mut line_starts: Vec<usize> = memchr::memchr_iter(b'\n', data)
            .map(|nl| nl + 1)
            .filter(|&s| s < data.len())
            .collect();
        line_starts.insert(0, 0);
        // Views always end in a newline, so the end is only a line start when it follows one.
        if data.ends_with(b"\n") {
            line_starts.push(data.len());
        }
        for before in line_starts {
            let prev = want.iter().copied().filter(|&s| s < before).last();
            assert_eq!(view.prev_record(before), prev, "{data:?} before={before}");
        }
    }

    fn xorshift(state: &mut u64) -> u64 {
        *state ^= *state << 13;
        *state ^= *state >> 7;
        *state ^= *state << 17;
        *state
    }

    #[test]
    fn record_walks_match_a_line_by_line_scan() {
        let hex = oid(1).to_hex();
        let inputs = [
            String::new(),
            "\n".to_owned(),
            format!("# pack-refs with: peeled \n{hex} refs/heads/a\n^{hex}\n{hex} refs/tags/b\n"),
            format!("{hex} refs/heads/z\n{hex} refs/heads/a\n"),
            format!("{hex} refs/heads/a\n\n{hex} refs/heads/b"),
            format!("{hex}\n{hex} \n{hex} x\nshort\n#{hex} refs/heads/c\n"),
            format!("{hex} refs/tags/a\n^{hex}\n^{hex}\n{hex} refs/tags/b\n^{hex}"),
            format!("^ab\n{}\n{hex} refs/heads/a\n", "x".repeat(37)),
            format!("^\n{hex} refs/heads/a\n^{hex}x\n{hex} refs/heads/b\n"),
            format!("^{hex}\n"),
            format!("^{}", &hex[1..]),
        ];
        for input in &inputs {
            assert_record_walks_match(input.as_bytes(), 40);
        }
    }

    #[test]
    fn record_walks_match_a_line_by_line_scan_on_random_bytes() {
        let alphabet = b"^\n #ab";
        let mut state = 0x2545_f491_4f6c_dd1du64;
        for len in 0..400 {
            let input: Vec<u8> = (0..len % 97)
                .map(|_| alphabet[(xorshift(&mut state) % alphabet.len() as u64) as usize])
                .collect();
            for hex_len in [1, 2, 3] {
                assert_record_walks_match(&input, hex_len);
            }
        }
    }

    /// On a file whose records really are in order, the byte-level search finds exactly what
    /// a linear scan finds, whatever peel and stray lines sit between the records.
    #[test]
    fn search_matches_a_linear_scan_on_sorted_records() {
        let hex_len = 2;
        let mut state = 0x9e37_79b9_7f4a_7c15u64;
        for _ in 0..300 {
            let mut names: Vec<String> = (0..xorshift(&mut state) % 12)
                .map(|_| format!("n{}", xorshift(&mut state) % 40))
                .collect();
            names.sort();
            names.dedup();
            let mut data = b"# h\n".to_vec();
            for name in &names {
                data.extend_from_slice(format!("ab {name}\n").as_bytes());
                match xorshift(&mut state) % 4 {
                    0 => data.extend_from_slice(b"^ab\n"),
                    1 => data.extend_from_slice(b"junk\n"),
                    _ => {}
                }
            }
            let mut view = raw_view(&data, hex_len);
            view.body_start = 4;
            let records: Vec<usize> = view.records().collect();
            for probe in 0..42 {
                let target = format!("n{probe}");
                let want = records
                    .iter()
                    .copied()
                    .find(|&s| view.record_cmp(s, &target).is_ge())
                    .unwrap_or(data.len());
                assert_eq!(view.lower_bound(&target), want, "{target} in {data:?}");
                let hit = view.search(&target).ok();
                assert_eq!(
                    hit,
                    names.contains(&target).then_some(want),
                    "{target} in {data:?}"
                );
            }
        }
    }
}