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