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