commit-graph: check all leading directories in changed path Bloom filters

[thirdparty/git.git] / revision.c

#include "cache.h"
#include "object-store.h"
#include "tag.h"
#include "blob.h"
#include "tree.h"
#include "commit.h"
#include "diff.h"
#include "refs.h"
#include "revision.h"
#include "repository.h"
#include "graph.h"
#include "grep.h"
#include "reflog-walk.h"
#include "patch-ids.h"
#include "decorate.h"
#include "log-tree.h"
#include "string-list.h"
#include "line-log.h"
#include "mailmap.h"
#include "commit-slab.h"
#include "dir.h"
#include "cache-tree.h"
#include "bisect.h"
#include "packfile.h"
#include "worktree.h"
#include "argv-array.h"
#include "commit-reach.h"
#include "commit-graph.h"
#include "prio-queue.h"
#include "hashmap.h"
#include "utf8.h"
#include "bloom.h"
#include "json-writer.h"

volatile show_early_output_fn_t show_early_output;

static const char *term_bad;
static const char *term_good;

implement_shared_commit_slab(revision_sources, char *);

static inline int want_ancestry(const struct rev_info *revs);

void show_object_with_name(FILE *out, struct object *obj, const char *name)
{
        const char *p;

        fprintf(out, "%s ", oid_to_hex(&obj->oid));
        for (p = name; *p && *p != '\n'; p++)
                fputc(*p, out);
        fputc('\n', out);
}

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

static void mark_tree_contents_uninteresting(struct repository *r,
                                             struct tree *tree)
{
        struct tree_desc desc;
        struct name_entry entry;

        if (parse_tree_gently(tree, 1) < 0)
                return;

        init_tree_desc(&desc, tree->buffer, tree->size);
        while (tree_entry(&desc, &entry)) {
                switch (object_type(entry.mode)) {
                case OBJ_TREE:
                        mark_tree_uninteresting(r, lookup_tree(r, &entry.oid));
                        break;
                case OBJ_BLOB:
                        mark_blob_uninteresting(lookup_blob(r, &entry.oid));
                        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);
}

void mark_tree_uninteresting(struct repository *r, struct tree *tree)
{
        struct object *obj;

        if (!tree)
                return;

        obj = &tree->object;
        if (obj->flags & UNINTERESTING)
                return;
        obj->flags |= UNINTERESTING;
        mark_tree_contents_uninteresting(r, tree);
}

struct path_and_oids_entry {
        struct hashmap_entry ent;
        char *path;
        struct oidset trees;
};

static int path_and_oids_cmp(const void *hashmap_cmp_fn_data,
                             const struct hashmap_entry *eptr,
                             const struct hashmap_entry *entry_or_key,
                             const void *keydata)
{
        const struct path_and_oids_entry *e1, *e2;

        e1 = container_of(eptr, const struct path_and_oids_entry, ent);
        e2 = container_of(entry_or_key, const struct path_and_oids_entry, ent);

        return strcmp(e1->path, e2->path);
}

static void paths_and_oids_init(struct hashmap *map)
{
        hashmap_init(map, path_and_oids_cmp, NULL, 0);
}

static void paths_and_oids_clear(struct hashmap *map)
{
        struct hashmap_iter iter;
        struct path_and_oids_entry *entry;

        hashmap_for_each_entry(map, &iter, entry, ent /* member name */) {
                oidset_clear(&entry->trees);
                free(entry->path);
        }

        hashmap_free_entries(map, struct path_and_oids_entry, ent);
}

static void paths_and_oids_insert(struct hashmap *map,
                                  const char *path,
                                  const struct object_id *oid)
{
        int hash = strhash(path);
        struct path_and_oids_entry key;
        struct path_and_oids_entry *entry;

        hashmap_entry_init(&key.ent, hash);

        /* use a shallow copy for the lookup */
        key.path = (char *)path;
        oidset_init(&key.trees, 0);

        entry = hashmap_get_entry(map, &key, ent, NULL);
        if (!entry) {
                entry = xcalloc(1, sizeof(struct path_and_oids_entry));
                hashmap_entry_init(&entry->ent, hash);
                entry->path = xstrdup(key.path);
                oidset_init(&entry->trees, 16);
                hashmap_put(map, &entry->ent);
        }

        oidset_insert(&entry->trees, oid);
}

static void add_children_by_path(struct repository *r,
                                 struct tree *tree,
                                 struct hashmap *map)
{
        struct tree_desc desc;
        struct name_entry entry;

        if (!tree)
                return;

        if (parse_tree_gently(tree, 1) < 0)
                return;

        init_tree_desc(&desc, tree->buffer, tree->size);
        while (tree_entry(&desc, &entry)) {
                switch (object_type(entry.mode)) {
                case OBJ_TREE:
                        paths_and_oids_insert(map, entry.path, &entry.oid);

                        if (tree->object.flags & UNINTERESTING) {
                                struct tree *child = lookup_tree(r, &entry.oid);
                                if (child)
                                        child->object.flags |= UNINTERESTING;
                        }
                        break;
                case OBJ_BLOB:
                        if (tree->object.flags & UNINTERESTING) {
                                struct blob *child = lookup_blob(r, &entry.oid);
                                if (child)
                                        child->object.flags |= UNINTERESTING;
                        }
                        break;
                default:
                        /* Subproject commit - not in this repository */
                        break;
                }
        }

        free_tree_buffer(tree);
}

void mark_trees_uninteresting_sparse(struct repository *r,
                                     struct oidset *trees)
{
        unsigned has_interesting = 0, has_uninteresting = 0;
        struct hashmap map;
        struct hashmap_iter map_iter;
        struct path_and_oids_entry *entry;
        struct object_id *oid;
        struct oidset_iter iter;

        oidset_iter_init(trees, &iter);
        while ((!has_interesting || !has_uninteresting) &&
               (oid = oidset_iter_next(&iter))) {
                struct tree *tree = lookup_tree(r, oid);

                if (!tree)
                        continue;

                if (tree->object.flags & UNINTERESTING)
                        has_uninteresting = 1;
                else
                        has_interesting = 1;
        }

        /* Do not walk unless we have both types of trees. */
        if (!has_uninteresting || !has_interesting)
                return;

        paths_and_oids_init(&map);

        oidset_iter_init(trees, &iter);
        while ((oid = oidset_iter_next(&iter))) {
                struct tree *tree = lookup_tree(r, oid);
                add_children_by_path(r, tree, &map);
        }

        hashmap_for_each_entry(&map, &map_iter, entry, ent /* member name */)
                mark_trees_uninteresting_sparse(r, &entry->trees);

        paths_and_oids_clear(&map);
}

struct commit_stack {
        struct commit **items;
        size_t nr, alloc;
};
#define COMMIT_STACK_INIT { NULL, 0, 0 }

static void commit_stack_push(struct commit_stack *stack, struct commit *commit)
{
        ALLOC_GROW(stack->items, stack->nr + 1, stack->alloc);
        stack->items[stack->nr++] = commit;
}

static struct commit *commit_stack_pop(struct commit_stack *stack)
{
        return stack->nr ? stack->items[--stack->nr] : NULL;
}

static void commit_stack_clear(struct commit_stack *stack)
{
        FREE_AND_NULL(stack->items);
        stack->nr = stack->alloc = 0;
}

static void mark_one_parent_uninteresting(struct commit *commit,
                                          struct commit_stack *pending)
{
        struct commit_list *l;

        if (commit->object.flags & UNINTERESTING)
                return;
        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..
         */
        for (l = commit->parents; l; l = l->next)
                commit_stack_push(pending, l->item);
}

void mark_parents_uninteresting(struct commit *commit)
{
        struct commit_stack pending = COMMIT_STACK_INIT;
        struct commit_list *l;

        for (l = commit->parents; l; l = l->next)
                mark_one_parent_uninteresting(l->item, &pending);

        while (pending.nr > 0)
                mark_one_parent_uninteresting(commit_stack_pop(&pending),
                                              &pending);

        commit_stack_clear(&pending);
}

static void add_pending_object_with_path(struct rev_info *revs,
                                         struct object *obj,
                                         const char *name, unsigned mode,
                                         const char *path)
{
        if (!obj)
                return;
        if (revs->no_walk && (obj->flags & UNINTERESTING))
                revs->no_walk = 0;
        if (revs->reflog_info && obj->type == OBJ_COMMIT) {
                struct strbuf buf = STRBUF_INIT;
                int len = interpret_branch_name(name, 0, &buf, 0);

                if (0 < len && name[len] && buf.len)
                        strbuf_addstr(&buf, name + len);
                add_reflog_for_walk(revs->reflog_info,
                                    (struct commit *)obj,
                                    buf.buf[0] ? buf.buf: name);
                strbuf_release(&buf);
                return; /* do not add the commit itself */
        }
        add_object_array_with_path(obj, name, &revs->pending, mode, path);
}

static void add_pending_object_with_mode(struct rev_info *revs,
                                         struct object *obj,
                                         const char *name, unsigned mode)
{
        add_pending_object_with_path(revs, obj, name, mode, NULL);
}

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)
{
        struct object_id oid;
        struct object *obj;
        if (get_oid("HEAD", &oid))
                return;
        obj = parse_object(revs->repo, &oid);
        if (!obj)
                return;
        add_pending_object(revs, obj, "HEAD");
}

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

        /*
         * If the repository has commit graphs, repo_parse_commit() avoids
         * reading the object buffer, so use it whenever possible.
         */
        if (oid_object_info(revs->repo, oid, NULL) == OBJ_COMMIT) {
                struct commit *c = lookup_commit(revs->repo, oid);
                if (!repo_parse_commit(revs->repo, c))
                        object = (struct object *) c;
                else
                        object = NULL;
        } else {
                object = parse_object(revs->repo, oid);
        }

        if (!object) {
                if (revs->ignore_missing)
                        return object;
                if (revs->exclude_promisor_objects && is_promisor_object(oid))
                        return NULL;
                die("bad object %s", name);
        }
        object->flags |= flags;
        return object;
}

void add_pending_oid(struct rev_info *revs, const char *name,
                      const struct object_id *oid, unsigned int flags)
{
        struct object *object = get_reference(revs, name, oid, flags);
        add_pending_object(revs, object, name);
}

static struct commit *handle_commit(struct rev_info *revs,
                                    struct object_array_entry *entry)
{
        struct object *object = entry->item;
        const char *name = entry->name;
        const char *path = entry->path;
        unsigned int mode = entry->mode;
        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);
                object = parse_object(revs->repo, get_tagged_oid(tag));
                if (!object) {
                        if (revs->ignore_missing_links || (flags & UNINTERESTING))
                                return NULL;
                        if (revs->exclude_promisor_objects &&
                            is_promisor_object(&tag->tagged->oid))
                                return NULL;
                        die("bad object %s", oid_to_hex(&tag->tagged->oid));
                }
                object->flags |= flags;
                /*
                 * We'll handle the tagged object by looping or dropping
                 * through to the non-tag handlers below. Do not
                 * propagate path data from the tag's pending entry.
                 */
                path = NULL;
                mode = 0;
        }

        /*
         * 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) {
                        mark_parents_uninteresting(commit);

                        if (!revs->topo_order || !generation_numbers_enabled(the_repository))
                                revs->limited = 1;
                }
                if (revs->sources) {
                        char **slot = revision_sources_at(revs->sources, commit);

                        if (!*slot)
                                *slot = xstrdup(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_contents_uninteresting(revs->repo, tree);
                        return NULL;
                }
                add_pending_object_with_path(revs, object, name, mode, path);
                return NULL;
        }

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

static int everybody_uninteresting(struct commit_list *orig,
                                   struct commit **interesting_cache)
{
        struct commit_list *list = orig;

        if (*interesting_cache) {
                struct commit *commit = *interesting_cache;
                if (!(commit->object.flags & UNINTERESTING))
                        return 0;
        }

        while (list) {
                struct commit *commit = list->item;
                list = list->next;
                if (commit->object.flags & UNINTERESTING)
                        continue;

                *interesting_cache = commit;
                return 0;
        }
        return 1;
}

/*
 * A definition of "relevant" commit that we can use to simplify limited graphs
 * by eliminating side branches.
 *
 * A "relevant" commit is one that is !UNINTERESTING (ie we are including it
 * in our list), or that is a specified BOTTOM commit. Then after computing
 * a limited list, during processing we can generally ignore boundary merges
 * coming from outside the graph, (ie from irrelevant parents), and treat
 * those merges as if they were single-parent. TREESAME is defined to consider
 * only relevant parents, if any. If we are TREESAME to our on-graph parents,
 * we don't care if we were !TREESAME to non-graph parents.
 *
 * Treating bottom commits as relevant ensures that a limited graph's
 * connection to the actual bottom commit is not viewed as a side branch, but
 * treated as part of the graph. For example:
 *
 *   ....Z...A---X---o---o---B
 *        .     /
 *         W---Y
 *
 * When computing "A..B", the A-X connection is at least as important as
 * Y-X, despite A being flagged UNINTERESTING.
 *
 * And when computing --ancestry-path "A..B", the A-X connection is more
 * important than Y-X, despite both A and Y being flagged UNINTERESTING.
 */
static inline int relevant_commit(struct commit *commit)
{
        return (commit->object.flags & (UNINTERESTING | BOTTOM)) != UNINTERESTING;
}

/*
 * Return a single relevant commit from a parent list. If we are a TREESAME
 * commit, and this selects one of our parents, then we can safely simplify to
 * that parent.
 */
static struct commit *one_relevant_parent(const struct rev_info *revs,
                                          struct commit_list *orig)
{
        struct commit_list *list = orig;
        struct commit *relevant = NULL;

        if (!orig)
                return NULL;

        /*
         * For 1-parent commits, or if first-parent-only, then return that
         * first parent (even if not "relevant" by the above definition).
         * TREESAME will have been set purely on that parent.
         */
        if (revs->first_parent_only || !orig->next)
                return orig->item;

        /*
         * For multi-parent commits, identify a sole relevant parent, if any.
         * If we have only one relevant parent, then TREESAME will be set purely
         * with regard to that parent, and we can simplify accordingly.
         *
         * If we have more than one relevant parent, or no relevant parents
         * (and multiple irrelevant ones), then we can't select a parent here
         * and return NULL.
         */
        while (list) {
                struct commit *commit = list->item;
                list = list->next;
                if (relevant_commit(commit)) {
                        if (relevant)
                                return NULL;
                        relevant = commit;
                }
        }
        return relevant;
}

/*
 * 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).
 *
 * The only time we care about the distinction is when
 * remove_empty_trees is in effect, in which case we care only about
 * whether the whole change is REV_TREE_NEW, or if there's another type
 * of change. Which means we can stop the diff early in either of these
 * cases:
 *
 *   1. We're not using remove_empty_trees at all.
 *
 *   2. We saw anything except REV_TREE_NEW.
 */
static int tree_difference = REV_TREE_SAME;

static void file_add_remove(struct diff_options *options,
                    int addremove, unsigned mode,
                    const struct object_id *oid,
                    int oid_valid,
                    const char *fullpath, unsigned dirty_submodule)
{
        int diff = addremove == '+' ? REV_TREE_NEW : REV_TREE_OLD;
        struct rev_info *revs = options->change_fn_data;

        tree_difference |= diff;
        if (!revs->remove_empty_trees || tree_difference != REV_TREE_NEW)
                options->flags.has_changes = 1;
}

static void file_change(struct diff_options *options,
                 unsigned old_mode, unsigned new_mode,
                 const struct object_id *old_oid,
                 const struct object_id *new_oid,
                 int old_oid_valid, int new_oid_valid,
                 const char *fullpath,
                 unsigned old_dirty_submodule, unsigned new_dirty_submodule)
{
        tree_difference = REV_TREE_DIFFERENT;
        options->flags.has_changes = 1;
}

static int bloom_filter_atexit_registered;
static unsigned int count_bloom_filter_maybe;
static unsigned int count_bloom_filter_definitely_not;
static unsigned int count_bloom_filter_false_positive;
static unsigned int count_bloom_filter_not_present;

static void trace2_bloom_filter_statistics_atexit(void)
{
        struct json_writer jw = JSON_WRITER_INIT;

        jw_object_begin(&jw, 0);
        jw_object_intmax(&jw, "filter_not_present", count_bloom_filter_not_present);
        jw_object_intmax(&jw, "maybe", count_bloom_filter_maybe);
        jw_object_intmax(&jw, "definitely_not", count_bloom_filter_definitely_not);
        jw_object_intmax(&jw, "false_positive", count_bloom_filter_false_positive);
        jw_end(&jw);

        trace2_data_json("bloom", the_repository, "statistics", &jw);

        jw_release(&jw);
}

static int forbid_bloom_filters(struct pathspec *spec)
{
        if (spec->has_wildcard)
                return 1;
        if (spec->nr > 1)
                return 1;
        if (spec->magic & ~PATHSPEC_LITERAL)
                return 1;
        if (spec->nr && (spec->items[0].magic & ~PATHSPEC_LITERAL))
                return 1;

        return 0;
}

static void prepare_to_use_bloom_filter(struct rev_info *revs)
{
        struct pathspec_item *pi;
        char *path_alloc = NULL;
        const char *path, *p;
        int last_index;
        size_t len;
        int path_component_nr = 1;

        if (!revs->commits)
                return;

        if (forbid_bloom_filters(&revs->prune_data))
                return;

        repo_parse_commit(revs->repo, revs->commits->item);

        if (!revs->repo->objects->commit_graph)
                return;

        revs->bloom_filter_settings = revs->repo->objects->commit_graph->bloom_filter_settings;
        if (!revs->bloom_filter_settings)
                return;

        if (!revs->pruning.pathspec.nr)
                return;

        pi = &revs->pruning.pathspec.items[0];
        last_index = pi->len - 1;

        /* remove single trailing slash from path, if needed */
        if (pi->match[last_index] == '/') {
                path_alloc = xstrdup(pi->match);
                path_alloc[last_index] = '\0';
                path = path_alloc;
        } else
                path = pi->match;

        len = strlen(path);
        if (!len) {
                revs->bloom_filter_settings = NULL;
                return;
        }

        p = path;
        while (*p) {
                /*
                 * At this point, the path is normalized to use Unix-style
                 * path separators. This is required due to how the
                 * changed-path Bloom filters store the paths.
                 */
                if (*p == '/')
                        path_component_nr++;
                p++;
        }

        revs->bloom_keys_nr = path_component_nr;
        ALLOC_ARRAY(revs->bloom_keys, revs->bloom_keys_nr);

        fill_bloom_key(path, len, &revs->bloom_keys[0],
                       revs->bloom_filter_settings);
        path_component_nr = 1;

        p = path + len - 1;
        while (p > path) {
                if (*p == '/')
                        fill_bloom_key(path, p - path,
                                       &revs->bloom_keys[path_component_nr++],
                                       revs->bloom_filter_settings);
                p--;
        }

        if (trace2_is_enabled() && !bloom_filter_atexit_registered) {
                atexit(trace2_bloom_filter_statistics_atexit);
                bloom_filter_atexit_registered = 1;
        }

        free(path_alloc);
}

static int check_maybe_different_in_bloom_filter(struct rev_info *revs,
                                                 struct commit *commit)
{
        struct bloom_filter *filter;
        int result = 1, j;

        if (!revs->repo->objects->commit_graph)
                return -1;

        if (commit->generation == GENERATION_NUMBER_INFINITY)
                return -1;

        filter = get_bloom_filter(revs->repo, commit, 0);

        if (!filter) {
                count_bloom_filter_not_present++;
                return -1;
        }

        for (j = 0; result && j < revs->bloom_keys_nr; j++) {
                result = bloom_filter_contains(filter,
                                               &revs->bloom_keys[j],
                                               revs->bloom_filter_settings);
        }

        if (result)
                count_bloom_filter_maybe++;
        else
                count_bloom_filter_definitely_not++;

        return result;
}

static int rev_compare_tree(struct rev_info *revs,
                            struct commit *parent, struct commit *commit, int nth_parent)
{
        struct tree *t1 = get_commit_tree(parent);
        struct tree *t2 = get_commit_tree(commit);
        int bloom_ret = 1;

        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 (get_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.nr)
                        return REV_TREE_SAME;
        }

        if (revs->bloom_keys_nr && !nth_parent) {
                bloom_ret = check_maybe_different_in_bloom_filter(revs, commit);

                if (bloom_ret == 0)
                        return REV_TREE_SAME;
        }

        tree_difference = REV_TREE_SAME;
        revs->pruning.flags.has_changes = 0;
        diff_tree_oid(&t1->object.oid, &t2->object.oid, "", &revs->pruning);

        if (!nth_parent)
                if (bloom_ret == 1 && tree_difference == REV_TREE_SAME)
                        count_bloom_filter_false_positive++;

        return tree_difference;
}

static int rev_same_tree_as_empty(struct rev_info *revs, struct commit *commit)
{
        struct tree *t1 = get_commit_tree(commit);

        if (!t1)
                return 0;

        tree_difference = REV_TREE_SAME;
        revs->pruning.flags.has_changes = 0;
        diff_tree_oid(NULL, &t1->object.oid, "", &revs->pruning);

        return tree_difference == REV_TREE_SAME;
}

struct treesame_state {
        unsigned int nparents;
        unsigned char treesame[FLEX_ARRAY];
};

static struct treesame_state *initialise_treesame(struct rev_info *revs, struct commit *commit)
{
        unsigned n = commit_list_count(commit->parents);
        struct treesame_state *st = xcalloc(1, st_add(sizeof(*st), n));
        st->nparents = n;
        add_decoration(&revs->treesame, &commit->object, st);
        return st;
}

/*
 * Must be called immediately after removing the nth_parent from a commit's
 * parent list, if we are maintaining the per-parent treesame[] decoration.
 * This does not recalculate the master TREESAME flag - update_treesame()
 * should be called to update it after a sequence of treesame[] modifications
 * that may have affected it.
 */
static int compact_treesame(struct rev_info *revs, struct commit *commit, unsigned nth_parent)
{
        struct treesame_state *st;
        int old_same;

        if (!commit->parents) {
                /*
                 * Have just removed the only parent from a non-merge.
                 * Different handling, as we lack decoration.
                 */
                if (nth_parent != 0)
                        die("compact_treesame %u", nth_parent);
                old_same = !!(commit->object.flags & TREESAME);
                if (rev_same_tree_as_empty(revs, commit))
                        commit->object.flags |= TREESAME;
                else
                        commit->object.flags &= ~TREESAME;
                return old_same;
        }

        st = lookup_decoration(&revs->treesame, &commit->object);
        if (!st || nth_parent >= st->nparents)
                die("compact_treesame %u", nth_parent);

        old_same = st->treesame[nth_parent];
        memmove(st->treesame + nth_parent,
                st->treesame + nth_parent + 1,
                st->nparents - nth_parent - 1);

        /*
         * If we've just become a non-merge commit, update TREESAME
         * immediately, and remove the no-longer-needed decoration.
         * If still a merge, defer update until update_treesame().
         */
        if (--st->nparents == 1) {
                if (commit->parents->next)
                        die("compact_treesame parents mismatch");
                if (st->treesame[0] && revs->dense)
                        commit->object.flags |= TREESAME;
                else
                        commit->object.flags &= ~TREESAME;
                free(add_decoration(&revs->treesame, &commit->object, NULL));
        }

        return old_same;
}

static unsigned update_treesame(struct rev_info *revs, struct commit *commit)
{
        if (commit->parents && commit->parents->next) {
                unsigned n;
                struct treesame_state *st;
                struct commit_list *p;
                unsigned relevant_parents;
                unsigned relevant_change, irrelevant_change;

                st = lookup_decoration(&revs->treesame, &commit->object);
                if (!st)
                        die("update_treesame %s", oid_to_hex(&commit->object.oid));
                relevant_parents = 0;
                relevant_change = irrelevant_change = 0;
                for (p = commit->parents, n = 0; p; n++, p = p->next) {
                        if (relevant_commit(p->item)) {
                                relevant_change |= !st->treesame[n];
                                relevant_parents++;
                        } else
                                irrelevant_change |= !st->treesame[n];
                }
                if (relevant_parents ? relevant_change : irrelevant_change)
                        commit->object.flags &= ~TREESAME;
                else
                        commit->object.flags |= TREESAME;
        }

        return commit->object.flags & TREESAME;
}

static inline int limiting_can_increase_treesame(const struct rev_info *revs)
{
        /*
         * TREESAME is irrelevant unless prune && dense;
         * if simplify_history is set, we can't have a mixture of TREESAME and
         *    !TREESAME INTERESTING parents (and we don't have treesame[]
         *    decoration anyway);
         * if first_parent_only is set, then the TREESAME flag is locked
         *    against the first parent (and again we lack treesame[] decoration).
         */
        return revs->prune && revs->dense &&
               !revs->simplify_history &&
               !revs->first_parent_only;
}

static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
{
        struct commit_list **pp, *parent;
        struct treesame_state *ts = NULL;
        int relevant_change = 0, irrelevant_change = 0;
        int relevant_parents, nth_parent;

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

        if (!get_commit_tree(commit))
                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;

        for (pp = &commit->parents, nth_parent = 0, relevant_parents = 0;
             (parent = *pp) != NULL;
             pp = &parent->next, nth_parent++) {
                struct commit *p = parent->item;
                if (relevant_commit(p))
                        relevant_parents++;

                if (nth_parent == 1) {
                        /*
                         * This our second loop iteration - so we now know
                         * we're dealing with a merge.
                         *
                         * Do not compare with later parents when we care only about
                         * the first parent chain, in order to avoid derailing the
                         * traversal to follow a side branch that brought everything
                         * in the path we are limited to by the pathspec.
                         */
                        if (revs->first_parent_only)
                                break;
                        /*
                         * If this will remain a potentially-simplifiable
                         * merge, remember per-parent treesame if needed.
                         * Initialise the array with the comparison from our
                         * first iteration.
                         */
                        if (revs->treesame.name &&
                            !revs->simplify_history &&
                            !(commit->object.flags & UNINTERESTING)) {
                                ts = initialise_treesame(revs, commit);
                                if (!(irrelevant_change || relevant_change))
                                        ts->treesame[0] = 1;
                        }
                }
                if (parse_commit(p) < 0)
                        die("cannot simplify commit %s (because of %s)",
                            oid_to_hex(&commit->object.oid),
                            oid_to_hex(&p->object.oid));
                switch (rev_compare_tree(revs, p, commit, nth_parent)) {
                case REV_TREE_SAME:
                        if (!revs->simplify_history || !relevant_commit(p)) {
                                /* 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.
                                 */
                                if (ts)
                                        ts->treesame[nth_parent] = 1;
                                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)",
                                            oid_to_hex(&commit->object.oid),
                                            oid_to_hex(&p->object.oid));
                                p->parents = NULL;
                        }
                /* fallthrough */
                case REV_TREE_OLD:
                case REV_TREE_DIFFERENT:
                        if (relevant_commit(p))
                                relevant_change = 1;
                        else
                                irrelevant_change = 1;
                        continue;
                }
                die("bad tree compare for commit %s", oid_to_hex(&commit->object.oid));
        }

        /*
         * TREESAME is straightforward for single-parent commits. For merge
         * commits, it is most useful to define it so that "irrelevant"
         * parents cannot make us !TREESAME - if we have any relevant
         * parents, then we only consider TREESAMEness with respect to them,
         * allowing irrelevant merges from uninteresting branches to be
         * simplified away. Only if we have only irrelevant parents do we
         * base TREESAME on them. Note that this logic is replicated in
         * update_treesame, which should be kept in sync.
         */
        if (relevant_parents ? !relevant_change : !irrelevant_change)
                commit->object.flags |= TREESAME;
}

static int process_parents(struct rev_info *revs, struct commit *commit,
                           struct commit_list **list, struct prio_queue *queue)
{
        struct commit_list *parent = commit->parents;
        unsigned left_flag;

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

        if (revs->include_check &&
            !revs->include_check(commit, revs->include_check_data))
                return 0;

        /*
         * 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_gently(p, 1) < 0)
                                continue;
                        if (p->parents)
                                mark_parents_uninteresting(p);
                        if (p->object.flags & SEEN)
                                continue;
                        p->object.flags |= SEEN;
                        if (list)
                                commit_list_insert_by_date(p, list);
                        if (queue)
                                prio_queue_put(queue, p);
                }
                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;
                int gently = revs->ignore_missing_links ||
                             revs->exclude_promisor_objects;
                if (parse_commit_gently(p, gently) < 0) {
                        if (revs->exclude_promisor_objects &&
                            is_promisor_object(&p->object.oid)) {
                                if (revs->first_parent_only)
                                        break;
                                continue;
                        }
                        return -1;
                }
                if (revs->sources) {
                        char **slot = revision_sources_at(revs->sources, p);

                        if (!*slot)
                                *slot = *revision_sources_at(revs->sources, commit);
                }
                p->object.flags |= left_flag;
                if (!(p->object.flags & SEEN)) {
                        p->object.flags |= SEEN;
                        if (list)
                                commit_list_insert_by_date(p, list);
                        if (queue)
                                prio_queue_put(queue, p);
                }
                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;
        unsigned cherry_flag;

        /* 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++;
        }

        if (!left_count || !right_count)
                return;

        left_first = left_count < right_count;
        init_patch_ids(revs->repo, &ids);
        ids.diffopts.pathspec = revs->diffopt.pathspec;

        /* 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;
                add_commit_patch_id(commit, &ids);
        }

        /* either cherry_mark or cherry_pick are true */
        cherry_flag = revs->cherry_mark ? PATCHSAME : SHOWN;

        /* 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;

                commit->object.flags |= cherry_flag;
                id->commit->object.flags |= cherry_flag;
        }

        free_patch_ids(&ids);
}

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

static int still_interesting(struct commit_list *src, timestamp_t date, int slop,
                             struct commit **interesting_cache)
{
        /*
         * 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, interesting_cache))
                return SLOP;

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

/*
 * "rev-list --ancestry-path A..B" computes commits that are ancestors
 * of B but not ancestors of A but further limits the result to those
 * that are descendants of A.  This takes the list of bottom commits and
 * the result of "A..B" without --ancestry-path, and limits the latter
 * further to the ones that can reach one of the commits in "bottom".
 */
static void limit_to_ancestry(struct commit_list *bottom, struct commit_list *list)
{
        struct commit_list *p;
        struct commit_list *rlist = NULL;
        int made_progress;

        /*
         * Reverse the list so that it will be likely that we would
         * process parents before children.
         */
        for (p = list; p; p = p->next)
                commit_list_insert(p->item, &rlist);

        for (p = bottom; p; p = p->next)
                p->item->object.flags |= TMP_MARK;

        /*
         * Mark the ones that can reach bottom commits in "list",
         * in a bottom-up fashion.
         */
        do {
                made_progress = 0;
                for (p = rlist; p; p = p->next) {
                        struct commit *c = p->item;
                        struct commit_list *parents;
                        if (c->object.flags & (TMP_MARK | UNINTERESTING))
                                continue;
                        for (parents = c->parents;
                             parents;
                             parents = parents->next) {
                                if (!(parents->item->object.flags & TMP_MARK))
                                        continue;
                                c->object.flags |= TMP_MARK;
                                made_progress = 1;
                                break;
                        }
                }
        } while (made_progress);

        /*
         * NEEDSWORK: decide if we want to remove parents that are
         * not marked with TMP_MARK from commit->parents for commits
         * in the resulting list.  We may not want to do that, though.
         */

        /*
         * The ones that are not marked with TMP_MARK are uninteresting
         */
        for (p = list; p; p = p->next) {
                struct commit *c = p->item;
                if (c->object.flags & TMP_MARK)
                        continue;
                c->object.flags |= UNINTERESTING;
        }

        /* We are done with the TMP_MARK */
        for (p = list; p; p = p->next)
                p->item->object.flags &= ~TMP_MARK;
        for (p = bottom; p; p = p->next)
                p->item->object.flags &= ~TMP_MARK;
        free_commit_list(rlist);
}

/*
 * Before walking the history, keep the set of "negative" refs the
 * caller has asked to exclude.
 *
 * This is used to compute "rev-list --ancestry-path A..B", as we need
 * to filter the result of "A..B" further to the ones that can actually
 * reach A.
 */
static struct commit_list *collect_bottom_commits(struct commit_list *list)
{
        struct commit_list *elem, *bottom = NULL;
        for (elem = list; elem; elem = elem->next)
                if (elem->item->object.flags & BOTTOM)
                        commit_list_insert(elem->item, &bottom);
        return bottom;
}

/* Assumes either left_only or right_only is set */
static void limit_left_right(struct commit_list *list, struct rev_info *revs)
{
        struct commit_list *p;

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

                if (revs->right_only) {
                        if (commit->object.flags & SYMMETRIC_LEFT)
                                commit->object.flags |= SHOWN;
                } else  /* revs->left_only is set */
                        if (!(commit->object.flags & SYMMETRIC_LEFT))
                                commit->object.flags |= SHOWN;
        }
}

static int limit_list(struct rev_info *revs)
{
        int slop = SLOP;
        timestamp_t date = TIME_MAX;
        struct commit_list *list = revs->commits;
        struct commit_list *newlist = NULL;
        struct commit_list **p = &newlist;
        struct commit_list *bottom = NULL;
        struct commit *interesting_cache = NULL;

        if (revs->ancestry_path) {
                bottom = collect_bottom_commits(list);
                if (!bottom)
                        die("--ancestry-path given but there are no bottom commits");
        }

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

                if (commit == interesting_cache)
                        interesting_cache = NULL;

                if (revs->max_age != -1 && (commit->date < revs->max_age))
                        obj->flags |= UNINTERESTING;
                if (process_parents(revs, commit, &list, NULL) < 0)
                        return -1;
                if (obj->flags & UNINTERESTING) {
                        mark_parents_uninteresting(commit);
                        slop = still_interesting(list, date, slop, &interesting_cache);
                        if (slop)
                                continue;
                        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 || revs->cherry_mark)
                cherry_pick_list(newlist, revs);

        if (revs->left_only || revs->right_only)
                limit_left_right(newlist, revs);

        if (bottom) {
                limit_to_ancestry(bottom, newlist);
                free_commit_list(bottom);
        }

        /*
         * Check if any commits have become TREESAME by some of their parents
         * becoming UNINTERESTING.
         */
        if (limiting_can_increase_treesame(revs))
                for (list = newlist; list; list = list->next) {
                        struct commit *c = list->item;
                        if (c->object.flags & (UNINTERESTING | TREESAME))
                                continue;
                        update_treesame(revs, c);
                }

        revs->commits = newlist;
        return 0;
}

/*
 * Add an entry to refs->cmdline with the specified information.
 * *name is copied.
 */
static void add_rev_cmdline(struct rev_info *revs,
                            struct object *item,
                            const char *name,
                            int whence,
                            unsigned flags)
{
        struct rev_cmdline_info *info = &revs->cmdline;
        unsigned int nr = info->nr;

        ALLOC_GROW(info->rev, nr + 1, info->alloc);
        info->rev[nr].item = item;
        info->rev[nr].name = xstrdup(name);
        info->rev[nr].whence = whence;
        info->rev[nr].flags = flags;
        info->nr++;
}

static void add_rev_cmdline_list(struct rev_info *revs,
                                 struct commit_list *commit_list,
                                 int whence,
                                 unsigned flags)
{
        while (commit_list) {
                struct object *object = &commit_list->item->object;
                add_rev_cmdline(revs, object, oid_to_hex(&object->oid),
                                whence, flags);
                commit_list = commit_list->next;
        }
}

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

int ref_excluded(struct string_list *ref_excludes, const char *path)
{
        struct string_list_item *item;

        if (!ref_excludes)
                return 0;
        for_each_string_list_item(item, ref_excludes) {
                if (!wildmatch(item->string, path, 0))
                        return 1;
        }
        return 0;
}

static int handle_one_ref(const char *path, const struct object_id *oid,
                          int flag, void *cb_data)
{
        struct all_refs_cb *cb = cb_data;
        struct object *object;

        if (ref_excluded(cb->all_revs->ref_excludes, path))
            return 0;

        object = get_reference(cb->all_revs, path, oid, cb->all_flags);
        add_rev_cmdline(cb->all_revs, object, path, REV_CMD_REF, cb->all_flags);
        add_pending_oid(cb->all_revs, path, oid, cb->all_flags);
        return 0;
}

static void init_all_refs_cb(struct all_refs_cb *cb, struct rev_info *revs,
        unsigned flags)
{
        cb->all_revs = revs;
        cb->all_flags = flags;
        revs->rev_input_given = 1;
        cb->wt = NULL;
}

void clear_ref_exclusion(struct string_list **ref_excludes_p)
{
        if (*ref_excludes_p) {
                string_list_clear(*ref_excludes_p, 0);
                free(*ref_excludes_p);
        }
        *ref_excludes_p = NULL;
}

void add_ref_exclusion(struct string_list **ref_excludes_p, const char *exclude)
{
        if (!*ref_excludes_p) {
                *ref_excludes_p = xcalloc(1, sizeof(**ref_excludes_p));
                (*ref_excludes_p)->strdup_strings = 1;
        }
        string_list_append(*ref_excludes_p, exclude);
}

static void handle_refs(struct ref_store *refs,
                        struct rev_info *revs, unsigned flags,
                        int (*for_each)(struct ref_store *, each_ref_fn, void *))
{
        struct all_refs_cb cb;

        if (!refs) {
                /* this could happen with uninitialized submodules */
                return;
        }

        init_all_refs_cb(&cb, revs, flags);
        for_each(refs, handle_one_ref, &cb);
}

static void handle_one_reflog_commit(struct object_id *oid, void *cb_data)
{
        struct all_refs_cb *cb = cb_data;
        if (!is_null_oid(oid)) {
                struct object *o = parse_object(cb->all_revs->repo, oid);
                if (o) {
                        o->flags |= cb->all_flags;
                        /* ??? CMDLINEFLAGS ??? */
                        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(struct object_id *ooid, struct object_id *noid,
                const char *email, timestamp_t timestamp, int tz,
                const char *message, void *cb_data)
{
        handle_one_reflog_commit(ooid, cb_data);
        handle_one_reflog_commit(noid, cb_data);
        return 0;
}

static int handle_one_reflog(const char *refname_in_wt,
                             const struct object_id *oid,
                             int flag, void *cb_data)
{
        struct all_refs_cb *cb = cb_data;
        struct strbuf refname = STRBUF_INIT;

        cb->warned_bad_reflog = 0;
        strbuf_worktree_ref(cb->wt, &refname, refname_in_wt);
        cb->name_for_errormsg = refname.buf;
        refs_for_each_reflog_ent(get_main_ref_store(the_repository),
                                 refname.buf,
                                 handle_one_reflog_ent, cb_data);
        strbuf_release(&refname);
        return 0;
}

static void add_other_reflogs_to_pending(struct all_refs_cb *cb)
{
        struct worktree **worktrees, **p;

        worktrees = get_worktrees(0);
        for (p = worktrees; *p; p++) {
                struct worktree *wt = *p;

                if (wt->is_current)
                        continue;

                cb->wt = wt;
                refs_for_each_reflog(get_worktree_ref_store(wt),
                                     handle_one_reflog,
                                     cb);
        }
        free_worktrees(worktrees);
}

void add_reflogs_to_pending(struct rev_info *revs, unsigned flags)
{
        struct all_refs_cb cb;

        cb.all_revs = revs;
        cb.all_flags = flags;
        cb.wt = NULL;
        for_each_reflog(handle_one_reflog, &cb);

        if (!revs->single_worktree)
                add_other_reflogs_to_pending(&cb);
}

static void add_cache_tree(struct cache_tree *it, struct rev_info *revs,
                           struct strbuf *path, unsigned int flags)
{
        size_t baselen = path->len;
        int i;

        if (it->entry_count >= 0) {
                struct tree *tree = lookup_tree(revs->repo, &it->oid);
                tree->object.flags |= flags;
                add_pending_object_with_path(revs, &tree->object, "",
                                             040000, path->buf);
        }

        for (i = 0; i < it->subtree_nr; i++) {
                struct cache_tree_sub *sub = it->down[i];
                strbuf_addf(path, "%s%s", baselen ? "/" : "", sub->name);
                add_cache_tree(sub->cache_tree, revs, path, flags);
                strbuf_setlen(path, baselen);
        }

}

static void do_add_index_objects_to_pending(struct rev_info *revs,
                                            struct index_state *istate,
                                            unsigned int flags)
{
        int i;

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

                if (S_ISGITLINK(ce->ce_mode))
                        continue;

                blob = lookup_blob(revs->repo, &ce->oid);
                if (!blob)
                        die("unable to add index blob to traversal");
                blob->object.flags |= flags;
                add_pending_object_with_path(revs, &blob->object, "",
                                             ce->ce_mode, ce->name);
        }

        if (istate->cache_tree) {
                struct strbuf path = STRBUF_INIT;
                add_cache_tree(istate->cache_tree, revs, &path, flags);
                strbuf_release(&path);
        }
}

void add_index_objects_to_pending(struct rev_info *revs, unsigned int flags)
{
        struct worktree **worktrees, **p;

        repo_read_index(revs->repo);
        do_add_index_objects_to_pending(revs, revs->repo->index, flags);

        if (revs->single_worktree)
                return;

        worktrees = get_worktrees(0);
        for (p = worktrees; *p; p++) {
                struct worktree *wt = *p;
                struct index_state istate = { NULL };

                if (wt->is_current)
                        continue; /* current index already taken care of */

                if (read_index_from(&istate,
                                    worktree_git_path(wt, "index"),
                                    get_worktree_git_dir(wt)) > 0)
                        do_add_index_objects_to_pending(revs, &istate, flags);
                discard_index(&istate);
        }
        free_worktrees(worktrees);
}

struct add_alternate_refs_data {
        struct rev_info *revs;
        unsigned int flags;
};

static void add_one_alternate_ref(const struct object_id *oid,
                                  void *vdata)
{
        const char *name = ".alternate";
        struct add_alternate_refs_data *data = vdata;
        struct object *obj;

        obj = get_reference(data->revs, name, oid, data->flags);
        add_rev_cmdline(data->revs, obj, name, REV_CMD_REV, data->flags);
        add_pending_object(data->revs, obj, name);
}

static void add_alternate_refs_to_pending(struct rev_info *revs,
                                          unsigned int flags)
{
        struct add_alternate_refs_data data;
        data.revs = revs;
        data.flags = flags;
        for_each_alternate_ref(add_one_alternate_ref, &data);
}

static int add_parents_only(struct rev_info *revs, const char *arg_, int flags,
                            int exclude_parent)
{
        struct object_id oid;
        struct object *it;
        struct commit *commit;
        struct commit_list *parents;
        int parent_number;
        const char *arg = arg_;

        if (*arg == '^') {
                flags ^= UNINTERESTING | BOTTOM;
                arg++;
        }
        if (get_oid_committish(arg, &oid))
                return 0;
        while (1) {
                it = get_reference(revs, arg, &oid, 0);
                if (!it && revs->ignore_missing)
                        return 0;
                if (it->type != OBJ_TAG)
                        break;
                if (!((struct tag*)it)->tagged)
                        return 0;
                oidcpy(&oid, &((struct tag*)it)->tagged->oid);
        }
        if (it->type != OBJ_COMMIT)
                return 0;
        commit = (struct commit *)it;
        if (exclude_parent &&
            exclude_parent > commit_list_count(commit->parents))
                return 0;
        for (parents = commit->parents, parent_number = 1;
             parents;
             parents = parents->next, parent_number++) {
                if (exclude_parent && parent_number != exclude_parent)
                        continue;

                it = &parents->item->object;
                it->flags |= flags;
                add_rev_cmdline(revs, it, arg_, REV_CMD_PARENTS_ONLY, flags);
                add_pending_object(revs, it, arg);
        }
        return 1;
}

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

        revs->repo = r;
        revs->abbrev = DEFAULT_ABBREV;
        revs->ignore_merges = 1;
        revs->simplify_history = 1;
        revs->pruning.repo = r;
        revs->pruning.flags.recursive = 1;
        revs->pruning.flags.quick = 1;
        revs->pruning.add_remove = file_add_remove;
        revs->pruning.change = file_change;
        revs->pruning.change_fn_data = revs;
        revs->sort_order = REV_SORT_IN_GRAPH_ORDER;
        revs->dense = 1;
        revs->prefix = prefix;
        revs->max_age = -1;
        revs->min_age = -1;
        revs->skip_count = -1;
        revs->max_count = -1;
        revs->max_parents = -1;
        revs->expand_tabs_in_log = -1;

        revs->commit_format = CMIT_FMT_DEFAULT;
        revs->expand_tabs_in_log_default = 8;

        init_grep_defaults(revs->repo);
        grep_init(&revs->grep_filter, revs->repo, prefix);
        revs->grep_filter.status_only = 1;

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

        init_display_notes(&revs->notes_opt);
}

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, oid_to_hex(&object->oid));
                commit_list = commit_list->next;
        }
}

static void prepare_show_merge(struct rev_info *revs)
{
        struct commit_list *bases;
        struct commit *head, *other;
        struct object_id oid;
        const char **prune = NULL;
        int i, prune_num = 1; /* counting terminating NULL */
        struct index_state *istate = revs->repo->index;

        if (get_oid("HEAD", &oid))
                die("--merge without HEAD?");
        head = lookup_commit_or_die(&oid, "HEAD");
        if (get_oid("MERGE_HEAD", &oid))
                die("--merge without MERGE_HEAD?");
        other = lookup_commit_or_die(&oid, "MERGE_HEAD");
        add_pending_object(revs, &head->object, "HEAD");
        add_pending_object(revs, &other->object, "MERGE_HEAD");
        bases = get_merge_bases(head, other);
        add_rev_cmdline_list(revs, bases, REV_CMD_MERGE_BASE, UNINTERESTING | BOTTOM);
        add_pending_commit_list(revs, bases, UNINTERESTING | BOTTOM);
        free_commit_list(bases);
        head->object.flags |= SYMMETRIC_LEFT;

        if (!istate->cache_nr)
                repo_read_index(revs->repo);
        for (i = 0; i < istate->cache_nr; i++) {
                const struct cache_entry *ce = istate->cache[i];
                if (!ce_stage(ce))
                        continue;
                if (ce_path_match(istate, ce, &revs->prune_data, NULL)) {
                        prune_num++;
                        REALLOC_ARRAY(prune, prune_num);
                        prune[prune_num-2] = ce->name;
                        prune[prune_num-1] = NULL;
                }
                while ((i+1 < istate->cache_nr) &&
                       ce_same_name(ce, istate->cache[i+1]))
                        i++;
        }
        clear_pathspec(&revs->prune_data);
        parse_pathspec(&revs->prune_data, PATHSPEC_ALL_MAGIC & ~PATHSPEC_LITERAL,
                       PATHSPEC_PREFER_FULL | PATHSPEC_LITERAL_PATH, "", prune);
        revs->limited = 1;
}

static int dotdot_missing(const char *arg, char *dotdot,
                          struct rev_info *revs, int symmetric)
{
        if (revs->ignore_missing)
                return 0;
        /* de-munge so we report the full argument */
        *dotdot = '.';
        die(symmetric
            ? "Invalid symmetric difference expression %s"
            : "Invalid revision range %s", arg);
}

static int handle_dotdot_1(const char *arg, char *dotdot,
                           struct rev_info *revs, int flags,
                           int cant_be_filename,
                           struct object_context *a_oc,
                           struct object_context *b_oc)
{
        const char *a_name, *b_name;
        struct object_id a_oid, b_oid;
        struct object *a_obj, *b_obj;
        unsigned int a_flags, b_flags;
        int symmetric = 0;
        unsigned int flags_exclude = flags ^ (UNINTERESTING | BOTTOM);
        unsigned int oc_flags = GET_OID_COMMITTISH | GET_OID_RECORD_PATH;

        a_name = arg;
        if (!*a_name)
                a_name = "HEAD";

        b_name = dotdot + 2;
        if (*b_name == '.') {
                symmetric = 1;
                b_name++;
        }
        if (!*b_name)
                b_name = "HEAD";

        if (get_oid_with_context(revs->repo, a_name, oc_flags, &a_oid, a_oc) ||
            get_oid_with_context(revs->repo, b_name, oc_flags, &b_oid, b_oc))
                return -1;

        if (!cant_be_filename) {
                *dotdot = '.';
                verify_non_filename(revs->prefix, arg);
                *dotdot = '\0';
        }

        a_obj = parse_object(revs->repo, &a_oid);
        b_obj = parse_object(revs->repo, &b_oid);
        if (!a_obj || !b_obj)
                return dotdot_missing(arg, dotdot, revs, symmetric);

        if (!symmetric) {
                /* just A..B */
                b_flags = flags;
                a_flags = flags_exclude;
        } else {
                /* A...B -- find merge bases between the two */
                struct commit *a, *b;
                struct commit_list *exclude;

                a = lookup_commit_reference(revs->repo, &a_obj->oid);
                b = lookup_commit_reference(revs->repo, &b_obj->oid);
                if (!a || !b)
                        return dotdot_missing(arg, dotdot, revs, symmetric);

                exclude = get_merge_bases(a, b);
                add_rev_cmdline_list(revs, exclude, REV_CMD_MERGE_BASE,
                                     flags_exclude);
                add_pending_commit_list(revs, exclude, flags_exclude);
                free_commit_list(exclude);

                b_flags = flags;
                a_flags = flags | SYMMETRIC_LEFT;
        }

        a_obj->flags |= a_flags;
        b_obj->flags |= b_flags;
        add_rev_cmdline(revs, a_obj, a_name, REV_CMD_LEFT, a_flags);
        add_rev_cmdline(revs, b_obj, b_name, REV_CMD_RIGHT, b_flags);
        add_pending_object_with_path(revs, a_obj, a_name, a_oc->mode, a_oc->path);
        add_pending_object_with_path(revs, b_obj, b_name, b_oc->mode, b_oc->path);
        return 0;
}

static int handle_dotdot(const char *arg,
                         struct rev_info *revs, int flags,
                         int cant_be_filename)
{
        struct object_context a_oc, b_oc;
        char *dotdot = strstr(arg, "..");
        int ret;

        if (!dotdot)
                return -1;

        memset(&a_oc, 0, sizeof(a_oc));
        memset(&b_oc, 0, sizeof(b_oc));

        *dotdot = '\0';
        ret = handle_dotdot_1(arg, dotdot, revs, flags, cant_be_filename,
                              &a_oc, &b_oc);
        *dotdot = '.';

        free(a_oc.path);
        free(b_oc.path);

        return ret;
}

int handle_revision_arg(const char *arg_, struct rev_info *revs, int flags, unsigned revarg_opt)
{
        struct object_context oc;
        char *mark;
        struct object *object;
        struct object_id oid;
        int local_flags;
        const char *arg = arg_;
        int cant_be_filename = revarg_opt & REVARG_CANNOT_BE_FILENAME;
        unsigned get_sha1_flags = GET_OID_RECORD_PATH;

        flags = flags & UNINTERESTING ? flags | BOTTOM : flags & ~BOTTOM;

        if (!cant_be_filename && !strcmp(arg, "..")) {
                /*
                 * Just ".."?  That is not a range but the
                 * pathspec for the parent directory.
                 */
                return -1;
        }

        if (!handle_dotdot(arg, revs, flags, revarg_opt))
                return 0;

        mark = strstr(arg, "^@");
        if (mark && !mark[2]) {
                *mark = 0;
                if (add_parents_only(revs, arg, flags, 0))
                        return 0;
                *mark = '^';
        }
        mark = strstr(arg, "^!");
        if (mark && !mark[2]) {
                *mark = 0;
                if (!add_parents_only(revs, arg, flags ^ (UNINTERESTING | BOTTOM), 0))
                        *mark = '^';
        }
        mark = strstr(arg, "^-");
        if (mark) {
                int exclude_parent = 1;

                if (mark[2]) {
                        char *end;
                        exclude_parent = strtoul(mark + 2, &end, 10);
                        if (*end != '\0' || !exclude_parent)
                                return -1;
                }

                *mark = 0;
                if (!add_parents_only(revs, arg, flags ^ (UNINTERESTING | BOTTOM), exclude_parent))
                        *mark = '^';
        }

        local_flags = 0;
        if (*arg == '^') {
                local_flags = UNINTERESTING | BOTTOM;
                arg++;
        }

        if (revarg_opt & REVARG_COMMITTISH)
                get_sha1_flags |= GET_OID_COMMITTISH;

        if (get_oid_with_context(revs->repo, arg, get_sha1_flags, &oid, &oc))
                return revs->ignore_missing ? 0 : -1;
        if (!cant_be_filename)
                verify_non_filename(revs->prefix, arg);
        object = get_reference(revs, arg, &oid, flags ^ local_flags);
        if (!object)
                return revs->ignore_missing ? 0 : -1;
        add_rev_cmdline(revs, object, arg_, REV_CMD_REV, flags ^ local_flags);
        add_pending_object_with_path(revs, object, arg, oc.mode, oc.path);
        free(oc.path);
        return 0;
}

static void read_pathspec_from_stdin(struct strbuf *sb,
                                     struct argv_array *prune)
{
        while (strbuf_getline(sb, stdin) != EOF)
                argv_array_push(prune, sb->buf);
}

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

        save_warning = warn_on_object_refname_ambiguity;
        warn_on_object_refname_ambiguity = 0;

        strbuf_init(&sb, 1000);
        while (strbuf_getline(&sb, stdin) != EOF) {
                int len = sb.len;
                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,
                                        REVARG_CANNOT_BE_FILENAME))
                        die("bad revision '%s'", sb.buf);
        }
        if (seen_dashdash)
                read_pathspec_from_stdin(&sb, prune);

        strbuf_release(&sb);
        warn_on_object_refname_ambiguity = save_warning;
}

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 struct setup_revision_opt* opt)
{
        const char *arg = argv[0];
        const char *optarg;
        int argcount;
        const unsigned hexsz = the_hash_algo->hexsz;

        /* 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") || starts_with(arg, "--glob=") ||
            !strcmp(arg, "--indexed-objects") ||
            !strcmp(arg, "--alternate-refs") ||
            starts_with(arg, "--exclude=") ||
            starts_with(arg, "--branches=") || starts_with(arg, "--tags=") ||
            starts_with(arg, "--remotes=") || starts_with(arg, "--no-walk="))
        {
                unkv[(*unkc)++] = arg;
                return 1;
        }

        if ((argcount = parse_long_opt("max-count", argv, &optarg))) {
                revs->max_count = atoi(optarg);
                revs->no_walk = 0;
                return argcount;
        } else if ((argcount = parse_long_opt("skip", argv, &optarg))) {
                revs->skip_count = atoi(optarg);
                return argcount;
        } else if ((*arg == '-') && isdigit(arg[1])) {
                /* accept -<digit>, like traditional "head" */
                if (strtol_i(arg + 1, 10, &revs->max_count) < 0 ||
                    revs->max_count < 0)
                        die("'%s': not a non-negative integer", arg + 1);
                revs->no_walk = 0;
        } else if (!strcmp(arg, "-n")) {
                if (argc <= 1)
                        return error("-n requires an argument");
                revs->max_count = atoi(argv[1]);
                revs->no_walk = 0;
                return 2;
        } else if (skip_prefix(arg, "-n", &optarg)) {
                revs->max_count = atoi(optarg);
                revs->no_walk = 0;
        } else if ((argcount = parse_long_opt("max-age", argv, &optarg))) {
                revs->max_age = atoi(optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("since", argv, &optarg))) {
                revs->max_age = approxidate(optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("after", argv, &optarg))) {
                revs->max_age = approxidate(optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("min-age", argv, &optarg))) {
                revs->min_age = atoi(optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("before", argv, &optarg))) {
                revs->min_age = approxidate(optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("until", argv, &optarg))) {
                revs->min_age = approxidate(optarg);
                return argcount;
        } else if (!strcmp(arg, "--first-parent")) {
                revs->first_parent_only = 1;
        } else if (!strcmp(arg, "--ancestry-path")) {
                revs->ancestry_path = 1;
                revs->simplify_history = 0;
                revs->limited = 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->sort_order = REV_SORT_IN_GRAPH_ORDER;
                revs->topo_order = 1;
        } else if (!strcmp(arg, "--simplify-merges")) {
                revs->simplify_merges = 1;
                revs->topo_order = 1;
                revs->rewrite_parents = 1;
                revs->simplify_history = 0;
                revs->limited = 1;
        } else if (!strcmp(arg, "--simplify-by-decoration")) {
                revs->simplify_merges = 1;
                revs->topo_order = 1;
                revs->rewrite_parents = 1;
                revs->simplify_history = 0;
                revs->simplify_by_decoration = 1;
                revs->limited = 1;
                revs->prune = 1;
        } else if (!strcmp(arg, "--date-order")) {
                revs->sort_order = REV_SORT_BY_COMMIT_DATE;
                revs->topo_order = 1;
        } else if (!strcmp(arg, "--author-date-order")) {
                revs->sort_order = REV_SORT_BY_AUTHOR_DATE;
                revs->topo_order = 1;
        } else if (!strcmp(arg, "--early-output")) {
                revs->early_output = 100;
                revs->topo_order = 1;
        } else if (skip_prefix(arg, "--early-output=", &optarg)) {
                if (strtoul_ui(optarg, 10, &revs->early_output) < 0)
                        die("'%s': not a non-negative integer", optarg);
                revs->topo_order = 1;
        } 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, "--in-commit-order")) {
                revs->tree_blobs_in_commit_order = 1;
        } else if (!strcmp(arg, "--remove-empty")) {
                revs->remove_empty_trees = 1;
        } else if (!strcmp(arg, "--merges")) {
                revs->min_parents = 2;
        } else if (!strcmp(arg, "--no-merges")) {
                revs->max_parents = 1;
        } else if (skip_prefix(arg, "--min-parents=", &optarg)) {
                revs->min_parents = atoi(optarg);
        } else if (!strcmp(arg, "--no-min-parents")) {
                revs->min_parents = 0;
        } else if (skip_prefix(arg, "--max-parents=", &optarg)) {
                revs->max_parents = atoi(optarg);
        } else if (!strcmp(arg, "--no-max-parents")) {
                revs->max_parents = -1;
        } else if (!strcmp(arg, "--boundary")) {
                revs->boundary = 1;
        } else if (!strcmp(arg, "--left-right")) {
                revs->left_right = 1;
        } else if (!strcmp(arg, "--left-only")) {
                if (revs->right_only)
                        die("--left-only is incompatible with --right-only"
                            " or --cherry");
                revs->left_only = 1;
        } else if (!strcmp(arg, "--right-only")) {
                if (revs->left_only)
                        die("--right-only is incompatible with --left-only");
                revs->right_only = 1;
        } else if (!strcmp(arg, "--cherry")) {
                if (revs->left_only)
                        die("--cherry is incompatible with --left-only");
                revs->cherry_mark = 1;
                revs->right_only = 1;
                revs->max_parents = 1;
                revs->limited = 1;
        } else if (!strcmp(arg, "--count")) {
                revs->count = 1;
        } else if (!strcmp(arg, "--cherry-mark")) {
                if (revs->cherry_pick)
                        die("--cherry-mark is incompatible with --cherry-pick");
                revs->cherry_mark = 1;
                revs->limited = 1; /* needs limit_list() */
        } else if (!strcmp(arg, "--cherry-pick")) {
                if (revs->cherry_mark)
                        die("--cherry-pick is incompatible with --cherry-mark");
                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, "--objects-edge-aggressive")) {
                revs->tag_objects = 1;
                revs->tree_objects = 1;
                revs->blob_objects = 1;
                revs->edge_hint = 1;
                revs->edge_hint_aggressive = 1;
        } else if (!strcmp(arg, "--verify-objects")) {
                revs->tag_objects = 1;
                revs->tree_objects = 1;
                revs->blob_objects = 1;
                revs->verify_objects = 1;
        } else if (!strcmp(arg, "--unpacked")) {
                revs->unpacked = 1;
        } else if (starts_with(arg, "--unpacked=")) {
                die("--unpacked=<packfile> no longer supported.");
        } else if (!strcmp(arg, "-r")) {
                revs->diff = 1;
                revs->diffopt.flags.recursive = 1;
        } else if (!strcmp(arg, "-t")) {
                revs->diff = 1;
                revs->diffopt.flags.recursive = 1;
                revs->diffopt.flags.tree_in_recursive = 1;
        } 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, "--combined-all-paths")) {
                revs->diff = 1;
                revs->combined_all_paths = 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;
                revs->pretty_given = 1;
                get_commit_format(NULL, revs);
        } else if (skip_prefix(arg, "--pretty=", &optarg) ||
                   skip_prefix(arg, "--format=", &optarg)) {
                /*
                 * Detached form ("--pretty X" as opposed to "--pretty=X")
                 * not allowed, since the argument is optional.
                 */
                revs->verbose_header = 1;
                revs->pretty_given = 1;
                get_commit_format(optarg, revs);
        } else if (!strcmp(arg, "--expand-tabs")) {
                revs->expand_tabs_in_log = 8;
        } else if (!strcmp(arg, "--no-expand-tabs")) {
                revs->expand_tabs_in_log = 0;
        } else if (skip_prefix(arg, "--expand-tabs=", &arg)) {
                int val;
                if (strtol_i(arg, 10, &val) < 0 || val < 0)
                        die("'%s': not a non-negative integer", arg);
                revs->expand_tabs_in_log = val;
        } else if (!strcmp(arg, "--show-notes") || !strcmp(arg, "--notes")) {
                enable_default_display_notes(&revs->notes_opt, &revs->show_notes);
                revs->show_notes_given = 1;
        } else if (!strcmp(arg, "--show-signature")) {
                revs->show_signature = 1;
        } else if (!strcmp(arg, "--no-show-signature")) {
                revs->show_signature = 0;
        } else if (!strcmp(arg, "--show-linear-break")) {
                revs->break_bar = "                    ..........";
                revs->track_linear = 1;
                revs->track_first_time = 1;
        } else if (skip_prefix(arg, "--show-linear-break=", &optarg)) {
                revs->break_bar = xstrdup(optarg);
                revs->track_linear = 1;
                revs->track_first_time = 1;
        } else if (skip_prefix(arg, "--show-notes=", &optarg) ||
                   skip_prefix(arg, "--notes=", &optarg)) {
                if (starts_with(arg, "--show-notes=") &&
                    revs->notes_opt.use_default_notes < 0)
                        revs->notes_opt.use_default_notes = 1;
                enable_ref_display_notes(&revs->notes_opt, &revs->show_notes, optarg);
                revs->show_notes_given = 1;
        } else if (!strcmp(arg, "--no-notes")) {
                disable_display_notes(&revs->notes_opt, &revs->show_notes);
                revs->show_notes_given = 1;
        } else if (!strcmp(arg, "--standard-notes")) {
                revs->show_notes_given = 1;
                revs->notes_opt.use_default_notes = 1;
        } else if (!strcmp(arg, "--no-standard-notes")) {
                revs->notes_opt.use_default_notes = 0;
        } else if (!strcmp(arg, "--oneline")) {
                revs->verbose_header = 1;
                get_commit_format("oneline", revs);
                revs->pretty_given = 1;
                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 (skip_prefix(arg, "--abbrev=", &optarg)) {
                revs->abbrev = strtoul(optarg, NULL, 10);
                if (revs->abbrev < MINIMUM_ABBREV)
                        revs->abbrev = MINIMUM_ABBREV;
                else if (revs->abbrev > hexsz)
                        revs->abbrev = hexsz;
        } else if (!strcmp(arg, "--abbrev-commit")) {
                revs->abbrev_commit = 1;
                revs->abbrev_commit_given = 1;
        } else if (!strcmp(arg, "--no-abbrev-commit")) {
                revs->abbrev_commit = 0;
        } 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.type = DATE_RELATIVE;
                revs->date_mode_explicit = 1;
        } else if ((argcount = parse_long_opt("date", argv, &optarg))) {
                parse_date_format(optarg, &revs->date_mode);
                revs->date_mode_explicit = 1;
                return argcount;
        } else if (!strcmp(arg, "--log-size")) {
                revs->show_log_size = 1;
        }
        /*
         * Grepping the commit log
         */
        else if ((argcount = parse_long_opt("author", argv, &optarg))) {
                add_header_grep(revs, GREP_HEADER_AUTHOR, optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("committer", argv, &optarg))) {
                add_header_grep(revs, GREP_HEADER_COMMITTER, optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("grep-reflog", argv, &optarg))) {
                add_header_grep(revs, GREP_HEADER_REFLOG, optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("grep", argv, &optarg))) {
                add_message_grep(revs, optarg);
                return argcount;
        } else if (!strcmp(arg, "--grep-debug")) {
                revs->grep_filter.debug = 1;
        } else if (!strcmp(arg, "--basic-regexp")) {
                revs->grep_filter.pattern_type_option = GREP_PATTERN_TYPE_BRE;
        } else if (!strcmp(arg, "--extended-regexp") || !strcmp(arg, "-E")) {
                revs->grep_filter.pattern_type_option = GREP_PATTERN_TYPE_ERE;
        } else if (!strcmp(arg, "--regexp-ignore-case") || !strcmp(arg, "-i")) {
                revs->grep_filter.ignore_case = 1;
                revs->diffopt.pickaxe_opts |= DIFF_PICKAXE_IGNORE_CASE;
        } else if (!strcmp(arg, "--fixed-strings") || !strcmp(arg, "-F")) {
                revs->grep_filter.pattern_type_option = GREP_PATTERN_TYPE_FIXED;
        } else if (!strcmp(arg, "--perl-regexp") || !strcmp(arg, "-P")) {
                revs->grep_filter.pattern_type_option = GREP_PATTERN_TYPE_PCRE;
        } else if (!strcmp(arg, "--all-match")) {
                revs->grep_filter.all_match = 1;
        } else if (!strcmp(arg, "--invert-grep")) {
                revs->invert_grep = 1;
        } else if ((argcount = parse_long_opt("encoding", argv, &optarg))) {
                if (strcmp(optarg, "none"))
                        git_log_output_encoding = xstrdup(optarg);
                else
                        git_log_output_encoding = "";
                return argcount;
        } else if (!strcmp(arg, "--reverse")) {
                revs->reverse ^= 1;
        } else if (!strcmp(arg, "--children")) {
                revs->children.name = "children";
                revs->limited = 1;
        } else if (!strcmp(arg, "--ignore-missing")) {
                revs->ignore_missing = 1;
        } else if (opt && opt->allow_exclude_promisor_objects &&
                   !strcmp(arg, "--exclude-promisor-objects")) {
                if (fetch_if_missing)
                        BUG("exclude_promisor_objects can only be used when fetch_if_missing is 0");
                revs->exclude_promisor_objects = 1;
        } else {
                int opts = diff_opt_parse(&revs->diffopt, argv, argc, revs->prefix);
                if (!opts)
                        unkv[(*unkc)++] = arg;
                return opts;
        }
        if (revs->graph && revs->track_linear)
                die("--show-linear-break and --graph are incompatible");

        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, NULL);
        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_bisect_ref(struct ref_store *refs, each_ref_fn fn,
                               void *cb_data, const char *term)
{
        struct strbuf bisect_refs = STRBUF_INIT;
        int status;
        strbuf_addf(&bisect_refs, "refs/bisect/%s", term);
        status = refs_for_each_fullref_in(refs, bisect_refs.buf, fn, cb_data, 0);
        strbuf_release(&bisect_refs);
        return status;
}

static int for_each_bad_bisect_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
        return for_each_bisect_ref(refs, fn, cb_data, term_bad);
}

static int for_each_good_bisect_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
        return for_each_bisect_ref(refs, fn, cb_data, term_good);
}

static int handle_revision_pseudo_opt(const char *submodule,
                                struct rev_info *revs,
                                int argc, const char **argv, int *flags)
{
        const char *arg = argv[0];
        const char *optarg;
        struct ref_store *refs;
        int argcount;

        if (submodule) {
                /*
                 * We need some something like get_submodule_worktrees()
                 * before we can go through all worktrees of a submodule,
                 * .e.g with adding all HEADs from --all, which is not
                 * supported right now, so stick to single worktree.
                 */
                if (!revs->single_worktree)
                        BUG("--single-worktree cannot be used together with submodule");
                refs = get_submodule_ref_store(submodule);
        } else
                refs = get_main_ref_store(revs->repo);

        /*
         * NOTE!
         *
         * Commands like "git shortlog" will not accept the options below
         * unless parse_revision_opt queues them (as opposed to erroring
         * out).
         *
         * When implementing your new pseudo-option, remember to
         * register it in the list at the top of handle_revision_opt.
         */
        if (!strcmp(arg, "--all")) {
                handle_refs(refs, revs, *flags, refs_for_each_ref);
                handle_refs(refs, revs, *flags, refs_head_ref);
                if (!revs->single_worktree) {
                        struct all_refs_cb cb;

                        init_all_refs_cb(&cb, revs, *flags);
                        other_head_refs(handle_one_ref, &cb);
                }
                clear_ref_exclusion(&revs->ref_excludes);
        } else if (!strcmp(arg, "--branches")) {
                handle_refs(refs, revs, *flags, refs_for_each_branch_ref);
                clear_ref_exclusion(&revs->ref_excludes);
        } else if (!strcmp(arg, "--bisect")) {
                read_bisect_terms(&term_bad, &term_good);
                handle_refs(refs, revs, *flags, for_each_bad_bisect_ref);
                handle_refs(refs, revs, *flags ^ (UNINTERESTING | BOTTOM),
                            for_each_good_bisect_ref);
                revs->bisect = 1;
        } else if (!strcmp(arg, "--tags")) {
                handle_refs(refs, revs, *flags, refs_for_each_tag_ref);
                clear_ref_exclusion(&revs->ref_excludes);
        } else if (!strcmp(arg, "--remotes")) {
                handle_refs(refs, revs, *flags, refs_for_each_remote_ref);
                clear_ref_exclusion(&revs->ref_excludes);
        } else if ((argcount = parse_long_opt("glob", argv, &optarg))) {
                struct all_refs_cb cb;
                init_all_refs_cb(&cb, revs, *flags);
                for_each_glob_ref(handle_one_ref, optarg, &cb);
                clear_ref_exclusion(&revs->ref_excludes);
                return argcount;
        } else if ((argcount = parse_long_opt("exclude", argv, &optarg))) {
                add_ref_exclusion(&revs->ref_excludes, optarg);
                return argcount;
        } else if (skip_prefix(arg, "--branches=", &optarg)) {
                struct all_refs_cb cb;
                init_all_refs_cb(&cb, revs, *flags);
                for_each_glob_ref_in(handle_one_ref, optarg, "refs/heads/", &cb);
                clear_ref_exclusion(&revs->ref_excludes);
        } else if (skip_prefix(arg, "--tags=", &optarg)) {
                struct all_refs_cb cb;
                init_all_refs_cb(&cb, revs, *flags);
                for_each_glob_ref_in(handle_one_ref, optarg, "refs/tags/", &cb);
                clear_ref_exclusion(&revs->ref_excludes);
        } else if (skip_prefix(arg, "--remotes=", &optarg)) {
                struct all_refs_cb cb;
                init_all_refs_cb(&cb, revs, *flags);
                for_each_glob_ref_in(handle_one_ref, optarg, "refs/remotes/", &cb);
                clear_ref_exclusion(&revs->ref_excludes);
        } else if (!strcmp(arg, "--reflog")) {
                add_reflogs_to_pending(revs, *flags);
        } else if (!strcmp(arg, "--indexed-objects")) {
                add_index_objects_to_pending(revs, *flags);
        } else if (!strcmp(arg, "--alternate-refs")) {
                add_alternate_refs_to_pending(revs, *flags);
        } else if (!strcmp(arg, "--not")) {
                *flags ^= UNINTERESTING | BOTTOM;
        } else if (!strcmp(arg, "--no-walk")) {
                revs->no_walk = REVISION_WALK_NO_WALK_SORTED;
        } else if (skip_prefix(arg, "--no-walk=", &optarg)) {
                /*
                 * Detached form ("--no-walk X" as opposed to "--no-walk=X")
                 * not allowed, since the argument is optional.
                 */
                if (!strcmp(optarg, "sorted"))
                        revs->no_walk = REVISION_WALK_NO_WALK_SORTED;
                else if (!strcmp(optarg, "unsorted"))
                        revs->no_walk = REVISION_WALK_NO_WALK_UNSORTED;
                else
                        return error("invalid argument to --no-walk");
        } else if (!strcmp(arg, "--do-walk")) {
                revs->no_walk = 0;
        } else if (!strcmp(arg, "--single-worktree")) {
                revs->single_worktree = 1;
        } else {
                return 0;
        }

        return 1;
}

static void NORETURN diagnose_missing_default(const char *def)
{
        int flags;
        const char *refname;

        refname = resolve_ref_unsafe(def, 0, NULL, &flags);
        if (!refname || !(flags & REF_ISSYMREF) || (flags & REF_ISBROKEN))
                die(_("your current branch appears to be broken"));

        skip_prefix(refname, "refs/heads/", &refname);
        die(_("your current branch '%s' does not have any commits yet"),
            refname);
}

/*
 * 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, struct setup_revision_opt *opt)
{
        int i, flags, left, seen_dashdash, got_rev_arg = 0, revarg_opt;
        struct argv_array prune_data = ARGV_ARRAY_INIT;
        const char *submodule = NULL;
        int seen_end_of_options = 0;

        if (opt)
                submodule = opt->submodule;

        /* First, search for "--" */
        if (opt && opt->assume_dashdash) {
                seen_dashdash = 1;
        } else {
                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])
                                argv_array_pushv(&prune_data, argv + i + 1);
                        seen_dashdash = 1;
                        break;
                }
        }

        /* Second, deal with arguments and options */
        flags = 0;
        revarg_opt = opt ? opt->revarg_opt : 0;
        if (seen_dashdash)
                revarg_opt |= REVARG_CANNOT_BE_FILENAME;
        for (left = i = 1; i < argc; i++) {
                const char *arg = argv[i];
                if (!seen_end_of_options && *arg == '-') {
                        int opts;

                        opts = handle_revision_pseudo_opt(submodule,
                                                revs, argc - i, argv + i,
                                                &flags);
                        if (opts > 0) {
                                i += opts - 1;
                                continue;
                        }

                        if (!strcmp(arg, "--stdin")) {
                                if (revs->disable_stdin) {
                                        argv[left++] = arg;
                                        continue;
                                }
                                if (revs->read_from_stdin++)
                                        die("--stdin given twice?");
                                read_revisions_from_stdin(revs, &prune_data);
                                continue;
                        }

                        if (!strcmp(arg, "--end-of-options")) {
                                seen_end_of_options = 1;
                                continue;
                        }

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


                if (handle_revision_arg(arg, revs, flags, revarg_opt)) {
                        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], j == i);

                        argv_array_pushv(&prune_data, argv + i);
                        break;
                }
                else
                        got_rev_arg = 1;
        }

        if (prune_data.argc) {
                /*
                 * If we need to introduce the magic "a lone ':' means no
                 * pathspec whatsoever", here is the place to do so.
                 *
                 * if (prune_data.nr == 1 && !strcmp(prune_data[0], ":")) {
                 *      prune_data.nr = 0;
                 *      prune_data.alloc = 0;
                 *      free(prune_data.path);
                 *      prune_data.path = NULL;
                 * } else {
                 *      terminate prune_data.alloc with NULL and
                 *      call init_pathspec() to set revs->prune_data here.
                 * }
                 */
                parse_pathspec(&revs->prune_data, 0, 0,
                               revs->prefix, prune_data.argv);
        }
        argv_array_clear(&prune_data);

        if (revs->def == NULL)
                revs->def = opt ? opt->def : NULL;
        if (opt && opt->tweak)
                opt->tweak(revs, opt);
        if (revs->show_merge)
                prepare_show_merge(revs);
        if (revs->def && !revs->pending.nr && !revs->rev_input_given && !got_rev_arg) {
                struct object_id oid;
                struct object *object;
                struct object_context oc;
                if (get_oid_with_context(revs->repo, revs->def, 0, &oid, &oc))
                        diagnose_missing_default(revs->def);
                object = get_reference(revs, revs->def, &oid, 0);
                add_pending_object_with_mode(revs, object, revs->def, oc.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_opts & DIFF_PICKAXE_KINDS_MASK) ||
            revs->diffopt.filter ||
            revs->diffopt.flags.follow_renames)
                revs->diff = 1;

        if (revs->diffopt.objfind)
                revs->simplify_history = 0;

        if (revs->line_level_traverse) {
                if (want_ancestry(revs))
                        revs->limited = 1;
                revs->topo_order = 1;
        }

        if (revs->topo_order && !generation_numbers_enabled(the_repository))
                revs->limited = 1;

        if (revs->prune_data.nr) {
                copy_pathspec(&revs->pruning.pathspec, &revs->prune_data);
                /* Can't prune commits with rename following: the paths change.. */
                if (!revs->diffopt.flags.follow_renames)
                        revs->prune = 1;
                if (!revs->full_diff)
                        copy_pathspec(&revs->diffopt.pathspec,
                                      &revs->prune_data);
        }
        if (revs->combine_merges)
                revs->ignore_merges = 0;
        if (revs->combined_all_paths && !revs->combine_merges)
                die("--combined-all-paths makes no sense without -c or --cc");

        revs->diffopt.abbrev = revs->abbrev;

        diff_setup_done(&revs->diffopt);

        grep_commit_pattern_type(GREP_PATTERN_TYPE_UNSPECIFIED,
                                 &revs->grep_filter);
        if (!is_encoding_utf8(get_log_output_encoding()))
                revs->grep_filter.ignore_locale = 1;
        compile_grep_patterns(&revs->grep_filter);

        if (revs->reverse && revs->reflog_info)
                die("cannot combine --reverse with --walk-reflogs");
        if (revs->reflog_info && revs->limited)
                die("cannot combine --walk-reflogs with history-limiting options");
        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");
        if (revs->no_walk && revs->graph)
                die("cannot combine --no-walk with --graph");
        if (!revs->reflog_info && revs->grep_filter.use_reflog_filter)
                die("cannot use --grep-reflog without --walk-reflogs");

        if (revs->first_parent_only && revs->bisect)
                die(_("--first-parent is incompatible with --bisect"));

        if (revs->line_level_traverse &&
            (revs->diffopt.output_format & ~(DIFF_FORMAT_PATCH | DIFF_FORMAT_NO_OUTPUT)))
                die(_("-L does not yet support diff formats besides -p and -s"));

        if (revs->expand_tabs_in_log < 0)
                revs->expand_tabs_in_log = revs->expand_tabs_in_log_default;

        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 rev_info *revs, struct commit *commit)
{
        struct treesame_state *ts = lookup_decoration(&revs->treesame, &commit->object);
        struct commit_list **pp, *p;
        int surviving_parents;

        /* Examine existing parents while marking ones we have seen... */
        pp = &commit->parents;
        surviving_parents = 0;
        while ((p = *pp) != NULL) {
                struct commit *parent = p->item;
                if (parent->object.flags & TMP_MARK) {
                        *pp = p->next;
                        if (ts)
                                compact_treesame(revs, commit, surviving_parents);
                        continue;
                }
                parent->object.flags |= TMP_MARK;
                surviving_parents++;
                pp = &p->next;
        }
        /* clear the temporary mark */
        for (p = commit->parents; p; p = p->next) {
                p->item->object.flags &= ~TMP_MARK;
        }
        /* no update_treesame() - removing duplicates can't affect TREESAME */
        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 int mark_redundant_parents(struct commit *commit)
{
        struct commit_list *h = reduce_heads(commit->parents);
        int i = 0, marked = 0;
        struct commit_list *po, *pn;

        /* Want these for sanity-checking only */
        int orig_cnt = commit_list_count(commit->parents);
        int cnt = commit_list_count(h);

        /*
         * Not ready to remove items yet, just mark them for now, based
         * on the output of reduce_heads(). reduce_heads outputs the reduced
         * set in its original order, so this isn't too hard.
         */
        po = commit->parents;
        pn = h;
        while (po) {
                if (pn && po->item == pn->item) {
                        pn = pn->next;
                        i++;
                } else {
                        po->item->object.flags |= TMP_MARK;
                        marked++;
                }
                po=po->next;
        }

        if (i != cnt || cnt+marked != orig_cnt)
                die("mark_redundant_parents %d %d %d %d", orig_cnt, cnt, i, marked);

        free_commit_list(h);

        return marked;
}

static int mark_treesame_root_parents(struct commit *commit)
{
        struct commit_list *p;
        int marked = 0;

        for (p = commit->parents; p; p = p->next) {
                struct commit *parent = p->item;
                if (!parent->parents && (parent->object.flags & TREESAME)) {
                        parent->object.flags |= TMP_MARK;
                        marked++;
                }
        }

        return marked;
}

/*
 * Awkward naming - this means one parent we are TREESAME to.
 * cf mark_treesame_root_parents: root parents that are TREESAME (to an
 * empty tree). Better name suggestions?
 */
static int leave_one_treesame_to_parent(struct rev_info *revs, struct commit *commit)
{
        struct treesame_state *ts = lookup_decoration(&revs->treesame, &commit->object);
        struct commit *unmarked = NULL, *marked = NULL;
        struct commit_list *p;
        unsigned n;

        for (p = commit->parents, n = 0; p; p = p->next, n++) {
                if (ts->treesame[n]) {
                        if (p->item->object.flags & TMP_MARK) {
                                if (!marked)
                                        marked = p->item;
                        } else {
                                if (!unmarked) {
                                        unmarked = p->item;
                                        break;
                                }
                        }
                }
        }

        /*
         * If we are TREESAME to a marked-for-deletion parent, but not to any
         * unmarked parents, unmark the first TREESAME parent. This is the
         * parent that the default simplify_history==1 scan would have followed,
         * and it doesn't make sense to omit that path when asking for a
         * simplified full history. Retaining it improves the chances of
         * understanding odd missed merges that took an old version of a file.
         *
         * Example:
         *
         *   I--------*X       A modified the file, but mainline merge X used
         *    \       /        "-s ours", so took the version from I. X is
         *     `-*A--'         TREESAME to I and !TREESAME to A.
         *
         * Default log from X would produce "I". Without this check,
         * --full-history --simplify-merges would produce "I-A-X", showing
         * the merge commit X and that it changed A, but not making clear that
         * it had just taken the I version. With this check, the topology above
         * is retained.
         *
         * Note that it is possible that the simplification chooses a different
         * TREESAME parent from the default, in which case this test doesn't
         * activate, and we _do_ drop the default parent. Example:
         *
         *   I------X         A modified the file, but it was reverted in B,
         *    \    /          meaning mainline merge X is TREESAME to both
         *    *A-*B           parents.
         *
         * Default log would produce "I" by following the first parent;
         * --full-history --simplify-merges will produce "I-A-B". But this is a
         * reasonable result - it presents a logical full history leading from
         * I to X, and X is not an important merge.
         */
        if (!unmarked && marked) {
                marked->object.flags &= ~TMP_MARK;
                return 1;
        }

        return 0;
}

static int remove_marked_parents(struct rev_info *revs, struct commit *commit)
{
        struct commit_list **pp, *p;
        int nth_parent, removed = 0;

        pp = &commit->parents;
        nth_parent = 0;
        while ((p = *pp) != NULL) {
                struct commit *parent = p->item;
                if (parent->object.flags & TMP_MARK) {
                        parent->object.flags &= ~TMP_MARK;
                        *pp = p->next;
                        free(p);
                        removed++;
                        compact_treesame(revs, commit, nth_parent);
                        continue;
                }
                pp = &p->next;
                nth_parent++;
        }

        /* Removing parents can only increase TREESAMEness */
        if (removed && !(commit->object.flags & TREESAME))
                update_treesame(revs, commit);

        return nth_parent;
}

static struct commit_list **simplify_one(struct rev_info *revs, struct commit *commit, struct commit_list **tail)
{
        struct commit_list *p;
        struct commit *parent;
        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 that matter
         * 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 (revs->first_parent_only)
                        break;
        }
        if (cnt) {
                tail = &commit_list_insert(commit, tail)->next;
                return tail;
        }

        /*
         * Rewrite our list of parents. Note that this cannot
         * affect our TREESAME flags in any way - a commit is
         * always TREESAME to its simplification.
         */
        for (p = commit->parents; p; p = p->next) {
                pst = locate_simplify_state(revs, p->item);
                p->item = pst->simplified;
                if (revs->first_parent_only)
                        break;
        }

        if (revs->first_parent_only)
                cnt = 1;
        else
                cnt = remove_duplicate_parents(revs, 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 parent from that branch
         * will be rewritten to be the merge base.
         *
         *      o----X          X: the commit we are looking at;
         *     /    /           o: a commit that touches the paths;
         * ---o----'
         *
         * Further, a merge of an independent branch that doesn't
         * touch the path will reduce to a treesame root parent:
         *
         *  ----o----X          X: the commit we are looking at;
         *          /           o: a commit that touches the paths;
         *         r            r: a root commit not touching the paths
         *
         * Detect and simplify both cases.
         */
        if (1 < cnt) {
                int marked = mark_redundant_parents(commit);
                marked += mark_treesame_root_parents(commit);
                if (marked)
                        marked -= leave_one_treesame_to_parent(revs, commit);
                if (marked)
                        cnt = remove_marked_parents(revs, commit);
        }

        /*
         * 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 don't simplify to one relevant commit
         * (the first two cases are already handled at the beginning of
         * this function).
         *
         * Otherwise, it simplifies to what its sole relevant parent
         * simplifies to.
         */
        if (!cnt ||
            (commit->object.flags & UNINTERESTING) ||
            !(commit->object.flags & TREESAME) ||
            (parent = one_relevant_parent(revs, commit->parents)) == NULL)
                st->simplified = commit;
        else {
                pst = locate_simplify_state(revs, parent);
                st->simplified = pst->simplified;
        }
        return tail;
}

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

        if (!revs->prune)
                return;

        /* feed the list reversed */
        yet_to_do = NULL;
        for (list = revs->commits; list; list = next) {
                commit = list->item;
                next = list->next;
                /*
                 * Do not free(list) here yet; the original list
                 * is used later in this function.
                 */
                commit_list_insert(commit, &yet_to_do);
        }
        while (yet_to_do) {
                list = yet_to_do;
                yet_to_do = NULL;
                tail = &yet_to_do;
                while (list) {
                        commit = pop_commit(&list);
                        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 merge_simplify_state *st;

                commit = pop_commit(&list);
                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);
        }
}

void reset_revision_walk(void)
{
        clear_object_flags(SEEN | ADDED | SHOWN | TOPO_WALK_EXPLORED | TOPO_WALK_INDEGREE);
}

static int mark_uninteresting(const struct object_id *oid,
                              struct packed_git *pack,
                              uint32_t pos,
                              void *cb)
{
        struct rev_info *revs = cb;
        struct object *o = parse_object(revs->repo, oid);
        o->flags |= UNINTERESTING | SEEN;
        return 0;
}

define_commit_slab(indegree_slab, int);
define_commit_slab(author_date_slab, timestamp_t);

struct topo_walk_info {
        uint32_t min_generation;
        struct prio_queue explore_queue;
        struct prio_queue indegree_queue;
        struct prio_queue topo_queue;
        struct indegree_slab indegree;
        struct author_date_slab author_date;
};

static inline void test_flag_and_insert(struct prio_queue *q, struct commit *c, int flag)
{
        if (c->object.flags & flag)
                return;

        c->object.flags |= flag;
        prio_queue_put(q, c);
}

static void explore_walk_step(struct rev_info *revs)
{
        struct topo_walk_info *info = revs->topo_walk_info;
        struct commit_list *p;
        struct commit *c = prio_queue_get(&info->explore_queue);

        if (!c)
                return;

        if (parse_commit_gently(c, 1) < 0)
                return;

        if (revs->sort_order == REV_SORT_BY_AUTHOR_DATE)
                record_author_date(&info->author_date, c);

        if (revs->max_age != -1 && (c->date < revs->max_age))
                c->object.flags |= UNINTERESTING;

        if (process_parents(revs, c, NULL, NULL) < 0)
                return;

        if (c->object.flags & UNINTERESTING)
                mark_parents_uninteresting(c);

        for (p = c->parents; p; p = p->next)
                test_flag_and_insert(&info->explore_queue, p->item, TOPO_WALK_EXPLORED);
}

static void explore_to_depth(struct rev_info *revs,
                             uint32_t gen_cutoff)
{
        struct topo_walk_info *info = revs->topo_walk_info;
        struct commit *c;
        while ((c = prio_queue_peek(&info->explore_queue)) &&
               c->generation >= gen_cutoff)
                explore_walk_step(revs);
}

static void indegree_walk_step(struct rev_info *revs)
{
        struct commit_list *p;
        struct topo_walk_info *info = revs->topo_walk_info;
        struct commit *c = prio_queue_get(&info->indegree_queue);

        if (!c)
                return;

        if (parse_commit_gently(c, 1) < 0)
                return;

        explore_to_depth(revs, c->generation);

        for (p = c->parents; p; p = p->next) {
                struct commit *parent = p->item;
                int *pi = indegree_slab_at(&info->indegree, parent);

                if (*pi)
                        (*pi)++;
                else
                        *pi = 2;

                test_flag_and_insert(&info->indegree_queue, parent, TOPO_WALK_INDEGREE);

                if (revs->first_parent_only)
                        return;
        }
}

static void compute_indegrees_to_depth(struct rev_info *revs,
                                       uint32_t gen_cutoff)
{
        struct topo_walk_info *info = revs->topo_walk_info;
        struct commit *c;
        while ((c = prio_queue_peek(&info->indegree_queue)) &&
               c->generation >= gen_cutoff)
                indegree_walk_step(revs);
}

static void reset_topo_walk(struct rev_info *revs)
{
        struct topo_walk_info *info = revs->topo_walk_info;

        clear_prio_queue(&info->explore_queue);
        clear_prio_queue(&info->indegree_queue);
        clear_prio_queue(&info->topo_queue);
        clear_indegree_slab(&info->indegree);
        clear_author_date_slab(&info->author_date);

        FREE_AND_NULL(revs->topo_walk_info);
}

static void init_topo_walk(struct rev_info *revs)
{
        struct topo_walk_info *info;
        struct commit_list *list;
        if (revs->topo_walk_info)
                reset_topo_walk(revs);

        revs->topo_walk_info = xmalloc(sizeof(struct topo_walk_info));
        info = revs->topo_walk_info;
        memset(info, 0, sizeof(struct topo_walk_info));

        init_indegree_slab(&info->indegree);
        memset(&info->explore_queue, 0, sizeof(info->explore_queue));
        memset(&info->indegree_queue, 0, sizeof(info->indegree_queue));
        memset(&info->topo_queue, 0, sizeof(info->topo_queue));

        switch (revs->sort_order) {
        default: /* REV_SORT_IN_GRAPH_ORDER */
                info->topo_queue.compare = NULL;
                break;
        case REV_SORT_BY_COMMIT_DATE:
                info->topo_queue.compare = compare_commits_by_commit_date;
                break;
        case REV_SORT_BY_AUTHOR_DATE:
                init_author_date_slab(&info->author_date);
                info->topo_queue.compare = compare_commits_by_author_date;
                info->topo_queue.cb_data = &info->author_date;
                break;
        }

        info->explore_queue.compare = compare_commits_by_gen_then_commit_date;
        info->indegree_queue.compare = compare_commits_by_gen_then_commit_date;

        info->min_generation = GENERATION_NUMBER_INFINITY;
        for (list = revs->commits; list; list = list->next) {
                struct commit *c = list->item;

                if (parse_commit_gently(c, 1))
                        continue;

                test_flag_and_insert(&info->explore_queue, c, TOPO_WALK_EXPLORED);
                test_flag_and_insert(&info->indegree_queue, c, TOPO_WALK_INDEGREE);

                if (c->generation < info->min_generation)
                        info->min_generation = c->generation;

                *(indegree_slab_at(&info->indegree, c)) = 1;

                if (revs->sort_order == REV_SORT_BY_AUTHOR_DATE)
                        record_author_date(&info->author_date, c);
        }
        compute_indegrees_to_depth(revs, info->min_generation);

        for (list = revs->commits; list; list = list->next) {
                struct commit *c = list->item;

                if (*(indegree_slab_at(&info->indegree, c)) == 1)
                        prio_queue_put(&info->topo_queue, c);
        }

        /*
         * This is unfortunate; the initial tips need to be shown
         * in the order given from the revision traversal machinery.
         */
        if (revs->sort_order == REV_SORT_IN_GRAPH_ORDER)
                prio_queue_reverse(&info->topo_queue);
}

static struct commit *next_topo_commit(struct rev_info *revs)
{
        struct commit *c;
        struct topo_walk_info *info = revs->topo_walk_info;

        /* pop next off of topo_queue */
        c = prio_queue_get(&info->topo_queue);

        if (c)
                *(indegree_slab_at(&info->indegree, c)) = 0;

        return c;
}

static void expand_topo_walk(struct rev_info *revs, struct commit *commit)
{
        struct commit_list *p;
        struct topo_walk_info *info = revs->topo_walk_info;
        if (process_parents(revs, commit, NULL, NULL) < 0) {
                if (!revs->ignore_missing_links)
                        die("Failed to traverse parents of commit %s",
                            oid_to_hex(&commit->object.oid));
        }

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

                if (parent->object.flags & UNINTERESTING)
                        continue;

                if (parse_commit_gently(parent, 1) < 0)
                        continue;

                if (parent->generation < info->min_generation) {
                        info->min_generation = parent->generation;
                        compute_indegrees_to_depth(revs, info->min_generation);
                }

                pi = indegree_slab_at(&info->indegree, parent);

                (*pi)--;
                if (*pi == 1)
                        prio_queue_put(&info->topo_queue, parent);

                if (revs->first_parent_only)
                        return;
        }
}

int prepare_revision_walk(struct rev_info *revs)
{
        int i;
        struct object_array old_pending;
        struct commit_list **next = &revs->commits;

        memcpy(&old_pending, &revs->pending, sizeof(old_pending));
        revs->pending.nr = 0;
        revs->pending.alloc = 0;
        revs->pending.objects = NULL;
        for (i = 0; i < old_pending.nr; i++) {
                struct object_array_entry *e = old_pending.objects + i;
                struct commit *commit = handle_commit(revs, e);
                if (commit) {
                        if (!(commit->object.flags & SEEN)) {
                                commit->object.flags |= SEEN;
                                next = commit_list_append(commit, next);
                        }
                }
        }
        object_array_clear(&old_pending);

        /* Signal whether we need per-parent treesame decoration */
        if (revs->simplify_merges ||
            (revs->limited && limiting_can_increase_treesame(revs)))
                revs->treesame.name = "treesame";

        if (revs->exclude_promisor_objects) {
                for_each_packed_object(mark_uninteresting, revs,
                                       FOR_EACH_OBJECT_PROMISOR_ONLY);
        }

        if (!revs->reflog_info)
                prepare_to_use_bloom_filter(revs);
        if (revs->no_walk != REVISION_WALK_NO_WALK_UNSORTED)
                commit_list_sort_by_date(&revs->commits);
        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->sort_order);
        } else if (revs->topo_order)
                init_topo_walk(revs);
        if (revs->line_level_traverse && want_ancestry(revs))
                /*
                 * At the moment we can only do line-level log with parent
                 * rewriting by performing this expensive pre-filtering step.
                 * If parent rewriting is not requested, then we rather
                 * perform the line-level log filtering during the regular
                 * history traversal.
                 */
                line_log_filter(revs);
        if (revs->simplify_merges)
                simplify_merges(revs);
        if (revs->children.name)
                set_children(revs);

        return 0;
}

static enum rewrite_result rewrite_one_1(struct rev_info *revs,
                                         struct commit **pp,
                                         struct prio_queue *queue)
{
        for (;;) {
                struct commit *p = *pp;
                if (!revs->limited)
                        if (process_parents(revs, p, NULL, queue) < 0)
                                return rewrite_one_error;
                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;
                if ((p = one_relevant_parent(revs, p->parents)) == NULL)
                        return rewrite_one_ok;
                *pp = p;
        }
}

static void merge_queue_into_list(struct prio_queue *q, struct commit_list **list)
{
        while (q->nr) {
                struct commit *item = prio_queue_peek(q);
                struct commit_list *p = *list;

                if (p && p->item->date >= item->date)
                        list = &p->next;
                else {
                        p = commit_list_insert(item, list);
                        list = &p->next; /* skip newly added item */
                        prio_queue_get(q); /* pop item */
                }
        }
}

static enum rewrite_result rewrite_one(struct rev_info *revs, struct commit **pp)
{
        struct prio_queue queue = { compare_commits_by_commit_date };
        enum rewrite_result ret = rewrite_one_1(revs, pp, &queue);
        merge_queue_into_list(&queue, &revs->commits);
        clear_prio_queue(&queue);
        return ret;
}

int rewrite_parents(struct rev_info *revs, struct commit *commit,
        rewrite_parent_fn_t rewrite_parent)
{
        struct commit_list **pp = &commit->parents;
        while (*pp) {
                struct commit_list *parent = *pp;
                switch (rewrite_parent(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(revs, commit);
        return 0;
}

static int commit_rewrite_person(struct strbuf *buf, const char *what, struct string_list *mailmap)
{
        char *person, *endp;
        size_t len, namelen, maillen;
        const char *name;
        const char *mail;
        struct ident_split ident;

        person = strstr(buf->buf, what);
        if (!person)
                return 0;

        person += strlen(what);
        endp = strchr(person, '\n');
        if (!endp)
                return 0;

        len = endp - person;

        if (split_ident_line(&ident, person, len))
                return 0;

        mail = ident.mail_begin;
        maillen = ident.mail_end - ident.mail_begin;
        name = ident.name_begin;
        namelen = ident.name_end - ident.name_begin;

        if (map_user(mailmap, &mail, &maillen, &name, &namelen)) {
                struct strbuf namemail = STRBUF_INIT;

                strbuf_addf(&namemail, "%.*s <%.*s>",
                            (int)namelen, name, (int)maillen, mail);

                strbuf_splice(buf, ident.name_begin - buf->buf,
                              ident.mail_end - ident.name_begin + 1,
                              namemail.buf, namemail.len);

                strbuf_release(&namemail);

                return 1;
        }

        return 0;
}

static int commit_match(struct commit *commit, struct rev_info *opt)
{
        int retval;
        const char *encoding;
        const char *message;
        struct strbuf buf = STRBUF_INIT;

        if (!opt->grep_filter.pattern_list && !opt->grep_filter.header_list)
                return 1;

        /* Prepend "fake" headers as needed */
        if (opt->grep_filter.use_reflog_filter) {
                strbuf_addstr(&buf, "reflog ");
                get_reflog_message(&buf, opt->reflog_info);
                strbuf_addch(&buf, '\n');
        }

        /*
         * We grep in the user's output encoding, under the assumption that it
         * is the encoding they are most likely to write their grep pattern
         * for. In addition, it means we will match the "notes" encoding below,
         * so we will not end up with a buffer that has two different encodings
         * in it.
         */
        encoding = get_log_output_encoding();
        message = logmsg_reencode(commit, NULL, encoding);

        /* Copy the commit to temporary if we are using "fake" headers */
        if (buf.len)
                strbuf_addstr(&buf, message);

        if (opt->grep_filter.header_list && opt->mailmap) {
                if (!buf.len)
                        strbuf_addstr(&buf, message);

                commit_rewrite_person(&buf, "\nauthor ", opt->mailmap);
                commit_rewrite_person(&buf, "\ncommitter ", opt->mailmap);
        }

        /* Append "fake" message parts as needed */
        if (opt->show_notes) {
                if (!buf.len)
                        strbuf_addstr(&buf, message);
                format_display_notes(&commit->object.oid, &buf, encoding, 1);
        }

        /*
         * Find either in the original commit message, or in the temporary.
         * Note that we cast away the constness of "message" here. It is
         * const because it may come from the cached commit buffer. That's OK,
         * because we know that it is modifiable heap memory, and that while
         * grep_buffer may modify it for speed, it will restore any
         * changes before returning.
         */
        if (buf.len)
                retval = grep_buffer(&opt->grep_filter, buf.buf, buf.len);
        else
                retval = grep_buffer(&opt->grep_filter,
                                     (char *)message, strlen(message));
        strbuf_release(&buf);
        unuse_commit_buffer(commit, message);
        return opt->invert_grep ? !retval : retval;
}

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

/*
 * Return a timestamp to be used for --since/--until comparisons for this
 * commit, based on the revision options.
 */
static timestamp_t comparison_date(const struct rev_info *revs,
                                   struct commit *commit)
{
        return revs->reflog_info ?
                get_reflog_timestamp(revs->reflog_info) :
                commit->date;
}

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_object_pack(&commit->object.oid))
                return commit_ignore;
        if (commit->object.flags & UNINTERESTING)
                return commit_ignore;
        if (revs->line_level_traverse && !want_ancestry(revs)) {
                /*
                 * In case of line-level log with parent rewriting
                 * prepare_revision_walk() already took care of all line-level
                 * log filtering, and there is nothing left to do here.
                 *
                 * If parent rewriting was not requested, then this is the
                 * place to perform the line-level log filtering.  Notably,
                 * this check, though expensive, must come before the other,
                 * cheaper filtering conditions, because the tracked line
                 * ranges must be adjusted even when the commit will end up
                 * being ignored based on other conditions.
                 */
                if (!line_log_process_ranges_arbitrary_commit(revs, commit))
                        return commit_ignore;
        }
        if (revs->min_age != -1 &&
            comparison_date(revs, commit) > revs->min_age)
                        return commit_ignore;
        if (revs->min_parents || (revs->max_parents >= 0)) {
                int n = commit_list_count(commit->parents);
                if ((n < revs->min_parents) ||
                    ((revs->max_parents >= 0) && (n > revs->max_parents)))
                        return commit_ignore;
        }
        if (!commit_match(commit, revs))
                return commit_ignore;
        if (revs->prune && revs->dense) {
                /* Commit without changes? */
                if (commit->object.flags & TREESAME) {
                        int n;
                        struct commit_list *p;
                        /* drop merges unless we want parenthood */
                        if (!want_ancestry(revs))
                                return commit_ignore;
                        /*
                         * If we want ancestry, then need to keep any merges
                         * between relevant commits to tie together topology.
                         * For consistency with TREESAME and simplification
                         * use "relevant" here rather than just INTERESTING,
                         * to treat bottom commit(s) as part of the topology.
                         */
                        for (n = 0, p = commit->parents; p; p = p->next)
                                if (relevant_commit(p->item))
                                        if (++n >= 2)
                                                return commit_show;
                        return commit_ignore;
                }
        }
        return commit_show;
}

define_commit_slab(saved_parents, struct commit_list *);

#define EMPTY_PARENT_LIST ((struct commit_list *)-1)

/*
 * You may only call save_parents() once per commit (this is checked
 * for non-root commits).
 */
static void save_parents(struct rev_info *revs, struct commit *commit)
{
        struct commit_list **pp;

        if (!revs->saved_parents_slab) {
                revs->saved_parents_slab = xmalloc(sizeof(struct saved_parents));
                init_saved_parents(revs->saved_parents_slab);
        }

        pp = saved_parents_at(revs->saved_parents_slab, commit);

        /*
         * When walking with reflogs, we may visit the same commit
         * several times: once for each appearance in the reflog.
         *
         * In this case, save_parents() will be called multiple times.
         * We want to keep only the first set of parents.  We need to
         * store a sentinel value for an empty (i.e., NULL) parent
         * list to distinguish it from a not-yet-saved list, however.
         */
        if (*pp)
                return;
        if (commit->parents)
                *pp = copy_commit_list(commit->parents);
        else
                *pp = EMPTY_PARENT_LIST;
}

static void free_saved_parents(struct rev_info *revs)
{
        if (revs->saved_parents_slab)
                clear_saved_parents(revs->saved_parents_slab);
}

struct commit_list *get_saved_parents(struct rev_info *revs, const struct commit *commit)
{
        struct commit_list *parents;

        if (!revs->saved_parents_slab)
                return commit->parents;

        parents = *saved_parents_at(revs->saved_parents_slab, commit);
        if (parents == EMPTY_PARENT_LIST)
                return NULL;
        return parents;
}

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->prune && revs->dense && want_ancestry(revs)) {
                /*
                 * --full-diff on simplified parents is no good: it
                 * will show spurious changes from the commits that
                 * were elided.  So we save the parents on the side
                 * when --full-diff is in effect.
                 */
                if (revs->full_diff)
                        save_parents(revs, commit);
                if (rewrite_parents(revs, commit, rewrite_one) < 0)
                        return commit_error;
        }
        return action;
}

static void track_linear(struct rev_info *revs, struct commit *commit)
{
        if (revs->track_first_time) {
                revs->linear = 1;
                revs->track_first_time = 0;
        } else {
                struct commit_list *p;
                for (p = revs->previous_parents; p; p = p->next)
                        if (p->item == NULL || /* first commit */
                            oideq(&p->item->object.oid, &commit->object.oid))
                                break;
                revs->linear = p != NULL;
        }
        if (revs->reverse) {
                if (revs->linear)
                        commit->object.flags |= TRACK_LINEAR;
        }
        free_commit_list(revs->previous_parents);
        revs->previous_parents = copy_commit_list(commit->parents);
}

static struct commit *get_revision_1(struct rev_info *revs)
{
        while (1) {
                struct commit *commit;

                if (revs->reflog_info)
                        commit = next_reflog_entry(revs->reflog_info);
                else if (revs->topo_walk_info)
                        commit = next_topo_commit(revs);
                else
                        commit = pop_commit(&revs->commits);

                if (!commit)
                        return NULL;

                if (revs->reflog_info)
                        commit->object.flags &= ~(ADDED | SEEN | SHOWN);

                /*
                 * 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 &&
                            comparison_date(revs, commit) < revs->max_age)
                                continue;

                        if (revs->reflog_info)
                                try_to_simplify_commit(revs, commit);
                        else if (revs->topo_walk_info)
                                expand_topo_walk(revs, commit);
                        else if (process_parents(revs, commit, &revs->commits, NULL) < 0) {
                                if (!revs->ignore_missing_links)
                                        die("Failed to traverse parents of commit %s",
                                                oid_to_hex(&commit->object.oid));
                        }
                }

                switch (simplify_commit(revs, commit)) {
                case commit_ignore:
                        continue;
                case commit_error:
                        die("Failed to simplify parents of commit %s",
                            oid_to_hex(&commit->object.oid));
                default:
                        if (revs->track_linear)
                                track_linear(revs, commit);
                        return commit;
                }
        }
}

/*
 * Return true for entries that have not yet been shown.  (This is an
 * object_array_each_func_t.)
 */
static int entry_unshown(struct object_array_entry *entry, void *cb_data_unused)
{
        return !(entry->item->flags & SHOWN);
}

/*
 * If array is on the verge of a realloc, garbage-collect any entries
 * that have already been shown to try to free up some space.
 */
static void gc_boundary(struct object_array *array)
{
        if (array->nr == array->alloc)
                object_array_filter(array, entry_unshown, NULL);
}

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->sort_order);
}

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;
        }

        /*
         * If our max_count counter has reached zero, then we are done. We
         * don't simply return NULL because we still might need to show
         * boundary commits. But we want to avoid calling get_revision_1, which
         * might do a considerable amount of work finding the next commit only
         * for us to throw it away.
         *
         * If it is non-zero, then either we don't have a max_count at all
         * (-1), or it is still counting, in which case we decrement.
         */
        if (revs->max_count) {
                c = get_revision_1(revs);
                if (c) {
                        while (revs->skip_count > 0) {
                                revs->skip_count--;
                                c = get_revision_1(revs);
                                if (!c)
                                        break;
                        }
                }

                if (revs->max_count > 0)
                        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) {
                c = pop_commit(&revs->commits);
                if (revs->track_linear)
                        revs->linear = !!(c && c->object.flags & TRACK_LINEAR);
                return c;
        }

        c = get_revision_internal(revs);
        if (c && revs->graph)
                graph_update(revs->graph, c);
        if (!c) {
                free_saved_parents(revs);
                if (revs->previous_parents) {
                        free_commit_list(revs->previous_parents);
                        revs->previous_parents = NULL;
                }
        }
        return c;
}

const char *get_revision_mark(const struct rev_info *revs, const struct commit *commit)
{
        if (commit->object.flags & BOUNDARY)
                return "-";
        else if (commit->object.flags & UNINTERESTING)
                return "^";
        else if (commit->object.flags & PATCHSAME)
                return "=";
        else if (!revs || revs->left_right) {
                if (commit->object.flags & SYMMETRIC_LEFT)
                        return "<";
                else
                        return ">";
        } else if (revs->graph)
                return "*";
        else if (revs->cherry_mark)
                return "+";
        return "";
}

void put_revision_mark(const struct rev_info *revs, const struct commit *commit)
{
        const char *mark = get_revision_mark(revs, commit);
        if (!strlen(mark))
                return;
        fputs(mark, stdout);
        putchar(' ');
}