#include "cache.h"
#include "tag.h"
#include "blob.h"
#include "tree.h"
#include "commit.h"
#include "diff.h"
#include "refs.h"
#include "revision.h"
#include "graph.h"
#include "grep.h"
#include "reflog-walk.h"
#include "patch-ids.h"
#include "decorate.h"
#include "log-tree.h"

volatile show_early_output_fn_t show_early_output;

char *path_name(const struct name_path *path, const char *name)
{
        const struct name_path *p;
        char *n, *m;
        int nlen = strlen(name);
        int len = nlen + 1;

        for (p = path; p; p = p->up) {
                if (p->elem_len)
                        len += p->elem_len + 1;
        }
        n = xmalloc(len);
        m = n + len - (nlen + 1);
        strcpy(m, name);
        for (p = path; p; p = p->up) {
                if (p->elem_len) {
                        m -= p->elem_len + 1;
                        memcpy(m, p->elem, p->elem_len);
                        m[p->elem_len] = '/';
                }
        }
        return n;
}

void add_object(struct object *obj,
                struct object_array *p,
                struct name_path *path,
                const char *name)
{
        add_object_array(obj, path_name(path, name), p);
}

static void mark_blob_uninteresting(struct blob *blob)
{
        if (!blob)
                return;
        if (blob->object.flags & UNINTERESTING)
                return;
        blob->object.flags |= UNINTERESTING;
}

void mark_tree_uninteresting(struct tree *tree)
{
        struct tree_desc desc;
        struct name_entry entry;
        struct object *obj = &tree->object;

        if (!tree)
                return;
        if (obj->flags & UNINTERESTING)
                return;
        obj->flags |= UNINTERESTING;
        if (!has_sha1_file(obj->sha1))
                return;
        if (parse_tree(tree) < 0)
                die("bad tree %s", sha1_to_hex(obj->sha1));

        init_tree_desc(&desc, tree->buffer, tree->size);
        while (tree_entry(&desc, &entry)) {
                switch (object_type(entry.mode)) {
                case OBJ_TREE:
                        mark_tree_uninteresting(lookup_tree(entry.sha1));
                        break;
                case OBJ_BLOB:
                        mark_blob_uninteresting(lookup_blob(entry.sha1));
                        break;
                default:
                        /* Subproject commit - not in this repository */
                        break;
                }
        }

        /*
         * We don't care about the tree any more
         * after it has been marked uninteresting.
         */
        free(tree->buffer);
        tree->buffer = NULL;
}

void mark_parents_uninteresting(struct commit *commit)
{
        struct commit_list *parents = commit->parents;

        while (parents) {
                struct commit *commit = parents->item;
                if (!(commit->object.flags & UNINTERESTING)) {
                        commit->object.flags |= UNINTERESTING;

                        /*
                         * Normally we haven't parsed the parent
                         * yet, so we won't have a parent of a parent
                         * here. However, it may turn out that we've
                         * reached this commit some other way (where it
                         * wasn't uninteresting), in which case we need
                         * to mark its parents recursively too..
                         */
                        if (commit->parents)
                                mark_parents_uninteresting(commit);
                }

                /*
                 * A missing commit is ok iff its parent is marked
                 * uninteresting.
                 *
                 * We just mark such a thing parsed, so that when
                 * it is popped next time around, we won't be trying
                 * to parse it and get an error.
                 */
                if (!has_sha1_file(commit->object.sha1))
                        commit->object.parsed = 1;
                parents = parents->next;
        }
}

static void add_pending_object_with_mode(struct rev_info *revs, struct object *obj, const char *name, unsigned mode)
{
        if (revs->no_walk && (obj->flags & UNINTERESTING))
                revs->no_walk = 0;
        if (revs->reflog_info && obj->type == OBJ_COMMIT &&
                        add_reflog_for_walk(revs->reflog_info,
                                (struct commit *)obj, name))
                return;
        add_object_array_with_mode(obj, name, &revs->pending, mode);
}

void add_pending_object(struct rev_info *revs, struct object *obj, const char *name)
{
        add_pending_object_with_mode(revs, obj, name, S_IFINVALID);
}

void add_head_to_pending(struct rev_info *revs)
{
        unsigned char sha1[20];
        struct object *obj;
        if (get_sha1("HEAD", sha1))
                return;
        obj = parse_object(sha1);
        if (!obj)
                return;
        add_pending_object(revs, obj, "HEAD");
}

static struct object *get_reference(struct rev_info *revs, const char *name, const unsigned char *sha1, unsigned int flags)
{
        struct object *object;

        object = parse_object(sha1);
        if (!object)
                die("bad object %s", name);
        object->flags |= flags;
        return object;
}

static struct commit *handle_commit(struct rev_info *revs, struct object *object, const char *name)
{
        unsigned long flags = object->flags;

        /*
         * Tag object? Look what it points to..
         */
        while (object->type == OBJ_TAG) {
                struct tag *tag = (struct tag *) object;
                if (revs->tag_objects && !(flags & UNINTERESTING))
                        add_pending_object(revs, object, tag->tag);
                if (!tag->tagged)
                        die("bad tag");
                object = parse_object(tag->tagged->sha1);
                if (!object) {
                        if (flags & UNINTERESTING)
                                return NULL;
                        die("bad object %s", sha1_to_hex(tag->tagged->sha1));
                }
        }

        /*
         * Commit object? Just return it, we'll do all the complex
         * reachability crud.
         */
        if (object->type == OBJ_COMMIT) {
                struct commit *commit = (struct commit *)object;
                if (parse_commit(commit) < 0)
                        die("unable to parse commit %s", name);
                if (flags & UNINTERESTING) {
                        commit->object.flags |= UNINTERESTING;
                        mark_parents_uninteresting(commit);
                        revs->limited = 1;
                }
                if (revs->show_source && !commit->util)
                        commit->util = (void *) name;
                return commit;
        }

        /*
         * Tree object? Either mark it uninteresting, or add it
         * to the list of objects to look at later..
         */
        if (object->type == OBJ_TREE) {
                struct tree *tree = (struct tree *)object;
                if (!revs->tree_objects)
                        return NULL;
                if (flags & UNINTERESTING) {
                        mark_tree_uninteresting(tree);
                        return NULL;
                }
                add_pending_object(revs, object, "");
                return NULL;
        }

        /*
         * Blob object? You know the drill by now..
         */
        if (object->type == OBJ_BLOB) {
                struct blob *blob = (struct blob *)object;
                if (!revs->blob_objects)
                        return NULL;
                if (flags & UNINTERESTING) {
                        mark_blob_uninteresting(blob);
                        return NULL;
                }
                add_pending_object(revs, object, "");
                return NULL;
        }
        die("%s is unknown object", name);
}

static int everybody_uninteresting(struct commit_list *orig)
{
        struct commit_list *list = orig;
        while (list) {
                struct commit *commit = list->item;
                list = list->next;
                if (commit->object.flags & UNINTERESTING)
                        continue;
                return 0;
        }
        return 1;
}

/*
 * The goal is to get REV_TREE_NEW as the result only if the
 * diff consists of all '+' (and no other changes), REV_TREE_OLD
 * if the whole diff is removal of old data, and otherwise
 * REV_TREE_DIFFERENT (of course if the trees are the same we
 * want REV_TREE_SAME).
 * That means that once we get to REV_TREE_DIFFERENT, we do not
 * have to look any further.
 */
static int tree_difference = REV_TREE_SAME;

static void file_add_remove(struct diff_options *options,
                    int addremove, unsigned mode,
                    const unsigned char *sha1,
                    const char *fullpath, unsigned dirty_submodule)
{
        int diff = addremove == '+' ? REV_TREE_NEW : REV_TREE_OLD;

        tree_difference |= diff;
        if (tree_difference == REV_TREE_DIFFERENT)
                DIFF_OPT_SET(options, HAS_CHANGES);
}

static void file_change(struct diff_options *options,
                 unsigned old_mode, unsigned new_mode,
                 const unsigned char *old_sha1,
                 const unsigned char *new_sha1,
                 const char *fullpath,
                 unsigned old_dirty_submodule, unsigned new_dirty_submodule)
{
        tree_difference = REV_TREE_DIFFERENT;
        DIFF_OPT_SET(options, HAS_CHANGES);
}

static int rev_compare_tree(struct rev_info *revs, struct commit *parent, struct commit *commit)
{
        struct tree *t1 = parent->tree;
        struct tree *t2 = commit->tree;

        if (!t1)
                return REV_TREE_NEW;
        if (!t2)
                return REV_TREE_OLD;

        if (revs->simplify_by_decoration) {
                /*
                 * If we are simplifying by decoration, then the commit
                 * is worth showing if it has a tag pointing at it.
                 */
                if (lookup_decoration(&name_decoration, &commit->object))
                        return REV_TREE_DIFFERENT;
                /*
                 * A commit that is not pointed by a tag is uninteresting
                 * if we are not limited by path.  This means that you will
                 * see the usual "commits that touch the paths" plus any
                 * tagged commit by specifying both --simplify-by-decoration
                 * and pathspec.
                 */
                if (!revs->prune_data)
                        return REV_TREE_SAME;
        }

        tree_difference = REV_TREE_SAME;
        DIFF_OPT_CLR(&revs->pruning, HAS_CHANGES);
        if (diff_tree_sha1(t1->object.sha1, t2->object.sha1, "",
                           &revs->pruning) < 0)
                return REV_TREE_DIFFERENT;
        return tree_difference;
}

static int rev_same_tree_as_empty(struct rev_info *revs, struct commit *commit)
{
        int retval;
        void *tree;
        unsigned long size;
        struct tree_desc empty, real;
        struct tree *t1 = commit->tree;

        if (!t1)
                return 0;

        tree = read_object_with_reference(t1->object.sha1, tree_type, &size, NULL);
        if (!tree)
                return 0;
        init_tree_desc(&real, tree, size);
        init_tree_desc(&empty, "", 0);

        tree_difference = REV_TREE_SAME;
        DIFF_OPT_CLR(&revs->pruning, HAS_CHANGES);
        retval = diff_tree(&empty, &real, "", &revs->pruning);
        free(tree);

        return retval >= 0 && (tree_difference == REV_TREE_SAME);
}

static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
{
        struct commit_list **pp, *parent;
        int tree_changed = 0, tree_same = 0;

        /*
         * If we don't do pruning, everything is interesting
         */
        if (!revs->prune)
                return;

        if (!commit->tree)
                return;

        if (!commit->parents) {
                if (rev_same_tree_as_empty(revs, commit))
                        commit->object.flags |= TREESAME;
                return;
        }

        /*
         * Normal non-merge commit? If we don't want to make the
         * history dense, we consider it always to be a change..
         */
        if (!revs->dense && !commit->parents->next)
                return;

        pp = &commit->parents;
        while ((parent = *pp) != NULL) {
                struct commit *p = parent->item;

                if (parse_commit(p) < 0)
                        die("cannot simplify commit %s (because of %s)",
                            sha1_to_hex(commit->object.sha1),
                            sha1_to_hex(p->object.sha1));
                switch (rev_compare_tree(revs, p, commit)) {
                case REV_TREE_SAME:
                        tree_same = 1;
                        if (!revs->simplify_history || (p->object.flags & UNINTERESTING)) {
                                /* Even if a merge with an uninteresting
                                 * side branch brought the entire change
                                 * we are interested in, we do not want
                                 * to lose the other branches of this
                                 * merge, so we just keep going.
                                 */
                                pp = &parent->next;
                                continue;
                        }
                        parent->next = NULL;
                        commit->parents = parent;
                        commit->object.flags |= TREESAME;
                        return;

                case REV_TREE_NEW:
                        if (revs->remove_empty_trees &&
                            rev_same_tree_as_empty(revs, p)) {
                                /* We are adding all the specified
                                 * paths from this parent, so the
                                 * history beyond this parent is not
                                 * interesting.  Remove its parents
                                 * (they are grandparents for us).
                                 * IOW, we pretend this parent is a
                                 * "root" commit.
                                 */
                                if (parse_commit(p) < 0)
                                        die("cannot simplify commit %s (invalid %s)",
                                            sha1_to_hex(commit->object.sha1),
                                            sha1_to_hex(p->object.sha1));
                                p->parents = NULL;
                        }
                /* fallthrough */
                case REV_TREE_OLD:
                case REV_TREE_DIFFERENT:
                        tree_changed = 1;
                        pp = &parent->next;
                        continue;
                }
                die("bad tree compare for commit %s", sha1_to_hex(commit->object.sha1));
        }
        if (tree_changed && !tree_same)
                return;
        commit->object.flags |= TREESAME;
}

static void insert_by_date_cached(struct commit *p, struct commit_list **head,
                    struct commit_list *cached_base, struct commit_list **cache)
{
        struct commit_list *new_entry;

        if (cached_base && p->date < cached_base->item->date)
                new_entry = insert_by_date(p, &cached_base->next);
        else
                new_entry = insert_by_date(p, head);

        if (cache && (!*cache || p->date < (*cache)->item->date))
                *cache = new_entry;
}

static int add_parents_to_list(struct rev_info *revs, struct commit *commit,
                    struct commit_list **list, struct commit_list **cache_ptr)
{
        struct commit_list *parent = commit->parents;
        unsigned left_flag;
        struct commit_list *cached_base = cache_ptr ? *cache_ptr : NULL;

        if (commit->object.flags & ADDED)
                return 0;
        commit->object.flags |= ADDED;

        /*
         * If the commit is uninteresting, don't try to
         * prune parents - we want the maximal uninteresting
         * set.
         *
         * Normally we haven't parsed the parent
         * yet, so we won't have a parent of a parent
         * here. However, it may turn out that we've
         * reached this commit some other way (where it
         * wasn't uninteresting), in which case we need
         * to mark its parents recursively too..
         */
        if (commit->object.flags & UNINTERESTING) {
                while (parent) {
                        struct commit *p = parent->item;
                        parent = parent->next;
                        if (p)
                                p->object.flags |= UNINTERESTING;
                        if (parse_commit(p) < 0)
                                continue;
                        if (p->parents)
                                mark_parents_uninteresting(p);
                        if (p->object.flags & SEEN)
                                continue;
                        p->object.flags |= SEEN;
                        insert_by_date_cached(p, list, cached_base, cache_ptr);
                }
                return 0;
        }

        /*
         * Ok, the commit wasn't uninteresting. Try to
         * simplify the commit history and find the parent
         * that has no differences in the path set if one exists.
         */
        try_to_simplify_commit(revs, commit);

        if (revs->no_walk)
                return 0;

        left_flag = (commit->object.flags & SYMMETRIC_LEFT);

        for (parent = commit->parents; parent; parent = parent->next) {
                struct commit *p = parent->item;

                if (parse_commit(p) < 0)
                        return -1;
                if (revs->show_source && !p->util)
                        p->util = commit->util;
                p->object.flags |= left_flag;
                if (!(p->object.flags & SEEN)) {
                        p->object.flags |= SEEN;
                        insert_by_date_cached(p, list, cached_base, cache_ptr);
                }
                if (revs->first_parent_only)
                        break;
        }
        return 0;
}

static void cherry_pick_list(struct commit_list *list, struct rev_info *revs)
{
        struct commit_list *p;
        int left_count = 0, right_count = 0;
        int left_first;
        struct patch_ids ids;

        /* First count the commits on the left and on the right */
        for (p = list; p; p = p->next) {
                struct commit *commit = p->item;
                unsigned flags = commit->object.flags;
                if (flags & BOUNDARY)
                        ;
                else if (flags & SYMMETRIC_LEFT)
                        left_count++;
                else
                        right_count++;
        }

        left_first = left_count < right_count;
        init_patch_ids(&ids);
        if (revs->diffopt.nr_paths) {
                ids.diffopts.nr_paths = revs->diffopt.nr_paths;
                ids.diffopts.paths = revs->diffopt.paths;
                ids.diffopts.pathlens = revs->diffopt.pathlens;
        }

        /* Compute patch-ids for one side */
        for (p = list; p; p = p->next) {
                struct commit *commit = p->item;
                unsigned flags = commit->object.flags;

                if (flags & BOUNDARY)
                        continue;
                /*
                 * If we have fewer left, left_first is set and we omit
                 * commits on the right branch in this loop.  If we have
                 * fewer right, we skip the left ones.
                 */
                if (left_first != !!(flags & SYMMETRIC_LEFT))
                        continue;
                commit->util = add_commit_patch_id(commit, &ids);
        }

        /* Check the other side */
        for (p = list; p; p = p->next) {
                struct commit *commit = p->item;
                struct patch_id *id;
                unsigned flags = commit->object.flags;

                if (flags & BOUNDARY)
                        continue;
                /*
                 * If we have fewer left, left_first is set and we omit
                 * commits on the left branch in this loop.
                 */
                if (left_first == !!(flags & SYMMETRIC_LEFT))
                        continue;

                /*
                 * Have we seen the same patch id?
                 */
                id = has_commit_patch_id(commit, &ids);
                if (!id)
                        continue;
                id->seen = 1;
                commit->object.flags |= SHOWN;
        }

        /* Now check the original side for seen ones */
        for (p = list; p; p = p->next) {
                struct commit *commit = p->item;
                struct patch_id *ent;

                ent = commit->util;
                if (!ent)
                        continue;
                if (ent->seen)
                        commit->object.flags |= SHOWN;
                commit->util = NULL;
        }

        free_patch_ids(&ids);
}

/* How many extra uninteresting commits we want to see.. */
#define SLOP 5

static int still_interesting(struct commit_list *src, unsigned long date, int slop)
{
        /*
         * No source list at all? We're definitely done..
         */
        if (!src)
                return 0;

        /*
         * Does the destination list contain entries with a date
         * before the source list? Definitely _not_ done.
         */
        if (date < src->item->date)
                return SLOP;

        /*
         * Does the source list still have interesting commits in
         * it? Definitely not done..
         */
        if (!everybody_uninteresting(src))
                return SLOP;

        /* Ok, we're closing in.. */
        return slop-1;
}

static int limit_list(struct rev_info *revs)
{
        int slop = SLOP;
        unsigned long date = ~0ul;
        struct commit_list *list = revs->commits;
        struct commit_list *newlist = NULL;
        struct commit_list **p = &newlist;

        while (list) {
                struct commit_list *entry = list;
                struct commit *commit = list->item;
                struct object *obj = &commit->object;
                show_early_output_fn_t show;

                list = list->next;
                free(entry);

                if (revs->max_age != -1 && (commit->date < revs->max_age))
                        obj->flags |= UNINTERESTING;
                if (add_parents_to_list(revs, commit, &list, NULL) < 0)
                        return -1;
                if (obj->flags & UNINTERESTING) {
                        mark_parents_uninteresting(commit);
                        if (revs->show_all)
                                p = &commit_list_insert(commit, p)->next;
                        slop = still_interesting(list, date, slop);
                        if (slop)
                                continue;
                        /* If showing all, add the whole pending list to the end */
                        if (revs->show_all)
                                *p = list;
                        break;
                }
                if (revs->min_age != -1 && (commit->date > revs->min_age))
                        continue;
                date = commit->date;
                p = &commit_list_insert(commit, p)->next;

                show = show_early_output;
                if (!show)
                        continue;

                show(revs, newlist);
                show_early_output = NULL;
        }
        if (revs->cherry_pick)
                cherry_pick_list(newlist, revs);

        revs->commits = newlist;
        return 0;
}

struct all_refs_cb {
        int all_flags;
        int warned_bad_reflog;
        struct rev_info *all_revs;
        const char *name_for_errormsg;
};

static int handle_one_ref(const char *path, const unsigned char *sha1, int flag, void *cb_data)
{
        struct all_refs_cb *cb = cb_data;
        struct object *object = get_reference(cb->all_revs, path, sha1,
                                              cb->all_flags);
        add_pending_object(cb->all_revs, object, path);
        return 0;
}

static void handle_refs(struct rev_info *revs, unsigned flags,
                int (*for_each)(each_ref_fn, void *))
{
        struct all_refs_cb cb;
        cb.all_revs = revs;
        cb.all_flags = flags;
        for_each(handle_one_ref, &cb);
}

static void handle_one_reflog_commit(unsigned char *sha1, void *cb_data)
{
        struct all_refs_cb *cb = cb_data;
        if (!is_null_sha1(sha1)) {
                struct object *o = parse_object(sha1);
                if (o) {
                        o->flags |= cb->all_flags;
                        add_pending_object(cb->all_revs, o, "");
                }
                else if (!cb->warned_bad_reflog) {
                        warning("reflog of '%s' references pruned commits",
                                cb->name_for_errormsg);
                        cb->warned_bad_reflog = 1;
                }
        }
}

static int handle_one_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
                const char *email, unsigned long timestamp, int tz,
                const char *message, void *cb_data)
{
        handle_one_reflog_commit(osha1, cb_data);
        handle_one_reflog_commit(nsha1, cb_data);
        return 0;
}

static int handle_one_reflog(const char *path, const unsigned char *sha1, int flag, void *cb_data)
{
        struct all_refs_cb *cb = cb_data;
        cb->warned_bad_reflog = 0;
        cb->name_for_errormsg = path;
        for_each_reflog_ent(path, handle_one_reflog_ent, cb_data);
        return 0;
}

static void handle_reflog(struct rev_info *revs, unsigned flags)
{
        struct all_refs_cb cb;
        cb.all_revs = revs;
        cb.all_flags = flags;
        for_each_reflog(handle_one_reflog, &cb);
}

static int add_parents_only(struct rev_info *revs, const char *arg, int flags)
{
        unsigned char sha1[20];
        struct object *it;
        struct commit *commit;
        struct commit_list *parents;

        if (*arg == '^') {
                flags ^= UNINTERESTING;
                arg++;
        }
        if (get_sha1(arg, sha1))
                return 0;
        while (1) {
                it = get_reference(revs, arg, sha1, 0);
                if (it->type != OBJ_TAG)
                        break;
                if (!((struct tag*)it)->tagged)
                        return 0;
                hashcpy(sha1, ((struct tag*)it)->tagged->sha1);
        }
        if (it->type != OBJ_COMMIT)
                return 0;
        commit = (struct commit *)it;
        for (parents = commit->parents; parents; parents = parents->next) {
                it = &parents->item->object;
                it->flags |= flags;
                add_pending_object(revs, it, arg);
        }
        return 1;
}

void init_revisions(struct rev_info *revs, const char *prefix)
{
        memset(revs, 0, sizeof(*revs));

        revs->abbrev = DEFAULT_ABBREV;
        revs->ignore_merges = 1;
        revs->simplify_history = 1;
        DIFF_OPT_SET(&revs->pruning, RECURSIVE);
        DIFF_OPT_SET(&revs->pruning, QUICK);
        revs->pruning.add_remove = file_add_remove;
        revs->pruning.change = file_change;
        revs->lifo = 1;
        revs->dense = 1;
        revs->prefix = prefix;
        revs->max_age = -1;
        revs->min_age = -1;
        revs->skip_count = -1;
        revs->max_count = -1;

        revs->commit_format = CMIT_FMT_DEFAULT;

        revs->grep_filter.status_only = 1;
        revs->grep_filter.pattern_tail = &(revs->grep_filter.pattern_list);
        revs->grep_filter.regflags = REG_NEWLINE;

        diff_setup(&revs->diffopt);
        if (prefix && !revs->diffopt.prefix) {
                revs->diffopt.prefix = prefix;
                revs->diffopt.prefix_length = strlen(prefix);
        }
}

static void add_pending_commit_list(struct rev_info *revs,
                                    struct commit_list *commit_list,
                                    unsigned int flags)
{
        while (commit_list) {
                struct object *object = &commit_list->item->object;
                object->flags |= flags;
                add_pending_object(revs, object, sha1_to_hex(object->sha1));
                commit_list = commit_list->next;
        }
}

static void prepare_show_merge(struct rev_info *revs)
{
        struct commit_list *bases;
        struct commit *head, *other;
        unsigned char sha1[20];
        const char **prune = NULL;
        int i, prune_num = 1; /* counting terminating NULL */

        if (get_sha1("HEAD", sha1) || !(head = lookup_commit(sha1)))
                die("--merge without HEAD?");
        if (get_sha1("MERGE_HEAD", sha1) || !(other = lookup_commit(sha1)))
                die("--merge without MERGE_HEAD?");
        add_pending_object(revs, &head->object, "HEAD");
        add_pending_object(revs, &other->object, "MERGE_HEAD");
        bases = get_merge_bases(head, other, 1);
        add_pending_commit_list(revs, bases, UNINTERESTING);
        free_commit_list(bases);
        head->object.flags |= SYMMETRIC_LEFT;

        if (!active_nr)
                read_cache();
        for (i = 0; i < active_nr; i++) {
                struct cache_entry *ce = active_cache[i];
                if (!ce_stage(ce))
                        continue;
                if (ce_path_match(ce, revs->prune_data)) {
                        prune_num++;
                        prune = xrealloc(prune, sizeof(*prune) * prune_num);
                        prune[prune_num-2] = ce->name;
                        prune[prune_num-1] = NULL;
                }
                while ((i+1 < active_nr) &&
                       ce_same_name(ce, active_cache[i+1]))
                        i++;
        }
        revs->prune_data = prune;
        revs->limited = 1;
}

int handle_revision_arg(const char *arg, struct rev_info *revs,
                        int flags,
                        int cant_be_filename)
{
        unsigned mode;
        char *dotdot;
        struct object *object;
        unsigned char sha1[20];
        int local_flags;

        dotdot = strstr(arg, "..");
        if (dotdot) {
                unsigned char from_sha1[20];
                const char *next = dotdot + 2;
                const char *this = arg;
                int symmetric = *next == '.';
                unsigned int flags_exclude = flags ^ UNINTERESTING;

                *dotdot = 0;
                next += symmetric;

                if (!*next)
                        next = "HEAD";
                if (dotdot == arg)
                        this = "HEAD";
                if (!get_sha1(this, from_sha1) &&
                    !get_sha1(next, sha1)) {
                        struct commit *a, *b;
                        struct commit_list *exclude;

                        a = lookup_commit_reference(from_sha1);
                        b = lookup_commit_reference(sha1);
                        if (!a || !b) {
                                die(symmetric ?
                                    "Invalid symmetric difference expression %s...%s" :
                                    "Invalid revision range %s..%s",
                                    arg, next);
                        }

                        if (!cant_be_filename) {
                                *dotdot = '.';
                                verify_non_filename(revs->prefix, arg);
                        }

                        if (symmetric) {
                                exclude = get_merge_bases(a, b, 1);
                                add_pending_commit_list(revs, exclude,
                                                        flags_exclude);
                                free_commit_list(exclude);
                                a->object.flags |= flags | SYMMETRIC_LEFT;
                        } else
                                a->object.flags |= flags_exclude;
                        b->object.flags |= flags;
                        add_pending_object(revs, &a->object, this);
                        add_pending_object(revs, &b->object, next);
                        return 0;
                }
                *dotdot = '.';
        }
        dotdot = strstr(arg, "^@");
        if (dotdot && !dotdot[2]) {
                *dotdot = 0;
                if (add_parents_only(revs, arg, flags))
                        return 0;
                *dotdot = '^';
        }
        dotdot = strstr(arg, "^!");
        if (dotdot && !dotdot[2]) {
                *dotdot = 0;
                if (!add_parents_only(revs, arg, flags ^ UNINTERESTING))
                        *dotdot = '^';
        }

        local_flags = 0;
        if (*arg == '^') {
                local_flags = UNINTERESTING;
                arg++;
        }
        if (get_sha1_with_mode(arg, sha1, &mode))
                return -1;
        if (!cant_be_filename)
                verify_non_filename(revs->prefix, arg);
        object = get_reference(revs, arg, sha1, flags ^ local_flags);
        add_pending_object_with_mode(revs, object, arg, mode);
        return 0;
}

static void read_pathspec_from_stdin(struct rev_info *revs, struct strbuf *sb, const char ***prune_data)
{
        const char **prune = *prune_data;
        int prune_nr;
        int prune_alloc;

        /* count existing ones */
        if (!prune)
                prune_nr = 0;
        else
                for (prune_nr = 0; prune[prune_nr]; prune_nr++)
                        ;
        prune_alloc = prune_nr; /* not really, but we do not know */

        while (strbuf_getwholeline(sb, stdin, '\n') != EOF) {
                int len = sb->len;
                if (len && sb->buf[len - 1] == '\n')
                        sb->buf[--len] = '\0';
                ALLOC_GROW(prune, prune_nr+1, prune_alloc);
                prune[prune_nr++] = xstrdup(sb->buf);
        }
        if (prune) {
                ALLOC_GROW(prune, prune_nr+1, prune_alloc);
                prune[prune_nr] = NULL;
        }
        *prune_data = prune;
}

static void read_revisions_from_stdin(struct rev_info *revs, const char ***prune)
{
        struct strbuf sb;
        int seen_dashdash = 0;

        strbuf_init(&sb, 1000);
        while (strbuf_getwholeline(&sb, stdin, '\n') != EOF) {
                int len = sb.len;
                if (len && sb.buf[len - 1] == '\n')
                        sb.buf[--len] = '\0';
                if (!len)
                        break;
                if (sb.buf[0] == '-') {
                        if (len == 2 && sb.buf[1] == '-') {
                                seen_dashdash = 1;
                                break;
                        }
                        die("options not supported in --stdin mode");
                }
                if (handle_revision_arg(sb.buf, revs, 0, 1))
                        die("bad revision '%s'", sb.buf);
        }
        if (seen_dashdash)
                read_pathspec_from_stdin(revs, &sb, prune);
        strbuf_release(&sb);
}

static void add_grep(struct rev_info *revs, const char *ptn, enum grep_pat_token what)
{
        append_grep_pattern(&revs->grep_filter, ptn, "command line", 0, what);
}

static void add_header_grep(struct rev_info *revs, enum grep_header_field field, const char *pattern)
{
        append_header_grep_pattern(&revs->grep_filter, field, pattern);
}

static void add_message_grep(struct rev_info *revs, const char *pattern)
{
        add_grep(revs, pattern, GREP_PATTERN_BODY);
}

static int handle_revision_opt(struct rev_info *revs, int argc, const char **argv,
                               int *unkc, const char **unkv)
{
        const char *arg = argv[0];

        /* pseudo revision arguments */
        if (!strcmp(arg, "--all") || !strcmp(arg, "--branches") ||
            !strcmp(arg, "--tags") || !strcmp(arg, "--remotes") ||
            !strcmp(arg, "--reflog") || !strcmp(arg, "--not") ||
            !strcmp(arg, "--no-walk") || !strcmp(arg, "--do-walk") ||
            !strcmp(arg, "--bisect"))
        {
                unkv[(*unkc)++] = arg;
                return 1;
        }

        if (!prefixcmp(arg, "--max-count=")) {
                revs->max_count = atoi(arg + 12);
        } else if (!prefixcmp(arg, "--skip=")) {
                revs->skip_count = atoi(arg + 7);
        } else if ((*arg == '-') && isdigit(arg[1])) {
        /* accept -<digit>, like traditional "head" */
                revs->max_count = atoi(arg + 1);
        } else if (!strcmp(arg, "-n")) {
                if (argc <= 1)
                        return error("-n requires an argument");
                revs->max_count = atoi(argv[1]);
                return 2;
        } else if (!prefixcmp(arg, "-n")) {
                revs->max_count = atoi(arg + 2);
        } else if (!prefixcmp(arg, "--max-age=")) {
                revs->max_age = atoi(arg + 10);
        } else if (!prefixcmp(arg, "--since=")) {
                revs->max_age = approxidate(arg + 8);
        } else if (!prefixcmp(arg, "--after=")) {
                revs->max_age = approxidate(arg + 8);
        } else if (!prefixcmp(arg, "--min-age=")) {
                revs->min_age = atoi(arg + 10);
        } else if (!prefixcmp(arg, "--before=")) {
                revs->min_age = approxidate(arg + 9);
        } else if (!prefixcmp(arg, "--until=")) {
                revs->min_age = approxidate(arg + 8);
        } else if (!strcmp(arg, "--first-parent")) {
                revs->first_parent_only = 1;
        } else if (!strcmp(arg, "-g") || !strcmp(arg, "--walk-reflogs")) {
                init_reflog_walk(&revs->reflog_info);
        } else if (!strcmp(arg, "--default")) {
                if (argc <= 1)
                        return error("bad --default argument");
                revs->def = argv[1];
                return 2;
        } else if (!strcmp(arg, "--merge")) {
                revs->show_merge = 1;
        } else if (!strcmp(arg, "--topo-order")) {
                revs->lifo = 1;
                revs->topo_order = 1;
        } else if (!strcmp(arg, "--simplify-merges")) {
                revs->simplify_merges = 1;
                revs->rewrite_parents = 1;
                revs->simplify_history = 0;
                revs->limited = 1;
        } else if (!strcmp(arg, "--simplify-by-decoration")) {
                revs->simplify_merges = 1;
                revs->rewrite_parents = 1;
                revs->simplify_history = 0;
                revs->simplify_by_decoration = 1;
                revs->limited = 1;
                revs->prune = 1;
                load_ref_decorations(DECORATE_SHORT_REFS);
        } else if (!strcmp(arg, "--date-order")) {
                revs->lifo = 0;
                revs->topo_order = 1;
        } else if (!prefixcmp(arg, "--early-output")) {
                int count = 100;
                switch (arg[14]) {
                case '=':
                        count = atoi(arg+15);
                        /* Fallthrough */
                case 0:
                        revs->topo_order = 1;
                       revs->early_output = count;
                }
        } else if (!strcmp(arg, "--parents")) {
                revs->rewrite_parents = 1;
                revs->print_parents = 1;
        } else if (!strcmp(arg, "--dense")) {
                revs->dense = 1;
        } else if (!strcmp(arg, "--sparse")) {
                revs->dense = 0;
        } else if (!strcmp(arg, "--show-all")) {
                revs->show_all = 1;
        } else if (!strcmp(arg, "--remove-empty")) {
                revs->remove_empty_trees = 1;
        } else if (!strcmp(arg, "--merges")) {
                revs->merges_only = 1;
        } else if (!strcmp(arg, "--no-merges")) {
                revs->no_merges = 1;
        } else if (!strcmp(arg, "--boundary")) {
                revs->boundary = 1;
        } else if (!strcmp(arg, "--left-right")) {
                revs->left_right = 1;
        } else if (!strcmp(arg, "--cherry-pick")) {
                revs->cherry_pick = 1;
                revs->limited = 1;
        } else if (!strcmp(arg, "--objects")) {
                revs->tag_objects = 1;
                revs->tree_objects = 1;
                revs->blob_objects = 1;
        } else if (!strcmp(arg, "--objects-edge")) {
                revs->tag_objects = 1;
                revs->tree_objects = 1;
                revs->blob_objects = 1;
                revs->edge_hint = 1;
        } else if (!strcmp(arg, "--unpacked")) {
                revs->unpacked = 1;
        } else if (!prefixcmp(arg, "--unpacked=")) {
                die("--unpacked=<packfile> no longer supported.");
        } else if (!strcmp(arg, "-r")) {
                revs->diff = 1;
                DIFF_OPT_SET(&revs->diffopt, RECURSIVE);
        } else if (!strcmp(arg, "-t")) {
                revs->diff = 1;
                DIFF_OPT_SET(&revs->diffopt, RECURSIVE);
                DIFF_OPT_SET(&revs->diffopt, TREE_IN_RECURSIVE);
        } else if (!strcmp(arg, "-m")) {
                revs->ignore_merges = 0;
        } else if (!strcmp(arg, "-c")) {
                revs->diff = 1;
                revs->dense_combined_merges = 0;
                revs->combine_merges = 1;
        } else if (!strcmp(arg, "--cc")) {
                revs->diff = 1;
                revs->dense_combined_merges = 1;
                revs->combine_merges = 1;
        } else if (!strcmp(arg, "-v")) {
                revs->verbose_header = 1;
        } else if (!strcmp(arg, "--pretty")) {
                revs->verbose_header = 1;
                get_commit_format(arg+8, revs);
        } else if (!prefixcmp(arg, "--pretty=") || !prefixcmp(arg, "--format=")) {
                revs->verbose_header = 1;
                get_commit_format(arg+9, revs);
        } else if (!strcmp(arg, "--oneline")) {
                revs->verbose_header = 1;
                get_commit_format("oneline", revs);
                revs->abbrev_commit = 1;
        } else if (!strcmp(arg, "--graph")) {
                revs->topo_order = 1;
                revs->rewrite_parents = 1;
                revs->graph = graph_init(revs);
        } else if (!strcmp(arg, "--root")) {
                revs->show_root_diff = 1;
        } else if (!strcmp(arg, "--no-commit-id")) {
                revs->no_commit_id = 1;
        } else if (!strcmp(arg, "--always")) {
                revs->always_show_header = 1;
        } else if (!strcmp(arg, "--no-abbrev")) {
                revs->abbrev = 0;
        } else if (!strcmp(arg, "--abbrev")) {
                revs->abbrev = DEFAULT_ABBREV;
        } else if (!prefixcmp(arg, "--abbrev=")) {
                revs->abbrev = strtoul(arg + 9, NULL, 10);
                if (revs->abbrev < MINIMUM_ABBREV)
                        revs->abbrev = MINIMUM_ABBREV;
                else if (revs->abbrev > 40)
                        revs->abbrev = 40;
        } else if (!strcmp(arg, "--abbrev-commit")) {
                revs->abbrev_commit = 1;
        } else if (!strcmp(arg, "--full-diff")) {
                revs->diff = 1;
                revs->full_diff = 1;
        } else if (!strcmp(arg, "--full-history")) {
                revs->simplify_history = 0;
        } else if (!strcmp(arg, "--relative-date")) {
                revs->date_mode = DATE_RELATIVE;
                revs->date_mode_explicit = 1;
        } else if (!strncmp(arg, "--date=", 7)) {
                revs->date_mode = parse_date_format(arg + 7);
                revs->date_mode_explicit = 1;
        } else if (!strcmp(arg, "--log-size")) {
                revs->show_log_size = 1;
        }
        /*
         * Grepping the commit log
         */
        else if (!prefixcmp(arg, "--author=")) {
                add_header_grep(revs, GREP_HEADER_AUTHOR, arg+9);
        } else if (!prefixcmp(arg, "--committer=")) {
                add_header_grep(revs, GREP_HEADER_COMMITTER, arg+12);
        } else if (!prefixcmp(arg, "--grep=")) {
                add_message_grep(revs, arg+7);
        } else if (!strcmp(arg, "--extended-regexp") || !strcmp(arg, "-E")) {
                revs->grep_filter.regflags |= REG_EXTENDED;
        } else if (!strcmp(arg, "--regexp-ignore-case") || !strcmp(arg, "-i")) {
                revs->grep_filter.regflags |= REG_ICASE;
        } else if (!strcmp(arg, "--fixed-strings") || !strcmp(arg, "-F")) {
                revs->grep_filter.fixed = 1;
        } else if (!strcmp(arg, "--all-match")) {
                revs->grep_filter.all_match = 1;
        } else if (!prefixcmp(arg, "--encoding=")) {
                arg += 11;
                if (strcmp(arg, "none"))
                        git_log_output_encoding = xstrdup(arg);
                else
                        git_log_output_encoding = "";
        } else if (!strcmp(arg, "--reverse")) {
                revs->reverse ^= 1;
        } else if (!strcmp(arg, "--children")) {
                revs->children.name = "children";
                revs->limited = 1;
        } else {
                int opts = diff_opt_parse(&revs->diffopt, argv, argc);
                if (!opts)
                        unkv[(*unkc)++] = arg;
                return opts;
        }

        return 1;
}

void parse_revision_opt(struct rev_info *revs, struct parse_opt_ctx_t *ctx,
                        const struct option *options,
                        const char * const usagestr[])
{
        int n = handle_revision_opt(revs, ctx->argc, ctx->argv,
                                    &ctx->cpidx, ctx->out);
        if (n <= 0) {
                error("unknown option `%s'", ctx->argv[0]);
                usage_with_options(usagestr, options);
        }
        ctx->argv += n;
        ctx->argc -= n;
}

static int for_each_bad_bisect_ref(each_ref_fn fn, void *cb_data)
{
        return for_each_ref_in("refs/bisect/bad", fn, cb_data);
}

static int for_each_good_bisect_ref(each_ref_fn fn, void *cb_data)
{
        return for_each_ref_in("refs/bisect/good", fn, cb_data);
}

static void append_prune_data(const char ***prune_data, const char **av)
{
        const char **prune = *prune_data;
        int prune_nr;
        int prune_alloc;

        if (!prune) {
                *prune_data = av;
                return;
        }

        /* count existing ones */
        for (prune_nr = 0; prune[prune_nr]; prune_nr++)
                ;
        prune_alloc = prune_nr; /* not really, but we do not know */

        while (*av) {
                ALLOC_GROW(prune, prune_nr+1, prune_alloc);
                prune[prune_nr++] = *av;
                av++;
        }
        if (prune) {
                ALLOC_GROW(prune, prune_nr+1, prune_alloc);
                prune[prune_nr] = NULL;
        }
        *prune_data = prune;
}

/*
 * Parse revision information, filling in the "rev_info" structure,
 * and removing the used arguments from the argument list.
 *
 * Returns the number of arguments left that weren't recognized
 * (which are also moved to the head of the argument list)
 */
int setup_revisions(int argc, const char **argv, struct rev_info *revs, const char *def)
{
        int i, flags, left, seen_dashdash, read_from_stdin;
        const char **prune_data = NULL;

        /* First, search for "--" */
        seen_dashdash = 0;
        for (i = 1; i < argc; i++) {
                const char *arg = argv[i];
                if (strcmp(arg, "--"))
                        continue;
                argv[i] = NULL;
                argc = i;
                if (argv[i + 1])
                        prune_data = argv + i + 1;
                seen_dashdash = 1;
                break;
        }

        /* Second, deal with arguments and options */
        flags = 0;
        read_from_stdin = 0;
        for (left = i = 1; i < argc; i++) {
                const char *arg = argv[i];
                if (*arg == '-') {
                        int opts;

                        if (!strcmp(arg, "--all")) {
                                handle_refs(revs, flags, for_each_ref);
                                handle_refs(revs, flags, head_ref);
                                continue;
                        }
                        if (!strcmp(arg, "--branches")) {
                                handle_refs(revs, flags, for_each_branch_ref);
                                continue;
                        }
                        if (!strcmp(arg, "--bisect")) {
                                handle_refs(revs, flags, for_each_bad_bisect_ref);
                                handle_refs(revs, flags ^ UNINTERESTING, for_each_good_bisect_ref);
                                revs->bisect = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--tags")) {
                                handle_refs(revs, flags, for_each_tag_ref);
                                continue;
                        }
                        if (!strcmp(arg, "--remotes")) {
                                handle_refs(revs, flags, for_each_remote_ref);
                                continue;
                        }
                        if (!strcmp(arg, "--reflog")) {
                                handle_reflog(revs, flags);
                                continue;
                        }
                        if (!strcmp(arg, "--not")) {
                                flags ^= UNINTERESTING;
                                continue;
                        }
                        if (!strcmp(arg, "--no-walk")) {
                                revs->no_walk = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--do-walk")) {
                                revs->no_walk = 0;
                                continue;
                        }
                        if (!strcmp(arg, "--stdin")) {
                                if (revs->disable_stdin) {
                                        argv[left++] = arg;
                                        continue;
                                }
                                if (read_from_stdin++)
                                        die("--stdin given twice?");
                                read_revisions_from_stdin(revs, &prune_data);
                                continue;
                        }

                        opts = handle_revision_opt(revs, argc - i, argv + i, &left, argv);
                        if (opts > 0) {
                                i += opts - 1;
                                continue;
                        }
                        if (opts < 0)
                                exit(128);
                        continue;
                }

                if (handle_revision_arg(arg, revs, flags, seen_dashdash)) {
                        int j;
                        if (seen_dashdash || *arg == '^')
                                die("bad revision '%s'", arg);

                        /* If we didn't have a "--":
                         * (1) all filenames must exist;
                         * (2) all rev-args must not be interpretable
                         *     as a valid filename.
                         * but the latter we have checked in the main loop.
                         */
                        for (j = i; j < argc; j++)
                                verify_filename(revs->prefix, argv[j]);

                        append_prune_data(&prune_data, argv + i);
                        break;
                }
        }

        if (prune_data)
                revs->prune_data = get_pathspec(revs->prefix, prune_data);

        if (revs->def == NULL)
                revs->def = def;
        if (revs->show_merge)
                prepare_show_merge(revs);
        if (revs->def && !revs->pending.nr) {
                unsigned char sha1[20];
                struct object *object;
                unsigned mode;
                if (get_sha1_with_mode(revs->def, sha1, &mode))
                        die("bad default revision '%s'", revs->def);
                object = get_reference(revs, revs->def, sha1, 0);
                add_pending_object_with_mode(revs, object, revs->def, mode);
        }

        /* Did the user ask for any diff output? Run the diff! */
        if (revs->diffopt.output_format & ~DIFF_FORMAT_NO_OUTPUT)
                revs->diff = 1;

        /* Pickaxe, diff-filter and rename following need diffs */
        if (revs->diffopt.pickaxe ||
            revs->diffopt.filter ||
            DIFF_OPT_TST(&revs->diffopt, FOLLOW_RENAMES))
                revs->diff = 1;

        if (revs->topo_order)
                revs->limited = 1;

        if (revs->prune_data) {
                diff_tree_setup_paths(revs->prune_data, &revs->pruning);
                /* Can't prune commits with rename following: the paths change.. */
                if (!DIFF_OPT_TST(&revs->diffopt, FOLLOW_RENAMES))
                        revs->prune = 1;
                if (!revs->full_diff)
                        diff_tree_setup_paths(revs->prune_data, &revs->diffopt);
        }
        if (revs->combine_merges) {
                revs->ignore_merges = 0;
                if (revs->dense_combined_merges && !revs->diffopt.output_format)
                        revs->diffopt.output_format = DIFF_FORMAT_PATCH;
        }
        revs->diffopt.abbrev = revs->abbrev;
        if (diff_setup_done(&revs->diffopt) < 0)
                die("diff_setup_done failed");

        compile_grep_patterns(&revs->grep_filter);

        if (revs->reverse && revs->reflog_info)
                die("cannot combine --reverse with --walk-reflogs");
        if (revs->rewrite_parents && revs->children.name)
                die("cannot combine --parents and --children");

        /*
         * Limitations on the graph functionality
         */
        if (revs->reverse && revs->graph)
                die("cannot combine --reverse with --graph");

        if (revs->reflog_info && revs->graph)
                die("cannot combine --walk-reflogs with --graph");

        return left;
}

static void add_child(struct rev_info *revs, struct commit *parent, struct commit *child)
{
        struct commit_list *l = xcalloc(1, sizeof(*l));

        l->item = child;
        l->next = add_decoration(&revs->children, &parent->object, l);
}

static int remove_duplicate_parents(struct commit *commit)
{
        struct commit_list **pp, *p;
        int surviving_parents;

        /* Examine existing parents while marking ones we have seen... */
        pp = &commit->parents;
        while ((p = *pp) != NULL) {
                struct commit *parent = p->item;
                if (parent->object.flags & TMP_MARK) {
                        *pp = p->next;
                        continue;
                }
                parent->object.flags |= TMP_MARK;
                pp = &p->next;
        }
        /* count them while clearing the temporary mark */
        surviving_parents = 0;
        for (p = commit->parents; p; p = p->next) {
                p->item->object.flags &= ~TMP_MARK;
                surviving_parents++;
        }
        return surviving_parents;
}

struct merge_simplify_state {
        struct commit *simplified;
};

static struct merge_simplify_state *locate_simplify_state(struct rev_info *revs, struct commit *commit)
{
        struct merge_simplify_state *st;

        st = lookup_decoration(&revs->merge_simplification, &commit->object);
        if (!st) {
                st = xcalloc(1, sizeof(*st));
                add_decoration(&revs->merge_simplification, &commit->object, st);
        }
        return st;
}

static struct commit_list **simplify_one(struct rev_info *revs, struct commit *commit, struct commit_list **tail)
{
        struct commit_list *p;
        struct merge_simplify_state *st, *pst;
        int cnt;

        st = locate_simplify_state(revs, commit);

        /*
         * Have we handled this one?
         */
        if (st->simplified)
                return tail;

        /*
         * An UNINTERESTING commit simplifies to itself, so does a
         * root commit.  We do not rewrite parents of such commit
         * anyway.
         */
        if ((commit->object.flags & UNINTERESTING) || !commit->parents) {
                st->simplified = commit;
                return tail;
        }

        /*
         * Do we know what commit all of our parents should be rewritten to?
         * Otherwise we are not ready to rewrite this one yet.
         */
        for (cnt = 0, p = commit->parents; p; p = p->next) {
                pst = locate_simplify_state(revs, p->item);
                if (!pst->simplified) {
                        tail = &commit_list_insert(p->item, tail)->next;
                        cnt++;
                }
        }
        if (cnt) {
                tail = &commit_list_insert(commit, tail)->next;
                return tail;
        }

        /*
         * Rewrite our list of parents.
         */
        for (p = commit->parents; p; p = p->next) {
                pst = locate_simplify_state(revs, p->item);
                p->item = pst->simplified;
        }
        cnt = remove_duplicate_parents(commit);

        /*
         * It is possible that we are a merge and one side branch
         * does not have any commit that touches the given paths;
         * in such a case, the immediate parents will be rewritten
         * to different commits.
         *
         *      o----X          X: the commit we are looking at;
         *     /    /           o: a commit that touches the paths;
         * ---o----'
         *
         * Further reduce the parents by removing redundant parents.
         */
        if (1 < cnt) {
                struct commit_list *h = reduce_heads(commit->parents);
                cnt = commit_list_count(h);
                free_commit_list(commit->parents);
                commit->parents = h;
        }

        /*
         * A commit simplifies to itself if it is a root, if it is
         * UNINTERESTING, if it touches the given paths, or if it is a
         * merge and its parents simplifies to more than one commits
         * (the first two cases are already handled at the beginning of
         * this function).
         *
         * Otherwise, it simplifies to what its sole parent simplifies to.
         */
        if (!cnt ||
            (commit->object.flags & UNINTERESTING) ||
            !(commit->object.flags & TREESAME) ||
            (1 < cnt))
                st->simplified = commit;
        else {
                pst = locate_simplify_state(revs, commit->parents->item);
                st->simplified = pst->simplified;
        }
        return tail;
}

static void simplify_merges(struct rev_info *revs)
{
        struct commit_list *list;
        struct commit_list *yet_to_do, **tail;

        if (!revs->topo_order)
                sort_in_topological_order(&revs->commits, revs->lifo);
        if (!revs->prune)
                return;

        /* feed the list reversed */
        yet_to_do = NULL;
        for (list = revs->commits; list; list = list->next)
                commit_list_insert(list->item, &yet_to_do);
        while (yet_to_do) {
                list = yet_to_do;
                yet_to_do = NULL;
                tail = &yet_to_do;
                while (list) {
                        struct commit *commit = list->item;
                        struct commit_list *next = list->next;
                        free(list);
                        list = next;
                        tail = simplify_one(revs, commit, tail);
                }
        }

        /* clean up the result, removing the simplified ones */
        list = revs->commits;
        revs->commits = NULL;
        tail = &revs->commits;
        while (list) {
                struct commit *commit = list->item;
                struct commit_list *next = list->next;
                struct merge_simplify_state *st;
                free(list);
                list = next;
                st = locate_simplify_state(revs, commit);
                if (st->simplified == commit)
                        tail = &commit_list_insert(commit, tail)->next;
        }
}

static void set_children(struct rev_info *revs)
{
        struct commit_list *l;
        for (l = revs->commits; l; l = l->next) {
                struct commit *commit = l->item;
                struct commit_list *p;

                for (p = commit->parents; p; p = p->next)
                        add_child(revs, p->item, commit);
        }
}

int prepare_revision_walk(struct rev_info *revs)
{
        int nr = revs->pending.nr;
        struct object_array_entry *e, *list;

        e = list = revs->pending.objects;
        revs->pending.nr = 0;
        revs->pending.alloc = 0;
        revs->pending.objects = NULL;
        while (--nr >= 0) {
                struct commit *commit = handle_commit(revs, e->item, e->name);
                if (commit) {
                        if (!(commit->object.flags & SEEN)) {
                                commit->object.flags |= SEEN;
                                insert_by_date(commit, &revs->commits);
                        }
                }
                e++;
        }
        free(list);

        if (revs->no_walk)
                return 0;
        if (revs->limited)
                if (limit_list(revs) < 0)
                        return -1;
        if (revs->topo_order)
                sort_in_topological_order(&revs->commits, revs->lifo);
        if (revs->simplify_merges)
                simplify_merges(revs);
        if (revs->children.name)
                set_children(revs);
        return 0;
}

enum rewrite_result {
        rewrite_one_ok,
        rewrite_one_noparents,
        rewrite_one_error,
};

static enum rewrite_result rewrite_one(struct rev_info *revs, struct commit **pp)
{
        struct commit_list *cache = NULL;

        for (;;) {
                struct commit *p = *pp;
                if (!revs->limited)
                        if (add_parents_to_list(revs, p, &revs->commits, &cache) < 0)
                                return rewrite_one_error;
                if (p->parents && p->parents->next)
                        return rewrite_one_ok;
                if (p->object.flags & UNINTERESTING)
                        return rewrite_one_ok;
                if (!(p->object.flags & TREESAME))
                        return rewrite_one_ok;
                if (!p->parents)
                        return rewrite_one_noparents;
                *pp = p->parents->item;
        }
}

static int rewrite_parents(struct rev_info *revs, struct commit *commit)
{
        struct commit_list **pp = &commit->parents;
        while (*pp) {
                struct commit_list *parent = *pp;
                switch (rewrite_one(revs, &parent->item)) {
                case rewrite_one_ok:
                        break;
                case rewrite_one_noparents:
                        *pp = parent->next;
                        continue;
                case rewrite_one_error:
                        return -1;
                }
                pp = &parent->next;
        }
        remove_duplicate_parents(commit);
        return 0;
}

static int commit_match(struct commit *commit, struct rev_info *opt)
{
        if (!opt->grep_filter.pattern_list)
                return 1;
        return grep_buffer(&opt->grep_filter,
                           NULL, /* we say nothing, not even filename */
                           commit->buffer, strlen(commit->buffer));
}

static inline int want_ancestry(struct rev_info *revs)
{
        return (revs->rewrite_parents || revs->children.name);
}

enum commit_action get_commit_action(struct rev_info *revs, struct commit *commit)
{
        if (commit->object.flags & SHOWN)
                return commit_ignore;
        if (revs->unpacked && has_sha1_pack(commit->object.sha1))
                return commit_ignore;
        if (revs->show_all)
                return commit_show;
        if (commit->object.flags & UNINTERESTING)
                return commit_ignore;
        if (revs->min_age != -1 && (commit->date > revs->min_age))
                return commit_ignore;
        if (revs->no_merges && commit->parents && commit->parents->next)
                return commit_ignore;
        if (revs->merges_only && !(commit->parents && commit->parents->next))
                return commit_ignore;
        if (!commit_match(commit, revs))
                return commit_ignore;
        if (revs->prune && revs->dense) {
                /* Commit without changes? */
                if (commit->object.flags & TREESAME) {
                        /* drop merges unless we want parenthood */
                        if (!want_ancestry(revs))
                                return commit_ignore;
                        /* non-merge - always ignore it */
                        if (!commit->parents || !commit->parents->next)
                                return commit_ignore;
                }
        }
        return commit_show;
}

enum commit_action simplify_commit(struct rev_info *revs, struct commit *commit)
{
        enum commit_action action = get_commit_action(revs, commit);

        if (action == commit_show &&
            !revs->show_all &&
            revs->prune && revs->dense && want_ancestry(revs)) {
                if (rewrite_parents(revs, commit) < 0)
                        return commit_error;
        }
        return action;
}

static struct commit *get_revision_1(struct rev_info *revs)
{
        if (!revs->commits)
                return NULL;

        do {
                struct commit_list *entry = revs->commits;
                struct commit *commit = entry->item;

                revs->commits = entry->next;
                free(entry);

                if (revs->reflog_info)
                        fake_reflog_parent(revs->reflog_info, commit);

                /*
                 * If we haven't done the list limiting, we need to look at
                 * the parents here. We also need to do the date-based limiting
                 * that we'd otherwise have done in limit_list().
                 */
                if (!revs->limited) {
                        if (revs->max_age != -1 &&
                            (commit->date < revs->max_age))
                                continue;
                        if (add_parents_to_list(revs, commit, &revs->commits, NULL) < 0)
                                die("Failed to traverse parents of commit %s",
                                    sha1_to_hex(commit->object.sha1));
                }

                switch (simplify_commit(revs, commit)) {
                case commit_ignore:
                        continue;
                case commit_error:
                        die("Failed to simplify parents of commit %s",
                            sha1_to_hex(commit->object.sha1));
                default:
                        return commit;
                }
        } while (revs->commits);
        return NULL;
}

static void gc_boundary(struct object_array *array)
{
        unsigned nr = array->nr;
        unsigned alloc = array->alloc;
        struct object_array_entry *objects = array->objects;

        if (alloc <= nr) {
                unsigned i, j;
                for (i = j = 0; i < nr; i++) {
                        if (objects[i].item->flags & SHOWN)
                                continue;
                        if (i != j)
                                objects[j] = objects[i];
                        j++;
                }
                for (i = j; i < nr; i++)
                        objects[i].item = NULL;
                array->nr = j;
        }
}

static void create_boundary_commit_list(struct rev_info *revs)
{
        unsigned i;
        struct commit *c;
        struct object_array *array = &revs->boundary_commits;
        struct object_array_entry *objects = array->objects;

        /*
         * If revs->commits is non-NULL at this point, an error occurred in
         * get_revision_1().  Ignore the error and continue printing the
         * boundary commits anyway.  (This is what the code has always
         * done.)
         */
        if (revs->commits) {
                free_commit_list(revs->commits);
                revs->commits = NULL;
        }

        /*
         * Put all of the actual boundary commits from revs->boundary_commits
         * into revs->commits
         */
        for (i = 0; i < array->nr; i++) {
                c = (struct commit *)(objects[i].item);
                if (!c)
                        continue;
                if (!(c->object.flags & CHILD_SHOWN))
                        continue;
                if (c->object.flags & (SHOWN | BOUNDARY))
                        continue;
                c->object.flags |= BOUNDARY;
                commit_list_insert(c, &revs->commits);
        }

        /*
         * If revs->topo_order is set, sort the boundary commits
         * in topological order
         */
        sort_in_topological_order(&revs->commits, revs->lifo);
}

static struct commit *get_revision_internal(struct rev_info *revs)
{
        struct commit *c = NULL;
        struct commit_list *l;

        if (revs->boundary == 2) {
                /*
                 * All of the normal commits have already been returned,
                 * and we are now returning boundary commits.
                 * create_boundary_commit_list() has populated
                 * revs->commits with the remaining commits to return.
                 */
                c = pop_commit(&revs->commits);
                if (c)
                        c->object.flags |= SHOWN;
                return c;
        }

        /*
         * Now pick up what they want to give us
         */
        c = get_revision_1(revs);
        if (c) {
                while (0 < revs->skip_count) {
                        revs->skip_count--;
                        c = get_revision_1(revs);
                        if (!c)
                                break;
                }
        }

        /*
         * Check the max_count.
         */
        switch (revs->max_count) {
        case -1:
                break;
        case 0:
                c = NULL;
                break;
        default:
                revs->max_count--;
        }

        if (c)
                c->object.flags |= SHOWN;

        if (!revs->boundary) {
                return c;
        }

        if (!c) {
                /*
                 * get_revision_1() runs out the commits, and
                 * we are done computing the boundaries.
                 * switch to boundary commits output mode.
                 */
                revs->boundary = 2;

                /*
                 * Update revs->commits to contain the list of
                 * boundary commits.
                 */
                create_boundary_commit_list(revs);

                return get_revision_internal(revs);
        }

        /*
         * boundary commits are the commits that are parents of the
         * ones we got from get_revision_1() but they themselves are
         * not returned from get_revision_1().  Before returning
         * 'c', we need to mark its parents that they could be boundaries.
         */

        for (l = c->parents; l; l = l->next) {
                struct object *p;
                p = &(l->item->object);
                if (p->flags & (CHILD_SHOWN | SHOWN))
                        continue;
                p->flags |= CHILD_SHOWN;
                gc_boundary(&revs->boundary_commits);
                add_object_array(p, NULL, &revs->boundary_commits);
        }

        return c;
}

struct commit *get_revision(struct rev_info *revs)
{
        struct commit *c;
        struct commit_list *reversed;

        if (revs->reverse) {
                reversed = NULL;
                while ((c = get_revision_internal(revs))) {
                        commit_list_insert(c, &reversed);
                }
                revs->commits = reversed;
                revs->reverse = 0;
                revs->reverse_output_stage = 1;
        }

        if (revs->reverse_output_stage)
                return pop_commit(&revs->commits);

        c = get_revision_internal(revs);
        if (c && revs->graph)
                graph_update(revs->graph, c);
        return c;
}