Andrew's git / gitweb.git / read-tree.c
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read-tree.con commit Replace xmalloc+memset(0) with xcalloc. (90321c1)
   1/*
   2 * GIT - The information manager from hell
   3 *
   4 * Copyright (C) Linus Torvalds, 2005
   5 */
   6#define DBRT_DEBUG 1
   7
   8#include "cache.h"
   9
  10#include "object.h"
  11#include "tree.h"
  12#include <sys/time.h>
  13#include <signal.h>
  14
  15static int merge = 0;
  16static int update = 0;
  17static int index_only = 0;
  18static int nontrivial_merge = 0;
  19static int trivial_merges_only = 0;
  20static int aggressive = 0;
  21static int verbose_update = 0;
  22static volatile int progress_update = 0;
  23
  24static int head_idx = -1;
  25static int merge_size = 0;
  26
  27static struct object_list *trees = NULL;
  28
  29static struct cache_entry df_conflict_entry = { 
  30};
  31
  32static struct tree_entry_list df_conflict_list = {
  33        .name = NULL,
  34        .next = &df_conflict_list
  35};
  36
  37typedef int (*merge_fn_t)(struct cache_entry **src);
  38
  39static int entcmp(char *name1, int dir1, char *name2, int dir2)
  40{
  41        int len1 = strlen(name1);
  42        int len2 = strlen(name2);
  43        int len = len1 < len2 ? len1 : len2;
  44        int ret = memcmp(name1, name2, len);
  45        unsigned char c1, c2;
  46        if (ret)
  47                return ret;
  48        c1 = name1[len];
  49        c2 = name2[len];
  50        if (!c1 && dir1)
  51                c1 = '/';
  52        if (!c2 && dir2)
  53                c2 = '/';
  54        ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
  55        if (c1 && c2 && !ret)
  56                ret = len1 - len2;
  57        return ret;
  58}
  59
  60static int unpack_trees_rec(struct tree_entry_list **posns, int len,
  61                            const char *base, merge_fn_t fn, int *indpos)
  62{
  63        int baselen = strlen(base);
  64        int src_size = len + 1;
  65        do {
  66                int i;
  67                char *first;
  68                int firstdir = 0;
  69                int pathlen;
  70                unsigned ce_size;
  71                struct tree_entry_list **subposns;
  72                struct cache_entry **src;
  73                int any_files = 0;
  74                int any_dirs = 0;
  75                char *cache_name;
  76                int ce_stage;
  77
  78                /* Find the first name in the input. */
  79
  80                first = NULL;
  81                cache_name = NULL;
  82
  83                /* Check the cache */
  84                if (merge && *indpos < active_nr) {
  85                        /* This is a bit tricky: */
  86                        /* If the index has a subdirectory (with
  87                         * contents) as the first name, it'll get a
  88                         * filename like "foo/bar". But that's after
  89                         * "foo", so the entry in trees will get
  90                         * handled first, at which point we'll go into
  91                         * "foo", and deal with "bar" from the index,
  92                         * because the base will be "foo/". The only
  93                         * way we can actually have "foo/bar" first of
  94                         * all the things is if the trees don't
  95                         * contain "foo" at all, in which case we'll
  96                         * handle "foo/bar" without going into the
  97                         * directory, but that's fine (and will return
  98                         * an error anyway, with the added unknown
  99                         * file case.
 100                         */
 101
 102                        cache_name = active_cache[*indpos]->name;
 103                        if (strlen(cache_name) > baselen &&
 104                            !memcmp(cache_name, base, baselen)) {
 105                                cache_name += baselen;
 106                                first = cache_name;
 107                        } else {
 108                                cache_name = NULL;
 109                        }
 110                }
 111
 112#if DBRT_DEBUG > 1
 113                if (first)
 114                        printf("index %s\n", first);
 115#endif
 116                for (i = 0; i < len; i++) {
 117                        if (!posns[i] || posns[i] == &df_conflict_list)
 118                                continue;
 119#if DBRT_DEBUG > 1
 120                        printf("%d %s\n", i + 1, posns[i]->name);
 121#endif
 122                        if (!first || entcmp(first, firstdir,
 123                                             posns[i]->name, 
 124                                             posns[i]->directory) > 0) {
 125                                first = posns[i]->name;
 126                                firstdir = posns[i]->directory;
 127                        }
 128                }
 129                /* No name means we're done */
 130                if (!first)
 131                        return 0;
 132
 133                pathlen = strlen(first);
 134                ce_size = cache_entry_size(baselen + pathlen);
 135
 136                src = xcalloc(src_size, sizeof(struct cache_entry *));
 137
 138                subposns = xcalloc(len, sizeof(struct tree_list_entry *));
 139
 140                if (cache_name && !strcmp(cache_name, first)) {
 141                        any_files = 1;
 142                        src[0] = active_cache[*indpos];
 143                        remove_cache_entry_at(*indpos);
 144                }
 145
 146                for (i = 0; i < len; i++) {
 147                        struct cache_entry *ce;
 148
 149                        if (!posns[i] ||
 150                            (posns[i] != &df_conflict_list &&
 151                             strcmp(first, posns[i]->name))) {
 152                                continue;
 153                        }
 154
 155                        if (posns[i] == &df_conflict_list) {
 156                                src[i + merge] = &df_conflict_entry;
 157                                continue;
 158                        }
 159
 160                        if (posns[i]->directory) {
 161                                any_dirs = 1;
 162                                parse_tree(posns[i]->item.tree);
 163                                subposns[i] = posns[i]->item.tree->entries;
 164                                posns[i] = posns[i]->next;
 165                                src[i + merge] = &df_conflict_entry;
 166                                continue;
 167                        }
 168
 169                        if (!merge)
 170                                ce_stage = 0;
 171                        else if (i + 1 < head_idx)
 172                                ce_stage = 1;
 173                        else if (i + 1 > head_idx)
 174                                ce_stage = 3;
 175                        else
 176                                ce_stage = 2;
 177
 178                        ce = xcalloc(1, ce_size);
 179                        ce->ce_mode = create_ce_mode(posns[i]->mode);
 180                        ce->ce_flags = create_ce_flags(baselen + pathlen,
 181                                                       ce_stage);
 182                        memcpy(ce->name, base, baselen);
 183                        memcpy(ce->name + baselen, first, pathlen + 1);
 184
 185                        any_files = 1;
 186
 187                        memcpy(ce->sha1, posns[i]->item.any->sha1, 20);
 188                        src[i + merge] = ce;
 189                        subposns[i] = &df_conflict_list;
 190                        posns[i] = posns[i]->next;
 191                }
 192                if (any_files) {
 193                        if (merge) {
 194                                int ret;
 195
 196#if DBRT_DEBUG > 1
 197                                printf("%s:\n", first);
 198                                for (i = 0; i < src_size; i++) {
 199                                        printf(" %d ", i);
 200                                        if (src[i])
 201                                                printf("%s\n", sha1_to_hex(src[i]->sha1));
 202                                        else
 203                                                printf("\n");
 204                                }
 205#endif
 206                                ret = fn(src);
 207                                
 208#if DBRT_DEBUG > 1
 209                                printf("Added %d entries\n", ret);
 210#endif
 211                                *indpos += ret;
 212                        } else {
 213                                for (i = 0; i < src_size; i++) {
 214                                        if (src[i]) {
 215                                                add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
 216                                        }
 217                                }
 218                        }
 219                }
 220                if (any_dirs) {
 221                        char *newbase = xmalloc(baselen + 2 + pathlen);
 222                        memcpy(newbase, base, baselen);
 223                        memcpy(newbase + baselen, first, pathlen);
 224                        newbase[baselen + pathlen] = '/';
 225                        newbase[baselen + pathlen + 1] = '\0';
 226                        if (unpack_trees_rec(subposns, len, newbase, fn,
 227                                             indpos))
 228                                return -1;
 229                        free(newbase);
 230                }
 231                free(subposns);
 232                free(src);
 233        } while (1);
 234}
 235
 236static void reject_merge(struct cache_entry *ce)
 237{
 238        die("Entry '%s' would be overwritten by merge. Cannot merge.", 
 239            ce->name);
 240}
 241
 242/* Unlink the last component and attempt to remove leading
 243 * directories, in case this unlink is the removal of the
 244 * last entry in the directory -- empty directories are removed.
 245 */
 246static void unlink_entry(char *name)
 247{
 248        char *cp, *prev;
 249
 250        if (unlink(name))
 251                return;
 252        prev = NULL;
 253        while (1) {
 254                int status;
 255                cp = strrchr(name, '/');
 256                if (prev)
 257                        *prev = '/';
 258                if (!cp)
 259                        break;
 260
 261                *cp = 0;
 262                status = rmdir(name);
 263                if (status) {
 264                        *cp = '/';
 265                        break;
 266                }
 267                prev = cp;
 268        }
 269}
 270
 271static void progress_interval(int signum)
 272{
 273        signal(SIGALRM, progress_interval);
 274        progress_update = 1;
 275}
 276
 277static void check_updates(struct cache_entry **src, int nr)
 278{
 279        static struct checkout state = {
 280                .base_dir = "",
 281                .force = 1,
 282                .quiet = 1,
 283                .refresh_cache = 1,
 284        };
 285        unsigned short mask = htons(CE_UPDATE);
 286        unsigned last_percent = 200, cnt = 0, total = 0;
 287
 288        if (update && verbose_update) {
 289                struct itimerval v;
 290
 291                for (total = cnt = 0; cnt < nr; cnt++) {
 292                        struct cache_entry *ce = src[cnt];
 293                        if (!ce->ce_mode || ce->ce_flags & mask)
 294                                total++;
 295                }
 296
 297                /* Don't bother doing this for very small updates */
 298                if (total < 250)
 299                        total = 0;
 300
 301                if (total) {
 302                        v.it_interval.tv_sec = 1;
 303                        v.it_interval.tv_usec = 0;
 304                        v.it_value = v.it_interval;
 305                        signal(SIGALRM, progress_interval);
 306                        setitimer(ITIMER_REAL, &v, NULL);
 307                        fprintf(stderr, "Checking files out...\n");
 308                        progress_update = 1;
 309                }
 310                cnt = 0;
 311        }
 312
 313        while (nr--) {
 314                struct cache_entry *ce = *src++;
 315
 316                if (total) {
 317                        if (!ce->ce_mode || ce->ce_flags & mask) {
 318                                unsigned percent;
 319                                cnt++;
 320                                percent = (cnt * 100) / total;
 321                                if (percent != last_percent ||
 322                                    progress_update) {
 323                                        fprintf(stderr, "%4u%% (%u/%u) done\r",
 324                                                percent, cnt, total);
 325                                        last_percent = percent;
 326                                }
 327                        }
 328                }
 329                if (!ce->ce_mode) {
 330                        if (update)
 331                                unlink_entry(ce->name);
 332                        continue;
 333                }
 334                if (ce->ce_flags & mask) {
 335                        ce->ce_flags &= ~mask;
 336                        if (update)
 337                                checkout_entry(ce, &state, NULL);
 338                }
 339        }
 340        if (total) {
 341                fputc('\n', stderr);
 342                signal(SIGALRM, SIG_IGN);
 343        }
 344}
 345
 346static int unpack_trees(merge_fn_t fn)
 347{
 348        int indpos = 0;
 349        unsigned len = object_list_length(trees);
 350        struct tree_entry_list **posns;
 351        int i;
 352        struct object_list *posn = trees;
 353        merge_size = len;
 354
 355        if (len) {
 356                posns = xmalloc(len * sizeof(struct tree_entry_list *));
 357                for (i = 0; i < len; i++) {
 358                        posns[i] = ((struct tree *) posn->item)->entries;
 359                        posn = posn->next;
 360                }
 361                if (unpack_trees_rec(posns, len, "", fn, &indpos))
 362                        return -1;
 363        }
 364
 365        if (trivial_merges_only && nontrivial_merge)
 366                die("Merge requires file-level merging");
 367
 368        check_updates(active_cache, active_nr);
 369        return 0;
 370}
 371
 372static int list_tree(unsigned char *sha1)
 373{
 374        struct tree *tree = parse_tree_indirect(sha1);
 375        if (!tree)
 376                return -1;
 377        object_list_append(&tree->object, &trees);
 378        return 0;
 379}
 380
 381static int same(struct cache_entry *a, struct cache_entry *b)
 382{
 383        if (!!a != !!b)
 384                return 0;
 385        if (!a && !b)
 386                return 1;
 387        return a->ce_mode == b->ce_mode && 
 388                !memcmp(a->sha1, b->sha1, 20);
 389}
 390
 391
 392/*
 393 * When a CE gets turned into an unmerged entry, we
 394 * want it to be up-to-date
 395 */
 396static void verify_uptodate(struct cache_entry *ce)
 397{
 398        struct stat st;
 399
 400        if (index_only)
 401                return;
 402
 403        if (!lstat(ce->name, &st)) {
 404                unsigned changed = ce_match_stat(ce, &st, 1);
 405                if (!changed)
 406                        return;
 407                errno = 0;
 408        }
 409        if (errno == ENOENT)
 410                return;
 411        die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 412}
 413
 414static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
 415{
 416        merge->ce_flags |= htons(CE_UPDATE);
 417        if (old) {
 418                /*
 419                 * See if we can re-use the old CE directly?
 420                 * That way we get the uptodate stat info.
 421                 *
 422                 * This also removes the UPDATE flag on
 423                 * a match.
 424                 */
 425                if (same(old, merge)) {
 426                        *merge = *old;
 427                } else {
 428                        verify_uptodate(old);
 429                }
 430        }
 431        merge->ce_flags &= ~htons(CE_STAGEMASK);
 432        add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
 433        return 1;
 434}
 435
 436static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
 437{
 438        if (old)
 439                verify_uptodate(old);
 440        ce->ce_mode = 0;
 441        add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 442        return 1;
 443}
 444
 445static int keep_entry(struct cache_entry *ce)
 446{
 447        add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 448        return 1;
 449}
 450
 451#if DBRT_DEBUG
 452static void show_stage_entry(FILE *o,
 453                             const char *label, const struct cache_entry *ce)
 454{
 455        if (!ce)
 456                fprintf(o, "%s (missing)\n", label);
 457        else
 458                fprintf(o, "%s%06o %s %d\t%s\n",
 459                        label,
 460                        ntohl(ce->ce_mode),
 461                        sha1_to_hex(ce->sha1),
 462                        ce_stage(ce),
 463                        ce->name);
 464}
 465#endif
 466
 467static int threeway_merge(struct cache_entry **stages)
 468{
 469        struct cache_entry *index;
 470        struct cache_entry *head; 
 471        struct cache_entry *remote = stages[head_idx + 1];
 472        int count;
 473        int head_match = 0;
 474        int remote_match = 0;
 475
 476        int df_conflict_head = 0;
 477        int df_conflict_remote = 0;
 478
 479        int any_anc_missing = 0;
 480        int no_anc_exists = 1;
 481        int i;
 482
 483        for (i = 1; i < head_idx; i++) {
 484                if (!stages[i])
 485                        any_anc_missing = 1;
 486                else
 487                        no_anc_exists = 0;
 488        }
 489
 490        index = stages[0];
 491        head = stages[head_idx];
 492
 493        if (head == &df_conflict_entry) {
 494                df_conflict_head = 1;
 495                head = NULL;
 496        }
 497
 498        if (remote == &df_conflict_entry) {
 499                df_conflict_remote = 1;
 500                remote = NULL;
 501        }
 502
 503        /* First, if there's a #16 situation, note that to prevent #13
 504         * and #14. 
 505         */
 506        if (!same(remote, head)) {
 507                for (i = 1; i < head_idx; i++) {
 508                        if (same(stages[i], head)) {
 509                                head_match = i;
 510                        }
 511                        if (same(stages[i], remote)) {
 512                                remote_match = i;
 513                        }
 514                }
 515        }
 516
 517        /* We start with cases where the index is allowed to match
 518         * something other than the head: #14(ALT) and #2ALT, where it
 519         * is permitted to match the result instead.
 520         */
 521        /* #14, #14ALT, #2ALT */
 522        if (remote && !df_conflict_head && head_match && !remote_match) {
 523                if (index && !same(index, remote) && !same(index, head))
 524                        reject_merge(index);
 525                return merged_entry(remote, index);
 526        }
 527        /*
 528         * If we have an entry in the index cache, then we want to
 529         * make sure that it matches head.
 530         */
 531        if (index && !same(index, head)) {
 532                reject_merge(index);
 533        }
 534
 535        if (head) {
 536                /* #5ALT, #15 */
 537                if (same(head, remote))
 538                        return merged_entry(head, index);
 539                /* #13, #3ALT */
 540                if (!df_conflict_remote && remote_match && !head_match)
 541                        return merged_entry(head, index);
 542        }
 543
 544        /* #1 */
 545        if (!head && !remote && any_anc_missing)
 546                return 0;
 547
 548        /* Under the new "aggressive" rule, we resolve mostly trivial
 549         * cases that we historically had git-merge-one-file resolve.
 550         */
 551        if (aggressive) {
 552                int head_deleted = !head && !df_conflict_head;
 553                int remote_deleted = !remote && !df_conflict_remote;
 554                /*
 555                 * Deleted in both.
 556                 * Deleted in one and unchanged in the other.
 557                 */
 558                if ((head_deleted && remote_deleted) ||
 559                    (head_deleted && remote && remote_match) ||
 560                    (remote_deleted && head && head_match)) {
 561                        if (index)
 562                                return deleted_entry(index, index);
 563                        return 0;
 564                }
 565                /*
 566                 * Added in both, identically.
 567                 */
 568                if (no_anc_exists && head && remote && same(head, remote))
 569                        return merged_entry(head, index);
 570
 571        }
 572
 573        /* Below are "no merge" cases, which require that the index be
 574         * up-to-date to avoid the files getting overwritten with
 575         * conflict resolution files. 
 576         */
 577        if (index) {
 578                verify_uptodate(index);
 579        }
 580
 581        nontrivial_merge = 1;
 582
 583        /* #2, #3, #4, #6, #7, #9, #11. */
 584        count = 0;
 585        if (!head_match || !remote_match) {
 586                for (i = 1; i < head_idx; i++) {
 587                        if (stages[i]) {
 588                                keep_entry(stages[i]);
 589                                count++;
 590                                break;
 591                        }
 592                }
 593        }
 594#if DBRT_DEBUG
 595        else {
 596                fprintf(stderr, "read-tree: warning #16 detected\n");
 597                show_stage_entry(stderr, "head   ", stages[head_match]);
 598                show_stage_entry(stderr, "remote ", stages[remote_match]);
 599        }
 600#endif
 601        if (head) { count += keep_entry(head); }
 602        if (remote) { count += keep_entry(remote); }
 603        return count;
 604}
 605
 606/*
 607 * Two-way merge.
 608 *
 609 * The rule is to "carry forward" what is in the index without losing
 610 * information across a "fast forward", favoring a successful merge
 611 * over a merge failure when it makes sense.  For details of the
 612 * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 613 *
 614 */
 615static int twoway_merge(struct cache_entry **src)
 616{
 617        struct cache_entry *current = src[0];
 618        struct cache_entry *oldtree = src[1], *newtree = src[2];
 619
 620        if (merge_size != 2)
 621                return error("Cannot do a twoway merge of %d trees",
 622                             merge_size);
 623
 624        if (current) {
 625                if ((!oldtree && !newtree) || /* 4 and 5 */
 626                    (!oldtree && newtree &&
 627                     same(current, newtree)) || /* 6 and 7 */
 628                    (oldtree && newtree &&
 629                     same(oldtree, newtree)) || /* 14 and 15 */
 630                    (oldtree && newtree &&
 631                     !same(oldtree, newtree) && /* 18 and 19*/
 632                     same(current, newtree))) {
 633                        return keep_entry(current);
 634                }
 635                else if (oldtree && !newtree && same(current, oldtree)) {
 636                        /* 10 or 11 */
 637                        return deleted_entry(oldtree, current);
 638                }
 639                else if (oldtree && newtree &&
 640                         same(current, oldtree) && !same(current, newtree)) {
 641                        /* 20 or 21 */
 642                        return merged_entry(newtree, current);
 643                }
 644                else {
 645                        /* all other failures */
 646                        if (oldtree)
 647                                reject_merge(oldtree);
 648                        if (current)
 649                                reject_merge(current);
 650                        if (newtree)
 651                                reject_merge(newtree);
 652                        return -1;
 653                }
 654        }
 655        else if (newtree)
 656                return merged_entry(newtree, current);
 657        else
 658                return deleted_entry(oldtree, current);
 659}
 660
 661/*
 662 * One-way merge.
 663 *
 664 * The rule is:
 665 * - take the stat information from stage0, take the data from stage1
 666 */
 667static int oneway_merge(struct cache_entry **src)
 668{
 669        struct cache_entry *old = src[0];
 670        struct cache_entry *a = src[1];
 671
 672        if (merge_size != 1)
 673                return error("Cannot do a oneway merge of %d trees",
 674                             merge_size);
 675
 676        if (!a)
 677                return 0;
 678        if (old && same(old, a)) {
 679                return keep_entry(old);
 680        }
 681        return merged_entry(a, NULL);
 682}
 683
 684static int read_cache_unmerged(void)
 685{
 686        int i, deleted;
 687        struct cache_entry **dst;
 688
 689        read_cache();
 690        dst = active_cache;
 691        deleted = 0;
 692        for (i = 0; i < active_nr; i++) {
 693                struct cache_entry *ce = active_cache[i];
 694                if (ce_stage(ce)) {
 695                        deleted++;
 696                        continue;
 697                }
 698                if (deleted)
 699                        *dst = ce;
 700                dst++;
 701        }
 702        active_nr -= deleted;
 703        return deleted;
 704}
 705
 706static const char read_tree_usage[] = "git-read-tree (<sha> | -m [--aggressive] [-u | -i] <sha1> [<sha2> [<sha3>]])";
 707
 708static struct cache_file cache_file;
 709
 710int main(int argc, char **argv)
 711{
 712        int i, newfd, reset, stage = 0;
 713        unsigned char sha1[20];
 714        merge_fn_t fn = NULL;
 715
 716        setup_git_directory();
 717        git_config(git_default_config);
 718
 719        newfd = hold_index_file_for_update(&cache_file, get_index_file());
 720        if (newfd < 0)
 721                die("unable to create new cachefile");
 722
 723        git_config(git_default_config);
 724
 725        merge = 0;
 726        reset = 0;
 727        for (i = 1; i < argc; i++) {
 728                const char *arg = argv[i];
 729
 730                /* "-u" means "update", meaning that a merge will update
 731                 * the working tree.
 732                 */
 733                if (!strcmp(arg, "-u")) {
 734                        update = 1;
 735                        continue;
 736                }
 737
 738                if (!strcmp(arg, "-v")) {
 739                        verbose_update = 1;
 740                        continue;
 741                }
 742
 743                /* "-i" means "index only", meaning that a merge will
 744                 * not even look at the working tree.
 745                 */
 746                if (!strcmp(arg, "-i")) {
 747                        index_only = 1;
 748                        continue;
 749                }
 750
 751                /* This differs from "-m" in that we'll silently ignore unmerged entries */
 752                if (!strcmp(arg, "--reset")) {
 753                        if (stage || merge)
 754                                usage(read_tree_usage);
 755                        reset = 1;
 756                        merge = 1;
 757                        stage = 1;
 758                        read_cache_unmerged();
 759                        continue;
 760                }
 761
 762                if (!strcmp(arg, "--trivial")) {
 763                        trivial_merges_only = 1;
 764                        continue;
 765                }
 766
 767                if (!strcmp(arg, "--aggressive")) {
 768                        aggressive = 1;
 769                        continue;
 770                }
 771
 772                /* "-m" stands for "merge", meaning we start in stage 1 */
 773                if (!strcmp(arg, "-m")) {
 774                        if (stage || merge)
 775                                usage(read_tree_usage);
 776                        if (read_cache_unmerged())
 777                                die("you need to resolve your current index first");
 778                        stage = 1;
 779                        merge = 1;
 780                        continue;
 781                }
 782
 783                /* using -u and -i at the same time makes no sense */
 784                if (1 < index_only + update)
 785                        usage(read_tree_usage);
 786
 787                if (get_sha1(arg, sha1) < 0)
 788                        usage(read_tree_usage);
 789                if (list_tree(sha1) < 0)
 790                        die("failed to unpack tree object %s", arg);
 791                stage++;
 792        }
 793        if ((update||index_only) && !merge)
 794                usage(read_tree_usage);
 795
 796        if (merge) {
 797                if (stage < 2)
 798                        die("just how do you expect me to merge %d trees?", stage-1);
 799                switch (stage - 1) {
 800                case 1:
 801                        fn = oneway_merge;
 802                        break;
 803                case 2:
 804                        fn = twoway_merge;
 805                        break;
 806                case 3:
 807                        fn = threeway_merge;
 808                        break;
 809                default:
 810                        fn = threeway_merge;
 811                        break;
 812                }
 813
 814                if (stage - 1 >= 3)
 815                        head_idx = stage - 2;
 816                else
 817                        head_idx = 1;
 818        }
 819
 820        unpack_trees(fn);
 821        if (write_cache(newfd, active_cache, active_nr) ||
 822            commit_index_file(&cache_file))
 823                die("unable to write new index file");
 824        return 0;
 825}