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