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 *tree)
  20 {
  21         struct tree_desc desc;
  22         struct name_entry one;
  23         struct tree_entry_list *ret = NULL;
  24         struct tree_entry_list **list_p = &ret;
  25
  26         if (!tree->object.parsed)
  27                 parse_tree(tree);
  28
  29         init_tree_desc(&desc, tree->buffer, tree->size);
  30
  31         while (tree_entry(&desc, &one)) {
  32                 struct tree_entry_list *entry;
  33
  34                 entry = xmalloc(sizeof(struct tree_entry_list));
  35                 entry->name = one.path;
  36                 entry->sha1 = one.sha1;
  37                 entry->mode = one.mode;
  38                 entry->next = NULL;
  39
  40                 *list_p = entry;
  41                 list_p = &entry->next;
  42         }
  43         return ret;
  44 }
  45
  46 static int entcmp(const char *name1, int dir1, const char *name2, int dir2)
  47 {
  48         int len1 = strlen(name1);
  49         int len2 = strlen(name2);
  50         int len = len1 < len2 ? len1 : len2;
  51         int ret = memcmp(name1, name2, len);
  52         unsigned char c1, c2;
  53         if (ret)
  54                 return ret;
  55         c1 = name1[len];
  56         c2 = name2[len];
  57         if (!c1 && dir1)
  58                 c1 = '/';
  59         if (!c2 && dir2)
  60                 c2 = '/';
  61         ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
  62         if (c1 && c2 && !ret)
  63                 ret = len1 - len2;
  64         return ret;
  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 baselen = strlen(base);
  72         int src_size = len + 1;
  73         int i_stk = i_stk;
  74         int retval = 0;
  75
  76         if (o->dir)
  77                 i_stk = push_exclude_per_directory(o->dir, base, strlen(base));
  78
  79         do {
  80                 int i;
  81                 const char *first;
  82                 int firstdir = 0;
  83                 int pathlen;
  84                 unsigned ce_size;
  85                 struct tree_entry_list **subposns;
  86                 struct cache_entry **src;
  87                 int any_files = 0;
  88                 int any_dirs = 0;
  89                 char *cache_name;
  90                 int ce_stage;
  91
  92                 /* Find the first name in the input. */
  93
  94                 first = NULL;
  95                 cache_name = NULL;
  96
  97                 /* Check the cache */
  98                 if (o->merge && o->pos < active_nr) {
  99                         /* This is a bit tricky: */
 100                         /* If the index has a subdirectory (with
 101                          * contents) as the first name, it'll get a
 102                          * filename like "foo/bar". But that's after
 103                          * "foo", so the entry in trees will get
 104                          * handled first, at which point we'll go into
 105                          * "foo", and deal with "bar" from the index,
 106                          * because the base will be "foo/". The only
 107                          * way we can actually have "foo/bar" first of
 108                          * all the things is if the trees don't
 109                          * contain "foo" at all, in which case we'll
 110                          * handle "foo/bar" without going into the
 111                          * directory, but that's fine (and will return
 112                          * an error anyway, with the added unknown
 113                          * file case.
 114                          */
 115
 116                         cache_name = active_cache[o->pos]->name;
 117                         if (strlen(cache_name) > baselen &&
 118                             !memcmp(cache_name, base, baselen)) {
 119                                 cache_name += baselen;
 120                                 first = cache_name;
 121                         } else {
 122                                 cache_name = NULL;
 123                         }
 124                 }
 125
 126 #if DBRT_DEBUG > 1
 127                 if (first)
 128                         printf("index %s\n", first);
 129 #endif
 130                 for (i = 0; i < len; i++) {
 131                         if (!posns[i] || posns[i] == df_conflict_list)
 132                                 continue;
 133 #if DBRT_DEBUG > 1
 134                         printf("%d %s\n", i + 1, posns[i]->name);
 135 #endif
 136                         if (!first || entcmp(first, firstdir,
 137                                              posns[i]->name,
 138                                              S_ISDIR(posns[i]->mode)) > 0) {
 139                                 first = posns[i]->name;
 140                                 firstdir = S_ISDIR(posns[i]->mode);
 141                         }
 142                 }
 143                 /* No name means we're done */
 144                 if (!first)
 145                         goto leave_directory;
 146
 147                 pathlen = strlen(first);
 148                 ce_size = cache_entry_size(baselen + pathlen);
 149
 150                 src = xcalloc(src_size, sizeof(struct cache_entry *));
 151
 152                 subposns = xcalloc(len, sizeof(struct tree_list_entry *));
 153
 154                 if (cache_name && !strcmp(cache_name, first)) {
 155                         any_files = 1;
 156                         src[0] = active_cache[o->pos];
 157                         remove_cache_entry_at(o->pos);
 158                 }
 159
 160                 for (i = 0; i < len; i++) {
 161                         struct cache_entry *ce;
 162
 163                         if (!posns[i] ||
 164                             (posns[i] != df_conflict_list &&
 165                              strcmp(first, posns[i]->name))) {
 166                                 continue;
 167                         }
 168
 169                         if (posns[i] == df_conflict_list) {
 170                                 src[i + o->merge] = o->df_conflict_entry;
 171                                 continue;
 172                         }
 173
 174                         if (S_ISDIR(posns[i]->mode)) {
 175                                 struct tree *tree = lookup_tree(posns[i]->sha1);
 176                                 any_dirs = 1;
 177                                 parse_tree(tree);
 178                                 subposns[i] = create_tree_entry_list(tree);
 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);
 222
 223 #if DBRT_DEBUG > 1
 224                                 printf("Added %d entries\n", ret);
 225 #endif
 226                                 o->pos += ret;
 227                         } else {
 228                                 for (i = 0; i < src_size; i++) {
 229                                         if (src[i]) {
 230                                                 add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
 231                                         }
 232                                 }
 233                         }
 234                 }
 235                 if (any_dirs) {
 236                         char *newbase = xmalloc(baselen + 2 + pathlen);
 237                         memcpy(newbase, base, baselen);
 238                         memcpy(newbase + baselen, first, pathlen);
 239                         newbase[baselen + pathlen] = '/';
 240                         newbase[baselen + pathlen + 1] = '\0';
 241                         if (unpack_trees_rec(subposns, len, newbase, o,
 242                                              df_conflict_list)) {
 243                                 retval = -1;
 244                                 goto leave_directory;
 245                         }
 246                         free(newbase);
 247                 }
 248                 free(subposns);
 249                 free(src);
 250         } while (1);
 251
 252  leave_directory:
 253         if (o->dir)
 254                 pop_exclude_per_directory(o->dir, i_stk);
 255         return retval;
 256 }
 257
 258 /* Unlink the last component and attempt to remove leading
 259  * directories, in case this unlink is the removal of the
 260  * last entry in the directory -- empty directories are removed.
 261  */
 262 static void unlink_entry(char *name, char *last_symlink)
 263 {
 264         char *cp, *prev;
 265
 266         if (has_symlink_leading_path(name, last_symlink))
 267                 return;
 268         if (unlink(name))
 269                 return;
 270         prev = NULL;
 271         while (1) {
 272                 int status;
 273                 cp = strrchr(name, '/');
 274                 if (prev)
 275                         *prev = '/';
 276                 if (!cp)
 277                         break;
 278
 279                 *cp = 0;
 280                 status = rmdir(name);
 281                 if (status) {
 282                         *cp = '/';
 283                         break;
 284                 }
 285                 prev = cp;
 286         }
 287 }
 288
 289 static struct checkout state;
 290 static void check_updates(struct cache_entry **src, int nr,
 291                         struct unpack_trees_options *o)
 292 {
 293         unsigned short mask = htons(CE_UPDATE);
 294         unsigned cnt = 0, total = 0;
 295         struct progress progress;
 296         char last_symlink[PATH_MAX];
 297
 298         if (o->update && o->verbose_update) {
 299                 for (total = cnt = 0; cnt < nr; cnt++) {
 300                         struct cache_entry *ce = src[cnt];
 301                         if (!ce->ce_mode || ce->ce_flags & mask)
 302                                 total++;
 303                 }
 304
 305                 start_progress_delay(&progress, "Checking %u files out...",
 306                                      "", total, 50, 2);
 307                 cnt = 0;
 308         }
 309
 310         *last_symlink = '\0';
 311         while (nr--) {
 312                 struct cache_entry *ce = *src++;
 313
 314                 if (total)
 315                         if (!ce->ce_mode || ce->ce_flags & mask)
 316                                 display_progress(&progress, ++cnt);
 317                 if (!ce->ce_mode) {
 318                         if (o->update)
 319                                 unlink_entry(ce->name, last_symlink);
 320                         continue;
 321                 }
 322                 if (ce->ce_flags & mask) {
 323                         ce->ce_flags &= ~mask;
 324                         if (o->update) {
 325                                 checkout_entry(ce, &state, NULL);
 326                                 *last_symlink = '\0';
 327                         }
 328                 }
 329         }
 330         if (total)
 331                 stop_progress(&progress);;
 332 }
 333
 334 int unpack_trees(struct object_list *trees, struct unpack_trees_options *o)
 335 {
 336         unsigned len = object_list_length(trees);
 337         struct tree_entry_list **posns;
 338         int i;
 339         struct object_list *posn = trees;
 340         struct tree_entry_list df_conflict_list;
 341         static struct cache_entry *dfc;
 342
 343         memset(&df_conflict_list, 0, sizeof(df_conflict_list));
 344         df_conflict_list.next = &df_conflict_list;
 345         memset(&state, 0, sizeof(state));
 346         state.base_dir = "";
 347         state.force = 1;
 348         state.quiet = 1;
 349         state.refresh_cache = 1;
 350
 351         o->merge_size = len;
 352
 353         if (!dfc)
 354                 dfc = xcalloc(1, sizeof(struct cache_entry) + 1);
 355         o->df_conflict_entry = dfc;
 356
 357         if (len) {
 358                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
 359                 for (i = 0; i < len; i++) {
 360                         posns[i] = create_tree_entry_list((struct tree *) posn->item);
 361                         posn = posn->next;
 362                 }
 363                 if (unpack_trees_rec(posns, len, o->prefix ? o->prefix : "",
 364                                      o, &df_conflict_list))
 365                         return -1;
 366         }
 367
 368         if (o->trivial_merges_only && o->nontrivial_merge)
 369                 die("Merge requires file-level merging");
 370
 371         check_updates(active_cache, active_nr, o);
 372         return 0;
 373 }
 374
 375 /* Here come the merge functions */
 376
 377 static void reject_merge(struct cache_entry *ce)
 378 {
 379         die("Entry '%s' would be overwritten by merge. Cannot merge.",
 380             ce->name);
 381 }
 382
 383 static int same(struct cache_entry *a, struct cache_entry *b)
 384 {
 385         if (!!a != !!b)
 386                 return 0;
 387         if (!a && !b)
 388                 return 1;
 389         return a->ce_mode == b->ce_mode &&
 390                !hashcmp(a->sha1, b->sha1);
 391 }
 392
 393
 394 /*
 395  * When a CE gets turned into an unmerged entry, we
 396  * want it to be up-to-date
 397  */
 398 static void verify_uptodate(struct cache_entry *ce,
 399                 struct unpack_trees_options *o)
 400 {
 401         struct stat st;
 402
 403         if (o->index_only || o->reset)
 404                 return;
 405
 406         if (!lstat(ce->name, &st)) {
 407                 unsigned changed = ce_match_stat(ce, &st, 1);
 408                 if (!changed)
 409                         return;
 410                 /*
 411                  * NEEDSWORK: the current default policy is to allow
 412                  * submodule to be out of sync wrt the supermodule
 413                  * index.  This needs to be tightened later for
 414                  * submodules that are marked to be automatically
 415                  * checked out.
 416                  */
 417                 if (S_ISGITLINK(ntohl(ce->ce_mode)))
 418                         return;
 419                 errno = 0;
 420         }
 421         if (errno == ENOENT)
 422                 return;
 423         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 424 }
 425
 426 static void invalidate_ce_path(struct cache_entry *ce)
 427 {
 428         if (ce)
 429                 cache_tree_invalidate_path(active_cache_tree, ce->name);
 430 }
 431
 432 /*
 433  * Check that checking out ce->sha1 in subdir ce->name is not
 434  * going to overwrite any working files.
 435  *
 436  * Currently, git does not checkout subprojects during a superproject
 437  * checkout, so it is not going to overwrite anything.
 438  */
 439 static int verify_clean_submodule(struct cache_entry *ce, const char *action,
 440                                       struct unpack_trees_options *o)
 441 {
 442         return 0;
 443 }
 444
 445 static int verify_clean_subdirectory(struct cache_entry *ce, const char *action,
 446                                       struct unpack_trees_options *o)
 447 {
 448         /*
 449          * we are about to extract "ce->name"; we would not want to lose
 450          * anything in the existing directory there.
 451          */
 452         int namelen;
 453         int pos, i;
 454         struct dir_struct d;
 455         char *pathbuf;
 456         int cnt = 0;
 457         unsigned char sha1[20];
 458
 459         if (S_ISGITLINK(ntohl(ce->ce_mode)) &&
 460             resolve_gitlink_ref(ce->name, "HEAD", sha1) == 0) {
 461                 /* If we are not going to update the submodule, then
 462                  * we don't care.
 463                  */
 464                 if (!hashcmp(sha1, ce->sha1))
 465                         return 0;
 466                 return verify_clean_submodule(ce, action, o);
 467         }
 468
 469         /*
 470          * First let's make sure we do not have a local modification
 471          * in that directory.
 472          */
 473         namelen = strlen(ce->name);
 474         pos = cache_name_pos(ce->name, namelen);
 475         if (0 <= pos)
 476                 return cnt; /* we have it as nondirectory */
 477         pos = -pos - 1;
 478         for (i = pos; i < active_nr; i++) {
 479                 struct cache_entry *ce = active_cache[i];
 480                 int len = ce_namelen(ce);
 481                 if (len < namelen ||
 482                     strncmp(ce->name, ce->name, namelen) ||
 483                     ce->name[namelen] != '/')
 484                         break;
 485                 /*
 486                  * ce->name is an entry in the subdirectory.
 487                  */
 488                 if (!ce_stage(ce)) {
 489                         verify_uptodate(ce, o);
 490                         ce->ce_mode = 0;
 491                 }
 492                 cnt++;
 493         }
 494
 495         /*
 496          * Then we need to make sure that we do not lose a locally
 497          * present file that is not ignored.
 498          */
 499         pathbuf = xmalloc(namelen + 2);
 500         memcpy(pathbuf, ce->name, namelen);
 501         strcpy(pathbuf+namelen, "/");
 502
 503         memset(&d, 0, sizeof(d));
 504         if (o->dir)
 505                 d.exclude_per_dir = o->dir->exclude_per_dir;
 506         i = read_directory(&d, ce->name, pathbuf, namelen+1, NULL);
 507         if (i)
 508                 die("Updating '%s' would lose untracked files in it",
 509                     ce->name);
 510         free(pathbuf);
 511         return cnt;
 512 }
 513
 514 /*
 515  * We do not want to remove or overwrite a working tree file that
 516  * is not tracked, unless it is ignored.
 517  */
 518 static void verify_absent(struct cache_entry *ce, const char *action,
 519                 struct unpack_trees_options *o)
 520 {
 521         struct stat st;
 522
 523         if (o->index_only || o->reset || !o->update)
 524                 return;
 525
 526         if (has_symlink_leading_path(ce->name, NULL))
 527                 return;
 528
 529         if (!lstat(ce->name, &st)) {
 530                 int cnt;
 531
 532                 if (o->dir && excluded(o->dir, ce->name))
 533                         /*
 534                          * ce->name is explicitly excluded, so it is Ok to
 535                          * overwrite it.
 536                          */
 537                         return;
 538                 if (S_ISDIR(st.st_mode)) {
 539                         /*
 540                          * We are checking out path "foo" and
 541                          * found "foo/." in the working tree.
 542                          * This is tricky -- if we have modified
 543                          * files that are in "foo/" we would lose
 544                          * it.
 545                          */
 546                         cnt = verify_clean_subdirectory(ce, action, o);
 547
 548                         /*
 549                          * If this removed entries from the index,
 550                          * what that means is:
 551                          *
 552                          * (1) the caller unpack_trees_rec() saw path/foo
 553                          * in the index, and it has not removed it because
 554                          * it thinks it is handling 'path' as blob with
 555                          * D/F conflict;
 556                          * (2) we will return "ok, we placed a merged entry
 557                          * in the index" which would cause o->pos to be
 558                          * incremented by one;
 559                          * (3) however, original o->pos now has 'path/foo'
 560                          * marked with "to be removed".
 561                          *
 562                          * We need to increment it by the number of
 563                          * deleted entries here.
 564                          */
 565                         o->pos += cnt;
 566                         return;
 567                 }
 568
 569                 /*
 570                  * The previous round may already have decided to
 571                  * delete this path, which is in a subdirectory that
 572                  * is being replaced with a blob.
 573                  */
 574                 cnt = cache_name_pos(ce->name, strlen(ce->name));
 575                 if (0 <= cnt) {
 576                         struct cache_entry *ce = active_cache[cnt];
 577                         if (!ce_stage(ce) && !ce->ce_mode)
 578                                 return;
 579                 }
 580
 581                 die("Untracked working tree file '%s' "
 582                     "would be %s by merge.", ce->name, action);
 583         }
 584 }
 585
 586 static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
 587                 struct unpack_trees_options *o)
 588 {
 589         merge->ce_flags |= htons(CE_UPDATE);
 590         if (old) {
 591                 /*
 592                  * See if we can re-use the old CE directly?
 593                  * That way we get the uptodate stat info.
 594                  *
 595                  * This also removes the UPDATE flag on
 596                  * a match.
 597                  */
 598                 if (same(old, merge)) {
 599                         *merge = *old;
 600                 } else {
 601                         verify_uptodate(old, o);
 602                         invalidate_ce_path(old);
 603                 }
 604         }
 605         else {
 606                 verify_absent(merge, "overwritten", o);
 607                 invalidate_ce_path(merge);
 608         }
 609
 610         merge->ce_flags &= ~htons(CE_STAGEMASK);
 611         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
 612         return 1;
 613 }
 614
 615 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old,
 616                 struct unpack_trees_options *o)
 617 {
 618         if (old)
 619                 verify_uptodate(old, o);
 620         else
 621                 verify_absent(ce, "removed", o);
 622         ce->ce_mode = 0;
 623         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
 624         invalidate_ce_path(ce);
 625         return 1;
 626 }
 627
 628 static int keep_entry(struct cache_entry *ce, struct unpack_trees_options *o)
 629 {
 630         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 631         return 1;
 632 }
 633
 634 #if DBRT_DEBUG
 635 static void show_stage_entry(FILE *o,
 636                              const char *label, const struct cache_entry *ce)
 637 {
 638         if (!ce)
 639                 fprintf(o, "%s (missing)\n", label);
 640         else
 641                 fprintf(o, "%s%06o %s %d\t%s\n",
 642                         label,
 643                         ntohl(ce->ce_mode),
 644                         sha1_to_hex(ce->sha1),
 645                         ce_stage(ce),
 646                         ce->name);
 647 }
 648 #endif
 649
 650 int threeway_merge(struct cache_entry **stages,
 651                 struct unpack_trees_options *o)
 652 {
 653         struct cache_entry *index;
 654         struct cache_entry *head;
 655         struct cache_entry *remote = stages[o->head_idx + 1];
 656         int count;
 657         int head_match = 0;
 658         int remote_match = 0;
 659
 660         int df_conflict_head = 0;
 661         int df_conflict_remote = 0;
 662
 663         int any_anc_missing = 0;
 664         int no_anc_exists = 1;
 665         int i;
 666
 667         for (i = 1; i < o->head_idx; i++) {
 668                 if (!stages[i] || stages[i] == o->df_conflict_entry)
 669                         any_anc_missing = 1;
 670                 else
 671                         no_anc_exists = 0;
 672         }
 673
 674         index = stages[0];
 675         head = stages[o->head_idx];
 676
 677         if (head == o->df_conflict_entry) {
 678                 df_conflict_head = 1;
 679                 head = NULL;
 680         }
 681
 682         if (remote == o->df_conflict_entry) {
 683                 df_conflict_remote = 1;
 684                 remote = NULL;
 685         }
 686
 687         /* First, if there's a #16 situation, note that to prevent #13
 688          * and #14.
 689          */
 690         if (!same(remote, head)) {
 691                 for (i = 1; i < o->head_idx; i++) {
 692                         if (same(stages[i], head)) {
 693                                 head_match = i;
 694                         }
 695                         if (same(stages[i], remote)) {
 696                                 remote_match = i;
 697                         }
 698                 }
 699         }
 700
 701         /* We start with cases where the index is allowed to match
 702          * something other than the head: #14(ALT) and #2ALT, where it
 703          * is permitted to match the result instead.
 704          */
 705         /* #14, #14ALT, #2ALT */
 706         if (remote && !df_conflict_head && head_match && !remote_match) {
 707                 if (index && !same(index, remote) && !same(index, head))
 708                         reject_merge(index);
 709                 return merged_entry(remote, index, o);
 710         }
 711         /*
 712          * If we have an entry in the index cache, then we want to
 713          * make sure that it matches head.
 714          */
 715         if (index && !same(index, head)) {
 716                 reject_merge(index);
 717         }
 718
 719         if (head) {
 720                 /* #5ALT, #15 */
 721                 if (same(head, remote))
 722                         return merged_entry(head, index, o);
 723                 /* #13, #3ALT */
 724                 if (!df_conflict_remote && remote_match && !head_match)
 725                         return merged_entry(head, index, o);
 726         }
 727
 728         /* #1 */
 729         if (!head && !remote && any_anc_missing)
 730                 return 0;
 731
 732         /* Under the new "aggressive" rule, we resolve mostly trivial
 733          * cases that we historically had git-merge-one-file resolve.
 734          */
 735         if (o->aggressive) {
 736                 int head_deleted = !head && !df_conflict_head;
 737                 int remote_deleted = !remote && !df_conflict_remote;
 738                 struct cache_entry *ce = NULL;
 739
 740                 if (index)
 741                         ce = index;
 742                 else if (head)
 743                         ce = head;
 744                 else if (remote)
 745                         ce = remote;
 746                 else {
 747                         for (i = 1; i < o->head_idx; i++) {
 748                                 if (stages[i] && stages[i] != o->df_conflict_entry) {
 749                                         ce = stages[i];
 750                                         break;
 751                                 }
 752                         }
 753                 }
 754
 755                 /*
 756                  * Deleted in both.
 757                  * Deleted in one and unchanged in the other.
 758                  */
 759                 if ((head_deleted && remote_deleted) ||
 760                     (head_deleted && remote && remote_match) ||
 761                     (remote_deleted && head && head_match)) {
 762                         if (index)
 763                                 return deleted_entry(index, index, o);
 764                         else if (ce && !head_deleted)
 765                                 verify_absent(ce, "removed", o);
 766                         return 0;
 767                 }
 768                 /*
 769                  * Added in both, identically.
 770                  */
 771                 if (no_anc_exists && head && remote && same(head, remote))
 772                         return merged_entry(head, index, o);
 773
 774         }
 775
 776         /* Below are "no merge" cases, which require that the index be
 777          * up-to-date to avoid the files getting overwritten with
 778          * conflict resolution files.
 779          */
 780         if (index) {
 781                 verify_uptodate(index, o);
 782         }
 783
 784         o->nontrivial_merge = 1;
 785
 786         /* #2, #3, #4, #6, #7, #9, #10, #11. */
 787         count = 0;
 788         if (!head_match || !remote_match) {
 789                 for (i = 1; i < o->head_idx; i++) {
 790                         if (stages[i] && stages[i] != o->df_conflict_entry) {
 791                                 keep_entry(stages[i], o);
 792                                 count++;
 793                                 break;
 794                         }
 795                 }
 796         }
 797 #if DBRT_DEBUG
 798         else {
 799                 fprintf(stderr, "read-tree: warning #16 detected\n");
 800                 show_stage_entry(stderr, "head   ", stages[head_match]);
 801                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 802         }
 803 #endif
 804         if (head) { count += keep_entry(head, o); }
 805         if (remote) { count += keep_entry(remote, o); }
 806         return count;
 807 }
 808
 809 /*
 810  * Two-way merge.
 811  *
 812  * The rule is to "carry forward" what is in the index without losing
 813  * information across a "fast forward", favoring a successful merge
 814  * over a merge failure when it makes sense.  For details of the
 815  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 816  *
 817  */
 818 int twoway_merge(struct cache_entry **src,
 819                 struct unpack_trees_options *o)
 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                         return deleted_entry(oldtree, current, o);
 848                 }
 849                 else if (oldtree && newtree &&
 850                          same(current, oldtree) && !same(current, newtree)) {
 851                         /* 20 or 21 */
 852                         return merged_entry(newtree, current, o);
 853                 }
 854                 else {
 855                         /* all other failures */
 856                         if (oldtree)
 857                                 reject_merge(oldtree);
 858                         if (current)
 859                                 reject_merge(current);
 860                         if (newtree)
 861                                 reject_merge(newtree);
 862                         return -1;
 863                 }
 864         }
 865         else if (newtree)
 866                 return merged_entry(newtree, current, o);
 867         else
 868                 return deleted_entry(oldtree, current, o);
 869 }
 870
 871 /*
 872  * Bind merge.
 873  *
 874  * Keep the index entries at stage0, collapse stage1 but make sure
 875  * stage0 does not have anything there.
 876  */
 877 int bind_merge(struct cache_entry **src,
 878                 struct unpack_trees_options *o)
 879 {
 880         struct cache_entry *old = src[0];
 881         struct cache_entry *a = src[1];
 882
 883         if (o->merge_size != 1)
 884                 return error("Cannot do a bind merge of %d trees\n",
 885                              o->merge_size);
 886         if (a && old)
 887                 die("Entry '%s' overlaps.  Cannot bind.", a->name);
 888         if (!a)
 889                 return keep_entry(old, o);
 890         else
 891                 return merged_entry(a, NULL, o);
 892 }
 893
 894 /*
 895  * One-way merge.
 896  *
 897  * The rule is:
 898  * - take the stat information from stage0, take the data from stage1
 899  */
 900 int oneway_merge(struct cache_entry **src,
 901                 struct unpack_trees_options *o)
 902 {
 903         struct cache_entry *old = src[0];
 904         struct cache_entry *a = src[1];
 905
 906         if (o->merge_size != 1)
 907                 return error("Cannot do a oneway merge of %d trees",
 908                              o->merge_size);
 909
 910         if (!a)
 911                 return deleted_entry(old, old, o);
 912         if (old && same(old, a)) {
 913                 if (o->reset) {
 914                         struct stat st;
 915                         if (lstat(old->name, &st) ||
 916                             ce_match_stat(old, &st, 1))
 917                                 old->ce_flags |= htons(CE_UPDATE);
 918                 }
 919                 return keep_entry(old, o);
 920         }
 921         return merged_entry(a, old, o);
 922 }