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                 if (graft)
 270                         continue;
 271                 new_parent = lookup_commit(parent);
 272                 if (new_parent)
 273                         pptr = &commit_list_insert(new_parent, pptr)->next;
 274         }
 275         if (graft) {
 276                 int i;
 277                 struct commit *new_parent;
 278                 for (i = 0; i < graft->nr_parent; i++) {
 279                         new_parent = lookup_commit(graft->parent[i]);
 280                         if (!new_parent)
 281                                 continue;
 282                         pptr = &commit_list_insert(new_parent, pptr)->next;
 283                 }
 284         }
 285         item->date = parse_commit_date(bufptr, tail);
 286
 287         return 0;
 288 }
 289
 290 int parse_commit(struct commit *item)
 291 {
 292         enum object_type type;
 293         void *buffer;
 294         unsigned long size;
 295         int ret;
 296
 297         if (!item)
 298                 return -1;
 299         if (item->object.parsed)
 300                 return 0;
 301         buffer = read_sha1_file(item->object.sha1, &type, &size);
 302         if (!buffer)
 303                 return error("Could not read %s",
 304                              sha1_to_hex(item->object.sha1));
 305         if (type != OBJ_COMMIT) {
 306                 free(buffer);
 307                 return error("Object %s not a commit",
 308                              sha1_to_hex(item->object.sha1));
 309         }
 310         ret = parse_commit_buffer(item, buffer, size);
 311         if (save_commit_buffer && !ret) {
 312                 item->buffer = buffer;
 313                 return 0;
 314         }
 315         free(buffer);
 316         return ret;
 317 }
 318
 319 static void unparse_commit_list(struct commit_list *list)
 320 {
 321         for (; list; list = list->next)
 322                 unparse_commit(list->item);
 323 }
 324
 325 void unparse_commit(struct commit *item)
 326 {
 327         item->object.flags = 0;
 328         item->object.used = 0;
 329         if (item->object.parsed) {
 330                 item->object.parsed = 0;
 331                 if (item->parents) {
 332                         unparse_commit_list(item->parents);
 333                         free_commit_list(item->parents);
 334                         item->parents = NULL;
 335                 }
 336         }
 337 }
 338
 339 struct commit_list *commit_list_insert(struct commit *item, struct commit_list **list_p)
 340 {
 341         struct commit_list *new_list = xmalloc(sizeof(struct commit_list));
 342         new_list->item = item;
 343         new_list->next = *list_p;
 344         *list_p = new_list;
 345         return new_list;
 346 }
 347
 348 unsigned commit_list_count(const struct commit_list *l)
 349 {
 350         unsigned c = 0;
 351         for (; l; l = l->next )
 352                 c++;
 353         return c;
 354 }
 355
 356 void free_commit_list(struct commit_list *list)
 357 {
 358         while (list) {
 359                 struct commit_list *temp = list;
 360                 list = temp->next;
 361                 free(temp);
 362         }
 363 }
 364
 365 struct commit_list * insert_by_date(struct commit *item, struct commit_list **list)
 366 {
 367         struct commit_list **pp = list;
 368         struct commit_list *p;
 369         while ((p = *pp) != NULL) {
 370                 if (p->item->date < item->date) {
 371                         break;
 372                 }
 373                 pp = &p->next;
 374         }
 375         return commit_list_insert(item, pp);
 376 }
 377
 378
 379 void sort_by_date(struct commit_list **list)
 380 {
 381         struct commit_list *ret = NULL;
 382         while (*list) {
 383                 insert_by_date((*list)->item, &ret);
 384                 *list = (*list)->next;
 385         }
 386         *list = ret;
 387 }
 388
 389 struct commit *pop_most_recent_commit(struct commit_list **list,
 390                                       unsigned int mark)
 391 {
 392         struct commit *ret = (*list)->item;
 393         struct commit_list *parents = ret->parents;
 394         struct commit_list *old = *list;
 395
 396         *list = (*list)->next;
 397         free(old);
 398
 399         while (parents) {
 400                 struct commit *commit = parents->item;
 401                 if (!parse_commit(commit) && !(commit->object.flags & mark)) {
 402                         commit->object.flags |= mark;
 403                         insert_by_date(commit, list);
 404                 }
 405                 parents = parents->next;
 406         }
 407         return ret;
 408 }
 409
 410 void clear_commit_marks(struct commit *commit, unsigned int mark)
 411 {
 412         while (commit) {
 413                 struct commit_list *parents;
 414
 415                 if (!(mark & commit->object.flags))
 416                         return;
 417
 418                 commit->object.flags &= ~mark;
 419
 420                 parents = commit->parents;
 421                 if (!parents)
 422                         return;
 423
 424                 while ((parents = parents->next))
 425                         clear_commit_marks(parents->item, mark);
 426
 427                 commit = commit->parents->item;
 428         }
 429 }
 430
 431 struct commit *pop_commit(struct commit_list **stack)
 432 {
 433         struct commit_list *top = *stack;
 434         struct commit *item = top ? top->item : NULL;
 435
 436         if (top) {
 437                 *stack = top->next;
 438                 free(top);
 439         }
 440         return item;
 441 }
 442
 443 /*
 444  * Performs an in-place topological sort on the list supplied.
 445  */
 446 void sort_in_topological_order(struct commit_list ** list, int lifo)
 447 {
 448         struct commit_list *next, *orig = *list;
 449         struct commit_list *work, **insert;
 450         struct commit_list **pptr;
 451
 452         if (!orig)
 453                 return;
 454         *list = NULL;
 455
 456         /* Mark them and clear the indegree */
 457         for (next = orig; next; next = next->next) {
 458                 struct commit *commit = next->item;
 459                 commit->indegree = 1;
 460         }
 461
 462         /* update the indegree */
 463         for (next = orig; next; next = next->next) {
 464                 struct commit_list * parents = next->item->parents;
 465                 while (parents) {
 466                         struct commit *parent = parents->item;
 467
 468                         if (parent->indegree)
 469                                 parent->indegree++;
 470                         parents = parents->next;
 471                 }
 472         }
 473
 474         /*
 475          * find the tips
 476          *
 477          * tips are nodes not reachable from any other node in the list
 478          *
 479          * the tips serve as a starting set for the work queue.
 480          */
 481         work = NULL;
 482         insert = &work;
 483         for (next = orig; next; next = next->next) {
 484                 struct commit *commit = next->item;
 485
 486                 if (commit->indegree == 1)
 487                         insert = &commit_list_insert(commit, insert)->next;
 488         }
 489
 490         /* process the list in topological order */
 491         if (!lifo)
 492                 sort_by_date(&work);
 493
 494         pptr = list;
 495         *list = NULL;
 496         while (work) {
 497                 struct commit *commit;
 498                 struct commit_list *parents, *work_item;
 499
 500                 work_item = work;
 501                 work = work_item->next;
 502                 work_item->next = NULL;
 503
 504                 commit = work_item->item;
 505                 for (parents = commit->parents; parents ; parents = parents->next) {
 506                         struct commit *parent=parents->item;
 507
 508                         if (!parent->indegree)
 509                                 continue;
 510
 511                         /*
 512                          * parents are only enqueued for emission
 513                          * when all their children have been emitted thereby
 514                          * guaranteeing topological order.
 515                          */
 516                         if (--parent->indegree == 1) {
 517                                 if (!lifo)
 518                                         insert_by_date(parent, &work);
 519                                 else
 520                                         commit_list_insert(parent, &work);
 521                         }
 522                 }
 523                 /*
 524                  * work_item is a commit all of whose children
 525                  * have already been emitted. we can emit it now.
 526                  */
 527                 commit->indegree = 0;
 528                 *pptr = work_item;
 529                 pptr = &work_item->next;
 530         }
 531 }
 532
 533 /* merge-base stuff */
 534
 535 /* bits #0..15 in revision.h */
 536 #define PARENT1         (1u<<16)
 537 #define PARENT2         (1u<<17)
 538 #define STALE           (1u<<18)
 539 #define RESULT          (1u<<19)
 540
 541 static const unsigned all_flags = (PARENT1 | PARENT2 | STALE | RESULT);
 542
 543 static struct commit *interesting(struct commit_list *list)
 544 {
 545         while (list) {
 546                 struct commit *commit = list->item;
 547                 list = list->next;
 548                 if (commit->object.flags & STALE)
 549                         continue;
 550                 return commit;
 551         }
 552         return NULL;
 553 }
 554
 555 static struct commit_list *merge_bases_many(struct commit *one, int n, struct commit **twos)
 556 {
 557         struct commit_list *list = NULL;
 558         struct commit_list *result = NULL;
 559         int i;
 560
 561         for (i = 0; i < n; i++) {
 562                 if (one == twos[i])
 563                         /*
 564                          * We do not mark this even with RESULT so we do not
 565                          * have to clean it up.
 566                          */
 567                         return commit_list_insert(one, &result);
 568         }
 569
 570         if (parse_commit(one))
 571                 return NULL;
 572         for (i = 0; i < n; i++) {
 573                 if (parse_commit(twos[i]))
 574                         return NULL;
 575         }
 576
 577         one->object.flags |= PARENT1;
 578         insert_by_date(one, &list);
 579         for (i = 0; i < n; i++) {
 580                 twos[i]->object.flags |= PARENT2;
 581                 insert_by_date(twos[i], &list);
 582         }
 583
 584         while (interesting(list)) {
 585                 struct commit *commit;
 586                 struct commit_list *parents;
 587                 struct commit_list *n;
 588                 int flags;
 589
 590                 commit = list->item;
 591                 n = list->next;
 592                 free(list);
 593                 list = n;
 594
 595                 flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
 596                 if (flags == (PARENT1 | PARENT2)) {
 597                         if (!(commit->object.flags & RESULT)) {
 598                                 commit->object.flags |= RESULT;
 599                                 insert_by_date(commit, &result);
 600                         }
 601                         /* Mark parents of a found merge stale */
 602                         flags |= STALE;
 603                 }
 604                 parents = commit->parents;
 605                 while (parents) {
 606                         struct commit *p = parents->item;
 607                         parents = parents->next;
 608                         if ((p->object.flags & flags) == flags)
 609                                 continue;
 610                         if (parse_commit(p))
 611                                 return NULL;
 612                         p->object.flags |= flags;
 613                         insert_by_date(p, &list);
 614                 }
 615         }
 616
 617         /* Clean up the result to remove stale ones */
 618         free_commit_list(list);
 619         list = result; result = NULL;
 620         while (list) {
 621                 struct commit_list *n = list->next;
 622                 if (!(list->item->object.flags & STALE))
 623                         insert_by_date(list->item, &result);
 624                 free(list);
 625                 list = n;
 626         }
 627         return result;
 628 }
 629
 630 struct commit_list *get_octopus_merge_bases(struct commit_list *in)
 631 {
 632         struct commit_list *i, *j, *k, *ret = NULL;
 633         struct commit_list **pptr = &ret;
 634
 635         for (i = in; i; i = i->next) {
 636                 if (!ret)
 637                         pptr = &commit_list_insert(i->item, pptr)->next;
 638                 else {
 639                         struct commit_list *new = NULL, *end = NULL;
 640
 641                         for (j = ret; j; j = j->next) {
 642                                 struct commit_list *bases;
 643                                 bases = get_merge_bases(i->item, j->item, 1);
 644                                 if (!new)
 645                                         new = bases;
 646                                 else
 647                                         end->next = bases;
 648                                 for (k = bases; k; k = k->next)
 649                                         end = k;
 650                         }
 651                         ret = new;
 652                 }
 653         }
 654         return ret;
 655 }
 656
 657 struct commit_list *get_merge_bases_many(struct commit *one,
 658                                          int n,
 659                                          struct commit **twos,
 660                                          int cleanup)
 661 {
 662         struct commit_list *list;
 663         struct commit **rslt;
 664         struct commit_list *result;
 665         int cnt, i, j;
 666
 667         result = merge_bases_many(one, n, twos);
 668         for (i = 0; i < n; i++) {
 669                 if (one == twos[i])
 670                         return result;
 671         }
 672         if (!result || !result->next) {
 673                 if (cleanup) {
 674                         clear_commit_marks(one, all_flags);
 675                         for (i = 0; i < n; i++)
 676                                 clear_commit_marks(twos[i], all_flags);
 677                 }
 678                 return result;
 679         }
 680
 681         /* There are more than one */
 682         cnt = 0;
 683         list = result;
 684         while (list) {
 685                 list = list->next;
 686                 cnt++;
 687         }
 688         rslt = xcalloc(cnt, sizeof(*rslt));
 689         for (list = result, i = 0; list; list = list->next)
 690                 rslt[i++] = list->item;
 691         free_commit_list(result);
 692
 693         clear_commit_marks(one, all_flags);
 694         for (i = 0; i < n; i++)
 695                 clear_commit_marks(twos[i], all_flags);
 696         for (i = 0; i < cnt - 1; i++) {
 697                 for (j = i+1; j < cnt; j++) {
 698                         if (!rslt[i] || !rslt[j])
 699                                 continue;
 700                         result = merge_bases_many(rslt[i], 1, &rslt[j]);
 701                         clear_commit_marks(rslt[i], all_flags);
 702                         clear_commit_marks(rslt[j], all_flags);
 703                         for (list = result; list; list = list->next) {
 704                                 if (rslt[i] == list->item)
 705                                         rslt[i] = NULL;
 706                                 if (rslt[j] == list->item)
 707                                         rslt[j] = NULL;
 708                         }
 709                 }
 710         }
 711
 712         /* Surviving ones in rslt[] are the independent results */
 713         result = NULL;
 714         for (i = 0; i < cnt; i++) {
 715                 if (rslt[i])
 716                         insert_by_date(rslt[i], &result);
 717         }
 718         free(rslt);
 719         return result;
 720 }
 721
 722 struct commit_list *get_merge_bases(struct commit *one, struct commit *two,
 723                                     int cleanup)
 724 {
 725         return get_merge_bases_many(one, 1, &two, cleanup);
 726 }
 727
 728 int is_descendant_of(struct commit *commit, struct commit_list *with_commit)
 729 {
 730         if (!with_commit)
 731                 return 1;
 732         while (with_commit) {
 733                 struct commit *other;
 734
 735                 other = with_commit->item;
 736                 with_commit = with_commit->next;
 737                 if (in_merge_bases(other, &commit, 1))
 738                         return 1;
 739         }
 740         return 0;
 741 }
 742
 743 int in_merge_bases(struct commit *commit, struct commit **reference, int num)
 744 {
 745         struct commit_list *bases, *b;
 746         int ret = 0;
 747
 748         if (num == 1)
 749                 bases = get_merge_bases(commit, *reference, 1);
 750         else
 751                 die("not yet");
 752         for (b = bases; b; b = b->next) {
 753                 if (!hashcmp(commit->object.sha1, b->item->object.sha1)) {
 754                         ret = 1;
 755                         break;
 756                 }
 757         }
 758
 759         free_commit_list(bases);
 760         return ret;
 761 }
 762
 763 struct commit_list *reduce_heads(struct commit_list *heads)
 764 {
 765         struct commit_list *p;
 766         struct commit_list *result = NULL, **tail = &result;
 767         struct commit **other;
 768         size_t num_head, num_other;
 769
 770         if (!heads)
 771                 return NULL;
 772
 773         /* Avoid unnecessary reallocations */
 774         for (p = heads, num_head = 0; p; p = p->next)
 775                 num_head++;
 776         other = xcalloc(sizeof(*other), num_head);
 777
 778         /* For each commit, see if it can be reached by others */
 779         for (p = heads; p; p = p->next) {
 780                 struct commit_list *q, *base;
 781
 782                 /* Do we already have this in the result? */
 783                 for (q = result; q; q = q->next)
 784                         if (p->item == q->item)
 785                                 break;
 786                 if (q)
 787                         continue;
 788
 789                 num_other = 0;
 790                 for (q = heads; q; q = q->next) {
 791                         if (p->item == q->item)
 792                                 continue;
 793                         other[num_other++] = q->item;
 794                 }
 795                 if (num_other)
 796                         base = get_merge_bases_many(p->item, num_other, other, 1);
 797                 else
 798                         base = NULL;
 799                 /*
 800                  * If p->item does not have anything common with other
 801                  * commits, there won't be any merge base.  If it is
 802                  * reachable from some of the others, p->item will be
 803                  * the merge base.  If its history is connected with
 804                  * others, but p->item is not reachable by others, we
 805                  * will get something other than p->item back.
 806                  */
 807                 if (!base || (base->item != p->item))
 808                         tail = &(commit_list_insert(p->item, tail)->next);
 809                 free_commit_list(base);
 810         }
 811         free(other);
 812         return result;
 813 }