read-tree.c

   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
  15 static int merge = 0;
  16 static int update = 0;
  17 static int index_only = 0;
  18 static int nontrivial_merge = 0;
  19 static int trivial_merges_only = 0;
  20 static int aggressive = 0;
  21 static int verbose_update = 0;
  22 static volatile int progress_update = 0;
  23
  24 static int head_idx = -1;
  25 static int merge_size = 0;
  26
  27 static struct object_list *trees = NULL;
  28
  29 static struct cache_entry df_conflict_entry = {
  30 };
  31
  32 static struct tree_entry_list df_conflict_list = {
  33         .name = NULL,
  34         .next = &df_conflict_list
  35 };
  36
  37 typedef int (*merge_fn_t)(struct cache_entry **src);
  38
  39 static 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
  60 static 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
 236 static 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  */
 246 static 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
 271 static void progress_interval(int signum)
 272 {
 273         signal(SIGALRM, progress_interval);
 274         progress_update = 1;
 275 }
 276
 277 static 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
 346 static 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
 372 static 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
 381 static 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  */
 396 static 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
 414 static 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
 436 static 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
 445 static 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
 452 static 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
 467 static 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  */
 615 static 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  */
 667 static 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
 684 static 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
 706 static const char read_tree_usage[] = "git-read-tree (<sha> | -m [--aggressive] [-u | -i] <sha1> [<sha2> [<sha3>]])";
 707
 708 static struct cache_file cache_file;
 709
 710 int 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 }