unpack-trees.c

   1 #include "cache.h"
   2 #include "dir.h"
   3 #include "tree.h"
   4 #include "tree-walk.h"
   5 #include "cache-tree.h"
   6 #include "unpack-trees.h"
   7 #include "progress.h"
   8
   9 #define DBRT_DEBUG 1
  10
  11 struct tree_entry_list {
  12         struct tree_entry_list *next;
  13         unsigned directory : 1;
  14         unsigned executable : 1;
  15         unsigned symlink : 1;
  16         unsigned int mode;
  17         const char *name;
  18         const unsigned char *sha1;
  19 };
  20
  21 static struct tree_entry_list *create_tree_entry_list(struct tree *tree)
  22 {
  23         struct tree_desc desc;
  24         struct name_entry one;
  25         struct tree_entry_list *ret = NULL;
  26         struct tree_entry_list **list_p = &ret;
  27
  28         if (!tree->object.parsed)
  29                 parse_tree(tree);
  30
  31         init_tree_desc(&desc, tree->buffer, tree->size);
  32
  33         while (tree_entry(&desc, &one)) {
  34                 struct tree_entry_list *entry;
  35
  36                 entry = xmalloc(sizeof(struct tree_entry_list));
  37                 entry->name = one.path;
  38                 entry->sha1 = one.sha1;
  39                 entry->mode = one.mode;
  40                 entry->directory = S_ISDIR(one.mode) != 0;
  41                 entry->executable = (one.mode & S_IXUSR) != 0;
  42                 entry->symlink = S_ISLNK(one.mode) != 0;
  43                 entry->next = NULL;
  44
  45                 *list_p = entry;
  46                 list_p = &entry->next;
  47         }
  48         return ret;
  49 }
  50
  51 static int entcmp(const char *name1, int dir1, const char *name2, int dir2)
  52 {
  53         int len1 = strlen(name1);
  54         int len2 = strlen(name2);
  55         int len = len1 < len2 ? len1 : len2;
  56         int ret = memcmp(name1, name2, len);
  57         unsigned char c1, c2;
  58         if (ret)
  59                 return ret;
  60         c1 = name1[len];
  61         c2 = name2[len];
  62         if (!c1 && dir1)
  63                 c1 = '/';
  64         if (!c2 && dir2)
  65                 c2 = '/';
  66         ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
  67         if (c1 && c2 && !ret)
  68                 ret = len1 - len2;
  69         return ret;
  70 }
  71
  72 static int unpack_trees_rec(struct tree_entry_list **posns, int len,
  73                             const char *base, struct unpack_trees_options *o,
  74                             struct tree_entry_list *df_conflict_list)
  75 {
  76         int baselen = strlen(base);
  77         int src_size = len + 1;
  78         int i_stk = i_stk;
  79         int retval = 0;
  80
  81         if (o->dir)
  82                 i_stk = push_exclude_per_directory(o->dir, base, strlen(base));
  83
  84         do {
  85                 int i;
  86                 const char *first;
  87                 int firstdir = 0;
  88                 int pathlen;
  89                 unsigned ce_size;
  90                 struct tree_entry_list **subposns;
  91                 struct cache_entry **src;
  92                 int any_files = 0;
  93                 int any_dirs = 0;
  94                 char *cache_name;
  95                 int ce_stage;
  96
  97                 /* Find the first name in the input. */
  98
  99                 first = NULL;
 100                 cache_name = NULL;
 101
 102                 /* Check the cache */
 103                 if (o->merge && o->pos < active_nr) {
 104                         /* This is a bit tricky: */
 105                         /* If the index has a subdirectory (with
 106                          * contents) as the first name, it'll get a
 107                          * filename like "foo/bar". But that's after
 108                          * "foo", so the entry in trees will get
 109                          * handled first, at which point we'll go into
 110                          * "foo", and deal with "bar" from the index,
 111                          * because the base will be "foo/". The only
 112                          * way we can actually have "foo/bar" first of
 113                          * all the things is if the trees don't
 114                          * contain "foo" at all, in which case we'll
 115                          * handle "foo/bar" without going into the
 116                          * directory, but that's fine (and will return
 117                          * an error anyway, with the added unknown
 118                          * file case.
 119                          */
 120
 121                         cache_name = active_cache[o->pos]->name;
 122                         if (strlen(cache_name) > baselen &&
 123                             !memcmp(cache_name, base, baselen)) {
 124                                 cache_name += baselen;
 125                                 first = cache_name;
 126                         } else {
 127                                 cache_name = NULL;
 128                         }
 129                 }
 130
 131 #if DBRT_DEBUG > 1
 132                 if (first)
 133                         printf("index %s\n", first);
 134 #endif
 135                 for (i = 0; i < len; i++) {
 136                         if (!posns[i] || posns[i] == df_conflict_list)
 137                                 continue;
 138 #if DBRT_DEBUG > 1
 139                         printf("%d %s\n", i + 1, posns[i]->name);
 140 #endif
 141                         if (!first || entcmp(first, firstdir,
 142                                              posns[i]->name,
 143                                              posns[i]->directory) > 0) {
 144                                 first = posns[i]->name;
 145                                 firstdir = posns[i]->directory;
 146                         }
 147                 }
 148                 /* No name means we're done */
 149                 if (!first)
 150                         goto leave_directory;
 151
 152                 pathlen = strlen(first);
 153                 ce_size = cache_entry_size(baselen + pathlen);
 154
 155                 src = xcalloc(src_size, sizeof(struct cache_entry *));
 156
 157                 subposns = xcalloc(len, sizeof(struct tree_list_entry *));
 158
 159                 if (cache_name && !strcmp(cache_name, first)) {
 160                         any_files = 1;
 161                         src[0] = active_cache[o->pos];
 162                         remove_cache_entry_at(o->pos);
 163                 }
 164
 165                 for (i = 0; i < len; i++) {
 166                         struct cache_entry *ce;
 167
 168                         if (!posns[i] ||
 169                             (posns[i] != df_conflict_list &&
 170                              strcmp(first, posns[i]->name))) {
 171                                 continue;
 172                         }
 173
 174                         if (posns[i] == df_conflict_list) {
 175                                 src[i + o->merge] = o->df_conflict_entry;
 176                                 continue;
 177                         }
 178
 179                         if (posns[i]->directory) {
 180                                 struct tree *tree = lookup_tree(posns[i]->sha1);
 181                                 any_dirs = 1;
 182                                 parse_tree(tree);
 183                                 subposns[i] = create_tree_entry_list(tree);
 184                                 posns[i] = posns[i]->next;
 185                                 src[i + o->merge] = o->df_conflict_entry;
 186                                 continue;
 187                         }
 188
 189                         if (!o->merge)
 190                                 ce_stage = 0;
 191                         else if (i + 1 < o->head_idx)
 192                                 ce_stage = 1;
 193                         else if (i + 1 > o->head_idx)
 194                                 ce_stage = 3;
 195                         else
 196                                 ce_stage = 2;
 197
 198                         ce = xcalloc(1, ce_size);
 199                         ce->ce_mode = create_ce_mode(posns[i]->mode);
 200                         ce->ce_flags = create_ce_flags(baselen + pathlen,
 201                                                        ce_stage);
 202                         memcpy(ce->name, base, baselen);
 203                         memcpy(ce->name + baselen, first, pathlen + 1);
 204
 205                         any_files = 1;
 206
 207                         hashcpy(ce->sha1, posns[i]->sha1);
 208                         src[i + o->merge] = ce;
 209                         subposns[i] = df_conflict_list;
 210                         posns[i] = posns[i]->next;
 211                 }
 212                 if (any_files) {
 213                         if (o->merge) {
 214                                 int ret;
 215
 216 #if DBRT_DEBUG > 1
 217                                 printf("%s:\n", first);
 218                                 for (i = 0; i < src_size; i++) {
 219                                         printf(" %d ", i);
 220                                         if (src[i])
 221                                                 printf("%s\n", sha1_to_hex(src[i]->sha1));
 222                                         else
 223                                                 printf("\n");
 224                                 }
 225 #endif
 226                                 ret = o->fn(src, o);
 227
 228 #if DBRT_DEBUG > 1
 229                                 printf("Added %d entries\n", ret);
 230 #endif
 231                                 o->pos += ret;
 232                         } else {
 233                                 for (i = 0; i < src_size; i++) {
 234                                         if (src[i]) {
 235                                                 add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
 236                                         }
 237                                 }
 238                         }
 239                 }
 240                 if (any_dirs) {
 241                         char *newbase = xmalloc(baselen + 2 + pathlen);
 242                         memcpy(newbase, base, baselen);
 243                         memcpy(newbase + baselen, first, pathlen);
 244                         newbase[baselen + pathlen] = '/';
 245                         newbase[baselen + pathlen + 1] = '\0';
 246                         if (unpack_trees_rec(subposns, len, newbase, o,
 247                                              df_conflict_list)) {
 248                                 retval = -1;
 249                                 goto leave_directory;
 250                         }
 251                         free(newbase);
 252                 }
 253                 free(subposns);
 254                 free(src);
 255         } while (1);
 256
 257  leave_directory:
 258         if (o->dir)
 259                 pop_exclude_per_directory(o->dir, i_stk);
 260         return retval;
 261 }
 262
 263 /* Unlink the last component and attempt to remove leading
 264  * directories, in case this unlink is the removal of the
 265  * last entry in the directory -- empty directories are removed.
 266  */
 267 static void unlink_entry(char *name, char *last_symlink)
 268 {
 269         char *cp, *prev;
 270
 271         if (has_symlink_leading_path(name, last_symlink))
 272                 return;
 273         if (unlink(name))
 274                 return;
 275         prev = NULL;
 276         while (1) {
 277                 int status;
 278                 cp = strrchr(name, '/');
 279                 if (prev)
 280                         *prev = '/';
 281                 if (!cp)
 282                         break;
 283
 284                 *cp = 0;
 285                 status = rmdir(name);
 286                 if (status) {
 287                         *cp = '/';
 288                         break;
 289                 }
 290                 prev = cp;
 291         }
 292 }
 293
 294 static struct checkout state;
 295 static void check_updates(struct cache_entry **src, int nr,
 296                         struct unpack_trees_options *o)
 297 {
 298         unsigned short mask = htons(CE_UPDATE);
 299         unsigned cnt = 0, total = 0;
 300         struct progress progress;
 301         char last_symlink[PATH_MAX];
 302
 303         if (o->update && o->verbose_update) {
 304                 for (total = cnt = 0; cnt < nr; cnt++) {
 305                         struct cache_entry *ce = src[cnt];
 306                         if (!ce->ce_mode || ce->ce_flags & mask)
 307                                 total++;
 308                 }
 309
 310                 start_progress_delay(&progress, "Checking %u files out...",
 311                                      "", total, 50, 2);
 312                 cnt = 0;
 313         }
 314
 315         *last_symlink = '\0';
 316         while (nr--) {
 317                 struct cache_entry *ce = *src++;
 318
 319                 if (total)
 320                         if (!ce->ce_mode || ce->ce_flags & mask)
 321                                 display_progress(&progress, ++cnt);
 322                 if (!ce->ce_mode) {
 323                         if (o->update)
 324                                 unlink_entry(ce->name, last_symlink);
 325                         continue;
 326                 }
 327                 if (ce->ce_flags & mask) {
 328                         ce->ce_flags &= ~mask;
 329                         if (o->update) {
 330                                 checkout_entry(ce, &state, NULL);
 331                                 *last_symlink = '\0';
 332                         }
 333                 }
 334         }
 335         if (total)
 336                 stop_progress(&progress);;
 337 }
 338
 339 int unpack_trees(struct object_list *trees, struct unpack_trees_options *o)
 340 {
 341         unsigned len = object_list_length(trees);
 342         struct tree_entry_list **posns;
 343         int i;
 344         struct object_list *posn = trees;
 345         struct tree_entry_list df_conflict_list;
 346         static struct cache_entry *dfc;
 347
 348         memset(&df_conflict_list, 0, sizeof(df_conflict_list));
 349         df_conflict_list.next = &df_conflict_list;
 350         memset(&state, 0, sizeof(state));
 351         state.base_dir = "";
 352         state.force = 1;
 353         state.quiet = 1;
 354         state.refresh_cache = 1;
 355
 356         o->merge_size = len;
 357
 358         if (!dfc)
 359                 dfc = xcalloc(1, sizeof(struct cache_entry) + 1);
 360         o->df_conflict_entry = dfc;
 361
 362         if (len) {
 363                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
 364                 for (i = 0; i < len; i++) {
 365                         posns[i] = create_tree_entry_list((struct tree *) posn->item);
 366                         posn = posn->next;
 367                 }
 368                 if (unpack_trees_rec(posns, len, o->prefix ? o->prefix : "",
 369                                      o, &df_conflict_list))
 370                         return -1;
 371         }
 372
 373         if (o->trivial_merges_only && o->nontrivial_merge)
 374                 die("Merge requires file-level merging");
 375
 376         check_updates(active_cache, active_nr, o);
 377         return 0;
 378 }
 379
 380 /* Here come the merge functions */
 381
 382 static void reject_merge(struct cache_entry *ce)
 383 {
 384         die("Entry '%s' would be overwritten by merge. Cannot merge.",
 385             ce->name);
 386 }
 387
 388 static int same(struct cache_entry *a, struct cache_entry *b)
 389 {
 390         if (!!a != !!b)
 391                 return 0;
 392         if (!a && !b)
 393                 return 1;
 394         return a->ce_mode == b->ce_mode &&
 395                !hashcmp(a->sha1, b->sha1);
 396 }
 397
 398
 399 /*
 400  * When a CE gets turned into an unmerged entry, we
 401  * want it to be up-to-date
 402  */
 403 static void verify_uptodate(struct cache_entry *ce,
 404                 struct unpack_trees_options *o)
 405 {
 406         struct stat st;
 407
 408         if (o->index_only || o->reset)
 409                 return;
 410
 411         if (!lstat(ce->name, &st)) {
 412                 unsigned changed = ce_match_stat(ce, &st, 1);
 413                 if (!changed)
 414                         return;
 415                 errno = 0;
 416         }
 417         if (errno == ENOENT)
 418                 return;
 419         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 420 }
 421
 422 static void invalidate_ce_path(struct cache_entry *ce)
 423 {
 424         if (ce)
 425                 cache_tree_invalidate_path(active_cache_tree, ce->name);
 426 }
 427
 428 static int verify_clean_subdirectory(const char *path, const char *action,
 429                                       struct unpack_trees_options *o)
 430 {
 431         /*
 432          * we are about to extract "path"; we would not want to lose
 433          * anything in the existing directory there.
 434          */
 435         int namelen;
 436         int pos, i;
 437         struct dir_struct d;
 438         char *pathbuf;
 439         int cnt = 0;
 440
 441         /*
 442          * First let's make sure we do not have a local modification
 443          * in that directory.
 444          */
 445         namelen = strlen(path);
 446         pos = cache_name_pos(path, namelen);
 447         if (0 <= pos)
 448                 return cnt; /* we have it as nondirectory */
 449         pos = -pos - 1;
 450         for (i = pos; i < active_nr; i++) {
 451                 struct cache_entry *ce = active_cache[i];
 452                 int len = ce_namelen(ce);
 453                 if (len < namelen ||
 454                     strncmp(path, ce->name, namelen) ||
 455                     ce->name[namelen] != '/')
 456                         break;
 457                 /*
 458                  * ce->name is an entry in the subdirectory.
 459                  */
 460                 if (!ce_stage(ce)) {
 461                         verify_uptodate(ce, o);
 462                         ce->ce_mode = 0;
 463                 }
 464                 cnt++;
 465         }
 466
 467         /*
 468          * Then we need to make sure that we do not lose a locally
 469          * present file that is not ignored.
 470          */
 471         pathbuf = xmalloc(namelen + 2);
 472         memcpy(pathbuf, path, namelen);
 473         strcpy(pathbuf+namelen, "/");
 474
 475         memset(&d, 0, sizeof(d));
 476         if (o->dir)
 477                 d.exclude_per_dir = o->dir->exclude_per_dir;
 478         i = read_directory(&d, path, pathbuf, namelen+1, NULL);
 479         if (i)
 480                 die("Updating '%s' would lose untracked files in it",
 481                     path);
 482         free(pathbuf);
 483         return cnt;
 484 }
 485
 486 /*
 487  * We do not want to remove or overwrite a working tree file that
 488  * is not tracked, unless it is ignored.
 489  */
 490 static void verify_absent(const char *path, const char *action,
 491                 struct unpack_trees_options *o)
 492 {
 493         struct stat st;
 494
 495         if (o->index_only || o->reset || !o->update)
 496                 return;
 497
 498         if (!lstat(path, &st)) {
 499                 int cnt;
 500
 501                 if (o->dir && excluded(o->dir, path))
 502                         /*
 503                          * path is explicitly excluded, so it is Ok to
 504                          * overwrite it.
 505                          */
 506                         return;
 507                 if (S_ISDIR(st.st_mode)) {
 508                         /*
 509                          * We are checking out path "foo" and
 510                          * found "foo/." in the working tree.
 511                          * This is tricky -- if we have modified
 512                          * files that are in "foo/" we would lose
 513                          * it.
 514                          */
 515                         cnt = verify_clean_subdirectory(path, action, o);
 516
 517                         /*
 518                          * If this removed entries from the index,
 519                          * what that means is:
 520                          *
 521                          * (1) the caller unpack_trees_rec() saw path/foo
 522                          * in the index, and it has not removed it because
 523                          * it thinks it is handling 'path' as blob with
 524                          * D/F conflict;
 525                          * (2) we will return "ok, we placed a merged entry
 526                          * in the index" which would cause o->pos to be
 527                          * incremented by one;
 528                          * (3) however, original o->pos now has 'path/foo'
 529                          * marked with "to be removed".
 530                          *
 531                          * We need to increment it by the number of
 532                          * deleted entries here.
 533                          */
 534                         o->pos += cnt;
 535                         return;
 536                 }
 537
 538                 /*
 539                  * The previous round may already have decided to
 540                  * delete this path, which is in a subdirectory that
 541                  * is being replaced with a blob.
 542                  */
 543                 cnt = cache_name_pos(path, strlen(path));
 544                 if (0 <= cnt) {
 545                         struct cache_entry *ce = active_cache[cnt];
 546                         if (!ce_stage(ce) && !ce->ce_mode)
 547                                 return;
 548                 }
 549
 550                 die("Untracked working tree file '%s' "
 551                     "would be %s by merge.", path, action);
 552         }
 553 }
 554
 555 static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
 556                 struct unpack_trees_options *o)
 557 {
 558         merge->ce_flags |= htons(CE_UPDATE);
 559         if (old) {
 560                 /*
 561                  * See if we can re-use the old CE directly?
 562                  * That way we get the uptodate stat info.
 563                  *
 564                  * This also removes the UPDATE flag on
 565                  * a match.
 566                  */
 567                 if (same(old, merge)) {
 568                         *merge = *old;
 569                 } else {
 570                         verify_uptodate(old, o);
 571                         invalidate_ce_path(old);
 572                 }
 573         }
 574         else {
 575                 verify_absent(merge->name, "overwritten", o);
 576                 invalidate_ce_path(merge);
 577         }
 578
 579         merge->ce_flags &= ~htons(CE_STAGEMASK);
 580         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
 581         return 1;
 582 }
 583
 584 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old,
 585                 struct unpack_trees_options *o)
 586 {
 587         if (old)
 588                 verify_uptodate(old, o);
 589         else
 590                 verify_absent(ce->name, "removed", o);
 591         ce->ce_mode = 0;
 592         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
 593         invalidate_ce_path(ce);
 594         return 1;
 595 }
 596
 597 static int keep_entry(struct cache_entry *ce, struct unpack_trees_options *o)
 598 {
 599         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 600         return 1;
 601 }
 602
 603 #if DBRT_DEBUG
 604 static void show_stage_entry(FILE *o,
 605                              const char *label, const struct cache_entry *ce)
 606 {
 607         if (!ce)
 608                 fprintf(o, "%s (missing)\n", label);
 609         else
 610                 fprintf(o, "%s%06o %s %d\t%s\n",
 611                         label,
 612                         ntohl(ce->ce_mode),
 613                         sha1_to_hex(ce->sha1),
 614                         ce_stage(ce),
 615                         ce->name);
 616 }
 617 #endif
 618
 619 int threeway_merge(struct cache_entry **stages,
 620                 struct unpack_trees_options *o)
 621 {
 622         struct cache_entry *index;
 623         struct cache_entry *head;
 624         struct cache_entry *remote = stages[o->head_idx + 1];
 625         int count;
 626         int head_match = 0;
 627         int remote_match = 0;
 628
 629         int df_conflict_head = 0;
 630         int df_conflict_remote = 0;
 631
 632         int any_anc_missing = 0;
 633         int no_anc_exists = 1;
 634         int i;
 635
 636         for (i = 1; i < o->head_idx; i++) {
 637                 if (!stages[i] || stages[i] == o->df_conflict_entry)
 638                         any_anc_missing = 1;
 639                 else
 640                         no_anc_exists = 0;
 641         }
 642
 643         index = stages[0];
 644         head = stages[o->head_idx];
 645
 646         if (head == o->df_conflict_entry) {
 647                 df_conflict_head = 1;
 648                 head = NULL;
 649         }
 650
 651         if (remote == o->df_conflict_entry) {
 652                 df_conflict_remote = 1;
 653                 remote = NULL;
 654         }
 655
 656         /* First, if there's a #16 situation, note that to prevent #13
 657          * and #14.
 658          */
 659         if (!same(remote, head)) {
 660                 for (i = 1; i < o->head_idx; i++) {
 661                         if (same(stages[i], head)) {
 662                                 head_match = i;
 663                         }
 664                         if (same(stages[i], remote)) {
 665                                 remote_match = i;
 666                         }
 667                 }
 668         }
 669
 670         /* We start with cases where the index is allowed to match
 671          * something other than the head: #14(ALT) and #2ALT, where it
 672          * is permitted to match the result instead.
 673          */
 674         /* #14, #14ALT, #2ALT */
 675         if (remote && !df_conflict_head && head_match && !remote_match) {
 676                 if (index && !same(index, remote) && !same(index, head))
 677                         reject_merge(index);
 678                 return merged_entry(remote, index, o);
 679         }
 680         /*
 681          * If we have an entry in the index cache, then we want to
 682          * make sure that it matches head.
 683          */
 684         if (index && !same(index, head)) {
 685                 reject_merge(index);
 686         }
 687
 688         if (head) {
 689                 /* #5ALT, #15 */
 690                 if (same(head, remote))
 691                         return merged_entry(head, index, o);
 692                 /* #13, #3ALT */
 693                 if (!df_conflict_remote && remote_match && !head_match)
 694                         return merged_entry(head, index, o);
 695         }
 696
 697         /* #1 */
 698         if (!head && !remote && any_anc_missing)
 699                 return 0;
 700
 701         /* Under the new "aggressive" rule, we resolve mostly trivial
 702          * cases that we historically had git-merge-one-file resolve.
 703          */
 704         if (o->aggressive) {
 705                 int head_deleted = !head && !df_conflict_head;
 706                 int remote_deleted = !remote && !df_conflict_remote;
 707                 const char *path = NULL;
 708
 709                 if (index)
 710                         path = index->name;
 711                 else if (head)
 712                         path = head->name;
 713                 else if (remote)
 714                         path = remote->name;
 715                 else {
 716                         for (i = 1; i < o->head_idx; i++) {
 717                                 if (stages[i] && stages[i] != o->df_conflict_entry) {
 718                                         path = stages[i]->name;
 719                                         break;
 720                                 }
 721                         }
 722                 }
 723
 724                 /*
 725                  * Deleted in both.
 726                  * Deleted in one and unchanged in the other.
 727                  */
 728                 if ((head_deleted && remote_deleted) ||
 729                     (head_deleted && remote && remote_match) ||
 730                     (remote_deleted && head && head_match)) {
 731                         if (index)
 732                                 return deleted_entry(index, index, o);
 733                         else if (path && !head_deleted)
 734                                 verify_absent(path, "removed", o);
 735                         return 0;
 736                 }
 737                 /*
 738                  * Added in both, identically.
 739                  */
 740                 if (no_anc_exists && head && remote && same(head, remote))
 741                         return merged_entry(head, index, o);
 742
 743         }
 744
 745         /* Below are "no merge" cases, which require that the index be
 746          * up-to-date to avoid the files getting overwritten with
 747          * conflict resolution files.
 748          */
 749         if (index) {
 750                 verify_uptodate(index, o);
 751         }
 752
 753         o->nontrivial_merge = 1;
 754
 755         /* #2, #3, #4, #6, #7, #9, #10, #11. */
 756         count = 0;
 757         if (!head_match || !remote_match) {
 758                 for (i = 1; i < o->head_idx; i++) {
 759                         if (stages[i] && stages[i] != o->df_conflict_entry) {
 760                                 keep_entry(stages[i], o);
 761                                 count++;
 762                                 break;
 763                         }
 764                 }
 765         }
 766 #if DBRT_DEBUG
 767         else {
 768                 fprintf(stderr, "read-tree: warning #16 detected\n");
 769                 show_stage_entry(stderr, "head   ", stages[head_match]);
 770                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 771         }
 772 #endif
 773         if (head) { count += keep_entry(head, o); }
 774         if (remote) { count += keep_entry(remote, o); }
 775         return count;
 776 }
 777
 778 /*
 779  * Two-way merge.
 780  *
 781  * The rule is to "carry forward" what is in the index without losing
 782  * information across a "fast forward", favoring a successful merge
 783  * over a merge failure when it makes sense.  For details of the
 784  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 785  *
 786  */
 787 int twoway_merge(struct cache_entry **src,
 788                 struct unpack_trees_options *o)
 789 {
 790         struct cache_entry *current = src[0];
 791         struct cache_entry *oldtree = src[1];
 792         struct cache_entry *newtree = src[2];
 793
 794         if (o->merge_size != 2)
 795                 return error("Cannot do a twoway merge of %d trees",
 796                              o->merge_size);
 797
 798         if (oldtree == o->df_conflict_entry)
 799                 oldtree = NULL;
 800         if (newtree == o->df_conflict_entry)
 801                 newtree = NULL;
 802
 803         if (current) {
 804                 if ((!oldtree && !newtree) || /* 4 and 5 */
 805                     (!oldtree && newtree &&
 806                      same(current, newtree)) || /* 6 and 7 */
 807                     (oldtree && newtree &&
 808                      same(oldtree, newtree)) || /* 14 and 15 */
 809                     (oldtree && newtree &&
 810                      !same(oldtree, newtree) && /* 18 and 19 */
 811                      same(current, newtree))) {
 812                         return keep_entry(current, o);
 813                 }
 814                 else if (oldtree && !newtree && same(current, oldtree)) {
 815                         /* 10 or 11 */
 816                         return deleted_entry(oldtree, current, o);
 817                 }
 818                 else if (oldtree && newtree &&
 819                          same(current, oldtree) && !same(current, newtree)) {
 820                         /* 20 or 21 */
 821                         return merged_entry(newtree, current, o);
 822                 }
 823                 else {
 824                         /* all other failures */
 825                         if (oldtree)
 826                                 reject_merge(oldtree);
 827                         if (current)
 828                                 reject_merge(current);
 829                         if (newtree)
 830                                 reject_merge(newtree);
 831                         return -1;
 832                 }
 833         }
 834         else if (newtree)
 835                 return merged_entry(newtree, current, o);
 836         else
 837                 return deleted_entry(oldtree, current, o);
 838 }
 839
 840 /*
 841  * Bind merge.
 842  *
 843  * Keep the index entries at stage0, collapse stage1 but make sure
 844  * stage0 does not have anything there.
 845  */
 846 int bind_merge(struct cache_entry **src,
 847                 struct unpack_trees_options *o)
 848 {
 849         struct cache_entry *old = src[0];
 850         struct cache_entry *a = src[1];
 851
 852         if (o->merge_size != 1)
 853                 return error("Cannot do a bind merge of %d trees\n",
 854                              o->merge_size);
 855         if (a && old)
 856                 die("Entry '%s' overlaps.  Cannot bind.", a->name);
 857         if (!a)
 858                 return keep_entry(old, o);
 859         else
 860                 return merged_entry(a, NULL, o);
 861 }
 862
 863 /*
 864  * One-way merge.
 865  *
 866  * The rule is:
 867  * - take the stat information from stage0, take the data from stage1
 868  */
 869 int oneway_merge(struct cache_entry **src,
 870                 struct unpack_trees_options *o)
 871 {
 872         struct cache_entry *old = src[0];
 873         struct cache_entry *a = src[1];
 874
 875         if (o->merge_size != 1)
 876                 return error("Cannot do a oneway merge of %d trees",
 877                              o->merge_size);
 878
 879         if (!a)
 880                 return deleted_entry(old, old, o);
 881         if (old && same(old, a)) {
 882                 if (o->reset) {
 883                         struct stat st;
 884                         if (lstat(old->name, &st) ||
 885                             ce_match_stat(old, &st, 1))
 886                                 old->ce_flags |= htons(CE_UPDATE);
 887                 }
 888                 return keep_entry(old, o);
 889         }
 890         return merged_entry(a, old, o);
 891 }