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         progress_update = 1;
 274 }
 275
 276 static void setup_progress_signal(void)
 277 {
 278         struct sigaction sa;
 279         struct itimerval v;
 280
 281         memset(&sa, 0, sizeof(sa));
 282         sa.sa_handler = progress_interval;
 283         sigemptyset(&sa.sa_mask);
 284         sa.sa_flags = SA_RESTART;
 285         sigaction(SIGALRM, &sa, NULL);
 286
 287         v.it_interval.tv_sec = 1;
 288         v.it_interval.tv_usec = 0;
 289         v.it_value = v.it_interval;
 290         setitimer(ITIMER_REAL, &v, NULL);
 291 }
 292
 293 static void check_updates(struct cache_entry **src, int nr)
 294 {
 295         static struct checkout state = {
 296                 .base_dir = "",
 297                 .force = 1,
 298                 .quiet = 1,
 299                 .refresh_cache = 1,
 300         };
 301         unsigned short mask = htons(CE_UPDATE);
 302         unsigned last_percent = 200, cnt = 0, total = 0;
 303
 304         if (update && verbose_update) {
 305                 for (total = cnt = 0; cnt < nr; cnt++) {
 306                         struct cache_entry *ce = src[cnt];
 307                         if (!ce->ce_mode || ce->ce_flags & mask)
 308                                 total++;
 309                 }
 310
 311                 /* Don't bother doing this for very small updates */
 312                 if (total < 250)
 313                         total = 0;
 314
 315                 if (total) {
 316                         fprintf(stderr, "Checking files out...\n");
 317                         setup_progress_signal();
 318                         progress_update = 1;
 319                 }
 320                 cnt = 0;
 321         }
 322
 323         while (nr--) {
 324                 struct cache_entry *ce = *src++;
 325
 326                 if (total) {
 327                         if (!ce->ce_mode || ce->ce_flags & mask) {
 328                                 unsigned percent;
 329                                 cnt++;
 330                                 percent = (cnt * 100) / total;
 331                                 if (percent != last_percent ||
 332                                     progress_update) {
 333                                         fprintf(stderr, "%4u%% (%u/%u) done\r",
 334                                                 percent, cnt, total);
 335                                         last_percent = percent;
 336                                 }
 337                         }
 338                 }
 339                 if (!ce->ce_mode) {
 340                         if (update)
 341                                 unlink_entry(ce->name);
 342                         continue;
 343                 }
 344                 if (ce->ce_flags & mask) {
 345                         ce->ce_flags &= ~mask;
 346                         if (update)
 347                                 checkout_entry(ce, &state, NULL);
 348                 }
 349         }
 350         if (total) {
 351                 signal(SIGALRM, SIG_IGN);
 352                 fputc('\n', stderr);
 353         }
 354 }
 355
 356 static int unpack_trees(merge_fn_t fn)
 357 {
 358         int indpos = 0;
 359         unsigned len = object_list_length(trees);
 360         struct tree_entry_list **posns;
 361         int i;
 362         struct object_list *posn = trees;
 363         merge_size = len;
 364
 365         if (len) {
 366                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
 367                 for (i = 0; i < len; i++) {
 368                         posns[i] = ((struct tree *) posn->item)->entries;
 369                         posn = posn->next;
 370                 }
 371                 if (unpack_trees_rec(posns, len, "", fn, &indpos))
 372                         return -1;
 373         }
 374
 375         if (trivial_merges_only && nontrivial_merge)
 376                 die("Merge requires file-level merging");
 377
 378         check_updates(active_cache, active_nr);
 379         return 0;
 380 }
 381
 382 static int list_tree(unsigned char *sha1)
 383 {
 384         struct tree *tree = parse_tree_indirect(sha1);
 385         if (!tree)
 386                 return -1;
 387         object_list_append(&tree->object, &trees);
 388         return 0;
 389 }
 390
 391 static int same(struct cache_entry *a, struct cache_entry *b)
 392 {
 393         if (!!a != !!b)
 394                 return 0;
 395         if (!a && !b)
 396                 return 1;
 397         return a->ce_mode == b->ce_mode &&
 398                 !memcmp(a->sha1, b->sha1, 20);
 399 }
 400
 401
 402 /*
 403  * When a CE gets turned into an unmerged entry, we
 404  * want it to be up-to-date
 405  */
 406 static void verify_uptodate(struct cache_entry *ce)
 407 {
 408         struct stat st;
 409
 410         if (index_only)
 411                 return;
 412
 413         if (!lstat(ce->name, &st)) {
 414                 unsigned changed = ce_match_stat(ce, &st, 1);
 415                 if (!changed)
 416                         return;
 417                 errno = 0;
 418         }
 419         if (errno == ENOENT)
 420                 return;
 421         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 422 }
 423
 424 static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
 425 {
 426         merge->ce_flags |= htons(CE_UPDATE);
 427         if (old) {
 428                 /*
 429                  * See if we can re-use the old CE directly?
 430                  * That way we get the uptodate stat info.
 431                  *
 432                  * This also removes the UPDATE flag on
 433                  * a match.
 434                  */
 435                 if (same(old, merge)) {
 436                         *merge = *old;
 437                 } else {
 438                         verify_uptodate(old);
 439                 }
 440         }
 441         merge->ce_flags &= ~htons(CE_STAGEMASK);
 442         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
 443         return 1;
 444 }
 445
 446 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
 447 {
 448         if (old)
 449                 verify_uptodate(old);
 450         ce->ce_mode = 0;
 451         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 452         return 1;
 453 }
 454
 455 static int keep_entry(struct cache_entry *ce)
 456 {
 457         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 458         return 1;
 459 }
 460
 461 #if DBRT_DEBUG
 462 static void show_stage_entry(FILE *o,
 463                              const char *label, const struct cache_entry *ce)
 464 {
 465         if (!ce)
 466                 fprintf(o, "%s (missing)\n", label);
 467         else
 468                 fprintf(o, "%s%06o %s %d\t%s\n",
 469                         label,
 470                         ntohl(ce->ce_mode),
 471                         sha1_to_hex(ce->sha1),
 472                         ce_stage(ce),
 473                         ce->name);
 474 }
 475 #endif
 476
 477 static int threeway_merge(struct cache_entry **stages)
 478 {
 479         struct cache_entry *index;
 480         struct cache_entry *head;
 481         struct cache_entry *remote = stages[head_idx + 1];
 482         int count;
 483         int head_match = 0;
 484         int remote_match = 0;
 485
 486         int df_conflict_head = 0;
 487         int df_conflict_remote = 0;
 488
 489         int any_anc_missing = 0;
 490         int no_anc_exists = 1;
 491         int i;
 492
 493         for (i = 1; i < head_idx; i++) {
 494                 if (!stages[i])
 495                         any_anc_missing = 1;
 496                 else
 497                         no_anc_exists = 0;
 498         }
 499
 500         index = stages[0];
 501         head = stages[head_idx];
 502
 503         if (head == &df_conflict_entry) {
 504                 df_conflict_head = 1;
 505                 head = NULL;
 506         }
 507
 508         if (remote == &df_conflict_entry) {
 509                 df_conflict_remote = 1;
 510                 remote = NULL;
 511         }
 512
 513         /* First, if there's a #16 situation, note that to prevent #13
 514          * and #14.
 515          */
 516         if (!same(remote, head)) {
 517                 for (i = 1; i < head_idx; i++) {
 518                         if (same(stages[i], head)) {
 519                                 head_match = i;
 520                         }
 521                         if (same(stages[i], remote)) {
 522                                 remote_match = i;
 523                         }
 524                 }
 525         }
 526
 527         /* We start with cases where the index is allowed to match
 528          * something other than the head: #14(ALT) and #2ALT, where it
 529          * is permitted to match the result instead.
 530          */
 531         /* #14, #14ALT, #2ALT */
 532         if (remote && !df_conflict_head && head_match && !remote_match) {
 533                 if (index && !same(index, remote) && !same(index, head))
 534                         reject_merge(index);
 535                 return merged_entry(remote, index);
 536         }
 537         /*
 538          * If we have an entry in the index cache, then we want to
 539          * make sure that it matches head.
 540          */
 541         if (index && !same(index, head)) {
 542                 reject_merge(index);
 543         }
 544
 545         if (head) {
 546                 /* #5ALT, #15 */
 547                 if (same(head, remote))
 548                         return merged_entry(head, index);
 549                 /* #13, #3ALT */
 550                 if (!df_conflict_remote && remote_match && !head_match)
 551                         return merged_entry(head, index);
 552         }
 553
 554         /* #1 */
 555         if (!head && !remote && any_anc_missing)
 556                 return 0;
 557
 558         /* Under the new "aggressive" rule, we resolve mostly trivial
 559          * cases that we historically had git-merge-one-file resolve.
 560          */
 561         if (aggressive) {
 562                 int head_deleted = !head && !df_conflict_head;
 563                 int remote_deleted = !remote && !df_conflict_remote;
 564                 /*
 565                  * Deleted in both.
 566                  * Deleted in one and unchanged in the other.
 567                  */
 568                 if ((head_deleted && remote_deleted) ||
 569                     (head_deleted && remote && remote_match) ||
 570                     (remote_deleted && head && head_match)) {
 571                         if (index)
 572                                 return deleted_entry(index, index);
 573                         return 0;
 574                 }
 575                 /*
 576                  * Added in both, identically.
 577                  */
 578                 if (no_anc_exists && head && remote && same(head, remote))
 579                         return merged_entry(head, index);
 580
 581         }
 582
 583         /* Below are "no merge" cases, which require that the index be
 584          * up-to-date to avoid the files getting overwritten with
 585          * conflict resolution files.
 586          */
 587         if (index) {
 588                 verify_uptodate(index);
 589         }
 590
 591         nontrivial_merge = 1;
 592
 593         /* #2, #3, #4, #6, #7, #9, #11. */
 594         count = 0;
 595         if (!head_match || !remote_match) {
 596                 for (i = 1; i < head_idx; i++) {
 597                         if (stages[i]) {
 598                                 keep_entry(stages[i]);
 599                                 count++;
 600                                 break;
 601                         }
 602                 }
 603         }
 604 #if DBRT_DEBUG
 605         else {
 606                 fprintf(stderr, "read-tree: warning #16 detected\n");
 607                 show_stage_entry(stderr, "head   ", stages[head_match]);
 608                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 609         }
 610 #endif
 611         if (head) { count += keep_entry(head); }
 612         if (remote) { count += keep_entry(remote); }
 613         return count;
 614 }
 615
 616 /*
 617  * Two-way merge.
 618  *
 619  * The rule is to "carry forward" what is in the index without losing
 620  * information across a "fast forward", favoring a successful merge
 621  * over a merge failure when it makes sense.  For details of the
 622  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 623  *
 624  */
 625 static int twoway_merge(struct cache_entry **src)
 626 {
 627         struct cache_entry *current = src[0];
 628         struct cache_entry *oldtree = src[1], *newtree = src[2];
 629
 630         if (merge_size != 2)
 631                 return error("Cannot do a twoway merge of %d trees",
 632                              merge_size);
 633
 634         if (current) {
 635                 if ((!oldtree && !newtree) || /* 4 and 5 */
 636                     (!oldtree && newtree &&
 637                      same(current, newtree)) || /* 6 and 7 */
 638                     (oldtree && newtree &&
 639                      same(oldtree, newtree)) || /* 14 and 15 */
 640                     (oldtree && newtree &&
 641                      !same(oldtree, newtree) && /* 18 and 19*/
 642                      same(current, newtree))) {
 643                         return keep_entry(current);
 644                 }
 645                 else if (oldtree && !newtree && same(current, oldtree)) {
 646                         /* 10 or 11 */
 647                         return deleted_entry(oldtree, current);
 648                 }
 649                 else if (oldtree && newtree &&
 650                          same(current, oldtree) && !same(current, newtree)) {
 651                         /* 20 or 21 */
 652                         return merged_entry(newtree, current);
 653                 }
 654                 else {
 655                         /* all other failures */
 656                         if (oldtree)
 657                                 reject_merge(oldtree);
 658                         if (current)
 659                                 reject_merge(current);
 660                         if (newtree)
 661                                 reject_merge(newtree);
 662                         return -1;
 663                 }
 664         }
 665         else if (newtree)
 666                 return merged_entry(newtree, current);
 667         else
 668                 return deleted_entry(oldtree, current);
 669 }
 670
 671 /*
 672  * One-way merge.
 673  *
 674  * The rule is:
 675  * - take the stat information from stage0, take the data from stage1
 676  */
 677 static int oneway_merge(struct cache_entry **src)
 678 {
 679         struct cache_entry *old = src[0];
 680         struct cache_entry *a = src[1];
 681
 682         if (merge_size != 1)
 683                 return error("Cannot do a oneway merge of %d trees",
 684                              merge_size);
 685
 686         if (!a)
 687                 return 0;
 688         if (old && same(old, a)) {
 689                 return keep_entry(old);
 690         }
 691         return merged_entry(a, NULL);
 692 }
 693
 694 static int read_cache_unmerged(void)
 695 {
 696         int i, deleted;
 697         struct cache_entry **dst;
 698
 699         read_cache();
 700         dst = active_cache;
 701         deleted = 0;
 702         for (i = 0; i < active_nr; i++) {
 703                 struct cache_entry *ce = active_cache[i];
 704                 if (ce_stage(ce)) {
 705                         deleted++;
 706                         continue;
 707                 }
 708                 if (deleted)
 709                         *dst = ce;
 710                 dst++;
 711         }
 712         active_nr -= deleted;
 713         return deleted;
 714 }
 715
 716 static const char read_tree_usage[] = "git-read-tree (<sha> | -m [--aggressive] [-u | -i] <sha1> [<sha2> [<sha3>]])";
 717
 718 static struct cache_file cache_file;
 719
 720 int main(int argc, char **argv)
 721 {
 722         int i, newfd, reset, stage = 0;
 723         unsigned char sha1[20];
 724         merge_fn_t fn = NULL;
 725
 726         setup_git_directory();
 727         git_config(git_default_config);
 728
 729         newfd = hold_index_file_for_update(&cache_file, get_index_file());
 730         if (newfd < 0)
 731                 die("unable to create new cachefile");
 732
 733         git_config(git_default_config);
 734
 735         merge = 0;
 736         reset = 0;
 737         for (i = 1; i < argc; i++) {
 738                 const char *arg = argv[i];
 739
 740                 /* "-u" means "update", meaning that a merge will update
 741                  * the working tree.
 742                  */
 743                 if (!strcmp(arg, "-u")) {
 744                         update = 1;
 745                         continue;
 746                 }
 747
 748                 if (!strcmp(arg, "-v")) {
 749                         verbose_update = 1;
 750                         continue;
 751                 }
 752
 753                 /* "-i" means "index only", meaning that a merge will
 754                  * not even look at the working tree.
 755                  */
 756                 if (!strcmp(arg, "-i")) {
 757                         index_only = 1;
 758                         continue;
 759                 }
 760
 761                 /* This differs from "-m" in that we'll silently ignore unmerged entries */
 762                 if (!strcmp(arg, "--reset")) {
 763                         if (stage || merge)
 764                                 usage(read_tree_usage);
 765                         reset = 1;
 766                         merge = 1;
 767                         stage = 1;
 768                         read_cache_unmerged();
 769                         continue;
 770                 }
 771
 772                 if (!strcmp(arg, "--trivial")) {
 773                         trivial_merges_only = 1;
 774                         continue;
 775                 }
 776
 777                 if (!strcmp(arg, "--aggressive")) {
 778                         aggressive = 1;
 779                         continue;
 780                 }
 781
 782                 /* "-m" stands for "merge", meaning we start in stage 1 */
 783                 if (!strcmp(arg, "-m")) {
 784                         if (stage || merge)
 785                                 usage(read_tree_usage);
 786                         if (read_cache_unmerged())
 787                                 die("you need to resolve your current index first");
 788                         stage = 1;
 789                         merge = 1;
 790                         continue;
 791                 }
 792
 793                 /* using -u and -i at the same time makes no sense */
 794                 if (1 < index_only + update)
 795                         usage(read_tree_usage);
 796
 797                 if (get_sha1(arg, sha1) < 0)
 798                         usage(read_tree_usage);
 799                 if (list_tree(sha1) < 0)
 800                         die("failed to unpack tree object %s", arg);
 801                 stage++;
 802         }
 803         if ((update||index_only) && !merge)
 804                 usage(read_tree_usage);
 805
 806         if (merge) {
 807                 if (stage < 2)
 808                         die("just how do you expect me to merge %d trees?", stage-1);
 809                 switch (stage - 1) {
 810                 case 1:
 811                         fn = oneway_merge;
 812                         break;
 813                 case 2:
 814                         fn = twoway_merge;
 815                         break;
 816                 case 3:
 817                         fn = threeway_merge;
 818                         break;
 819                 default:
 820                         fn = threeway_merge;
 821                         break;
 822                 }
 823
 824                 if (stage - 1 >= 3)
 825                         head_idx = stage - 2;
 826                 else
 827                         head_idx = 1;
 828         }
 829
 830         unpack_trees(fn);
 831         if (write_cache(newfd, active_cache, active_nr) ||
 832             commit_index_file(&cache_file))
 833                 die("unable to write new index file");
 834         return 0;
 835 }