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 #include "refs.h"
   9
  10 #define DBRT_DEBUG 1
  11
  12 struct tree_entry_list {
  13         struct tree_entry_list *next;
  14         unsigned int mode;
  15         const char *name;
  16         const unsigned char *sha1;
  17 };
  18
  19 static struct tree_entry_list *create_tree_entry_list(struct tree_desc *desc)
  20 {
  21         struct name_entry one;
  22         struct tree_entry_list *ret = NULL;
  23         struct tree_entry_list **list_p = &ret;
  24
  25         while (tree_entry(desc, &one)) {
  26                 struct tree_entry_list *entry;
  27
  28                 entry = xmalloc(sizeof(struct tree_entry_list));
  29                 entry->name = one.path;
  30                 entry->sha1 = one.sha1;
  31                 entry->mode = one.mode;
  32                 entry->next = NULL;
  33
  34                 *list_p = entry;
  35                 list_p = &entry->next;
  36         }
  37         return ret;
  38 }
  39
  40 static int entcmp(const char *name1, int dir1, const 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 inline void remove_entry(int remove)
  62 {
  63         if (remove >= 0)
  64                 remove_cache_entry_at(remove);
  65 }
  66
  67 static int unpack_trees_rec(struct tree_entry_list **posns, int len,
  68                             const char *base, struct unpack_trees_options *o,
  69                             struct tree_entry_list *df_conflict_list)
  70 {
  71         int remove;
  72         int baselen = strlen(base);
  73         int src_size = len + 1;
  74         int retval = 0;
  75
  76         do {
  77                 int i;
  78                 const char *first;
  79                 int firstdir = 0;
  80                 int pathlen;
  81                 unsigned ce_size;
  82                 struct tree_entry_list **subposns;
  83                 struct cache_entry **src;
  84                 int any_files = 0;
  85                 int any_dirs = 0;
  86                 char *cache_name;
  87                 int ce_stage;
  88
  89                 /* Find the first name in the input. */
  90
  91                 first = NULL;
  92                 cache_name = NULL;
  93
  94                 /* Check the cache */
  95                 if (o->merge && o->pos < active_nr) {
  96                         /* This is a bit tricky: */
  97                         /* If the index has a subdirectory (with
  98                          * contents) as the first name, it'll get a
  99                          * filename like "foo/bar". But that's after
 100                          * "foo", so the entry in trees will get
 101                          * handled first, at which point we'll go into
 102                          * "foo", and deal with "bar" from the index,
 103                          * because the base will be "foo/". The only
 104                          * way we can actually have "foo/bar" first of
 105                          * all the things is if the trees don't
 106                          * contain "foo" at all, in which case we'll
 107                          * handle "foo/bar" without going into the
 108                          * directory, but that's fine (and will return
 109                          * an error anyway, with the added unknown
 110                          * file case.
 111                          */
 112
 113                         cache_name = active_cache[o->pos]->name;
 114                         if (strlen(cache_name) > baselen &&
 115                             !memcmp(cache_name, base, baselen)) {
 116                                 cache_name += baselen;
 117                                 first = cache_name;
 118                         } else {
 119                                 cache_name = NULL;
 120                         }
 121                 }
 122
 123 #if DBRT_DEBUG > 1
 124                 if (first)
 125                         printf("index %s\n", first);
 126 #endif
 127                 for (i = 0; i < len; i++) {
 128                         if (!posns[i] || posns[i] == df_conflict_list)
 129                                 continue;
 130 #if DBRT_DEBUG > 1
 131                         printf("%d %s\n", i + 1, posns[i]->name);
 132 #endif
 133                         if (!first || entcmp(first, firstdir,
 134                                              posns[i]->name,
 135                                              S_ISDIR(posns[i]->mode)) > 0) {
 136                                 first = posns[i]->name;
 137                                 firstdir = S_ISDIR(posns[i]->mode);
 138                         }
 139                 }
 140                 /* No name means we're done */
 141                 if (!first)
 142                         goto leave_directory;
 143
 144                 pathlen = strlen(first);
 145                 ce_size = cache_entry_size(baselen + pathlen);
 146
 147                 src = xcalloc(src_size, sizeof(struct cache_entry *));
 148
 149                 subposns = xcalloc(len, sizeof(struct tree_list_entry *));
 150
 151                 remove = -1;
 152                 if (cache_name && !strcmp(cache_name, first)) {
 153                         any_files = 1;
 154                         src[0] = active_cache[o->pos];
 155                         remove = o->pos;
 156                 }
 157
 158                 for (i = 0; i < len; i++) {
 159                         struct cache_entry *ce;
 160
 161                         if (!posns[i] ||
 162                             (posns[i] != df_conflict_list &&
 163                              strcmp(first, posns[i]->name))) {
 164                                 continue;
 165                         }
 166
 167                         if (posns[i] == df_conflict_list) {
 168                                 src[i + o->merge] = o->df_conflict_entry;
 169                                 continue;
 170                         }
 171
 172                         if (S_ISDIR(posns[i]->mode)) {
 173                                 struct tree *tree = lookup_tree(posns[i]->sha1);
 174                                 struct tree_desc t;
 175                                 any_dirs = 1;
 176                                 parse_tree(tree);
 177                                 init_tree_desc(&t, tree->buffer, tree->size);
 178                                 subposns[i] = create_tree_entry_list(&t);
 179                                 posns[i] = posns[i]->next;
 180                                 src[i + o->merge] = o->df_conflict_entry;
 181                                 continue;
 182                         }
 183
 184                         if (!o->merge)
 185                                 ce_stage = 0;
 186                         else if (i + 1 < o->head_idx)
 187                                 ce_stage = 1;
 188                         else if (i + 1 > o->head_idx)
 189                                 ce_stage = 3;
 190                         else
 191                                 ce_stage = 2;
 192
 193                         ce = xcalloc(1, ce_size);
 194                         ce->ce_mode = create_ce_mode(posns[i]->mode);
 195                         ce->ce_flags = create_ce_flags(baselen + pathlen,
 196                                                        ce_stage);
 197                         memcpy(ce->name, base, baselen);
 198                         memcpy(ce->name + baselen, first, pathlen + 1);
 199
 200                         any_files = 1;
 201
 202                         hashcpy(ce->sha1, posns[i]->sha1);
 203                         src[i + o->merge] = ce;
 204                         subposns[i] = df_conflict_list;
 205                         posns[i] = posns[i]->next;
 206                 }
 207                 if (any_files) {
 208                         if (o->merge) {
 209                                 int ret;
 210
 211 #if DBRT_DEBUG > 1
 212                                 printf("%s:\n", first);
 213                                 for (i = 0; i < src_size; i++) {
 214                                         printf(" %d ", i);
 215                                         if (src[i])
 216                                                 printf("%s\n", sha1_to_hex(src[i]->sha1));
 217                                         else
 218                                                 printf("\n");
 219                                 }
 220 #endif
 221                                 ret = o->fn(src, o, remove);
 222
 223 #if DBRT_DEBUG > 1
 224                                 printf("Added %d entries\n", ret);
 225 #endif
 226                                 o->pos += ret;
 227                         } else {
 228                                 remove_entry(remove);
 229                                 for (i = 0; i < src_size; i++) {
 230                                         if (src[i]) {
 231                                                 add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
 232                                         }
 233                                 }
 234                         }
 235                 }
 236                 if (any_dirs) {
 237                         char *newbase = xmalloc(baselen + 2 + pathlen);
 238                         memcpy(newbase, base, baselen);
 239                         memcpy(newbase + baselen, first, pathlen);
 240                         newbase[baselen + pathlen] = '/';
 241                         newbase[baselen + pathlen + 1] = '\0';
 242                         if (unpack_trees_rec(subposns, len, newbase, o,
 243                                              df_conflict_list)) {
 244                                 retval = -1;
 245                                 goto leave_directory;
 246                         }
 247                         free(newbase);
 248                 }
 249                 free(subposns);
 250                 free(src);
 251         } while (1);
 252
 253  leave_directory:
 254         return retval;
 255 }
 256
 257 /* Unlink the last component and attempt to remove leading
 258  * directories, in case this unlink is the removal of the
 259  * last entry in the directory -- empty directories are removed.
 260  */
 261 static void unlink_entry(char *name, char *last_symlink)
 262 {
 263         char *cp, *prev;
 264
 265         if (has_symlink_leading_path(name, last_symlink))
 266                 return;
 267         if (unlink(name))
 268                 return;
 269         prev = NULL;
 270         while (1) {
 271                 int status;
 272                 cp = strrchr(name, '/');
 273                 if (prev)
 274                         *prev = '/';
 275                 if (!cp)
 276                         break;
 277
 278                 *cp = 0;
 279                 status = rmdir(name);
 280                 if (status) {
 281                         *cp = '/';
 282                         break;
 283                 }
 284                 prev = cp;
 285         }
 286 }
 287
 288 static struct checkout state;
 289 static void check_updates(struct cache_entry **src, int nr,
 290                         struct unpack_trees_options *o)
 291 {
 292         unsigned short mask = htons(CE_UPDATE);
 293         unsigned cnt = 0, total = 0;
 294         struct progress *progress = NULL;
 295         char last_symlink[PATH_MAX];
 296
 297         if (o->update && o->verbose_update) {
 298                 for (total = cnt = 0; cnt < nr; cnt++) {
 299                         struct cache_entry *ce = src[cnt];
 300                         if (!ce->ce_mode || ce->ce_flags & mask)
 301                                 total++;
 302                 }
 303
 304                 progress = start_progress_delay("Checking out files",
 305                                                 total, 50, 2);
 306                 cnt = 0;
 307         }
 308
 309         *last_symlink = '\0';
 310         while (nr--) {
 311                 struct cache_entry *ce = *src++;
 312
 313                 if (!ce->ce_mode || ce->ce_flags & mask)
 314                         display_progress(progress, ++cnt);
 315                 if (!ce->ce_mode) {
 316                         if (o->update)
 317                                 unlink_entry(ce->name, last_symlink);
 318                         continue;
 319                 }
 320                 if (ce->ce_flags & mask) {
 321                         ce->ce_flags &= ~mask;
 322                         if (o->update) {
 323                                 checkout_entry(ce, &state, NULL);
 324                                 *last_symlink = '\0';
 325                         }
 326                 }
 327         }
 328         stop_progress(&progress);
 329 }
 330
 331 int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options *o)
 332 {
 333         struct tree_entry_list **posns;
 334         int i;
 335         struct tree_entry_list df_conflict_list;
 336         static struct cache_entry *dfc;
 337
 338         memset(&df_conflict_list, 0, sizeof(df_conflict_list));
 339         df_conflict_list.next = &df_conflict_list;
 340         memset(&state, 0, sizeof(state));
 341         state.base_dir = "";
 342         state.force = 1;
 343         state.quiet = 1;
 344         state.refresh_cache = 1;
 345
 346         o->merge_size = len;
 347
 348         if (!dfc)
 349                 dfc = xcalloc(1, sizeof(struct cache_entry) + 1);
 350         o->df_conflict_entry = dfc;
 351
 352         if (len) {
 353                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
 354                 for (i = 0; i < len; i++)
 355                         posns[i] = create_tree_entry_list(t+i);
 356
 357                 if (unpack_trees_rec(posns, len, o->prefix ? o->prefix : "",
 358                                      o, &df_conflict_list))
 359                         return -1;
 360         }
 361
 362         if (o->trivial_merges_only && o->nontrivial_merge)
 363                 die("Merge requires file-level merging");
 364
 365         check_updates(active_cache, active_nr, o);
 366         return 0;
 367 }
 368
 369 /* Here come the merge functions */
 370
 371 static void reject_merge(struct cache_entry *ce)
 372 {
 373         die("Entry '%s' would be overwritten by merge. Cannot merge.",
 374             ce->name);
 375 }
 376
 377 static int same(struct cache_entry *a, struct cache_entry *b)
 378 {
 379         if (!!a != !!b)
 380                 return 0;
 381         if (!a && !b)
 382                 return 1;
 383         return a->ce_mode == b->ce_mode &&
 384                !hashcmp(a->sha1, b->sha1);
 385 }
 386
 387
 388 /*
 389  * When a CE gets turned into an unmerged entry, we
 390  * want it to be up-to-date
 391  */
 392 static void verify_uptodate(struct cache_entry *ce,
 393                 struct unpack_trees_options *o)
 394 {
 395         struct stat st;
 396
 397         if (o->index_only || o->reset)
 398                 return;
 399
 400         if (!lstat(ce->name, &st)) {
 401                 unsigned changed = ce_match_stat(ce, &st, CE_MATCH_IGNORE_VALID);
 402                 if (!changed)
 403                         return;
 404                 /*
 405                  * NEEDSWORK: the current default policy is to allow
 406                  * submodule to be out of sync wrt the supermodule
 407                  * index.  This needs to be tightened later for
 408                  * submodules that are marked to be automatically
 409                  * checked out.
 410                  */
 411                 if (S_ISGITLINK(ntohl(ce->ce_mode)))
 412                         return;
 413                 errno = 0;
 414         }
 415         if (errno == ENOENT)
 416                 return;
 417         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 418 }
 419
 420 static void invalidate_ce_path(struct cache_entry *ce)
 421 {
 422         if (ce)
 423                 cache_tree_invalidate_path(active_cache_tree, ce->name);
 424 }
 425
 426 /*
 427  * Check that checking out ce->sha1 in subdir ce->name is not
 428  * going to overwrite any working files.
 429  *
 430  * Currently, git does not checkout subprojects during a superproject
 431  * checkout, so it is not going to overwrite anything.
 432  */
 433 static int verify_clean_submodule(struct cache_entry *ce, const char *action,
 434                                       struct unpack_trees_options *o)
 435 {
 436         return 0;
 437 }
 438
 439 static int verify_clean_subdirectory(struct cache_entry *ce, const char *action,
 440                                       struct unpack_trees_options *o)
 441 {
 442         /*
 443          * we are about to extract "ce->name"; we would not want to lose
 444          * anything in the existing directory there.
 445          */
 446         int namelen;
 447         int pos, i;
 448         struct dir_struct d;
 449         char *pathbuf;
 450         int cnt = 0;
 451         unsigned char sha1[20];
 452
 453         if (S_ISGITLINK(ntohl(ce->ce_mode)) &&
 454             resolve_gitlink_ref(ce->name, "HEAD", sha1) == 0) {
 455                 /* If we are not going to update the submodule, then
 456                  * we don't care.
 457                  */
 458                 if (!hashcmp(sha1, ce->sha1))
 459                         return 0;
 460                 return verify_clean_submodule(ce, action, o);
 461         }
 462
 463         /*
 464          * First let's make sure we do not have a local modification
 465          * in that directory.
 466          */
 467         namelen = strlen(ce->name);
 468         pos = cache_name_pos(ce->name, namelen);
 469         if (0 <= pos)
 470                 return cnt; /* we have it as nondirectory */
 471         pos = -pos - 1;
 472         for (i = pos; i < active_nr; i++) {
 473                 struct cache_entry *ce = active_cache[i];
 474                 int len = ce_namelen(ce);
 475                 if (len < namelen ||
 476                     strncmp(ce->name, ce->name, namelen) ||
 477                     ce->name[namelen] != '/')
 478                         break;
 479                 /*
 480                  * ce->name is an entry in the subdirectory.
 481                  */
 482                 if (!ce_stage(ce)) {
 483                         verify_uptodate(ce, o);
 484                         ce->ce_mode = 0;
 485                 }
 486                 cnt++;
 487         }
 488
 489         /*
 490          * Then we need to make sure that we do not lose a locally
 491          * present file that is not ignored.
 492          */
 493         pathbuf = xmalloc(namelen + 2);
 494         memcpy(pathbuf, ce->name, namelen);
 495         strcpy(pathbuf+namelen, "/");
 496
 497         memset(&d, 0, sizeof(d));
 498         if (o->dir)
 499                 d.exclude_per_dir = o->dir->exclude_per_dir;
 500         i = read_directory(&d, ce->name, pathbuf, namelen+1, NULL);
 501         if (i)
 502                 die("Updating '%s' would lose untracked files in it",
 503                     ce->name);
 504         free(pathbuf);
 505         return cnt;
 506 }
 507
 508 /*
 509  * We do not want to remove or overwrite a working tree file that
 510  * is not tracked, unless it is ignored.
 511  */
 512 static void verify_absent(struct cache_entry *ce, const char *action,
 513                 struct unpack_trees_options *o)
 514 {
 515         struct stat st;
 516
 517         if (o->index_only || o->reset || !o->update)
 518                 return;
 519
 520         if (has_symlink_leading_path(ce->name, NULL))
 521                 return;
 522
 523         if (!lstat(ce->name, &st)) {
 524                 int cnt;
 525
 526                 if (o->dir && excluded(o->dir, ce->name))
 527                         /*
 528                          * ce->name is explicitly excluded, so it is Ok to
 529                          * overwrite it.
 530                          */
 531                         return;
 532                 if (S_ISDIR(st.st_mode)) {
 533                         /*
 534                          * We are checking out path "foo" and
 535                          * found "foo/." in the working tree.
 536                          * This is tricky -- if we have modified
 537                          * files that are in "foo/" we would lose
 538                          * it.
 539                          */
 540                         cnt = verify_clean_subdirectory(ce, action, o);
 541
 542                         /*
 543                          * If this removed entries from the index,
 544                          * what that means is:
 545                          *
 546                          * (1) the caller unpack_trees_rec() saw path/foo
 547                          * in the index, and it has not removed it because
 548                          * it thinks it is handling 'path' as blob with
 549                          * D/F conflict;
 550                          * (2) we will return "ok, we placed a merged entry
 551                          * in the index" which would cause o->pos to be
 552                          * incremented by one;
 553                          * (3) however, original o->pos now has 'path/foo'
 554                          * marked with "to be removed".
 555                          *
 556                          * We need to increment it by the number of
 557                          * deleted entries here.
 558                          */
 559                         o->pos += cnt;
 560                         return;
 561                 }
 562
 563                 /*
 564                  * The previous round may already have decided to
 565                  * delete this path, which is in a subdirectory that
 566                  * is being replaced with a blob.
 567                  */
 568                 cnt = cache_name_pos(ce->name, strlen(ce->name));
 569                 if (0 <= cnt) {
 570                         struct cache_entry *ce = active_cache[cnt];
 571                         if (!ce_stage(ce) && !ce->ce_mode)
 572                                 return;
 573                 }
 574
 575                 die("Untracked working tree file '%s' "
 576                     "would be %s by merge.", ce->name, action);
 577         }
 578 }
 579
 580 static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
 581                 struct unpack_trees_options *o)
 582 {
 583         merge->ce_flags |= htons(CE_UPDATE);
 584         if (old) {
 585                 /*
 586                  * See if we can re-use the old CE directly?
 587                  * That way we get the uptodate stat info.
 588                  *
 589                  * This also removes the UPDATE flag on
 590                  * a match.
 591                  */
 592                 if (same(old, merge)) {
 593                         memcpy(merge, old, offsetof(struct cache_entry, name));
 594                 } else {
 595                         verify_uptodate(old, o);
 596                         invalidate_ce_path(old);
 597                 }
 598         }
 599         else {
 600                 verify_absent(merge, "overwritten", o);
 601                 invalidate_ce_path(merge);
 602         }
 603
 604         merge->ce_flags &= ~htons(CE_STAGEMASK);
 605         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
 606         return 1;
 607 }
 608
 609 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old,
 610                 struct unpack_trees_options *o)
 611 {
 612         if (old)
 613                 verify_uptodate(old, o);
 614         else
 615                 verify_absent(ce, "removed", o);
 616         ce->ce_mode = 0;
 617         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
 618         invalidate_ce_path(ce);
 619         return 1;
 620 }
 621
 622 static int keep_entry(struct cache_entry *ce, struct unpack_trees_options *o)
 623 {
 624         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 625         return 1;
 626 }
 627
 628 #if DBRT_DEBUG
 629 static void show_stage_entry(FILE *o,
 630                              const char *label, const struct cache_entry *ce)
 631 {
 632         if (!ce)
 633                 fprintf(o, "%s (missing)\n", label);
 634         else
 635                 fprintf(o, "%s%06o %s %d\t%s\n",
 636                         label,
 637                         ntohl(ce->ce_mode),
 638                         sha1_to_hex(ce->sha1),
 639                         ce_stage(ce),
 640                         ce->name);
 641 }
 642 #endif
 643
 644 int threeway_merge(struct cache_entry **stages,
 645                 struct unpack_trees_options *o,
 646                 int remove)
 647 {
 648         struct cache_entry *index;
 649         struct cache_entry *head;
 650         struct cache_entry *remote = stages[o->head_idx + 1];
 651         int count;
 652         int head_match = 0;
 653         int remote_match = 0;
 654
 655         int df_conflict_head = 0;
 656         int df_conflict_remote = 0;
 657
 658         int any_anc_missing = 0;
 659         int no_anc_exists = 1;
 660         int i;
 661
 662         for (i = 1; i < o->head_idx; i++) {
 663                 if (!stages[i] || stages[i] == o->df_conflict_entry)
 664                         any_anc_missing = 1;
 665                 else
 666                         no_anc_exists = 0;
 667         }
 668
 669         index = stages[0];
 670         head = stages[o->head_idx];
 671
 672         if (head == o->df_conflict_entry) {
 673                 df_conflict_head = 1;
 674                 head = NULL;
 675         }
 676
 677         if (remote == o->df_conflict_entry) {
 678                 df_conflict_remote = 1;
 679                 remote = NULL;
 680         }
 681
 682         /* First, if there's a #16 situation, note that to prevent #13
 683          * and #14.
 684          */
 685         if (!same(remote, head)) {
 686                 for (i = 1; i < o->head_idx; i++) {
 687                         if (same(stages[i], head)) {
 688                                 head_match = i;
 689                         }
 690                         if (same(stages[i], remote)) {
 691                                 remote_match = i;
 692                         }
 693                 }
 694         }
 695
 696         /* We start with cases where the index is allowed to match
 697          * something other than the head: #14(ALT) and #2ALT, where it
 698          * is permitted to match the result instead.
 699          */
 700         /* #14, #14ALT, #2ALT */
 701         if (remote && !df_conflict_head && head_match && !remote_match) {
 702                 if (index && !same(index, remote) && !same(index, head))
 703                         reject_merge(index);
 704                 return merged_entry(remote, index, o);
 705         }
 706         /*
 707          * If we have an entry in the index cache, then we want to
 708          * make sure that it matches head.
 709          */
 710         if (index && !same(index, head)) {
 711                 reject_merge(index);
 712         }
 713
 714         if (head) {
 715                 /* #5ALT, #15 */
 716                 if (same(head, remote))
 717                         return merged_entry(head, index, o);
 718                 /* #13, #3ALT */
 719                 if (!df_conflict_remote && remote_match && !head_match)
 720                         return merged_entry(head, index, o);
 721         }
 722
 723         /* #1 */
 724         if (!head && !remote && any_anc_missing) {
 725                 remove_entry(remove);
 726                 return 0;
 727         }
 728
 729         /* Under the new "aggressive" rule, we resolve mostly trivial
 730          * cases that we historically had git-merge-one-file resolve.
 731          */
 732         if (o->aggressive) {
 733                 int head_deleted = !head && !df_conflict_head;
 734                 int remote_deleted = !remote && !df_conflict_remote;
 735                 struct cache_entry *ce = NULL;
 736
 737                 if (index)
 738                         ce = index;
 739                 else if (head)
 740                         ce = head;
 741                 else if (remote)
 742                         ce = remote;
 743                 else {
 744                         for (i = 1; i < o->head_idx; i++) {
 745                                 if (stages[i] && stages[i] != o->df_conflict_entry) {
 746                                         ce = stages[i];
 747                                         break;
 748                                 }
 749                         }
 750                 }
 751
 752                 /*
 753                  * Deleted in both.
 754                  * Deleted in one and unchanged in the other.
 755                  */
 756                 if ((head_deleted && remote_deleted) ||
 757                     (head_deleted && remote && remote_match) ||
 758                     (remote_deleted && head && head_match)) {
 759                         remove_entry(remove);
 760                         if (index)
 761                                 return deleted_entry(index, index, o);
 762                         else if (ce && !head_deleted)
 763                                 verify_absent(ce, "removed", o);
 764                         return 0;
 765                 }
 766                 /*
 767                  * Added in both, identically.
 768                  */
 769                 if (no_anc_exists && head && remote && same(head, remote))
 770                         return merged_entry(head, index, o);
 771
 772         }
 773
 774         /* Below are "no merge" cases, which require that the index be
 775          * up-to-date to avoid the files getting overwritten with
 776          * conflict resolution files.
 777          */
 778         if (index) {
 779                 verify_uptodate(index, o);
 780         }
 781
 782         remove_entry(remove);
 783         o->nontrivial_merge = 1;
 784
 785         /* #2, #3, #4, #6, #7, #9, #10, #11. */
 786         count = 0;
 787         if (!head_match || !remote_match) {
 788                 for (i = 1; i < o->head_idx; i++) {
 789                         if (stages[i] && stages[i] != o->df_conflict_entry) {
 790                                 keep_entry(stages[i], o);
 791                                 count++;
 792                                 break;
 793                         }
 794                 }
 795         }
 796 #if DBRT_DEBUG
 797         else {
 798                 fprintf(stderr, "read-tree: warning #16 detected\n");
 799                 show_stage_entry(stderr, "head   ", stages[head_match]);
 800                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 801         }
 802 #endif
 803         if (head) { count += keep_entry(head, o); }
 804         if (remote) { count += keep_entry(remote, o); }
 805         return count;
 806 }
 807
 808 /*
 809  * Two-way merge.
 810  *
 811  * The rule is to "carry forward" what is in the index without losing
 812  * information across a "fast forward", favoring a successful merge
 813  * over a merge failure when it makes sense.  For details of the
 814  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 815  *
 816  */
 817 int twoway_merge(struct cache_entry **src,
 818                 struct unpack_trees_options *o,
 819                 int remove)
 820 {
 821         struct cache_entry *current = src[0];
 822         struct cache_entry *oldtree = src[1];
 823         struct cache_entry *newtree = src[2];
 824
 825         if (o->merge_size != 2)
 826                 return error("Cannot do a twoway merge of %d trees",
 827                              o->merge_size);
 828
 829         if (oldtree == o->df_conflict_entry)
 830                 oldtree = NULL;
 831         if (newtree == o->df_conflict_entry)
 832                 newtree = NULL;
 833
 834         if (current) {
 835                 if ((!oldtree && !newtree) || /* 4 and 5 */
 836                     (!oldtree && newtree &&
 837                      same(current, newtree)) || /* 6 and 7 */
 838                     (oldtree && newtree &&
 839                      same(oldtree, newtree)) || /* 14 and 15 */
 840                     (oldtree && newtree &&
 841                      !same(oldtree, newtree) && /* 18 and 19 */
 842                      same(current, newtree))) {
 843                         return keep_entry(current, o);
 844                 }
 845                 else if (oldtree && !newtree && same(current, oldtree)) {
 846                         /* 10 or 11 */
 847                         remove_entry(remove);
 848                         return deleted_entry(oldtree, current, o);
 849                 }
 850                 else if (oldtree && newtree &&
 851                          same(current, oldtree) && !same(current, newtree)) {
 852                         /* 20 or 21 */
 853                         return merged_entry(newtree, current, o);
 854                 }
 855                 else {
 856                         /* all other failures */
 857                         remove_entry(remove);
 858                         if (oldtree)
 859                                 reject_merge(oldtree);
 860                         if (current)
 861                                 reject_merge(current);
 862                         if (newtree)
 863                                 reject_merge(newtree);
 864                         return -1;
 865                 }
 866         }
 867         else if (newtree)
 868                 return merged_entry(newtree, current, o);
 869         remove_entry(remove);
 870         return deleted_entry(oldtree, current, o);
 871 }
 872
 873 /*
 874  * Bind merge.
 875  *
 876  * Keep the index entries at stage0, collapse stage1 but make sure
 877  * stage0 does not have anything there.
 878  */
 879 int bind_merge(struct cache_entry **src,
 880                 struct unpack_trees_options *o,
 881                 int remove)
 882 {
 883         struct cache_entry *old = src[0];
 884         struct cache_entry *a = src[1];
 885
 886         if (o->merge_size != 1)
 887                 return error("Cannot do a bind merge of %d trees\n",
 888                              o->merge_size);
 889         if (a && old)
 890                 die("Entry '%s' overlaps.  Cannot bind.", a->name);
 891         if (!a)
 892                 return keep_entry(old, o);
 893         else
 894                 return merged_entry(a, NULL, o);
 895 }
 896
 897 /*
 898  * One-way merge.
 899  *
 900  * The rule is:
 901  * - take the stat information from stage0, take the data from stage1
 902  */
 903 int oneway_merge(struct cache_entry **src,
 904                 struct unpack_trees_options *o,
 905                 int remove)
 906 {
 907         struct cache_entry *old = src[0];
 908         struct cache_entry *a = src[1];
 909
 910         if (o->merge_size != 1)
 911                 return error("Cannot do a oneway merge of %d trees",
 912                              o->merge_size);
 913
 914         if (!a) {
 915                 remove_entry(remove);
 916                 return deleted_entry(old, old, o);
 917         }
 918         if (old && same(old, a)) {
 919                 if (o->reset) {
 920                         struct stat st;
 921                         if (lstat(old->name, &st) ||
 922                             ce_match_stat(old, &st, CE_MATCH_IGNORE_VALID))
 923                                 old->ce_flags |= htons(CE_UPDATE);
 924                 }
 925                 return keep_entry(old, o);
 926         }
 927         return merged_entry(a, old, o);
 928 }