The eleventh batch

[alt-git.git] / commit.c

#include "git-compat-util.h"
#include "tag.h"
#include "commit.h"
#include "commit-graph.h"
#include "environment.h"
#include "gettext.h"
#include "hex.h"
#include "repository.h"
#include "object-name.h"
#include "object-store-ll.h"
#include "utf8.h"
#include "diff.h"
#include "revision.h"
#include "notes.h"
#include "alloc.h"
#include "gpg-interface.h"
#include "mergesort.h"
#include "commit-slab.h"
#include "prio-queue.h"
#include "hash-lookup.h"
#include "wt-status.h"
#include "advice.h"
#include "refs.h"
#include "commit-reach.h"
#include "setup.h"
#include "shallow.h"
#include "tree.h"
#include "hook.h"
#include "parse.h"

static struct commit_extra_header *read_commit_extra_header_lines(const char *buf, size_t len, const char **);

int save_commit_buffer = 1;
int no_graft_file_deprecated_advice;

const char *commit_type = "commit";

struct commit *lookup_commit_reference_gently(struct repository *r,
                const struct object_id *oid, int quiet)
{
        struct object *obj = deref_tag(r,
                                       parse_object(r, oid),
                                       NULL, 0);

        if (!obj)
                return NULL;
        return object_as_type(obj, OBJ_COMMIT, quiet);
}

struct commit *lookup_commit_reference(struct repository *r, const struct object_id *oid)
{
        return lookup_commit_reference_gently(r, oid, 0);
}

struct commit *lookup_commit_or_die(const struct object_id *oid, const char *ref_name)
{
        struct commit *c = lookup_commit_reference(the_repository, oid);
        if (!c)
                die(_("could not parse %s"), ref_name);
        if (!oideq(oid, &c->object.oid)) {
                warning(_("%s %s is not a commit!"),
                        ref_name, oid_to_hex(oid));
        }
        return c;
}

struct commit *lookup_commit_object(struct repository *r,
                                    const struct object_id *oid)
{
        struct object *obj = parse_object(r, oid);
        return obj ? object_as_type(obj, OBJ_COMMIT, 0) : NULL;

}

struct commit *lookup_commit(struct repository *r, const struct object_id *oid)
{
        struct object *obj = lookup_object(r, oid);
        if (!obj)
                return create_object(r, oid, alloc_commit_node(r));
        return object_as_type(obj, OBJ_COMMIT, 0);
}

struct commit *lookup_commit_reference_by_name(const char *name)
{
        struct object_id oid;
        struct commit *commit;

        if (repo_get_oid_committish(the_repository, name, &oid))
                return NULL;
        commit = lookup_commit_reference(the_repository, &oid);
        if (repo_parse_commit(the_repository, commit))
                return NULL;
        return commit;
}

static timestamp_t parse_commit_date(const char *buf, const char *tail)
{
        const char *dateptr;
        const char *eol;

        if (buf + 6 >= tail)
                return 0;
        if (memcmp(buf, "author", 6))
                return 0;
        while (buf < tail && *buf++ != '\n')
                /* nada */;
        if (buf + 9 >= tail)
                return 0;
        if (memcmp(buf, "committer", 9))
                return 0;

        /*
         * Jump to end-of-line so that we can walk backwards to find the
         * end-of-email ">". This is more forgiving of malformed cases
         * because unexpected characters tend to be in the name and email
         * fields.
         */
        eol = memchr(buf, '\n', tail - buf);
        if (!eol)
                return 0;
        dateptr = eol;
        while (dateptr > buf && dateptr[-1] != '>')
                dateptr--;
        if (dateptr == buf)
                return 0;

        /*
         * Trim leading whitespace, but make sure we have at least one
         * non-whitespace character, as parse_timestamp() will otherwise walk
         * right past the newline we found in "eol" when skipping whitespace
         * itself.
         *
         * In theory it would be sufficient to allow any character not matched
         * by isspace(), but there's a catch: our isspace() does not
         * necessarily match the behavior of parse_timestamp(), as the latter
         * is implemented by system routines which match more exotic control
         * codes, or even locale-dependent sequences.
         *
         * Since we expect the timestamp to be a number, we can check for that.
         * Anything else (e.g., a non-numeric token like "foo") would just
         * cause parse_timestamp() to return 0 anyway.
         */
        while (dateptr < eol && isspace(*dateptr))
                dateptr++;
        if (!isdigit(*dateptr) && *dateptr != '-')
                return 0;

        /*
         * We know there is at least one digit (or dash), so we'll begin
         * parsing there and stop at worst case at eol.
         *
         * Note that we may feed parse_timestamp() extra characters here if the
         * commit is malformed, and it will parse as far as it can. For
         * example, "123foo456" would return "123". That might be questionable
         * (versus returning "0"), but it would help in a hypothetical case
         * like "123456+0100", where the whitespace from the timezone is
         * missing. Since such syntactic errors may be baked into history and
         * hard to correct now, let's err on trying to make our best guess
         * here, rather than insist on perfect syntax.
         */
        return parse_timestamp(dateptr, NULL, 10);
}

static const struct object_id *commit_graft_oid_access(size_t index, const void *table)
{
        const struct commit_graft * const *commit_graft_table = table;
        return &commit_graft_table[index]->oid;
}

int commit_graft_pos(struct repository *r, const struct object_id *oid)
{
        return oid_pos(oid, r->parsed_objects->grafts,
                       r->parsed_objects->grafts_nr,
                       commit_graft_oid_access);
}

static void unparse_commit(struct repository *r, const struct object_id *oid)
{
        struct commit *c = lookup_commit(r, oid);

        if (!c->object.parsed)
                return;
        free_commit_list(c->parents);
        c->parents = NULL;
        c->object.parsed = 0;
}

int register_commit_graft(struct repository *r, struct commit_graft *graft,
                          int ignore_dups)
{
        int pos = commit_graft_pos(r, &graft->oid);

        if (0 <= pos) {
                if (ignore_dups)
                        free(graft);
                else {
                        free(r->parsed_objects->grafts[pos]);
                        r->parsed_objects->grafts[pos] = graft;
                }
                return 1;
        }
        pos = -pos - 1;
        ALLOC_GROW(r->parsed_objects->grafts,
                   r->parsed_objects->grafts_nr + 1,
                   r->parsed_objects->grafts_alloc);
        r->parsed_objects->grafts_nr++;
        if (pos < r->parsed_objects->grafts_nr)
                memmove(r->parsed_objects->grafts + pos + 1,
                        r->parsed_objects->grafts + pos,
                        (r->parsed_objects->grafts_nr - pos - 1) *
                        sizeof(*r->parsed_objects->grafts));
        r->parsed_objects->grafts[pos] = graft;
        unparse_commit(r, &graft->oid);
        return 0;
}

struct commit_graft *read_graft_line(struct strbuf *line)
{
        /* The format is just "Commit Parent1 Parent2 ...\n" */
        int i, phase;
        const char *tail = NULL;
        struct commit_graft *graft = NULL;
        struct object_id dummy_oid, *oid;

        strbuf_rtrim(line);
        if (!line->len || line->buf[0] == '#')
                return NULL;
        /*
         * phase 0 verifies line, counts hashes in line and allocates graft
         * phase 1 fills graft
         */
        for (phase = 0; phase < 2; phase++) {
                oid = graft ? &graft->oid : &dummy_oid;
                if (parse_oid_hex(line->buf, oid, &tail))
                        goto bad_graft_data;
                for (i = 0; *tail != '\0'; i++) {
                        oid = graft ? &graft->parent[i] : &dummy_oid;
                        if (!isspace(*tail++) || parse_oid_hex(tail, oid, &tail))
                                goto bad_graft_data;
                }
                if (!graft) {
                        graft = xmalloc(st_add(sizeof(*graft),
                                               st_mult(sizeof(struct object_id), i)));
                        graft->nr_parent = i;
                }
        }
        return graft;

bad_graft_data:
        error("bad graft data: %s", line->buf);
        assert(!graft);
        return NULL;
}

static int read_graft_file(struct repository *r, const char *graft_file)
{
        FILE *fp = fopen_or_warn(graft_file, "r");
        struct strbuf buf = STRBUF_INIT;
        if (!fp)
                return -1;
        if (!no_graft_file_deprecated_advice &&
            advice_enabled(ADVICE_GRAFT_FILE_DEPRECATED))
                advise(_("Support for <GIT_DIR>/info/grafts is deprecated\n"
                         "and will be removed in a future Git version.\n"
                         "\n"
                         "Please use \"git replace --convert-graft-file\"\n"
                         "to convert the grafts into replace refs.\n"
                         "\n"
                         "Turn this message off by running\n"
                         "\"git config advice.graftFileDeprecated false\""));
        while (!strbuf_getwholeline(&buf, fp, '\n')) {
                /* The format is just "Commit Parent1 Parent2 ...\n" */
                struct commit_graft *graft = read_graft_line(&buf);
                if (!graft)
                        continue;
                if (register_commit_graft(r, graft, 1))
                        error("duplicate graft data: %s", buf.buf);
        }
        fclose(fp);
        strbuf_release(&buf);
        return 0;
}

void prepare_commit_graft(struct repository *r)
{
        char *graft_file;

        if (r->parsed_objects->commit_graft_prepared)
                return;
        if (!startup_info->have_repository)
                return;

        graft_file = get_graft_file(r);
        read_graft_file(r, graft_file);
        /* make sure shallows are read */
        is_repository_shallow(r);
        r->parsed_objects->commit_graft_prepared = 1;
}

struct commit_graft *lookup_commit_graft(struct repository *r, const struct object_id *oid)
{
        int pos;
        prepare_commit_graft(r);
        pos = commit_graft_pos(r, oid);
        if (pos < 0)
                return NULL;
        return r->parsed_objects->grafts[pos];
}

int for_each_commit_graft(each_commit_graft_fn fn, void *cb_data)
{
        int i, ret;
        for (i = ret = 0; i < the_repository->parsed_objects->grafts_nr && !ret; i++)
                ret = fn(the_repository->parsed_objects->grafts[i], cb_data);
        return ret;
}

void reset_commit_grafts(struct repository *r)
{
        int i;

        for (i = 0; i < r->parsed_objects->grafts_nr; i++) {
                unparse_commit(r, &r->parsed_objects->grafts[i]->oid);
                free(r->parsed_objects->grafts[i]);
        }
        r->parsed_objects->grafts_nr = 0;
        r->parsed_objects->commit_graft_prepared = 0;
}

struct commit_buffer {
        void *buffer;
        unsigned long size;
};
define_commit_slab(buffer_slab, struct commit_buffer);

struct buffer_slab *allocate_commit_buffer_slab(void)
{
        struct buffer_slab *bs = xmalloc(sizeof(*bs));
        init_buffer_slab(bs);
        return bs;
}

void free_commit_buffer_slab(struct buffer_slab *bs)
{
        clear_buffer_slab(bs);
        free(bs);
}

void set_commit_buffer(struct repository *r, struct commit *commit, void *buffer, unsigned long size)
{
        struct commit_buffer *v = buffer_slab_at(
                r->parsed_objects->buffer_slab, commit);
        v->buffer = buffer;
        v->size = size;
}

const void *get_cached_commit_buffer(struct repository *r, const struct commit *commit, unsigned long *sizep)
{
        struct commit_buffer *v = buffer_slab_peek(
                r->parsed_objects->buffer_slab, commit);
        if (!v) {
                if (sizep)
                        *sizep = 0;
                return NULL;
        }
        if (sizep)
                *sizep = v->size;
        return v->buffer;
}

const void *repo_get_commit_buffer(struct repository *r,
                                   const struct commit *commit,
                                   unsigned long *sizep)
{
        const void *ret = get_cached_commit_buffer(r, commit, sizep);
        if (!ret) {
                enum object_type type;
                unsigned long size;
                ret = repo_read_object_file(r, &commit->object.oid, &type, &size);
                if (!ret)
                        die("cannot read commit object %s",
                            oid_to_hex(&commit->object.oid));
                if (type != OBJ_COMMIT)
                        die("expected commit for %s, got %s",
                            oid_to_hex(&commit->object.oid), type_name(type));
                if (sizep)
                        *sizep = size;
        }
        return ret;
}

void repo_unuse_commit_buffer(struct repository *r,
                              const struct commit *commit,
                              const void *buffer)
{
        struct commit_buffer *v = buffer_slab_peek(
                r->parsed_objects->buffer_slab, commit);
        if (!(v && v->buffer == buffer))
                free((void *)buffer);
}

void free_commit_buffer(struct parsed_object_pool *pool, struct commit *commit)
{
        struct commit_buffer *v = buffer_slab_peek(
                pool->buffer_slab, commit);
        if (v) {
                FREE_AND_NULL(v->buffer);
                v->size = 0;
        }
}

static inline void set_commit_tree(struct commit *c, struct tree *t)
{
        c->maybe_tree = t;
}

struct tree *repo_get_commit_tree(struct repository *r,
                                  const struct commit *commit)
{
        if (commit->maybe_tree || !commit->object.parsed)
                return commit->maybe_tree;

        if (commit_graph_position(commit) != COMMIT_NOT_FROM_GRAPH)
                return get_commit_tree_in_graph(r, commit);

        return NULL;
}

struct object_id *get_commit_tree_oid(const struct commit *commit)
{
        struct tree *tree = repo_get_commit_tree(the_repository, commit);
        return tree ? &tree->object.oid : NULL;
}

void release_commit_memory(struct parsed_object_pool *pool, struct commit *c)
{
        set_commit_tree(c, NULL);
        free_commit_buffer(pool, c);
        c->index = 0;
        free_commit_list(c->parents);

        c->object.parsed = 0;
}

const void *detach_commit_buffer(struct commit *commit, unsigned long *sizep)
{
        struct commit_buffer *v = buffer_slab_peek(
                the_repository->parsed_objects->buffer_slab, commit);
        void *ret;

        if (!v) {
                if (sizep)
                        *sizep = 0;
                return NULL;
        }
        ret = v->buffer;
        if (sizep)
                *sizep = v->size;

        v->buffer = NULL;
        v->size = 0;
        return ret;
}

int parse_commit_buffer(struct repository *r, struct commit *item, const void *buffer, unsigned long size, int check_graph)
{
        const char *tail = buffer;
        const char *bufptr = buffer;
        struct object_id parent;
        struct commit_list **pptr;
        struct commit_graft *graft;
        const int tree_entry_len = the_hash_algo->hexsz + 5;
        const int parent_entry_len = the_hash_algo->hexsz + 7;
        struct tree *tree;

        if (item->object.parsed)
                return 0;
        /*
         * Presumably this is leftover from an earlier failed parse;
         * clear it out in preparation for us re-parsing (we'll hit the
         * same error, but that's good, since it lets our caller know
         * the result cannot be trusted.
         */
        free_commit_list(item->parents);
        item->parents = NULL;

        tail += size;
        if (tail <= bufptr + tree_entry_len + 1 || memcmp(bufptr, "tree ", 5) ||
                        bufptr[tree_entry_len] != '\n')
                return error("bogus commit object %s", oid_to_hex(&item->object.oid));
        if (get_oid_hex(bufptr + 5, &parent) < 0)
                return error("bad tree pointer in commit %s",
                             oid_to_hex(&item->object.oid));
        tree = lookup_tree(r, &parent);
        if (!tree)
                return error("bad tree pointer %s in commit %s",
                             oid_to_hex(&parent),
                             oid_to_hex(&item->object.oid));
        set_commit_tree(item, tree);
        bufptr += tree_entry_len + 1; /* "tree " + "hex sha1" + "\n" */
        pptr = &item->parents;

        graft = lookup_commit_graft(r, &item->object.oid);
        if (graft)
                r->parsed_objects->substituted_parent = 1;
        while (bufptr + parent_entry_len < tail && !memcmp(bufptr, "parent ", 7)) {
                struct commit *new_parent;

                if (tail <= bufptr + parent_entry_len + 1 ||
                    get_oid_hex(bufptr + 7, &parent) ||
                    bufptr[parent_entry_len] != '\n')
                        return error("bad parents in commit %s", oid_to_hex(&item->object.oid));
                bufptr += parent_entry_len + 1;
                /*
                 * The clone is shallow if nr_parent < 0, and we must
                 * not traverse its real parents even when we unhide them.
                 */
                if (graft && (graft->nr_parent < 0 || !grafts_keep_true_parents))
                        continue;
                new_parent = lookup_commit(r, &parent);
                if (!new_parent)
                        return error("bad parent %s in commit %s",
                                     oid_to_hex(&parent),
                                     oid_to_hex(&item->object.oid));
                pptr = &commit_list_insert(new_parent, pptr)->next;
        }
        if (graft) {
                int i;
                struct commit *new_parent;
                for (i = 0; i < graft->nr_parent; i++) {
                        new_parent = lookup_commit(r,
                                                   &graft->parent[i]);
                        if (!new_parent)
                                return error("bad graft parent %s in commit %s",
                                             oid_to_hex(&graft->parent[i]),
                                             oid_to_hex(&item->object.oid));
                        pptr = &commit_list_insert(new_parent, pptr)->next;
                }
        }
        item->date = parse_commit_date(bufptr, tail);

        if (check_graph)
                load_commit_graph_info(r, item);

        item->object.parsed = 1;
        return 0;
}

int repo_parse_commit_internal(struct repository *r,
                               struct commit *item,
                               int quiet_on_missing,
                               int use_commit_graph)
{
        enum object_type type;
        void *buffer;
        unsigned long size;
        struct object_info oi = {
                .typep = &type,
                .sizep = &size,
                .contentp = &buffer,
        };
        /*
         * Git does not support partial clones that exclude commits, so set
         * OBJECT_INFO_SKIP_FETCH_OBJECT to fail fast when an object is missing.
         */
        int flags = OBJECT_INFO_LOOKUP_REPLACE | OBJECT_INFO_SKIP_FETCH_OBJECT |
                OBJECT_INFO_DIE_IF_CORRUPT;
        int ret;

        if (!item)
                return -1;
        if (item->object.parsed)
                return 0;
        if (use_commit_graph && parse_commit_in_graph(r, item)) {
                static int commit_graph_paranoia = -1;

                if (commit_graph_paranoia == -1)
                        commit_graph_paranoia = git_env_bool(GIT_COMMIT_GRAPH_PARANOIA, 0);

                if (commit_graph_paranoia && !has_object(r, &item->object.oid, 0)) {
                        unparse_commit(r, &item->object.oid);
                        return quiet_on_missing ? -1 :
                                error(_("commit %s exists in commit-graph but not in the object database"),
                                      oid_to_hex(&item->object.oid));
                }

                return 0;
        }

        if (oid_object_info_extended(r, &item->object.oid, &oi, flags) < 0)
                return quiet_on_missing ? -1 :
                        error("Could not read %s",
                             oid_to_hex(&item->object.oid));
        if (type != OBJ_COMMIT) {
                free(buffer);
                return error("Object %s not a commit",
                             oid_to_hex(&item->object.oid));
        }

        ret = parse_commit_buffer(r, item, buffer, size, 0);
        if (save_commit_buffer && !ret) {
                set_commit_buffer(r, item, buffer, size);
                return 0;
        }
        free(buffer);
        return ret;
}

int repo_parse_commit_gently(struct repository *r,
                             struct commit *item, int quiet_on_missing)
{
        return repo_parse_commit_internal(r, item, quiet_on_missing, 1);
}

void parse_commit_or_die(struct commit *item)
{
        if (repo_parse_commit(the_repository, item))
                die("unable to parse commit %s",
                    item ? oid_to_hex(&item->object.oid) : "(null)");
}

int find_commit_subject(const char *commit_buffer, const char **subject)
{
        const char *eol;
        const char *p = commit_buffer;

        while (*p && (*p != '\n' || p[1] != '\n'))
                p++;
        if (*p) {
                p = skip_blank_lines(p + 2);
                eol = strchrnul(p, '\n');
        } else
                eol = p;

        *subject = p;

        return eol - p;
}

size_t commit_subject_length(const char *body)
{
        const char *p = body;
        while (*p) {
                const char *next = skip_blank_lines(p);
                if (next != p)
                        break;
                p = strchrnul(p, '\n');
                if (*p)
                        p++;
        }
        return p - body;
}

struct commit_list *commit_list_insert(struct commit *item, struct commit_list **list_p)
{
        struct commit_list *new_list = xmalloc(sizeof(struct commit_list));
        new_list->item = item;
        new_list->next = *list_p;
        *list_p = new_list;
        return new_list;
}

int commit_list_contains(struct commit *item, struct commit_list *list)
{
        while (list) {
                if (list->item == item)
                        return 1;
                list = list->next;
        }

        return 0;
}

unsigned commit_list_count(const struct commit_list *l)
{
        unsigned c = 0;
        for (; l; l = l->next )
                c++;
        return c;
}

struct commit_list *copy_commit_list(struct commit_list *list)
{
        struct commit_list *head = NULL;
        struct commit_list **pp = &head;
        while (list) {
                pp = commit_list_append(list->item, pp);
                list = list->next;
        }
        return head;
}

struct commit_list *reverse_commit_list(struct commit_list *list)
{
        struct commit_list *next = NULL, *current, *backup;
        for (current = list; current; current = backup) {
                backup = current->next;
                current->next = next;
                next = current;
        }
        return next;
}

void free_commit_list(struct commit_list *list)
{
        while (list)
                pop_commit(&list);
}

struct commit_list * commit_list_insert_by_date(struct commit *item, struct commit_list **list)
{
        struct commit_list **pp = list;
        struct commit_list *p;
        while ((p = *pp) != NULL) {
                if (p->item->date < item->date) {
                        break;
                }
                pp = &p->next;
        }
        return commit_list_insert(item, pp);
}

static int commit_list_compare_by_date(const struct commit_list *a,
                                       const struct commit_list *b)
{
        timestamp_t a_date = a->item->date;
        timestamp_t b_date = b->item->date;
        if (a_date < b_date)
                return 1;
        if (a_date > b_date)
                return -1;
        return 0;
}

DEFINE_LIST_SORT(static, commit_list_sort, struct commit_list, next);

void commit_list_sort_by_date(struct commit_list **list)
{
        commit_list_sort(list, commit_list_compare_by_date);
}

struct commit *pop_most_recent_commit(struct commit_list **list,
                                      unsigned int mark)
{
        struct commit *ret = pop_commit(list);
        struct commit_list *parents = ret->parents;

        while (parents) {
                struct commit *commit = parents->item;
                if (!repo_parse_commit(the_repository, commit) && !(commit->object.flags & mark)) {
                        commit->object.flags |= mark;
                        commit_list_insert_by_date(commit, list);
                }
                parents = parents->next;
        }
        return ret;
}

static void clear_commit_marks_1(struct commit_list **plist,
                                 struct commit *commit, unsigned int mark)
{
        while (commit) {
                struct commit_list *parents;

                if (!(mark & commit->object.flags))
                        return;

                commit->object.flags &= ~mark;

                parents = commit->parents;
                if (!parents)
                        return;

                while ((parents = parents->next)) {
                        if (parents->item->object.flags & mark)
                                commit_list_insert(parents->item, plist);
                }

                commit = commit->parents->item;
        }
}

void clear_commit_marks_many(int nr, struct commit **commit, unsigned int mark)
{
        struct commit_list *list = NULL;

        while (nr--) {
                clear_commit_marks_1(&list, *commit, mark);
                commit++;
        }
        while (list)
                clear_commit_marks_1(&list, pop_commit(&list), mark);
}

void clear_commit_marks(struct commit *commit, unsigned int mark)
{
        clear_commit_marks_many(1, &commit, mark);
}

struct commit *pop_commit(struct commit_list **stack)
{
        struct commit_list *top = *stack;
        struct commit *item = top ? top->item : NULL;

        if (top) {
                *stack = top->next;
                free(top);
        }
        return item;
}

/*
 * Topological sort support
 */

/* count number of children that have not been emitted */
define_commit_slab(indegree_slab, int);

define_commit_slab(author_date_slab, timestamp_t);

void record_author_date(struct author_date_slab *author_date,
                        struct commit *commit)
{
        const char *buffer = repo_get_commit_buffer(the_repository, commit,
                                                    NULL);
        struct ident_split ident;
        const char *ident_line;
        size_t ident_len;
        char *date_end;
        timestamp_t date;

        ident_line = find_commit_header(buffer, "author", &ident_len);
        if (!ident_line)
                goto fail_exit; /* no author line */
        if (split_ident_line(&ident, ident_line, ident_len) ||
            !ident.date_begin || !ident.date_end)
                goto fail_exit; /* malformed "author" line */

        date = parse_timestamp(ident.date_begin, &date_end, 10);
        if (date_end != ident.date_end)
                goto fail_exit; /* malformed date */
        *(author_date_slab_at(author_date, commit)) = date;

fail_exit:
        repo_unuse_commit_buffer(the_repository, commit, buffer);
}

int compare_commits_by_author_date(const void *a_, const void *b_,
                                   void *cb_data)
{
        const struct commit *a = a_, *b = b_;
        struct author_date_slab *author_date = cb_data;
        timestamp_t a_date = *(author_date_slab_at(author_date, a));
        timestamp_t b_date = *(author_date_slab_at(author_date, b));

        /* newer commits with larger date first */
        if (a_date < b_date)
                return 1;
        else if (a_date > b_date)
                return -1;
        return 0;
}

int compare_commits_by_gen_then_commit_date(const void *a_, const void *b_,
                                            void *unused UNUSED)
{
        const struct commit *a = a_, *b = b_;
        const timestamp_t generation_a = commit_graph_generation(a),
                          generation_b = commit_graph_generation(b);

        /* newer commits first */
        if (generation_a < generation_b)
                return 1;
        else if (generation_a > generation_b)
                return -1;

        /* use date as a heuristic when generations are equal */
        if (a->date < b->date)
                return 1;
        else if (a->date > b->date)
                return -1;
        return 0;
}

int compare_commits_by_commit_date(const void *a_, const void *b_,
                                   void *unused UNUSED)
{
        const struct commit *a = a_, *b = b_;
        /* newer commits with larger date first */
        if (a->date < b->date)
                return 1;
        else if (a->date > b->date)
                return -1;
        return 0;
}

/*
 * Performs an in-place topological sort on the list supplied.
 */
void sort_in_topological_order(struct commit_list **list, enum rev_sort_order sort_order)
{
        struct commit_list *next, *orig = *list;
        struct commit_list **pptr;
        struct indegree_slab indegree;
        struct prio_queue queue;
        struct commit *commit;
        struct author_date_slab author_date;

        if (!orig)
                return;
        *list = NULL;

        init_indegree_slab(&indegree);
        memset(&queue, '\0', sizeof(queue));

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

        /* Mark them and clear the indegree */
        for (next = orig; next; next = next->next) {
                struct commit *commit = next->item;
                *(indegree_slab_at(&indegree, commit)) = 1;
                /* also record the author dates, if needed */
                if (sort_order == REV_SORT_BY_AUTHOR_DATE)
                        record_author_date(&author_date, commit);
        }

        /* update the indegree */
        for (next = orig; next; next = next->next) {
                struct commit_list *parents = next->item->parents;
                while (parents) {
                        struct commit *parent = parents->item;
                        int *pi = indegree_slab_at(&indegree, parent);

                        if (*pi)
                                (*pi)++;
                        parents = parents->next;
                }
        }

        /*
         * find the tips
         *
         * tips are nodes not reachable from any other node in the list
         *
         * the tips serve as a starting set for the work queue.
         */
        for (next = orig; next; next = next->next) {
                struct commit *commit = next->item;

                if (*(indegree_slab_at(&indegree, commit)) == 1)
                        prio_queue_put(&queue, commit);
        }

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

        /* We no longer need the commit list */
        free_commit_list(orig);

        pptr = list;
        *list = NULL;
        while ((commit = prio_queue_get(&queue)) != NULL) {
                struct commit_list *parents;

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

                        if (!*pi)
                                continue;

                        /*
                         * parents are only enqueued for emission
                         * when all their children have been emitted thereby
                         * guaranteeing topological order.
                         */
                        if (--(*pi) == 1)
                                prio_queue_put(&queue, parent);
                }
                /*
                 * all children of commit have already been
                 * emitted. we can emit it now.
                 */
                *(indegree_slab_at(&indegree, commit)) = 0;

                pptr = &commit_list_insert(commit, pptr)->next;
        }

        clear_indegree_slab(&indegree);
        clear_prio_queue(&queue);
        if (sort_order == REV_SORT_BY_AUTHOR_DATE)
                clear_author_date_slab(&author_date);
}

struct rev_collect {
        struct commit **commit;
        int nr;
        int alloc;
        unsigned int initial : 1;
};

static void add_one_commit(struct object_id *oid, struct rev_collect *revs)
{
        struct commit *commit;

        if (is_null_oid(oid))
                return;

        commit = lookup_commit(the_repository, oid);
        if (!commit ||
            (commit->object.flags & TMP_MARK) ||
            repo_parse_commit(the_repository, commit))
                return;

        ALLOC_GROW(revs->commit, revs->nr + 1, revs->alloc);
        revs->commit[revs->nr++] = commit;
        commit->object.flags |= TMP_MARK;
}

static int collect_one_reflog_ent(struct object_id *ooid, struct object_id *noid,
                                  const char *ident UNUSED,
                                  timestamp_t timestamp UNUSED, int tz UNUSED,
                                  const char *message UNUSED, void *cbdata)
{
        struct rev_collect *revs = cbdata;

        if (revs->initial) {
                revs->initial = 0;
                add_one_commit(ooid, revs);
        }
        add_one_commit(noid, revs);
        return 0;
}

struct commit *get_fork_point(const char *refname, struct commit *commit)
{
        struct object_id oid;
        struct rev_collect revs;
        struct commit_list *bases = NULL;
        int i;
        struct commit *ret = NULL;
        char *full_refname;

        switch (repo_dwim_ref(the_repository, refname, strlen(refname), &oid,
                              &full_refname, 0)) {
        case 0:
                die("No such ref: '%s'", refname);
        case 1:
                break; /* good */
        default:
                die("Ambiguous refname: '%s'", refname);
        }

        memset(&revs, 0, sizeof(revs));
        revs.initial = 1;
        for_each_reflog_ent(full_refname, collect_one_reflog_ent, &revs);

        if (!revs.nr)
                add_one_commit(&oid, &revs);

        for (i = 0; i < revs.nr; i++)
                revs.commit[i]->object.flags &= ~TMP_MARK;

        if (repo_get_merge_bases_many(the_repository, commit, revs.nr,
                                      revs.commit, &bases) < 0)
                exit(128);

        /*
         * There should be one and only one merge base, when we found
         * a common ancestor among reflog entries.
         */
        if (!bases || bases->next)
                goto cleanup_return;

        /* And the found one must be one of the reflog entries */
        for (i = 0; i < revs.nr; i++)
                if (&bases->item->object == &revs.commit[i]->object)
                        break; /* found */
        if (revs.nr <= i)
                goto cleanup_return;

        ret = bases->item;

cleanup_return:
        free(revs.commit);
        free_commit_list(bases);
        free(full_refname);
        return ret;
}

/*
 * Indexed by hash algorithm identifier.
 */
static const char *gpg_sig_headers[] = {
        NULL,
        "gpgsig",
        "gpgsig-sha256",
};

int sign_with_header(struct strbuf *buf, const char *keyid)
{
        struct strbuf sig = STRBUF_INIT;
        int inspos, copypos;
        const char *eoh;
        const char *gpg_sig_header = gpg_sig_headers[hash_algo_by_ptr(the_hash_algo)];
        int gpg_sig_header_len = strlen(gpg_sig_header);

        /* find the end of the header */
        eoh = strstr(buf->buf, "\n\n");
        if (!eoh)
                inspos = buf->len;
        else
                inspos = eoh - buf->buf + 1;

        if (!keyid || !*keyid)
                keyid = get_signing_key();
        if (sign_buffer(buf, &sig, keyid)) {
                strbuf_release(&sig);
                return -1;
        }

        for (copypos = 0; sig.buf[copypos]; ) {
                const char *bol = sig.buf + copypos;
                const char *eol = strchrnul(bol, '\n');
                int len = (eol - bol) + !!*eol;

                if (!copypos) {
                        strbuf_insert(buf, inspos, gpg_sig_header, gpg_sig_header_len);
                        inspos += gpg_sig_header_len;
                }
                strbuf_insertstr(buf, inspos++, " ");
                strbuf_insert(buf, inspos, bol, len);
                inspos += len;
                copypos += len;
        }
        strbuf_release(&sig);
        return 0;
}



int parse_signed_commit(const struct commit *commit,
                        struct strbuf *payload, struct strbuf *signature,
                        const struct git_hash_algo *algop)
{
        unsigned long size;
        const char *buffer = repo_get_commit_buffer(the_repository, commit,
                                                    &size);
        int ret = parse_buffer_signed_by_header(buffer, size, payload, signature, algop);

        repo_unuse_commit_buffer(the_repository, commit, buffer);
        return ret;
}

int parse_buffer_signed_by_header(const char *buffer,
                                  unsigned long size,
                                  struct strbuf *payload,
                                  struct strbuf *signature,
                                  const struct git_hash_algo *algop)
{
        int in_signature = 0, saw_signature = 0, other_signature = 0;
        const char *line, *tail, *p;
        const char *gpg_sig_header = gpg_sig_headers[hash_algo_by_ptr(algop)];

        line = buffer;
        tail = buffer + size;
        while (line < tail) {
                const char *sig = NULL;
                const char *next = memchr(line, '\n', tail - line);

                next = next ? next + 1 : tail;
                if (in_signature && line[0] == ' ')
                        sig = line + 1;
                else if (skip_prefix(line, gpg_sig_header, &p) &&
                         *p == ' ') {
                        sig = line + strlen(gpg_sig_header) + 1;
                        other_signature = 0;
                }
                else if (starts_with(line, "gpgsig"))
                        other_signature = 1;
                else if (other_signature && line[0] != ' ')
                        other_signature = 0;
                if (sig) {
                        strbuf_add(signature, sig, next - sig);
                        saw_signature = 1;
                        in_signature = 1;
                } else {
                        if (*line == '\n')
                                /* dump the whole remainder of the buffer */
                                next = tail;
                        if (!other_signature)
                                strbuf_add(payload, line, next - line);
                        in_signature = 0;
                }
                line = next;
        }
        return saw_signature;
}

int remove_signature(struct strbuf *buf)
{
        const char *line = buf->buf;
        const char *tail = buf->buf + buf->len;
        int in_signature = 0;
        struct sigbuf {
                const char *start;
                const char *end;
        } sigs[2], *sigp = &sigs[0];
        int i;
        const char *orig_buf = buf->buf;

        memset(sigs, 0, sizeof(sigs));

        while (line < tail) {
                const char *next = memchr(line, '\n', tail - line);
                next = next ? next + 1 : tail;

                if (in_signature && line[0] == ' ')
                        sigp->end = next;
                else if (starts_with(line, "gpgsig")) {
                        int i;
                        for (i = 1; i < GIT_HASH_NALGOS; i++) {
                                const char *p;
                                if (skip_prefix(line, gpg_sig_headers[i], &p) &&
                                    *p == ' ') {
                                        sigp->start = line;
                                        sigp->end = next;
                                        in_signature = 1;
                                }
                        }
                } else {
                        if (*line == '\n')
                                /* dump the whole remainder of the buffer */
                                next = tail;
                        if (in_signature && sigp - sigs != ARRAY_SIZE(sigs))
                                sigp++;
                        in_signature = 0;
                }
                line = next;
        }

        for (i = ARRAY_SIZE(sigs) - 1; i >= 0; i--)
                if (sigs[i].start)
                        strbuf_remove(buf, sigs[i].start - orig_buf, sigs[i].end - sigs[i].start);

        return sigs[0].start != NULL;
}

static void handle_signed_tag(struct commit *parent, struct commit_extra_header ***tail)
{
        struct merge_remote_desc *desc;
        struct commit_extra_header *mergetag;
        char *buf;
        unsigned long size;
        enum object_type type;
        struct strbuf payload = STRBUF_INIT;
        struct strbuf signature = STRBUF_INIT;

        desc = merge_remote_util(parent);
        if (!desc || !desc->obj)
                return;
        buf = repo_read_object_file(the_repository, &desc->obj->oid, &type,
                                    &size);
        if (!buf || type != OBJ_TAG)
                goto free_return;
        if (!parse_signature(buf, size, &payload, &signature))
                goto free_return;
        /*
         * We could verify this signature and either omit the tag when
         * it does not validate, but the integrator may not have the
         * public key of the signer of the tag being merged, while a
         * later auditor may have it while auditing, so let's not run
         * verify-signed-buffer here for now...
         *
         * if (verify_signed_buffer(buf, len, buf + len, size - len, ...))
         *      warn("warning: signed tag unverified.");
         */
        CALLOC_ARRAY(mergetag, 1);
        mergetag->key = xstrdup("mergetag");
        mergetag->value = buf;
        mergetag->len = size;

        **tail = mergetag;
        *tail = &mergetag->next;
        strbuf_release(&payload);
        strbuf_release(&signature);
        return;

free_return:
        free(buf);
}

int check_commit_signature(const struct commit *commit, struct signature_check *sigc)
{
        struct strbuf payload = STRBUF_INIT;
        struct strbuf signature = STRBUF_INIT;
        int ret = 1;

        sigc->result = 'N';

        if (parse_signed_commit(commit, &payload, &signature, the_hash_algo) <= 0)
                goto out;

        sigc->payload_type = SIGNATURE_PAYLOAD_COMMIT;
        sigc->payload = strbuf_detach(&payload, &sigc->payload_len);
        ret = check_signature(sigc, signature.buf, signature.len);

 out:
        strbuf_release(&payload);
        strbuf_release(&signature);

        return ret;
}

void verify_merge_signature(struct commit *commit, int verbosity,
                            int check_trust)
{
        char hex[GIT_MAX_HEXSZ + 1];
        struct signature_check signature_check;
        int ret;
        memset(&signature_check, 0, sizeof(signature_check));

        ret = check_commit_signature(commit, &signature_check);

        repo_find_unique_abbrev_r(the_repository, hex, &commit->object.oid,
                                  DEFAULT_ABBREV);
        switch (signature_check.result) {
        case 'G':
                if (ret || (check_trust && signature_check.trust_level < TRUST_MARGINAL))
                        die(_("Commit %s has an untrusted GPG signature, "
                              "allegedly by %s."), hex, signature_check.signer);
                break;
        case 'B':
                die(_("Commit %s has a bad GPG signature "
                      "allegedly by %s."), hex, signature_check.signer);
        default: /* 'N' */
                die(_("Commit %s does not have a GPG signature."), hex);
        }
        if (verbosity >= 0 && signature_check.result == 'G')
                printf(_("Commit %s has a good GPG signature by %s\n"),
                       hex, signature_check.signer);

        signature_check_clear(&signature_check);
}

void append_merge_tag_headers(struct commit_list *parents,
                              struct commit_extra_header ***tail)
{
        while (parents) {
                struct commit *parent = parents->item;
                handle_signed_tag(parent, tail);
                parents = parents->next;
        }
}

static void add_extra_header(struct strbuf *buffer,
                             struct commit_extra_header *extra)
{
        strbuf_addstr(buffer, extra->key);
        if (extra->len)
                strbuf_add_lines(buffer, " ", extra->value, extra->len);
        else
                strbuf_addch(buffer, '\n');
}

struct commit_extra_header *read_commit_extra_headers(struct commit *commit,
                                                      const char **exclude)
{
        struct commit_extra_header *extra = NULL;
        unsigned long size;
        const char *buffer = repo_get_commit_buffer(the_repository, commit,
                                                    &size);
        extra = read_commit_extra_header_lines(buffer, size, exclude);
        repo_unuse_commit_buffer(the_repository, commit, buffer);
        return extra;
}

int for_each_mergetag(each_mergetag_fn fn, struct commit *commit, void *data)
{
        struct commit_extra_header *extra, *to_free;
        int res = 0;

        to_free = read_commit_extra_headers(commit, NULL);
        for (extra = to_free; !res && extra; extra = extra->next) {
                if (strcmp(extra->key, "mergetag"))
                        continue; /* not a merge tag */
                res = fn(commit, extra, data);
        }
        free_commit_extra_headers(to_free);
        return res;
}

static inline int standard_header_field(const char *field, size_t len)
{
        return ((len == 4 && !memcmp(field, "tree", 4)) ||
                (len == 6 && !memcmp(field, "parent", 6)) ||
                (len == 6 && !memcmp(field, "author", 6)) ||
                (len == 9 && !memcmp(field, "committer", 9)) ||
                (len == 8 && !memcmp(field, "encoding", 8)));
}

static int excluded_header_field(const char *field, size_t len, const char **exclude)
{
        if (!exclude)
                return 0;

        while (*exclude) {
                size_t xlen = strlen(*exclude);
                if (len == xlen && !memcmp(field, *exclude, xlen))
                        return 1;
                exclude++;
        }
        return 0;
}

static struct commit_extra_header *read_commit_extra_header_lines(
        const char *buffer, size_t size,
        const char **exclude)
{
        struct commit_extra_header *extra = NULL, **tail = &extra, *it = NULL;
        const char *line, *next, *eof, *eob;
        struct strbuf buf = STRBUF_INIT;

        for (line = buffer, eob = line + size;
             line < eob && *line != '\n';
             line = next) {
                next = memchr(line, '\n', eob - line);
                next = next ? next + 1 : eob;
                if (*line == ' ') {
                        /* continuation */
                        if (it)
                                strbuf_add(&buf, line + 1, next - (line + 1));
                        continue;
                }
                if (it)
                        it->value = strbuf_detach(&buf, &it->len);
                strbuf_reset(&buf);
                it = NULL;

                eof = memchr(line, ' ', next - line);
                if (!eof)
                        eof = next;
                else if (standard_header_field(line, eof - line) ||
                         excluded_header_field(line, eof - line, exclude))
                        continue;

                CALLOC_ARRAY(it, 1);
                it->key = xmemdupz(line, eof-line);
                *tail = it;
                tail = &it->next;
                if (eof + 1 < next)
                        strbuf_add(&buf, eof + 1, next - (eof + 1));
        }
        if (it)
                it->value = strbuf_detach(&buf, &it->len);
        return extra;
}

void free_commit_extra_headers(struct commit_extra_header *extra)
{
        while (extra) {
                struct commit_extra_header *next = extra->next;
                free(extra->key);
                free(extra->value);
                free(extra);
                extra = next;
        }
}

int commit_tree(const char *msg, size_t msg_len, const struct object_id *tree,
                struct commit_list *parents, struct object_id *ret,
                const char *author, const char *sign_commit)
{
        struct commit_extra_header *extra = NULL, **tail = &extra;
        int result;

        append_merge_tag_headers(parents, &tail);
        result = commit_tree_extended(msg, msg_len, tree, parents, ret, author,
                                      NULL, sign_commit, extra);
        free_commit_extra_headers(extra);
        return result;
}

static int find_invalid_utf8(const char *buf, int len)
{
        int offset = 0;
        static const unsigned int max_codepoint[] = {
                0x7f, 0x7ff, 0xffff, 0x10ffff
        };

        while (len) {
                unsigned char c = *buf++;
                int bytes, bad_offset;
                unsigned int codepoint;
                unsigned int min_val, max_val;

                len--;
                offset++;

                /* Simple US-ASCII? No worries. */
                if (c < 0x80)
                        continue;

                bad_offset = offset-1;

                /*
                 * Count how many more high bits set: that's how
                 * many more bytes this sequence should have.
                 */
                bytes = 0;
                while (c & 0x40) {
                        c <<= 1;
                        bytes++;
                }

                /*
                 * Must be between 1 and 3 more bytes.  Longer sequences result in
                 * codepoints beyond U+10FFFF, which are guaranteed never to exist.
                 */
                if (bytes < 1 || 3 < bytes)
                        return bad_offset;

                /* Do we *have* that many bytes? */
                if (len < bytes)
                        return bad_offset;

                /*
                 * Place the encoded bits at the bottom of the value and compute the
                 * valid range.
                 */
                codepoint = (c & 0x7f) >> bytes;
                min_val = max_codepoint[bytes-1] + 1;
                max_val = max_codepoint[bytes];

                offset += bytes;
                len -= bytes;

                /* And verify that they are good continuation bytes */
                do {
                        codepoint <<= 6;
                        codepoint |= *buf & 0x3f;
                        if ((*buf++ & 0xc0) != 0x80)
                                return bad_offset;
                } while (--bytes);

                /* Reject codepoints that are out of range for the sequence length. */
                if (codepoint < min_val || codepoint > max_val)
                        return bad_offset;
                /* Surrogates are only for UTF-16 and cannot be encoded in UTF-8. */
                if ((codepoint & 0x1ff800) == 0xd800)
                        return bad_offset;
                /* U+xxFFFE and U+xxFFFF are guaranteed non-characters. */
                if ((codepoint & 0xfffe) == 0xfffe)
                        return bad_offset;
                /* So are anything in the range U+FDD0..U+FDEF. */
                if (codepoint >= 0xfdd0 && codepoint <= 0xfdef)
                        return bad_offset;
        }
        return -1;
}

/*
 * This verifies that the buffer is in proper utf8 format.
 *
 * If it isn't, it assumes any non-utf8 characters are Latin1,
 * and does the conversion.
 */
static int verify_utf8(struct strbuf *buf)
{
        int ok = 1;
        long pos = 0;

        for (;;) {
                int bad;
                unsigned char c;
                unsigned char replace[2];

                bad = find_invalid_utf8(buf->buf + pos, buf->len - pos);
                if (bad < 0)
                        return ok;
                pos += bad;
                ok = 0;
                c = buf->buf[pos];
                strbuf_remove(buf, pos, 1);

                /* We know 'c' must be in the range 128-255 */
                replace[0] = 0xc0 + (c >> 6);
                replace[1] = 0x80 + (c & 0x3f);
                strbuf_insert(buf, pos, replace, 2);
                pos += 2;
        }
}

static const char commit_utf8_warn[] =
N_("Warning: commit message did not conform to UTF-8.\n"
   "You may want to amend it after fixing the message, or set the config\n"
   "variable i18n.commitEncoding to the encoding your project uses.\n");

int commit_tree_extended(const char *msg, size_t msg_len,
                         const struct object_id *tree,
                         struct commit_list *parents, struct object_id *ret,
                         const char *author, const char *committer,
                         const char *sign_commit,
                         struct commit_extra_header *extra)
{
        int result;
        int encoding_is_utf8;
        struct strbuf buffer;

        assert_oid_type(tree, OBJ_TREE);

        if (memchr(msg, '\0', msg_len))
                return error("a NUL byte in commit log message not allowed.");

        /* Not having i18n.commitencoding is the same as having utf-8 */
        encoding_is_utf8 = is_encoding_utf8(git_commit_encoding);

        strbuf_init(&buffer, 8192); /* should avoid reallocs for the headers */
        strbuf_addf(&buffer, "tree %s\n", oid_to_hex(tree));

        /*
         * NOTE! This ordering means that the same exact tree merged with a
         * different order of parents will be a _different_ changeset even
         * if everything else stays the same.
         */
        while (parents) {
                struct commit *parent = pop_commit(&parents);
                strbuf_addf(&buffer, "parent %s\n",
                            oid_to_hex(&parent->object.oid));
        }

        /* Person/date information */
        if (!author)
                author = git_author_info(IDENT_STRICT);
        strbuf_addf(&buffer, "author %s\n", author);
        if (!committer)
                committer = git_committer_info(IDENT_STRICT);
        strbuf_addf(&buffer, "committer %s\n", committer);
        if (!encoding_is_utf8)
                strbuf_addf(&buffer, "encoding %s\n", git_commit_encoding);

        while (extra) {
                add_extra_header(&buffer, extra);
                extra = extra->next;
        }
        strbuf_addch(&buffer, '\n');

        /* And add the comment */
        strbuf_add(&buffer, msg, msg_len);

        /* And check the encoding */
        if (encoding_is_utf8 && !verify_utf8(&buffer))
                fprintf(stderr, _(commit_utf8_warn));

        if (sign_commit && sign_with_header(&buffer, sign_commit)) {
                result = -1;
                goto out;
        }

        result = write_object_file(buffer.buf, buffer.len, OBJ_COMMIT, ret);
out:
        strbuf_release(&buffer);
        return result;
}

define_commit_slab(merge_desc_slab, struct merge_remote_desc *);
static struct merge_desc_slab merge_desc_slab = COMMIT_SLAB_INIT(1, merge_desc_slab);

struct merge_remote_desc *merge_remote_util(struct commit *commit)
{
        return *merge_desc_slab_at(&merge_desc_slab, commit);
}

void set_merge_remote_desc(struct commit *commit,
                           const char *name, struct object *obj)
{
        struct merge_remote_desc *desc;
        FLEX_ALLOC_STR(desc, name, name);
        desc->obj = obj;
        *merge_desc_slab_at(&merge_desc_slab, commit) = desc;
}

struct commit *get_merge_parent(const char *name)
{
        struct object *obj;
        struct commit *commit;
        struct object_id oid;
        if (repo_get_oid(the_repository, name, &oid))
                return NULL;
        obj = parse_object(the_repository, &oid);
        commit = (struct commit *)repo_peel_to_type(the_repository, name, 0,
                                                    obj, OBJ_COMMIT);
        if (commit && !merge_remote_util(commit))
                set_merge_remote_desc(commit, name, obj);
        return commit;
}

/*
 * Append a commit to the end of the commit_list.
 *
 * next starts by pointing to the variable that holds the head of an
 * empty commit_list, and is updated to point to the "next" field of
 * the last item on the list as new commits are appended.
 *
 * Usage example:
 *
 *     struct commit_list *list;
 *     struct commit_list **next = &list;
 *
 *     next = commit_list_append(c1, next);
 *     next = commit_list_append(c2, next);
 *     assert(commit_list_count(list) == 2);
 *     return list;
 */
struct commit_list **commit_list_append(struct commit *commit,
                                        struct commit_list **next)
{
        struct commit_list *new_commit = xmalloc(sizeof(struct commit_list));
        new_commit->item = commit;
        *next = new_commit;
        new_commit->next = NULL;
        return &new_commit->next;
}

const char *find_header_mem(const char *msg, size_t len,
                        const char *key, size_t *out_len)
{
        int key_len = strlen(key);
        const char *line = msg;

        /*
         * NEEDSWORK: It's possible for strchrnul() to scan beyond the range
         * given by len. However, current callers are safe because they compute
         * len by scanning a NUL-terminated block of memory starting at msg.
         * Nonetheless, it would be better to ensure the function does not look
         * at msg beyond the len provided by the caller.
         */
        while (line && line < msg + len) {
                const char *eol = strchrnul(line, '\n');

                if (line == eol)
                        return NULL;

                if (eol - line > key_len &&
                    !strncmp(line, key, key_len) &&
                    line[key_len] == ' ') {
                        *out_len = eol - line - key_len - 1;
                        return line + key_len + 1;
                }
                line = *eol ? eol + 1 : NULL;
        }
        return NULL;
}

const char *find_commit_header(const char *msg, const char *key, size_t *out_len)
{
        return find_header_mem(msg, strlen(msg), key, out_len);
}
/*
 * Inspect the given string and determine the true "end" of the log message, in
 * order to find where to put a new Signed-off-by trailer.  Ignored are
 * trailing comment lines and blank lines.  To support "git commit -s
 * --amend" on an existing commit, we also ignore "Conflicts:".  To
 * support "git commit -v", we truncate at cut lines.
 *
 * Returns the number of bytes from the tail to ignore, to be fed as
 * the second parameter to append_signoff().
 */
size_t ignored_log_message_bytes(const char *buf, size_t len)
{
        size_t boc = 0;
        size_t bol = 0;
        int in_old_conflicts_block = 0;
        size_t cutoff = wt_status_locate_end(buf, len);

        while (bol < cutoff) {
                const char *next_line = memchr(buf + bol, '\n', len - bol);

                if (!next_line)
                        next_line = buf + len;
                else
                        next_line++;

                if (buf[bol] == comment_line_char || buf[bol] == '\n') {
                        /* is this the first of the run of comments? */
                        if (!boc)
                                boc = bol;
                        /* otherwise, it is just continuing */
                } else if (starts_with(buf + bol, "Conflicts:\n")) {
                        in_old_conflicts_block = 1;
                        if (!boc)
                                boc = bol;
                } else if (in_old_conflicts_block && buf[bol] == '\t') {
                        ; /* a pathname in the conflicts block */
                } else if (boc) {
                        /* the previous was not trailing comment */
                        boc = 0;
                        in_old_conflicts_block = 0;
                }
                bol = next_line - buf;
        }
        return boc ? len - boc : len - cutoff;
}

int run_commit_hook(int editor_is_used, const char *index_file,
                    int *invoked_hook, const char *name, ...)
{
        struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT;
        va_list args;
        const char *arg;

        strvec_pushf(&opt.env, "GIT_INDEX_FILE=%s", index_file);

        /*
         * Let the hook know that no editor will be launched.
         */
        if (!editor_is_used)
                strvec_push(&opt.env, "GIT_EDITOR=:");

        va_start(args, name);
        while ((arg = va_arg(args, const char *)))
                strvec_push(&opt.args, arg);
        va_end(args);

        opt.invoked_hook = invoked_hook;
        return run_hooks_opt(name, &opt);
}