commit.con commit Accept tags in HEAD or MERGE_HEAD (baf18fc)
   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
  10int save_commit_buffer = 1;
  11
  12const char *commit_type = "commit";
  13
  14static 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
  27struct 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
  37struct commit *lookup_commit_reference(const unsigned char *sha1)
  38{
  39        return lookup_commit_reference_gently(sha1, 0);
  40}
  41
  42struct commit *lookup_commit_or_die(const unsigned char *sha1, const char *ref_name)
  43{
  44        struct commit *c = lookup_commit_reference(sha1);
  45        if (!c)
  46                die(_("could not parse %s"), ref_name);
  47        if (hashcmp(sha1, c->object.sha1)) {
  48                warning(_("%s %s is not a commit!"),
  49                        ref_name, sha1_to_hex(sha1));
  50        }
  51        return c;
  52}
  53
  54struct commit *lookup_commit(const unsigned char *sha1)
  55{
  56        struct object *obj = lookup_object(sha1);
  57        if (!obj)
  58                return create_object(sha1, OBJ_COMMIT, alloc_commit_node());
  59        if (!obj->type)
  60                obj->type = OBJ_COMMIT;
  61        return check_commit(obj, sha1, 0);
  62}
  63
  64struct commit *lookup_commit_reference_by_name(const char *name)
  65{
  66        unsigned char sha1[20];
  67        struct commit *commit;
  68
  69        if (get_sha1(name, sha1))
  70                return NULL;
  71        commit = lookup_commit_reference(sha1);
  72        if (!commit || parse_commit(commit))
  73                return NULL;
  74        return commit;
  75}
  76
  77static unsigned long parse_commit_date(const char *buf, const char *tail)
  78{
  79        const char *dateptr;
  80
  81        if (buf + 6 >= tail)
  82                return 0;
  83        if (memcmp(buf, "author", 6))
  84                return 0;
  85        while (buf < tail && *buf++ != '\n')
  86                /* nada */;
  87        if (buf + 9 >= tail)
  88                return 0;
  89        if (memcmp(buf, "committer", 9))
  90                return 0;
  91        while (buf < tail && *buf++ != '>')
  92                /* nada */;
  93        if (buf >= tail)
  94                return 0;
  95        dateptr = buf;
  96        while (buf < tail && *buf++ != '\n')
  97                /* nada */;
  98        if (buf >= tail)
  99                return 0;
 100        /* dateptr < buf && buf[-1] == '\n', so strtoul will stop at buf-1 */
 101        return strtoul(dateptr, NULL, 10);
 102}
 103
 104static struct commit_graft **commit_graft;
 105static int commit_graft_alloc, commit_graft_nr;
 106
 107static int commit_graft_pos(const unsigned char *sha1)
 108{
 109        int lo, hi;
 110        lo = 0;
 111        hi = commit_graft_nr;
 112        while (lo < hi) {
 113                int mi = (lo + hi) / 2;
 114                struct commit_graft *graft = commit_graft[mi];
 115                int cmp = hashcmp(sha1, graft->sha1);
 116                if (!cmp)
 117                        return mi;
 118                if (cmp < 0)
 119                        hi = mi;
 120                else
 121                        lo = mi + 1;
 122        }
 123        return -lo - 1;
 124}
 125
 126int register_commit_graft(struct commit_graft *graft, int ignore_dups)
 127{
 128        int pos = commit_graft_pos(graft->sha1);
 129
 130        if (0 <= pos) {
 131                if (ignore_dups)
 132                        free(graft);
 133                else {
 134                        free(commit_graft[pos]);
 135                        commit_graft[pos] = graft;
 136                }
 137                return 1;
 138        }
 139        pos = -pos - 1;
 140        if (commit_graft_alloc <= ++commit_graft_nr) {
 141                commit_graft_alloc = alloc_nr(commit_graft_alloc);
 142                commit_graft = xrealloc(commit_graft,
 143                                        sizeof(*commit_graft) *
 144                                        commit_graft_alloc);
 145        }
 146        if (pos < commit_graft_nr)
 147                memmove(commit_graft + pos + 1,
 148                        commit_graft + pos,
 149                        (commit_graft_nr - pos - 1) *
 150                        sizeof(*commit_graft));
 151        commit_graft[pos] = graft;
 152        return 0;
 153}
 154
 155struct commit_graft *read_graft_line(char *buf, int len)
 156{
 157        /* The format is just "Commit Parent1 Parent2 ...\n" */
 158        int i;
 159        struct commit_graft *graft = NULL;
 160
 161        while (len && isspace(buf[len-1]))
 162                buf[--len] = '\0';
 163        if (buf[0] == '#' || buf[0] == '\0')
 164                return NULL;
 165        if ((len + 1) % 41)
 166                goto bad_graft_data;
 167        i = (len + 1) / 41 - 1;
 168        graft = xmalloc(sizeof(*graft) + 20 * i);
 169        graft->nr_parent = i;
 170        if (get_sha1_hex(buf, graft->sha1))
 171                goto bad_graft_data;
 172        for (i = 40; i < len; i += 41) {
 173                if (buf[i] != ' ')
 174                        goto bad_graft_data;
 175                if (get_sha1_hex(buf + i + 1, graft->parent[i/41]))
 176                        goto bad_graft_data;
 177        }
 178        return graft;
 179
 180bad_graft_data:
 181        error("bad graft data: %s", buf);
 182        free(graft);
 183        return NULL;
 184}
 185
 186static int read_graft_file(const char *graft_file)
 187{
 188        FILE *fp = fopen(graft_file, "r");
 189        char buf[1024];
 190        if (!fp)
 191                return -1;
 192        while (fgets(buf, sizeof(buf), fp)) {
 193                /* The format is just "Commit Parent1 Parent2 ...\n" */
 194                int len = strlen(buf);
 195                struct commit_graft *graft = read_graft_line(buf, len);
 196                if (!graft)
 197                        continue;
 198                if (register_commit_graft(graft, 1))
 199                        error("duplicate graft data: %s", buf);
 200        }
 201        fclose(fp);
 202        return 0;
 203}
 204
 205static void prepare_commit_graft(void)
 206{
 207        static int commit_graft_prepared;
 208        char *graft_file;
 209
 210        if (commit_graft_prepared)
 211                return;
 212        graft_file = get_graft_file();
 213        read_graft_file(graft_file);
 214        /* make sure shallows are read */
 215        is_repository_shallow();
 216        commit_graft_prepared = 1;
 217}
 218
 219struct commit_graft *lookup_commit_graft(const unsigned char *sha1)
 220{
 221        int pos;
 222        prepare_commit_graft();
 223        pos = commit_graft_pos(sha1);
 224        if (pos < 0)
 225                return NULL;
 226        return commit_graft[pos];
 227}
 228
 229int write_shallow_commits(struct strbuf *out, int use_pack_protocol)
 230{
 231        int i, count = 0;
 232        for (i = 0; i < commit_graft_nr; i++)
 233                if (commit_graft[i]->nr_parent < 0) {
 234                        const char *hex =
 235                                sha1_to_hex(commit_graft[i]->sha1);
 236                        count++;
 237                        if (use_pack_protocol)
 238                                packet_buf_write(out, "shallow %s", hex);
 239                        else {
 240                                strbuf_addstr(out, hex);
 241                                strbuf_addch(out, '\n');
 242                        }
 243                }
 244        return count;
 245}
 246
 247int unregister_shallow(const unsigned char *sha1)
 248{
 249        int pos = commit_graft_pos(sha1);
 250        if (pos < 0)
 251                return -1;
 252        if (pos + 1 < commit_graft_nr)
 253                memmove(commit_graft + pos, commit_graft + pos + 1,
 254                                sizeof(struct commit_graft *)
 255                                * (commit_graft_nr - pos - 1));
 256        commit_graft_nr--;
 257        return 0;
 258}
 259
 260int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size)
 261{
 262        const char *tail = buffer;
 263        const char *bufptr = buffer;
 264        unsigned char parent[20];
 265        struct commit_list **pptr;
 266        struct commit_graft *graft;
 267
 268        if (item->object.parsed)
 269                return 0;
 270        item->object.parsed = 1;
 271        tail += size;
 272        if (tail <= bufptr + 46 || memcmp(bufptr, "tree ", 5) || bufptr[45] != '\n')
 273                return error("bogus commit object %s", sha1_to_hex(item->object.sha1));
 274        if (get_sha1_hex(bufptr + 5, parent) < 0)
 275                return error("bad tree pointer in commit %s",
 276                             sha1_to_hex(item->object.sha1));
 277        item->tree = lookup_tree(parent);
 278        bufptr += 46; /* "tree " + "hex sha1" + "\n" */
 279        pptr = &item->parents;
 280
 281        graft = lookup_commit_graft(item->object.sha1);
 282        while (bufptr + 48 < tail && !memcmp(bufptr, "parent ", 7)) {
 283                struct commit *new_parent;
 284
 285                if (tail <= bufptr + 48 ||
 286                    get_sha1_hex(bufptr + 7, parent) ||
 287                    bufptr[47] != '\n')
 288                        return error("bad parents in commit %s", sha1_to_hex(item->object.sha1));
 289                bufptr += 48;
 290                /*
 291                 * The clone is shallow if nr_parent < 0, and we must
 292                 * not traverse its real parents even when we unhide them.
 293                 */
 294                if (graft && (graft->nr_parent < 0 || grafts_replace_parents))
 295                        continue;
 296                new_parent = lookup_commit(parent);
 297                if (new_parent)
 298                        pptr = &commit_list_insert(new_parent, pptr)->next;
 299        }
 300        if (graft) {
 301                int i;
 302                struct commit *new_parent;
 303                for (i = 0; i < graft->nr_parent; i++) {
 304                        new_parent = lookup_commit(graft->parent[i]);
 305                        if (!new_parent)
 306                                continue;
 307                        pptr = &commit_list_insert(new_parent, pptr)->next;
 308                }
 309        }
 310        item->date = parse_commit_date(bufptr, tail);
 311
 312        return 0;
 313}
 314
 315int parse_commit(struct commit *item)
 316{
 317        enum object_type type;
 318        void *buffer;
 319        unsigned long size;
 320        int ret;
 321
 322        if (!item)
 323                return -1;
 324        if (item->object.parsed)
 325                return 0;
 326        buffer = read_sha1_file(item->object.sha1, &type, &size);
 327        if (!buffer)
 328                return error("Could not read %s",
 329                             sha1_to_hex(item->object.sha1));
 330        if (type != OBJ_COMMIT) {
 331                free(buffer);
 332                return error("Object %s not a commit",
 333                             sha1_to_hex(item->object.sha1));
 334        }
 335        ret = parse_commit_buffer(item, buffer, size);
 336        if (save_commit_buffer && !ret) {
 337                item->buffer = buffer;
 338                return 0;
 339        }
 340        free(buffer);
 341        return ret;
 342}
 343
 344int find_commit_subject(const char *commit_buffer, const char **subject)
 345{
 346        const char *eol;
 347        const char *p = commit_buffer;
 348
 349        while (*p && (*p != '\n' || p[1] != '\n'))
 350                p++;
 351        if (*p) {
 352                p += 2;
 353                for (eol = p; *eol && *eol != '\n'; eol++)
 354                        ; /* do nothing */
 355        } else
 356                eol = p;
 357
 358        *subject = p;
 359
 360        return eol - p;
 361}
 362
 363struct commit_list *commit_list_insert(struct commit *item, struct commit_list **list_p)
 364{
 365        struct commit_list *new_list = xmalloc(sizeof(struct commit_list));
 366        new_list->item = item;
 367        new_list->next = *list_p;
 368        *list_p = new_list;
 369        return new_list;
 370}
 371
 372unsigned commit_list_count(const struct commit_list *l)
 373{
 374        unsigned c = 0;
 375        for (; l; l = l->next )
 376                c++;
 377        return c;
 378}
 379
 380void free_commit_list(struct commit_list *list)
 381{
 382        while (list) {
 383                struct commit_list *temp = list;
 384                list = temp->next;
 385                free(temp);
 386        }
 387}
 388
 389struct commit_list * commit_list_insert_by_date(struct commit *item, struct commit_list **list)
 390{
 391        struct commit_list **pp = list;
 392        struct commit_list *p;
 393        while ((p = *pp) != NULL) {
 394                if (p->item->date < item->date) {
 395                        break;
 396                }
 397                pp = &p->next;
 398        }
 399        return commit_list_insert(item, pp);
 400}
 401
 402
 403void commit_list_sort_by_date(struct commit_list **list)
 404{
 405        struct commit_list *ret = NULL;
 406        while (*list) {
 407                commit_list_insert_by_date((*list)->item, &ret);
 408                *list = (*list)->next;
 409        }
 410        *list = ret;
 411}
 412
 413struct commit *pop_most_recent_commit(struct commit_list **list,
 414                                      unsigned int mark)
 415{
 416        struct commit *ret = (*list)->item;
 417        struct commit_list *parents = ret->parents;
 418        struct commit_list *old = *list;
 419
 420        *list = (*list)->next;
 421        free(old);
 422
 423        while (parents) {
 424                struct commit *commit = parents->item;
 425                if (!parse_commit(commit) && !(commit->object.flags & mark)) {
 426                        commit->object.flags |= mark;
 427                        commit_list_insert_by_date(commit, list);
 428                }
 429                parents = parents->next;
 430        }
 431        return ret;
 432}
 433
 434void clear_commit_marks(struct commit *commit, unsigned int mark)
 435{
 436        while (commit) {
 437                struct commit_list *parents;
 438
 439                if (!(mark & commit->object.flags))
 440                        return;
 441
 442                commit->object.flags &= ~mark;
 443
 444                parents = commit->parents;
 445                if (!parents)
 446                        return;
 447
 448                while ((parents = parents->next))
 449                        clear_commit_marks(parents->item, mark);
 450
 451                commit = commit->parents->item;
 452        }
 453}
 454
 455struct commit *pop_commit(struct commit_list **stack)
 456{
 457        struct commit_list *top = *stack;
 458        struct commit *item = top ? top->item : NULL;
 459
 460        if (top) {
 461                *stack = top->next;
 462                free(top);
 463        }
 464        return item;
 465}
 466
 467/*
 468 * Performs an in-place topological sort on the list supplied.
 469 */
 470void sort_in_topological_order(struct commit_list ** list, int lifo)
 471{
 472        struct commit_list *next, *orig = *list;
 473        struct commit_list *work, **insert;
 474        struct commit_list **pptr;
 475
 476        if (!orig)
 477                return;
 478        *list = NULL;
 479
 480        /* Mark them and clear the indegree */
 481        for (next = orig; next; next = next->next) {
 482                struct commit *commit = next->item;
 483                commit->indegree = 1;
 484        }
 485
 486        /* update the indegree */
 487        for (next = orig; next; next = next->next) {
 488                struct commit_list * parents = next->item->parents;
 489                while (parents) {
 490                        struct commit *parent = parents->item;
 491
 492                        if (parent->indegree)
 493                                parent->indegree++;
 494                        parents = parents->next;
 495                }
 496        }
 497
 498        /*
 499         * find the tips
 500         *
 501         * tips are nodes not reachable from any other node in the list
 502         *
 503         * the tips serve as a starting set for the work queue.
 504         */
 505        work = NULL;
 506        insert = &work;
 507        for (next = orig; next; next = next->next) {
 508                struct commit *commit = next->item;
 509
 510                if (commit->indegree == 1)
 511                        insert = &commit_list_insert(commit, insert)->next;
 512        }
 513
 514        /* process the list in topological order */
 515        if (!lifo)
 516                commit_list_sort_by_date(&work);
 517
 518        pptr = list;
 519        *list = NULL;
 520        while (work) {
 521                struct commit *commit;
 522                struct commit_list *parents, *work_item;
 523
 524                work_item = work;
 525                work = work_item->next;
 526                work_item->next = NULL;
 527
 528                commit = work_item->item;
 529                for (parents = commit->parents; parents ; parents = parents->next) {
 530                        struct commit *parent=parents->item;
 531
 532                        if (!parent->indegree)
 533                                continue;
 534
 535                        /*
 536                         * parents are only enqueued for emission
 537                         * when all their children have been emitted thereby
 538                         * guaranteeing topological order.
 539                         */
 540                        if (--parent->indegree == 1) {
 541                                if (!lifo)
 542                                        commit_list_insert_by_date(parent, &work);
 543                                else
 544                                        commit_list_insert(parent, &work);
 545                        }
 546                }
 547                /*
 548                 * work_item is a commit all of whose children
 549                 * have already been emitted. we can emit it now.
 550                 */
 551                commit->indegree = 0;
 552                *pptr = work_item;
 553                pptr = &work_item->next;
 554        }
 555}
 556
 557/* merge-base stuff */
 558
 559/* bits #0..15 in revision.h */
 560#define PARENT1         (1u<<16)
 561#define PARENT2         (1u<<17)
 562#define STALE           (1u<<18)
 563#define RESULT          (1u<<19)
 564
 565static const unsigned all_flags = (PARENT1 | PARENT2 | STALE | RESULT);
 566
 567static struct commit *interesting(struct commit_list *list)
 568{
 569        while (list) {
 570                struct commit *commit = list->item;
 571                list = list->next;
 572                if (commit->object.flags & STALE)
 573                        continue;
 574                return commit;
 575        }
 576        return NULL;
 577}
 578
 579static struct commit_list *merge_bases_many(struct commit *one, int n, struct commit **twos)
 580{
 581        struct commit_list *list = NULL;
 582        struct commit_list *result = NULL;
 583        int i;
 584
 585        for (i = 0; i < n; i++) {
 586                if (one == twos[i])
 587                        /*
 588                         * We do not mark this even with RESULT so we do not
 589                         * have to clean it up.
 590                         */
 591                        return commit_list_insert(one, &result);
 592        }
 593
 594        if (parse_commit(one))
 595                return NULL;
 596        for (i = 0; i < n; i++) {
 597                if (parse_commit(twos[i]))
 598                        return NULL;
 599        }
 600
 601        one->object.flags |= PARENT1;
 602        commit_list_insert_by_date(one, &list);
 603        for (i = 0; i < n; i++) {
 604                twos[i]->object.flags |= PARENT2;
 605                commit_list_insert_by_date(twos[i], &list);
 606        }
 607
 608        while (interesting(list)) {
 609                struct commit *commit;
 610                struct commit_list *parents;
 611                struct commit_list *next;
 612                int flags;
 613
 614                commit = list->item;
 615                next = list->next;
 616                free(list);
 617                list = next;
 618
 619                flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
 620                if (flags == (PARENT1 | PARENT2)) {
 621                        if (!(commit->object.flags & RESULT)) {
 622                                commit->object.flags |= RESULT;
 623                                commit_list_insert_by_date(commit, &result);
 624                        }
 625                        /* Mark parents of a found merge stale */
 626                        flags |= STALE;
 627                }
 628                parents = commit->parents;
 629                while (parents) {
 630                        struct commit *p = parents->item;
 631                        parents = parents->next;
 632                        if ((p->object.flags & flags) == flags)
 633                                continue;
 634                        if (parse_commit(p))
 635                                return NULL;
 636                        p->object.flags |= flags;
 637                        commit_list_insert_by_date(p, &list);
 638                }
 639        }
 640
 641        /* Clean up the result to remove stale ones */
 642        free_commit_list(list);
 643        list = result; result = NULL;
 644        while (list) {
 645                struct commit_list *next = list->next;
 646                if (!(list->item->object.flags & STALE))
 647                        commit_list_insert_by_date(list->item, &result);
 648                free(list);
 649                list = next;
 650        }
 651        return result;
 652}
 653
 654struct commit_list *get_octopus_merge_bases(struct commit_list *in)
 655{
 656        struct commit_list *i, *j, *k, *ret = NULL;
 657        struct commit_list **pptr = &ret;
 658
 659        for (i = in; i; i = i->next) {
 660                if (!ret)
 661                        pptr = &commit_list_insert(i->item, pptr)->next;
 662                else {
 663                        struct commit_list *new = NULL, *end = NULL;
 664
 665                        for (j = ret; j; j = j->next) {
 666                                struct commit_list *bases;
 667                                bases = get_merge_bases(i->item, j->item, 1);
 668                                if (!new)
 669                                        new = bases;
 670                                else
 671                                        end->next = bases;
 672                                for (k = bases; k; k = k->next)
 673                                        end = k;
 674                        }
 675                        ret = new;
 676                }
 677        }
 678        return ret;
 679}
 680
 681struct commit_list *get_merge_bases_many(struct commit *one,
 682                                         int n,
 683                                         struct commit **twos,
 684                                         int cleanup)
 685{
 686        struct commit_list *list;
 687        struct commit **rslt;
 688        struct commit_list *result;
 689        int cnt, i, j;
 690
 691        result = merge_bases_many(one, n, twos);
 692        for (i = 0; i < n; i++) {
 693                if (one == twos[i])
 694                        return result;
 695        }
 696        if (!result || !result->next) {
 697                if (cleanup) {
 698                        clear_commit_marks(one, all_flags);
 699                        for (i = 0; i < n; i++)
 700                                clear_commit_marks(twos[i], all_flags);
 701                }
 702                return result;
 703        }
 704
 705        /* There are more than one */
 706        cnt = 0;
 707        list = result;
 708        while (list) {
 709                list = list->next;
 710                cnt++;
 711        }
 712        rslt = xcalloc(cnt, sizeof(*rslt));
 713        for (list = result, i = 0; list; list = list->next)
 714                rslt[i++] = list->item;
 715        free_commit_list(result);
 716
 717        clear_commit_marks(one, all_flags);
 718        for (i = 0; i < n; i++)
 719                clear_commit_marks(twos[i], all_flags);
 720        for (i = 0; i < cnt - 1; i++) {
 721                for (j = i+1; j < cnt; j++) {
 722                        if (!rslt[i] || !rslt[j])
 723                                continue;
 724                        result = merge_bases_many(rslt[i], 1, &rslt[j]);
 725                        clear_commit_marks(rslt[i], all_flags);
 726                        clear_commit_marks(rslt[j], all_flags);
 727                        for (list = result; list; list = list->next) {
 728                                if (rslt[i] == list->item)
 729                                        rslt[i] = NULL;
 730                                if (rslt[j] == list->item)
 731                                        rslt[j] = NULL;
 732                        }
 733                }
 734        }
 735
 736        /* Surviving ones in rslt[] are the independent results */
 737        result = NULL;
 738        for (i = 0; i < cnt; i++) {
 739                if (rslt[i])
 740                        commit_list_insert_by_date(rslt[i], &result);
 741        }
 742        free(rslt);
 743        return result;
 744}
 745
 746struct commit_list *get_merge_bases(struct commit *one, struct commit *two,
 747                                    int cleanup)
 748{
 749        return get_merge_bases_many(one, 1, &two, cleanup);
 750}
 751
 752int is_descendant_of(struct commit *commit, struct commit_list *with_commit)
 753{
 754        if (!with_commit)
 755                return 1;
 756        while (with_commit) {
 757                struct commit *other;
 758
 759                other = with_commit->item;
 760                with_commit = with_commit->next;
 761                if (in_merge_bases(other, &commit, 1))
 762                        return 1;
 763        }
 764        return 0;
 765}
 766
 767int in_merge_bases(struct commit *commit, struct commit **reference, int num)
 768{
 769        struct commit_list *bases, *b;
 770        int ret = 0;
 771
 772        if (num == 1)
 773                bases = get_merge_bases(commit, *reference, 1);
 774        else
 775                die("not yet");
 776        for (b = bases; b; b = b->next) {
 777                if (!hashcmp(commit->object.sha1, b->item->object.sha1)) {
 778                        ret = 1;
 779                        break;
 780                }
 781        }
 782
 783        free_commit_list(bases);
 784        return ret;
 785}
 786
 787struct commit_list *reduce_heads(struct commit_list *heads)
 788{
 789        struct commit_list *p;
 790        struct commit_list *result = NULL, **tail = &result;
 791        struct commit **other;
 792        size_t num_head, num_other;
 793
 794        if (!heads)
 795                return NULL;
 796
 797        /* Avoid unnecessary reallocations */
 798        for (p = heads, num_head = 0; p; p = p->next)
 799                num_head++;
 800        other = xcalloc(sizeof(*other), num_head);
 801
 802        /* For each commit, see if it can be reached by others */
 803        for (p = heads; p; p = p->next) {
 804                struct commit_list *q, *base;
 805
 806                /* Do we already have this in the result? */
 807                for (q = result; q; q = q->next)
 808                        if (p->item == q->item)
 809                                break;
 810                if (q)
 811                        continue;
 812
 813                num_other = 0;
 814                for (q = heads; q; q = q->next) {
 815                        if (p->item == q->item)
 816                                continue;
 817                        other[num_other++] = q->item;
 818                }
 819                if (num_other)
 820                        base = get_merge_bases_many(p->item, num_other, other, 1);
 821                else
 822                        base = NULL;
 823                /*
 824                 * If p->item does not have anything common with other
 825                 * commits, there won't be any merge base.  If it is
 826                 * reachable from some of the others, p->item will be
 827                 * the merge base.  If its history is connected with
 828                 * others, but p->item is not reachable by others, we
 829                 * will get something other than p->item back.
 830                 */
 831                if (!base || (base->item != p->item))
 832                        tail = &(commit_list_insert(p->item, tail)->next);
 833                free_commit_list(base);
 834        }
 835        free(other);
 836        return result;
 837}
 838
 839static const char commit_utf8_warn[] =
 840"Warning: commit message does not conform to UTF-8.\n"
 841"You may want to amend it after fixing the message, or set the config\n"
 842"variable i18n.commitencoding to the encoding your project uses.\n";
 843
 844int commit_tree(const char *msg, unsigned char *tree,
 845                struct commit_list *parents, unsigned char *ret,
 846                const char *author)
 847{
 848        int result;
 849        int encoding_is_utf8;
 850        struct strbuf buffer;
 851
 852        assert_sha1_type(tree, OBJ_TREE);
 853
 854        /* Not having i18n.commitencoding is the same as having utf-8 */
 855        encoding_is_utf8 = is_encoding_utf8(git_commit_encoding);
 856
 857        strbuf_init(&buffer, 8192); /* should avoid reallocs for the headers */
 858        strbuf_addf(&buffer, "tree %s\n", sha1_to_hex(tree));
 859
 860        /*
 861         * NOTE! This ordering means that the same exact tree merged with a
 862         * different order of parents will be a _different_ changeset even
 863         * if everything else stays the same.
 864         */
 865        while (parents) {
 866                struct commit_list *next = parents->next;
 867                strbuf_addf(&buffer, "parent %s\n",
 868                        sha1_to_hex(parents->item->object.sha1));
 869                free(parents);
 870                parents = next;
 871        }
 872
 873        /* Person/date information */
 874        if (!author)
 875                author = git_author_info(IDENT_ERROR_ON_NO_NAME);
 876        strbuf_addf(&buffer, "author %s\n", author);
 877        strbuf_addf(&buffer, "committer %s\n", git_committer_info(IDENT_ERROR_ON_NO_NAME));
 878        if (!encoding_is_utf8)
 879                strbuf_addf(&buffer, "encoding %s\n", git_commit_encoding);
 880        strbuf_addch(&buffer, '\n');
 881
 882        /* And add the comment */
 883        strbuf_addstr(&buffer, msg);
 884
 885        /* And check the encoding */
 886        if (encoding_is_utf8 && !is_utf8(buffer.buf))
 887                fprintf(stderr, commit_utf8_warn);
 888
 889        result = write_sha1_file(buffer.buf, buffer.len, commit_type, ret);
 890        strbuf_release(&buffer);
 891        return result;
 892}