unpack-trees.c

   1 #define NO_THE_INDEX_COMPATIBILITY_MACROS
   2 #include "cache.h"
   3 #include "dir.h"
   4 #include "tree.h"
   5 #include "tree-walk.h"
   6 #include "cache-tree.h"
   7 #include "unpack-trees.h"
   8 #include "progress.h"
   9 #include "refs.h"
  10
  11 static void add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
  12         unsigned int set, unsigned int clear)
  13 {
  14         unsigned int size = ce_size(ce);
  15         struct cache_entry *new = xmalloc(size);
  16
  17         clear |= CE_HASHED | CE_UNHASHED;
  18
  19         memcpy(new, ce, size);
  20         new->next = NULL;
  21         new->ce_flags = (new->ce_flags & ~clear) | set;
  22         add_index_entry(&o->result, new, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE|ADD_CACHE_SKIP_DFCHECK);
  23 }
  24
  25 /* Unlink the last component and attempt to remove leading
  26  * directories, in case this unlink is the removal of the
  27  * last entry in the directory -- empty directories are removed.
  28  */
  29 static void unlink_entry(char *name, char *last_symlink)
  30 {
  31         char *cp, *prev;
  32
  33         if (has_symlink_leading_path(name, last_symlink))
  34                 return;
  35         if (unlink(name))
  36                 return;
  37         prev = NULL;
  38         while (1) {
  39                 int status;
  40                 cp = strrchr(name, '/');
  41                 if (prev)
  42                         *prev = '/';
  43                 if (!cp)
  44                         break;
  45
  46                 *cp = 0;
  47                 status = rmdir(name);
  48                 if (status) {
  49                         *cp = '/';
  50                         break;
  51                 }
  52                 prev = cp;
  53         }
  54 }
  55
  56 static struct checkout state;
  57 static void check_updates(struct unpack_trees_options *o)
  58 {
  59         unsigned cnt = 0, total = 0;
  60         struct progress *progress = NULL;
  61         char last_symlink[PATH_MAX];
  62         struct index_state *index = &o->result;
  63         int i;
  64
  65         if (o->update && o->verbose_update) {
  66                 for (total = cnt = 0; cnt < index->cache_nr; cnt++) {
  67                         struct cache_entry *ce = index->cache[cnt];
  68                         if (ce->ce_flags & (CE_UPDATE | CE_REMOVE))
  69                                 total++;
  70                 }
  71
  72                 progress = start_progress_delay("Checking out files",
  73                                                 total, 50, 1);
  74                 cnt = 0;
  75         }
  76
  77         *last_symlink = '\0';
  78         for (i = 0; i < index->cache_nr; i++) {
  79                 struct cache_entry *ce = index->cache[i];
  80
  81                 if (ce->ce_flags & (CE_UPDATE | CE_REMOVE))
  82                         display_progress(progress, ++cnt);
  83                 if (ce->ce_flags & CE_REMOVE) {
  84                         if (o->update)
  85                                 unlink_entry(ce->name, last_symlink);
  86                         remove_index_entry_at(&o->result, i);
  87                         i--;
  88                         continue;
  89                 }
  90                 if (ce->ce_flags & CE_UPDATE) {
  91                         ce->ce_flags &= ~CE_UPDATE;
  92                         if (o->update) {
  93                                 checkout_entry(ce, &state, NULL);
  94                                 *last_symlink = '\0';
  95                         }
  96                 }
  97         }
  98         stop_progress(&progress);
  99 }
 100
 101 static inline int call_unpack_fn(struct cache_entry **src, struct unpack_trees_options *o)
 102 {
 103         int ret = o->fn(src, o);
 104         if (ret > 0)
 105                 ret = 0;
 106         return ret;
 107 }
 108
 109 static int unpack_index_entry(struct cache_entry *ce, struct unpack_trees_options *o)
 110 {
 111         struct cache_entry *src[5] = { ce, };
 112
 113         o->pos++;
 114         if (ce_stage(ce)) {
 115                 if (o->skip_unmerged) {
 116                         add_entry(o, ce, 0, 0);
 117                         return 0;
 118                 }
 119         }
 120         return call_unpack_fn(src, o);
 121 }
 122
 123 int traverse_trees_recursive(int n, unsigned long dirmask, unsigned long df_conflicts, struct name_entry *names, struct traverse_info *info)
 124 {
 125         int i;
 126         struct tree_desc t[MAX_UNPACK_TREES];
 127         struct traverse_info newinfo;
 128         struct name_entry *p;
 129
 130         p = names;
 131         while (!p->mode)
 132                 p++;
 133
 134         newinfo = *info;
 135         newinfo.prev = info;
 136         newinfo.name = *p;
 137         newinfo.pathlen += tree_entry_len(p->path, p->sha1) + 1;
 138         newinfo.conflicts |= df_conflicts;
 139
 140         for (i = 0; i < n; i++, dirmask >>= 1) {
 141                 const unsigned char *sha1 = NULL;
 142                 if (dirmask & 1)
 143                         sha1 = names[i].sha1;
 144                 fill_tree_descriptor(t+i, sha1);
 145         }
 146         return traverse_trees(n, t, &newinfo);
 147 }
 148
 149 /*
 150  * Compare the traverse-path to the cache entry without actually
 151  * having to generate the textual representation of the traverse
 152  * path.
 153  *
 154  * NOTE! This *only* compares up to the size of the traverse path
 155  * itself - the caller needs to do the final check for the cache
 156  * entry having more data at the end!
 157  */
 158 static int do_compare_entry(const struct cache_entry *ce, const struct traverse_info *info, const struct name_entry *n)
 159 {
 160         int len, pathlen, ce_len;
 161         const char *ce_name;
 162
 163         if (info->prev) {
 164                 int cmp = do_compare_entry(ce, info->prev, &info->name);
 165                 if (cmp)
 166                         return cmp;
 167         }
 168         pathlen = info->pathlen;
 169         ce_len = ce_namelen(ce);
 170
 171         /* If ce_len < pathlen then we must have previously hit "name == directory" entry */
 172         if (ce_len < pathlen)
 173                 return -1;
 174
 175         ce_len -= pathlen;
 176         ce_name = ce->name + pathlen;
 177
 178         len = tree_entry_len(n->path, n->sha1);
 179         return df_name_compare(ce_name, ce_len, S_IFREG, n->path, len, n->mode);
 180 }
 181
 182 static int compare_entry(const struct cache_entry *ce, const struct traverse_info *info, const struct name_entry *n)
 183 {
 184         int cmp = do_compare_entry(ce, info, n);
 185         if (cmp)
 186                 return cmp;
 187
 188         /*
 189          * Even if the beginning compared identically, the ce should
 190          * compare as bigger than a directory leading up to it!
 191          */
 192         return ce_namelen(ce) > traverse_path_len(info, n);
 193 }
 194
 195 static struct cache_entry *create_ce_entry(const struct traverse_info *info, const struct name_entry *n, int stage)
 196 {
 197         int len = traverse_path_len(info, n);
 198         struct cache_entry *ce = xcalloc(1, cache_entry_size(len));
 199
 200         ce->ce_mode = create_ce_mode(n->mode);
 201         ce->ce_flags = create_ce_flags(len, stage);
 202         hashcpy(ce->sha1, n->sha1);
 203         make_traverse_path(ce->name, info, n);
 204
 205         return ce;
 206 }
 207
 208 static int unpack_nondirectories(int n, unsigned long mask, unsigned long dirmask, struct cache_entry *src[5],
 209         const struct name_entry *names, const struct traverse_info *info)
 210 {
 211         int i;
 212         struct unpack_trees_options *o = info->data;
 213         unsigned long conflicts;
 214
 215         /* Do we have *only* directories? Nothing to do */
 216         if (mask == dirmask && !src[0])
 217                 return 0;
 218
 219         conflicts = info->conflicts;
 220         if (o->merge)
 221                 conflicts >>= 1;
 222         conflicts |= dirmask;
 223
 224         /*
 225          * Ok, we've filled in up to any potential index entry in src[0],
 226          * now do the rest.
 227          */
 228         for (i = 0; i < n; i++) {
 229                 int stage;
 230                 unsigned int bit = 1ul << i;
 231                 if (conflicts & bit) {
 232                         src[i + o->merge] = o->df_conflict_entry;
 233                         continue;
 234                 }
 235                 if (!(mask & bit))
 236                         continue;
 237                 if (!o->merge)
 238                         stage = 0;
 239                 else if (i + 1 < o->head_idx)
 240                         stage = 1;
 241                 else if (i + 1 > o->head_idx)
 242                         stage = 3;
 243                 else
 244                         stage = 2;
 245                 src[i + o->merge] = create_ce_entry(info, names + i, stage);
 246         }
 247
 248         if (o->merge)
 249                 return call_unpack_fn(src, o);
 250
 251         n += o->merge;
 252         for (i = 0; i < n; i++)
 253                 add_entry(o, src[i], 0, 0);
 254         return 0;
 255 }
 256
 257 static int unpack_callback(int n, unsigned long mask, unsigned long dirmask, struct name_entry *names, struct traverse_info *info)
 258 {
 259         struct cache_entry *src[5] = { NULL, };
 260         struct unpack_trees_options *o = info->data;
 261         const struct name_entry *p = names;
 262
 263         /* Find first entry with a real name (we could use "mask" too) */
 264         while (!p->mode)
 265                 p++;
 266
 267         /* Are we supposed to look at the index too? */
 268         if (o->merge) {
 269                 while (o->pos < o->src_index->cache_nr) {
 270                         struct cache_entry *ce = o->src_index->cache[o->pos];
 271                         int cmp = compare_entry(ce, info, p);
 272                         if (cmp < 0) {
 273                                 if (unpack_index_entry(ce, o) < 0)
 274                                         return -1;
 275                                 continue;
 276                         }
 277                         if (!cmp) {
 278                                 o->pos++;
 279                                 if (ce_stage(ce)) {
 280                                         /*
 281                                          * If we skip unmerged index entries, we'll skip this
 282                                          * entry *and* the tree entries associated with it!
 283                                          */
 284                                         if (o->skip_unmerged) {
 285                                                 add_entry(o, ce, 0, 0);
 286                                                 return mask;
 287                                         }
 288                                 }
 289                                 src[0] = ce;
 290                         }
 291                         break;
 292                 }
 293         }
 294
 295         if (unpack_nondirectories(n, mask, dirmask, src, names, info) < 0)
 296                 return -1;
 297
 298         /* Now handle any directories.. */
 299         if (dirmask) {
 300                 unsigned long conflicts = mask & ~dirmask;
 301                 if (o->merge) {
 302                         conflicts <<= 1;
 303                         if (src[0])
 304                                 conflicts |= 1;
 305                 }
 306                 if (traverse_trees_recursive(n, dirmask, conflicts,
 307                                              names, info) < 0)
 308                         return -1;
 309                 return mask;
 310         }
 311
 312         return mask;
 313 }
 314
 315 static int unpack_failed(struct unpack_trees_options *o, const char *message)
 316 {
 317         discard_index(&o->result);
 318         if (!o->gently) {
 319                 if (message)
 320                         return error(message);
 321                 return -1;
 322         }
 323         return -1;
 324 }
 325
 326 int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options *o)
 327 {
 328         static struct cache_entry *dfc;
 329
 330         if (len > MAX_UNPACK_TREES)
 331                 die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
 332         memset(&state, 0, sizeof(state));
 333         state.base_dir = "";
 334         state.force = 1;
 335         state.quiet = 1;
 336         state.refresh_cache = 1;
 337
 338         memset(&o->result, 0, sizeof(o->result));
 339         if (o->src_index)
 340                 o->result.timestamp = o->src_index->timestamp;
 341         o->merge_size = len;
 342
 343         if (!dfc)
 344                 dfc = xcalloc(1, sizeof(struct cache_entry) + 1);
 345         o->df_conflict_entry = dfc;
 346
 347         if (len) {
 348                 const char *prefix = o->prefix ? o->prefix : "";
 349                 struct traverse_info info;
 350
 351                 setup_traverse_info(&info, prefix);
 352                 info.fn = unpack_callback;
 353                 info.data = o;
 354
 355                 if (traverse_trees(len, t, &info) < 0)
 356                         return unpack_failed(o, NULL);
 357         }
 358
 359         /* Any left-over entries in the index? */
 360         if (o->merge) {
 361                 while (o->pos < o->src_index->cache_nr) {
 362                         struct cache_entry *ce = o->src_index->cache[o->pos];
 363                         if (unpack_index_entry(ce, o) < 0)
 364                                 return unpack_failed(o, NULL);
 365                 }
 366         }
 367
 368         if (o->trivial_merges_only && o->nontrivial_merge)
 369                 return unpack_failed(o, "Merge requires file-level merging");
 370
 371         o->src_index = NULL;
 372         check_updates(o);
 373         if (o->dst_index)
 374                 *o->dst_index = o->result;
 375         return 0;
 376 }
 377
 378 /* Here come the merge functions */
 379
 380 static int reject_merge(struct cache_entry *ce)
 381 {
 382         return error("Entry '%s' would be overwritten by merge. Cannot merge.",
 383                      ce->name);
 384 }
 385
 386 static int same(struct cache_entry *a, struct cache_entry *b)
 387 {
 388         if (!!a != !!b)
 389                 return 0;
 390         if (!a && !b)
 391                 return 1;
 392         return a->ce_mode == b->ce_mode &&
 393                !hashcmp(a->sha1, b->sha1);
 394 }
 395
 396
 397 /*
 398  * When a CE gets turned into an unmerged entry, we
 399  * want it to be up-to-date
 400  */
 401 static int verify_uptodate(struct cache_entry *ce,
 402                 struct unpack_trees_options *o)
 403 {
 404         struct stat st;
 405
 406         if (o->index_only || o->reset)
 407                 return 0;
 408
 409         if (!lstat(ce->name, &st)) {
 410                 unsigned changed = ie_match_stat(o->src_index, ce, &st, CE_MATCH_IGNORE_VALID);
 411                 if (!changed)
 412                         return 0;
 413                 /*
 414                  * NEEDSWORK: the current default policy is to allow
 415                  * submodule to be out of sync wrt the supermodule
 416                  * index.  This needs to be tightened later for
 417                  * submodules that are marked to be automatically
 418                  * checked out.
 419                  */
 420                 if (S_ISGITLINK(ce->ce_mode))
 421                         return 0;
 422                 errno = 0;
 423         }
 424         if (errno == ENOENT)
 425                 return 0;
 426         return o->gently ? -1 :
 427                 error("Entry '%s' not uptodate. Cannot merge.", ce->name);
 428 }
 429
 430 static void invalidate_ce_path(struct cache_entry *ce, struct unpack_trees_options *o)
 431 {
 432         if (ce)
 433                 cache_tree_invalidate_path(o->src_index->cache_tree, ce->name);
 434 }
 435
 436 /*
 437  * Check that checking out ce->sha1 in subdir ce->name is not
 438  * going to overwrite any working files.
 439  *
 440  * Currently, git does not checkout subprojects during a superproject
 441  * checkout, so it is not going to overwrite anything.
 442  */
 443 static int verify_clean_submodule(struct cache_entry *ce, const char *action,
 444                                       struct unpack_trees_options *o)
 445 {
 446         return 0;
 447 }
 448
 449 static int verify_clean_subdirectory(struct cache_entry *ce, const char *action,
 450                                       struct unpack_trees_options *o)
 451 {
 452         /*
 453          * we are about to extract "ce->name"; we would not want to lose
 454          * anything in the existing directory there.
 455          */
 456         int namelen;
 457         int pos, i;
 458         struct dir_struct d;
 459         char *pathbuf;
 460         int cnt = 0;
 461         unsigned char sha1[20];
 462
 463         if (S_ISGITLINK(ce->ce_mode) &&
 464             resolve_gitlink_ref(ce->name, "HEAD", sha1) == 0) {
 465                 /* If we are not going to update the submodule, then
 466                  * we don't care.
 467                  */
 468                 if (!hashcmp(sha1, ce->sha1))
 469                         return 0;
 470                 return verify_clean_submodule(ce, action, o);
 471         }
 472
 473         /*
 474          * First let's make sure we do not have a local modification
 475          * in that directory.
 476          */
 477         namelen = strlen(ce->name);
 478         pos = index_name_pos(o->src_index, ce->name, namelen);
 479         if (0 <= pos)
 480                 return cnt; /* we have it as nondirectory */
 481         pos = -pos - 1;
 482         for (i = pos; i < o->src_index->cache_nr; i++) {
 483                 struct cache_entry *ce = o->src_index->cache[i];
 484                 int len = ce_namelen(ce);
 485                 if (len < namelen ||
 486                     strncmp(ce->name, ce->name, namelen) ||
 487                     ce->name[namelen] != '/')
 488                         break;
 489                 /*
 490                  * ce->name is an entry in the subdirectory.
 491                  */
 492                 if (!ce_stage(ce)) {
 493                         if (verify_uptodate(ce, o))
 494                                 return -1;
 495                         add_entry(o, ce, CE_REMOVE, 0);
 496                 }
 497                 cnt++;
 498         }
 499
 500         /*
 501          * Then we need to make sure that we do not lose a locally
 502          * present file that is not ignored.
 503          */
 504         pathbuf = xmalloc(namelen + 2);
 505         memcpy(pathbuf, ce->name, namelen);
 506         strcpy(pathbuf+namelen, "/");
 507
 508         memset(&d, 0, sizeof(d));
 509         if (o->dir)
 510                 d.exclude_per_dir = o->dir->exclude_per_dir;
 511         i = read_directory(&d, ce->name, pathbuf, namelen+1, NULL);
 512         if (i)
 513                 return o->gently ? -1 :
 514                         error("Updating '%s' would lose untracked files in it",
 515                               ce->name);
 516         free(pathbuf);
 517         return cnt;
 518 }
 519
 520 /*
 521  * We do not want to remove or overwrite a working tree file that
 522  * is not tracked, unless it is ignored.
 523  */
 524 static int verify_absent(struct cache_entry *ce, const char *action,
 525                          struct unpack_trees_options *o)
 526 {
 527         struct stat st;
 528
 529         if (o->index_only || o->reset || !o->update)
 530                 return 0;
 531
 532         if (has_symlink_leading_path(ce->name, NULL))
 533                 return 0;
 534
 535         if (!lstat(ce->name, &st)) {
 536                 int cnt;
 537                 int dtype = ce_to_dtype(ce);
 538
 539                 if (o->dir && excluded(o->dir, ce->name, &dtype))
 540                         /*
 541                          * ce->name is explicitly excluded, so it is Ok to
 542                          * overwrite it.
 543                          */
 544                         return 0;
 545                 if (S_ISDIR(st.st_mode)) {
 546                         /*
 547                          * We are checking out path "foo" and
 548                          * found "foo/." in the working tree.
 549                          * This is tricky -- if we have modified
 550                          * files that are in "foo/" we would lose
 551                          * it.
 552                          */
 553                         cnt = verify_clean_subdirectory(ce, action, o);
 554
 555                         /*
 556                          * If this removed entries from the index,
 557                          * what that means is:
 558                          *
 559                          * (1) the caller unpack_trees_rec() saw path/foo
 560                          * in the index, and it has not removed it because
 561                          * it thinks it is handling 'path' as blob with
 562                          * D/F conflict;
 563                          * (2) we will return "ok, we placed a merged entry
 564                          * in the index" which would cause o->pos to be
 565                          * incremented by one;
 566                          * (3) however, original o->pos now has 'path/foo'
 567                          * marked with "to be removed".
 568                          *
 569                          * We need to increment it by the number of
 570                          * deleted entries here.
 571                          */
 572                         o->pos += cnt;
 573                         return 0;
 574                 }
 575
 576                 /*
 577                  * The previous round may already have decided to
 578                  * delete this path, which is in a subdirectory that
 579                  * is being replaced with a blob.
 580                  */
 581                 cnt = index_name_pos(&o->result, ce->name, strlen(ce->name));
 582                 if (0 <= cnt) {
 583                         struct cache_entry *ce = o->result.cache[cnt];
 584                         if (ce->ce_flags & CE_REMOVE)
 585                                 return 0;
 586                 }
 587
 588                 return o->gently ? -1 :
 589                         error("Untracked working tree file '%s' "
 590                               "would be %s by merge.", ce->name, action);
 591         }
 592         return 0;
 593 }
 594
 595 static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
 596                 struct unpack_trees_options *o)
 597 {
 598         if (old) {
 599                 /*
 600                  * See if we can re-use the old CE directly?
 601                  * That way we get the uptodate stat info.
 602                  *
 603                  * This also removes the UPDATE flag on
 604                  * a match.
 605                  */
 606                 if (same(old, merge)) {
 607                         copy_cache_entry(merge, old);
 608                 } else {
 609                         if (verify_uptodate(old, o))
 610                                 return -1;
 611                         invalidate_ce_path(old, o);
 612                 }
 613         }
 614         else {
 615                 if (verify_absent(merge, "overwritten", o))
 616                         return -1;
 617                 invalidate_ce_path(merge, o);
 618         }
 619
 620         add_entry(o, merge, CE_UPDATE, CE_STAGEMASK);
 621         return 1;
 622 }
 623
 624 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old,
 625                 struct unpack_trees_options *o)
 626 {
 627         /* Did it exist in the index? */
 628         if (!old) {
 629                 if (verify_absent(ce, "removed", o))
 630                         return -1;
 631                 return 0;
 632         }
 633         if (verify_uptodate(old, o))
 634                 return -1;
 635         add_entry(o, ce, CE_REMOVE, 0);
 636         invalidate_ce_path(ce, o);
 637         return 1;
 638 }
 639
 640 static int keep_entry(struct cache_entry *ce, struct unpack_trees_options *o)
 641 {
 642         add_entry(o, ce, 0, 0);
 643         return 1;
 644 }
 645
 646 #if DBRT_DEBUG
 647 static void show_stage_entry(FILE *o,
 648                              const char *label, const struct cache_entry *ce)
 649 {
 650         if (!ce)
 651                 fprintf(o, "%s (missing)\n", label);
 652         else
 653                 fprintf(o, "%s%06o %s %d\t%s\n",
 654                         label,
 655                         ce->ce_mode,
 656                         sha1_to_hex(ce->sha1),
 657                         ce_stage(ce),
 658                         ce->name);
 659 }
 660 #endif
 661
 662 int threeway_merge(struct cache_entry **stages, struct unpack_trees_options *o)
 663 {
 664         struct cache_entry *index;
 665         struct cache_entry *head;
 666         struct cache_entry *remote = stages[o->head_idx + 1];
 667         int count;
 668         int head_match = 0;
 669         int remote_match = 0;
 670
 671         int df_conflict_head = 0;
 672         int df_conflict_remote = 0;
 673
 674         int any_anc_missing = 0;
 675         int no_anc_exists = 1;
 676         int i;
 677
 678         for (i = 1; i < o->head_idx; i++) {
 679                 if (!stages[i] || stages[i] == o->df_conflict_entry)
 680                         any_anc_missing = 1;
 681                 else
 682                         no_anc_exists = 0;
 683         }
 684
 685         index = stages[0];
 686         head = stages[o->head_idx];
 687
 688         if (head == o->df_conflict_entry) {
 689                 df_conflict_head = 1;
 690                 head = NULL;
 691         }
 692
 693         if (remote == o->df_conflict_entry) {
 694                 df_conflict_remote = 1;
 695                 remote = NULL;
 696         }
 697
 698         /* First, if there's a #16 situation, note that to prevent #13
 699          * and #14.
 700          */
 701         if (!same(remote, head)) {
 702                 for (i = 1; i < o->head_idx; i++) {
 703                         if (same(stages[i], head)) {
 704                                 head_match = i;
 705                         }
 706                         if (same(stages[i], remote)) {
 707                                 remote_match = i;
 708                         }
 709                 }
 710         }
 711
 712         /* We start with cases where the index is allowed to match
 713          * something other than the head: #14(ALT) and #2ALT, where it
 714          * is permitted to match the result instead.
 715          */
 716         /* #14, #14ALT, #2ALT */
 717         if (remote && !df_conflict_head && head_match && !remote_match) {
 718                 if (index && !same(index, remote) && !same(index, head))
 719                         return o->gently ? -1 : reject_merge(index);
 720                 return merged_entry(remote, index, o);
 721         }
 722         /*
 723          * If we have an entry in the index cache, then we want to
 724          * make sure that it matches head.
 725          */
 726         if (index && !same(index, head))
 727                 return o->gently ? -1 : reject_merge(index);
 728
 729         if (head) {
 730                 /* #5ALT, #15 */
 731                 if (same(head, remote))
 732                         return merged_entry(head, index, o);
 733                 /* #13, #3ALT */
 734                 if (!df_conflict_remote && remote_match && !head_match)
 735                         return merged_entry(head, index, o);
 736         }
 737
 738         /* #1 */
 739         if (!head && !remote && any_anc_missing)
 740                 return 0;
 741
 742         /* Under the new "aggressive" rule, we resolve mostly trivial
 743          * cases that we historically had git-merge-one-file resolve.
 744          */
 745         if (o->aggressive) {
 746                 int head_deleted = !head && !df_conflict_head;
 747                 int remote_deleted = !remote && !df_conflict_remote;
 748                 struct cache_entry *ce = NULL;
 749
 750                 if (index)
 751                         ce = index;
 752                 else if (head)
 753                         ce = head;
 754                 else if (remote)
 755                         ce = remote;
 756                 else {
 757                         for (i = 1; i < o->head_idx; i++) {
 758                                 if (stages[i] && stages[i] != o->df_conflict_entry) {
 759                                         ce = stages[i];
 760                                         break;
 761                                 }
 762                         }
 763                 }
 764
 765                 /*
 766                  * Deleted in both.
 767                  * Deleted in one and unchanged in the other.
 768                  */
 769                 if ((head_deleted && remote_deleted) ||
 770                     (head_deleted && remote && remote_match) ||
 771                     (remote_deleted && head && head_match)) {
 772                         if (index)
 773                                 return deleted_entry(index, index, o);
 774                         if (ce && !head_deleted) {
 775                                 if (verify_absent(ce, "removed", o))
 776                                         return -1;
 777                         }
 778                         return 0;
 779                 }
 780                 /*
 781                  * Added in both, identically.
 782                  */
 783                 if (no_anc_exists && head && remote && same(head, remote))
 784                         return merged_entry(head, index, o);
 785
 786         }
 787
 788         /* Below are "no merge" cases, which require that the index be
 789          * up-to-date to avoid the files getting overwritten with
 790          * conflict resolution files.
 791          */
 792         if (index) {
 793                 if (verify_uptodate(index, o))
 794                         return -1;
 795         }
 796
 797         o->nontrivial_merge = 1;
 798
 799         /* #2, #3, #4, #6, #7, #9, #10, #11. */
 800         count = 0;
 801         if (!head_match || !remote_match) {
 802                 for (i = 1; i < o->head_idx; i++) {
 803                         if (stages[i] && stages[i] != o->df_conflict_entry) {
 804                                 keep_entry(stages[i], o);
 805                                 count++;
 806                                 break;
 807                         }
 808                 }
 809         }
 810 #if DBRT_DEBUG
 811         else {
 812                 fprintf(stderr, "read-tree: warning #16 detected\n");
 813                 show_stage_entry(stderr, "head   ", stages[head_match]);
 814                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 815         }
 816 #endif
 817         if (head) { count += keep_entry(head, o); }
 818         if (remote) { count += keep_entry(remote, o); }
 819         return count;
 820 }
 821
 822 /*
 823  * Two-way merge.
 824  *
 825  * The rule is to "carry forward" what is in the index without losing
 826  * information across a "fast forward", favoring a successful merge
 827  * over a merge failure when it makes sense.  For details of the
 828  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 829  *
 830  */
 831 int twoway_merge(struct cache_entry **src, struct unpack_trees_options *o)
 832 {
 833         struct cache_entry *current = src[0];
 834         struct cache_entry *oldtree = src[1];
 835         struct cache_entry *newtree = src[2];
 836
 837         if (o->merge_size != 2)
 838                 return error("Cannot do a twoway merge of %d trees",
 839                              o->merge_size);
 840
 841         if (oldtree == o->df_conflict_entry)
 842                 oldtree = NULL;
 843         if (newtree == o->df_conflict_entry)
 844                 newtree = NULL;
 845
 846         if (current) {
 847                 if ((!oldtree && !newtree) || /* 4 and 5 */
 848                     (!oldtree && newtree &&
 849                      same(current, newtree)) || /* 6 and 7 */
 850                     (oldtree && newtree &&
 851                      same(oldtree, newtree)) || /* 14 and 15 */
 852                     (oldtree && newtree &&
 853                      !same(oldtree, newtree) && /* 18 and 19 */
 854                      same(current, newtree))) {
 855                         return keep_entry(current, o);
 856                 }
 857                 else if (oldtree && !newtree && same(current, oldtree)) {
 858                         /* 10 or 11 */
 859                         return deleted_entry(oldtree, current, o);
 860                 }
 861                 else if (oldtree && newtree &&
 862                          same(current, oldtree) && !same(current, newtree)) {
 863                         /* 20 or 21 */
 864                         return merged_entry(newtree, current, o);
 865                 }
 866                 else {
 867                         /* all other failures */
 868                         if (oldtree)
 869                                 return o->gently ? -1 : reject_merge(oldtree);
 870                         if (current)
 871                                 return o->gently ? -1 : reject_merge(current);
 872                         if (newtree)
 873                                 return o->gently ? -1 : reject_merge(newtree);
 874                         return -1;
 875                 }
 876         }
 877         else if (newtree)
 878                 return merged_entry(newtree, current, o);
 879         return deleted_entry(oldtree, current, o);
 880 }
 881
 882 /*
 883  * Bind merge.
 884  *
 885  * Keep the index entries at stage0, collapse stage1 but make sure
 886  * stage0 does not have anything there.
 887  */
 888 int bind_merge(struct cache_entry **src,
 889                 struct unpack_trees_options *o)
 890 {
 891         struct cache_entry *old = src[0];
 892         struct cache_entry *a = src[1];
 893
 894         if (o->merge_size != 1)
 895                 return error("Cannot do a bind merge of %d trees\n",
 896                              o->merge_size);
 897         if (a && old)
 898                 return o->gently ? -1 :
 899                         error("Entry '%s' overlaps with '%s'.  Cannot bind.", a->name, old->name);
 900         if (!a)
 901                 return keep_entry(old, o);
 902         else
 903                 return merged_entry(a, NULL, o);
 904 }
 905
 906 /*
 907  * One-way merge.
 908  *
 909  * The rule is:
 910  * - take the stat information from stage0, take the data from stage1
 911  */
 912 int oneway_merge(struct cache_entry **src, struct unpack_trees_options *o)
 913 {
 914         struct cache_entry *old = src[0];
 915         struct cache_entry *a = src[1];
 916
 917         if (o->merge_size != 1)
 918                 return error("Cannot do a oneway merge of %d trees",
 919                              o->merge_size);
 920
 921         if (!a)
 922                 return deleted_entry(old, old, o);
 923
 924         if (old && same(old, a)) {
 925                 int update = 0;
 926                 if (o->reset) {
 927                         struct stat st;
 928                         if (lstat(old->name, &st) ||
 929                             ie_match_stat(o->src_index, old, &st, CE_MATCH_IGNORE_VALID))
 930                                 update |= CE_UPDATE;
 931                 }
 932                 add_entry(o, old, update, 0);
 933                 return 0;
 934         }
 935         return merged_entry(a, old, o);
 936 }