unpack-trees.c

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#include "git-compat-util.h"
#include "advice.h"
#include "strvec.h"
#include "repository.h"
#include "parse.h"
#include "dir.h"
#include "environment.h"
#include "gettext.h"
#include "hex.h"
#include "name-hash.h"
#include "tree.h"
#include "tree-walk.h"
#include "cache-tree.h"
#include "unpack-trees.h"
#include "progress.h"
#include "refs.h"
#include "attr.h"
#include "read-cache.h"
#include "split-index.h"
#include "sparse-index.h"
#include "submodule.h"
#include "submodule-config.h"
#include "symlinks.h"
#include "trace2.h"
#include "fsmonitor.h"
#include "object-store-ll.h"
#include "promisor-remote.h"
#include "entry.h"
#include "parallel-checkout.h"
#include "setup.h"

/*
 * Error messages expected by scripts out of plumbing commands such as
 * read-tree.  Non-scripted Porcelain is not required to use these messages
 * and in fact are encouraged to reword them to better suit their particular
 * situation better.  See how "git checkout" and "git merge" replaces
 * them using setup_unpack_trees_porcelain(), for example.
 */
static const char *unpack_plumbing_errors[NB_UNPACK_TREES_WARNING_TYPES] = {
    /* ERROR_WOULD_OVERWRITE */
    "Entry '%s' would be overwritten by merge. Cannot merge.",

    /* ERROR_NOT_UPTODATE_FILE */
    "Entry '%s' not uptodate. Cannot merge.",

    /* ERROR_NOT_UPTODATE_DIR */
    "Updating '%s' would lose untracked files in it",

    /* ERROR_CWD_IN_THE_WAY */
    "Refusing to remove '%s' since it is the current working directory.",

    /* ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN */
    "Untracked working tree file '%s' would be overwritten by merge.",

    /* ERROR_WOULD_LOSE_UNTRACKED_REMOVED */
    "Untracked working tree file '%s' would be removed by merge.",

    /* ERROR_BIND_OVERLAP */
    "Entry '%s' overlaps with '%s'.  Cannot bind.",

    /* ERROR_WOULD_LOSE_SUBMODULE */
    "Submodule '%s' cannot checkout new HEAD.",

    /* NB_UNPACK_TREES_ERROR_TYPES; just a meta value */
    "",

    /* WARNING_SPARSE_NOT_UPTODATE_FILE */
    "Path '%s' not uptodate; will not remove from working tree.",

    /* WARNING_SPARSE_UNMERGED_FILE */
    "Path '%s' unmerged; will not remove from working tree.",

    /* WARNING_SPARSE_ORPHANED_NOT_OVERWRITTEN */
    "Path '%s' already present; will not overwrite with sparse update.",
};

#define ERRORMSG(o,type) \
    ( ((o) && (o)->internal.msgs[(type)]) \
      ? ((o)->internal.msgs[(type)])      \
      : (unpack_plumbing_errors[(type)]) )

static const char *super_prefixed(const char *path, const char *super_prefix)
{
    /*
     * It is necessary and sufficient to have two static buffers
     * here, as the return value of this function is fed to
     * error() using the unpack_*_errors[] templates we see above.
     */
    static struct strbuf buf[2] = {STRBUF_INIT, STRBUF_INIT};
    static int super_prefix_len = -1;
    static unsigned idx = ARRAY_SIZE(buf) - 1;

    if (super_prefix_len < 0) {
        if (!super_prefix) {
            super_prefix_len = 0;
        } else {
            int i;
            for (i = 0; i < ARRAY_SIZE(buf); i++)
                strbuf_addstr(&buf[i], super_prefix);
            super_prefix_len = buf[0].len;
        }
    }

    if (!super_prefix_len)
        return path;

    if (++idx >= ARRAY_SIZE(buf))
        idx = 0;

    strbuf_setlen(&buf[idx], super_prefix_len);
    strbuf_addstr(&buf[idx], path);

    return buf[idx].buf;
}

void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
                  const char *cmd)
{
    int i;
    const char **msgs = opts->internal.msgs;
    const char *msg;

    strvec_init(&opts->internal.msgs_to_free);

    if (!strcmp(cmd, "checkout"))
        msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
              ? _("Your local changes to the following files would be overwritten by checkout:\n%%s"
              "Please commit your changes or stash them before you switch branches.")
              : _("Your local changes to the following files would be overwritten by checkout:\n%%s");
    else if (!strcmp(cmd, "merge"))
        msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
              ? _("Your local changes to the following files would be overwritten by merge:\n%%s"
              "Please commit your changes or stash them before you merge.")
              : _("Your local changes to the following files would be overwritten by merge:\n%%s");
    else
        msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
              ? _("Your local changes to the following files would be overwritten by %s:\n%%s"
              "Please commit your changes or stash them before you %s.")
              : _("Your local changes to the following files would be overwritten by %s:\n%%s");
    msgs[ERROR_WOULD_OVERWRITE] = msgs[ERROR_NOT_UPTODATE_FILE] =
        strvec_pushf(&opts->internal.msgs_to_free, msg, cmd, cmd);

    msgs[ERROR_NOT_UPTODATE_DIR] =
        _("Updating the following directories would lose untracked files in them:\n%s");

    msgs[ERROR_CWD_IN_THE_WAY] =
        _("Refusing to remove the current working directory:\n%s");

    if (!strcmp(cmd, "checkout"))
        msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
              ? _("The following untracked working tree files would be removed by checkout:\n%%s"
              "Please move or remove them before you switch branches.")
              : _("The following untracked working tree files would be removed by checkout:\n%%s");
    else if (!strcmp(cmd, "merge"))
        msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
              ? _("The following untracked working tree files would be removed by merge:\n%%s"
              "Please move or remove them before you merge.")
              : _("The following untracked working tree files would be removed by merge:\n%%s");
    else
        msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
              ? _("The following untracked working tree files would be removed by %s:\n%%s"
              "Please move or remove them before you %s.")
              : _("The following untracked working tree files would be removed by %s:\n%%s");
    msgs[ERROR_WOULD_LOSE_UNTRACKED_REMOVED] =
        strvec_pushf(&opts->internal.msgs_to_free, msg, cmd, cmd);

    if (!strcmp(cmd, "checkout"))
        msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
              ? _("The following untracked working tree files would be overwritten by checkout:\n%%s"
              "Please move or remove them before you switch branches.")
              : _("The following untracked working tree files would be overwritten by checkout:\n%%s");
    else if (!strcmp(cmd, "merge"))
        msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
              ? _("The following untracked working tree files would be overwritten by merge:\n%%s"
              "Please move or remove them before you merge.")
              : _("The following untracked working tree files would be overwritten by merge:\n%%s");
    else
        msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
              ? _("The following untracked working tree files would be overwritten by %s:\n%%s"
              "Please move or remove them before you %s.")
              : _("The following untracked working tree files would be overwritten by %s:\n%%s");
    msgs[ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN] =
        strvec_pushf(&opts->internal.msgs_to_free, msg, cmd, cmd);

    /*
     * Special case: ERROR_BIND_OVERLAP refers to a pair of paths, we
     * cannot easily display it as a list.
     */
    msgs[ERROR_BIND_OVERLAP] = _("Entry '%s' overlaps with '%s'.  Cannot bind.");

    msgs[ERROR_WOULD_LOSE_SUBMODULE] =
        _("Cannot update submodule:\n%s");

    msgs[WARNING_SPARSE_NOT_UPTODATE_FILE] =
        _("The following paths are not up to date and were left despite sparse patterns:\n%s");
    msgs[WARNING_SPARSE_UNMERGED_FILE] =
        _("The following paths are unmerged and were left despite sparse patterns:\n%s");
    msgs[WARNING_SPARSE_ORPHANED_NOT_OVERWRITTEN] =
        _("The following paths were already present and thus not updated despite sparse patterns:\n%s");

    opts->internal.show_all_errors = 1;
    /* rejected paths may not have a static buffer */
    for (i = 0; i < ARRAY_SIZE(opts->internal.unpack_rejects); i++)
        opts->internal.unpack_rejects[i].strdup_strings = 1;
}

void clear_unpack_trees_porcelain(struct unpack_trees_options *opts)
{
    strvec_clear(&opts->internal.msgs_to_free);
    memset(opts->internal.msgs, 0, sizeof(opts->internal.msgs));
}

static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
             unsigned int set, unsigned int clear)
{
    clear |= CE_HASHED;

    if (set & CE_REMOVE)
        set |= CE_WT_REMOVE;

    ce->ce_flags = (ce->ce_flags & ~clear) | set;
    return add_index_entry(&o->internal.result, ce,
                   ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
}

static void add_entry(struct unpack_trees_options *o,
              const struct cache_entry *ce,
              unsigned int set, unsigned int clear)
{
    do_add_entry(o, dup_cache_entry(ce, &o->internal.result), set, clear);
}

/*
 * add error messages on path <path>
 * corresponding to the type <e> with the message <msg>
 * indicating if it should be display in porcelain or not
 */
static int add_rejected_path(struct unpack_trees_options *o,
                 enum unpack_trees_error_types e,
                 const char *path)
{
    if (o->quiet)
        return -1;

    if (!o->internal.show_all_errors)
        return error(ERRORMSG(o, e), super_prefixed(path,
                                o->super_prefix));

    /*
     * Otherwise, insert in a list for future display by
     * display_(error|warning)_msgs()
     */
    string_list_append(&o->internal.unpack_rejects[e], path);
    return -1;
}

/*
 * display all the error messages stored in a nice way
 */
static void display_error_msgs(struct unpack_trees_options *o)
{
    int e;
    unsigned error_displayed = 0;
    for (e = 0; e < NB_UNPACK_TREES_ERROR_TYPES; e++) {
        struct string_list *rejects = &o->internal.unpack_rejects[e];

        if (rejects->nr > 0) {
            int i;
            struct strbuf path = STRBUF_INIT;

            error_displayed = 1;
            for (i = 0; i < rejects->nr; i++)
                strbuf_addf(&path, "\t%s\n", rejects->items[i].string);
            error(ERRORMSG(o, e), super_prefixed(path.buf,
                                 o->super_prefix));
            strbuf_release(&path);
        }
        string_list_clear(rejects, 0);
    }
    if (error_displayed)
        fprintf(stderr, _("Aborting\n"));
}

/*
 * display all the warning messages stored in a nice way
 */
static void display_warning_msgs(struct unpack_trees_options *o)
{
    int e;
    unsigned warning_displayed = 0;
    for (e = NB_UNPACK_TREES_ERROR_TYPES + 1;
         e < NB_UNPACK_TREES_WARNING_TYPES; e++) {
        struct string_list *rejects = &o->internal.unpack_rejects[e];

        if (rejects->nr > 0) {
            int i;
            struct strbuf path = STRBUF_INIT;

            warning_displayed = 1;
            for (i = 0; i < rejects->nr; i++)
                strbuf_addf(&path, "\t%s\n", rejects->items[i].string);
            warning(ERRORMSG(o, e), super_prefixed(path.buf,
                                   o->super_prefix));
            strbuf_release(&path);
        }
        string_list_clear(rejects, 0);
    }
    if (warning_displayed)
        fprintf(stderr, _("After fixing the above paths, you may want to run `git sparse-checkout reapply`.\n"));
}
static int check_submodule_move_head(const struct cache_entry *ce,
                     const char *old_id,
                     const char *new_id,
                     struct unpack_trees_options *o)
{
    unsigned flags = SUBMODULE_MOVE_HEAD_DRY_RUN;
    const struct submodule *sub = submodule_from_ce(ce);

    if (!sub)
        return 0;

    if (o->reset)
        flags |= SUBMODULE_MOVE_HEAD_FORCE;

    if (submodule_move_head(ce->name, o->super_prefix, old_id, new_id,
                flags))
        return add_rejected_path(o, ERROR_WOULD_LOSE_SUBMODULE, ce->name);
    return 0;
}

/*
 * Perform the loading of the repository's gitmodules file.  This function is
 * used by 'check_update()' to perform loading of the gitmodules file in two
 * different situations:
 * (1) before removing entries from the working tree if the gitmodules file has
 *     been marked for removal.  This situation is specified by 'state' == NULL.
 * (2) before checking out entries to the working tree if the gitmodules file
 *     has been marked for update.  This situation is specified by 'state' != NULL.
 */
static void load_gitmodules_file(struct index_state *index,
                 struct checkout *state)
{
    int pos = index_name_pos(index, GITMODULES_FILE, strlen(GITMODULES_FILE));

    if (pos >= 0) {
        struct cache_entry *ce = index->cache[pos];
        if (!state && ce->ce_flags & CE_WT_REMOVE) {
            repo_read_gitmodules(the_repository, 0);
        } else if (state && (ce->ce_flags & CE_UPDATE)) {
            submodule_free(the_repository);
            checkout_entry(ce, state, NULL, NULL);
            repo_read_gitmodules(the_repository, 0);
        }
    }
}

static struct progress *get_progress(struct unpack_trees_options *o,
                     struct index_state *index)
{
    unsigned cnt = 0, total = 0;

    if (!o->update || !o->verbose_update)
        return NULL;

    for (; cnt < index->cache_nr; cnt++) {
        const struct cache_entry *ce = index->cache[cnt];
        if (ce->ce_flags & (CE_UPDATE | CE_WT_REMOVE))
            total++;
    }

    return start_delayed_progress(_("Updating files"), total);
}

static void setup_collided_checkout_detection(struct checkout *state,
                          struct index_state *index)
{
    int i;

    state->clone = 1;
    for (i = 0; i < index->cache_nr; i++)
        index->cache[i]->ce_flags &= ~CE_MATCHED;
}

static void report_collided_checkout(struct index_state *index)
{
    struct string_list list = STRING_LIST_INIT_NODUP;
    int i;

    for (i = 0; i < index->cache_nr; i++) {
        struct cache_entry *ce = index->cache[i];

        if (!(ce->ce_flags & CE_MATCHED))
            continue;

        string_list_append(&list, ce->name);
        ce->ce_flags &= ~CE_MATCHED;
    }

    list.cmp = fspathcmp;
    string_list_sort(&list);

    if (list.nr) {
        warning(_("the following paths have collided (e.g. case-sensitive paths\n"
              "on a case-insensitive filesystem) and only one from the same\n"
              "colliding group is in the working tree:\n"));

        for (i = 0; i < list.nr; i++)
            fprintf(stderr, "  '%s'\n", list.items[i].string);
    }

    string_list_clear(&list, 0);
}

static int must_checkout(const struct cache_entry *ce)
{
    return ce->ce_flags & CE_UPDATE;
}

static int check_updates(struct unpack_trees_options *o,
             struct index_state *index)
{
    unsigned cnt = 0;
    int errs = 0;
    struct progress *progress;
    struct checkout state = CHECKOUT_INIT;
    int i, pc_workers, pc_threshold;

    trace_performance_enter();
    state.super_prefix = o->super_prefix;
    state.force = 1;
    state.quiet = 1;
    state.refresh_cache = 1;
    state.istate = index;
    clone_checkout_metadata(&state.meta, &o->meta, NULL);

    if (!o->update || o->dry_run) {
        remove_marked_cache_entries(index, 0);
        trace_performance_leave("check_updates");
        return 0;
    }

    if (o->clone)
        setup_collided_checkout_detection(&state, index);

    progress = get_progress(o, index);

    /* Start with clean cache to avoid using any possibly outdated info. */
    invalidate_lstat_cache();

    git_attr_set_direction(GIT_ATTR_CHECKOUT);

    if (should_update_submodules())
        load_gitmodules_file(index, NULL);

    for (i = 0; i < index->cache_nr; i++) {
        const struct cache_entry *ce = index->cache[i];

        if (ce->ce_flags & CE_WT_REMOVE) {
            display_progress(progress, ++cnt);
            unlink_entry(ce, o->super_prefix);
        }
    }

    remove_marked_cache_entries(index, 0);
    remove_scheduled_dirs();

    if (should_update_submodules())
        load_gitmodules_file(index, &state);

    if (repo_has_promisor_remote(the_repository))
        /*
         * Prefetch the objects that are to be checked out in the loop
         * below.
         */
        prefetch_cache_entries(index, must_checkout);

    get_parallel_checkout_configs(&pc_workers, &pc_threshold);

    enable_delayed_checkout(&state);
    if (pc_workers > 1)
        init_parallel_checkout();
    for (i = 0; i < index->cache_nr; i++) {
        struct cache_entry *ce = index->cache[i];

        if (must_checkout(ce)) {
            size_t last_pc_queue_size = pc_queue_size();

            if (ce->ce_flags & CE_WT_REMOVE)
                BUG("both update and delete flags are set on %s",
                    ce->name);
            ce->ce_flags &= ~CE_UPDATE;
            errs |= checkout_entry(ce, &state, NULL, NULL);

            if (last_pc_queue_size == pc_queue_size())
                display_progress(progress, ++cnt);
        }
    }
    if (pc_workers > 1)
        errs |= run_parallel_checkout(&state, pc_workers, pc_threshold,
                          progress, &cnt);
    stop_progress(&progress);
    errs |= finish_delayed_checkout(&state, o->verbose_update);
    git_attr_set_direction(GIT_ATTR_CHECKIN);

    if (o->clone)
        report_collided_checkout(index);

    trace_performance_leave("check_updates");
    return errs != 0;
}

static int verify_uptodate_sparse(const struct cache_entry *ce,
                  struct unpack_trees_options *o);
static int verify_absent_sparse(const struct cache_entry *ce,
                enum unpack_trees_error_types,
                struct unpack_trees_options *o);

static int apply_sparse_checkout(struct index_state *istate,
                 struct cache_entry *ce,
                 struct unpack_trees_options *o)
{
    int was_skip_worktree = ce_skip_worktree(ce);

    if (ce->ce_flags & CE_NEW_SKIP_WORKTREE)
        ce->ce_flags |= CE_SKIP_WORKTREE;
    else
        ce->ce_flags &= ~CE_SKIP_WORKTREE;
    if (was_skip_worktree != ce_skip_worktree(ce)) {
        ce->ce_flags |= CE_UPDATE_IN_BASE;
        mark_fsmonitor_invalid(istate, ce);
        istate->cache_changed |= CE_ENTRY_CHANGED;
    }

    /*
     * if (!was_skip_worktree && !ce_skip_worktree()) {
     *    This is perfectly normal. Move on;
     * }
     */

    /*
     * Merge strategies may set CE_UPDATE|CE_REMOVE outside checkout
     * area as a result of ce_skip_worktree() shortcuts in
     * verify_absent() and verify_uptodate().
     * Make sure they don't modify worktree if they are already
     * outside checkout area
     */
    if (was_skip_worktree && ce_skip_worktree(ce)) {
        ce->ce_flags &= ~CE_UPDATE;

        /*
         * By default, when CE_REMOVE is on, CE_WT_REMOVE is also
         * on to get that file removed from both index and worktree.
         * If that file is already outside worktree area, don't
         * bother remove it.
         */
        if (ce->ce_flags & CE_REMOVE)
            ce->ce_flags &= ~CE_WT_REMOVE;
    }

    if (!was_skip_worktree && ce_skip_worktree(ce)) {
        /*
         * If CE_UPDATE is set, verify_uptodate() must be called already
         * also stat info may have lost after merged_entry() so calling
         * verify_uptodate() again may fail
         */
        if (!(ce->ce_flags & CE_UPDATE) &&
            verify_uptodate_sparse(ce, o)) {
            ce->ce_flags &= ~CE_SKIP_WORKTREE;
            return -1;
        }
        ce->ce_flags |= CE_WT_REMOVE;
        ce->ce_flags &= ~CE_UPDATE;
    }
    if (was_skip_worktree && !ce_skip_worktree(ce)) {
        if (verify_absent_sparse(ce, WARNING_SPARSE_ORPHANED_NOT_OVERWRITTEN, o))
            return -1;
        ce->ce_flags |= CE_UPDATE;
    }
    return 0;
}

static int warn_conflicted_path(struct index_state *istate,
                int i,
                struct unpack_trees_options *o)
{
    char *conflicting_path = istate->cache[i]->name;
    int count = 0;

    add_rejected_path(o, WARNING_SPARSE_UNMERGED_FILE, conflicting_path);

    /* Find out how many higher stage entries are at same path */
    while ((++count) + i < istate->cache_nr &&
           !strcmp(conflicting_path, istate->cache[count + i]->name))
        ; /* do nothing */

    return count;
}

static inline int call_unpack_fn(const struct cache_entry * const *src,
                 struct unpack_trees_options *o)
{
    int ret = o->fn(src, o);
    if (ret > 0)
        ret = 0;
    return ret;
}

static void mark_ce_used(struct cache_entry *ce, struct unpack_trees_options *o)
{
    ce->ce_flags |= CE_UNPACKED;

    if (o->internal.cache_bottom < o->src_index->cache_nr &&
        o->src_index->cache[o->internal.cache_bottom] == ce) {
        int bottom = o->internal.cache_bottom;

        while (bottom < o->src_index->cache_nr &&
               o->src_index->cache[bottom]->ce_flags & CE_UNPACKED)
            bottom++;
        o->internal.cache_bottom = bottom;
    }
}

static void mark_all_ce_unused(struct index_state *index)
{
    int i;
    for (i = 0; i < index->cache_nr; i++)
        index->cache[i]->ce_flags &= ~(CE_UNPACKED | CE_ADDED | CE_NEW_SKIP_WORKTREE);
}

static int locate_in_src_index(const struct cache_entry *ce,
                   struct unpack_trees_options *o)
{
    struct index_state *index = o->src_index;
    int len = ce_namelen(ce);
    int pos = index_name_pos(index, ce->name, len);
    if (pos < 0)
        pos = -1 - pos;
    return pos;
}

/*
 * We call unpack_index_entry() with an unmerged cache entry
 * only in diff-index, and it wants a single callback.  Skip
 * the other unmerged entry with the same name.
 */
static void mark_ce_used_same_name(struct cache_entry *ce,
                   struct unpack_trees_options *o)
{
    struct index_state *index = o->src_index;
    int len = ce_namelen(ce);
    int pos;

    for (pos = locate_in_src_index(ce, o); pos < index->cache_nr; pos++) {
        struct cache_entry *next = index->cache[pos];
        if (len != ce_namelen(next) ||
            memcmp(ce->name, next->name, len))
            break;
        mark_ce_used(next, o);
    }
}

static struct cache_entry *next_cache_entry(struct unpack_trees_options *o)
{
    const struct index_state *index = o->src_index;
    int pos = o->internal.cache_bottom;

    while (pos < index->cache_nr) {
        struct cache_entry *ce = index->cache[pos];
        if (!(ce->ce_flags & CE_UNPACKED))
            return ce;
        pos++;
    }
    return NULL;
}

static void add_same_unmerged(const struct cache_entry *ce,
                  struct unpack_trees_options *o)
{
    struct index_state *index = o->src_index;
    int len = ce_namelen(ce);
    int pos = index_name_pos(index, ce->name, len);

    if (0 <= pos)
        die("programming error in a caller of mark_ce_used_same_name");
    for (pos = -pos - 1; pos < index->cache_nr; pos++) {
        struct cache_entry *next = index->cache[pos];
        if (len != ce_namelen(next) ||
            memcmp(ce->name, next->name, len))
            break;
        add_entry(o, next, 0, 0);
        mark_ce_used(next, o);
    }
}

static int unpack_index_entry(struct cache_entry *ce,
                  struct unpack_trees_options *o)
{
    const struct cache_entry *src[MAX_UNPACK_TREES + 1] = { NULL, };
    int ret;

    src[0] = ce;

    mark_ce_used(ce, o);
    if (ce_stage(ce)) {
        if (o->skip_unmerged) {
            add_entry(o, ce, 0, 0);
            return 0;
        }
    }
    ret = call_unpack_fn(src, o);
    if (ce_stage(ce))
        mark_ce_used_same_name(ce, o);
    return ret;
}

static int find_cache_pos(struct traverse_info *, const char *p, size_t len);

static void restore_cache_bottom(struct traverse_info *info, int bottom)
{
    struct unpack_trees_options *o = info->data;

    if (o->diff_index_cached)
        return;
    o->internal.cache_bottom = bottom;
}

static int switch_cache_bottom(struct traverse_info *info)
{
    struct unpack_trees_options *o = info->data;
    int ret, pos;

    if (o->diff_index_cached)
        return 0;
    ret = o->internal.cache_bottom;
    pos = find_cache_pos(info->prev, info->name, info->namelen);

    if (pos < -1)
        o->internal.cache_bottom = -2 - pos;
    else if (pos < 0)
        o->internal.cache_bottom = o->src_index->cache_nr;
    return ret;
}

static inline int are_same_oid(struct name_entry *name_j, struct name_entry *name_k)
{
    return !is_null_oid(&name_j->oid) && !is_null_oid(&name_k->oid) && oideq(&name_j->oid, &name_k->oid);
}

static int all_trees_same_as_cache_tree(int n, unsigned long dirmask,
                    struct name_entry *names,
                    struct traverse_info *info)
{
    struct unpack_trees_options *o = info->data;
    int i;

    if (!o->merge || dirmask != ((1 << n) - 1))
        return 0;

    for (i = 1; i < n; i++)
        if (!are_same_oid(names, names + i))
            return 0;

    return cache_tree_matches_traversal(o->src_index->cache_tree, names, info);
}

static int index_pos_by_traverse_info(struct name_entry *names,
                      struct traverse_info *info)
{
    struct unpack_trees_options *o = info->data;
    struct strbuf name = STRBUF_INIT;
    int pos;

    strbuf_make_traverse_path(&name, info, names->path, names->pathlen);
    strbuf_addch(&name, '/');
    pos = index_name_pos(o->src_index, name.buf, name.len);
    if (pos >= 0) {
        if (!o->src_index->sparse_index ||
            !(o->src_index->cache[pos]->ce_flags & CE_SKIP_WORKTREE))
            BUG("This is a directory and should not exist in index");
    } else {
        pos = -pos - 1;
    }
    if (pos >= o->src_index->cache_nr ||
        !starts_with(o->src_index->cache[pos]->name, name.buf) ||
        (pos > 0 && starts_with(o->src_index->cache[pos-1]->name, name.buf)))
        BUG("pos %d doesn't point to the first entry of %s in index",
            pos, name.buf);
    strbuf_release(&name);
    return pos;
}

/*
 * Fast path if we detect that all trees are the same as cache-tree at this
 * path. We'll walk these trees in an iterative loop using cache-tree/index
 * instead of ODB since we already know what these trees contain.
 */
static int traverse_by_cache_tree(int pos, int nr_entries, int nr_names,
                  struct traverse_info *info)
{
    struct cache_entry *src[MAX_UNPACK_TREES + 1] = { NULL, };
    struct unpack_trees_options *o = info->data;
    struct cache_entry *tree_ce = NULL;
    int ce_len = 0;
    int i, d;

    if (!o->merge)
        BUG("We need cache-tree to do this optimization");

    /*
     * Do what unpack_callback() and unpack_single_entry() normally
     * do. But we walk all paths in an iterative loop instead.
     *
     * D/F conflicts and higher stage entries are not a concern
     * because cache-tree would be invalidated and we would never
     * get here in the first place.
     */
    for (i = 0; i < nr_entries; i++) {
        int new_ce_len, len, rc;

        src[0] = o->src_index->cache[pos + i];

        len = ce_namelen(src[0]);
        new_ce_len = cache_entry_size(len);

        if (new_ce_len > ce_len) {
            new_ce_len <<= 1;
            tree_ce = xrealloc(tree_ce, new_ce_len);
            memset(tree_ce, 0, new_ce_len);
            ce_len = new_ce_len;

            tree_ce->ce_flags = create_ce_flags(0);

            for (d = 1; d <= nr_names; d++)
                src[d] = tree_ce;
        }

        tree_ce->ce_mode = src[0]->ce_mode;
        tree_ce->ce_namelen = len;
        oidcpy(&tree_ce->oid, &src[0]->oid);
        memcpy(tree_ce->name, src[0]->name, len + 1);

        rc = call_unpack_fn((const struct cache_entry * const *)src, o);
        if (rc < 0) {
            free(tree_ce);
            return rc;
        }

        mark_ce_used(src[0], o);
    }
    free(tree_ce);
    if (o->internal.debug_unpack)
        printf("Unpacked %d entries from %s to %s using cache-tree\n",
               nr_entries,
               o->src_index->cache[pos]->name,
               o->src_index->cache[pos + nr_entries - 1]->name);
    return 0;
}

static int traverse_trees_recursive(int n, unsigned long dirmask,
                    unsigned long df_conflicts,
                    struct name_entry *names,
                    struct traverse_info *info)
{
    struct unpack_trees_options *o = info->data;
    int i, ret, bottom;
    int nr_buf = 0;
    struct tree_desc *t;
    void **buf;
    struct traverse_info newinfo;
    struct name_entry *p;
    int nr_entries;

    nr_entries = all_trees_same_as_cache_tree(n, dirmask, names, info);
    if (nr_entries > 0) {
        int pos = index_pos_by_traverse_info(names, info);

        if (!o->merge || df_conflicts)
            BUG("Wrong condition to get here buddy");

        /*
         * All entries up to 'pos' must have been processed
         * (i.e. marked CE_UNPACKED) at this point. But to be safe,
         * save and restore cache_bottom anyway to not miss
         * unprocessed entries before 'pos'.
         */
        bottom = o->internal.cache_bottom;
        ret = traverse_by_cache_tree(pos, nr_entries, n, info);
        o->internal.cache_bottom = bottom;
        return ret;
    }

    p = names;
    while (!p->mode)
        p++;

    newinfo = *info;
    newinfo.prev = info;
    newinfo.pathspec = info->pathspec;
    newinfo.name = p->path;
    newinfo.namelen = p->pathlen;
    newinfo.mode = p->mode;
    newinfo.pathlen = st_add3(newinfo.pathlen, tree_entry_len(p), 1);
    newinfo.df_conflicts |= df_conflicts;

    ALLOC_ARRAY(t, n);
    ALLOC_ARRAY(buf, n);

    /*
     * Fetch the tree from the ODB for each peer directory in the
     * n commits.
     *
     * For 2- and 3-way traversals, we try to avoid hitting the
     * ODB twice for the same OID.  This should yield a nice speed
     * up in checkouts and merges when the commits are similar.
     *
     * We don't bother doing the full O(n^2) search for larger n,
     * because wider traversals don't happen that often and we
     * avoid the search setup.
     *
     * When 2 peer OIDs are the same, we just copy the tree
     * descriptor data.  This implicitly borrows the buffer
     * data from the earlier cell.
     */
    for (i = 0; i < n; i++, dirmask >>= 1) {
        if (i > 0 && are_same_oid(&names[i], &names[i - 1]))
            t[i] = t[i - 1];
        else if (i > 1 && are_same_oid(&names[i], &names[i - 2]))
            t[i] = t[i - 2];
        else {
            const struct object_id *oid = NULL;
            if (dirmask & 1)
                oid = &names[i].oid;
            buf[nr_buf++] = fill_tree_descriptor(the_repository, t + i, oid);
        }
    }

    bottom = switch_cache_bottom(&newinfo);
    ret = traverse_trees(o->src_index, n, t, &newinfo);
    restore_cache_bottom(&newinfo, bottom);

    for (i = 0; i < nr_buf; i++)
        free(buf[i]);
    free(buf);
    free(t);

    return ret;
}

/*
 * Compare the traverse-path to the cache entry without actually
 * having to generate the textual representation of the traverse
 * path.
 *
 * NOTE! This *only* compares up to the size of the traverse path
 * itself - the caller needs to do the final check for the cache
 * entry having more data at the end!
 */
static int do_compare_entry_piecewise(const struct cache_entry *ce,
                      const struct traverse_info *info,
                      const char *name, size_t namelen,
                      unsigned mode)
{
    int pathlen, ce_len;
    const char *ce_name;

    if (info->prev) {
        int cmp = do_compare_entry_piecewise(ce, info->prev,
                             info->name, info->namelen,
                             info->mode);
        if (cmp)
            return cmp;
    }
    pathlen = info->pathlen;
    ce_len = ce_namelen(ce);

    /* If ce_len < pathlen then we must have previously hit "name == directory" entry */
    if (ce_len < pathlen)
        return -1;

    ce_len -= pathlen;
    ce_name = ce->name + pathlen;

    return df_name_compare(ce_name, ce_len, S_IFREG, name, namelen, mode);
}

static int do_compare_entry(const struct cache_entry *ce,
                const struct traverse_info *info,
                const char *name, size_t namelen,
                unsigned mode)
{
    int pathlen, ce_len;
    const char *ce_name;
    int cmp;
    unsigned ce_mode;

    /*
     * If we have not precomputed the traverse path, it is quicker
     * to avoid doing so.  But if we have precomputed it,
     * it is quicker to use the precomputed version.
     */
    if (!info->traverse_path)
        return do_compare_entry_piecewise(ce, info, name, namelen, mode);

    cmp = strncmp(ce->name, info->traverse_path, info->pathlen);
    if (cmp)
        return cmp;

    pathlen = info->pathlen;
    ce_len = ce_namelen(ce);

    if (ce_len < pathlen)
        return -1;

    ce_len -= pathlen;
    ce_name = ce->name + pathlen;

    ce_mode = S_ISSPARSEDIR(ce->ce_mode) ? S_IFDIR : S_IFREG;
    return df_name_compare(ce_name, ce_len, ce_mode, name, namelen, mode);
}

static int compare_entry(const struct cache_entry *ce, const struct traverse_info *info, const struct name_entry *n)
{
    int cmp = do_compare_entry(ce, info, n->path, n->pathlen, n->mode);
    if (cmp)
        return cmp;

    /*
     * At this point, we know that we have a prefix match. If ce
     * is a sparse directory, then allow an exact match. This only
     * works when the input name is a directory, since ce->name
     * ends in a directory separator.
     */
    if (S_ISSPARSEDIR(ce->ce_mode) &&
        ce->ce_namelen == traverse_path_len(info, tree_entry_len(n)) + 1)
        return 0;

    /*
     * Even if the beginning compared identically, the ce should
     * compare as bigger than a directory leading up to it!
     */
    return ce_namelen(ce) > traverse_path_len(info, tree_entry_len(n));
}

static int ce_in_traverse_path(const struct cache_entry *ce,
                   const struct traverse_info *info)
{
    if (!info->prev)
        return 1;
    if (do_compare_entry(ce, info->prev,
                 info->name, info->namelen, info->mode))
        return 0;
    /*
     * If ce (blob) is the same name as the path (which is a tree
     * we will be descending into), it won't be inside it.
     */
    return (info->pathlen < ce_namelen(ce));
}

static struct cache_entry *create_ce_entry(const struct traverse_info *info,
    const struct name_entry *n,
    int stage,
    struct index_state *istate,
    int is_transient,
    int is_sparse_directory)
{
    size_t len = traverse_path_len(info, tree_entry_len(n));
    size_t alloc_len = is_sparse_directory ? len + 1 : len;
    struct cache_entry *ce =
        is_transient ?
        make_empty_transient_cache_entry(alloc_len, NULL) :
        make_empty_cache_entry(istate, alloc_len);

    ce->ce_mode = create_ce_mode(n->mode);
    ce->ce_flags = create_ce_flags(stage);
    ce->ce_namelen = len;
    oidcpy(&ce->oid, &n->oid);
    /* len+1 because the cache_entry allocates space for NUL */
    make_traverse_path(ce->name, len + 1, info, n->path, n->pathlen);

    if (is_sparse_directory) {
        ce->name[len] = '/';
        ce->name[len + 1] = '\0';
        ce->ce_namelen++;
        ce->ce_flags |= CE_SKIP_WORKTREE;
    }

    return ce;
}

/*
 * Determine whether the path specified by 'p' should be unpacked as a new
 * sparse directory in a sparse index. A new sparse directory 'A/':
 * - must be outside the sparse cone.
 * - must not already be in the index (i.e., no index entry with name 'A/'
 *   exists).
 * - must not have any child entries in the index (i.e., no index entry
 *   'A/<something>' exists).
 * If 'p' meets the above requirements, return 1; otherwise, return 0.
 */
static int entry_is_new_sparse_dir(const struct traverse_info *info,
                   const struct name_entry *p)
{
    int res, pos;
    struct strbuf dirpath = STRBUF_INIT;
    struct unpack_trees_options *o = info->data;

    if (!S_ISDIR(p->mode))
        return 0;

    /*
     * If the path is inside the sparse cone, it can't be a sparse directory.
     */
    strbuf_add(&dirpath, info->traverse_path, info->pathlen);
    strbuf_add(&dirpath, p->path, p->pathlen);
    strbuf_addch(&dirpath, '/');
    if (path_in_cone_mode_sparse_checkout(dirpath.buf, o->src_index)) {
        res = 0;
        goto cleanup;
    }

    pos = index_name_pos_sparse(o->src_index, dirpath.buf, dirpath.len);
    if (pos >= 0) {
        /* Path is already in the index, not a new sparse dir */
        res = 0;
        goto cleanup;
    }

    /* Where would this sparse dir be inserted into the index? */
    pos = -pos - 1;
    if (pos >= o->src_index->cache_nr) {
        /*
         * Sparse dir would be inserted at the end of the index, so we
         * know it has no child entries.
         */
        res = 1;
        goto cleanup;
    }

    /*
     * If the dir has child entries in the index, the first would be at the
     * position the sparse directory would be inserted. If the entry at this
     * position is inside the dir, not a new sparse dir.
     */
    res = strncmp(o->src_index->cache[pos]->name, dirpath.buf, dirpath.len);

cleanup:
    strbuf_release(&dirpath);
    return res;
}

/*
 * Note that traverse_by_cache_tree() duplicates some logic in this function
 * without actually calling it. If you change the logic here you may need to
 * check and change there as well.
 */
static int unpack_single_entry(int n, unsigned long mask,
                   unsigned long dirmask,
                   struct cache_entry **src,
                   const struct name_entry *names,
                   const struct traverse_info *info,
                   int *is_new_sparse_dir)
{
    int i;
    struct unpack_trees_options *o = info->data;
    unsigned long conflicts = info->df_conflicts | dirmask;
    const struct name_entry *p = names;

    *is_new_sparse_dir = 0;
    if (mask == dirmask && !src[0]) {
        /*
         * If we're not in a sparse index, we can't unpack a directory
         * without recursing into it, so we return.
         */
        if (!o->src_index->sparse_index)
            return 0;

        /* Find first entry with a real name (we could use "mask" too) */
        while (!p->mode)
            p++;

        /*
         * If the directory is completely missing from the index but
         * would otherwise be a sparse directory, we should unpack it.
         * If not, we'll return and continue recursively traversing the
         * tree.
         */
        *is_new_sparse_dir = entry_is_new_sparse_dir(info, p);
        if (!*is_new_sparse_dir)
            return 0;
    }

    /*
     * When we are unpacking a sparse directory, then this isn't necessarily
     * a directory-file conflict.
     */
    if (mask == dirmask &&
        (*is_new_sparse_dir || (src[0] && S_ISSPARSEDIR(src[0]->ce_mode))))
        conflicts = 0;

    /*
     * Ok, we've filled in up to any potential index entry in src[0],
     * now do the rest.
     */
    for (i = 0; i < n; i++) {
        int stage;
        unsigned int bit = 1ul << i;
        if (conflicts & bit) {
            src[i + o->merge] = o->df_conflict_entry;
            continue;
        }
        if (!(mask & bit))
            continue;
        if (!o->merge)
            stage = 0;
        else if (i + 1 < o->head_idx)
            stage = 1;
        else if (i + 1 > o->head_idx)
            stage = 3;
        else
            stage = 2;

        /*
         * If the merge bit is set, then the cache entries are
         * discarded in the following block.  In this case,
         * construct "transient" cache_entries, as they are
         * not stored in the index.  otherwise construct the
         * cache entry from the index aware logic.
         */
        src[i + o->merge] = create_ce_entry(info, names + i, stage,
                            &o->internal.result,
                            o->merge, bit & dirmask);
    }

    if (o->merge) {
        int rc = call_unpack_fn((const struct cache_entry * const *)src,
                    o);
        for (i = 0; i < n; i++) {
            struct cache_entry *ce = src[i + o->merge];
            if (ce != o->df_conflict_entry)
                discard_cache_entry(ce);
        }
        return rc;
    }

    for (i = 0; i < n; i++)
        if (src[i] && src[i] != o->df_conflict_entry)
            if (do_add_entry(o, src[i], 0, 0))
                return -1;

    return 0;
}

static int unpack_failed(struct unpack_trees_options *o, const char *message)
{
    discard_index(&o->internal.result);
    if (!o->quiet && !o->exiting_early) {
        if (message)
            return error("%s", message);
        return -1;
    }
    return -1;
}

/*
 * The tree traversal is looking at name p.  If we have a matching entry,
 * return it.  If name p is a directory in the index, do not return
 * anything, as we will want to match it when the traversal descends into
 * the directory.
 */
static int find_cache_pos(struct traverse_info *info,
              const char *p, size_t p_len)
{
    int pos;
    struct unpack_trees_options *o = info->data;
    struct index_state *index = o->src_index;
    int pfxlen = info->pathlen;

    for (pos = o->internal.cache_bottom; pos < index->cache_nr; pos++) {
        const struct cache_entry *ce = index->cache[pos];
        const char *ce_name, *ce_slash;
        int cmp, ce_len;

        if (ce->ce_flags & CE_UNPACKED) {
            /*
             * cache_bottom entry is already unpacked, so
             * we can never match it; don't check it
             * again.
             */
            if (pos == o->internal.cache_bottom)
                ++o->internal.cache_bottom;
            continue;
        }
        if (!ce_in_traverse_path(ce, info)) {
            /*
             * Check if we can skip future cache checks
             * (because we're already past all possible
             * entries in the traverse path).
             */
            if (info->traverse_path) {
                if (strncmp(ce->name, info->traverse_path,
                        info->pathlen) > 0)
                    break;
            }
            continue;
        }
        ce_name = ce->name + pfxlen;
        ce_slash = strchr(ce_name, '/');
        if (ce_slash)
            ce_len = ce_slash - ce_name;
        else
            ce_len = ce_namelen(ce) - pfxlen;
        cmp = name_compare(p, p_len, ce_name, ce_len);
        /*
         * Exact match; if we have a directory we need to
         * delay returning it.
         */
        if (!cmp)
            return ce_slash ? -2 - pos : pos;
        if (0 < cmp)
            continue; /* keep looking */
        /*
         * ce_name sorts after p->path; could it be that we
         * have files under p->path directory in the index?
         * E.g.  ce_name == "t-i", and p->path == "t"; we may
         * have "t/a" in the index.
         */
        if (p_len < ce_len && !memcmp(ce_name, p, p_len) &&
            ce_name[p_len] < '/')
            continue; /* keep looking */
        break;
    }
    return -1;
}

/*
 * Given a sparse directory entry 'ce', compare ce->name to
 * info->traverse_path + p->path + '/' if info->traverse_path
 * is non-empty.
 *
 * Compare ce->name to p->path + '/' otherwise. Note that
 * ce->name must end in a trailing '/' because it is a sparse
 * directory entry.
 */
static int sparse_dir_matches_path(const struct cache_entry *ce,
                   struct traverse_info *info,
                   const struct name_entry *p)
{
    assert(S_ISSPARSEDIR(ce->ce_mode));
    assert(ce->name[ce->ce_namelen - 1] == '/');

    if (info->pathlen)
        return ce->ce_namelen == info->pathlen + p->pathlen + 1 &&
               ce->name[info->pathlen - 1] == '/' &&
               !strncmp(ce->name, info->traverse_path, info->pathlen) &&
               !strncmp(ce->name + info->pathlen, p->path, p->pathlen);
    return ce->ce_namelen == p->pathlen + 1 &&
           !strncmp(ce->name, p->path, p->pathlen);
}

static struct cache_entry *find_cache_entry(struct traverse_info *info,
                        const struct name_entry *p)
{
    const char *path;
    int pos = find_cache_pos(info, p->path, p->pathlen);
    struct unpack_trees_options *o = info->data;

    if (0 <= pos)
        return o->src_index->cache[pos];

    /*
     * Check for a sparse-directory entry named "path/".
     * Due to the input p->path not having a trailing
     * slash, the negative 'pos' value overshoots the
     * expected position, hence "-2" instead of "-1".
     */
    pos = -pos - 2;

    if (pos < 0 || pos >= o->src_index->cache_nr)
        return NULL;

    /*
     * Due to lexicographic sorting and sparse directory
     * entries ending with a trailing slash, our path as a
     * sparse directory (e.g "subdir/") and    our path as a
     * file (e.g. "subdir") might be separated by other
     * paths (e.g. "subdir-").
     */
    while (pos >= 0) {
        struct cache_entry *ce = o->src_index->cache[pos];

        if (!skip_prefix(ce->name, info->traverse_path, &path) ||
            strncmp(path, p->path, p->pathlen) ||
            path[p->pathlen] != '/')
            return NULL;

        if (S_ISSPARSEDIR(ce->ce_mode) &&
            sparse_dir_matches_path(ce, info, p))
            return ce;

        pos--;
    }

    return NULL;
}

static void debug_path(struct traverse_info *info)
{
    if (info->prev) {
        debug_path(info->prev);
        if (*info->prev->name)
            putchar('/');
    }
    printf("%s", info->name);
}

static void debug_name_entry(int i, struct name_entry *n)
{
    printf("ent#%d %06o %s\n", i,
           n->path ? n->mode : 0,
           n->path ? n->path : "(missing)");
}

static void debug_unpack_callback(int n,
                  unsigned long mask,
                  unsigned long dirmask,
                  struct name_entry *names,
                  struct traverse_info *info)
{
    int i;
    printf("* unpack mask %lu, dirmask %lu, cnt %d ",
           mask, dirmask, n);
    debug_path(info);
    putchar('\n');
    for (i = 0; i < n; i++)
        debug_name_entry(i, names + i);
}

/*
 * Returns true if and only if the given cache_entry is a
 * sparse-directory entry that matches the given name_entry
 * from the tree walk at the given traverse_info.
 */
static int is_sparse_directory_entry(struct cache_entry *ce,
                     const struct name_entry *name,
                     struct traverse_info *info)
{
    if (!ce || !name || !S_ISSPARSEDIR(ce->ce_mode))
        return 0;

    return sparse_dir_matches_path(ce, info, name);
}

static int unpack_sparse_callback(int n, unsigned long mask, unsigned long dirmask, struct name_entry *names, struct traverse_info *info)
{
    struct cache_entry *src[MAX_UNPACK_TREES + 1] = { NULL, };
    struct unpack_trees_options *o = info->data;
    int ret, is_new_sparse_dir;

    assert(o->merge);

    /*
     * Unlike in 'unpack_callback', where src[0] is derived from the index when
     * merging, src[0] is a transient cache entry derived from the first tree
     * provided. Create the temporary entry as if it came from a non-sparse index.
     */
    if (!is_null_oid(&names[0].oid)) {
        src[0] = create_ce_entry(info, &names[0], 0,
                    &o->internal.result, 1,
                    dirmask & (1ul << 0));
        src[0]->ce_flags |= (CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE);
    }

    /*
     * 'unpack_single_entry' assumes that src[0] is derived directly from
     * the index, rather than from an entry in 'names'. This is *not* true when
     * merging a sparse directory, in which case names[0] is the "index" source
     * entry. To match the expectations of 'unpack_single_entry', shift past the
     * "index" tree (i.e., names[0]) and adjust 'names', 'n', 'mask', and
     * 'dirmask' accordingly.
     */
    ret = unpack_single_entry(n - 1, mask >> 1, dirmask >> 1, src, names + 1, info, &is_new_sparse_dir);

    if (src[0])
        discard_cache_entry(src[0]);

    return ret >= 0 ? mask : -1;
}

/*
 * Note that traverse_by_cache_tree() duplicates some logic in this function
 * without actually calling it. If you change the logic here you may need to
 * check and change there as well.
 */
static int unpack_callback(int n, unsigned long mask, unsigned long dirmask, struct name_entry *names, struct traverse_info *info)
{
    struct cache_entry *src[MAX_UNPACK_TREES + 1] = { NULL, };
    struct unpack_trees_options *o = info->data;
    const struct name_entry *p = names;
    int is_new_sparse_dir;

    /* Find first entry with a real name (we could use "mask" too) */
    while (!p->mode)
        p++;

    if (o->internal.debug_unpack)
        debug_unpack_callback(n, mask, dirmask, names, info);

    /* Are we supposed to look at the index too? */
    if (o->merge) {
        while (1) {
            int cmp;
            struct cache_entry *ce;

            if (o->diff_index_cached)
                ce = next_cache_entry(o);
            else
                ce = find_cache_entry(info, p);

            if (!ce)
                break;
            cmp = compare_entry(ce, info, p);
            if (cmp < 0) {
                if (unpack_index_entry(ce, o) < 0)
                    return unpack_failed(o, NULL);
                continue;
            }
            if (!cmp) {
                if (ce_stage(ce)) {
                    /*
                     * If we skip unmerged index
                     * entries, we'll skip this
                     * entry *and* the tree
                     * entries associated with it!
                     */
                    if (o->skip_unmerged) {
                        add_same_unmerged(ce, o);
                        return mask;
                    }
                }
                src[0] = ce;
            }
            break;
        }
    }

    if (unpack_single_entry(n, mask, dirmask, src, names, info, &is_new_sparse_dir))
        return -1;

    if (o->merge && src[0]) {
        if (ce_stage(src[0]))
            mark_ce_used_same_name(src[0], o);
        else
            mark_ce_used(src[0], o);
    }

    /* Now handle any directories.. */
    if (dirmask) {
        /* special case: "diff-index --cached" looking at a tree */
        if (o->diff_index_cached &&
            n == 1 && dirmask == 1 && S_ISDIR(names->mode)) {
            int matches;
            matches = cache_tree_matches_traversal(o->src_index->cache_tree,
                                   names, info);
            /*
             * Everything under the name matches; skip the
             * entire hierarchy.  diff_index_cached codepath
             * special cases D/F conflicts in such a way that
             * it does not do any look-ahead, so this is safe.
             */
            if (matches) {
                /*
                 * Only increment the cache_bottom if the
                 * directory isn't a sparse directory index
                 * entry (if it is, it was already incremented)
                 * in 'mark_ce_used()'
                 */
                if (!src[0] || !S_ISSPARSEDIR(src[0]->ce_mode))
                    o->internal.cache_bottom += matches;
                return mask;
            }
        }

        if (!is_sparse_directory_entry(src[0], p, info) &&
            !is_new_sparse_dir &&
            traverse_trees_recursive(n, dirmask, mask & ~dirmask,
                            names, info) < 0) {
            return -1;
        }

        return mask;
    }

    return mask;
}

static int clear_ce_flags_1(struct index_state *istate,
                struct cache_entry **cache, int nr,
                struct strbuf *prefix,
                int select_mask, int clear_mask,
                struct pattern_list *pl,
                enum pattern_match_result default_match,
                int progress_nr);

/* Whole directory matching */
static int clear_ce_flags_dir(struct index_state *istate,
                  struct cache_entry **cache, int nr,
                  struct strbuf *prefix,
                  char *basename,
                  int select_mask, int clear_mask,
                  struct pattern_list *pl,
                  enum pattern_match_result default_match,
                  int progress_nr)
{
    struct cache_entry **cache_end;
    int dtype = DT_DIR;
    int rc;
    enum pattern_match_result ret, orig_ret;
    orig_ret = path_matches_pattern_list(prefix->buf, prefix->len,
                         basename, &dtype, pl, istate);

    strbuf_addch(prefix, '/');

    /* If undecided, use matching result of parent dir in defval */
    if (orig_ret == UNDECIDED)
        ret = default_match;
    else
        ret = orig_ret;

    for (cache_end = cache; cache_end != cache + nr; cache_end++) {
        struct cache_entry *ce = *cache_end;
        if (strncmp(ce->name, prefix->buf, prefix->len))
            break;
    }

    if (pl->use_cone_patterns && orig_ret == MATCHED_RECURSIVE) {
        struct cache_entry **ce = cache;
        rc = cache_end - cache;

        while (ce < cache_end) {
            (*ce)->ce_flags &= ~clear_mask;
            ce++;
        }
    } else if (pl->use_cone_patterns && orig_ret == NOT_MATCHED) {
        rc = cache_end - cache;
    } else {
        rc = clear_ce_flags_1(istate, cache, cache_end - cache,
                      prefix,
                      select_mask, clear_mask,
                      pl, ret,
                      progress_nr);
    }

    strbuf_setlen(prefix, prefix->len - 1);
    return rc;
}

/*
 * Traverse the index, find every entry that matches according to
 * o->pl. Do "ce_flags &= ~clear_mask" on those entries. Return the
 * number of traversed entries.
 *
 * If select_mask is non-zero, only entries whose ce_flags has on of
 * those bits enabled are traversed.
 *
 * cache    : pointer to an index entry
 * prefix_len    : an offset to its path
 *
 * The current path ("prefix") including the trailing '/' is
 *   cache[0]->name[0..(prefix_len-1)]
 * Top level path has prefix_len zero.
 */
static int clear_ce_flags_1(struct index_state *istate,
                struct cache_entry **cache, int nr,
                struct strbuf *prefix,
                int select_mask, int clear_mask,
                struct pattern_list *pl,
                enum pattern_match_result default_match,
                int progress_nr)
{
    struct cache_entry **cache_end = nr ? cache + nr : cache;

    /*
     * Process all entries that have the given prefix and meet
     * select_mask condition
     */
    while(cache != cache_end) {
        struct cache_entry *ce = *cache;
        const char *name, *slash;
        int len, dtype;
        enum pattern_match_result ret;

        display_progress(istate->progress, progress_nr);

        if (select_mask && !(ce->ce_flags & select_mask)) {
            cache++;
            progress_nr++;
            continue;
        }

        if (prefix->len && strncmp(ce->name, prefix->buf, prefix->len))
            break;

        name = ce->name + prefix->len;
        slash = strchr(name, '/');

        /* If it's a directory, try whole directory match first */
        if (slash) {
            int processed;

            len = slash - name;
            strbuf_add(prefix, name, len);

            processed = clear_ce_flags_dir(istate, cache, cache_end - cache,
                               prefix,
                               prefix->buf + prefix->len - len,
                               select_mask, clear_mask,
                               pl, default_match,
                               progress_nr);

            /* clear_c_f_dir eats a whole dir already? */
            if (processed) {
                cache += processed;
                progress_nr += processed;
                strbuf_setlen(prefix, prefix->len - len);
                continue;
            }

            strbuf_addch(prefix, '/');
            processed = clear_ce_flags_1(istate, cache, cache_end - cache,
                             prefix,
                             select_mask, clear_mask, pl,
                             default_match, progress_nr);

            cache += processed;
            progress_nr += processed;

            strbuf_setlen(prefix, prefix->len - len - 1);
            continue;
        }

        /* Non-directory */
        dtype = ce_to_dtype(ce);
        ret = path_matches_pattern_list(ce->name,
                        ce_namelen(ce),
                        name, &dtype, pl, istate);
        if (ret == UNDECIDED)
            ret = default_match;
        if (ret == MATCHED || ret == MATCHED_RECURSIVE)
            ce->ce_flags &= ~clear_mask;
        cache++;
        progress_nr++;
    }

    display_progress(istate->progress, progress_nr);
    return nr - (cache_end - cache);
}

static int clear_ce_flags(struct index_state *istate,
              int select_mask, int clear_mask,
              struct pattern_list *pl,
              int show_progress)
{
    static struct strbuf prefix = STRBUF_INIT;
    char label[100];
    int rval;

    strbuf_reset(&prefix);
    if (show_progress)
        istate->progress = start_delayed_progress(
                    _("Updating index flags"),
                    istate->cache_nr);

    xsnprintf(label, sizeof(label), "clear_ce_flags(0x%08lx,0x%08lx)",
          (unsigned long)select_mask, (unsigned long)clear_mask);
    trace2_region_enter("unpack_trees", label, the_repository);
    rval = clear_ce_flags_1(istate,
                istate->cache,
                istate->cache_nr,
                &prefix,
                select_mask, clear_mask,
                pl, 0, 0);
    trace2_region_leave("unpack_trees", label, the_repository);

    stop_progress(&istate->progress);
    return rval;
}

/*
 * Set/Clear CE_NEW_SKIP_WORKTREE according to $GIT_DIR/info/sparse-checkout
 */
static void mark_new_skip_worktree(struct pattern_list *pl,
                   struct index_state *istate,
                   int select_flag, int skip_wt_flag,
                   int show_progress)
{
    int i;

    /*
     * 1. Pretend the narrowest worktree: only unmerged entries
     * are checked out
     */
    for (i = 0; i < istate->cache_nr; i++) {
        struct cache_entry *ce = istate->cache[i];

        if (select_flag && !(ce->ce_flags & select_flag))
            continue;

        if (!ce_stage(ce) && !(ce->ce_flags & CE_CONFLICTED))
            ce->ce_flags |= skip_wt_flag;
        else
            ce->ce_flags &= ~skip_wt_flag;
    }

    /*
     * 2. Widen worktree according to sparse-checkout file.
     * Matched entries will have skip_wt_flag cleared (i.e. "in")
     */
    clear_ce_flags(istate, select_flag, skip_wt_flag, pl, show_progress);
}

static void populate_from_existing_patterns(struct unpack_trees_options *o,
                        struct pattern_list *pl)
{
    if (get_sparse_checkout_patterns(pl) < 0)
        o->skip_sparse_checkout = 1;
    else
        o->internal.pl = pl;
}

static void update_sparsity_for_prefix(const char *prefix,
                       struct index_state *istate)
{
    int prefix_len = strlen(prefix);
    struct strbuf ce_prefix = STRBUF_INIT;

    if (!istate->sparse_index)
        return;

    while (prefix_len > 0 && prefix[prefix_len - 1] == '/')
        prefix_len--;

    if (prefix_len <= 0)
        BUG("Invalid prefix passed to update_sparsity_for_prefix");

    strbuf_grow(&ce_prefix, prefix_len + 1);
    strbuf_add(&ce_prefix, prefix, prefix_len);
    strbuf_addch(&ce_prefix, '/');

    /*
     * If the prefix points to a sparse directory or a path inside a sparse
     * directory, the index should be expanded. This is accomplished in one
     * of two ways:
     * - if the prefix is inside a sparse directory, it will be expanded by
     *   the 'ensure_full_index(...)' call in 'index_name_pos(...)'.
     * - if the prefix matches an existing sparse directory entry,
     *   'index_name_pos(...)' will return its index position, triggering
     *   the 'ensure_full_index(...)' below.
     */
    if (!path_in_cone_mode_sparse_checkout(ce_prefix.buf, istate) &&
        index_name_pos(istate, ce_prefix.buf, ce_prefix.len) >= 0)
        ensure_full_index(istate);

    strbuf_release(&ce_prefix);
}

static int verify_absent(const struct cache_entry *,
             enum unpack_trees_error_types,
             struct unpack_trees_options *);
/*
 * N-way merge "len" trees.  Returns 0 on success, -1 on failure to manipulate the
 * resulting index, -2 on failure to reflect the changes to the work tree.
 *
 * CE_ADDED, CE_UNPACKED and CE_NEW_SKIP_WORKTREE are used internally
 */
int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options *o)
{
    struct repository *repo = the_repository;
    int i, ret;
    static struct cache_entry *dfc;
    struct pattern_list pl;
    int free_pattern_list = 0;
    struct dir_struct dir = DIR_INIT;

    if (o->reset == UNPACK_RESET_INVALID)
        BUG("o->reset had a value of 1; should be UNPACK_TREES_*_UNTRACKED");

    if (len > MAX_UNPACK_TREES)
        die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
    if (o->internal.dir)
        BUG("o->internal.dir is for internal use only");
    if (o->internal.pl)
        BUG("o->internal.pl is for internal use only");
    if (o->df_conflict_entry)
        BUG("o->df_conflict_entry is an output only field");

    trace_performance_enter();
    trace2_region_enter("unpack_trees", "unpack_trees", the_repository);

    prepare_repo_settings(repo);
    if (repo->settings.command_requires_full_index) {
        ensure_full_index(o->src_index);
        if (o->dst_index)
            ensure_full_index(o->dst_index);
    }

    if (o->reset == UNPACK_RESET_OVERWRITE_UNTRACKED &&
        o->preserve_ignored)
        BUG("UNPACK_RESET_OVERWRITE_UNTRACKED incompatible with preserved ignored files");

    if (!o->preserve_ignored) {
        o->internal.dir = &dir;
        o->internal.dir->flags |= DIR_SHOW_IGNORED;
        setup_standard_excludes(o->internal.dir);
    }

    if (o->prefix)
        update_sparsity_for_prefix(o->prefix, o->src_index);

    if (!core_apply_sparse_checkout || !o->update)
        o->skip_sparse_checkout = 1;
    if (!o->skip_sparse_checkout) {
        memset(&pl, 0, sizeof(pl));
        free_pattern_list = 1;
        populate_from_existing_patterns(o, &pl);
    }

    index_state_init(&o->internal.result, o->src_index->repo);
    o->internal.result.initialized = 1;
    o->internal.result.timestamp.sec = o->src_index->timestamp.sec;
    o->internal.result.timestamp.nsec = o->src_index->timestamp.nsec;
    o->internal.result.version = o->src_index->version;
    if (!o->src_index->split_index) {
        o->internal.result.split_index = NULL;
    } else if (o->src_index == o->dst_index) {
        /*
         * o->dst_index (and thus o->src_index) will be discarded
         * and overwritten with o->internal.result at the end of
         * this function, so just use src_index's split_index to
         * avoid having to create a new one.
         */
        o->internal.result.split_index = o->src_index->split_index;
        if (o->src_index->cache_changed & SPLIT_INDEX_ORDERED)
            o->internal.result.cache_changed |= SPLIT_INDEX_ORDERED;
        o->internal.result.split_index->refcount++;
    } else {
        o->internal.result.split_index =
            init_split_index(&o->internal.result);
    }
    oidcpy(&o->internal.result.oid, &o->src_index->oid);
    o->internal.merge_size = len;
    mark_all_ce_unused(o->src_index);

    o->internal.result.fsmonitor_last_update =
        xstrdup_or_null(o->src_index->fsmonitor_last_update);
    o->internal.result.fsmonitor_has_run_once = o->src_index->fsmonitor_has_run_once;

    if (!o->src_index->initialized &&
        !repo->settings.command_requires_full_index &&
        is_sparse_index_allowed(&o->internal.result, 0))
        o->internal.result.sparse_index = 1;

    /*
     * Sparse checkout loop #1: set NEW_SKIP_WORKTREE on existing entries
     */
    if (!o->skip_sparse_checkout)
        mark_new_skip_worktree(o->internal.pl, o->src_index, 0,
                       CE_NEW_SKIP_WORKTREE, o->verbose_update);

    if (!dfc)
        dfc = xcalloc(1, cache_entry_size(0));
    o->df_conflict_entry = dfc;

    if (len) {
        const char *prefix = o->prefix ? o->prefix : "";
        struct traverse_info info;

        setup_traverse_info(&info, prefix);
        info.fn = unpack_callback;
        info.data = o;
        info.show_all_errors = o->internal.show_all_errors;
        info.pathspec = o->pathspec;

        if (o->prefix) {
            /*
             * Unpack existing index entries that sort before the
             * prefix the tree is spliced into.  Note that o->merge
             * is always true in this case.
             */
            while (1) {
                struct cache_entry *ce = next_cache_entry(o);
                if (!ce)
                    break;
                if (ce_in_traverse_path(ce, &info))
                    break;
                if (unpack_index_entry(ce, o) < 0)
                    goto return_failed;
            }
        }

        trace_performance_enter();
        trace2_region_enter("unpack_trees", "traverse_trees", the_repository);
        ret = traverse_trees(o->src_index, len, t, &info);
        trace2_region_leave("unpack_trees", "traverse_trees", the_repository);
        trace_performance_leave("traverse_trees");
        if (ret < 0)
            goto return_failed;
    }

    /* Any left-over entries in the index? */
    if (o->merge) {
        while (1) {
            struct cache_entry *ce = next_cache_entry(o);
            if (!ce)
                break;
            if (unpack_index_entry(ce, o) < 0)
                goto return_failed;
        }
    }
    mark_all_ce_unused(o->src_index);

    if (o->trivial_merges_only && o->internal.nontrivial_merge) {
        ret = unpack_failed(o, "Merge requires file-level merging");
        goto done;
    }

    if (!o->skip_sparse_checkout) {
        /*
         * Sparse checkout loop #2: set NEW_SKIP_WORKTREE on entries not in loop #1
         * If they will have NEW_SKIP_WORKTREE, also set CE_SKIP_WORKTREE
         * so apply_sparse_checkout() won't attempt to remove it from worktree
         */
        mark_new_skip_worktree(o->internal.pl, &o->internal.result,
                       CE_ADDED, CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE,
                       o->verbose_update);

        ret = 0;
        for (i = 0; i < o->internal.result.cache_nr; i++) {
            struct cache_entry *ce = o->internal.result.cache[i];

            /*
             * Entries marked with CE_ADDED in merged_entry() do not have
             * verify_absent() check (the check is effectively disabled
             * because CE_NEW_SKIP_WORKTREE is set unconditionally).
             *
             * Do the real check now because we have had
             * correct CE_NEW_SKIP_WORKTREE
             */
            if (ce->ce_flags & CE_ADDED &&
                verify_absent(ce, WARNING_SPARSE_ORPHANED_NOT_OVERWRITTEN, o))
                ret = 1;

            if (apply_sparse_checkout(&o->internal.result, ce, o))
                ret = 1;
        }
        if (ret == 1) {
            /*
             * Inability to sparsify or de-sparsify individual
             * paths is not an error, but just a warning.
             */
            if (o->internal.show_all_errors)
                display_warning_msgs(o);
            ret = 0;
        }
    }

    ret = check_updates(o, &o->internal.result) ? (-2) : 0;
    if (o->dst_index) {
        move_index_extensions(&o->internal.result, o->src_index);
        if (!ret) {
            if (git_env_bool("GIT_TEST_CHECK_CACHE_TREE", 0))
                cache_tree_verify(the_repository,
                          &o->internal.result);
            if (!o->skip_cache_tree_update &&
                !cache_tree_fully_valid(o->internal.result.cache_tree))
                cache_tree_update(&o->internal.result,
                          WRITE_TREE_SILENT |
                          WRITE_TREE_REPAIR);
        }

        o->internal.result.updated_workdir = 1;
        discard_index(o->dst_index);
        *o->dst_index = o->internal.result;
    } else {
        discard_index(&o->internal.result);
    }
    o->src_index = NULL;

done:
    if (free_pattern_list)
        clear_pattern_list(&pl);
    if (o->internal.dir) {
        dir_clear(o->internal.dir);
        o->internal.dir = NULL;
    }
    trace2_region_leave("unpack_trees", "unpack_trees", the_repository);
    trace_performance_leave("unpack_trees");
    return ret;

return_failed:
    if (o->internal.show_all_errors)
        display_error_msgs(o);
    mark_all_ce_unused(o->src_index);
    ret = unpack_failed(o, NULL);
    if (o->exiting_early)
        ret = 0;
    goto done;
}

/*
 * Update SKIP_WORKTREE bits according to sparsity patterns, and update
 * working directory to match.
 *
 * CE_NEW_SKIP_WORKTREE is used internally.
 */
enum update_sparsity_result update_sparsity(struct unpack_trees_options *o,
                        struct pattern_list *pl)
{
    enum update_sparsity_result ret = UPDATE_SPARSITY_SUCCESS;
    int i;
    unsigned old_show_all_errors;
    int free_pattern_list = 0;

    old_show_all_errors = o->internal.show_all_errors;
    o->internal.show_all_errors = 1;
    index_state_init(&o->internal.result, o->src_index->repo);

    /* Sanity checks */
    if (!o->update || o->index_only || o->skip_sparse_checkout)
        BUG("update_sparsity() is for reflecting sparsity patterns in working directory");
    if (o->src_index != o->dst_index || o->fn)
        BUG("update_sparsity() called wrong");

    trace_performance_enter();

    /* If we weren't given patterns, use the recorded ones */
    if (!pl) {
        free_pattern_list = 1;
        pl = xcalloc(1, sizeof(*pl));
        populate_from_existing_patterns(o, pl);
    }
    o->internal.pl = pl;

    /* Expand sparse directories as needed */
    expand_index(o->src_index, o->internal.pl);

    /* Set NEW_SKIP_WORKTREE on existing entries. */
    mark_all_ce_unused(o->src_index);
    mark_new_skip_worktree(o->internal.pl, o->src_index, 0,
                   CE_NEW_SKIP_WORKTREE, o->verbose_update);

    /* Then loop over entries and update/remove as needed */
    ret = UPDATE_SPARSITY_SUCCESS;
    for (i = 0; i < o->src_index->cache_nr; i++) {
        struct cache_entry *ce = o->src_index->cache[i];


        if (ce_stage(ce)) {
            /* -1 because for loop will increment by 1 */
            i += warn_conflicted_path(o->src_index, i, o) - 1;
            ret = UPDATE_SPARSITY_WARNINGS;
            continue;
        }

        if (apply_sparse_checkout(o->src_index, ce, o))
            ret = UPDATE_SPARSITY_WARNINGS;
    }

    if (check_updates(o, o->src_index))
        ret = UPDATE_SPARSITY_WORKTREE_UPDATE_FAILURES;

    display_warning_msgs(o);
    o->internal.show_all_errors = old_show_all_errors;
    if (free_pattern_list) {
        clear_pattern_list(pl);
        free(pl);
        o->internal.pl = NULL;
    }
    trace_performance_leave("update_sparsity");
    return ret;
}

/* Here come the merge functions */

static int reject_merge(const struct cache_entry *ce,
            struct unpack_trees_options *o)
{
    return add_rejected_path(o, ERROR_WOULD_OVERWRITE, ce->name);
}

static int same(const struct cache_entry *a, const struct cache_entry *b)
{
    if (!!a != !!b)
        return 0;
    if (!a && !b)
        return 1;
    if ((a->ce_flags | b->ce_flags) & CE_CONFLICTED)
        return 0;
    return a->ce_mode == b->ce_mode &&
           oideq(&a->oid, &b->oid);
}


/*
 * When a CE gets turned into an unmerged entry, we
 * want it to be up-to-date
 */
static int verify_uptodate_1(const struct cache_entry *ce,
                 struct unpack_trees_options *o,
                 enum unpack_trees_error_types error_type)
{
    struct stat st;

    if (o->index_only)
        return 0;

    /*
     * CE_VALID and CE_SKIP_WORKTREE cheat, we better check again
     * if this entry is truly up-to-date because this file may be
     * overwritten.
     */
    if ((ce->ce_flags & CE_VALID) || ce_skip_worktree(ce))
        ; /* keep checking */
    else if (o->reset || ce_uptodate(ce))
        return 0;

    if (!lstat(ce->name, &st)) {
        int flags = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE;
        unsigned changed = ie_match_stat(o->src_index, ce, &st, flags);

        if (submodule_from_ce(ce)) {
            int r = check_submodule_move_head(ce,
                "HEAD", oid_to_hex(&ce->oid), o);
            if (r)
                return add_rejected_path(o, error_type, ce->name);
            return 0;
        }

        if (!changed)
            return 0;
        /*
         * Historic default policy was to allow submodule to be out
         * of sync wrt the superproject index. If the submodule was
         * not considered interesting above, we don't care here.
         */
        if (S_ISGITLINK(ce->ce_mode))
            return 0;

        errno = 0;
    }
    if (errno == ENOENT)
        return 0;
    return add_rejected_path(o, error_type, ce->name);
}

int verify_uptodate(const struct cache_entry *ce,
            struct unpack_trees_options *o)
{
    if (!o->skip_sparse_checkout &&
        (ce->ce_flags & CE_SKIP_WORKTREE) &&
        (ce->ce_flags & CE_NEW_SKIP_WORKTREE))
        return 0;
    return verify_uptodate_1(ce, o, ERROR_NOT_UPTODATE_FILE);
}

static int verify_uptodate_sparse(const struct cache_entry *ce,
                  struct unpack_trees_options *o)
{
    return verify_uptodate_1(ce, o, WARNING_SPARSE_NOT_UPTODATE_FILE);
}

/*
 * TODO: We should actually invalidate o->internal.result, not src_index [1].
 * But since cache tree and untracked cache both are not copied to
 * o->internal.result until unpacking is complete, we invalidate them on
 * src_index instead with the assumption that they will be copied to
 * dst_index at the end.
 *
 * [1] src_index->cache_tree is also used in unpack_callback() so if
 * we invalidate o->internal.result, we need to update it to use
 * o->internal.result.cache_tree as well.
 */
static void invalidate_ce_path(const struct cache_entry *ce,
                   struct unpack_trees_options *o)
{
    if (!ce)
        return;
    cache_tree_invalidate_path(o->src_index, ce->name);
    untracked_cache_invalidate_path(o->src_index, ce->name, 1);
}

/*
 * Check that checking out ce->sha1 in subdir ce->name is not
 * going to overwrite any working files.
 */
static int verify_clean_submodule(const char *old_sha1,
                  const struct cache_entry *ce,
                  struct unpack_trees_options *o)
{
    if (!submodule_from_ce(ce))
        return 0;

    return check_submodule_move_head(ce, old_sha1,
                     oid_to_hex(&ce->oid), o);
}

static int verify_clean_subdirectory(const struct cache_entry *ce,
                     struct unpack_trees_options *o)
{
    /*
     * we are about to extract "ce->name"; we would not want to lose
     * anything in the existing directory there.
     */
    int namelen;
    int i;
    struct dir_struct d;
    char *pathbuf;
    int cnt = 0;

    if (S_ISGITLINK(ce->ce_mode)) {
        struct object_id oid;
        int sub_head = repo_resolve_gitlink_ref(the_repository, ce->name,
                            "HEAD", &oid);
        /*
         * If we are not going to update the submodule, then
         * we don't care.
         */
        if (!sub_head && oideq(&oid, &ce->oid))
            return 0;
        return verify_clean_submodule(sub_head ? NULL : oid_to_hex(&oid),
                          ce, o);
    }

    /*
     * First let's make sure we do not have a local modification
     * in that directory.
     */
    namelen = ce_namelen(ce);
    for (i = locate_in_src_index(ce, o);
         i < o->src_index->cache_nr;
         i++) {
        struct cache_entry *ce2 = o->src_index->cache[i];
        int len = ce_namelen(ce2);
        if (len < namelen ||
            strncmp(ce->name, ce2->name, namelen) ||
            ce2->name[namelen] != '/')
            break;
        /*
         * ce2->name is an entry in the subdirectory to be
         * removed.
         */
        if (!ce_stage(ce2)) {
            if (verify_uptodate(ce2, o))
                return -1;
            add_entry(o, ce2, CE_REMOVE, 0);
            invalidate_ce_path(ce, o);
            mark_ce_used(ce2, o);
        }
        cnt++;
    }

    /* Do not lose a locally present file that is not ignored. */
    pathbuf = xstrfmt("%.*s/", namelen, ce->name);

    memset(&d, 0, sizeof(d));
    if (o->internal.dir)
        setup_standard_excludes(&d);
    i = read_directory(&d, o->src_index, pathbuf, namelen+1, NULL);
    dir_clear(&d);
    free(pathbuf);
    if (i)
        return add_rejected_path(o, ERROR_NOT_UPTODATE_DIR, ce->name);

    /* Do not lose startup_info->original_cwd */
    if (startup_info->original_cwd &&
        !strcmp(startup_info->original_cwd, ce->name))
        return add_rejected_path(o, ERROR_CWD_IN_THE_WAY, ce->name);

    return cnt;
}

/*
 * This gets called when there was no index entry for the tree entry 'dst',
 * but we found a file in the working tree that 'lstat()' said was fine,
 * and we're on a case-insensitive filesystem.
 *
 * See if we can find a case-insensitive match in the index that also
 * matches the stat information, and assume it's that other file!
 */
static int icase_exists(struct unpack_trees_options *o, const char *name, int len, struct stat *st)
{
    const struct cache_entry *src;

    src = index_file_exists(o->src_index, name, len, 1);
    return src && !ie_match_stat(o->src_index, src, st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
}

enum absent_checking_type {
    COMPLETELY_ABSENT,
    ABSENT_ANY_DIRECTORY
};

static int check_ok_to_remove(const char *name, int len, int dtype,
                  const struct cache_entry *ce, struct stat *st,
                  enum unpack_trees_error_types error_type,
                  enum absent_checking_type absent_type,
                  struct unpack_trees_options *o)
{
    const struct cache_entry *result;

    /*
     * It may be that the 'lstat()' succeeded even though
     * target 'ce' was absent, because there is an old
     * entry that is different only in case..
     *
     * Ignore that lstat() if it matches.
     */
    if (ignore_case && icase_exists(o, name, len, st))
        return 0;

    if (o->internal.dir &&
        is_excluded(o->internal.dir, o->src_index, name, &dtype))
        /*
         * ce->name is explicitly excluded, so it is Ok to
         * overwrite it.
         */
        return 0;
    if (S_ISDIR(st->st_mode)) {
        /*
         * We are checking out path "foo" and
         * found "foo/." in the working tree.
         * This is tricky -- if we have modified
         * files that are in "foo/" we would lose
         * them.
         */
        if (verify_clean_subdirectory(ce, o) < 0)
            return -1;
        return 0;
    }

    /* If we only care about directories, then we can remove */
    if (absent_type == ABSENT_ANY_DIRECTORY)
        return 0;

    /*
     * The previous round may already have decided to
     * delete this path, which is in a subdirectory that
     * is being replaced with a blob.
     */
    result = index_file_exists(&o->internal.result, name, len, 0);
    if (result) {
        if (result->ce_flags & CE_REMOVE)
            return 0;
    }

    return add_rejected_path(o, error_type, name);
}

/*
 * We do not want to remove or overwrite a working tree file that
 * is not tracked, unless it is ignored.
 */
static int verify_absent_1(const struct cache_entry *ce,
               enum unpack_trees_error_types error_type,
               enum absent_checking_type absent_type,
               struct unpack_trees_options *o)
{
    int len;
    struct stat st;

    if (o->index_only || !o->update)
        return 0;

    if (o->reset == UNPACK_RESET_OVERWRITE_UNTRACKED) {
        /* Avoid nuking startup_info->original_cwd... */
        if (startup_info->original_cwd &&
            !strcmp(startup_info->original_cwd, ce->name))
            return add_rejected_path(o, ERROR_CWD_IN_THE_WAY,
                         ce->name);
        /* ...but nuke anything else. */
        return 0;
    }

    len = check_leading_path(ce->name, ce_namelen(ce), 0);
    if (!len)
        return 0;
    else if (len > 0) {
        char *path;
        int ret;

        path = xmemdupz(ce->name, len);
        if (lstat(path, &st))
            ret = error_errno("cannot stat '%s'", path);
        else {
            if (submodule_from_ce(ce))
                ret = check_submodule_move_head(ce,
                                oid_to_hex(&ce->oid),
                                NULL, o);
            else
                ret = check_ok_to_remove(path, len, DT_UNKNOWN, NULL,
                             &st, error_type,
                             absent_type, o);
        }
        free(path);
        return ret;
    } else if (lstat(ce->name, &st)) {
        if (errno != ENOENT)
            return error_errno("cannot stat '%s'", ce->name);
        return 0;
    } else {
        if (submodule_from_ce(ce))
            return check_submodule_move_head(ce, oid_to_hex(&ce->oid),
                             NULL, o);

        return check_ok_to_remove(ce->name, ce_namelen(ce),
                      ce_to_dtype(ce), ce, &st,
                      error_type, absent_type, o);
    }
}

static int verify_absent(const struct cache_entry *ce,
             enum unpack_trees_error_types error_type,
             struct unpack_trees_options *o)
{
    if (!o->skip_sparse_checkout && (ce->ce_flags & CE_NEW_SKIP_WORKTREE))
        return 0;
    return verify_absent_1(ce, error_type, COMPLETELY_ABSENT, o);
}

static int verify_absent_if_directory(const struct cache_entry *ce,
                      enum unpack_trees_error_types error_type,
                      struct unpack_trees_options *o)
{
    if (!o->skip_sparse_checkout && (ce->ce_flags & CE_NEW_SKIP_WORKTREE))
        return 0;
    return verify_absent_1(ce, error_type, ABSENT_ANY_DIRECTORY, o);
}

static int verify_absent_sparse(const struct cache_entry *ce,
                enum unpack_trees_error_types error_type,
                struct unpack_trees_options *o)
{
    return verify_absent_1(ce, error_type, COMPLETELY_ABSENT, o);
}

static int merged_entry(const struct cache_entry *ce,
            const struct cache_entry *old,
            struct unpack_trees_options *o)
{
    int update = CE_UPDATE;
    struct cache_entry *merge = dup_cache_entry(ce, &o->internal.result);

    if (!old) {
        /*
         * New index entries. In sparse checkout, the following
         * verify_absent() will be delayed until after
         * traverse_trees() finishes in unpack_trees(), then:
         *
         *  - CE_NEW_SKIP_WORKTREE will be computed correctly
         *  - verify_absent() be called again, this time with
         *    correct CE_NEW_SKIP_WORKTREE
         *
         * verify_absent() call here does nothing in sparse
         * checkout (i.e. o->skip_sparse_checkout == 0)
         */
        update |= CE_ADDED;
        merge->ce_flags |= CE_NEW_SKIP_WORKTREE;

        if (verify_absent(merge,
                  ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o)) {
            discard_cache_entry(merge);
            return -1;
        }
        invalidate_ce_path(merge, o);

        if (submodule_from_ce(ce) && file_exists(ce->name)) {
            int ret = check_submodule_move_head(ce, NULL,
                                oid_to_hex(&ce->oid),
                                o);
            if (ret)
                return ret;
        }

    } else if (!(old->ce_flags & CE_CONFLICTED)) {
        /*
         * See if we can re-use the old CE directly?
         * That way we get the uptodate stat info.
         *
         * This also removes the UPDATE flag on a match; otherwise
         * we will end up overwriting local changes in the work tree.
         */
        if (same(old, merge)) {
            copy_cache_entry(merge, old);
            update = 0;
        } else {
            if (verify_uptodate(old, o)) {
                discard_cache_entry(merge);
                return -1;
            }
            /* Migrate old flags over */
            update |= old->ce_flags & (CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE);
            invalidate_ce_path(old, o);
        }

        if (submodule_from_ce(ce) && file_exists(ce->name)) {
            int ret = check_submodule_move_head(ce, oid_to_hex(&old->oid),
                                oid_to_hex(&ce->oid),
                                o);
            if (ret)
                return ret;
        }
    } else {
        /*
         * Previously unmerged entry left as an existence
         * marker by read_index_unmerged();
         */
        if (verify_absent_if_directory(merge,
                  ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o)) {
            discard_cache_entry(merge);
            return -1;
        }

        invalidate_ce_path(old, o);
    }

    if (do_add_entry(o, merge, update, CE_STAGEMASK) < 0)
        return -1;
    return 1;
}

static int merged_sparse_dir(const struct cache_entry * const *src, int n,
                 struct unpack_trees_options *o)
{
    struct tree_desc t[MAX_UNPACK_TREES + 1];
    void * tree_bufs[MAX_UNPACK_TREES + 1];
    struct traverse_info info;
    int i, ret;

    /*
     * Create the tree traversal information for traversing into *only* the
     * sparse directory.
     */
    setup_traverse_info(&info, src[0]->name);
    info.fn = unpack_sparse_callback;
    info.data = o;
    info.show_all_errors = o->internal.show_all_errors;
    info.pathspec = o->pathspec;

    /* Get the tree descriptors of the sparse directory in each of the merging trees */
    for (i = 0; i < n; i++)
        tree_bufs[i] = fill_tree_descriptor(o->src_index->repo, &t[i],
                            src[i] && !is_null_oid(&src[i]->oid) ? &src[i]->oid : NULL);

    ret = traverse_trees(o->src_index, n, t, &info);

    for (i = 0; i < n; i++)
        free(tree_bufs[i]);

    return ret;
}

static int deleted_entry(const struct cache_entry *ce,
             const struct cache_entry *old,
             struct unpack_trees_options *o)
{
    /* Did it exist in the index? */
    if (!old) {
        if (verify_absent(ce, ERROR_WOULD_LOSE_UNTRACKED_REMOVED, o))
            return -1;
        return 0;
    } else if (verify_absent_if_directory(ce, ERROR_WOULD_LOSE_UNTRACKED_REMOVED, o)) {
        return -1;
    }

    if (!(old->ce_flags & CE_CONFLICTED) && verify_uptodate(old, o))
        return -1;
    add_entry(o, ce, CE_REMOVE, 0);
    invalidate_ce_path(ce, o);
    return 1;
}

static int keep_entry(const struct cache_entry *ce,
              struct unpack_trees_options *o)
{
    add_entry(o, ce, 0, 0);
    if (ce_stage(ce))
        invalidate_ce_path(ce, o);
    return 1;
}

#if DBRT_DEBUG
static void show_stage_entry(FILE *o,
                 const char *label, const struct cache_entry *ce)
{
    if (!ce)
        fprintf(o, "%s (missing)\n", label);
    else
        fprintf(o, "%s%06o %s %d\t%s\n",
            label,
            ce->ce_mode,
            oid_to_hex(&ce->oid),
            ce_stage(ce),
            ce->name);
}
#endif

int threeway_merge(const struct cache_entry * const *stages,
           struct unpack_trees_options *o)
{
    const struct cache_entry *index;
    const struct cache_entry *head;
    const struct cache_entry *remote = stages[o->head_idx + 1];
    int count;
    int head_match = 0;
    int remote_match = 0;

    int df_conflict_head = 0;
    int df_conflict_remote = 0;

    int any_anc_missing = 0;
    int no_anc_exists = 1;
    int i;

    for (i = 1; i < o->head_idx; i++) {
        if (!stages[i] || stages[i] == o->df_conflict_entry)
            any_anc_missing = 1;
        else
            no_anc_exists = 0;
    }

    index = stages[0];
    head = stages[o->head_idx];

    if (head == o->df_conflict_entry) {
        df_conflict_head = 1;
        head = NULL;
    }

    if (remote == o->df_conflict_entry) {
        df_conflict_remote = 1;
        remote = NULL;
    }

    /*
     * First, if there's a #16 situation, note that to prevent #13
     * and #14.
     */
    if (!same(remote, head)) {
        for (i = 1; i < o->head_idx; i++) {
            if (same(stages[i], head)) {
                head_match = i;
            }
            if (same(stages[i], remote)) {
                remote_match = i;
            }
        }
    }

    /*
     * We start with cases where the index is allowed to match
     * something other than the head: #14(ALT) and #2ALT, where it
     * is permitted to match the result instead.
     */
    /* #14, #14ALT, #2ALT */
    if (remote && !df_conflict_head && head_match && !remote_match) {
        if (index && !same(index, remote) && !same(index, head)) {
            if (S_ISSPARSEDIR(index->ce_mode))
                return merged_sparse_dir(stages, 4, o);
            else
                return reject_merge(index, o);
        }
        return merged_entry(remote, index, o);
    }
    /*
     * If we have an entry in the index cache, then we want to
     * make sure that it matches head.
     */
    if (index && !same(index, head)) {
        if (S_ISSPARSEDIR(index->ce_mode))
            return merged_sparse_dir(stages, 4, o);
        else
            return reject_merge(index, o);
    }

    if (head) {
        /* #5ALT, #15 */
        if (same(head, remote))
            return merged_entry(head, index, o);
        /* #13, #3ALT */
        if (!df_conflict_remote && remote_match && !head_match)
            return merged_entry(head, index, o);
    }

    /* #1 */
    if (!head && !remote && any_anc_missing)
        return 0;

    /*
     * Under the "aggressive" rule, we resolve mostly trivial
     * cases that we historically had git-merge-one-file resolve.
     */
    if (o->aggressive) {
        int head_deleted = !head;
        int remote_deleted = !remote;
        const struct cache_entry *ce = NULL;

        if (index)
            ce = index;
        else if (head)
            ce = head;
        else if (remote)
            ce = remote;
        else {
            for (i = 1; i < o->head_idx; i++) {
                if (stages[i] && stages[i] != o->df_conflict_entry) {
                    ce = stages[i];
                    break;
                }
            }
        }

        /*
         * Deleted in both.
         * Deleted in one and unchanged in the other.
         */
        if ((head_deleted && remote_deleted) ||
            (head_deleted && remote && remote_match) ||
            (remote_deleted && head && head_match)) {
            if (index)
                return deleted_entry(index, index, o);
            if (ce && !head_deleted) {
                if (verify_absent(ce, ERROR_WOULD_LOSE_UNTRACKED_REMOVED, o))
                    return -1;
            }
            return 0;
        }
        /*
         * Added in both, identically.
         */
        if (no_anc_exists && head && remote && same(head, remote))
            return merged_entry(head, index, o);

    }

    /* Handle "no merge" cases (see t/t1000-read-tree-m-3way.sh) */
    if (index) {
        /*
         * If we've reached the "no merge" cases and we're merging
         * a sparse directory, we may have an "edit/edit" conflict that
         * can be resolved by individually merging directory contents.
         */
        if (S_ISSPARSEDIR(index->ce_mode))
            return merged_sparse_dir(stages, 4, o);

        /*
         * If we're not merging a sparse directory, ensure the index is
         * up-to-date to avoid files getting overwritten with conflict
         * resolution files
         */
        if (verify_uptodate(index, o))
            return -1;
    }

    o->internal.nontrivial_merge = 1;

    /* #2, #3, #4, #6, #7, #9, #10, #11. */
    count = 0;
    if (!head_match || !remote_match) {
        for (i = 1; i < o->head_idx; i++) {
            if (stages[i] && stages[i] != o->df_conflict_entry) {
                keep_entry(stages[i], o);
                count++;
                break;
            }
        }
    }
#if DBRT_DEBUG
    else {
        fprintf(stderr, "read-tree: warning #16 detected\n");
        show_stage_entry(stderr, "head   ", stages[head_match]);
        show_stage_entry(stderr, "remote ", stages[remote_match]);
    }
#endif
    if (head) { count += keep_entry(head, o); }
    if (remote) { count += keep_entry(remote, o); }
    return count;
}

/*
 * Two-way merge.
 *
 * The rule is to "carry forward" what is in the index without losing
 * information across a "fast-forward", favoring a successful merge
 * over a merge failure when it makes sense.  For details of the
 * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 *
 */
int twoway_merge(const struct cache_entry * const *src,
         struct unpack_trees_options *o)
{
    const struct cache_entry *current = src[0];
    const struct cache_entry *oldtree = src[1];
    const struct cache_entry *newtree = src[2];

    if (o->internal.merge_size != 2)
        return error("Cannot do a twoway merge of %d trees",
                 o->internal.merge_size);

    if (oldtree == o->df_conflict_entry)
        oldtree = NULL;
    if (newtree == o->df_conflict_entry)
        newtree = NULL;

    if (current) {
        if (current->ce_flags & CE_CONFLICTED) {
            if (same(oldtree, newtree) || o->reset) {
                if (!newtree)
                    return deleted_entry(current, current, o);
                else
                    return merged_entry(newtree, current, o);
            }
            return reject_merge(current, o);
        } else if ((!oldtree && !newtree) || /* 4 and 5 */
             (!oldtree && newtree &&
              same(current, newtree)) || /* 6 and 7 */
             (oldtree && newtree &&
              same(oldtree, newtree)) || /* 14 and 15 */
             (oldtree && newtree &&
              !same(oldtree, newtree) && /* 18 and 19 */
              same(current, newtree))) {
            return keep_entry(current, o);
        } else if (oldtree && !newtree && same(current, oldtree)) {
            /* 10 or 11 */
            return deleted_entry(oldtree, current, o);
        } else if (oldtree && newtree &&
             same(current, oldtree) && !same(current, newtree)) {
            /* 20 or 21 */
            return merged_entry(newtree, current, o);
        } else if (current && !oldtree && newtree &&
               S_ISSPARSEDIR(current->ce_mode) != S_ISSPARSEDIR(newtree->ce_mode) &&
               ce_stage(current) == 0) {
            /*
             * This case is a directory/file conflict across the sparse-index
             * boundary. When we are changing from one path to another via
             * 'git checkout', then we want to replace one entry with another
             * via merged_entry(). If there are staged changes, then we should
             * reject the merge instead.
             */
            return merged_entry(newtree, current, o);
        } else if (S_ISSPARSEDIR(current->ce_mode)) {
            /*
             * The sparse directories differ, but we don't know whether that's
             * because of two different files in the directory being modified
             * (can be trivially merged) or if there is a real file conflict.
             * Merge the sparse directory by OID to compare file-by-file.
             */
            return merged_sparse_dir(src, 3, o);
        } else
            return reject_merge(current, o);
    }
    else if (newtree) {
        if (oldtree && !o->initial_checkout) {
            /*
             * deletion of the path was staged;
             */
            if (same(oldtree, newtree))
                return 1;
            return reject_merge(oldtree, o);
        }
        return merged_entry(newtree, current, o);
    }
    return deleted_entry(oldtree, current, o);
}

/*
 * Bind merge.
 *
 * Keep the index entries at stage0, collapse stage1 but make sure
 * stage0 does not have anything there.
 */
int bind_merge(const struct cache_entry * const *src,
           struct unpack_trees_options *o)
{
    const struct cache_entry *old = src[0];
    const struct cache_entry *a = src[1];

    if (o->internal.merge_size != 1)
        return error("Cannot do a bind merge of %d trees",
                 o->internal.merge_size);
    if (a && old)
        return o->quiet ? -1 :
            error(ERRORMSG(o, ERROR_BIND_OVERLAP),
                  super_prefixed(a->name, o->super_prefix),
                  super_prefixed(old->name, o->super_prefix));
    if (!a)
        return keep_entry(old, o);
    else
        return merged_entry(a, NULL, o);
}

/*
 * One-way merge.
 *
 * The rule is:
 * - take the stat information from stage0, take the data from stage1
 */
int oneway_merge(const struct cache_entry * const *src,
         struct unpack_trees_options *o)
{
    const struct cache_entry *old = src[0];
    const struct cache_entry *a = src[1];

    if (o->internal.merge_size != 1)
        return error("Cannot do a oneway merge of %d trees",
                 o->internal.merge_size);

    if (!a || a == o->df_conflict_entry)
        return deleted_entry(old, old, o);

    if (old && same(old, a)) {
        int update = 0;
        if (o->reset && o->update && !ce_uptodate(old) && !ce_skip_worktree(old) &&
            !(old->ce_flags & CE_FSMONITOR_VALID)) {
            struct stat st;
            if (lstat(old->name, &st) ||
                ie_match_stat(o->src_index, old, &st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE))
                update |= CE_UPDATE;
        }
        if (o->update && S_ISGITLINK(old->ce_mode) &&
            should_update_submodules() && !verify_uptodate(old, o))
            update |= CE_UPDATE;
        add_entry(o, old, update, CE_STAGEMASK);
        return 0;
    }
    return merged_entry(a, old, o);
}

/*
 * Merge worktree and untracked entries in a stash entry.
 *
 * Ignore all index entries. Collapse remaining trees but make sure that they
 * don't have any conflicting files.
 */
int stash_worktree_untracked_merge(const struct cache_entry * const *src,
                   struct unpack_trees_options *o)
{
    const struct cache_entry *worktree = src[1];
    const struct cache_entry *untracked = src[2];

    if (o->internal.merge_size != 2)
        BUG("invalid merge_size: %d", o->internal.merge_size);

    if (worktree && untracked)
        return error(_("worktree and untracked commit have duplicate entries: %s"),
                 super_prefixed(worktree->name, o->super_prefix));

    return merged_entry(worktree ? worktree : untracked, NULL, o);
}