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 "cache-tree.h"
  13 #include <sys/time.h>
  14 #include <signal.h>
  15
  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 (errno == ENOENT)
 421                 return;
 422         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 423 }
 424
 425 static void invalidate_ce_path(struct cache_entry *ce)
 426 {
 427         if (ce)
 428                 cache_tree_invalidate_path(active_cache_tree, ce->name);
 429 }
 430
 431 static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
 432 {
 433         merge->ce_flags |= htons(CE_UPDATE);
 434         if (old) {
 435                 /*
 436                  * See if we can re-use the old CE directly?
 437                  * That way we get the uptodate stat info.
 438                  *
 439                  * This also removes the UPDATE flag on
 440                  * a match.
 441                  */
 442                 if (same(old, merge)) {
 443                         *merge = *old;
 444                 } else {
 445                         verify_uptodate(old);
 446                         invalidate_ce_path(old);
 447                 }
 448         }
 449         else
 450                 invalidate_ce_path(merge);
 451         merge->ce_flags &= ~htons(CE_STAGEMASK);
 452         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
 453         return 1;
 454 }
 455
 456 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
 457 {
 458         if (old)
 459                 verify_uptodate(old);
 460         ce->ce_mode = 0;
 461         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 462         invalidate_ce_path(ce);
 463         return 1;
 464 }
 465
 466 static int keep_entry(struct cache_entry *ce)
 467 {
 468         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 469         return 1;
 470 }
 471
 472 #if DBRT_DEBUG
 473 static void show_stage_entry(FILE *o,
 474                              const char *label, const struct cache_entry *ce)
 475 {
 476         if (!ce)
 477                 fprintf(o, "%s (missing)\n", label);
 478         else
 479                 fprintf(o, "%s%06o %s %d\t%s\n",
 480                         label,
 481                         ntohl(ce->ce_mode),
 482                         sha1_to_hex(ce->sha1),
 483                         ce_stage(ce),
 484                         ce->name);
 485 }
 486 #endif
 487
 488 static int threeway_merge(struct cache_entry **stages)
 489 {
 490         struct cache_entry *index;
 491         struct cache_entry *head;
 492         struct cache_entry *remote = stages[head_idx + 1];
 493         int count;
 494         int head_match = 0;
 495         int remote_match = 0;
 496
 497         int df_conflict_head = 0;
 498         int df_conflict_remote = 0;
 499
 500         int any_anc_missing = 0;
 501         int no_anc_exists = 1;
 502         int i;
 503
 504         for (i = 1; i < head_idx; i++) {
 505                 if (!stages[i])
 506                         any_anc_missing = 1;
 507                 else
 508                         no_anc_exists = 0;
 509         }
 510
 511         index = stages[0];
 512         head = stages[head_idx];
 513
 514         if (head == &df_conflict_entry) {
 515                 df_conflict_head = 1;
 516                 head = NULL;
 517         }
 518
 519         if (remote == &df_conflict_entry) {
 520                 df_conflict_remote = 1;
 521                 remote = NULL;
 522         }
 523
 524         /* First, if there's a #16 situation, note that to prevent #13
 525          * and #14.
 526          */
 527         if (!same(remote, head)) {
 528                 for (i = 1; i < head_idx; i++) {
 529                         if (same(stages[i], head)) {
 530                                 head_match = i;
 531                         }
 532                         if (same(stages[i], remote)) {
 533                                 remote_match = i;
 534                         }
 535                 }
 536         }
 537
 538         /* We start with cases where the index is allowed to match
 539          * something other than the head: #14(ALT) and #2ALT, where it
 540          * is permitted to match the result instead.
 541          */
 542         /* #14, #14ALT, #2ALT */
 543         if (remote && !df_conflict_head && head_match && !remote_match) {
 544                 if (index && !same(index, remote) && !same(index, head))
 545                         reject_merge(index);
 546                 return merged_entry(remote, index);
 547         }
 548         /*
 549          * If we have an entry in the index cache, then we want to
 550          * make sure that it matches head.
 551          */
 552         if (index && !same(index, head)) {
 553                 reject_merge(index);
 554         }
 555
 556         if (head) {
 557                 /* #5ALT, #15 */
 558                 if (same(head, remote))
 559                         return merged_entry(head, index);
 560                 /* #13, #3ALT */
 561                 if (!df_conflict_remote && remote_match && !head_match)
 562                         return merged_entry(head, index);
 563         }
 564
 565         /* #1 */
 566         if (!head && !remote && any_anc_missing)
 567                 return 0;
 568
 569         /* Under the new "aggressive" rule, we resolve mostly trivial
 570          * cases that we historically had git-merge-one-file resolve.
 571          */
 572         if (aggressive) {
 573                 int head_deleted = !head && !df_conflict_head;
 574                 int remote_deleted = !remote && !df_conflict_remote;
 575                 /*
 576                  * Deleted in both.
 577                  * Deleted in one and unchanged in the other.
 578                  */
 579                 if ((head_deleted && remote_deleted) ||
 580                     (head_deleted && remote && remote_match) ||
 581                     (remote_deleted && head && head_match)) {
 582                         if (index)
 583                                 return deleted_entry(index, index);
 584                         return 0;
 585                 }
 586                 /*
 587                  * Added in both, identically.
 588                  */
 589                 if (no_anc_exists && head && remote && same(head, remote))
 590                         return merged_entry(head, index);
 591
 592         }
 593
 594         /* Below are "no merge" cases, which require that the index be
 595          * up-to-date to avoid the files getting overwritten with
 596          * conflict resolution files.
 597          */
 598         if (index) {
 599                 verify_uptodate(index);
 600         }
 601
 602         nontrivial_merge = 1;
 603
 604         /* #2, #3, #4, #6, #7, #9, #11. */
 605         count = 0;
 606         if (!head_match || !remote_match) {
 607                 for (i = 1; i < head_idx; i++) {
 608                         if (stages[i]) {
 609                                 keep_entry(stages[i]);
 610                                 count++;
 611                                 break;
 612                         }
 613                 }
 614         }
 615 #if DBRT_DEBUG
 616         else {
 617                 fprintf(stderr, "read-tree: warning #16 detected\n");
 618                 show_stage_entry(stderr, "head   ", stages[head_match]);
 619                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 620         }
 621 #endif
 622         if (head) { count += keep_entry(head); }
 623         if (remote) { count += keep_entry(remote); }
 624         return count;
 625 }
 626
 627 /*
 628  * Two-way merge.
 629  *
 630  * The rule is to "carry forward" what is in the index without losing
 631  * information across a "fast forward", favoring a successful merge
 632  * over a merge failure when it makes sense.  For details of the
 633  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 634  *
 635  */
 636 static int twoway_merge(struct cache_entry **src)
 637 {
 638         struct cache_entry *current = src[0];
 639         struct cache_entry *oldtree = src[1], *newtree = src[2];
 640
 641         if (merge_size != 2)
 642                 return error("Cannot do a twoway merge of %d trees",
 643                              merge_size);
 644
 645         if (current) {
 646                 if ((!oldtree && !newtree) || /* 4 and 5 */
 647                     (!oldtree && newtree &&
 648                      same(current, newtree)) || /* 6 and 7 */
 649                     (oldtree && newtree &&
 650                      same(oldtree, newtree)) || /* 14 and 15 */
 651                     (oldtree && newtree &&
 652                      !same(oldtree, newtree) && /* 18 and 19*/
 653                      same(current, newtree))) {
 654                         return keep_entry(current);
 655                 }
 656                 else if (oldtree && !newtree && same(current, oldtree)) {
 657                         /* 10 or 11 */
 658                         return deleted_entry(oldtree, current);
 659                 }
 660                 else if (oldtree && newtree &&
 661                          same(current, oldtree) && !same(current, newtree)) {
 662                         /* 20 or 21 */
 663                         return merged_entry(newtree, current);
 664                 }
 665                 else {
 666                         /* all other failures */
 667                         if (oldtree)
 668                                 reject_merge(oldtree);
 669                         if (current)
 670                                 reject_merge(current);
 671                         if (newtree)
 672                                 reject_merge(newtree);
 673                         return -1;
 674                 }
 675         }
 676         else if (newtree)
 677                 return merged_entry(newtree, current);
 678         else
 679                 return deleted_entry(oldtree, current);
 680 }
 681
 682 /*
 683  * One-way merge.
 684  *
 685  * The rule is:
 686  * - take the stat information from stage0, take the data from stage1
 687  */
 688 static int oneway_merge(struct cache_entry **src)
 689 {
 690         struct cache_entry *old = src[0];
 691         struct cache_entry *a = src[1];
 692
 693         if (merge_size != 1)
 694                 return error("Cannot do a oneway merge of %d trees",
 695                              merge_size);
 696
 697         if (!a) {
 698                 invalidate_ce_path(old);
 699                 return 0;
 700         }
 701         if (old && same(old, a)) {
 702                 return keep_entry(old);
 703         }
 704         return merged_entry(a, NULL);
 705 }
 706
 707 static int read_cache_unmerged(void)
 708 {
 709         int i, deleted;
 710         struct cache_entry **dst;
 711
 712         read_cache();
 713         dst = active_cache;
 714         deleted = 0;
 715         for (i = 0; i < active_nr; i++) {
 716                 struct cache_entry *ce = active_cache[i];
 717                 if (ce_stage(ce)) {
 718                         deleted++;
 719                         invalidate_ce_path(ce);
 720                         continue;
 721                 }
 722                 if (deleted)
 723                         *dst = ce;
 724                 dst++;
 725         }
 726         active_nr -= deleted;
 727         return deleted;
 728 }
 729
 730 static void prime_cache_tree_rec(struct cache_tree *it, struct tree *tree)
 731 {
 732         struct tree_entry_list *ent;
 733         int cnt;
 734
 735         memcpy(it->sha1, tree->object.sha1, 20);
 736         for (cnt = 0, ent = tree->entries; ent; ent = ent->next) {
 737                 if (!ent->directory)
 738                         cnt++;
 739                 else {
 740                         struct cache_tree_sub *sub;
 741                         struct tree *subtree = (struct tree *)ent->item.tree;
 742                         if (!subtree->object.parsed)
 743                                 parse_tree(subtree);
 744                         sub = cache_tree_sub(it, ent->name);
 745                         sub->cache_tree = cache_tree();
 746                         prime_cache_tree_rec(sub->cache_tree, subtree);
 747                         cnt += sub->cache_tree->entry_count;
 748                 }
 749         }
 750         it->entry_count = cnt;
 751 }
 752
 753 static void prime_cache_tree(void)
 754 {
 755         struct tree *tree = (struct tree *)trees->item;
 756         if (!tree)
 757                 return;
 758         active_cache_tree = cache_tree();
 759         prime_cache_tree_rec(active_cache_tree, tree);
 760
 761 }
 762
 763 static const char read_tree_usage[] = "git-read-tree (<sha> | -m [--aggressive] [-u | -i] <sha1> [<sha2> [<sha3>]])";
 764
 765 static struct cache_file cache_file;
 766
 767 int main(int argc, char **argv)
 768 {
 769         int i, newfd, reset, stage = 0;
 770         unsigned char sha1[20];
 771         merge_fn_t fn = NULL;
 772
 773         setup_git_directory();
 774         git_config(git_default_config);
 775
 776         newfd = hold_index_file_for_update(&cache_file, get_index_file());
 777         if (newfd < 0)
 778                 die("unable to create new cachefile");
 779
 780         git_config(git_default_config);
 781
 782         merge = 0;
 783         reset = 0;
 784         for (i = 1; i < argc; i++) {
 785                 const char *arg = argv[i];
 786
 787                 /* "-u" means "update", meaning that a merge will update
 788                  * the working tree.
 789                  */
 790                 if (!strcmp(arg, "-u")) {
 791                         update = 1;
 792                         continue;
 793                 }
 794
 795                 if (!strcmp(arg, "-v")) {
 796                         verbose_update = 1;
 797                         continue;
 798                 }
 799
 800                 /* "-i" means "index only", meaning that a merge will
 801                  * not even look at the working tree.
 802                  */
 803                 if (!strcmp(arg, "-i")) {
 804                         index_only = 1;
 805                         continue;
 806                 }
 807
 808                 /* This differs from "-m" in that we'll silently ignore unmerged entries */
 809                 if (!strcmp(arg, "--reset")) {
 810                         if (stage || merge)
 811                                 usage(read_tree_usage);
 812                         reset = 1;
 813                         merge = 1;
 814                         stage = 1;
 815                         read_cache_unmerged();
 816                         continue;
 817                 }
 818
 819                 if (!strcmp(arg, "--trivial")) {
 820                         trivial_merges_only = 1;
 821                         continue;
 822                 }
 823
 824                 if (!strcmp(arg, "--aggressive")) {
 825                         aggressive = 1;
 826                         continue;
 827                 }
 828
 829                 /* "-m" stands for "merge", meaning we start in stage 1 */
 830                 if (!strcmp(arg, "-m")) {
 831                         if (stage || merge)
 832                                 usage(read_tree_usage);
 833                         if (read_cache_unmerged())
 834                                 die("you need to resolve your current index first");
 835                         stage = 1;
 836                         merge = 1;
 837                         continue;
 838                 }
 839
 840                 /* using -u and -i at the same time makes no sense */
 841                 if (1 < index_only + update)
 842                         usage(read_tree_usage);
 843
 844                 if (get_sha1(arg, sha1) < 0)
 845                         usage(read_tree_usage);
 846                 if (list_tree(sha1) < 0)
 847                         die("failed to unpack tree object %s", arg);
 848                 stage++;
 849         }
 850         if ((update||index_only) && !merge)
 851                 usage(read_tree_usage);
 852
 853         if (merge) {
 854                 if (stage < 2)
 855                         die("just how do you expect me to merge %d trees?", stage-1);
 856                 switch (stage - 1) {
 857                 case 1:
 858                         fn = oneway_merge;
 859                         break;
 860                 case 2:
 861                         fn = twoway_merge;
 862                         break;
 863                 case 3:
 864                 default:
 865                         fn = threeway_merge;
 866                         cache_tree_free(&active_cache_tree);
 867                         break;
 868                 }
 869
 870                 if (stage - 1 >= 3)
 871                         head_idx = stage - 2;
 872                 else
 873                         head_idx = 1;
 874         }
 875
 876         unpack_trees(fn);
 877
 878         /*
 879          * When reading only one tree (either the most basic form,
 880          * "-m ent" or "--reset ent" form), we can obtain a fully
 881          * valid cache-tree because the index must match exactly
 882          * what came from the tree.
 883          */
 884         if (trees && trees->item && (!merge || (stage == 2))) {
 885                 cache_tree_free(&active_cache_tree);
 886                 prime_cache_tree();
 887         }
 888
 889         if (write_cache(newfd, active_cache, active_nr) ||
 890             commit_index_file(&cache_file))
 891                 die("unable to write new index file");
 892         return 0;
 893 }