commit.c

   1 #include "cache.h"
   2 #include "tag.h"
   3 #include "commit.h"
   4 #include "pkt-line.h"
   5 #include "utf8.h"
   6 #include "diff.h"
   7 #include "revision.h"
   8 #include "notes.h"
   9
  10 int save_commit_buffer = 1;
  11
  12 const char *commit_type = "commit";
  13
  14 static struct commit *check_commit(struct object *obj,
  15                                    const unsigned char *sha1,
  16                                    int quiet)
  17 {
  18         if (obj->type != OBJ_COMMIT) {
  19                 if (!quiet)
  20                         error("Object %s is a %s, not a commit",
  21                               sha1_to_hex(sha1), typename(obj->type));
  22                 return NULL;
  23         }
  24         return (struct commit *) obj;
  25 }
  26
  27 struct commit *lookup_commit_reference_gently(const unsigned char *sha1,
  28                                               int quiet)
  29 {
  30         struct object *obj = deref_tag(parse_object(sha1), NULL, 0);
  31
  32         if (!obj)
  33                 return NULL;
  34         return check_commit(obj, sha1, quiet);
  35 }
  36
  37 struct commit *lookup_commit_reference(const unsigned char *sha1)
  38 {
  39         return lookup_commit_reference_gently(sha1, 0);
  40 }
  41
  42 struct commit *lookup_commit(const unsigned char *sha1)
  43 {
  44         struct object *obj = lookup_object(sha1);
  45         if (!obj)
  46                 return create_object(sha1, OBJ_COMMIT, alloc_commit_node());
  47         if (!obj->type)
  48                 obj->type = OBJ_COMMIT;
  49         return check_commit(obj, sha1, 0);
  50 }
  51
  52 static unsigned long parse_commit_date(const char *buf, const char *tail)
  53 {
  54         const char *dateptr;
  55
  56         if (buf + 6 >= tail)
  57                 return 0;
  58         if (memcmp(buf, "author", 6))
  59                 return 0;
  60         while (buf < tail && *buf++ != '\n')
  61                 /* nada */;
  62         if (buf + 9 >= tail)
  63                 return 0;
  64         if (memcmp(buf, "committer", 9))
  65                 return 0;
  66         while (buf < tail && *buf++ != '>')
  67                 /* nada */;
  68         if (buf >= tail)
  69                 return 0;
  70         dateptr = buf;
  71         while (buf < tail && *buf++ != '\n')
  72                 /* nada */;
  73         if (buf >= tail)
  74                 return 0;
  75         /* dateptr < buf && buf[-1] == '\n', so strtoul will stop at buf-1 */
  76         return strtoul(dateptr, NULL, 10);
  77 }
  78
  79 static struct commit_graft **commit_graft;
  80 static int commit_graft_alloc, commit_graft_nr;
  81
  82 static int commit_graft_pos(const unsigned char *sha1)
  83 {
  84         int lo, hi;
  85         lo = 0;
  86         hi = commit_graft_nr;
  87         while (lo < hi) {
  88                 int mi = (lo + hi) / 2;
  89                 struct commit_graft *graft = commit_graft[mi];
  90                 int cmp = hashcmp(sha1, graft->sha1);
  91                 if (!cmp)
  92                         return mi;
  93                 if (cmp < 0)
  94                         hi = mi;
  95                 else
  96                         lo = mi + 1;
  97         }
  98         return -lo - 1;
  99 }
 100
 101 int register_commit_graft(struct commit_graft *graft, int ignore_dups)
 102 {
 103         int pos = commit_graft_pos(graft->sha1);
 104
 105         if (0 <= pos) {
 106                 if (ignore_dups)
 107                         free(graft);
 108                 else {
 109                         free(commit_graft[pos]);
 110                         commit_graft[pos] = graft;
 111                 }
 112                 return 1;
 113         }
 114         pos = -pos - 1;
 115         if (commit_graft_alloc <= ++commit_graft_nr) {
 116                 commit_graft_alloc = alloc_nr(commit_graft_alloc);
 117                 commit_graft = xrealloc(commit_graft,
 118                                         sizeof(*commit_graft) *
 119                                         commit_graft_alloc);
 120         }
 121         if (pos < commit_graft_nr)
 122                 memmove(commit_graft + pos + 1,
 123                         commit_graft + pos,
 124                         (commit_graft_nr - pos - 1) *
 125                         sizeof(*commit_graft));
 126         commit_graft[pos] = graft;
 127         return 0;
 128 }
 129
 130 struct commit_graft *read_graft_line(char *buf, int len)
 131 {
 132         /* The format is just "Commit Parent1 Parent2 ...\n" */
 133         int i;
 134         struct commit_graft *graft = NULL;
 135
 136         while (len && isspace(buf[len-1]))
 137                 buf[--len] = '\0';
 138         if (buf[0] == '#' || buf[0] == '\0')
 139                 return NULL;
 140         if ((len + 1) % 41) {
 141         bad_graft_data:
 142                 error("bad graft data: %s", buf);
 143                 free(graft);
 144                 return NULL;
 145         }
 146         i = (len + 1) / 41 - 1;
 147         graft = xmalloc(sizeof(*graft) + 20 * i);
 148         graft->nr_parent = i;
 149         if (get_sha1_hex(buf, graft->sha1))
 150                 goto bad_graft_data;
 151         for (i = 40; i < len; i += 41) {
 152                 if (buf[i] != ' ')
 153                         goto bad_graft_data;
 154                 if (get_sha1_hex(buf + i + 1, graft->parent[i/41]))
 155                         goto bad_graft_data;
 156         }
 157         return graft;
 158 }
 159
 160 static int read_graft_file(const char *graft_file)
 161 {
 162         FILE *fp = fopen(graft_file, "r");
 163         char buf[1024];
 164         if (!fp)
 165                 return -1;
 166         while (fgets(buf, sizeof(buf), fp)) {
 167                 /* The format is just "Commit Parent1 Parent2 ...\n" */
 168                 int len = strlen(buf);
 169                 struct commit_graft *graft = read_graft_line(buf, len);
 170                 if (!graft)
 171                         continue;
 172                 if (register_commit_graft(graft, 1))
 173                         error("duplicate graft data: %s", buf);
 174         }
 175         fclose(fp);
 176         return 0;
 177 }
 178
 179 static void prepare_commit_graft(void)
 180 {
 181         static int commit_graft_prepared;
 182         char *graft_file;
 183
 184         if (commit_graft_prepared)
 185                 return;
 186         graft_file = get_graft_file();
 187         read_graft_file(graft_file);
 188         /* make sure shallows are read */
 189         is_repository_shallow();
 190         commit_graft_prepared = 1;
 191 }
 192
 193 struct commit_graft *lookup_commit_graft(const unsigned char *sha1)
 194 {
 195         int pos;
 196         prepare_commit_graft();
 197         pos = commit_graft_pos(sha1);
 198         if (pos < 0)
 199                 return NULL;
 200         return commit_graft[pos];
 201 }
 202
 203 int write_shallow_commits(struct strbuf *out, int use_pack_protocol)
 204 {
 205         int i, count = 0;
 206         for (i = 0; i < commit_graft_nr; i++)
 207                 if (commit_graft[i]->nr_parent < 0) {
 208                         const char *hex =
 209                                 sha1_to_hex(commit_graft[i]->sha1);
 210                         count++;
 211                         if (use_pack_protocol)
 212                                 packet_buf_write(out, "shallow %s", hex);
 213                         else {
 214                                 strbuf_addstr(out, hex);
 215                                 strbuf_addch(out, '\n');
 216                         }
 217                 }
 218         return count;
 219 }
 220
 221 int unregister_shallow(const unsigned char *sha1)
 222 {
 223         int pos = commit_graft_pos(sha1);
 224         if (pos < 0)
 225                 return -1;
 226         if (pos + 1 < commit_graft_nr)
 227                 memcpy(commit_graft + pos, commit_graft + pos + 1,
 228                                 sizeof(struct commit_graft *)
 229                                 * (commit_graft_nr - pos - 1));
 230         commit_graft_nr--;
 231         return 0;
 232 }
 233
 234 int parse_commit_buffer(struct commit *item, void *buffer, unsigned long size)
 235 {
 236         char *tail = buffer;
 237         char *bufptr = buffer;
 238         unsigned char parent[20];
 239         struct commit_list **pptr;
 240         struct commit_graft *graft;
 241
 242         if (item->object.parsed)
 243                 return 0;
 244         item->object.parsed = 1;
 245         tail += size;
 246         if (tail <= bufptr + 46 || memcmp(bufptr, "tree ", 5) || bufptr[45] != '\n')
 247                 return error("bogus commit object %s", sha1_to_hex(item->object.sha1));
 248         if (get_sha1_hex(bufptr + 5, parent) < 0)
 249                 return error("bad tree pointer in commit %s",
 250                              sha1_to_hex(item->object.sha1));
 251         item->tree = lookup_tree(parent);
 252         bufptr += 46; /* "tree " + "hex sha1" + "\n" */
 253         pptr = &item->parents;
 254
 255         graft = lookup_commit_graft(item->object.sha1);
 256         while (bufptr + 48 < tail && !memcmp(bufptr, "parent ", 7)) {
 257                 struct commit *new_parent;
 258
 259                 if (tail <= bufptr + 48 ||
 260                     get_sha1_hex(bufptr + 7, parent) ||
 261                     bufptr[47] != '\n')
 262                         return error("bad parents in commit %s", sha1_to_hex(item->object.sha1));
 263                 bufptr += 48;
 264                 /*
 265                  * The clone is shallow if nr_parent < 0, and we must
 266                  * not traverse its real parents even when we unhide them.
 267                  */
 268                 if (graft && (graft->nr_parent < 0 || grafts_replace_parents))
 269                         continue;
 270                 new_parent = lookup_commit(parent);
 271                 if (new_parent)
 272                         pptr = &commit_list_insert(new_parent, pptr)->next;
 273         }
 274         if (graft) {
 275                 int i;
 276                 struct commit *new_parent;
 277                 for (i = 0; i < graft->nr_parent; i++) {
 278                         new_parent = lookup_commit(graft->parent[i]);
 279                         if (!new_parent)
 280                                 continue;
 281                         pptr = &commit_list_insert(new_parent, pptr)->next;
 282                 }
 283         }
 284         item->date = parse_commit_date(bufptr, tail);
 285
 286         return 0;
 287 }
 288
 289 int parse_commit(struct commit *item)
 290 {
 291         enum object_type type;
 292         void *buffer;
 293         unsigned long size;
 294         int ret;
 295
 296         if (!item)
 297                 return -1;
 298         if (item->object.parsed)
 299                 return 0;
 300         buffer = read_sha1_file(item->object.sha1, &type, &size);
 301         if (!buffer)
 302                 return error("Could not read %s",
 303                              sha1_to_hex(item->object.sha1));
 304         if (type != OBJ_COMMIT) {
 305                 free(buffer);
 306                 return error("Object %s not a commit",
 307                              sha1_to_hex(item->object.sha1));
 308         }
 309         ret = parse_commit_buffer(item, buffer, size);
 310         if (save_commit_buffer && !ret) {
 311                 item->buffer = buffer;
 312                 return 0;
 313         }
 314         free(buffer);
 315         return ret;
 316 }
 317
 318 struct commit_list *commit_list_insert(struct commit *item, struct commit_list **list_p)
 319 {
 320         struct commit_list *new_list = xmalloc(sizeof(struct commit_list));
 321         new_list->item = item;
 322         new_list->next = *list_p;
 323         *list_p = new_list;
 324         return new_list;
 325 }
 326
 327 unsigned commit_list_count(const struct commit_list *l)
 328 {
 329         unsigned c = 0;
 330         for (; l; l = l->next )
 331                 c++;
 332         return c;
 333 }
 334
 335 void free_commit_list(struct commit_list *list)
 336 {
 337         while (list) {
 338                 struct commit_list *temp = list;
 339                 list = temp->next;
 340                 free(temp);
 341         }
 342 }
 343
 344 struct commit_list * insert_by_date(struct commit *item, struct commit_list **list)
 345 {
 346         struct commit_list **pp = list;
 347         struct commit_list *p;
 348         while ((p = *pp) != NULL) {
 349                 if (p->item->date < item->date) {
 350                         break;
 351                 }
 352                 pp = &p->next;
 353         }
 354         return commit_list_insert(item, pp);
 355 }
 356
 357
 358 void sort_by_date(struct commit_list **list)
 359 {
 360         struct commit_list *ret = NULL;
 361         while (*list) {
 362                 insert_by_date((*list)->item, &ret);
 363                 *list = (*list)->next;
 364         }
 365         *list = ret;
 366 }
 367
 368 struct commit *pop_most_recent_commit(struct commit_list **list,
 369                                       unsigned int mark)
 370 {
 371         struct commit *ret = (*list)->item;
 372         struct commit_list *parents = ret->parents;
 373         struct commit_list *old = *list;
 374
 375         *list = (*list)->next;
 376         free(old);
 377
 378         while (parents) {
 379                 struct commit *commit = parents->item;
 380                 if (!parse_commit(commit) && !(commit->object.flags & mark)) {
 381                         commit->object.flags |= mark;
 382                         insert_by_date(commit, list);
 383                 }
 384                 parents = parents->next;
 385         }
 386         return ret;
 387 }
 388
 389 void clear_commit_marks(struct commit *commit, unsigned int mark)
 390 {
 391         while (commit) {
 392                 struct commit_list *parents;
 393
 394                 if (!(mark & commit->object.flags))
 395                         return;
 396
 397                 commit->object.flags &= ~mark;
 398
 399                 parents = commit->parents;
 400                 if (!parents)
 401                         return;
 402
 403                 while ((parents = parents->next))
 404                         clear_commit_marks(parents->item, mark);
 405
 406                 commit = commit->parents->item;
 407         }
 408 }
 409
 410 struct commit *pop_commit(struct commit_list **stack)
 411 {
 412         struct commit_list *top = *stack;
 413         struct commit *item = top ? top->item : NULL;
 414
 415         if (top) {
 416                 *stack = top->next;
 417                 free(top);
 418         }
 419         return item;
 420 }
 421
 422 /*
 423  * Performs an in-place topological sort on the list supplied.
 424  */
 425 void sort_in_topological_order(struct commit_list ** list, int lifo)
 426 {
 427         struct commit_list *next, *orig = *list;
 428         struct commit_list *work, **insert;
 429         struct commit_list **pptr;
 430
 431         if (!orig)
 432                 return;
 433         *list = NULL;
 434
 435         /* Mark them and clear the indegree */
 436         for (next = orig; next; next = next->next) {
 437                 struct commit *commit = next->item;
 438                 commit->indegree = 1;
 439         }
 440
 441         /* update the indegree */
 442         for (next = orig; next; next = next->next) {
 443                 struct commit_list * parents = next->item->parents;
 444                 while (parents) {
 445                         struct commit *parent = parents->item;
 446
 447                         if (parent->indegree)
 448                                 parent->indegree++;
 449                         parents = parents->next;
 450                 }
 451         }
 452
 453         /*
 454          * find the tips
 455          *
 456          * tips are nodes not reachable from any other node in the list
 457          *
 458          * the tips serve as a starting set for the work queue.
 459          */
 460         work = NULL;
 461         insert = &work;
 462         for (next = orig; next; next = next->next) {
 463                 struct commit *commit = next->item;
 464
 465                 if (commit->indegree == 1)
 466                         insert = &commit_list_insert(commit, insert)->next;
 467         }
 468
 469         /* process the list in topological order */
 470         if (!lifo)
 471                 sort_by_date(&work);
 472
 473         pptr = list;
 474         *list = NULL;
 475         while (work) {
 476                 struct commit *commit;
 477                 struct commit_list *parents, *work_item;
 478
 479                 work_item = work;
 480                 work = work_item->next;
 481                 work_item->next = NULL;
 482
 483                 commit = work_item->item;
 484                 for (parents = commit->parents; parents ; parents = parents->next) {
 485                         struct commit *parent=parents->item;
 486
 487                         if (!parent->indegree)
 488                                 continue;
 489
 490                         /*
 491                          * parents are only enqueued for emission
 492                          * when all their children have been emitted thereby
 493                          * guaranteeing topological order.
 494                          */
 495                         if (--parent->indegree == 1) {
 496                                 if (!lifo)
 497                                         insert_by_date(parent, &work);
 498                                 else
 499                                         commit_list_insert(parent, &work);
 500                         }
 501                 }
 502                 /*
 503                  * work_item is a commit all of whose children
 504                  * have already been emitted. we can emit it now.
 505                  */
 506                 commit->indegree = 0;
 507                 *pptr = work_item;
 508                 pptr = &work_item->next;
 509         }
 510 }
 511
 512 /* merge-base stuff */
 513
 514 /* bits #0..15 in revision.h */
 515 #define PARENT1         (1u<<16)
 516 #define PARENT2         (1u<<17)
 517 #define STALE           (1u<<18)
 518 #define RESULT          (1u<<19)
 519
 520 static const unsigned all_flags = (PARENT1 | PARENT2 | STALE | RESULT);
 521
 522 static struct commit *interesting(struct commit_list *list)
 523 {
 524         while (list) {
 525                 struct commit *commit = list->item;
 526                 list = list->next;
 527                 if (commit->object.flags & STALE)
 528                         continue;
 529                 return commit;
 530         }
 531         return NULL;
 532 }
 533
 534 static struct commit_list *merge_bases_many(struct commit *one, int n, struct commit **twos)
 535 {
 536         struct commit_list *list = NULL;
 537         struct commit_list *result = NULL;
 538         int i;
 539
 540         for (i = 0; i < n; i++) {
 541                 if (one == twos[i])
 542                         /*
 543                          * We do not mark this even with RESULT so we do not
 544                          * have to clean it up.
 545                          */
 546                         return commit_list_insert(one, &result);
 547         }
 548
 549         if (parse_commit(one))
 550                 return NULL;
 551         for (i = 0; i < n; i++) {
 552                 if (parse_commit(twos[i]))
 553                         return NULL;
 554         }
 555
 556         one->object.flags |= PARENT1;
 557         insert_by_date(one, &list);
 558         for (i = 0; i < n; i++) {
 559                 twos[i]->object.flags |= PARENT2;
 560                 insert_by_date(twos[i], &list);
 561         }
 562
 563         while (interesting(list)) {
 564                 struct commit *commit;
 565                 struct commit_list *parents;
 566                 struct commit_list *next;
 567                 int flags;
 568
 569                 commit = list->item;
 570                 next = list->next;
 571                 free(list);
 572                 list = next;
 573
 574                 flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
 575                 if (flags == (PARENT1 | PARENT2)) {
 576                         if (!(commit->object.flags & RESULT)) {
 577                                 commit->object.flags |= RESULT;
 578                                 insert_by_date(commit, &result);
 579                         }
 580                         /* Mark parents of a found merge stale */
 581                         flags |= STALE;
 582                 }
 583                 parents = commit->parents;
 584                 while (parents) {
 585                         struct commit *p = parents->item;
 586                         parents = parents->next;
 587                         if ((p->object.flags & flags) == flags)
 588                                 continue;
 589                         if (parse_commit(p))
 590                                 return NULL;
 591                         p->object.flags |= flags;
 592                         insert_by_date(p, &list);
 593                 }
 594         }
 595
 596         /* Clean up the result to remove stale ones */
 597         free_commit_list(list);
 598         list = result; result = NULL;
 599         while (list) {
 600                 struct commit_list *next = list->next;
 601                 if (!(list->item->object.flags & STALE))
 602                         insert_by_date(list->item, &result);
 603                 free(list);
 604                 list = next;
 605         }
 606         return result;
 607 }
 608
 609 struct commit_list *get_octopus_merge_bases(struct commit_list *in)
 610 {
 611         struct commit_list *i, *j, *k, *ret = NULL;
 612         struct commit_list **pptr = &ret;
 613
 614         for (i = in; i; i = i->next) {
 615                 if (!ret)
 616                         pptr = &commit_list_insert(i->item, pptr)->next;
 617                 else {
 618                         struct commit_list *new = NULL, *end = NULL;
 619
 620                         for (j = ret; j; j = j->next) {
 621                                 struct commit_list *bases;
 622                                 bases = get_merge_bases(i->item, j->item, 1);
 623                                 if (!new)
 624                                         new = bases;
 625                                 else
 626                                         end->next = bases;
 627                                 for (k = bases; k; k = k->next)
 628                                         end = k;
 629                         }
 630                         ret = new;
 631                 }
 632         }
 633         return ret;
 634 }
 635
 636 struct commit_list *get_merge_bases_many(struct commit *one,
 637                                          int n,
 638                                          struct commit **twos,
 639                                          int cleanup)
 640 {
 641         struct commit_list *list;
 642         struct commit **rslt;
 643         struct commit_list *result;
 644         int cnt, i, j;
 645
 646         result = merge_bases_many(one, n, twos);
 647         for (i = 0; i < n; i++) {
 648                 if (one == twos[i])
 649                         return result;
 650         }
 651         if (!result || !result->next) {
 652                 if (cleanup) {
 653                         clear_commit_marks(one, all_flags);
 654                         for (i = 0; i < n; i++)
 655                                 clear_commit_marks(twos[i], all_flags);
 656                 }
 657                 return result;
 658         }
 659
 660         /* There are more than one */
 661         cnt = 0;
 662         list = result;
 663         while (list) {
 664                 list = list->next;
 665                 cnt++;
 666         }
 667         rslt = xcalloc(cnt, sizeof(*rslt));
 668         for (list = result, i = 0; list; list = list->next)
 669                 rslt[i++] = list->item;
 670         free_commit_list(result);
 671
 672         clear_commit_marks(one, all_flags);
 673         for (i = 0; i < n; i++)
 674                 clear_commit_marks(twos[i], all_flags);
 675         for (i = 0; i < cnt - 1; i++) {
 676                 for (j = i+1; j < cnt; j++) {
 677                         if (!rslt[i] || !rslt[j])
 678                                 continue;
 679                         result = merge_bases_many(rslt[i], 1, &rslt[j]);
 680                         clear_commit_marks(rslt[i], all_flags);
 681                         clear_commit_marks(rslt[j], all_flags);
 682                         for (list = result; list; list = list->next) {
 683                                 if (rslt[i] == list->item)
 684                                         rslt[i] = NULL;
 685                                 if (rslt[j] == list->item)
 686                                         rslt[j] = NULL;
 687                         }
 688                 }
 689         }
 690
 691         /* Surviving ones in rslt[] are the independent results */
 692         result = NULL;
 693         for (i = 0; i < cnt; i++) {
 694                 if (rslt[i])
 695                         insert_by_date(rslt[i], &result);
 696         }
 697         free(rslt);
 698         return result;
 699 }
 700
 701 struct commit_list *get_merge_bases(struct commit *one, struct commit *two,
 702                                     int cleanup)
 703 {
 704         return get_merge_bases_many(one, 1, &two, cleanup);
 705 }
 706
 707 int is_descendant_of(struct commit *commit, struct commit_list *with_commit)
 708 {
 709         if (!with_commit)
 710                 return 1;
 711         while (with_commit) {
 712                 struct commit *other;
 713
 714                 other = with_commit->item;
 715                 with_commit = with_commit->next;
 716                 if (in_merge_bases(other, &commit, 1))
 717                         return 1;
 718         }
 719         return 0;
 720 }
 721
 722 int in_merge_bases(struct commit *commit, struct commit **reference, int num)
 723 {
 724         struct commit_list *bases, *b;
 725         int ret = 0;
 726
 727         if (num == 1)
 728                 bases = get_merge_bases(commit, *reference, 1);
 729         else
 730                 die("not yet");
 731         for (b = bases; b; b = b->next) {
 732                 if (!hashcmp(commit->object.sha1, b->item->object.sha1)) {
 733                         ret = 1;
 734                         break;
 735                 }
 736         }
 737
 738         free_commit_list(bases);
 739         return ret;
 740 }
 741
 742 struct commit_list *reduce_heads(struct commit_list *heads)
 743 {
 744         struct commit_list *p;
 745         struct commit_list *result = NULL, **tail = &result;
 746         struct commit **other;
 747         size_t num_head, num_other;
 748
 749         if (!heads)
 750                 return NULL;
 751
 752         /* Avoid unnecessary reallocations */
 753         for (p = heads, num_head = 0; p; p = p->next)
 754                 num_head++;
 755         other = xcalloc(sizeof(*other), num_head);
 756
 757         /* For each commit, see if it can be reached by others */
 758         for (p = heads; p; p = p->next) {
 759                 struct commit_list *q, *base;
 760
 761                 /* Do we already have this in the result? */
 762                 for (q = result; q; q = q->next)
 763                         if (p->item == q->item)
 764                                 break;
 765                 if (q)
 766                         continue;
 767
 768                 num_other = 0;
 769                 for (q = heads; q; q = q->next) {
 770                         if (p->item == q->item)
 771                                 continue;
 772                         other[num_other++] = q->item;
 773                 }
 774                 if (num_other)
 775                         base = get_merge_bases_many(p->item, num_other, other, 1);
 776                 else
 777                         base = NULL;
 778                 /*
 779                  * If p->item does not have anything common with other
 780                  * commits, there won't be any merge base.  If it is
 781                  * reachable from some of the others, p->item will be
 782                  * the merge base.  If its history is connected with
 783                  * others, but p->item is not reachable by others, we
 784                  * will get something other than p->item back.
 785                  */
 786                 if (!base || (base->item != p->item))
 787                         tail = &(commit_list_insert(p->item, tail)->next);
 788                 free_commit_list(base);
 789         }
 790         free(other);
 791         return result;
 792 }