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 struct commit *lookup_commit_reference_by_name(const char *name)
  53 {
  54         unsigned char sha1[20];
  55         struct commit *commit;
  56
  57         if (get_sha1(name, sha1))
  58                 return NULL;
  59         commit = lookup_commit_reference(sha1);
  60         if (!commit || parse_commit(commit))
  61                 return NULL;
  62         return commit;
  63 }
  64
  65 static unsigned long parse_commit_date(const char *buf, const char *tail)
  66 {
  67         const char *dateptr;
  68
  69         if (buf + 6 >= tail)
  70                 return 0;
  71         if (memcmp(buf, "author", 6))
  72                 return 0;
  73         while (buf < tail && *buf++ != '\n')
  74                 /* nada */;
  75         if (buf + 9 >= tail)
  76                 return 0;
  77         if (memcmp(buf, "committer", 9))
  78                 return 0;
  79         while (buf < tail && *buf++ != '>')
  80                 /* nada */;
  81         if (buf >= tail)
  82                 return 0;
  83         dateptr = buf;
  84         while (buf < tail && *buf++ != '\n')
  85                 /* nada */;
  86         if (buf >= tail)
  87                 return 0;
  88         /* dateptr < buf && buf[-1] == '\n', so strtoul will stop at buf-1 */
  89         return strtoul(dateptr, NULL, 10);
  90 }
  91
  92 static struct commit_graft **commit_graft;
  93 static int commit_graft_alloc, commit_graft_nr;
  94
  95 static int commit_graft_pos(const unsigned char *sha1)
  96 {
  97         int lo, hi;
  98         lo = 0;
  99         hi = commit_graft_nr;
 100         while (lo < hi) {
 101                 int mi = (lo + hi) / 2;
 102                 struct commit_graft *graft = commit_graft[mi];
 103                 int cmp = hashcmp(sha1, graft->sha1);
 104                 if (!cmp)
 105                         return mi;
 106                 if (cmp < 0)
 107                         hi = mi;
 108                 else
 109                         lo = mi + 1;
 110         }
 111         return -lo - 1;
 112 }
 113
 114 int register_commit_graft(struct commit_graft *graft, int ignore_dups)
 115 {
 116         int pos = commit_graft_pos(graft->sha1);
 117
 118         if (0 <= pos) {
 119                 if (ignore_dups)
 120                         free(graft);
 121                 else {
 122                         free(commit_graft[pos]);
 123                         commit_graft[pos] = graft;
 124                 }
 125                 return 1;
 126         }
 127         pos = -pos - 1;
 128         if (commit_graft_alloc <= ++commit_graft_nr) {
 129                 commit_graft_alloc = alloc_nr(commit_graft_alloc);
 130                 commit_graft = xrealloc(commit_graft,
 131                                         sizeof(*commit_graft) *
 132                                         commit_graft_alloc);
 133         }
 134         if (pos < commit_graft_nr)
 135                 memmove(commit_graft + pos + 1,
 136                         commit_graft + pos,
 137                         (commit_graft_nr - pos - 1) *
 138                         sizeof(*commit_graft));
 139         commit_graft[pos] = graft;
 140         return 0;
 141 }
 142
 143 struct commit_graft *read_graft_line(char *buf, int len)
 144 {
 145         /* The format is just "Commit Parent1 Parent2 ...\n" */
 146         int i;
 147         struct commit_graft *graft = NULL;
 148
 149         while (len && isspace(buf[len-1]))
 150                 buf[--len] = '\0';
 151         if (buf[0] == '#' || buf[0] == '\0')
 152                 return NULL;
 153         if ((len + 1) % 41) {
 154         bad_graft_data:
 155                 error("bad graft data: %s", buf);
 156                 free(graft);
 157                 return NULL;
 158         }
 159         i = (len + 1) / 41 - 1;
 160         graft = xmalloc(sizeof(*graft) + 20 * i);
 161         graft->nr_parent = i;
 162         if (get_sha1_hex(buf, graft->sha1))
 163                 goto bad_graft_data;
 164         for (i = 40; i < len; i += 41) {
 165                 if (buf[i] != ' ')
 166                         goto bad_graft_data;
 167                 if (get_sha1_hex(buf + i + 1, graft->parent[i/41]))
 168                         goto bad_graft_data;
 169         }
 170         return graft;
 171 }
 172
 173 static int read_graft_file(const char *graft_file)
 174 {
 175         FILE *fp = fopen(graft_file, "r");
 176         char buf[1024];
 177         if (!fp)
 178                 return -1;
 179         while (fgets(buf, sizeof(buf), fp)) {
 180                 /* The format is just "Commit Parent1 Parent2 ...\n" */
 181                 int len = strlen(buf);
 182                 struct commit_graft *graft = read_graft_line(buf, len);
 183                 if (!graft)
 184                         continue;
 185                 if (register_commit_graft(graft, 1))
 186                         error("duplicate graft data: %s", buf);
 187         }
 188         fclose(fp);
 189         return 0;
 190 }
 191
 192 static void prepare_commit_graft(void)
 193 {
 194         static int commit_graft_prepared;
 195         char *graft_file;
 196
 197         if (commit_graft_prepared)
 198                 return;
 199         graft_file = get_graft_file();
 200         read_graft_file(graft_file);
 201         /* make sure shallows are read */
 202         is_repository_shallow();
 203         commit_graft_prepared = 1;
 204 }
 205
 206 struct commit_graft *lookup_commit_graft(const unsigned char *sha1)
 207 {
 208         int pos;
 209         prepare_commit_graft();
 210         pos = commit_graft_pos(sha1);
 211         if (pos < 0)
 212                 return NULL;
 213         return commit_graft[pos];
 214 }
 215
 216 int write_shallow_commits(struct strbuf *out, int use_pack_protocol)
 217 {
 218         int i, count = 0;
 219         for (i = 0; i < commit_graft_nr; i++)
 220                 if (commit_graft[i]->nr_parent < 0) {
 221                         const char *hex =
 222                                 sha1_to_hex(commit_graft[i]->sha1);
 223                         count++;
 224                         if (use_pack_protocol)
 225                                 packet_buf_write(out, "shallow %s", hex);
 226                         else {
 227                                 strbuf_addstr(out, hex);
 228                                 strbuf_addch(out, '\n');
 229                         }
 230                 }
 231         return count;
 232 }
 233
 234 int unregister_shallow(const unsigned char *sha1)
 235 {
 236         int pos = commit_graft_pos(sha1);
 237         if (pos < 0)
 238                 return -1;
 239         if (pos + 1 < commit_graft_nr)
 240                 memmove(commit_graft + pos, commit_graft + pos + 1,
 241                                 sizeof(struct commit_graft *)
 242                                 * (commit_graft_nr - pos - 1));
 243         commit_graft_nr--;
 244         return 0;
 245 }
 246
 247 int parse_commit_buffer(struct commit *item, void *buffer, unsigned long size)
 248 {
 249         char *tail = buffer;
 250         char *bufptr = buffer;
 251         unsigned char parent[20];
 252         struct commit_list **pptr;
 253         struct commit_graft *graft;
 254
 255         if (item->object.parsed)
 256                 return 0;
 257         item->object.parsed = 1;
 258         tail += size;
 259         if (tail <= bufptr + 46 || memcmp(bufptr, "tree ", 5) || bufptr[45] != '\n')
 260                 return error("bogus commit object %s", sha1_to_hex(item->object.sha1));
 261         if (get_sha1_hex(bufptr + 5, parent) < 0)
 262                 return error("bad tree pointer in commit %s",
 263                              sha1_to_hex(item->object.sha1));
 264         item->tree = lookup_tree(parent);
 265         bufptr += 46; /* "tree " + "hex sha1" + "\n" */
 266         pptr = &item->parents;
 267
 268         graft = lookup_commit_graft(item->object.sha1);
 269         while (bufptr + 48 < tail && !memcmp(bufptr, "parent ", 7)) {
 270                 struct commit *new_parent;
 271
 272                 if (tail <= bufptr + 48 ||
 273                     get_sha1_hex(bufptr + 7, parent) ||
 274                     bufptr[47] != '\n')
 275                         return error("bad parents in commit %s", sha1_to_hex(item->object.sha1));
 276                 bufptr += 48;
 277                 /*
 278                  * The clone is shallow if nr_parent < 0, and we must
 279                  * not traverse its real parents even when we unhide them.
 280                  */
 281                 if (graft && (graft->nr_parent < 0 || grafts_replace_parents))
 282                         continue;
 283                 new_parent = lookup_commit(parent);
 284                 if (new_parent)
 285                         pptr = &commit_list_insert(new_parent, pptr)->next;
 286         }
 287         if (graft) {
 288                 int i;
 289                 struct commit *new_parent;
 290                 for (i = 0; i < graft->nr_parent; i++) {
 291                         new_parent = lookup_commit(graft->parent[i]);
 292                         if (!new_parent)
 293                                 continue;
 294                         pptr = &commit_list_insert(new_parent, pptr)->next;
 295                 }
 296         }
 297         item->date = parse_commit_date(bufptr, tail);
 298
 299         return 0;
 300 }
 301
 302 int parse_commit(struct commit *item)
 303 {
 304         enum object_type type;
 305         void *buffer;
 306         unsigned long size;
 307         int ret;
 308
 309         if (!item)
 310                 return -1;
 311         if (item->object.parsed)
 312                 return 0;
 313         buffer = read_sha1_file(item->object.sha1, &type, &size);
 314         if (!buffer)
 315                 return error("Could not read %s",
 316                              sha1_to_hex(item->object.sha1));
 317         if (type != OBJ_COMMIT) {
 318                 free(buffer);
 319                 return error("Object %s not a commit",
 320                              sha1_to_hex(item->object.sha1));
 321         }
 322         ret = parse_commit_buffer(item, buffer, size);
 323         if (save_commit_buffer && !ret) {
 324                 item->buffer = buffer;
 325                 return 0;
 326         }
 327         free(buffer);
 328         return ret;
 329 }
 330
 331 int find_commit_subject(const char *commit_buffer, const char **subject)
 332 {
 333         const char *eol;
 334         const char *p = commit_buffer;
 335
 336         while (*p && (*p != '\n' || p[1] != '\n'))
 337                 p++;
 338         if (*p) {
 339                 p += 2;
 340                 for (eol = p; *eol && *eol != '\n'; eol++)
 341                         ; /* do nothing */
 342         } else
 343                 eol = p;
 344
 345         *subject = p;
 346
 347         return eol - p;
 348 }
 349
 350 struct commit_list *commit_list_insert(struct commit *item, struct commit_list **list_p)
 351 {
 352         struct commit_list *new_list = xmalloc(sizeof(struct commit_list));
 353         new_list->item = item;
 354         new_list->next = *list_p;
 355         *list_p = new_list;
 356         return new_list;
 357 }
 358
 359 unsigned commit_list_count(const struct commit_list *l)
 360 {
 361         unsigned c = 0;
 362         for (; l; l = l->next )
 363                 c++;
 364         return c;
 365 }
 366
 367 void free_commit_list(struct commit_list *list)
 368 {
 369         while (list) {
 370                 struct commit_list *temp = list;
 371                 list = temp->next;
 372                 free(temp);
 373         }
 374 }
 375
 376 struct commit_list * insert_by_date(struct commit *item, struct commit_list **list)
 377 {
 378         struct commit_list **pp = list;
 379         struct commit_list *p;
 380         while ((p = *pp) != NULL) {
 381                 if (p->item->date < item->date) {
 382                         break;
 383                 }
 384                 pp = &p->next;
 385         }
 386         return commit_list_insert(item, pp);
 387 }
 388
 389
 390 void sort_by_date(struct commit_list **list)
 391 {
 392         struct commit_list *ret = NULL;
 393         while (*list) {
 394                 insert_by_date((*list)->item, &ret);
 395                 *list = (*list)->next;
 396         }
 397         *list = ret;
 398 }
 399
 400 struct commit *pop_most_recent_commit(struct commit_list **list,
 401                                       unsigned int mark)
 402 {
 403         struct commit *ret = (*list)->item;
 404         struct commit_list *parents = ret->parents;
 405         struct commit_list *old = *list;
 406
 407         *list = (*list)->next;
 408         free(old);
 409
 410         while (parents) {
 411                 struct commit *commit = parents->item;
 412                 if (!parse_commit(commit) && !(commit->object.flags & mark)) {
 413                         commit->object.flags |= mark;
 414                         insert_by_date(commit, list);
 415                 }
 416                 parents = parents->next;
 417         }
 418         return ret;
 419 }
 420
 421 void clear_commit_marks(struct commit *commit, unsigned int mark)
 422 {
 423         while (commit) {
 424                 struct commit_list *parents;
 425
 426                 if (!(mark & commit->object.flags))
 427                         return;
 428
 429                 commit->object.flags &= ~mark;
 430
 431                 parents = commit->parents;
 432                 if (!parents)
 433                         return;
 434
 435                 while ((parents = parents->next))
 436                         clear_commit_marks(parents->item, mark);
 437
 438                 commit = commit->parents->item;
 439         }
 440 }
 441
 442 struct commit *pop_commit(struct commit_list **stack)
 443 {
 444         struct commit_list *top = *stack;
 445         struct commit *item = top ? top->item : NULL;
 446
 447         if (top) {
 448                 *stack = top->next;
 449                 free(top);
 450         }
 451         return item;
 452 }
 453
 454 /*
 455  * Performs an in-place topological sort on the list supplied.
 456  */
 457 void sort_in_topological_order(struct commit_list ** list, int lifo)
 458 {
 459         struct commit_list *next, *orig = *list;
 460         struct commit_list *work, **insert;
 461         struct commit_list **pptr;
 462
 463         if (!orig)
 464                 return;
 465         *list = NULL;
 466
 467         /* Mark them and clear the indegree */
 468         for (next = orig; next; next = next->next) {
 469                 struct commit *commit = next->item;
 470                 commit->indegree = 1;
 471         }
 472
 473         /* update the indegree */
 474         for (next = orig; next; next = next->next) {
 475                 struct commit_list * parents = next->item->parents;
 476                 while (parents) {
 477                         struct commit *parent = parents->item;
 478
 479                         if (parent->indegree)
 480                                 parent->indegree++;
 481                         parents = parents->next;
 482                 }
 483         }
 484
 485         /*
 486          * find the tips
 487          *
 488          * tips are nodes not reachable from any other node in the list
 489          *
 490          * the tips serve as a starting set for the work queue.
 491          */
 492         work = NULL;
 493         insert = &work;
 494         for (next = orig; next; next = next->next) {
 495                 struct commit *commit = next->item;
 496
 497                 if (commit->indegree == 1)
 498                         insert = &commit_list_insert(commit, insert)->next;
 499         }
 500
 501         /* process the list in topological order */
 502         if (!lifo)
 503                 sort_by_date(&work);
 504
 505         pptr = list;
 506         *list = NULL;
 507         while (work) {
 508                 struct commit *commit;
 509                 struct commit_list *parents, *work_item;
 510
 511                 work_item = work;
 512                 work = work_item->next;
 513                 work_item->next = NULL;
 514
 515                 commit = work_item->item;
 516                 for (parents = commit->parents; parents ; parents = parents->next) {
 517                         struct commit *parent=parents->item;
 518
 519                         if (!parent->indegree)
 520                                 continue;
 521
 522                         /*
 523                          * parents are only enqueued for emission
 524                          * when all their children have been emitted thereby
 525                          * guaranteeing topological order.
 526                          */
 527                         if (--parent->indegree == 1) {
 528                                 if (!lifo)
 529                                         insert_by_date(parent, &work);
 530                                 else
 531                                         commit_list_insert(parent, &work);
 532                         }
 533                 }
 534                 /*
 535                  * work_item is a commit all of whose children
 536                  * have already been emitted. we can emit it now.
 537                  */
 538                 commit->indegree = 0;
 539                 *pptr = work_item;
 540                 pptr = &work_item->next;
 541         }
 542 }
 543
 544 /* merge-base stuff */
 545
 546 /* bits #0..15 in revision.h */
 547 #define PARENT1         (1u<<16)
 548 #define PARENT2         (1u<<17)
 549 #define STALE           (1u<<18)
 550 #define RESULT          (1u<<19)
 551
 552 static const unsigned all_flags = (PARENT1 | PARENT2 | STALE | RESULT);
 553
 554 static struct commit *interesting(struct commit_list *list)
 555 {
 556         while (list) {
 557                 struct commit *commit = list->item;
 558                 list = list->next;
 559                 if (commit->object.flags & STALE)
 560                         continue;
 561                 return commit;
 562         }
 563         return NULL;
 564 }
 565
 566 static struct commit_list *merge_bases_many(struct commit *one, int n, struct commit **twos)
 567 {
 568         struct commit_list *list = NULL;
 569         struct commit_list *result = NULL;
 570         int i;
 571
 572         for (i = 0; i < n; i++) {
 573                 if (one == twos[i])
 574                         /*
 575                          * We do not mark this even with RESULT so we do not
 576                          * have to clean it up.
 577                          */
 578                         return commit_list_insert(one, &result);
 579         }
 580
 581         if (parse_commit(one))
 582                 return NULL;
 583         for (i = 0; i < n; i++) {
 584                 if (parse_commit(twos[i]))
 585                         return NULL;
 586         }
 587
 588         one->object.flags |= PARENT1;
 589         insert_by_date(one, &list);
 590         for (i = 0; i < n; i++) {
 591                 twos[i]->object.flags |= PARENT2;
 592                 insert_by_date(twos[i], &list);
 593         }
 594
 595         while (interesting(list)) {
 596                 struct commit *commit;
 597                 struct commit_list *parents;
 598                 struct commit_list *next;
 599                 int flags;
 600
 601                 commit = list->item;
 602                 next = list->next;
 603                 free(list);
 604                 list = next;
 605
 606                 flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
 607                 if (flags == (PARENT1 | PARENT2)) {
 608                         if (!(commit->object.flags & RESULT)) {
 609                                 commit->object.flags |= RESULT;
 610                                 insert_by_date(commit, &result);
 611                         }
 612                         /* Mark parents of a found merge stale */
 613                         flags |= STALE;
 614                 }
 615                 parents = commit->parents;
 616                 while (parents) {
 617                         struct commit *p = parents->item;
 618                         parents = parents->next;
 619                         if ((p->object.flags & flags) == flags)
 620                                 continue;
 621                         if (parse_commit(p))
 622                                 return NULL;
 623                         p->object.flags |= flags;
 624                         insert_by_date(p, &list);
 625                 }
 626         }
 627
 628         /* Clean up the result to remove stale ones */
 629         free_commit_list(list);
 630         list = result; result = NULL;
 631         while (list) {
 632                 struct commit_list *next = list->next;
 633                 if (!(list->item->object.flags & STALE))
 634                         insert_by_date(list->item, &result);
 635                 free(list);
 636                 list = next;
 637         }
 638         return result;
 639 }
 640
 641 struct commit_list *get_octopus_merge_bases(struct commit_list *in)
 642 {
 643         struct commit_list *i, *j, *k, *ret = NULL;
 644         struct commit_list **pptr = &ret;
 645
 646         for (i = in; i; i = i->next) {
 647                 if (!ret)
 648                         pptr = &commit_list_insert(i->item, pptr)->next;
 649                 else {
 650                         struct commit_list *new = NULL, *end = NULL;
 651
 652                         for (j = ret; j; j = j->next) {
 653                                 struct commit_list *bases;
 654                                 bases = get_merge_bases(i->item, j->item, 1);
 655                                 if (!new)
 656                                         new = bases;
 657                                 else
 658                                         end->next = bases;
 659                                 for (k = bases; k; k = k->next)
 660                                         end = k;
 661                         }
 662                         ret = new;
 663                 }
 664         }
 665         return ret;
 666 }
 667
 668 struct commit_list *get_merge_bases_many(struct commit *one,
 669                                          int n,
 670                                          struct commit **twos,
 671                                          int cleanup)
 672 {
 673         struct commit_list *list;
 674         struct commit **rslt;
 675         struct commit_list *result;
 676         int cnt, i, j;
 677
 678         result = merge_bases_many(one, n, twos);
 679         for (i = 0; i < n; i++) {
 680                 if (one == twos[i])
 681                         return result;
 682         }
 683         if (!result || !result->next) {
 684                 if (cleanup) {
 685                         clear_commit_marks(one, all_flags);
 686                         for (i = 0; i < n; i++)
 687                                 clear_commit_marks(twos[i], all_flags);
 688                 }
 689                 return result;
 690         }
 691
 692         /* There are more than one */
 693         cnt = 0;
 694         list = result;
 695         while (list) {
 696                 list = list->next;
 697                 cnt++;
 698         }
 699         rslt = xcalloc(cnt, sizeof(*rslt));
 700         for (list = result, i = 0; list; list = list->next)
 701                 rslt[i++] = list->item;
 702         free_commit_list(result);
 703
 704         clear_commit_marks(one, all_flags);
 705         for (i = 0; i < n; i++)
 706                 clear_commit_marks(twos[i], all_flags);
 707         for (i = 0; i < cnt - 1; i++) {
 708                 for (j = i+1; j < cnt; j++) {
 709                         if (!rslt[i] || !rslt[j])
 710                                 continue;
 711                         result = merge_bases_many(rslt[i], 1, &rslt[j]);
 712                         clear_commit_marks(rslt[i], all_flags);
 713                         clear_commit_marks(rslt[j], all_flags);
 714                         for (list = result; list; list = list->next) {
 715                                 if (rslt[i] == list->item)
 716                                         rslt[i] = NULL;
 717                                 if (rslt[j] == list->item)
 718                                         rslt[j] = NULL;
 719                         }
 720                 }
 721         }
 722
 723         /* Surviving ones in rslt[] are the independent results */
 724         result = NULL;
 725         for (i = 0; i < cnt; i++) {
 726                 if (rslt[i])
 727                         insert_by_date(rslt[i], &result);
 728         }
 729         free(rslt);
 730         return result;
 731 }
 732
 733 struct commit_list *get_merge_bases(struct commit *one, struct commit *two,
 734                                     int cleanup)
 735 {
 736         return get_merge_bases_many(one, 1, &two, cleanup);
 737 }
 738
 739 int is_descendant_of(struct commit *commit, struct commit_list *with_commit)
 740 {
 741         if (!with_commit)
 742                 return 1;
 743         while (with_commit) {
 744                 struct commit *other;
 745
 746                 other = with_commit->item;
 747                 with_commit = with_commit->next;
 748                 if (in_merge_bases(other, &commit, 1))
 749                         return 1;
 750         }
 751         return 0;
 752 }
 753
 754 int in_merge_bases(struct commit *commit, struct commit **reference, int num)
 755 {
 756         struct commit_list *bases, *b;
 757         int ret = 0;
 758
 759         if (num == 1)
 760                 bases = get_merge_bases(commit, *reference, 1);
 761         else
 762                 die("not yet");
 763         for (b = bases; b; b = b->next) {
 764                 if (!hashcmp(commit->object.sha1, b->item->object.sha1)) {
 765                         ret = 1;
 766                         break;
 767                 }
 768         }
 769
 770         free_commit_list(bases);
 771         return ret;
 772 }
 773
 774 struct commit_list *reduce_heads(struct commit_list *heads)
 775 {
 776         struct commit_list *p;
 777         struct commit_list *result = NULL, **tail = &result;
 778         struct commit **other;
 779         size_t num_head, num_other;
 780
 781         if (!heads)
 782                 return NULL;
 783
 784         /* Avoid unnecessary reallocations */
 785         for (p = heads, num_head = 0; p; p = p->next)
 786                 num_head++;
 787         other = xcalloc(sizeof(*other), num_head);
 788
 789         /* For each commit, see if it can be reached by others */
 790         for (p = heads; p; p = p->next) {
 791                 struct commit_list *q, *base;
 792
 793                 /* Do we already have this in the result? */
 794                 for (q = result; q; q = q->next)
 795                         if (p->item == q->item)
 796                                 break;
 797                 if (q)
 798                         continue;
 799
 800                 num_other = 0;
 801                 for (q = heads; q; q = q->next) {
 802                         if (p->item == q->item)
 803                                 continue;
 804                         other[num_other++] = q->item;
 805                 }
 806                 if (num_other)
 807                         base = get_merge_bases_many(p->item, num_other, other, 1);
 808                 else
 809                         base = NULL;
 810                 /*
 811                  * If p->item does not have anything common with other
 812                  * commits, there won't be any merge base.  If it is
 813                  * reachable from some of the others, p->item will be
 814                  * the merge base.  If its history is connected with
 815                  * others, but p->item is not reachable by others, we
 816                  * will get something other than p->item back.
 817                  */
 818                 if (!base || (base->item != p->item))
 819                         tail = &(commit_list_insert(p->item, tail)->next);
 820                 free_commit_list(base);
 821         }
 822         free(other);
 823         return result;
 824 }
 825
 826 static const char commit_utf8_warn[] =
 827 "Warning: commit message does not conform to UTF-8.\n"
 828 "You may want to amend it after fixing the message, or set the config\n"
 829 "variable i18n.commitencoding to the encoding your project uses.\n";
 830
 831 int commit_tree(const char *msg, unsigned char *tree,
 832                 struct commit_list *parents, unsigned char *ret,
 833                 const char *author)
 834 {
 835         int result;
 836         int encoding_is_utf8;
 837         struct strbuf buffer;
 838
 839         assert_sha1_type(tree, OBJ_TREE);
 840
 841         /* Not having i18n.commitencoding is the same as having utf-8 */
 842         encoding_is_utf8 = is_encoding_utf8(git_commit_encoding);
 843
 844         strbuf_init(&buffer, 8192); /* should avoid reallocs for the headers */
 845         strbuf_addf(&buffer, "tree %s\n", sha1_to_hex(tree));
 846
 847         /*
 848          * NOTE! This ordering means that the same exact tree merged with a
 849          * different order of parents will be a _different_ changeset even
 850          * if everything else stays the same.
 851          */
 852         while (parents) {
 853                 struct commit_list *next = parents->next;
 854                 strbuf_addf(&buffer, "parent %s\n",
 855                         sha1_to_hex(parents->item->object.sha1));
 856                 free(parents);
 857                 parents = next;
 858         }
 859
 860         /* Person/date information */
 861         if (!author)
 862                 author = git_author_info(IDENT_ERROR_ON_NO_NAME);
 863         strbuf_addf(&buffer, "author %s\n", author);
 864         strbuf_addf(&buffer, "committer %s\n", git_committer_info(IDENT_ERROR_ON_NO_NAME));
 865         if (!encoding_is_utf8)
 866                 strbuf_addf(&buffer, "encoding %s\n", git_commit_encoding);
 867         strbuf_addch(&buffer, '\n');
 868
 869         /* And add the comment */
 870         strbuf_addstr(&buffer, msg);
 871
 872         /* And check the encoding */
 873         if (encoding_is_utf8 && !is_utf8(buffer.buf))
 874                 fprintf(stderr, commit_utf8_warn);
 875
 876         result = write_sha1_file(buffer.buf, buffer.len, commit_type, ret);
 877         strbuf_release(&buffer);
 878         return result;
 879 }