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 reset = 0;
  16 static int merge = 0;
  17 static int update = 0;
  18 static int index_only = 0;
  19 static int nontrivial_merge = 0;
  20 static int trivial_merges_only = 0;
  21 static int aggressive = 0;
  22 static int verbose_update = 0;
  23 static volatile int progress_update = 0;
  24
  25 static int head_idx = -1;
  26 static int merge_size = 0;
  27
  28 static struct object_list *trees = NULL;
  29
  30 static struct cache_entry df_conflict_entry = {
  31 };
  32
  33 static struct tree_entry_list df_conflict_list = {
  34         .name = NULL,
  35         .next = &df_conflict_list
  36 };
  37
  38 typedef int (*merge_fn_t)(struct cache_entry **src);
  39
  40 static int entcmp(char *name1, int dir1, char *name2, int dir2)
  41 {
  42         int len1 = strlen(name1);
  43         int len2 = strlen(name2);
  44         int len = len1 < len2 ? len1 : len2;
  45         int ret = memcmp(name1, name2, len);
  46         unsigned char c1, c2;
  47         if (ret)
  48                 return ret;
  49         c1 = name1[len];
  50         c2 = name2[len];
  51         if (!c1 && dir1)
  52                 c1 = '/';
  53         if (!c2 && dir2)
  54                 c2 = '/';
  55         ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
  56         if (c1 && c2 && !ret)
  57                 ret = len1 - len2;
  58         return ret;
  59 }
  60
  61 static int unpack_trees_rec(struct tree_entry_list **posns, int len,
  62                             const char *base, merge_fn_t fn, int *indpos)
  63 {
  64         int baselen = strlen(base);
  65         int src_size = len + 1;
  66         do {
  67                 int i;
  68                 char *first;
  69                 int firstdir = 0;
  70                 int pathlen;
  71                 unsigned ce_size;
  72                 struct tree_entry_list **subposns;
  73                 struct cache_entry **src;
  74                 int any_files = 0;
  75                 int any_dirs = 0;
  76                 char *cache_name;
  77                 int ce_stage;
  78
  79                 /* Find the first name in the input. */
  80
  81                 first = NULL;
  82                 cache_name = NULL;
  83
  84                 /* Check the cache */
  85                 if (merge && *indpos < active_nr) {
  86                         /* This is a bit tricky: */
  87                         /* If the index has a subdirectory (with
  88                          * contents) as the first name, it'll get a
  89                          * filename like "foo/bar". But that's after
  90                          * "foo", so the entry in trees will get
  91                          * handled first, at which point we'll go into
  92                          * "foo", and deal with "bar" from the index,
  93                          * because the base will be "foo/". The only
  94                          * way we can actually have "foo/bar" first of
  95                          * all the things is if the trees don't
  96                          * contain "foo" at all, in which case we'll
  97                          * handle "foo/bar" without going into the
  98                          * directory, but that's fine (and will return
  99                          * an error anyway, with the added unknown
 100                          * file case.
 101                          */
 102
 103                         cache_name = active_cache[*indpos]->name;
 104                         if (strlen(cache_name) > baselen &&
 105                             !memcmp(cache_name, base, baselen)) {
 106                                 cache_name += baselen;
 107                                 first = cache_name;
 108                         } else {
 109                                 cache_name = NULL;
 110                         }
 111                 }
 112
 113 #if DBRT_DEBUG > 1
 114                 if (first)
 115                         printf("index %s\n", first);
 116 #endif
 117                 for (i = 0; i < len; i++) {
 118                         if (!posns[i] || posns[i] == &df_conflict_list)
 119                                 continue;
 120 #if DBRT_DEBUG > 1
 121                         printf("%d %s\n", i + 1, posns[i]->name);
 122 #endif
 123                         if (!first || entcmp(first, firstdir,
 124                                              posns[i]->name,
 125                                              posns[i]->directory) > 0) {
 126                                 first = posns[i]->name;
 127                                 firstdir = posns[i]->directory;
 128                         }
 129                 }
 130                 /* No name means we're done */
 131                 if (!first)
 132                         return 0;
 133
 134                 pathlen = strlen(first);
 135                 ce_size = cache_entry_size(baselen + pathlen);
 136
 137                 src = xcalloc(src_size, sizeof(struct cache_entry *));
 138
 139                 subposns = xcalloc(len, sizeof(struct tree_list_entry *));
 140
 141                 if (cache_name && !strcmp(cache_name, first)) {
 142                         any_files = 1;
 143                         src[0] = active_cache[*indpos];
 144                         remove_cache_entry_at(*indpos);
 145                 }
 146
 147                 for (i = 0; i < len; i++) {
 148                         struct cache_entry *ce;
 149
 150                         if (!posns[i] ||
 151                             (posns[i] != &df_conflict_list &&
 152                              strcmp(first, posns[i]->name))) {
 153                                 continue;
 154                         }
 155
 156                         if (posns[i] == &df_conflict_list) {
 157                                 src[i + merge] = &df_conflict_entry;
 158                                 continue;
 159                         }
 160
 161                         if (posns[i]->directory) {
 162                                 any_dirs = 1;
 163                                 parse_tree(posns[i]->item.tree);
 164                                 subposns[i] = posns[i]->item.tree->entries;
 165                                 posns[i] = posns[i]->next;
 166                                 src[i + merge] = &df_conflict_entry;
 167                                 continue;
 168                         }
 169
 170                         if (!merge)
 171                                 ce_stage = 0;
 172                         else if (i + 1 < head_idx)
 173                                 ce_stage = 1;
 174                         else if (i + 1 > head_idx)
 175                                 ce_stage = 3;
 176                         else
 177                                 ce_stage = 2;
 178
 179                         ce = xcalloc(1, ce_size);
 180                         ce->ce_mode = create_ce_mode(posns[i]->mode);
 181                         ce->ce_flags = create_ce_flags(baselen + pathlen,
 182                                                        ce_stage);
 183                         memcpy(ce->name, base, baselen);
 184                         memcpy(ce->name + baselen, first, pathlen + 1);
 185
 186                         any_files = 1;
 187
 188                         memcpy(ce->sha1, posns[i]->item.any->sha1, 20);
 189                         src[i + merge] = ce;
 190                         subposns[i] = &df_conflict_list;
 191                         posns[i] = posns[i]->next;
 192                 }
 193                 if (any_files) {
 194                         if (merge) {
 195                                 int ret;
 196
 197 #if DBRT_DEBUG > 1
 198                                 printf("%s:\n", first);
 199                                 for (i = 0; i < src_size; i++) {
 200                                         printf(" %d ", i);
 201                                         if (src[i])
 202                                                 printf("%s\n", sha1_to_hex(src[i]->sha1));
 203                                         else
 204                                                 printf("\n");
 205                                 }
 206 #endif
 207                                 ret = fn(src);
 208
 209 #if DBRT_DEBUG > 1
 210                                 printf("Added %d entries\n", ret);
 211 #endif
 212                                 *indpos += ret;
 213                         } else {
 214                                 for (i = 0; i < src_size; i++) {
 215                                         if (src[i]) {
 216                                                 add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
 217                                         }
 218                                 }
 219                         }
 220                 }
 221                 if (any_dirs) {
 222                         char *newbase = xmalloc(baselen + 2 + pathlen);
 223                         memcpy(newbase, base, baselen);
 224                         memcpy(newbase + baselen, first, pathlen);
 225                         newbase[baselen + pathlen] = '/';
 226                         newbase[baselen + pathlen + 1] = '\0';
 227                         if (unpack_trees_rec(subposns, len, newbase, fn,
 228                                              indpos))
 229                                 return -1;
 230                         free(newbase);
 231                 }
 232                 free(subposns);
 233                 free(src);
 234         } while (1);
 235 }
 236
 237 static void reject_merge(struct cache_entry *ce)
 238 {
 239         die("Entry '%s' would be overwritten by merge. Cannot merge.",
 240             ce->name);
 241 }
 242
 243 /* Unlink the last component and attempt to remove leading
 244  * directories, in case this unlink is the removal of the
 245  * last entry in the directory -- empty directories are removed.
 246  */
 247 static void unlink_entry(char *name)
 248 {
 249         char *cp, *prev;
 250
 251         if (unlink(name))
 252                 return;
 253         prev = NULL;
 254         while (1) {
 255                 int status;
 256                 cp = strrchr(name, '/');
 257                 if (prev)
 258                         *prev = '/';
 259                 if (!cp)
 260                         break;
 261
 262                 *cp = 0;
 263                 status = rmdir(name);
 264                 if (status) {
 265                         *cp = '/';
 266                         break;
 267                 }
 268                 prev = cp;
 269         }
 270 }
 271
 272 static void progress_interval(int signum)
 273 {
 274         progress_update = 1;
 275 }
 276
 277 static void setup_progress_signal(void)
 278 {
 279         struct sigaction sa;
 280         struct itimerval v;
 281
 282         memset(&sa, 0, sizeof(sa));
 283         sa.sa_handler = progress_interval;
 284         sigemptyset(&sa.sa_mask);
 285         sa.sa_flags = SA_RESTART;
 286         sigaction(SIGALRM, &sa, NULL);
 287
 288         v.it_interval.tv_sec = 1;
 289         v.it_interval.tv_usec = 0;
 290         v.it_value = v.it_interval;
 291         setitimer(ITIMER_REAL, &v, NULL);
 292 }
 293
 294 static void check_updates(struct cache_entry **src, int nr)
 295 {
 296         static struct checkout state = {
 297                 .base_dir = "",
 298                 .force = 1,
 299                 .quiet = 1,
 300                 .refresh_cache = 1,
 301         };
 302         unsigned short mask = htons(CE_UPDATE);
 303         unsigned last_percent = 200, cnt = 0, total = 0;
 304
 305         if (update && verbose_update) {
 306                 for (total = cnt = 0; cnt < nr; cnt++) {
 307                         struct cache_entry *ce = src[cnt];
 308                         if (!ce->ce_mode || ce->ce_flags & mask)
 309                                 total++;
 310                 }
 311
 312                 /* Don't bother doing this for very small updates */
 313                 if (total < 250)
 314                         total = 0;
 315
 316                 if (total) {
 317                         fprintf(stderr, "Checking files out...\n");
 318                         setup_progress_signal();
 319                         progress_update = 1;
 320                 }
 321                 cnt = 0;
 322         }
 323
 324         while (nr--) {
 325                 struct cache_entry *ce = *src++;
 326
 327                 if (total) {
 328                         if (!ce->ce_mode || ce->ce_flags & mask) {
 329                                 unsigned percent;
 330                                 cnt++;
 331                                 percent = (cnt * 100) / total;
 332                                 if (percent != last_percent ||
 333                                     progress_update) {
 334                                         fprintf(stderr, "%4u%% (%u/%u) done\r",
 335                                                 percent, cnt, total);
 336                                         last_percent = percent;
 337                                 }
 338                         }
 339                 }
 340                 if (!ce->ce_mode) {
 341                         if (update)
 342                                 unlink_entry(ce->name);
 343                         continue;
 344                 }
 345                 if (ce->ce_flags & mask) {
 346                         ce->ce_flags &= ~mask;
 347                         if (update)
 348                                 checkout_entry(ce, &state, NULL);
 349                 }
 350         }
 351         if (total) {
 352                 signal(SIGALRM, SIG_IGN);
 353                 fputc('\n', stderr);
 354         }
 355 }
 356
 357 static int unpack_trees(merge_fn_t fn)
 358 {
 359         int indpos = 0;
 360         unsigned len = object_list_length(trees);
 361         struct tree_entry_list **posns;
 362         int i;
 363         struct object_list *posn = trees;
 364         merge_size = len;
 365
 366         if (len) {
 367                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
 368                 for (i = 0; i < len; i++) {
 369                         posns[i] = ((struct tree *) posn->item)->entries;
 370                         posn = posn->next;
 371                 }
 372                 if (unpack_trees_rec(posns, len, "", fn, &indpos))
 373                         return -1;
 374         }
 375
 376         if (trivial_merges_only && nontrivial_merge)
 377                 die("Merge requires file-level merging");
 378
 379         check_updates(active_cache, active_nr);
 380         return 0;
 381 }
 382
 383 static int list_tree(unsigned char *sha1)
 384 {
 385         struct tree *tree = parse_tree_indirect(sha1);
 386         if (!tree)
 387                 return -1;
 388         object_list_append(&tree->object, &trees);
 389         return 0;
 390 }
 391
 392 static int same(struct cache_entry *a, struct cache_entry *b)
 393 {
 394         if (!!a != !!b)
 395                 return 0;
 396         if (!a && !b)
 397                 return 1;
 398         return a->ce_mode == b->ce_mode &&
 399                 !memcmp(a->sha1, b->sha1, 20);
 400 }
 401
 402
 403 /*
 404  * When a CE gets turned into an unmerged entry, we
 405  * want it to be up-to-date
 406  */
 407 static void verify_uptodate(struct cache_entry *ce)
 408 {
 409         struct stat st;
 410
 411         if (index_only)
 412                 return;
 413
 414         if (!lstat(ce->name, &st)) {
 415                 unsigned changed = ce_match_stat(ce, &st, 1);
 416                 if (!changed)
 417                         return;
 418                 errno = 0;
 419         }
 420         if (reset) {
 421                 ce->ce_flags |= htons(CE_UPDATE);
 422                 return;
 423         }
 424         if (errno == ENOENT)
 425                 return;
 426         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 427 }
 428
 429 static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
 430 {
 431         merge->ce_flags |= htons(CE_UPDATE);
 432         if (old) {
 433                 /*
 434                  * See if we can re-use the old CE directly?
 435                  * That way we get the uptodate stat info.
 436                  *
 437                  * This also removes the UPDATE flag on
 438                  * a match.
 439                  */
 440                 if (same(old, merge)) {
 441                         *merge = *old;
 442                 } else {
 443                         verify_uptodate(old);
 444                 }
 445         }
 446         merge->ce_flags &= ~htons(CE_STAGEMASK);
 447         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
 448         return 1;
 449 }
 450
 451 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
 452 {
 453         if (old)
 454                 verify_uptodate(old);
 455         ce->ce_mode = 0;
 456         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 457         return 1;
 458 }
 459
 460 static int keep_entry(struct cache_entry *ce)
 461 {
 462         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 463         return 1;
 464 }
 465
 466 #if DBRT_DEBUG
 467 static void show_stage_entry(FILE *o,
 468                              const char *label, const struct cache_entry *ce)
 469 {
 470         if (!ce)
 471                 fprintf(o, "%s (missing)\n", label);
 472         else
 473                 fprintf(o, "%s%06o %s %d\t%s\n",
 474                         label,
 475                         ntohl(ce->ce_mode),
 476                         sha1_to_hex(ce->sha1),
 477                         ce_stage(ce),
 478                         ce->name);
 479 }
 480 #endif
 481
 482 static int threeway_merge(struct cache_entry **stages)
 483 {
 484         struct cache_entry *index;
 485         struct cache_entry *head;
 486         struct cache_entry *remote = stages[head_idx + 1];
 487         int count;
 488         int head_match = 0;
 489         int remote_match = 0;
 490
 491         int df_conflict_head = 0;
 492         int df_conflict_remote = 0;
 493
 494         int any_anc_missing = 0;
 495         int no_anc_exists = 1;
 496         int i;
 497
 498         for (i = 1; i < head_idx; i++) {
 499                 if (!stages[i])
 500                         any_anc_missing = 1;
 501                 else
 502                         no_anc_exists = 0;
 503         }
 504
 505         index = stages[0];
 506         head = stages[head_idx];
 507
 508         if (head == &df_conflict_entry) {
 509                 df_conflict_head = 1;
 510                 head = NULL;
 511         }
 512
 513         if (remote == &df_conflict_entry) {
 514                 df_conflict_remote = 1;
 515                 remote = NULL;
 516         }
 517
 518         /* First, if there's a #16 situation, note that to prevent #13
 519          * and #14.
 520          */
 521         if (!same(remote, head)) {
 522                 for (i = 1; i < head_idx; i++) {
 523                         if (same(stages[i], head)) {
 524                                 head_match = i;
 525                         }
 526                         if (same(stages[i], remote)) {
 527                                 remote_match = i;
 528                         }
 529                 }
 530         }
 531
 532         /* We start with cases where the index is allowed to match
 533          * something other than the head: #14(ALT) and #2ALT, where it
 534          * is permitted to match the result instead.
 535          */
 536         /* #14, #14ALT, #2ALT */
 537         if (remote && !df_conflict_head && head_match && !remote_match) {
 538                 if (index && !same(index, remote) && !same(index, head))
 539                         reject_merge(index);
 540                 return merged_entry(remote, index);
 541         }
 542         /*
 543          * If we have an entry in the index cache, then we want to
 544          * make sure that it matches head.
 545          */
 546         if (index && !same(index, head)) {
 547                 reject_merge(index);
 548         }
 549
 550         if (head) {
 551                 /* #5ALT, #15 */
 552                 if (same(head, remote))
 553                         return merged_entry(head, index);
 554                 /* #13, #3ALT */
 555                 if (!df_conflict_remote && remote_match && !head_match)
 556                         return merged_entry(head, index);
 557         }
 558
 559         /* #1 */
 560         if (!head && !remote && any_anc_missing)
 561                 return 0;
 562
 563         /* Under the new "aggressive" rule, we resolve mostly trivial
 564          * cases that we historically had git-merge-one-file resolve.
 565          */
 566         if (aggressive) {
 567                 int head_deleted = !head && !df_conflict_head;
 568                 int remote_deleted = !remote && !df_conflict_remote;
 569                 /*
 570                  * Deleted in both.
 571                  * Deleted in one and unchanged in the other.
 572                  */
 573                 if ((head_deleted && remote_deleted) ||
 574                     (head_deleted && remote && remote_match) ||
 575                     (remote_deleted && head && head_match)) {
 576                         if (index)
 577                                 return deleted_entry(index, index);
 578                         return 0;
 579                 }
 580                 /*
 581                  * Added in both, identically.
 582                  */
 583                 if (no_anc_exists && head && remote && same(head, remote))
 584                         return merged_entry(head, index);
 585
 586         }
 587
 588         /* Below are "no merge" cases, which require that the index be
 589          * up-to-date to avoid the files getting overwritten with
 590          * conflict resolution files.
 591          */
 592         if (index) {
 593                 verify_uptodate(index);
 594         }
 595
 596         nontrivial_merge = 1;
 597
 598         /* #2, #3, #4, #6, #7, #9, #11. */
 599         count = 0;
 600         if (!head_match || !remote_match) {
 601                 for (i = 1; i < head_idx; i++) {
 602                         if (stages[i]) {
 603                                 keep_entry(stages[i]);
 604                                 count++;
 605                                 break;
 606                         }
 607                 }
 608         }
 609 #if DBRT_DEBUG
 610         else {
 611                 fprintf(stderr, "read-tree: warning #16 detected\n");
 612                 show_stage_entry(stderr, "head   ", stages[head_match]);
 613                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 614         }
 615 #endif
 616         if (head) { count += keep_entry(head); }
 617         if (remote) { count += keep_entry(remote); }
 618         return count;
 619 }
 620
 621 /*
 622  * Two-way merge.
 623  *
 624  * The rule is to "carry forward" what is in the index without losing
 625  * information across a "fast forward", favoring a successful merge
 626  * over a merge failure when it makes sense.  For details of the
 627  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 628  *
 629  */
 630 static int twoway_merge(struct cache_entry **src)
 631 {
 632         struct cache_entry *current = src[0];
 633         struct cache_entry *oldtree = src[1], *newtree = src[2];
 634
 635         if (merge_size != 2)
 636                 return error("Cannot do a twoway merge of %d trees",
 637                              merge_size);
 638
 639         if (current) {
 640                 if ((!oldtree && !newtree) || /* 4 and 5 */
 641                     (!oldtree && newtree &&
 642                      same(current, newtree)) || /* 6 and 7 */
 643                     (oldtree && newtree &&
 644                      same(oldtree, newtree)) || /* 14 and 15 */
 645                     (oldtree && newtree &&
 646                      !same(oldtree, newtree) && /* 18 and 19*/
 647                      same(current, newtree))) {
 648                         return keep_entry(current);
 649                 }
 650                 else if (oldtree && !newtree && same(current, oldtree)) {
 651                         /* 10 or 11 */
 652                         return deleted_entry(oldtree, current);
 653                 }
 654                 else if (oldtree && newtree &&
 655                          same(current, oldtree) && !same(current, newtree)) {
 656                         /* 20 or 21 */
 657                         return merged_entry(newtree, current);
 658                 }
 659                 else {
 660                         /* all other failures */
 661                         if (oldtree)
 662                                 reject_merge(oldtree);
 663                         if (current)
 664                                 reject_merge(current);
 665                         if (newtree)
 666                                 reject_merge(newtree);
 667                         return -1;
 668                 }
 669         }
 670         else if (newtree)
 671                 return merged_entry(newtree, current);
 672         else
 673                 return deleted_entry(oldtree, current);
 674 }
 675
 676 /*
 677  * One-way merge.
 678  *
 679  * The rule is:
 680  * - take the stat information from stage0, take the data from stage1
 681  */
 682 static int oneway_merge(struct cache_entry **src)
 683 {
 684         struct cache_entry *old = src[0];
 685         struct cache_entry *a = src[1];
 686
 687         if (merge_size != 1)
 688                 return error("Cannot do a oneway merge of %d trees",
 689                              merge_size);
 690
 691         if (!a)
 692                 return deleted_entry(old, NULL);
 693         if (old && same(old, a)) {
 694                 if (reset) {
 695                         struct stat st;
 696                         if (lstat(old->name, &st) ||
 697                             ce_match_stat(old, &st, 1))
 698                                 old->ce_flags |= htons(CE_UPDATE);
 699                 }
 700                 return keep_entry(old);
 701         }
 702         return merged_entry(a, NULL);
 703 }
 704
 705 static int read_cache_unmerged(void)
 706 {
 707         int i, deleted;
 708         struct cache_entry **dst;
 709
 710         read_cache();
 711         dst = active_cache;
 712         deleted = 0;
 713         for (i = 0; i < active_nr; i++) {
 714                 struct cache_entry *ce = active_cache[i];
 715                 if (ce_stage(ce)) {
 716                         deleted++;
 717                         continue;
 718                 }
 719                 if (deleted)
 720                         *dst = ce;
 721                 dst++;
 722         }
 723         active_nr -= deleted;
 724         return deleted;
 725 }
 726
 727 static const char read_tree_usage[] = "git-read-tree (<sha> | -m [--aggressive] [-u | -i] <sha1> [<sha2> [<sha3>]])";
 728
 729 static struct cache_file cache_file;
 730
 731 int main(int argc, char **argv)
 732 {
 733         int i, newfd, stage = 0;
 734         unsigned char sha1[20];
 735         merge_fn_t fn = NULL;
 736
 737         setup_git_directory();
 738         git_config(git_default_config);
 739
 740         newfd = hold_index_file_for_update(&cache_file, get_index_file());
 741         if (newfd < 0)
 742                 die("unable to create new cachefile");
 743
 744         git_config(git_default_config);
 745
 746         merge = 0;
 747         reset = 0;
 748         for (i = 1; i < argc; i++) {
 749                 const char *arg = argv[i];
 750
 751                 /* "-u" means "update", meaning that a merge will update
 752                  * the working tree.
 753                  */
 754                 if (!strcmp(arg, "-u")) {
 755                         update = 1;
 756                         continue;
 757                 }
 758
 759                 if (!strcmp(arg, "-v")) {
 760                         verbose_update = 1;
 761                         continue;
 762                 }
 763
 764                 /* "-i" means "index only", meaning that a merge will
 765                  * not even look at the working tree.
 766                  */
 767                 if (!strcmp(arg, "-i")) {
 768                         index_only = 1;
 769                         continue;
 770                 }
 771
 772                 /* This differs from "-m" in that we'll silently ignore unmerged entries */
 773                 if (!strcmp(arg, "--reset")) {
 774                         if (stage || merge)
 775                                 usage(read_tree_usage);
 776                         reset = 1;
 777                         merge = 1;
 778                         stage = 1;
 779                         read_cache_unmerged();
 780                         continue;
 781                 }
 782
 783                 if (!strcmp(arg, "--trivial")) {
 784                         trivial_merges_only = 1;
 785                         continue;
 786                 }
 787
 788                 if (!strcmp(arg, "--aggressive")) {
 789                         aggressive = 1;
 790                         continue;
 791                 }
 792
 793                 /* "-m" stands for "merge", meaning we start in stage 1 */
 794                 if (!strcmp(arg, "-m")) {
 795                         if (stage || merge)
 796                                 usage(read_tree_usage);
 797                         if (read_cache_unmerged())
 798                                 die("you need to resolve your current index first");
 799                         stage = 1;
 800                         merge = 1;
 801                         continue;
 802                 }
 803
 804                 /* using -u and -i at the same time makes no sense */
 805                 if (1 < index_only + update)
 806                         usage(read_tree_usage);
 807
 808                 if (get_sha1(arg, sha1))
 809                         die("Not a valid object name %s", arg);
 810                 if (list_tree(sha1) < 0)
 811                         die("failed to unpack tree object %s", arg);
 812                 stage++;
 813         }
 814         if ((update||index_only) && !merge)
 815                 usage(read_tree_usage);
 816
 817         if (merge) {
 818                 if (stage < 2)
 819                         die("just how do you expect me to merge %d trees?", stage-1);
 820                 switch (stage - 1) {
 821                 case 1:
 822                         fn = oneway_merge;
 823                         break;
 824                 case 2:
 825                         fn = twoway_merge;
 826                         break;
 827                 case 3:
 828                         fn = threeway_merge;
 829                         break;
 830                 default:
 831                         fn = threeway_merge;
 832                         break;
 833                 }
 834
 835                 if (stage - 1 >= 3)
 836                         head_idx = stage - 2;
 837                 else
 838                         head_idx = 1;
 839         }
 840
 841         unpack_trees(fn);
 842         if (write_cache(newfd, active_cache, active_nr) ||
 843             commit_index_file(&cache_file))
 844                 die("unable to write new index file");
 845         return 0;
 846 }