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