mkit_cli/commands/

checkout.rs

//! `mkit checkout <branch>` — switch HEAD to a branch and materialise
//! the branch tip's tree into the working directory.
//!
//! The file-restoration half calls
//! `mkit_core::ops::restore::restore_tree_to_worktree_with` (via
//! `crate::restore_fanout::read_chunks_fanout`, this crate's rayon fan-out
//! for a `ChunkedBlob`'s per-chunk reads), which respects `.mkitignore`
//! and rejects symlinks that would escape the repo root.

use std::io::Write;

use clap::Parser;
use mkit_core::hash::Hash;
use mkit_core::index::EntryStatus;
use mkit_core::layout::RepoLayout;
use mkit_core::object::Object;
use mkit_core::ops::restore::{RestoreOptions, restore_tree_to_worktree_with};
use mkit_core::refs;
use mkit_core::store::ObjectStore;

use crate::clap_shim;
use crate::exit;
use crate::format;

#[derive(Debug, Parser)]
#[command(
    name = "mkit checkout",
    about = "Switch HEAD to a branch (or tag / commit hash) and restore files."
)]
struct CheckoutOpts {
    /// One or more path-prefix patterns selecting a subset of the
    /// commit's tree. Each pattern is interpreted the same way the
    /// `mkit sparse-checkout` config patterns are — a leading `/` is
    /// stripped, a trailing `/` marks a directory-only match, and `!`
    /// negates. Repeat the flag to add more patterns.
    ///
    /// Materialises only matching files. Patterns apply to this checkout;
    /// use `mkit sparse-checkout set` to persist them.
    #[cfg(feature = "sparse-checkout")]
    #[arg(long = "sparse", value_name = "PATTERN", num_args = 1..)]
    sparse: Vec<String>,
    /// Create a new branch at the start-point and switch to it
    /// (`git checkout -b <new>`). Refuses to clobber an existing branch.
    #[arg(short = 'b', value_name = "NEW", conflicts_with = "create_force")]
    create: Option<String>,
    /// Create-or-reset a branch at the start-point and switch to it
    /// (`git checkout -B <new>`).
    #[arg(short = 'B', value_name = "NEW")]
    create_force: Option<String>,
    /// Discard local changes that would block the switch, like
    /// `git checkout -f`: skip the dirty-tracked/staged safety gate and
    /// overwrite locally-modified tracked paths with the target's version.
    /// Untracked files are still preserved. Used by `bisect run` to
    /// materialize each candidate over the test command's scribbles.
    #[arg(short = 'f', long = "force")]
    force: bool,
    /// Branch name, tag, or 64-char commit hash. With `-b`/`-B` this is
    /// the optional start-point (defaults to HEAD).
    target: Option<String>,
}

#[must_use]
#[allow(clippy::too_many_lines)] // linear flow: create-branch + switch + report
pub fn run(args: &[String]) -> u8 {
    let opts = match clap_shim::parse::<CheckoutOpts>("mkit checkout", args) {
        Ok(o) => o,
        Err(code) => return code,
    };
    let cwd = match std::env::current_dir() {
        Ok(p) => p,
        Err(e) => return emit_err(&format!("cwd: {e}"), exit::NOINPUT),
    };
    let layout = match super::resolve_layout(&cwd) {
        Ok(layout) => layout,
        Err(code) => return code,
    };
    let store = match ObjectStore::open(&layout) {
        Ok(s) => s,
        Err(e) => return emit_err(&format!("not a mkit repo: {e}"), exit::GENERAL_ERROR),
    };
    // Registry lock first (global order, SPEC-WORKTREE §4.3): the
    // branch-checked-out-elsewhere guard below and the HEAD write must
    // be one atomic step against sibling checkouts and `worktree add`,
    // or two racing processes could land one branch on two trees.
    let _registry_lock = match super::acquire_worktrees_registry_lock(&layout) {
        Ok(l) => l,
        Err(code) => return code,
    };
    let _lock = match super::acquire_worktree_lock(&layout) {
        Ok(l) => l,
        Err(code) => return code,
    };

    // `-b`/`-B`: plan a branch create (or reset, for `-B`) at the
    // start-point (the optional positional, default HEAD). The ref is NOT
    // written here — only AFTER the destructive-restore gate passes — so a
    // refused switch creates nothing (git atomicity). `reset_existing`
    // tracks whether `-B` is resetting a pre-existing branch (→ git's
    // `Reset branch …` message rather than `Switched to a new branch …`).
    let create_new = opts.create.as_deref().or(opts.create_force.as_deref());
    let create_plan: Option<(String, Hash, refs::RefWriteCondition, bool)> =
        if let Some(new) = create_new {
            let start_spec = opts.target.as_deref().unwrap_or("HEAD");
            let start = match super::revspec::resolve_revision(&store, &layout, start_spec) {
                Ok(h) => h,
                Err(e) => {
                    return emit_err(
                        &format!("invalid start point '{start_spec}': {e}"),
                        exit::GENERAL_ERROR,
                    );
                }
            };
            let existed = matches!(refs::read_ref(&layout, new), Ok(Some(_)));
            if existed && opts.create_force.is_none() {
                return emit_err(&format!("branch '{new}' already exists"), exit::CANTCREAT);
            }
            let cond = if opts.create_force.is_some() {
                refs::RefWriteCondition::Any
            } else {
                refs::RefWriteCondition::Missing
            };
            Some((
                new.to_string(),
                start,
                cond,
                existed && opts.create_force.is_some(),
            ))
        } else {
            None
        };
    let created = create_plan.is_some();

    let name_owned: String = match &create_plan {
        Some((new, ..)) => new.clone(),
        None => match opts.target.as_deref() {
            Some(t) => t.to_string(),
            None => {
                return super::usage_error(
                    "usage: mkit checkout [-b|-B <new>] <branch|tag|commit>",
                );
            }
        },
    };
    let name = name_owned.as_str();

    // Remember whether we were already on the requested branch so the
    // final report can say `Already on '<name>'` for a no-op switch —
    // WITHOUT short-circuiting the safety gate (a dirty same-branch
    // checkout must still refuse, like mkit always has).
    let already_on = matches!(
        refs::read_head(&layout),
        Ok(mkit_core::refs::Head::Branch(ref cur)) if cur == name
    );

    // Single-writer-per-branch across worktrees (#493): if this
    // checkout would END on a branch (existing or being created),
    // refuse when a sibling tree already has it checked out — branch
    // moves flow through the history-MMB ref path, which assumes one
    // writer per branch. Applies to `--force` too, like git.
    let ends_on_branch = created || matches!(refs::read_ref(&layout, name), Ok(Some(_)));
    if ends_on_branch {
        match super::branch_checked_out_elsewhere(&layout, name) {
            Ok(Some(at)) => {
                return emit_err(
                    &format!(
                        "branch '{name}' is already checked out at '{}'",
                        at.display()
                    ),
                    exit::DATAERR,
                );
            }
            Ok(None) => {}
            Err(e) => return emit_err(&e, exit::DATAERR),
        }
    }

    // The target commit: for `-b`/`-B` it is the (resolved) start-point;
    // otherwise resolve `<name>` via the shared revspec resolver.
    let commit_hash: Hash = match &create_plan {
        Some((_, start, ..)) => *start,
        None => match super::revspec::resolve_revision(&store, &layout, name) {
            Ok(h) => h,
            Err(e) => {
                return emit_err(
                    &format!("no such branch, tag, or commit: {name} ({e})"),
                    exit::GENERAL_ERROR,
                );
            }
        },
    };

    // Resolve the commit's tree so we can materialise it.
    let tree_hash = match store.read_object(&commit_hash) {
        Ok(Object::Commit(c)) => c.tree_hash,
        Ok(Object::Remix(r)) => r.tree_hash,
        Ok(_) => {
            return emit_err(
                &format!(
                    "{} does not resolve to a commit or remix",
                    format::short_hash(&commit_hash, 8)
                ),
                exit::GENERAL_ERROR,
            );
        }
        Err(e) => return emit_err(&format!("read commit: {e}"), exit::GENERAL_ERROR),
    };

    // If `--sparse` was supplied, drive a verifiable sparse-checkout:
    // build a manifest from the commit's tree, re-verify the
    // delivered subset, cache the bitmap, then materialise with the
    // restore-side sparse patterns set. Empty `opts.sparse` falls
    // through to the full-tree restore below.
    //
    // `clean = false` everywhere: like git, switching branches PRESERVES
    // untracked files. Tracked paths the target drops are deleted
    // explicitly below (same pattern as `reset --hard`), so the restore
    // itself never sweeps the worktree.
    #[cfg(feature = "sparse-checkout")]
    let sparse_opts: RestoreOptions = if opts.sparse.is_empty() {
        RestoreOptions {
            clean: false,
            sparse_patterns: None,
        }
    } else {
        match prepare_sparse_restore(&layout, &store, tree_hash, &opts.sparse) {
            Ok(o) => o,
            Err((msg, code)) => return emit_err(&msg, code),
        }
    };
    #[cfg(not(feature = "sparse-checkout"))]
    let sparse_opts: RestoreOptions = RestoreOptions {
        clean: false,
        sparse_patterns: None,
    };

    // Run the destructive-restore safety gate (#176) BEFORE touching
    // anything. This is read-only — it refuses the checkout if dirty
    // tracked files, staged changes, or untracked-path collisions with
    // the target tree would be clobbered. Untracked files that do NOT
    // collide with the target are preserved (git branch-switch
    // semantics), so they no longer block the checkout.
    // `--force` (git checkout -f) skips the gate, discarding local edits.
    if !opts.force
        && let Err(e) =
            super::ensure_restore_safe_with_options(&layout, &store, tree_hash, &sparse_opts)
    {
        return emit_err(&e, exit::GENERAL_ERROR);
    }

    // Tracked paths the target drops — removed explicitly after
    // materialising (the `clean = false` restore never deletes). Refuses
    // first if any of them carries local edits (unless `--force`).
    let dropped = match dropped_paths_guarded(&layout, &store, tree_hash, &sparse_opts, opts.force)
    {
        Ok(d) => d,
        Err(code) => return code,
    };

    // Safety gate passed — NOW create the `-b`/`-B` branch ref. Deferring
    // it to here means a refused switch above leaves no orphan branch
    // behind (git creates nothing when it refuses the operation).
    if let Some((new, start, cond, _)) = &create_plan {
        match super::write_ref_recording_history(&layout, new, *cond, start) {
            Ok(()) => {}
            Err(refs::RefError::Conflict(_)) => {
                return emit_err(&format!("branch '{new}' already exists"), exit::CANTCREAT);
            }
            Err(e) => return emit_err(&format!("create branch {new}: {e}"), exit::CANTCREAT),
        }
    }

    // Update HEAD FIRST, before mutating the worktree/index (#223). The
    // failure modes are asymmetric: if we materialised the new tree and
    // *then* HEAD failed to advance, the worktree would hold the new
    // branch's files while HEAD still pointed at the old branch — a
    // silent, hard-to-diagnose split. Writing HEAD first inverts the
    // hazard: a subsequent worktree/index failure leaves HEAD on the new
    // branch with a stale worktree, which `mkit status` surfaces as
    // ordinary local changes and a re-run of `mkit checkout` repairs.
    // The `ensure_restore_safe` gate above already guaranteed no real
    // user work is at risk, so the stale-worktree window is benign.
    let is_branch = matches!(refs::read_ref(&layout, name), Ok(Some(_)));
    let head_err = if is_branch {
        refs::write_head_branch(&layout, name)
    } else {
        refs::write_head_detached(&layout, &commit_hash)
    };
    if let Err(e) = head_err {
        return emit_err(&format!("update HEAD: {e}"), exit::CANTCREAT);
    }

    // Materialise the tree with `clean = false`: tracked entries are
    // written/overwritten, untracked files are preserved. Then delete
    // the tracked paths the target drops (computed above) and prune any
    // directories that became empty — git removes those on a branch
    // switch; `fs::remove_dir` only succeeds on EMPTY dirs, so a dir
    // still holding untracked files survives.
    let report = match restore_tree_to_worktree_with(
        &store,
        &tree_hash,
        &cwd,
        &sparse_opts,
        &crate::restore_fanout::read_chunks_fanout,
    ) {
        Ok(r) => r,
        Err(e) => return emit_err(&format!("restore: {e}"), exit::CANTCREAT),
    };
    if let Err(code) = remove_dropped(&cwd, &dropped) {
        return code;
    }
    if let Err(e) = super::sync_index_to_tree(&layout, &store, tree_hash) {
        return emit_err(&e, exit::CANTCREAT);
    }

    // git-shaped switch confirmation (drop mkit's non-git restored-count
    // line). `report` is no longer printed; keep the binding consumed.
    let _ = &report;
    let reset_existing = matches!(&create_plan, Some((.., true)));
    let mut stderr = std::io::stderr().lock();
    if is_branch {
        if reset_existing {
            let _ = writeln!(stderr, "Reset branch '{name}'");
        } else if created {
            let _ = writeln!(stderr, "Switched to a new branch '{name}'");
        } else if already_on {
            let _ = writeln!(stderr, "Already on '{name}'");
        } else {
            let _ = writeln!(stderr, "Switched to branch '{name}'");
        }
    } else {
        let _ = writeln!(
            stderr,
            "HEAD is now at {} {}",
            format::short_hash(&commit_hash, format::SUMMARY_ABBREV),
            super::commit_subject(&store, &commit_hash),
        );
    }
    exit::OK
}

use super::error as emit_err;

/// Tracked paths the target drops — present in the current index but
/// absent from the target tree. The `clean = false` restore never
/// deletes, so `run` removes them explicitly after materialising.
/// Restricted to the sparse cone so `--sparse` keeps its old reach.
///
/// Direct per-dropped-path dirty check (mirrors `reset --hard`): a
/// locally-edited tracked file the target drops must never be deleted
/// silently, even when an ignore rule hides it from the shared guard's
/// worktree snapshot — refuses (returning the exit code) when one is
/// found.
fn dropped_paths_guarded(
    layout: &RepoLayout,
    store: &ObjectStore,
    tree_hash: Hash,
    opts: &RestoreOptions,
    force: bool,
) -> Result<Vec<(String, EntryStatus, Hash)>, u8> {
    let dropped: Vec<(String, EntryStatus, Hash)> =
        match super::dropped_tracked_paths(layout, store, tree_hash) {
            Ok(all) => all
                .into_iter()
                .filter(|(path, _, _)| super::restore_affects_path(opts, path))
                .collect(),
            Err(e) => return Err(emit_err(&e, exit::GENERAL_ERROR)),
        };
    // `--force` overwrites/removes dropped paths regardless of local edits.
    if force {
        return Ok(dropped);
    }
    match super::locally_modified_dropped_path(layout.worktree_root(), store, &dropped) {
        Ok(Some(path)) => Err(emit_err(
            &format!(
                "restore would overwrite local changes; commit, stash, or reset '{path}' first"
            ),
            exit::GENERAL_ERROR,
        )),
        Ok(None) => Ok(dropped),
        Err(e) => Err(emit_err(&e, exit::GENERAL_ERROR)),
    }
}

/// Delete the dropped tracked paths from the worktree and prune any
/// parent directories that became empty.
fn remove_dropped(
    cwd: &std::path::Path,
    dropped: &[(String, EntryStatus, Hash)],
) -> Result<(), u8> {
    for (path, _, _) in dropped {
        if let Err(e) = super::remove_dropped_path(&cwd.join(path)) {
            return Err(emit_err(
                &format!("restore: remove {path}: {e}"),
                exit::CANTCREAT,
            ));
        }
        prune_empty_parents(cwd, path);
    }
    Ok(())
}

/// After deleting the dropped tracked file at repo-relative `rel_path`,
/// remove its parent directories bottom-up while they are empty.
/// `fs::remove_dir` refuses non-empty directories, so a parent still
/// holding untracked (or ignored) files is left untouched, and the walk
/// stops at the first survivor. Errors are deliberately swallowed — a
/// leftover empty directory is cosmetic, never data loss.
fn prune_empty_parents(root: &std::path::Path, rel_path: &str) {
    let mut dir = std::path::Path::new(rel_path).parent();
    while let Some(d) = dir {
        if d.as_os_str().is_empty() {
            break;
        }
        if std::fs::remove_dir(root.join(d)).is_err() {
            break;
        }
        dir = d.parent();
    }
}

/// Authenticate and cache the top-level tree witness for literal prefixes.
/// Unsupported pattern grammar uses the authenticated full metadata already
/// available in the object store. Restoration always uses the CLI's patterns.
/// Returns `(message, exit_code)` for errors reported by the caller.
#[cfg(feature = "sparse-checkout")]
fn prepare_sparse_restore(
    layout: &RepoLayout,
    store: &ObjectStore,
    tree_hash: Hash,
    patterns: &[String],
) -> Result<RestoreOptions, (String, u8)> {
    use crate::sparse_cache::{SparseBuildError, SparseOutcome, load_or_build};
    use mkit_core::object::Object as CoreObject;
    use mkit_core::ops::restore::parse_sparse_patterns;
    use std::path::PathBuf;

    let tree = match store.read_object(&tree_hash) {
        Ok(CoreObject::Tree(t)) => t,
        Ok(_) => {
            return Err((
                "checkout: HEAD does not resolve to a tree".to_string(),
                exit::DATAERR,
            ));
        }
        Err(e) => return Err((format!("read tree: {e}"), exit::GENERAL_ERROR)),
    };

    // Preserve the CLI grammar verbatim. Unsupported sparse prefixes use the
    // authenticated full metadata already loaded above.
    let filter: Vec<PathBuf> = patterns.iter().map(PathBuf::from).collect();
    match load_or_build(layout, &tree, &filter) {
        Ok(SparseOutcome::CacheHit | SparseOutcome::FullMetadata) => {}
        Ok(SparseOutcome::Built { store_error }) => {
            if let Some(e) = store_error {
                let mut stderr = std::io::stderr().lock();
                let _ = writeln!(stderr, "warning: sparse cache write failed: {e}");
            }
        }
        Err(SparseBuildError::Build(e)) => {
            return Err((format!("sparse build: {e}"), exit::GENERAL_ERROR));
        }
        Err(SparseBuildError::VerifyFailed) => {
            return Err((
                "sparse build produced a manifest that fails verify".to_string(),
                exit::GENERAL_ERROR,
            ));
        }
    }

    // Translate the CLI patterns into the restore-side pattern grammar.
    // `clean = false`: untracked files inside the sparse cone are
    // preserved (same branch-switch semantics as the full-tree path);
    // tracked paths the target drops are deleted explicitly by `run`.
    let joined = patterns.join("\n");
    let parsed = parse_sparse_patterns(&joined);
    Ok(RestoreOptions {
        clean: false,
        sparse_patterns: Some(parsed),
    })
}