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 int 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         int errs = 0;
  65
  66         if (o->update && o->verbose_update) {
  67                 for (total = cnt = 0; cnt < index->cache_nr; cnt++) {
  68                         struct cache_entry *ce = index->cache[cnt];
  69                         if (ce->ce_flags & (CE_UPDATE | CE_REMOVE))
  70                                 total++;
  71                 }
  72
  73                 progress = start_progress_delay("Checking out files",
  74                                                 total, 50, 1);
  75                 cnt = 0;
  76         }
  77
  78         *last_symlink = '\0';
  79         for (i = 0; i < index->cache_nr; i++) {
  80                 struct cache_entry *ce = index->cache[i];
  81
  82                 if (ce->ce_flags & (CE_UPDATE | CE_REMOVE))
  83                         display_progress(progress, ++cnt);
  84                 if (ce->ce_flags & CE_REMOVE) {
  85                         if (o->update)
  86                                 unlink_entry(ce->name, last_symlink);
  87                         remove_index_entry_at(&o->result, i);
  88                         i--;
  89                         continue;
  90                 }
  91                 if (ce->ce_flags & CE_UPDATE) {
  92                         ce->ce_flags &= ~CE_UPDATE;
  93                         if (o->update) {
  94                                 errs |= checkout_entry(ce, &state, NULL);
  95                                 *last_symlink = '\0';
  96                         }
  97                 }
  98         }
  99         stop_progress(&progress);
 100         return errs != 0;
 101 }
 102
 103 static inline int call_unpack_fn(struct cache_entry **src, struct unpack_trees_options *o)
 104 {
 105         int ret = o->fn(src, o);
 106         if (ret > 0)
 107                 ret = 0;
 108         return ret;
 109 }
 110
 111 static int unpack_index_entry(struct cache_entry *ce, struct unpack_trees_options *o)
 112 {
 113         struct cache_entry *src[5] = { ce, };
 114
 115         o->pos++;
 116         if (ce_stage(ce)) {
 117                 if (o->skip_unmerged) {
 118                         add_entry(o, ce, 0, 0);
 119                         return 0;
 120                 }
 121         }
 122         return call_unpack_fn(src, o);
 123 }
 124
 125 int traverse_trees_recursive(int n, unsigned long dirmask, unsigned long df_conflicts, struct name_entry *names, struct traverse_info *info)
 126 {
 127         int i;
 128         struct tree_desc t[MAX_UNPACK_TREES];
 129         struct traverse_info newinfo;
 130         struct name_entry *p;
 131
 132         p = names;
 133         while (!p->mode)
 134                 p++;
 135
 136         newinfo = *info;
 137         newinfo.prev = info;
 138         newinfo.name = *p;
 139         newinfo.pathlen += tree_entry_len(p->path, p->sha1) + 1;
 140         newinfo.conflicts |= df_conflicts;
 141
 142         for (i = 0; i < n; i++, dirmask >>= 1) {
 143                 const unsigned char *sha1 = NULL;
 144                 if (dirmask & 1)
 145                         sha1 = names[i].sha1;
 146                 fill_tree_descriptor(t+i, sha1);
 147         }
 148         return traverse_trees(n, t, &newinfo);
 149 }
 150
 151 /*
 152  * Compare the traverse-path to the cache entry without actually
 153  * having to generate the textual representation of the traverse
 154  * path.
 155  *
 156  * NOTE! This *only* compares up to the size of the traverse path
 157  * itself - the caller needs to do the final check for the cache
 158  * entry having more data at the end!
 159  */
 160 static int do_compare_entry(const struct cache_entry *ce, const struct traverse_info *info, const struct name_entry *n)
 161 {
 162         int len, pathlen, ce_len;
 163         const char *ce_name;
 164
 165         if (info->prev) {
 166                 int cmp = do_compare_entry(ce, info->prev, &info->name);
 167                 if (cmp)
 168                         return cmp;
 169         }
 170         pathlen = info->pathlen;
 171         ce_len = ce_namelen(ce);
 172
 173         /* If ce_len < pathlen then we must have previously hit "name == directory" entry */
 174         if (ce_len < pathlen)
 175                 return -1;
 176
 177         ce_len -= pathlen;
 178         ce_name = ce->name + pathlen;
 179
 180         len = tree_entry_len(n->path, n->sha1);
 181         return df_name_compare(ce_name, ce_len, S_IFREG, n->path, len, n->mode);
 182 }
 183
 184 static int compare_entry(const struct cache_entry *ce, const struct traverse_info *info, const struct name_entry *n)
 185 {
 186         int cmp = do_compare_entry(ce, info, n);
 187         if (cmp)
 188                 return cmp;
 189
 190         /*
 191          * Even if the beginning compared identically, the ce should
 192          * compare as bigger than a directory leading up to it!
 193          */
 194         return ce_namelen(ce) > traverse_path_len(info, n);
 195 }
 196
 197 static struct cache_entry *create_ce_entry(const struct traverse_info *info, const struct name_entry *n, int stage)
 198 {
 199         int len = traverse_path_len(info, n);
 200         struct cache_entry *ce = xcalloc(1, cache_entry_size(len));
 201
 202         ce->ce_mode = create_ce_mode(n->mode);
 203         ce->ce_flags = create_ce_flags(len, stage);
 204         hashcpy(ce->sha1, n->sha1);
 205         make_traverse_path(ce->name, info, n);
 206
 207         return ce;
 208 }
 209
 210 static int unpack_nondirectories(int n, unsigned long mask, unsigned long dirmask, struct cache_entry *src[5],
 211         const struct name_entry *names, const struct traverse_info *info)
 212 {
 213         int i;
 214         struct unpack_trees_options *o = info->data;
 215         unsigned long conflicts;
 216
 217         /* Do we have *only* directories? Nothing to do */
 218         if (mask == dirmask && !src[0])
 219                 return 0;
 220
 221         conflicts = info->conflicts;
 222         if (o->merge)
 223                 conflicts >>= 1;
 224         conflicts |= dirmask;
 225
 226         /*
 227          * Ok, we've filled in up to any potential index entry in src[0],
 228          * now do the rest.
 229          */
 230         for (i = 0; i < n; i++) {
 231                 int stage;
 232                 unsigned int bit = 1ul << i;
 233                 if (conflicts & bit) {
 234                         src[i + o->merge] = o->df_conflict_entry;
 235                         continue;
 236                 }
 237                 if (!(mask & bit))
 238                         continue;
 239                 if (!o->merge)
 240                         stage = 0;
 241                 else if (i + 1 < o->head_idx)
 242                         stage = 1;
 243                 else if (i + 1 > o->head_idx)
 244                         stage = 3;
 245                 else
 246                         stage = 2;
 247                 src[i + o->merge] = create_ce_entry(info, names + i, stage);
 248         }
 249
 250         if (o->merge)
 251                 return call_unpack_fn(src, o);
 252
 253         n += o->merge;
 254         for (i = 0; i < n; i++)
 255                 add_entry(o, src[i], 0, 0);
 256         return 0;
 257 }
 258
 259 static int unpack_callback(int n, unsigned long mask, unsigned long dirmask, struct name_entry *names, struct traverse_info *info)
 260 {
 261         struct cache_entry *src[5] = { NULL, };
 262         struct unpack_trees_options *o = info->data;
 263         const struct name_entry *p = names;
 264
 265         /* Find first entry with a real name (we could use "mask" too) */
 266         while (!p->mode)
 267                 p++;
 268
 269         /* Are we supposed to look at the index too? */
 270         if (o->merge) {
 271                 while (o->pos < o->src_index->cache_nr) {
 272                         struct cache_entry *ce = o->src_index->cache[o->pos];
 273                         int cmp = compare_entry(ce, info, p);
 274                         if (cmp < 0) {
 275                                 if (unpack_index_entry(ce, o) < 0)
 276                                         return -1;
 277                                 continue;
 278                         }
 279                         if (!cmp) {
 280                                 o->pos++;
 281                                 if (ce_stage(ce)) {
 282                                         /*
 283                                          * If we skip unmerged index entries, we'll skip this
 284                                          * entry *and* the tree entries associated with it!
 285                                          */
 286                                         if (o->skip_unmerged) {
 287                                                 add_entry(o, ce, 0, 0);
 288                                                 return mask;
 289                                         }
 290                                 }
 291                                 src[0] = ce;
 292                         }
 293                         break;
 294                 }
 295         }
 296
 297         if (unpack_nondirectories(n, mask, dirmask, src, names, info) < 0)
 298                 return -1;
 299
 300         /* Now handle any directories.. */
 301         if (dirmask) {
 302                 unsigned long conflicts = mask & ~dirmask;
 303                 if (o->merge) {
 304                         conflicts <<= 1;
 305                         if (src[0])
 306                                 conflicts |= 1;
 307                 }
 308                 if (traverse_trees_recursive(n, dirmask, conflicts,
 309                                              names, info) < 0)
 310                         return -1;
 311                 return mask;
 312         }
 313
 314         return mask;
 315 }
 316
 317 static int unpack_failed(struct unpack_trees_options *o, const char *message)
 318 {
 319         discard_index(&o->result);
 320         if (!o->gently) {
 321                 if (message)
 322                         return error(message);
 323                 return -1;
 324         }
 325         return -1;
 326 }
 327
 328 int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options *o)
 329 {
 330         static struct cache_entry *dfc;
 331
 332         if (len > MAX_UNPACK_TREES)
 333                 die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
 334         memset(&state, 0, sizeof(state));
 335         state.base_dir = "";
 336         state.force = 1;
 337         state.quiet = 1;
 338         state.refresh_cache = 1;
 339
 340         memset(&o->result, 0, sizeof(o->result));
 341         if (o->src_index)
 342                 o->result.timestamp = o->src_index->timestamp;
 343         o->merge_size = len;
 344
 345         if (!dfc)
 346                 dfc = xcalloc(1, sizeof(struct cache_entry) + 1);
 347         o->df_conflict_entry = dfc;
 348
 349         if (len) {
 350                 const char *prefix = o->prefix ? o->prefix : "";
 351                 struct traverse_info info;
 352
 353                 setup_traverse_info(&info, prefix);
 354                 info.fn = unpack_callback;
 355                 info.data = o;
 356
 357                 if (traverse_trees(len, t, &info) < 0)
 358                         return unpack_failed(o, NULL);
 359         }
 360
 361         /* Any left-over entries in the index? */
 362         if (o->merge) {
 363                 while (o->pos < o->src_index->cache_nr) {
 364                         struct cache_entry *ce = o->src_index->cache[o->pos];
 365                         if (unpack_index_entry(ce, o) < 0)
 366                                 return unpack_failed(o, NULL);
 367                 }
 368         }
 369
 370         if (o->trivial_merges_only && o->nontrivial_merge)
 371                 return unpack_failed(o, "Merge requires file-level merging");
 372
 373         o->src_index = NULL;
 374         if (check_updates(o))
 375                 return -1;
 376         if (o->dst_index)
 377                 *o->dst_index = o->result;
 378         return 0;
 379 }
 380
 381 /* Here come the merge functions */
 382
 383 static int reject_merge(struct cache_entry *ce)
 384 {
 385         return error("Entry '%s' would be overwritten by merge. Cannot merge.",
 386                      ce->name);
 387 }
 388
 389 static int same(struct cache_entry *a, struct cache_entry *b)
 390 {
 391         if (!!a != !!b)
 392                 return 0;
 393         if (!a && !b)
 394                 return 1;
 395         return a->ce_mode == b->ce_mode &&
 396                !hashcmp(a->sha1, b->sha1);
 397 }
 398
 399
 400 /*
 401  * When a CE gets turned into an unmerged entry, we
 402  * want it to be up-to-date
 403  */
 404 static int verify_uptodate(struct cache_entry *ce,
 405                 struct unpack_trees_options *o)
 406 {
 407         struct stat st;
 408
 409         if (o->index_only || o->reset)
 410                 return 0;
 411
 412         if (!lstat(ce->name, &st)) {
 413                 unsigned changed = ie_match_stat(o->src_index, ce, &st, CE_MATCH_IGNORE_VALID);
 414                 if (!changed)
 415                         return 0;
 416                 /*
 417                  * NEEDSWORK: the current default policy is to allow
 418                  * submodule to be out of sync wrt the supermodule
 419                  * index.  This needs to be tightened later for
 420                  * submodules that are marked to be automatically
 421                  * checked out.
 422                  */
 423                 if (S_ISGITLINK(ce->ce_mode))
 424                         return 0;
 425                 errno = 0;
 426         }
 427         if (errno == ENOENT)
 428                 return 0;
 429         return o->gently ? -1 :
 430                 error("Entry '%s' not uptodate. Cannot merge.", ce->name);
 431 }
 432
 433 static void invalidate_ce_path(struct cache_entry *ce, struct unpack_trees_options *o)
 434 {
 435         if (ce)
 436                 cache_tree_invalidate_path(o->src_index->cache_tree, ce->name);
 437 }
 438
 439 /*
 440  * Check that checking out ce->sha1 in subdir ce->name is not
 441  * going to overwrite any working files.
 442  *
 443  * Currently, git does not checkout subprojects during a superproject
 444  * checkout, so it is not going to overwrite anything.
 445  */
 446 static int verify_clean_submodule(struct cache_entry *ce, const char *action,
 447                                       struct unpack_trees_options *o)
 448 {
 449         return 0;
 450 }
 451
 452 static int verify_clean_subdirectory(struct cache_entry *ce, const char *action,
 453                                       struct unpack_trees_options *o)
 454 {
 455         /*
 456          * we are about to extract "ce->name"; we would not want to lose
 457          * anything in the existing directory there.
 458          */
 459         int namelen;
 460         int pos, i;
 461         struct dir_struct d;
 462         char *pathbuf;
 463         int cnt = 0;
 464         unsigned char sha1[20];
 465
 466         if (S_ISGITLINK(ce->ce_mode) &&
 467             resolve_gitlink_ref(ce->name, "HEAD", sha1) == 0) {
 468                 /* If we are not going to update the submodule, then
 469                  * we don't care.
 470                  */
 471                 if (!hashcmp(sha1, ce->sha1))
 472                         return 0;
 473                 return verify_clean_submodule(ce, action, o);
 474         }
 475
 476         /*
 477          * First let's make sure we do not have a local modification
 478          * in that directory.
 479          */
 480         namelen = strlen(ce->name);
 481         pos = index_name_pos(o->src_index, ce->name, namelen);
 482         if (0 <= pos)
 483                 return cnt; /* we have it as nondirectory */
 484         pos = -pos - 1;
 485         for (i = pos; i < o->src_index->cache_nr; i++) {
 486                 struct cache_entry *ce = o->src_index->cache[i];
 487                 int len = ce_namelen(ce);
 488                 if (len < namelen ||
 489                     strncmp(ce->name, ce->name, namelen) ||
 490                     ce->name[namelen] != '/')
 491                         break;
 492                 /*
 493                  * ce->name is an entry in the subdirectory.
 494                  */
 495                 if (!ce_stage(ce)) {
 496                         if (verify_uptodate(ce, o))
 497                                 return -1;
 498                         add_entry(o, ce, CE_REMOVE, 0);
 499                 }
 500                 cnt++;
 501         }
 502
 503         /*
 504          * Then we need to make sure that we do not lose a locally
 505          * present file that is not ignored.
 506          */
 507         pathbuf = xmalloc(namelen + 2);
 508         memcpy(pathbuf, ce->name, namelen);
 509         strcpy(pathbuf+namelen, "/");
 510
 511         memset(&d, 0, sizeof(d));
 512         if (o->dir)
 513                 d.exclude_per_dir = o->dir->exclude_per_dir;
 514         i = read_directory(&d, ce->name, pathbuf, namelen+1, NULL);
 515         if (i)
 516                 return o->gently ? -1 :
 517                         error("Updating '%s' would lose untracked files in it",
 518                               ce->name);
 519         free(pathbuf);
 520         return cnt;
 521 }
 522
 523 /*
 524  * We do not want to remove or overwrite a working tree file that
 525  * is not tracked, unless it is ignored.
 526  */
 527 static int verify_absent(struct cache_entry *ce, const char *action,
 528                          struct unpack_trees_options *o)
 529 {
 530         struct stat st;
 531
 532         if (o->index_only || o->reset || !o->update)
 533                 return 0;
 534
 535         if (has_symlink_leading_path(ce->name, NULL))
 536                 return 0;
 537
 538         if (!lstat(ce->name, &st)) {
 539                 int cnt;
 540                 int dtype = ce_to_dtype(ce);
 541
 542                 if (o->dir && excluded(o->dir, ce->name, &dtype))
 543                         /*
 544                          * ce->name is explicitly excluded, so it is Ok to
 545                          * overwrite it.
 546                          */
 547                         return 0;
 548                 if (S_ISDIR(st.st_mode)) {
 549                         /*
 550                          * We are checking out path "foo" and
 551                          * found "foo/." in the working tree.
 552                          * This is tricky -- if we have modified
 553                          * files that are in "foo/" we would lose
 554                          * it.
 555                          */
 556                         cnt = verify_clean_subdirectory(ce, action, o);
 557
 558                         /*
 559                          * If this removed entries from the index,
 560                          * what that means is:
 561                          *
 562                          * (1) the caller unpack_trees_rec() saw path/foo
 563                          * in the index, and it has not removed it because
 564                          * it thinks it is handling 'path' as blob with
 565                          * D/F conflict;
 566                          * (2) we will return "ok, we placed a merged entry
 567                          * in the index" which would cause o->pos to be
 568                          * incremented by one;
 569                          * (3) however, original o->pos now has 'path/foo'
 570                          * marked with "to be removed".
 571                          *
 572                          * We need to increment it by the number of
 573                          * deleted entries here.
 574                          */
 575                         o->pos += cnt;
 576                         return 0;
 577                 }
 578
 579                 /*
 580                  * The previous round may already have decided to
 581                  * delete this path, which is in a subdirectory that
 582                  * is being replaced with a blob.
 583                  */
 584                 cnt = index_name_pos(&o->result, ce->name, strlen(ce->name));
 585                 if (0 <= cnt) {
 586                         struct cache_entry *ce = o->result.cache[cnt];
 587                         if (ce->ce_flags & CE_REMOVE)
 588                                 return 0;
 589                 }
 590
 591                 return o->gently ? -1 :
 592                         error("Untracked working tree file '%s' "
 593                               "would be %s by merge.", ce->name, action);
 594         }
 595         return 0;
 596 }
 597
 598 static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
 599                 struct unpack_trees_options *o)
 600 {
 601         int update = CE_UPDATE;
 602
 603         if (old) {
 604                 /*
 605                  * See if we can re-use the old CE directly?
 606                  * That way we get the uptodate stat info.
 607                  *
 608                  * This also removes the UPDATE flag on a match; otherwise
 609                  * we will end up overwriting local changes in the work tree.
 610                  */
 611                 if (same(old, merge)) {
 612                         copy_cache_entry(merge, old);
 613                         update = 0;
 614                 } else {
 615                         if (verify_uptodate(old, o))
 616                                 return -1;
 617                         invalidate_ce_path(old, o);
 618                 }
 619         }
 620         else {
 621                 if (verify_absent(merge, "overwritten", o))
 622                         return -1;
 623                 invalidate_ce_path(merge, o);
 624         }
 625
 626         add_entry(o, merge, update, CE_STAGEMASK);
 627         return 1;
 628 }
 629
 630 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old,
 631                 struct unpack_trees_options *o)
 632 {
 633         /* Did it exist in the index? */
 634         if (!old) {
 635                 if (verify_absent(ce, "removed", o))
 636                         return -1;
 637                 return 0;
 638         }
 639         if (verify_uptodate(old, o))
 640                 return -1;
 641         add_entry(o, ce, CE_REMOVE, 0);
 642         invalidate_ce_path(ce, o);
 643         return 1;
 644 }
 645
 646 static int keep_entry(struct cache_entry *ce, struct unpack_trees_options *o)
 647 {
 648         add_entry(o, ce, 0, 0);
 649         return 1;
 650 }
 651
 652 #if DBRT_DEBUG
 653 static void show_stage_entry(FILE *o,
 654                              const char *label, const struct cache_entry *ce)
 655 {
 656         if (!ce)
 657                 fprintf(o, "%s (missing)\n", label);
 658         else
 659                 fprintf(o, "%s%06o %s %d\t%s\n",
 660                         label,
 661                         ce->ce_mode,
 662                         sha1_to_hex(ce->sha1),
 663                         ce_stage(ce),
 664                         ce->name);
 665 }
 666 #endif
 667
 668 int threeway_merge(struct cache_entry **stages, struct unpack_trees_options *o)
 669 {
 670         struct cache_entry *index;
 671         struct cache_entry *head;
 672         struct cache_entry *remote = stages[o->head_idx + 1];
 673         int count;
 674         int head_match = 0;
 675         int remote_match = 0;
 676
 677         int df_conflict_head = 0;
 678         int df_conflict_remote = 0;
 679
 680         int any_anc_missing = 0;
 681         int no_anc_exists = 1;
 682         int i;
 683
 684         for (i = 1; i < o->head_idx; i++) {
 685                 if (!stages[i] || stages[i] == o->df_conflict_entry)
 686                         any_anc_missing = 1;
 687                 else
 688                         no_anc_exists = 0;
 689         }
 690
 691         index = stages[0];
 692         head = stages[o->head_idx];
 693
 694         if (head == o->df_conflict_entry) {
 695                 df_conflict_head = 1;
 696                 head = NULL;
 697         }
 698
 699         if (remote == o->df_conflict_entry) {
 700                 df_conflict_remote = 1;
 701                 remote = NULL;
 702         }
 703
 704         /* First, if there's a #16 situation, note that to prevent #13
 705          * and #14.
 706          */
 707         if (!same(remote, head)) {
 708                 for (i = 1; i < o->head_idx; i++) {
 709                         if (same(stages[i], head)) {
 710                                 head_match = i;
 711                         }
 712                         if (same(stages[i], remote)) {
 713                                 remote_match = i;
 714                         }
 715                 }
 716         }
 717
 718         /* We start with cases where the index is allowed to match
 719          * something other than the head: #14(ALT) and #2ALT, where it
 720          * is permitted to match the result instead.
 721          */
 722         /* #14, #14ALT, #2ALT */
 723         if (remote && !df_conflict_head && head_match && !remote_match) {
 724                 if (index && !same(index, remote) && !same(index, head))
 725                         return o->gently ? -1 : reject_merge(index);
 726                 return merged_entry(remote, index, o);
 727         }
 728         /*
 729          * If we have an entry in the index cache, then we want to
 730          * make sure that it matches head.
 731          */
 732         if (index && !same(index, head))
 733                 return o->gently ? -1 : reject_merge(index);
 734
 735         if (head) {
 736                 /* #5ALT, #15 */
 737                 if (same(head, remote))
 738                         return merged_entry(head, index, o);
 739                 /* #13, #3ALT */
 740                 if (!df_conflict_remote && remote_match && !head_match)
 741                         return merged_entry(head, index, o);
 742         }
 743
 744         /* #1 */
 745         if (!head && !remote && any_anc_missing)
 746                 return 0;
 747
 748         /* Under the new "aggressive" rule, we resolve mostly trivial
 749          * cases that we historically had git-merge-one-file resolve.
 750          */
 751         if (o->aggressive) {
 752                 int head_deleted = !head && !df_conflict_head;
 753                 int remote_deleted = !remote && !df_conflict_remote;
 754                 struct cache_entry *ce = NULL;
 755
 756                 if (index)
 757                         ce = index;
 758                 else if (head)
 759                         ce = head;
 760                 else if (remote)
 761                         ce = remote;
 762                 else {
 763                         for (i = 1; i < o->head_idx; i++) {
 764                                 if (stages[i] && stages[i] != o->df_conflict_entry) {
 765                                         ce = stages[i];
 766                                         break;
 767                                 }
 768                         }
 769                 }
 770
 771                 /*
 772                  * Deleted in both.
 773                  * Deleted in one and unchanged in the other.
 774                  */
 775                 if ((head_deleted && remote_deleted) ||
 776                     (head_deleted && remote && remote_match) ||
 777                     (remote_deleted && head && head_match)) {
 778                         if (index)
 779                                 return deleted_entry(index, index, o);
 780                         if (ce && !head_deleted) {
 781                                 if (verify_absent(ce, "removed", o))
 782                                         return -1;
 783                         }
 784                         return 0;
 785                 }
 786                 /*
 787                  * Added in both, identically.
 788                  */
 789                 if (no_anc_exists && head && remote && same(head, remote))
 790                         return merged_entry(head, index, o);
 791
 792         }
 793
 794         /* Below are "no merge" cases, which require that the index be
 795          * up-to-date to avoid the files getting overwritten with
 796          * conflict resolution files.
 797          */
 798         if (index) {
 799                 if (verify_uptodate(index, o))
 800                         return -1;
 801         }
 802
 803         o->nontrivial_merge = 1;
 804
 805         /* #2, #3, #4, #6, #7, #9, #10, #11. */
 806         count = 0;
 807         if (!head_match || !remote_match) {
 808                 for (i = 1; i < o->head_idx; i++) {
 809                         if (stages[i] && stages[i] != o->df_conflict_entry) {
 810                                 keep_entry(stages[i], o);
 811                                 count++;
 812                                 break;
 813                         }
 814                 }
 815         }
 816 #if DBRT_DEBUG
 817         else {
 818                 fprintf(stderr, "read-tree: warning #16 detected\n");
 819                 show_stage_entry(stderr, "head   ", stages[head_match]);
 820                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 821         }
 822 #endif
 823         if (head) { count += keep_entry(head, o); }
 824         if (remote) { count += keep_entry(remote, o); }
 825         return count;
 826 }
 827
 828 /*
 829  * Two-way merge.
 830  *
 831  * The rule is to "carry forward" what is in the index without losing
 832  * information across a "fast forward", favoring a successful merge
 833  * over a merge failure when it makes sense.  For details of the
 834  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 835  *
 836  */
 837 int twoway_merge(struct cache_entry **src, struct unpack_trees_options *o)
 838 {
 839         struct cache_entry *current = src[0];
 840         struct cache_entry *oldtree = src[1];
 841         struct cache_entry *newtree = src[2];
 842
 843         if (o->merge_size != 2)
 844                 return error("Cannot do a twoway merge of %d trees",
 845                              o->merge_size);
 846
 847         if (oldtree == o->df_conflict_entry)
 848                 oldtree = NULL;
 849         if (newtree == o->df_conflict_entry)
 850                 newtree = NULL;
 851
 852         if (current) {
 853                 if ((!oldtree && !newtree) || /* 4 and 5 */
 854                     (!oldtree && newtree &&
 855                      same(current, newtree)) || /* 6 and 7 */
 856                     (oldtree && newtree &&
 857                      same(oldtree, newtree)) || /* 14 and 15 */
 858                     (oldtree && newtree &&
 859                      !same(oldtree, newtree) && /* 18 and 19 */
 860                      same(current, newtree))) {
 861                         return keep_entry(current, o);
 862                 }
 863                 else if (oldtree && !newtree && same(current, oldtree)) {
 864                         /* 10 or 11 */
 865                         return deleted_entry(oldtree, current, o);
 866                 }
 867                 else if (oldtree && newtree &&
 868                          same(current, oldtree) && !same(current, newtree)) {
 869                         /* 20 or 21 */
 870                         return merged_entry(newtree, current, o);
 871                 }
 872                 else {
 873                         /* all other failures */
 874                         if (oldtree)
 875                                 return o->gently ? -1 : reject_merge(oldtree);
 876                         if (current)
 877                                 return o->gently ? -1 : reject_merge(current);
 878                         if (newtree)
 879                                 return o->gently ? -1 : reject_merge(newtree);
 880                         return -1;
 881                 }
 882         }
 883         else if (newtree)
 884                 return merged_entry(newtree, current, o);
 885         return deleted_entry(oldtree, current, o);
 886 }
 887
 888 /*
 889  * Bind merge.
 890  *
 891  * Keep the index entries at stage0, collapse stage1 but make sure
 892  * stage0 does not have anything there.
 893  */
 894 int bind_merge(struct cache_entry **src,
 895                 struct unpack_trees_options *o)
 896 {
 897         struct cache_entry *old = src[0];
 898         struct cache_entry *a = src[1];
 899
 900         if (o->merge_size != 1)
 901                 return error("Cannot do a bind merge of %d trees\n",
 902                              o->merge_size);
 903         if (a && old)
 904                 return o->gently ? -1 :
 905                         error("Entry '%s' overlaps with '%s'.  Cannot bind.", a->name, old->name);
 906         if (!a)
 907                 return keep_entry(old, o);
 908         else
 909                 return merged_entry(a, NULL, o);
 910 }
 911
 912 /*
 913  * One-way merge.
 914  *
 915  * The rule is:
 916  * - take the stat information from stage0, take the data from stage1
 917  */
 918 int oneway_merge(struct cache_entry **src, struct unpack_trees_options *o)
 919 {
 920         struct cache_entry *old = src[0];
 921         struct cache_entry *a = src[1];
 922
 923         if (o->merge_size != 1)
 924                 return error("Cannot do a oneway merge of %d trees",
 925                              o->merge_size);
 926
 927         if (!a)
 928                 return deleted_entry(old, old, o);
 929
 930         if (old && same(old, a)) {
 931                 int update = 0;
 932                 if (o->reset) {
 933                         struct stat st;
 934                         if (lstat(old->name, &st) ||
 935                             ie_match_stat(o->src_index, old, &st, CE_MATCH_IGNORE_VALID))
 936                                 update |= CE_UPDATE;
 937                 }
 938                 add_entry(o, old, update, 0);
 939                 return 0;
 940         }
 941         return merged_entry(a, old, o);
 942 }