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         if (buf[len-1] == '\n')
 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(int fd, 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_write(fd, "shallow %s", hex);
 213                         else {
 214                                 if (write_in_full(fd, hex,  40) != 40)
 215                                         break;
 216                                 if (write_str_in_full(fd, "\n") != 1)
 217                                         break;
 218                         }
 219                 }
 220         return count;
 221 }
 222
 223 int unregister_shallow(const unsigned char *sha1)
 224 {
 225         int pos = commit_graft_pos(sha1);
 226         if (pos < 0)
 227                 return -1;
 228         if (pos + 1 < commit_graft_nr)
 229                 memcpy(commit_graft + pos, commit_graft + pos + 1,
 230                                 sizeof(struct commit_graft *)
 231                                 * (commit_graft_nr - pos - 1));
 232         commit_graft_nr--;
 233         return 0;
 234 }
 235
 236 int parse_commit_buffer(struct commit *item, void *buffer, unsigned long size)
 237 {
 238         char *tail = buffer;
 239         char *bufptr = buffer;
 240         unsigned char parent[20];
 241         struct commit_list **pptr;
 242         struct commit_graft *graft;
 243
 244         if (item->object.parsed)
 245                 return 0;
 246         item->object.parsed = 1;
 247         tail += size;
 248         if (tail <= bufptr + 46 || memcmp(bufptr, "tree ", 5) || bufptr[45] != '\n')
 249                 return error("bogus commit object %s", sha1_to_hex(item->object.sha1));
 250         if (get_sha1_hex(bufptr + 5, parent) < 0)
 251                 return error("bad tree pointer in commit %s",
 252                              sha1_to_hex(item->object.sha1));
 253         item->tree = lookup_tree(parent);
 254         bufptr += 46; /* "tree " + "hex sha1" + "\n" */
 255         pptr = &item->parents;
 256         while (pop_commit(pptr))
 257                 ; /* clear anything from cache */
 258
 259         graft = lookup_commit_graft(item->object.sha1);
 260         while (bufptr + 48 < tail && !memcmp(bufptr, "parent ", 7)) {
 261                 struct commit *new_parent;
 262
 263                 if (tail <= bufptr + 48 ||
 264                     get_sha1_hex(bufptr + 7, parent) ||
 265                     bufptr[47] != '\n')
 266                         return error("bad parents in commit %s", sha1_to_hex(item->object.sha1));
 267                 bufptr += 48;
 268                 /*
 269                  * The clone is shallow if nr_parent < 0, and we must
 270                  * not traverse its real parents even when we unhide them.
 271                  */
 272                 if (graft && (graft->nr_parent < 0 || grafts_replace_parents))
 273                         continue;
 274                 new_parent = lookup_commit(parent);
 275                 if (new_parent)
 276                         pptr = &commit_list_insert(new_parent, pptr)->next;
 277         }
 278         if (graft) {
 279                 int i;
 280                 struct commit *new_parent;
 281                 for (i = 0; i < graft->nr_parent; i++) {
 282                         new_parent = lookup_commit(graft->parent[i]);
 283                         if (!new_parent)
 284                                 continue;
 285                         pptr = &commit_list_insert(new_parent, pptr)->next;
 286                 }
 287         }
 288         item->date = parse_commit_date(bufptr, tail);
 289
 290         return 0;
 291 }
 292
 293 int parse_commit(struct commit *item)
 294 {
 295         enum object_type type;
 296         void *buffer;
 297         unsigned long size;
 298         int ret;
 299
 300         if (!item)
 301                 return -1;
 302         if (item->object.parsed)
 303                 return 0;
 304         buffer = read_sha1_file(item->object.sha1, &type, &size);
 305         if (!buffer)
 306                 return error("Could not read %s",
 307                              sha1_to_hex(item->object.sha1));
 308         if (type != OBJ_COMMIT) {
 309                 free(buffer);
 310                 return error("Object %s not a commit",
 311                              sha1_to_hex(item->object.sha1));
 312         }
 313         ret = parse_commit_buffer(item, buffer, size);
 314         if (save_commit_buffer && !ret) {
 315                 item->buffer = buffer;
 316                 return 0;
 317         }
 318         free(buffer);
 319         return ret;
 320 }
 321
 322 struct commit_list *commit_list_insert(struct commit *item, struct commit_list **list_p)
 323 {
 324         struct commit_list *new_list = xmalloc(sizeof(struct commit_list));
 325         new_list->item = item;
 326         new_list->next = *list_p;
 327         *list_p = new_list;
 328         return new_list;
 329 }
 330
 331 unsigned commit_list_count(const struct commit_list *l)
 332 {
 333         unsigned c = 0;
 334         for (; l; l = l->next )
 335                 c++;
 336         return c;
 337 }
 338
 339 void free_commit_list(struct commit_list *list)
 340 {
 341         while (list) {
 342                 struct commit_list *temp = list;
 343                 list = temp->next;
 344                 free(temp);
 345         }
 346 }
 347
 348 struct commit_list * insert_by_date(struct commit *item, struct commit_list **list)
 349 {
 350         struct commit_list **pp = list;
 351         struct commit_list *p;
 352         while ((p = *pp) != NULL) {
 353                 if (p->item->date < item->date) {
 354                         break;
 355                 }
 356                 pp = &p->next;
 357         }
 358         return commit_list_insert(item, pp);
 359 }
 360
 361
 362 void sort_by_date(struct commit_list **list)
 363 {
 364         struct commit_list *ret = NULL;
 365         while (*list) {
 366                 insert_by_date((*list)->item, &ret);
 367                 *list = (*list)->next;
 368         }
 369         *list = ret;
 370 }
 371
 372 struct commit *pop_most_recent_commit(struct commit_list **list,
 373                                       unsigned int mark)
 374 {
 375         struct commit *ret = (*list)->item;
 376         struct commit_list *parents = ret->parents;
 377         struct commit_list *old = *list;
 378
 379         *list = (*list)->next;
 380         free(old);
 381
 382         while (parents) {
 383                 struct commit *commit = parents->item;
 384                 if (!parse_commit(commit) && !(commit->object.flags & mark)) {
 385                         commit->object.flags |= mark;
 386                         insert_by_date(commit, list);
 387                 }
 388                 parents = parents->next;
 389         }
 390         return ret;
 391 }
 392
 393 void clear_commit_marks(struct commit *commit, unsigned int mark)
 394 {
 395         while (commit) {
 396                 struct commit_list *parents;
 397
 398                 if (!(mark & commit->object.flags))
 399                         return;
 400
 401                 commit->object.flags &= ~mark;
 402
 403                 parents = commit->parents;
 404                 if (!parents)
 405                         return;
 406
 407                 while ((parents = parents->next))
 408                         clear_commit_marks(parents->item, mark);
 409
 410                 commit = commit->parents->item;
 411         }
 412 }
 413
 414 struct commit *pop_commit(struct commit_list **stack)
 415 {
 416         struct commit_list *top = *stack;
 417         struct commit *item = top ? top->item : NULL;
 418
 419         if (top) {
 420                 *stack = top->next;
 421                 free(top);
 422         }
 423         return item;
 424 }
 425
 426 /*
 427  * Performs an in-place topological sort on the list supplied.
 428  */
 429 void sort_in_topological_order(struct commit_list ** list, int lifo)
 430 {
 431         struct commit_list *next, *orig = *list;
 432         struct commit_list *work, **insert;
 433         struct commit_list **pptr;
 434
 435         if (!orig)
 436                 return;
 437         *list = NULL;
 438
 439         /* Mark them and clear the indegree */
 440         for (next = orig; next; next = next->next) {
 441                 struct commit *commit = next->item;
 442                 commit->indegree = 1;
 443         }
 444
 445         /* update the indegree */
 446         for (next = orig; next; next = next->next) {
 447                 struct commit_list * parents = next->item->parents;
 448                 while (parents) {
 449                         struct commit *parent = parents->item;
 450
 451                         if (parent->indegree)
 452                                 parent->indegree++;
 453                         parents = parents->next;
 454                 }
 455         }
 456
 457         /*
 458          * find the tips
 459          *
 460          * tips are nodes not reachable from any other node in the list
 461          *
 462          * the tips serve as a starting set for the work queue.
 463          */
 464         work = NULL;
 465         insert = &work;
 466         for (next = orig; next; next = next->next) {
 467                 struct commit *commit = next->item;
 468
 469                 if (commit->indegree == 1)
 470                         insert = &commit_list_insert(commit, insert)->next;
 471         }
 472
 473         /* process the list in topological order */
 474         if (!lifo)
 475                 sort_by_date(&work);
 476
 477         pptr = list;
 478         *list = NULL;
 479         while (work) {
 480                 struct commit *commit;
 481                 struct commit_list *parents, *work_item;
 482
 483                 work_item = work;
 484                 work = work_item->next;
 485                 work_item->next = NULL;
 486
 487                 commit = work_item->item;
 488                 for (parents = commit->parents; parents ; parents = parents->next) {
 489                         struct commit *parent=parents->item;
 490
 491                         if (!parent->indegree)
 492                                 continue;
 493
 494                         /*
 495                          * parents are only enqueued for emission
 496                          * when all their children have been emitted thereby
 497                          * guaranteeing topological order.
 498                          */
 499                         if (--parent->indegree == 1) {
 500                                 if (!lifo)
 501                                         insert_by_date(parent, &work);
 502                                 else
 503                                         commit_list_insert(parent, &work);
 504                         }
 505                 }
 506                 /*
 507                  * work_item is a commit all of whose children
 508                  * have already been emitted. we can emit it now.
 509                  */
 510                 commit->indegree = 0;
 511                 *pptr = work_item;
 512                 pptr = &work_item->next;
 513         }
 514 }
 515
 516 /* merge-base stuff */
 517
 518 /* bits #0..15 in revision.h */
 519 #define PARENT1         (1u<<16)
 520 #define PARENT2         (1u<<17)
 521 #define STALE           (1u<<18)
 522 #define RESULT          (1u<<19)
 523
 524 static const unsigned all_flags = (PARENT1 | PARENT2 | STALE | RESULT);
 525
 526 static struct commit *interesting(struct commit_list *list)
 527 {
 528         while (list) {
 529                 struct commit *commit = list->item;
 530                 list = list->next;
 531                 if (commit->object.flags & STALE)
 532                         continue;
 533                 return commit;
 534         }
 535         return NULL;
 536 }
 537
 538 static struct commit_list *merge_bases_many(struct commit *one, int n, struct commit **twos)
 539 {
 540         struct commit_list *list = NULL;
 541         struct commit_list *result = NULL;
 542         int i;
 543
 544         for (i = 0; i < n; i++) {
 545                 if (one == twos[i])
 546                         /*
 547                          * We do not mark this even with RESULT so we do not
 548                          * have to clean it up.
 549                          */
 550                         return commit_list_insert(one, &result);
 551         }
 552
 553         if (parse_commit(one))
 554                 return NULL;
 555         for (i = 0; i < n; i++) {
 556                 if (parse_commit(twos[i]))
 557                         return NULL;
 558         }
 559
 560         one->object.flags |= PARENT1;
 561         insert_by_date(one, &list);
 562         for (i = 0; i < n; i++) {
 563                 twos[i]->object.flags |= PARENT2;
 564                 insert_by_date(twos[i], &list);
 565         }
 566
 567         while (interesting(list)) {
 568                 struct commit *commit;
 569                 struct commit_list *parents;
 570                 struct commit_list *next;
 571                 int flags;
 572
 573                 commit = list->item;
 574                 next = list->next;
 575                 free(list);
 576                 list = next;
 577
 578                 flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
 579                 if (flags == (PARENT1 | PARENT2)) {
 580                         if (!(commit->object.flags & RESULT)) {
 581                                 commit->object.flags |= RESULT;
 582                                 insert_by_date(commit, &result);
 583                         }
 584                         /* Mark parents of a found merge stale */
 585                         flags |= STALE;
 586                 }
 587                 parents = commit->parents;
 588                 while (parents) {
 589                         struct commit *p = parents->item;
 590                         parents = parents->next;
 591                         if ((p->object.flags & flags) == flags)
 592                                 continue;
 593                         if (parse_commit(p))
 594                                 return NULL;
 595                         p->object.flags |= flags;
 596                         insert_by_date(p, &list);
 597                 }
 598         }
 599
 600         /* Clean up the result to remove stale ones */
 601         free_commit_list(list);
 602         list = result; result = NULL;
 603         while (list) {
 604                 struct commit_list *next = list->next;
 605                 if (!(list->item->object.flags & STALE))
 606                         insert_by_date(list->item, &result);
 607                 free(list);
 608                 list = next;
 609         }
 610         return result;
 611 }
 612
 613 struct commit_list *get_octopus_merge_bases(struct commit_list *in)
 614 {
 615         struct commit_list *i, *j, *k, *ret = NULL;
 616         struct commit_list **pptr = &ret;
 617
 618         for (i = in; i; i = i->next) {
 619                 if (!ret)
 620                         pptr = &commit_list_insert(i->item, pptr)->next;
 621                 else {
 622                         struct commit_list *new = NULL, *end = NULL;
 623
 624                         for (j = ret; j; j = j->next) {
 625                                 struct commit_list *bases;
 626                                 bases = get_merge_bases(i->item, j->item, 1);
 627                                 if (!new)
 628                                         new = bases;
 629                                 else
 630                                         end->next = bases;
 631                                 for (k = bases; k; k = k->next)
 632                                         end = k;
 633                         }
 634                         ret = new;
 635                 }
 636         }
 637         return ret;
 638 }
 639
 640 struct commit_list *get_merge_bases_many(struct commit *one,
 641                                          int n,
 642                                          struct commit **twos,
 643                                          int cleanup)
 644 {
 645         struct commit_list *list;
 646         struct commit **rslt;
 647         struct commit_list *result;
 648         int cnt, i, j;
 649
 650         result = merge_bases_many(one, n, twos);
 651         for (i = 0; i < n; i++) {
 652                 if (one == twos[i])
 653                         return result;
 654         }
 655         if (!result || !result->next) {
 656                 if (cleanup) {
 657                         clear_commit_marks(one, all_flags);
 658                         for (i = 0; i < n; i++)
 659                                 clear_commit_marks(twos[i], all_flags);
 660                 }
 661                 return result;
 662         }
 663
 664         /* There are more than one */
 665         cnt = 0;
 666         list = result;
 667         while (list) {
 668                 list = list->next;
 669                 cnt++;
 670         }
 671         rslt = xcalloc(cnt, sizeof(*rslt));
 672         for (list = result, i = 0; list; list = list->next)
 673                 rslt[i++] = list->item;
 674         free_commit_list(result);
 675
 676         clear_commit_marks(one, all_flags);
 677         for (i = 0; i < n; i++)
 678                 clear_commit_marks(twos[i], all_flags);
 679         for (i = 0; i < cnt - 1; i++) {
 680                 for (j = i+1; j < cnt; j++) {
 681                         if (!rslt[i] || !rslt[j])
 682                                 continue;
 683                         result = merge_bases_many(rslt[i], 1, &rslt[j]);
 684                         clear_commit_marks(rslt[i], all_flags);
 685                         clear_commit_marks(rslt[j], all_flags);
 686                         for (list = result; list; list = list->next) {
 687                                 if (rslt[i] == list->item)
 688                                         rslt[i] = NULL;
 689                                 if (rslt[j] == list->item)
 690                                         rslt[j] = NULL;
 691                         }
 692                 }
 693         }
 694
 695         /* Surviving ones in rslt[] are the independent results */
 696         result = NULL;
 697         for (i = 0; i < cnt; i++) {
 698                 if (rslt[i])
 699                         insert_by_date(rslt[i], &result);
 700         }
 701         free(rslt);
 702         return result;
 703 }
 704
 705 struct commit_list *get_merge_bases(struct commit *one, struct commit *two,
 706                                     int cleanup)
 707 {
 708         return get_merge_bases_many(one, 1, &two, cleanup);
 709 }
 710
 711 int is_descendant_of(struct commit *commit, struct commit_list *with_commit)
 712 {
 713         if (!with_commit)
 714                 return 1;
 715         while (with_commit) {
 716                 struct commit *other;
 717
 718                 other = with_commit->item;
 719                 with_commit = with_commit->next;
 720                 if (in_merge_bases(other, &commit, 1))
 721                         return 1;
 722         }
 723         return 0;
 724 }
 725
 726 int in_merge_bases(struct commit *commit, struct commit **reference, int num)
 727 {
 728         struct commit_list *bases, *b;
 729         int ret = 0;
 730
 731         if (num == 1)
 732                 bases = get_merge_bases(commit, *reference, 1);
 733         else
 734                 die("not yet");
 735         for (b = bases; b; b = b->next) {
 736                 if (!hashcmp(commit->object.sha1, b->item->object.sha1)) {
 737                         ret = 1;
 738                         break;
 739                 }
 740         }
 741
 742         free_commit_list(bases);
 743         return ret;
 744 }
 745
 746 struct commit_list *reduce_heads(struct commit_list *heads)
 747 {
 748         struct commit_list *p;
 749         struct commit_list *result = NULL, **tail = &result;
 750         struct commit **other;
 751         size_t num_head, num_other;
 752
 753         if (!heads)
 754                 return NULL;
 755
 756         /* Avoid unnecessary reallocations */
 757         for (p = heads, num_head = 0; p; p = p->next)
 758                 num_head++;
 759         other = xcalloc(sizeof(*other), num_head);
 760
 761         /* For each commit, see if it can be reached by others */
 762         for (p = heads; p; p = p->next) {
 763                 struct commit_list *q, *base;
 764
 765                 /* Do we already have this in the result? */
 766                 for (q = result; q; q = q->next)
 767                         if (p->item == q->item)
 768                                 break;
 769                 if (q)
 770                         continue;
 771
 772                 num_other = 0;
 773                 for (q = heads; q; q = q->next) {
 774                         if (p->item == q->item)
 775                                 continue;
 776                         other[num_other++] = q->item;
 777                 }
 778                 if (num_other)
 779                         base = get_merge_bases_many(p->item, num_other, other, 1);
 780                 else
 781                         base = NULL;
 782                 /*
 783                  * If p->item does not have anything common with other
 784                  * commits, there won't be any merge base.  If it is
 785                  * reachable from some of the others, p->item will be
 786                  * the merge base.  If its history is connected with
 787                  * others, but p->item is not reachable by others, we
 788                  * will get something other than p->item back.
 789                  */
 790                 if (!base || (base->item != p->item))
 791                         tail = &(commit_list_insert(p->item, tail)->next);
 792                 free_commit_list(base);
 793         }
 794         free(other);
 795         return result;
 796 }