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
   9 int save_commit_buffer = 1;
  10
  11 const char *commit_type = "commit";
  12
  13 static struct commit *check_commit(struct object *obj,
  14                                    const unsigned char *sha1,
  15                                    int quiet)
  16 {
  17         if (obj->type != OBJ_COMMIT) {
  18                 if (!quiet)
  19                         error("Object %s is a %s, not a commit",
  20                               sha1_to_hex(sha1), typename(obj->type));
  21                 return NULL;
  22         }
  23         return (struct commit *) obj;
  24 }
  25
  26 struct commit *lookup_commit_reference_gently(const unsigned char *sha1,
  27                                               int quiet)
  28 {
  29         struct object *obj = deref_tag(parse_object(sha1), NULL, 0);
  30
  31         if (!obj)
  32                 return NULL;
  33         return check_commit(obj, sha1, quiet);
  34 }
  35
  36 struct commit *lookup_commit_reference(const unsigned char *sha1)
  37 {
  38         return lookup_commit_reference_gently(sha1, 0);
  39 }
  40
  41 struct commit *lookup_commit(const unsigned char *sha1)
  42 {
  43         struct object *obj = lookup_object(sha1);
  44         if (!obj)
  45                 return create_object(sha1, OBJ_COMMIT, alloc_commit_node());
  46         if (!obj->type)
  47                 obj->type = OBJ_COMMIT;
  48         return check_commit(obj, sha1, 0);
  49 }
  50
  51 static unsigned long parse_commit_date(const char *buf, const char *tail)
  52 {
  53         unsigned long date;
  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         date = strtoul(dateptr, NULL, 10);
  77         if (date == ULONG_MAX)
  78                 date = 0;
  79         return date;
  80 }
  81
  82 static struct commit_graft **commit_graft;
  83 static int commit_graft_alloc, commit_graft_nr;
  84
  85 static int commit_graft_pos(const unsigned char *sha1)
  86 {
  87         int lo, hi;
  88         lo = 0;
  89         hi = commit_graft_nr;
  90         while (lo < hi) {
  91                 int mi = (lo + hi) / 2;
  92                 struct commit_graft *graft = commit_graft[mi];
  93                 int cmp = hashcmp(sha1, graft->sha1);
  94                 if (!cmp)
  95                         return mi;
  96                 if (cmp < 0)
  97                         hi = mi;
  98                 else
  99                         lo = mi + 1;
 100         }
 101         return -lo - 1;
 102 }
 103
 104 int register_commit_graft(struct commit_graft *graft, int ignore_dups)
 105 {
 106         int pos = commit_graft_pos(graft->sha1);
 107
 108         if (0 <= pos) {
 109                 if (ignore_dups)
 110                         free(graft);
 111                 else {
 112                         free(commit_graft[pos]);
 113                         commit_graft[pos] = graft;
 114                 }
 115                 return 1;
 116         }
 117         pos = -pos - 1;
 118         if (commit_graft_alloc <= ++commit_graft_nr) {
 119                 commit_graft_alloc = alloc_nr(commit_graft_alloc);
 120                 commit_graft = xrealloc(commit_graft,
 121                                         sizeof(*commit_graft) *
 122                                         commit_graft_alloc);
 123         }
 124         if (pos < commit_graft_nr)
 125                 memmove(commit_graft + pos + 1,
 126                         commit_graft + pos,
 127                         (commit_graft_nr - pos - 1) *
 128                         sizeof(*commit_graft));
 129         commit_graft[pos] = graft;
 130         return 0;
 131 }
 132
 133 struct commit_graft *read_graft_line(char *buf, int len)
 134 {
 135         /* The format is just "Commit Parent1 Parent2 ...\n" */
 136         int i;
 137         struct commit_graft *graft = NULL;
 138
 139         if (buf[len-1] == '\n')
 140                 buf[--len] = 0;
 141         if (buf[0] == '#' || buf[0] == '\0')
 142                 return NULL;
 143         if ((len + 1) % 41) {
 144         bad_graft_data:
 145                 error("bad graft data: %s", buf);
 146                 free(graft);
 147                 return NULL;
 148         }
 149         i = (len + 1) / 41 - 1;
 150         graft = xmalloc(sizeof(*graft) + 20 * i);
 151         graft->nr_parent = i;
 152         if (get_sha1_hex(buf, graft->sha1))
 153                 goto bad_graft_data;
 154         for (i = 40; i < len; i += 41) {
 155                 if (buf[i] != ' ')
 156                         goto bad_graft_data;
 157                 if (get_sha1_hex(buf + i + 1, graft->parent[i/41]))
 158                         goto bad_graft_data;
 159         }
 160         return graft;
 161 }
 162
 163 static int read_graft_file(const char *graft_file)
 164 {
 165         FILE *fp = fopen(graft_file, "r");
 166         char buf[1024];
 167         if (!fp)
 168                 return -1;
 169         while (fgets(buf, sizeof(buf), fp)) {
 170                 /* The format is just "Commit Parent1 Parent2 ...\n" */
 171                 int len = strlen(buf);
 172                 struct commit_graft *graft = read_graft_line(buf, len);
 173                 if (!graft)
 174                         continue;
 175                 if (register_commit_graft(graft, 1))
 176                         error("duplicate graft data: %s", buf);
 177         }
 178         fclose(fp);
 179         return 0;
 180 }
 181
 182 static void prepare_commit_graft(void)
 183 {
 184         static int commit_graft_prepared;
 185         char *graft_file;
 186
 187         if (commit_graft_prepared)
 188                 return;
 189         graft_file = get_graft_file();
 190         read_graft_file(graft_file);
 191         /* make sure shallows are read */
 192         is_repository_shallow();
 193         commit_graft_prepared = 1;
 194 }
 195
 196 struct commit_graft *lookup_commit_graft(const unsigned char *sha1)
 197 {
 198         int pos;
 199         prepare_commit_graft();
 200         pos = commit_graft_pos(sha1);
 201         if (pos < 0)
 202                 return NULL;
 203         return commit_graft[pos];
 204 }
 205
 206 int write_shallow_commits(int fd, int use_pack_protocol)
 207 {
 208         int i, count = 0;
 209         for (i = 0; i < commit_graft_nr; i++)
 210                 if (commit_graft[i]->nr_parent < 0) {
 211                         const char *hex =
 212                                 sha1_to_hex(commit_graft[i]->sha1);
 213                         count++;
 214                         if (use_pack_protocol)
 215                                 packet_write(fd, "shallow %s", hex);
 216                         else {
 217                                 if (write_in_full(fd, hex,  40) != 40)
 218                                         break;
 219                                 if (write_in_full(fd, "\n", 1) != 1)
 220                                         break;
 221                         }
 222                 }
 223         return count;
 224 }
 225
 226 int unregister_shallow(const unsigned char *sha1)
 227 {
 228         int pos = commit_graft_pos(sha1);
 229         if (pos < 0)
 230                 return -1;
 231         if (pos + 1 < commit_graft_nr)
 232                 memcpy(commit_graft + pos, commit_graft + pos + 1,
 233                                 sizeof(struct commit_graft *)
 234                                 * (commit_graft_nr - pos - 1));
 235         commit_graft_nr--;
 236         return 0;
 237 }
 238
 239 int parse_commit_buffer(struct commit *item, void *buffer, unsigned long size)
 240 {
 241         char *tail = buffer;
 242         char *bufptr = buffer;
 243         unsigned char parent[20];
 244         struct commit_list **pptr;
 245         struct commit_graft *graft;
 246
 247         if (item->object.parsed)
 248                 return 0;
 249         item->object.parsed = 1;
 250         tail += size;
 251         if (tail <= bufptr + 46 || memcmp(bufptr, "tree ", 5) || bufptr[45] != '\n')
 252                 return error("bogus commit object %s", sha1_to_hex(item->object.sha1));
 253         if (get_sha1_hex(bufptr + 5, parent) < 0)
 254                 return error("bad tree pointer in commit %s",
 255                              sha1_to_hex(item->object.sha1));
 256         item->tree = lookup_tree(parent);
 257         bufptr += 46; /* "tree " + "hex sha1" + "\n" */
 258         pptr = &item->parents;
 259
 260         graft = lookup_commit_graft(item->object.sha1);
 261         while (bufptr + 48 < tail && !memcmp(bufptr, "parent ", 7)) {
 262                 struct commit *new_parent;
 263
 264                 if (tail <= bufptr + 48 ||
 265                     get_sha1_hex(bufptr + 7, parent) ||
 266                     bufptr[47] != '\n')
 267                         return error("bad parents in commit %s", sha1_to_hex(item->object.sha1));
 268                 bufptr += 48;
 269                 /*
 270                  * The clone is shallow if nr_parent < 0, and we must
 271                  * not traverse its real parents even when we unhide them.
 272                  */
 273                 if (graft && (graft->nr_parent < 0 || grafts_replace_parents))
 274                         continue;
 275                 new_parent = lookup_commit(parent);
 276                 if (new_parent)
 277                         pptr = &commit_list_insert(new_parent, pptr)->next;
 278         }
 279         if (graft) {
 280                 int i;
 281                 struct commit *new_parent;
 282                 for (i = 0; i < graft->nr_parent; i++) {
 283                         new_parent = lookup_commit(graft->parent[i]);
 284                         if (!new_parent)
 285                                 continue;
 286                         pptr = &commit_list_insert(new_parent, pptr)->next;
 287                 }
 288         }
 289         item->date = parse_commit_date(bufptr, tail);
 290
 291         return 0;
 292 }
 293
 294 int parse_commit(struct commit *item)
 295 {
 296         enum object_type type;
 297         void *buffer;
 298         unsigned long size;
 299         int ret;
 300
 301         if (!item)
 302                 return -1;
 303         if (item->object.parsed)
 304                 return 0;
 305         buffer = read_sha1_file(item->object.sha1, &type, &size);
 306         if (!buffer)
 307                 return error("Could not read %s",
 308                              sha1_to_hex(item->object.sha1));
 309         if (type != OBJ_COMMIT) {
 310                 free(buffer);
 311                 return error("Object %s not a commit",
 312                              sha1_to_hex(item->object.sha1));
 313         }
 314         ret = parse_commit_buffer(item, buffer, size);
 315         if (save_commit_buffer && !ret) {
 316                 item->buffer = buffer;
 317                 return 0;
 318         }
 319         free(buffer);
 320         return ret;
 321 }
 322
 323 struct commit_list *commit_list_insert(struct commit *item, struct commit_list **list_p)
 324 {
 325         struct commit_list *new_list = xmalloc(sizeof(struct commit_list));
 326         new_list->item = item;
 327         new_list->next = *list_p;
 328         *list_p = new_list;
 329         return new_list;
 330 }
 331
 332 unsigned commit_list_count(const struct commit_list *l)
 333 {
 334         unsigned c = 0;
 335         for (; l; l = l->next )
 336                 c++;
 337         return c;
 338 }
 339
 340 void free_commit_list(struct commit_list *list)
 341 {
 342         while (list) {
 343                 struct commit_list *temp = list;
 344                 list = temp->next;
 345                 free(temp);
 346         }
 347 }
 348
 349 struct commit_list * insert_by_date(struct commit *item, struct commit_list **list)
 350 {
 351         struct commit_list **pp = list;
 352         struct commit_list *p;
 353         while ((p = *pp) != NULL) {
 354                 if (p->item->date < item->date) {
 355                         break;
 356                 }
 357                 pp = &p->next;
 358         }
 359         return commit_list_insert(item, pp);
 360 }
 361
 362
 363 void sort_by_date(struct commit_list **list)
 364 {
 365         struct commit_list *ret = NULL;
 366         while (*list) {
 367                 insert_by_date((*list)->item, &ret);
 368                 *list = (*list)->next;
 369         }
 370         *list = ret;
 371 }
 372
 373 struct commit *pop_most_recent_commit(struct commit_list **list,
 374                                       unsigned int mark)
 375 {
 376         struct commit *ret = (*list)->item;
 377         struct commit_list *parents = ret->parents;
 378         struct commit_list *old = *list;
 379
 380         *list = (*list)->next;
 381         free(old);
 382
 383         while (parents) {
 384                 struct commit *commit = parents->item;
 385                 if (!parse_commit(commit) && !(commit->object.flags & mark)) {
 386                         commit->object.flags |= mark;
 387                         insert_by_date(commit, list);
 388                 }
 389                 parents = parents->next;
 390         }
 391         return ret;
 392 }
 393
 394 void clear_commit_marks(struct commit *commit, unsigned int mark)
 395 {
 396         while (commit) {
 397                 struct commit_list *parents;
 398
 399                 if (!(mark & commit->object.flags))
 400                         return;
 401
 402                 commit->object.flags &= ~mark;
 403
 404                 parents = commit->parents;
 405                 if (!parents)
 406                         return;
 407
 408                 while ((parents = parents->next))
 409                         clear_commit_marks(parents->item, mark);
 410
 411                 commit = commit->parents->item;
 412         }
 413 }
 414
 415 struct commit *pop_commit(struct commit_list **stack)
 416 {
 417         struct commit_list *top = *stack;
 418         struct commit *item = top ? top->item : NULL;
 419
 420         if (top) {
 421                 *stack = top->next;
 422                 free(top);
 423         }
 424         return item;
 425 }
 426
 427 /*
 428  * Performs an in-place topological sort on the list supplied.
 429  */
 430 void sort_in_topological_order(struct commit_list ** list, int lifo)
 431 {
 432         struct commit_list *next, *orig = *list;
 433         struct commit_list *work, **insert;
 434         struct commit_list **pptr;
 435
 436         if (!orig)
 437                 return;
 438         *list = NULL;
 439
 440         /* Mark them and clear the indegree */
 441         for (next = orig; next; next = next->next) {
 442                 struct commit *commit = next->item;
 443                 commit->indegree = 1;
 444         }
 445
 446         /* update the indegree */
 447         for (next = orig; next; next = next->next) {
 448                 struct commit_list * parents = next->item->parents;
 449                 while (parents) {
 450                         struct commit *parent = parents->item;
 451
 452                         if (parent->indegree)
 453                                 parent->indegree++;
 454                         parents = parents->next;
 455                 }
 456         }
 457
 458         /*
 459          * find the tips
 460          *
 461          * tips are nodes not reachable from any other node in the list
 462          *
 463          * the tips serve as a starting set for the work queue.
 464          */
 465         work = NULL;
 466         insert = &work;
 467         for (next = orig; next; next = next->next) {
 468                 struct commit *commit = next->item;
 469
 470                 if (commit->indegree == 1)
 471                         insert = &commit_list_insert(commit, insert)->next;
 472         }
 473
 474         /* process the list in topological order */
 475         if (!lifo)
 476                 sort_by_date(&work);
 477
 478         pptr = list;
 479         *list = NULL;
 480         while (work) {
 481                 struct commit *commit;
 482                 struct commit_list *parents, *work_item;
 483
 484                 work_item = work;
 485                 work = work_item->next;
 486                 work_item->next = NULL;
 487
 488                 commit = work_item->item;
 489                 for (parents = commit->parents; parents ; parents = parents->next) {
 490                         struct commit *parent=parents->item;
 491
 492                         if (!parent->indegree)
 493                                 continue;
 494
 495                         /*
 496                          * parents are only enqueued for emission
 497                          * when all their children have been emitted thereby
 498                          * guaranteeing topological order.
 499                          */
 500                         if (--parent->indegree == 1) {
 501                                 if (!lifo)
 502                                         insert_by_date(parent, &work);
 503                                 else
 504                                         commit_list_insert(parent, &work);
 505                         }
 506                 }
 507                 /*
 508                  * work_item is a commit all of whose children
 509                  * have already been emitted. we can emit it now.
 510                  */
 511                 commit->indegree = 0;
 512                 *pptr = work_item;
 513                 pptr = &work_item->next;
 514         }
 515 }
 516
 517 /* merge-base stuff */
 518
 519 /* bits #0..15 in revision.h */
 520 #define PARENT1         (1u<<16)
 521 #define PARENT2         (1u<<17)
 522 #define STALE           (1u<<18)
 523 #define RESULT          (1u<<19)
 524
 525 static const unsigned all_flags = (PARENT1 | PARENT2 | STALE | RESULT);
 526
 527 static struct commit *interesting(struct commit_list *list)
 528 {
 529         while (list) {
 530                 struct commit *commit = list->item;
 531                 list = list->next;
 532                 if (commit->object.flags & STALE)
 533                         continue;
 534                 return commit;
 535         }
 536         return NULL;
 537 }
 538
 539 static struct commit_list *merge_bases_many(struct commit *one, int n, struct commit **twos)
 540 {
 541         struct commit_list *list = NULL;
 542         struct commit_list *result = NULL;
 543         int i;
 544
 545         for (i = 0; i < n; i++) {
 546                 if (one == twos[i])
 547                         /*
 548                          * We do not mark this even with RESULT so we do not
 549                          * have to clean it up.
 550                          */
 551                         return commit_list_insert(one, &result);
 552         }
 553
 554         if (parse_commit(one))
 555                 return NULL;
 556         for (i = 0; i < n; i++) {
 557                 if (parse_commit(twos[i]))
 558                         return NULL;
 559         }
 560
 561         one->object.flags |= PARENT1;
 562         insert_by_date(one, &list);
 563         for (i = 0; i < n; i++) {
 564                 twos[i]->object.flags |= PARENT2;
 565                 insert_by_date(twos[i], &list);
 566         }
 567
 568         while (interesting(list)) {
 569                 struct commit *commit;
 570                 struct commit_list *parents;
 571                 struct commit_list *n;
 572                 int flags;
 573
 574                 commit = list->item;
 575                 n = list->next;
 576                 free(list);
 577                 list = n;
 578
 579                 flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
 580                 if (flags == (PARENT1 | PARENT2)) {
 581                         if (!(commit->object.flags & RESULT)) {
 582                                 commit->object.flags |= RESULT;
 583                                 insert_by_date(commit, &result);
 584                         }
 585                         /* Mark parents of a found merge stale */
 586                         flags |= STALE;
 587                 }
 588                 parents = commit->parents;
 589                 while (parents) {
 590                         struct commit *p = parents->item;
 591                         parents = parents->next;
 592                         if ((p->object.flags & flags) == flags)
 593                                 continue;
 594                         if (parse_commit(p))
 595                                 return NULL;
 596                         p->object.flags |= flags;
 597                         insert_by_date(p, &list);
 598                 }
 599         }
 600
 601         /* Clean up the result to remove stale ones */
 602         free_commit_list(list);
 603         list = result; result = NULL;
 604         while (list) {
 605                 struct commit_list *n = list->next;
 606                 if (!(list->item->object.flags & STALE))
 607                         insert_by_date(list->item, &result);
 608                 free(list);
 609                 list = n;
 610         }
 611         return result;
 612 }
 613
 614 struct commit_list *get_octopus_merge_bases(struct commit_list *in)
 615 {
 616         struct commit_list *i, *j, *k, *ret = NULL;
 617         struct commit_list **pptr = &ret;
 618
 619         for (i = in; i; i = i->next) {
 620                 if (!ret)
 621                         pptr = &commit_list_insert(i->item, pptr)->next;
 622                 else {
 623                         struct commit_list *new = NULL, *end = NULL;
 624
 625                         for (j = ret; j; j = j->next) {
 626                                 struct commit_list *bases;
 627                                 bases = get_merge_bases(i->item, j->item, 1);
 628                                 if (!new)
 629                                         new = bases;
 630                                 else
 631                                         end->next = bases;
 632                                 for (k = bases; k; k = k->next)
 633                                         end = k;
 634                         }
 635                         ret = new;
 636                 }
 637         }
 638         return ret;
 639 }
 640
 641 struct commit_list *get_merge_bases_many(struct commit *one,
 642                                          int n,
 643                                          struct commit **twos,
 644                                          int cleanup)
 645 {
 646         struct commit_list *list;
 647         struct commit **rslt;
 648         struct commit_list *result;
 649         int cnt, i, j;
 650
 651         result = merge_bases_many(one, n, twos);
 652         for (i = 0; i < n; i++) {
 653                 if (one == twos[i])
 654                         return result;
 655         }
 656         if (!result || !result->next) {
 657                 if (cleanup) {
 658                         clear_commit_marks(one, all_flags);
 659                         for (i = 0; i < n; i++)
 660                                 clear_commit_marks(twos[i], all_flags);
 661                 }
 662                 return result;
 663         }
 664
 665         /* There are more than one */
 666         cnt = 0;
 667         list = result;
 668         while (list) {
 669                 list = list->next;
 670                 cnt++;
 671         }
 672         rslt = xcalloc(cnt, sizeof(*rslt));
 673         for (list = result, i = 0; list; list = list->next)
 674                 rslt[i++] = list->item;
 675         free_commit_list(result);
 676
 677         clear_commit_marks(one, all_flags);
 678         for (i = 0; i < n; i++)
 679                 clear_commit_marks(twos[i], all_flags);
 680         for (i = 0; i < cnt - 1; i++) {
 681                 for (j = i+1; j < cnt; j++) {
 682                         if (!rslt[i] || !rslt[j])
 683                                 continue;
 684                         result = merge_bases_many(rslt[i], 1, &rslt[j]);
 685                         clear_commit_marks(rslt[i], all_flags);
 686                         clear_commit_marks(rslt[j], all_flags);
 687                         for (list = result; list; list = list->next) {
 688                                 if (rslt[i] == list->item)
 689                                         rslt[i] = NULL;
 690                                 if (rslt[j] == list->item)
 691                                         rslt[j] = NULL;
 692                         }
 693                 }
 694         }
 695
 696         /* Surviving ones in rslt[] are the independent results */
 697         result = NULL;
 698         for (i = 0; i < cnt; i++) {
 699                 if (rslt[i])
 700                         insert_by_date(rslt[i], &result);
 701         }
 702         free(rslt);
 703         return result;
 704 }
 705
 706 struct commit_list *get_merge_bases(struct commit *one, struct commit *two,
 707                                     int cleanup)
 708 {
 709         return get_merge_bases_many(one, 1, &two, cleanup);
 710 }
 711
 712 int is_descendant_of(struct commit *commit, struct commit_list *with_commit)
 713 {
 714         if (!with_commit)
 715                 return 1;
 716         while (with_commit) {
 717                 struct commit *other;
 718
 719                 other = with_commit->item;
 720                 with_commit = with_commit->next;
 721                 if (in_merge_bases(other, &commit, 1))
 722                         return 1;
 723         }
 724         return 0;
 725 }
 726
 727 int in_merge_bases(struct commit *commit, struct commit **reference, int num)
 728 {
 729         struct commit_list *bases, *b;
 730         int ret = 0;
 731
 732         if (num == 1)
 733                 bases = get_merge_bases(commit, *reference, 1);
 734         else
 735                 die("not yet");
 736         for (b = bases; b; b = b->next) {
 737                 if (!hashcmp(commit->object.sha1, b->item->object.sha1)) {
 738                         ret = 1;
 739                         break;
 740                 }
 741         }
 742
 743         free_commit_list(bases);
 744         return ret;
 745 }
 746
 747 struct commit_list *reduce_heads(struct commit_list *heads)
 748 {
 749         struct commit_list *p;
 750         struct commit_list *result = NULL, **tail = &result;
 751         struct commit **other;
 752         size_t num_head, num_other;
 753
 754         if (!heads)
 755                 return NULL;
 756
 757         /* Avoid unnecessary reallocations */
 758         for (p = heads, num_head = 0; p; p = p->next)
 759                 num_head++;
 760         other = xcalloc(sizeof(*other), num_head);
 761
 762         /* For each commit, see if it can be reached by others */
 763         for (p = heads; p; p = p->next) {
 764                 struct commit_list *q, *base;
 765
 766                 /* Do we already have this in the result? */
 767                 for (q = result; q; q = q->next)
 768                         if (p->item == q->item)
 769                                 break;
 770                 if (q)
 771                         continue;
 772
 773                 num_other = 0;
 774                 for (q = heads; q; q = q->next) {
 775                         if (p->item == q->item)
 776                                 continue;
 777                         other[num_other++] = q->item;
 778                 }
 779                 if (num_other)
 780                         base = get_merge_bases_many(p->item, num_other, other, 1);
 781                 else
 782                         base = NULL;
 783                 /*
 784                  * If p->item does not have anything common with other
 785                  * commits, there won't be any merge base.  If it is
 786                  * reachable from some of the others, p->item will be
 787                  * the merge base.  If its history is connected with
 788                  * others, but p->item is not reachable by others, we
 789                  * will get something other than p->item back.
 790                  */
 791                 if (!base || (base->item != p->item))
 792                         tail = &(commit_list_insert(p->item, tail)->next);
 793                 free_commit_list(base);
 794         }
 795         free(other);
 796         return result;
 797 }