git.oblomov.eu Git - git/blob - builtin-read-tree.c

   1 /*
   2  * GIT - The information manager from hell
   3  *
   4  * Copyright (C) Linus Torvalds, 2005
   5  */
   6 #define DBRT_DEBUG 1
   7
   8 #include "cache.h"
   9
  10 #include "object.h"
  11 #include "tree.h"
  12 #include "tree-walk.h"
  13 #include "cache-tree.h"
  14 #include <sys/time.h>
  15 #include <signal.h>
  16 #include "builtin.h"
  17
  18 static int reset = 0;
  19 static int merge = 0;
  20 static int update = 0;
  21 static int index_only = 0;
  22 static int nontrivial_merge = 0;
  23 static int trivial_merges_only = 0;
  24 static int aggressive = 0;
  25 static int verbose_update = 0;
  26 static volatile int progress_update = 0;
  27 static const char *prefix = NULL;
  28
  29 static int head_idx = -1;
  30 static int merge_size = 0;
  31
  32 static struct object_list *trees = NULL;
  33
  34 static struct cache_entry df_conflict_entry;
  35
  36 struct tree_entry_list {
  37         struct tree_entry_list *next;
  38         unsigned directory : 1;
  39         unsigned executable : 1;
  40         unsigned symlink : 1;
  41         unsigned int mode;
  42         const char *name;
  43         const unsigned char *sha1;
  44 };
  45
  46 static struct tree_entry_list df_conflict_list;
  47
  48 typedef int (*merge_fn_t)(struct cache_entry **src);
  49
  50 static struct tree_entry_list *create_tree_entry_list(struct tree *tree)
  51 {
  52         struct tree_desc desc;
  53         struct name_entry one;
  54         struct tree_entry_list *ret = NULL;
  55         struct tree_entry_list **list_p = &ret;
  56
  57         desc.buf = tree->buffer;
  58         desc.size = tree->size;
  59
  60         while (tree_entry(&desc, &one)) {
  61                 struct tree_entry_list *entry;
  62
  63                 entry = xmalloc(sizeof(struct tree_entry_list));
  64                 entry->name = one.path;
  65                 entry->sha1 = one.sha1;
  66                 entry->mode = one.mode;
  67                 entry->directory = S_ISDIR(one.mode) != 0;
  68                 entry->executable = (one.mode & S_IXUSR) != 0;
  69                 entry->symlink = S_ISLNK(one.mode) != 0;
  70                 entry->next = NULL;
  71
  72                 *list_p = entry;
  73                 list_p = &entry->next;
  74         }
  75         return ret;
  76 }
  77
  78 static int entcmp(const char *name1, int dir1, const char *name2, int dir2)
  79 {
  80         int len1 = strlen(name1);
  81         int len2 = strlen(name2);
  82         int len = len1 < len2 ? len1 : len2;
  83         int ret = memcmp(name1, name2, len);
  84         unsigned char c1, c2;
  85         if (ret)
  86                 return ret;
  87         c1 = name1[len];
  88         c2 = name2[len];
  89         if (!c1 && dir1)
  90                 c1 = '/';
  91         if (!c2 && dir2)
  92                 c2 = '/';
  93         ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
  94         if (c1 && c2 && !ret)
  95                 ret = len1 - len2;
  96         return ret;
  97 }
  98
  99 static int unpack_trees_rec(struct tree_entry_list **posns, int len,
 100                             const char *base, merge_fn_t fn, int *indpos)
 101 {
 102         int baselen = strlen(base);
 103         int src_size = len + 1;
 104         do {
 105                 int i;
 106                 const char *first;
 107                 int firstdir = 0;
 108                 int pathlen;
 109                 unsigned ce_size;
 110                 struct tree_entry_list **subposns;
 111                 struct cache_entry **src;
 112                 int any_files = 0;
 113                 int any_dirs = 0;
 114                 char *cache_name;
 115                 int ce_stage;
 116
 117                 /* Find the first name in the input. */
 118
 119                 first = NULL;
 120                 cache_name = NULL;
 121
 122                 /* Check the cache */
 123                 if (merge && *indpos < active_nr) {
 124                         /* This is a bit tricky: */
 125                         /* If the index has a subdirectory (with
 126                          * contents) as the first name, it'll get a
 127                          * filename like "foo/bar". But that's after
 128                          * "foo", so the entry in trees will get
 129                          * handled first, at which point we'll go into
 130                          * "foo", and deal with "bar" from the index,
 131                          * because the base will be "foo/". The only
 132                          * way we can actually have "foo/bar" first of
 133                          * all the things is if the trees don't
 134                          * contain "foo" at all, in which case we'll
 135                          * handle "foo/bar" without going into the
 136                          * directory, but that's fine (and will return
 137                          * an error anyway, with the added unknown
 138                          * file case.
 139                          */
 140
 141                         cache_name = active_cache[*indpos]->name;
 142                         if (strlen(cache_name) > baselen &&
 143                             !memcmp(cache_name, base, baselen)) {
 144                                 cache_name += baselen;
 145                                 first = cache_name;
 146                         } else {
 147                                 cache_name = NULL;
 148                         }
 149                 }
 150
 151 #if DBRT_DEBUG > 1
 152                 if (first)
 153                         printf("index %s\n", first);
 154 #endif
 155                 for (i = 0; i < len; i++) {
 156                         if (!posns[i] || posns[i] == &df_conflict_list)
 157                                 continue;
 158 #if DBRT_DEBUG > 1
 159                         printf("%d %s\n", i + 1, posns[i]->name);
 160 #endif
 161                         if (!first || entcmp(first, firstdir,
 162                                              posns[i]->name,
 163                                              posns[i]->directory) > 0) {
 164                                 first = posns[i]->name;
 165                                 firstdir = posns[i]->directory;
 166                         }
 167                 }
 168                 /* No name means we're done */
 169                 if (!first)
 170                         return 0;
 171
 172                 pathlen = strlen(first);
 173                 ce_size = cache_entry_size(baselen + pathlen);
 174
 175                 src = xcalloc(src_size, sizeof(struct cache_entry *));
 176
 177                 subposns = xcalloc(len, sizeof(struct tree_list_entry *));
 178
 179                 if (cache_name && !strcmp(cache_name, first)) {
 180                         any_files = 1;
 181                         src[0] = active_cache[*indpos];
 182                         remove_cache_entry_at(*indpos);
 183                 }
 184
 185                 for (i = 0; i < len; i++) {
 186                         struct cache_entry *ce;
 187
 188                         if (!posns[i] ||
 189                             (posns[i] != &df_conflict_list &&
 190                              strcmp(first, posns[i]->name))) {
 191                                 continue;
 192                         }
 193
 194                         if (posns[i] == &df_conflict_list) {
 195                                 src[i + merge] = &df_conflict_entry;
 196                                 continue;
 197                         }
 198
 199                         if (posns[i]->directory) {
 200                                 struct tree *tree = lookup_tree(posns[i]->sha1);
 201                                 any_dirs = 1;
 202                                 parse_tree(tree);
 203                                 subposns[i] = create_tree_entry_list(tree);
 204                                 posns[i] = posns[i]->next;
 205                                 src[i + merge] = &df_conflict_entry;
 206                                 continue;
 207                         }
 208
 209                         if (!merge)
 210                                 ce_stage = 0;
 211                         else if (i + 1 < head_idx)
 212                                 ce_stage = 1;
 213                         else if (i + 1 > head_idx)
 214                                 ce_stage = 3;
 215                         else
 216                                 ce_stage = 2;
 217
 218                         ce = xcalloc(1, ce_size);
 219                         ce->ce_mode = create_ce_mode(posns[i]->mode);
 220                         ce->ce_flags = create_ce_flags(baselen + pathlen,
 221                                                        ce_stage);
 222                         memcpy(ce->name, base, baselen);
 223                         memcpy(ce->name + baselen, first, pathlen + 1);
 224
 225                         any_files = 1;
 226
 227                         memcpy(ce->sha1, posns[i]->sha1, 20);
 228                         src[i + merge] = ce;
 229                         subposns[i] = &df_conflict_list;
 230                         posns[i] = posns[i]->next;
 231                 }
 232                 if (any_files) {
 233                         if (merge) {
 234                                 int ret;
 235
 236 #if DBRT_DEBUG > 1
 237                                 printf("%s:\n", first);
 238                                 for (i = 0; i < src_size; i++) {
 239                                         printf(" %d ", i);
 240                                         if (src[i])
 241                                                 printf("%s\n", sha1_to_hex(src[i]->sha1));
 242                                         else
 243                                                 printf("\n");
 244                                 }
 245 #endif
 246                                 ret = fn(src);
 247
 248 #if DBRT_DEBUG > 1
 249                                 printf("Added %d entries\n", ret);
 250 #endif
 251                                 *indpos += ret;
 252                         } else {
 253                                 for (i = 0; i < src_size; i++) {
 254                                         if (src[i]) {
 255                                                 add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
 256                                         }
 257                                 }
 258                         }
 259                 }
 260                 if (any_dirs) {
 261                         char *newbase = xmalloc(baselen + 2 + pathlen);
 262                         memcpy(newbase, base, baselen);
 263                         memcpy(newbase + baselen, first, pathlen);
 264                         newbase[baselen + pathlen] = '/';
 265                         newbase[baselen + pathlen + 1] = '\0';
 266                         if (unpack_trees_rec(subposns, len, newbase, fn,
 267                                              indpos))
 268                                 return -1;
 269                         free(newbase);
 270                 }
 271                 free(subposns);
 272                 free(src);
 273         } while (1);
 274 }
 275
 276 static void reject_merge(struct cache_entry *ce)
 277 {
 278         die("Entry '%s' would be overwritten by merge. Cannot merge.",
 279             ce->name);
 280 }
 281
 282 /* Unlink the last component and attempt to remove leading
 283  * directories, in case this unlink is the removal of the
 284  * last entry in the directory -- empty directories are removed.
 285  */
 286 static void unlink_entry(char *name)
 287 {
 288         char *cp, *prev;
 289
 290         if (unlink(name))
 291                 return;
 292         prev = NULL;
 293         while (1) {
 294                 int status;
 295                 cp = strrchr(name, '/');
 296                 if (prev)
 297                         *prev = '/';
 298                 if (!cp)
 299                         break;
 300
 301                 *cp = 0;
 302                 status = rmdir(name);
 303                 if (status) {
 304                         *cp = '/';
 305                         break;
 306                 }
 307                 prev = cp;
 308         }
 309 }
 310
 311 static void progress_interval(int signum)
 312 {
 313         progress_update = 1;
 314 }
 315
 316 static void setup_progress_signal(void)
 317 {
 318         struct sigaction sa;
 319         struct itimerval v;
 320
 321         memset(&sa, 0, sizeof(sa));
 322         sa.sa_handler = progress_interval;
 323         sigemptyset(&sa.sa_mask);
 324         sa.sa_flags = SA_RESTART;
 325         sigaction(SIGALRM, &sa, NULL);
 326
 327         v.it_interval.tv_sec = 1;
 328         v.it_interval.tv_usec = 0;
 329         v.it_value = v.it_interval;
 330         setitimer(ITIMER_REAL, &v, NULL);
 331 }
 332
 333 static struct checkout state;
 334 static void check_updates(struct cache_entry **src, int nr)
 335 {
 336         unsigned short mask = htons(CE_UPDATE);
 337         unsigned last_percent = 200, cnt = 0, total = 0;
 338
 339         if (update && verbose_update) {
 340                 for (total = cnt = 0; cnt < nr; cnt++) {
 341                         struct cache_entry *ce = src[cnt];
 342                         if (!ce->ce_mode || ce->ce_flags & mask)
 343                                 total++;
 344                 }
 345
 346                 /* Don't bother doing this for very small updates */
 347                 if (total < 250)
 348                         total = 0;
 349
 350                 if (total) {
 351                         fprintf(stderr, "Checking files out...\n");
 352                         setup_progress_signal();
 353                         progress_update = 1;
 354                 }
 355                 cnt = 0;
 356         }
 357
 358         while (nr--) {
 359                 struct cache_entry *ce = *src++;
 360
 361                 if (total) {
 362                         if (!ce->ce_mode || ce->ce_flags & mask) {
 363                                 unsigned percent;
 364                                 cnt++;
 365                                 percent = (cnt * 100) / total;
 366                                 if (percent != last_percent ||
 367                                     progress_update) {
 368                                         fprintf(stderr, "%4u%% (%u/%u) done\r",
 369                                                 percent, cnt, total);
 370                                         last_percent = percent;
 371                                         progress_update = 0;
 372                                 }
 373                         }
 374                 }
 375                 if (!ce->ce_mode) {
 376                         if (update)
 377                                 unlink_entry(ce->name);
 378                         continue;
 379                 }
 380                 if (ce->ce_flags & mask) {
 381                         ce->ce_flags &= ~mask;
 382                         if (update)
 383                                 checkout_entry(ce, &state, NULL);
 384                 }
 385         }
 386         if (total) {
 387                 signal(SIGALRM, SIG_IGN);
 388                 fputc('\n', stderr);
 389         }
 390 }
 391
 392 static int unpack_trees(merge_fn_t fn)
 393 {
 394         int indpos = 0;
 395         unsigned len = object_list_length(trees);
 396         struct tree_entry_list **posns;
 397         int i;
 398         struct object_list *posn = trees;
 399         merge_size = len;
 400
 401         if (len) {
 402                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
 403                 for (i = 0; i < len; i++) {
 404                         posns[i] = create_tree_entry_list((struct tree *) posn->item);
 405                         posn = posn->next;
 406                 }
 407                 if (unpack_trees_rec(posns, len, prefix ? prefix : "",
 408                                      fn, &indpos))
 409                         return -1;
 410         }
 411
 412         if (trivial_merges_only && nontrivial_merge)
 413                 die("Merge requires file-level merging");
 414
 415         check_updates(active_cache, active_nr);
 416         return 0;
 417 }
 418
 419 static int list_tree(unsigned char *sha1)
 420 {
 421         struct tree *tree = parse_tree_indirect(sha1);
 422         if (!tree)
 423                 return -1;
 424         object_list_append(&tree->object, &trees);
 425         return 0;
 426 }
 427
 428 static int same(struct cache_entry *a, struct cache_entry *b)
 429 {
 430         if (!!a != !!b)
 431                 return 0;
 432         if (!a && !b)
 433                 return 1;
 434         return a->ce_mode == b->ce_mode &&
 435                 !memcmp(a->sha1, b->sha1, 20);
 436 }
 437
 438
 439 /*
 440  * When a CE gets turned into an unmerged entry, we
 441  * want it to be up-to-date
 442  */
 443 static void verify_uptodate(struct cache_entry *ce)
 444 {
 445         struct stat st;
 446
 447         if (index_only || reset)
 448                 return;
 449
 450         if (!lstat(ce->name, &st)) {
 451                 unsigned changed = ce_match_stat(ce, &st, 1);
 452                 if (!changed)
 453                         return;
 454                 errno = 0;
 455         }
 456         if (reset) {
 457                 ce->ce_flags |= htons(CE_UPDATE);
 458                 return;
 459         }
 460         if (errno == ENOENT)
 461                 return;
 462         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 463 }
 464
 465 static void invalidate_ce_path(struct cache_entry *ce)
 466 {
 467         if (ce)
 468                 cache_tree_invalidate_path(active_cache_tree, ce->name);
 469 }
 470
 471 /*
 472  * We do not want to remove or overwrite a working tree file that
 473  * is not tracked.
 474  */
 475 static void verify_absent(const char *path, const char *action)
 476 {
 477         struct stat st;
 478
 479         if (index_only || reset || !update)
 480                 return;
 481         if (!lstat(path, &st))
 482                 die("Untracked working tree file '%s' "
 483                     "would be %s by merge.", path, action);
 484 }
 485
 486 static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
 487 {
 488         merge->ce_flags |= htons(CE_UPDATE);
 489         if (old) {
 490                 /*
 491                  * See if we can re-use the old CE directly?
 492                  * That way we get the uptodate stat info.
 493                  *
 494                  * This also removes the UPDATE flag on
 495                  * a match.
 496                  */
 497                 if (same(old, merge)) {
 498                         *merge = *old;
 499                 } else {
 500                         verify_uptodate(old);
 501                         invalidate_ce_path(old);
 502                 }
 503         }
 504         else {
 505                 verify_absent(merge->name, "overwritten");
 506                 invalidate_ce_path(merge);
 507         }
 508
 509         merge->ce_flags &= ~htons(CE_STAGEMASK);
 510         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
 511         return 1;
 512 }
 513
 514 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
 515 {
 516         if (old)
 517                 verify_uptodate(old);
 518         else
 519                 verify_absent(ce->name, "removed");
 520         ce->ce_mode = 0;
 521         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 522         invalidate_ce_path(ce);
 523         return 1;
 524 }
 525
 526 static int keep_entry(struct cache_entry *ce)
 527 {
 528         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 529         return 1;
 530 }
 531
 532 #if DBRT_DEBUG
 533 static void show_stage_entry(FILE *o,
 534                              const char *label, const struct cache_entry *ce)
 535 {
 536         if (!ce)
 537                 fprintf(o, "%s (missing)\n", label);
 538         else
 539                 fprintf(o, "%s%06o %s %d\t%s\n",
 540                         label,
 541                         ntohl(ce->ce_mode),
 542                         sha1_to_hex(ce->sha1),
 543                         ce_stage(ce),
 544                         ce->name);
 545 }
 546 #endif
 547
 548 static int threeway_merge(struct cache_entry **stages)
 549 {
 550         struct cache_entry *index;
 551         struct cache_entry *head;
 552         struct cache_entry *remote = stages[head_idx + 1];
 553         int count;
 554         int head_match = 0;
 555         int remote_match = 0;
 556         const char *path = NULL;
 557
 558         int df_conflict_head = 0;
 559         int df_conflict_remote = 0;
 560
 561         int any_anc_missing = 0;
 562         int no_anc_exists = 1;
 563         int i;
 564
 565         for (i = 1; i < head_idx; i++) {
 566                 if (!stages[i])
 567                         any_anc_missing = 1;
 568                 else {
 569                         if (!path)
 570                                 path = stages[i]->name;
 571                         no_anc_exists = 0;
 572                 }
 573         }
 574
 575         index = stages[0];
 576         head = stages[head_idx];
 577
 578         if (head == &df_conflict_entry) {
 579                 df_conflict_head = 1;
 580                 head = NULL;
 581         }
 582
 583         if (remote == &df_conflict_entry) {
 584                 df_conflict_remote = 1;
 585                 remote = NULL;
 586         }
 587
 588         if (!path && index)
 589                 path = index->name;
 590         if (!path && head)
 591                 path = head->name;
 592         if (!path && remote)
 593                 path = remote->name;
 594
 595         /* First, if there's a #16 situation, note that to prevent #13
 596          * and #14.
 597          */
 598         if (!same(remote, head)) {
 599                 for (i = 1; i < head_idx; i++) {
 600                         if (same(stages[i], head)) {
 601                                 head_match = i;
 602                         }
 603                         if (same(stages[i], remote)) {
 604                                 remote_match = i;
 605                         }
 606                 }
 607         }
 608
 609         /* We start with cases where the index is allowed to match
 610          * something other than the head: #14(ALT) and #2ALT, where it
 611          * is permitted to match the result instead.
 612          */
 613         /* #14, #14ALT, #2ALT */
 614         if (remote && !df_conflict_head && head_match && !remote_match) {
 615                 if (index && !same(index, remote) && !same(index, head))
 616                         reject_merge(index);
 617                 return merged_entry(remote, index);
 618         }
 619         /*
 620          * If we have an entry in the index cache, then we want to
 621          * make sure that it matches head.
 622          */
 623         if (index && !same(index, head)) {
 624                 reject_merge(index);
 625         }
 626
 627         if (head) {
 628                 /* #5ALT, #15 */
 629                 if (same(head, remote))
 630                         return merged_entry(head, index);
 631                 /* #13, #3ALT */
 632                 if (!df_conflict_remote && remote_match && !head_match)
 633                         return merged_entry(head, index);
 634         }
 635
 636         /* #1 */
 637         if (!head && !remote && any_anc_missing)
 638                 return 0;
 639
 640         /* Under the new "aggressive" rule, we resolve mostly trivial
 641          * cases that we historically had git-merge-one-file resolve.
 642          */
 643         if (aggressive) {
 644                 int head_deleted = !head && !df_conflict_head;
 645                 int remote_deleted = !remote && !df_conflict_remote;
 646                 /*
 647                  * Deleted in both.
 648                  * Deleted in one and unchanged in the other.
 649                  */
 650                 if ((head_deleted && remote_deleted) ||
 651                     (head_deleted && remote && remote_match) ||
 652                     (remote_deleted && head && head_match)) {
 653                         if (index)
 654                                 return deleted_entry(index, index);
 655                         else if (path)
 656                                 verify_absent(path, "removed");
 657                         return 0;
 658                 }
 659                 /*
 660                  * Added in both, identically.
 661                  */
 662                 if (no_anc_exists && head && remote && same(head, remote))
 663                         return merged_entry(head, index);
 664
 665         }
 666
 667         /* Below are "no merge" cases, which require that the index be
 668          * up-to-date to avoid the files getting overwritten with
 669          * conflict resolution files.
 670          */
 671         if (index) {
 672                 verify_uptodate(index);
 673         }
 674         else if (path)
 675                 verify_absent(path, "overwritten");
 676
 677         nontrivial_merge = 1;
 678
 679         /* #2, #3, #4, #6, #7, #9, #11. */
 680         count = 0;
 681         if (!head_match || !remote_match) {
 682                 for (i = 1; i < head_idx; i++) {
 683                         if (stages[i]) {
 684                                 keep_entry(stages[i]);
 685                                 count++;
 686                                 break;
 687                         }
 688                 }
 689         }
 690 #if DBRT_DEBUG
 691         else {
 692                 fprintf(stderr, "read-tree: warning #16 detected\n");
 693                 show_stage_entry(stderr, "head   ", stages[head_match]);
 694                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 695         }
 696 #endif
 697         if (head) { count += keep_entry(head); }
 698         if (remote) { count += keep_entry(remote); }
 699         return count;
 700 }
 701
 702 /*
 703  * Two-way merge.
 704  *
 705  * The rule is to "carry forward" what is in the index without losing
 706  * information across a "fast forward", favoring a successful merge
 707  * over a merge failure when it makes sense.  For details of the
 708  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 709  *
 710  */
 711 static int twoway_merge(struct cache_entry **src)
 712 {
 713         struct cache_entry *current = src[0];
 714         struct cache_entry *oldtree = src[1], *newtree = src[2];
 715
 716         if (merge_size != 2)
 717                 return error("Cannot do a twoway merge of %d trees",
 718                              merge_size);
 719
 720         if (current) {
 721                 if ((!oldtree && !newtree) || /* 4 and 5 */
 722                     (!oldtree && newtree &&
 723                      same(current, newtree)) || /* 6 and 7 */
 724                     (oldtree && newtree &&
 725                      same(oldtree, newtree)) || /* 14 and 15 */
 726                     (oldtree && newtree &&
 727                      !same(oldtree, newtree) && /* 18 and 19*/
 728                      same(current, newtree))) {
 729                         return keep_entry(current);
 730                 }
 731                 else if (oldtree && !newtree && same(current, oldtree)) {
 732                         /* 10 or 11 */
 733                         return deleted_entry(oldtree, current);
 734                 }
 735                 else if (oldtree && newtree &&
 736                          same(current, oldtree) && !same(current, newtree)) {
 737                         /* 20 or 21 */
 738                         return merged_entry(newtree, current);
 739                 }
 740                 else {
 741                         /* all other failures */
 742                         if (oldtree)
 743                                 reject_merge(oldtree);
 744                         if (current)
 745                                 reject_merge(current);
 746                         if (newtree)
 747                                 reject_merge(newtree);
 748                         return -1;
 749                 }
 750         }
 751         else if (newtree)
 752                 return merged_entry(newtree, current);
 753         else
 754                 return deleted_entry(oldtree, current);
 755 }
 756
 757 /*
 758  * Bind merge.
 759  *
 760  * Keep the index entries at stage0, collapse stage1 but make sure
 761  * stage0 does not have anything there.
 762  */
 763 static int bind_merge(struct cache_entry **src)
 764 {
 765         struct cache_entry *old = src[0];
 766         struct cache_entry *a = src[1];
 767
 768         if (merge_size != 1)
 769                 return error("Cannot do a bind merge of %d trees\n",
 770                              merge_size);
 771         if (a && old)
 772                 die("Entry '%s' overlaps.  Cannot bind.", a->name);
 773         if (!a)
 774                 return keep_entry(old);
 775         else
 776                 return merged_entry(a, NULL);
 777 }
 778
 779 /*
 780  * One-way merge.
 781  *
 782  * The rule is:
 783  * - take the stat information from stage0, take the data from stage1
 784  */
 785 static int oneway_merge(struct cache_entry **src)
 786 {
 787         struct cache_entry *old = src[0];
 788         struct cache_entry *a = src[1];
 789
 790         if (merge_size != 1)
 791                 return error("Cannot do a oneway merge of %d trees",
 792                              merge_size);
 793
 794         if (!a)
 795                 return deleted_entry(old, old);
 796         if (old && same(old, a)) {
 797                 if (reset) {
 798                         struct stat st;
 799                         if (lstat(old->name, &st) ||
 800                             ce_match_stat(old, &st, 1))
 801                                 old->ce_flags |= htons(CE_UPDATE);
 802                 }
 803                 return keep_entry(old);
 804         }
 805         return merged_entry(a, old);
 806 }
 807
 808 static int read_cache_unmerged(void)
 809 {
 810         int i;
 811         struct cache_entry **dst;
 812         struct cache_entry *last = NULL;
 813
 814         read_cache();
 815         dst = active_cache;
 816         for (i = 0; i < active_nr; i++) {
 817                 struct cache_entry *ce = active_cache[i];
 818                 if (ce_stage(ce)) {
 819                         if (last && !strcmp(ce->name, last->name))
 820                                 continue;
 821                         invalidate_ce_path(ce);
 822                         last = ce;
 823                         ce->ce_mode = 0;
 824                         ce->ce_flags &= ~htons(CE_STAGEMASK);
 825                 }
 826                 *dst++ = ce;
 827         }
 828         active_nr = dst - active_cache;
 829         return !!last;
 830 }
 831
 832 static void prime_cache_tree_rec(struct cache_tree *it, struct tree *tree)
 833 {
 834         struct tree_desc desc;
 835         struct name_entry entry;
 836         int cnt;
 837
 838         memcpy(it->sha1, tree->object.sha1, 20);
 839         desc.buf = tree->buffer;
 840         desc.size = tree->size;
 841         cnt = 0;
 842         while (tree_entry(&desc, &entry)) {
 843                 if (!S_ISDIR(entry.mode))
 844                         cnt++;
 845                 else {
 846                         struct cache_tree_sub *sub;
 847                         struct tree *subtree = lookup_tree(entry.sha1);
 848                         if (!subtree->object.parsed)
 849                                 parse_tree(subtree);
 850                         sub = cache_tree_sub(it, entry.path);
 851                         sub->cache_tree = cache_tree();
 852                         prime_cache_tree_rec(sub->cache_tree, subtree);
 853                         cnt += sub->cache_tree->entry_count;
 854                 }
 855         }
 856         it->entry_count = cnt;
 857 }
 858
 859 static void prime_cache_tree(void)
 860 {
 861         struct tree *tree = (struct tree *)trees->item;
 862         if (!tree)
 863                 return;
 864         active_cache_tree = cache_tree();
 865         prime_cache_tree_rec(active_cache_tree, tree);
 866
 867 }
 868
 869 static const char read_tree_usage[] = "git-read-tree (<sha> | [[-m [--aggressive] | --reset | --prefix=<prefix>] [-u | -i]] <sha1> [<sha2> [<sha3>]])";
 870
 871 static struct lock_file lock_file;
 872
 873 int cmd_read_tree(int argc, const char **argv, char **envp)
 874 {
 875         int i, newfd, stage = 0;
 876         unsigned char sha1[20];
 877         merge_fn_t fn = NULL;
 878
 879         df_conflict_list.next = &df_conflict_list;
 880         state.base_dir = "";
 881         state.force = 1;
 882         state.quiet = 1;
 883         state.refresh_cache = 1;
 884
 885         setup_git_directory();
 886         git_config(git_default_config);
 887
 888         newfd = hold_lock_file_for_update(&lock_file, get_index_file());
 889         if (newfd < 0)
 890                 die("unable to create new index file");
 891
 892         git_config(git_default_config);
 893
 894         merge = 0;
 895         reset = 0;
 896         for (i = 1; i < argc; i++) {
 897                 const char *arg = argv[i];
 898
 899                 /* "-u" means "update", meaning that a merge will update
 900                  * the working tree.
 901                  */
 902                 if (!strcmp(arg, "-u")) {
 903                         update = 1;
 904                         continue;
 905                 }
 906
 907                 if (!strcmp(arg, "-v")) {
 908                         verbose_update = 1;
 909                         continue;
 910                 }
 911
 912                 /* "-i" means "index only", meaning that a merge will
 913                  * not even look at the working tree.
 914                  */
 915                 if (!strcmp(arg, "-i")) {
 916                         index_only = 1;
 917                         continue;
 918                 }
 919
 920                 /* "--prefix=<subdirectory>/" means keep the current index
 921                  *  entries and put the entries from the tree under the
 922                  * given subdirectory.
 923                  */
 924                 if (!strncmp(arg, "--prefix=", 9)) {
 925                         if (stage || merge || prefix)
 926                                 usage(read_tree_usage);
 927                         prefix = arg + 9;
 928                         merge = 1;
 929                         stage = 1;
 930                         if (read_cache_unmerged())
 931                                 die("you need to resolve your current index first");
 932                         continue;
 933                 }
 934
 935                 /* This differs from "-m" in that we'll silently ignore
 936                  * unmerged entries and overwrite working tree files that
 937                  * correspond to them.
 938                  */
 939                 if (!strcmp(arg, "--reset")) {
 940                         if (stage || merge || prefix)
 941                                 usage(read_tree_usage);
 942                         reset = 1;
 943                         merge = 1;
 944                         stage = 1;
 945                         read_cache_unmerged();
 946                         continue;
 947                 }
 948
 949                 if (!strcmp(arg, "--trivial")) {
 950                         trivial_merges_only = 1;
 951                         continue;
 952                 }
 953
 954                 if (!strcmp(arg, "--aggressive")) {
 955                         aggressive = 1;
 956                         continue;
 957                 }
 958
 959                 /* "-m" stands for "merge", meaning we start in stage 1 */
 960                 if (!strcmp(arg, "-m")) {
 961                         if (stage || merge || prefix)
 962                                 usage(read_tree_usage);
 963                         if (read_cache_unmerged())
 964                                 die("you need to resolve your current index first");
 965                         stage = 1;
 966                         merge = 1;
 967                         continue;
 968                 }
 969
 970                 /* using -u and -i at the same time makes no sense */
 971                 if (1 < index_only + update)
 972                         usage(read_tree_usage);
 973
 974                 if (get_sha1(arg, sha1))
 975                         die("Not a valid object name %s", arg);
 976                 if (list_tree(sha1) < 0)
 977                         die("failed to unpack tree object %s", arg);
 978                 stage++;
 979         }
 980         if ((update||index_only) && !merge)
 981                 usage(read_tree_usage);
 982
 983         if (prefix) {
 984                 int pfxlen = strlen(prefix);
 985                 int pos;
 986                 if (prefix[pfxlen-1] != '/')
 987                         die("prefix must end with /");
 988                 if (stage != 2)
 989                         die("binding merge takes only one tree");
 990                 pos = cache_name_pos(prefix, pfxlen);
 991                 if (0 <= pos)
 992                         die("corrupt index file");
 993                 pos = -pos-1;
 994                 if (pos < active_nr &&
 995                     !strncmp(active_cache[pos]->name, prefix, pfxlen))
 996                         die("subdirectory '%s' already exists.", prefix);
 997                 pos = cache_name_pos(prefix, pfxlen-1);
 998                 if (0 <= pos)
 999                         die("file '%.*s' already exists.", pfxlen-1, prefix);
1000         }
1001
1002         if (merge) {
1003                 if (stage < 2)
1004                         die("just how do you expect me to merge %d trees?", stage-1);
1005                 switch (stage - 1) {
1006                 case 1:
1007                         fn = prefix ? bind_merge : oneway_merge;
1008                         break;
1009                 case 2:
1010                         fn = twoway_merge;
1011                         break;
1012                 case 3:
1013                 default:
1014                         fn = threeway_merge;
1015                         cache_tree_free(&active_cache_tree);
1016                         break;
1017                 }
1018
1019                 if (stage - 1 >= 3)
1020                         head_idx = stage - 2;
1021                 else
1022                         head_idx = 1;
1023         }
1024
1025         unpack_trees(fn);
1026
1027         /*
1028          * When reading only one tree (either the most basic form,
1029          * "-m ent" or "--reset ent" form), we can obtain a fully
1030          * valid cache-tree because the index must match exactly
1031          * what came from the tree.
1032          */
1033         if (trees && trees->item && !prefix && (!merge || (stage == 2))) {
1034                 cache_tree_free(&active_cache_tree);
1035                 prime_cache_tree();
1036         }
1037
1038         if (write_cache(newfd, active_cache, active_nr) ||
1039             close(newfd) || commit_lock_file(&lock_file))
1040                 die("unable to write new index file");
1041         return 0;
1042 }