+static int do_merge(struct commit *commit, const char *arg, int arg_len,
+ int flags, struct replay_opts *opts)
+{
+ int run_commit_flags = (flags & TODO_EDIT_MERGE_MSG) ?
+ EDIT_MSG | VERIFY_MSG : 0;
+ struct strbuf ref_name = STRBUF_INIT;
+ struct commit *head_commit, *merge_commit, *i;
+ struct commit_list *bases, *j, *reversed = NULL;
+ struct merge_options o;
+ int merge_arg_len, oneline_offset, ret;
+ static struct lock_file lock;
+ const char *p;
+
+ if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0) {
+ ret = -1;
+ goto leave_merge;
+ }
+
+ head_commit = lookup_commit_reference_by_name("HEAD");
+ if (!head_commit) {
+ ret = error(_("cannot merge without a current revision"));
+ goto leave_merge;
+ }
+
+ oneline_offset = arg_len;
+ merge_arg_len = strcspn(arg, " \t\n");
+ p = arg + merge_arg_len;
+ p += strspn(p, " \t\n");
+ if (*p == '#' && (!p[1] || isspace(p[1]))) {
+ p += 1 + strspn(p + 1, " \t\n");
+ oneline_offset = p - arg;
+ } else if (p - arg < arg_len)
+ BUG("octopus merges are not supported yet: '%s'", p);
+
+ strbuf_addf(&ref_name, "refs/rewritten/%.*s", merge_arg_len, arg);
+ merge_commit = lookup_commit_reference_by_name(ref_name.buf);
+ if (!merge_commit) {
+ /* fall back to non-rewritten ref or commit */
+ strbuf_splice(&ref_name, 0, strlen("refs/rewritten/"), "", 0);
+ merge_commit = lookup_commit_reference_by_name(ref_name.buf);
+ }
+
+ if (!merge_commit) {
+ ret = error(_("could not resolve '%s'"), ref_name.buf);
+ goto leave_merge;
+ }
+
+ if (commit) {
+ const char *message = get_commit_buffer(commit, NULL);
+ const char *body;
+ int len;
+
+ if (!message) {
+ ret = error(_("could not get commit message of '%s'"),
+ oid_to_hex(&commit->object.oid));
+ goto leave_merge;
+ }
+ write_author_script(message);
+ find_commit_subject(message, &body);
+ len = strlen(body);
+ ret = write_message(body, len, git_path_merge_msg(), 0);
+ unuse_commit_buffer(commit, message);
+ if (ret) {
+ error_errno(_("could not write '%s'"),
+ git_path_merge_msg());
+ goto leave_merge;
+ }
+ } else {
+ struct strbuf buf = STRBUF_INIT;
+ int len;
+
+ strbuf_addf(&buf, "author %s", git_author_info(0));
+ write_author_script(buf.buf);
+ strbuf_reset(&buf);
+
+ if (oneline_offset < arg_len) {
+ p = arg + oneline_offset;
+ len = arg_len - oneline_offset;
+ } else {
+ strbuf_addf(&buf, "Merge branch '%.*s'",
+ merge_arg_len, arg);
+ p = buf.buf;
+ len = buf.len;
+ }
+
+ ret = write_message(p, len, git_path_merge_msg(), 0);
+ strbuf_release(&buf);
+ if (ret) {
+ error_errno(_("could not write '%s'"),
+ git_path_merge_msg());
+ goto leave_merge;
+ }
+ }
+
+ write_message(oid_to_hex(&merge_commit->object.oid), GIT_SHA1_HEXSZ,
+ git_path_merge_head(), 0);
+ write_message("no-ff", 5, git_path_merge_mode(), 0);
+
+ bases = get_merge_bases(head_commit, merge_commit);
+ for (j = bases; j; j = j->next)
+ commit_list_insert(j->item, &reversed);
+ free_commit_list(bases);
+
+ read_cache();
+ init_merge_options(&o);
+ o.branch1 = "HEAD";
+ o.branch2 = ref_name.buf;
+ o.buffer_output = 2;
+
+ ret = merge_recursive(&o, head_commit, merge_commit, reversed, &i);
+ if (ret <= 0)
+ fputs(o.obuf.buf, stdout);
+ strbuf_release(&o.obuf);
+ if (ret < 0) {
+ error(_("could not even attempt to merge '%.*s'"),
+ merge_arg_len, arg);
+ goto leave_merge;
+ }
+ /*
+ * The return value of merge_recursive() is 1 on clean, and 0 on
+ * unclean merge.
+ *
+ * Let's reverse that, so that do_merge() returns 0 upon success and
+ * 1 upon failed merge (keeping the return value -1 for the cases where
+ * we will want to reschedule the `merge` command).
+ */
+ ret = !ret;
+
+ if (active_cache_changed &&
+ write_locked_index(&the_index, &lock, COMMIT_LOCK)) {
+ ret = error(_("merge: Unable to write new index file"));
+ goto leave_merge;
+ }
+
+ rollback_lock_file(&lock);
+ if (ret)
+ rerere(opts->allow_rerere_auto);
+ else
+ /*
+ * In case of problems, we now want to return a positive
+ * value (a negative one would indicate that the `merge`
+ * command needs to be rescheduled).
+ */
+ ret = !!run_git_commit(git_path_merge_msg(), opts,
+ run_commit_flags);
+
+leave_merge:
+ strbuf_release(&ref_name);
+ rollback_lock_file(&lock);
+ return ret;
+}
+