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