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         .name = NULL,
  48         .next = &df_conflict_list
  49 };
  50
  51 typedef int (*merge_fn_t)(struct cache_entry **src);
  52
  53 static struct tree_entry_list *create_tree_entry_list(struct tree *tree)
  54 {
  55         struct tree_desc desc;
  56         struct name_entry one;
  57         struct tree_entry_list *ret = NULL;
  58         struct tree_entry_list **list_p = &ret;
  59
  60         desc.buf = tree->buffer;
  61         desc.size = tree->size;
  62
  63         while (tree_entry(&desc, &one)) {
  64                 struct tree_entry_list *entry;
  65
  66                 entry = xmalloc(sizeof(struct tree_entry_list));
  67                 entry->name = one.path;
  68                 entry->sha1 = one.sha1;
  69                 entry->mode = one.mode;
  70                 entry->directory = S_ISDIR(one.mode) != 0;
  71                 entry->executable = (one.mode & S_IXUSR) != 0;
  72                 entry->symlink = S_ISLNK(one.mode) != 0;
  73                 entry->next = NULL;
  74
  75                 *list_p = entry;
  76                 list_p = &entry->next;
  77         }
  78         return ret;
  79 }
  80
  81 static int entcmp(const char *name1, int dir1, const char *name2, int dir2)
  82 {
  83         int len1 = strlen(name1);
  84         int len2 = strlen(name2);
  85         int len = len1 < len2 ? len1 : len2;
  86         int ret = memcmp(name1, name2, len);
  87         unsigned char c1, c2;
  88         if (ret)
  89                 return ret;
  90         c1 = name1[len];
  91         c2 = name2[len];
  92         if (!c1 && dir1)
  93                 c1 = '/';
  94         if (!c2 && dir2)
  95                 c2 = '/';
  96         ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
  97         if (c1 && c2 && !ret)
  98                 ret = len1 - len2;
  99         return ret;
 100 }
 101
 102 static int unpack_trees_rec(struct tree_entry_list **posns, int len,
 103                             const char *base, merge_fn_t fn, int *indpos)
 104 {
 105         int baselen = strlen(base);
 106         int src_size = len + 1;
 107         do {
 108                 int i;
 109                 const char *first;
 110                 int firstdir = 0;
 111                 int pathlen;
 112                 unsigned ce_size;
 113                 struct tree_entry_list **subposns;
 114                 struct cache_entry **src;
 115                 int any_files = 0;
 116                 int any_dirs = 0;
 117                 char *cache_name;
 118                 int ce_stage;
 119
 120                 /* Find the first name in the input. */
 121
 122                 first = NULL;
 123                 cache_name = NULL;
 124
 125                 /* Check the cache */
 126                 if (merge && *indpos < active_nr) {
 127                         /* This is a bit tricky: */
 128                         /* If the index has a subdirectory (with
 129                          * contents) as the first name, it'll get a
 130                          * filename like "foo/bar". But that's after
 131                          * "foo", so the entry in trees will get
 132                          * handled first, at which point we'll go into
 133                          * "foo", and deal with "bar" from the index,
 134                          * because the base will be "foo/". The only
 135                          * way we can actually have "foo/bar" first of
 136                          * all the things is if the trees don't
 137                          * contain "foo" at all, in which case we'll
 138                          * handle "foo/bar" without going into the
 139                          * directory, but that's fine (and will return
 140                          * an error anyway, with the added unknown
 141                          * file case.
 142                          */
 143
 144                         cache_name = active_cache[*indpos]->name;
 145                         if (strlen(cache_name) > baselen &&
 146                             !memcmp(cache_name, base, baselen)) {
 147                                 cache_name += baselen;
 148                                 first = cache_name;
 149                         } else {
 150                                 cache_name = NULL;
 151                         }
 152                 }
 153
 154 #if DBRT_DEBUG > 1
 155                 if (first)
 156                         printf("index %s\n", first);
 157 #endif
 158                 for (i = 0; i < len; i++) {
 159                         if (!posns[i] || posns[i] == &df_conflict_list)
 160                                 continue;
 161 #if DBRT_DEBUG > 1
 162                         printf("%d %s\n", i + 1, posns[i]->name);
 163 #endif
 164                         if (!first || entcmp(first, firstdir,
 165                                              posns[i]->name,
 166                                              posns[i]->directory) > 0) {
 167                                 first = posns[i]->name;
 168                                 firstdir = posns[i]->directory;
 169                         }
 170                 }
 171                 /* No name means we're done */
 172                 if (!first)
 173                         return 0;
 174
 175                 pathlen = strlen(first);
 176                 ce_size = cache_entry_size(baselen + pathlen);
 177
 178                 src = xcalloc(src_size, sizeof(struct cache_entry *));
 179
 180                 subposns = xcalloc(len, sizeof(struct tree_list_entry *));
 181
 182                 if (cache_name && !strcmp(cache_name, first)) {
 183                         any_files = 1;
 184                         src[0] = active_cache[*indpos];
 185                         remove_cache_entry_at(*indpos);
 186                 }
 187
 188                 for (i = 0; i < len; i++) {
 189                         struct cache_entry *ce;
 190
 191                         if (!posns[i] ||
 192                             (posns[i] != &df_conflict_list &&
 193                              strcmp(first, posns[i]->name))) {
 194                                 continue;
 195                         }
 196
 197                         if (posns[i] == &df_conflict_list) {
 198                                 src[i + merge] = &df_conflict_entry;
 199                                 continue;
 200                         }
 201
 202                         if (posns[i]->directory) {
 203                                 struct tree *tree = lookup_tree(posns[i]->sha1);
 204                                 any_dirs = 1;
 205                                 parse_tree(tree);
 206                                 subposns[i] = create_tree_entry_list(tree);
 207                                 posns[i] = posns[i]->next;
 208                                 src[i + merge] = &df_conflict_entry;
 209                                 continue;
 210                         }
 211
 212                         if (!merge)
 213                                 ce_stage = 0;
 214                         else if (i + 1 < head_idx)
 215                                 ce_stage = 1;
 216                         else if (i + 1 > head_idx)
 217                                 ce_stage = 3;
 218                         else
 219                                 ce_stage = 2;
 220
 221                         ce = xcalloc(1, ce_size);
 222                         ce->ce_mode = create_ce_mode(posns[i]->mode);
 223                         ce->ce_flags = create_ce_flags(baselen + pathlen,
 224                                                        ce_stage);
 225                         memcpy(ce->name, base, baselen);
 226                         memcpy(ce->name + baselen, first, pathlen + 1);
 227
 228                         any_files = 1;
 229
 230                         memcpy(ce->sha1, posns[i]->sha1, 20);
 231                         src[i + merge] = ce;
 232                         subposns[i] = &df_conflict_list;
 233                         posns[i] = posns[i]->next;
 234                 }
 235                 if (any_files) {
 236                         if (merge) {
 237                                 int ret;
 238
 239 #if DBRT_DEBUG > 1
 240                                 printf("%s:\n", first);
 241                                 for (i = 0; i < src_size; i++) {
 242                                         printf(" %d ", i);
 243                                         if (src[i])
 244                                                 printf("%s\n", sha1_to_hex(src[i]->sha1));
 245                                         else
 246                                                 printf("\n");
 247                                 }
 248 #endif
 249                                 ret = fn(src);
 250
 251 #if DBRT_DEBUG > 1
 252                                 printf("Added %d entries\n", ret);
 253 #endif
 254                                 *indpos += ret;
 255                         } else {
 256                                 for (i = 0; i < src_size; i++) {
 257                                         if (src[i]) {
 258                                                 add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
 259                                         }
 260                                 }
 261                         }
 262                 }
 263                 if (any_dirs) {
 264                         char *newbase = xmalloc(baselen + 2 + pathlen);
 265                         memcpy(newbase, base, baselen);
 266                         memcpy(newbase + baselen, first, pathlen);
 267                         newbase[baselen + pathlen] = '/';
 268                         newbase[baselen + pathlen + 1] = '\0';
 269                         if (unpack_trees_rec(subposns, len, newbase, fn,
 270                                              indpos))
 271                                 return -1;
 272                         free(newbase);
 273                 }
 274                 free(subposns);
 275                 free(src);
 276         } while (1);
 277 }
 278
 279 static void reject_merge(struct cache_entry *ce)
 280 {
 281         die("Entry '%s' would be overwritten by merge. Cannot merge.",
 282             ce->name);
 283 }
 284
 285 /* Unlink the last component and attempt to remove leading
 286  * directories, in case this unlink is the removal of the
 287  * last entry in the directory -- empty directories are removed.
 288  */
 289 static void unlink_entry(char *name)
 290 {
 291         char *cp, *prev;
 292
 293         if (unlink(name))
 294                 return;
 295         prev = NULL;
 296         while (1) {
 297                 int status;
 298                 cp = strrchr(name, '/');
 299                 if (prev)
 300                         *prev = '/';
 301                 if (!cp)
 302                         break;
 303
 304                 *cp = 0;
 305                 status = rmdir(name);
 306                 if (status) {
 307                         *cp = '/';
 308                         break;
 309                 }
 310                 prev = cp;
 311         }
 312 }
 313
 314 static void progress_interval(int signum)
 315 {
 316         progress_update = 1;
 317 }
 318
 319 static void setup_progress_signal(void)
 320 {
 321         struct sigaction sa;
 322         struct itimerval v;
 323
 324         memset(&sa, 0, sizeof(sa));
 325         sa.sa_handler = progress_interval;
 326         sigemptyset(&sa.sa_mask);
 327         sa.sa_flags = SA_RESTART;
 328         sigaction(SIGALRM, &sa, NULL);
 329
 330         v.it_interval.tv_sec = 1;
 331         v.it_interval.tv_usec = 0;
 332         v.it_value = v.it_interval;
 333         setitimer(ITIMER_REAL, &v, NULL);
 334 }
 335
 336 static void check_updates(struct cache_entry **src, int nr)
 337 {
 338         static struct checkout state = {
 339                 .base_dir = "",
 340                 .force = 1,
 341                 .quiet = 1,
 342                 .refresh_cache = 1,
 343         };
 344         unsigned short mask = htons(CE_UPDATE);
 345         unsigned last_percent = 200, cnt = 0, total = 0;
 346
 347         if (update && verbose_update) {
 348                 for (total = cnt = 0; cnt < nr; cnt++) {
 349                         struct cache_entry *ce = src[cnt];
 350                         if (!ce->ce_mode || ce->ce_flags & mask)
 351                                 total++;
 352                 }
 353
 354                 /* Don't bother doing this for very small updates */
 355                 if (total < 250)
 356                         total = 0;
 357
 358                 if (total) {
 359                         fprintf(stderr, "Checking files out...\n");
 360                         setup_progress_signal();
 361                         progress_update = 1;
 362                 }
 363                 cnt = 0;
 364         }
 365
 366         while (nr--) {
 367                 struct cache_entry *ce = *src++;
 368
 369                 if (total) {
 370                         if (!ce->ce_mode || ce->ce_flags & mask) {
 371                                 unsigned percent;
 372                                 cnt++;
 373                                 percent = (cnt * 100) / total;
 374                                 if (percent != last_percent ||
 375                                     progress_update) {
 376                                         fprintf(stderr, "%4u%% (%u/%u) done\r",
 377                                                 percent, cnt, total);
 378                                         last_percent = percent;
 379                                         progress_update = 0;
 380                                 }
 381                         }
 382                 }
 383                 if (!ce->ce_mode) {
 384                         if (update)
 385                                 unlink_entry(ce->name);
 386                         continue;
 387                 }
 388                 if (ce->ce_flags & mask) {
 389                         ce->ce_flags &= ~mask;
 390                         if (update)
 391                                 checkout_entry(ce, &state, NULL);
 392                 }
 393         }
 394         if (total) {
 395                 signal(SIGALRM, SIG_IGN);
 396                 fputc('\n', stderr);
 397         }
 398 }
 399
 400 static int unpack_trees(merge_fn_t fn)
 401 {
 402         int indpos = 0;
 403         unsigned len = object_list_length(trees);
 404         struct tree_entry_list **posns;
 405         int i;
 406         struct object_list *posn = trees;
 407         merge_size = len;
 408
 409         if (len) {
 410                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
 411                 for (i = 0; i < len; i++) {
 412                         posns[i] = create_tree_entry_list((struct tree *) posn->item);
 413                         posn = posn->next;
 414                 }
 415                 if (unpack_trees_rec(posns, len, prefix ? prefix : "",
 416                                      fn, &indpos))
 417                         return -1;
 418         }
 419
 420         if (trivial_merges_only && nontrivial_merge)
 421                 die("Merge requires file-level merging");
 422
 423         check_updates(active_cache, active_nr);
 424         return 0;
 425 }
 426
 427 static int list_tree(unsigned char *sha1)
 428 {
 429         struct tree *tree = parse_tree_indirect(sha1);
 430         if (!tree)
 431                 return -1;
 432         object_list_append(&tree->object, &trees);
 433         return 0;
 434 }
 435
 436 static int same(struct cache_entry *a, struct cache_entry *b)
 437 {
 438         if (!!a != !!b)
 439                 return 0;
 440         if (!a && !b)
 441                 return 1;
 442         return a->ce_mode == b->ce_mode &&
 443                 !memcmp(a->sha1, b->sha1, 20);
 444 }
 445
 446
 447 /*
 448  * When a CE gets turned into an unmerged entry, we
 449  * want it to be up-to-date
 450  */
 451 static void verify_uptodate(struct cache_entry *ce)
 452 {
 453         struct stat st;
 454
 455         if (index_only || reset)
 456                 return;
 457
 458         if (!lstat(ce->name, &st)) {
 459                 unsigned changed = ce_match_stat(ce, &st, 1);
 460                 if (!changed)
 461                         return;
 462                 errno = 0;
 463         }
 464         if (reset) {
 465                 ce->ce_flags |= htons(CE_UPDATE);
 466                 return;
 467         }
 468         if (errno == ENOENT)
 469                 return;
 470         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 471 }
 472
 473 static void invalidate_ce_path(struct cache_entry *ce)
 474 {
 475         if (ce)
 476                 cache_tree_invalidate_path(active_cache_tree, ce->name);
 477 }
 478
 479 /*
 480  * We do not want to remove or overwrite a working tree file that
 481  * is not tracked.
 482  */
 483 static void verify_absent(const char *path, const char *action)
 484 {
 485         struct stat st;
 486
 487         if (index_only || reset || !update)
 488                 return;
 489         if (!lstat(path, &st))
 490                 die("Untracked working tree file '%s' "
 491                     "would be %s by merge.", path, action);
 492 }
 493
 494 static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
 495 {
 496         merge->ce_flags |= htons(CE_UPDATE);
 497         if (old) {
 498                 /*
 499                  * See if we can re-use the old CE directly?
 500                  * That way we get the uptodate stat info.
 501                  *
 502                  * This also removes the UPDATE flag on
 503                  * a match.
 504                  */
 505                 if (same(old, merge)) {
 506                         *merge = *old;
 507                 } else {
 508                         verify_uptodate(old);
 509                         invalidate_ce_path(old);
 510                 }
 511         }
 512         else {
 513                 verify_absent(merge->name, "overwritten");
 514                 invalidate_ce_path(merge);
 515         }
 516
 517         merge->ce_flags &= ~htons(CE_STAGEMASK);
 518         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
 519         return 1;
 520 }
 521
 522 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
 523 {
 524         if (old)
 525                 verify_uptodate(old);
 526         else
 527                 verify_absent(ce->name, "removed");
 528         ce->ce_mode = 0;
 529         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 530         invalidate_ce_path(ce);
 531         return 1;
 532 }
 533
 534 static int keep_entry(struct cache_entry *ce)
 535 {
 536         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 537         return 1;
 538 }
 539
 540 #if DBRT_DEBUG
 541 static void show_stage_entry(FILE *o,
 542                              const char *label, const struct cache_entry *ce)
 543 {
 544         if (!ce)
 545                 fprintf(o, "%s (missing)\n", label);
 546         else
 547                 fprintf(o, "%s%06o %s %d\t%s\n",
 548                         label,
 549                         ntohl(ce->ce_mode),
 550                         sha1_to_hex(ce->sha1),
 551                         ce_stage(ce),
 552                         ce->name);
 553 }
 554 #endif
 555
 556 static int threeway_merge(struct cache_entry **stages)
 557 {
 558         struct cache_entry *index;
 559         struct cache_entry *head;
 560         struct cache_entry *remote = stages[head_idx + 1];
 561         int count;
 562         int head_match = 0;
 563         int remote_match = 0;
 564         const char *path = NULL;
 565
 566         int df_conflict_head = 0;
 567         int df_conflict_remote = 0;
 568
 569         int any_anc_missing = 0;
 570         int no_anc_exists = 1;
 571         int i;
 572
 573         for (i = 1; i < head_idx; i++) {
 574                 if (!stages[i])
 575                         any_anc_missing = 1;
 576                 else {
 577                         if (!path)
 578                                 path = stages[i]->name;
 579                         no_anc_exists = 0;
 580                 }
 581         }
 582
 583         index = stages[0];
 584         head = stages[head_idx];
 585
 586         if (head == &df_conflict_entry) {
 587                 df_conflict_head = 1;
 588                 head = NULL;
 589         }
 590
 591         if (remote == &df_conflict_entry) {
 592                 df_conflict_remote = 1;
 593                 remote = NULL;
 594         }
 595
 596         if (!path && index)
 597                 path = index->name;
 598         if (!path && head)
 599                 path = head->name;
 600         if (!path && remote)
 601                 path = remote->name;
 602
 603         /* First, if there's a #16 situation, note that to prevent #13
 604          * and #14.
 605          */
 606         if (!same(remote, head)) {
 607                 for (i = 1; i < head_idx; i++) {
 608                         if (same(stages[i], head)) {
 609                                 head_match = i;
 610                         }
 611                         if (same(stages[i], remote)) {
 612                                 remote_match = i;
 613                         }
 614                 }
 615         }
 616
 617         /* We start with cases where the index is allowed to match
 618          * something other than the head: #14(ALT) and #2ALT, where it
 619          * is permitted to match the result instead.
 620          */
 621         /* #14, #14ALT, #2ALT */
 622         if (remote && !df_conflict_head && head_match && !remote_match) {
 623                 if (index && !same(index, remote) && !same(index, head))
 624                         reject_merge(index);
 625                 return merged_entry(remote, index);
 626         }
 627         /*
 628          * If we have an entry in the index cache, then we want to
 629          * make sure that it matches head.
 630          */
 631         if (index && !same(index, head)) {
 632                 reject_merge(index);
 633         }
 634
 635         if (head) {
 636                 /* #5ALT, #15 */
 637                 if (same(head, remote))
 638                         return merged_entry(head, index);
 639                 /* #13, #3ALT */
 640                 if (!df_conflict_remote && remote_match && !head_match)
 641                         return merged_entry(head, index);
 642         }
 643
 644         /* #1 */
 645         if (!head && !remote && any_anc_missing)
 646                 return 0;
 647
 648         /* Under the new "aggressive" rule, we resolve mostly trivial
 649          * cases that we historically had git-merge-one-file resolve.
 650          */
 651         if (aggressive) {
 652                 int head_deleted = !head && !df_conflict_head;
 653                 int remote_deleted = !remote && !df_conflict_remote;
 654                 /*
 655                  * Deleted in both.
 656                  * Deleted in one and unchanged in the other.
 657                  */
 658                 if ((head_deleted && remote_deleted) ||
 659                     (head_deleted && remote && remote_match) ||
 660                     (remote_deleted && head && head_match)) {
 661                         if (index)
 662                                 return deleted_entry(index, index);
 663                         else if (path)
 664                                 verify_absent(path, "removed");
 665                         return 0;
 666                 }
 667                 /*
 668                  * Added in both, identically.
 669                  */
 670                 if (no_anc_exists && head && remote && same(head, remote))
 671                         return merged_entry(head, index);
 672
 673         }
 674
 675         /* Below are "no merge" cases, which require that the index be
 676          * up-to-date to avoid the files getting overwritten with
 677          * conflict resolution files.
 678          */
 679         if (index) {
 680                 verify_uptodate(index);
 681         }
 682         else if (path)
 683                 verify_absent(path, "overwritten");
 684
 685         nontrivial_merge = 1;
 686
 687         /* #2, #3, #4, #6, #7, #9, #11. */
 688         count = 0;
 689         if (!head_match || !remote_match) {
 690                 for (i = 1; i < head_idx; i++) {
 691                         if (stages[i]) {
 692                                 keep_entry(stages[i]);
 693                                 count++;
 694                                 break;
 695                         }
 696                 }
 697         }
 698 #if DBRT_DEBUG
 699         else {
 700                 fprintf(stderr, "read-tree: warning #16 detected\n");
 701                 show_stage_entry(stderr, "head   ", stages[head_match]);
 702                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 703         }
 704 #endif
 705         if (head) { count += keep_entry(head); }
 706         if (remote) { count += keep_entry(remote); }
 707         return count;
 708 }
 709
 710 /*
 711  * Two-way merge.
 712  *
 713  * The rule is to "carry forward" what is in the index without losing
 714  * information across a "fast forward", favoring a successful merge
 715  * over a merge failure when it makes sense.  For details of the
 716  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 717  *
 718  */
 719 static int twoway_merge(struct cache_entry **src)
 720 {
 721         struct cache_entry *current = src[0];
 722         struct cache_entry *oldtree = src[1], *newtree = src[2];
 723
 724         if (merge_size != 2)
 725                 return error("Cannot do a twoway merge of %d trees",
 726                              merge_size);
 727
 728         if (current) {
 729                 if ((!oldtree && !newtree) || /* 4 and 5 */
 730                     (!oldtree && newtree &&
 731                      same(current, newtree)) || /* 6 and 7 */
 732                     (oldtree && newtree &&
 733                      same(oldtree, newtree)) || /* 14 and 15 */
 734                     (oldtree && newtree &&
 735                      !same(oldtree, newtree) && /* 18 and 19*/
 736                      same(current, newtree))) {
 737                         return keep_entry(current);
 738                 }
 739                 else if (oldtree && !newtree && same(current, oldtree)) {
 740                         /* 10 or 11 */
 741                         return deleted_entry(oldtree, current);
 742                 }
 743                 else if (oldtree && newtree &&
 744                          same(current, oldtree) && !same(current, newtree)) {
 745                         /* 20 or 21 */
 746                         return merged_entry(newtree, current);
 747                 }
 748                 else {
 749                         /* all other failures */
 750                         if (oldtree)
 751                                 reject_merge(oldtree);
 752                         if (current)
 753                                 reject_merge(current);
 754                         if (newtree)
 755                                 reject_merge(newtree);
 756                         return -1;
 757                 }
 758         }
 759         else if (newtree)
 760                 return merged_entry(newtree, current);
 761         else
 762                 return deleted_entry(oldtree, current);
 763 }
 764
 765 /*
 766  * Bind merge.
 767  *
 768  * Keep the index entries at stage0, collapse stage1 but make sure
 769  * stage0 does not have anything there.
 770  */
 771 static int bind_merge(struct cache_entry **src)
 772 {
 773         struct cache_entry *old = src[0];
 774         struct cache_entry *a = src[1];
 775
 776         if (merge_size != 1)
 777                 return error("Cannot do a bind merge of %d trees\n",
 778                              merge_size);
 779         if (a && old)
 780                 die("Entry '%s' overlaps.  Cannot bind.", a->name);
 781         if (!a)
 782                 return keep_entry(old);
 783         else
 784                 return merged_entry(a, NULL);
 785 }
 786
 787 /*
 788  * One-way merge.
 789  *
 790  * The rule is:
 791  * - take the stat information from stage0, take the data from stage1
 792  */
 793 static int oneway_merge(struct cache_entry **src)
 794 {
 795         struct cache_entry *old = src[0];
 796         struct cache_entry *a = src[1];
 797
 798         if (merge_size != 1)
 799                 return error("Cannot do a oneway merge of %d trees",
 800                              merge_size);
 801
 802         if (!a)
 803                 return deleted_entry(old, old);
 804         if (old && same(old, a)) {
 805                 if (reset) {
 806                         struct stat st;
 807                         if (lstat(old->name, &st) ||
 808                             ce_match_stat(old, &st, 1))
 809                                 old->ce_flags |= htons(CE_UPDATE);
 810                 }
 811                 return keep_entry(old);
 812         }
 813         return merged_entry(a, old);
 814 }
 815
 816 static int read_cache_unmerged(void)
 817 {
 818         int i;
 819         struct cache_entry **dst;
 820         struct cache_entry *last = NULL;
 821
 822         read_cache();
 823         dst = active_cache;
 824         for (i = 0; i < active_nr; i++) {
 825                 struct cache_entry *ce = active_cache[i];
 826                 if (ce_stage(ce)) {
 827                         if (last && !strcmp(ce->name, last->name))
 828                                 continue;
 829                         invalidate_ce_path(ce);
 830                         last = ce;
 831                         ce->ce_mode = 0;
 832                         ce->ce_flags &= ~htons(CE_STAGEMASK);
 833                 }
 834                 *dst++ = ce;
 835         }
 836         active_nr = dst - active_cache;
 837         return !!last;
 838 }
 839
 840 static void prime_cache_tree_rec(struct cache_tree *it, struct tree *tree)
 841 {
 842         struct tree_desc desc;
 843         struct name_entry entry;
 844         int cnt;
 845
 846         memcpy(it->sha1, tree->object.sha1, 20);
 847         desc.buf = tree->buffer;
 848         desc.size = tree->size;
 849         cnt = 0;
 850         while (tree_entry(&desc, &entry)) {
 851                 if (!S_ISDIR(entry.mode))
 852                         cnt++;
 853                 else {
 854                         struct cache_tree_sub *sub;
 855                         struct tree *subtree = lookup_tree(entry.sha1);
 856                         if (!subtree->object.parsed)
 857                                 parse_tree(subtree);
 858                         sub = cache_tree_sub(it, entry.path);
 859                         sub->cache_tree = cache_tree();
 860                         prime_cache_tree_rec(sub->cache_tree, subtree);
 861                         cnt += sub->cache_tree->entry_count;
 862                 }
 863         }
 864         it->entry_count = cnt;
 865 }
 866
 867 static void prime_cache_tree(void)
 868 {
 869         struct tree *tree = (struct tree *)trees->item;
 870         if (!tree)
 871                 return;
 872         active_cache_tree = cache_tree();
 873         prime_cache_tree_rec(active_cache_tree, tree);
 874
 875 }
 876
 877 static const char read_tree_usage[] = "git-read-tree (<sha> | [[-m [--aggressive] | --reset | --prefix=<prefix>] [-u | -i]] <sha1> [<sha2> [<sha3>]])";
 878
 879 static struct lock_file lock_file;
 880
 881 int cmd_read_tree(int argc, const char **argv, char **envp)
 882 {
 883         int i, newfd, stage = 0;
 884         unsigned char sha1[20];
 885         merge_fn_t fn = NULL;
 886
 887         setup_git_directory();
 888         git_config(git_default_config);
 889
 890         newfd = hold_lock_file_for_update(&lock_file, get_index_file());
 891         if (newfd < 0)
 892                 die("unable to create new index file");
 893
 894         git_config(git_default_config);
 895
 896         merge = 0;
 897         reset = 0;
 898         for (i = 1; i < argc; i++) {
 899                 const char *arg = argv[i];
 900
 901                 /* "-u" means "update", meaning that a merge will update
 902                  * the working tree.
 903                  */
 904                 if (!strcmp(arg, "-u")) {
 905                         update = 1;
 906                         continue;
 907                 }
 908
 909                 if (!strcmp(arg, "-v")) {
 910                         verbose_update = 1;
 911                         continue;
 912                 }
 913
 914                 /* "-i" means "index only", meaning that a merge will
 915                  * not even look at the working tree.
 916                  */
 917                 if (!strcmp(arg, "-i")) {
 918                         index_only = 1;
 919                         continue;
 920                 }
 921
 922                 /* "--prefix=<subdirectory>/" means keep the current index
 923                  *  entries and put the entries from the tree under the
 924                  * given subdirectory.
 925                  */
 926                 if (!strncmp(arg, "--prefix=", 9)) {
 927                         if (stage || merge || prefix)
 928                                 usage(read_tree_usage);
 929                         prefix = arg + 9;
 930                         merge = 1;
 931                         stage = 1;
 932                         if (read_cache_unmerged())
 933                                 die("you need to resolve your current index first");
 934                         continue;
 935                 }
 936
 937                 /* This differs from "-m" in that we'll silently ignore
 938                  * unmerged entries and overwrite working tree files that
 939                  * correspond to them.
 940                  */
 941                 if (!strcmp(arg, "--reset")) {
 942                         if (stage || merge || prefix)
 943                                 usage(read_tree_usage);
 944                         reset = 1;
 945                         merge = 1;
 946                         stage = 1;
 947                         read_cache_unmerged();
 948                         continue;
 949                 }
 950
 951                 if (!strcmp(arg, "--trivial")) {
 952                         trivial_merges_only = 1;
 953                         continue;
 954                 }
 955
 956                 if (!strcmp(arg, "--aggressive")) {
 957                         aggressive = 1;
 958                         continue;
 959                 }
 960
 961                 /* "-m" stands for "merge", meaning we start in stage 1 */
 962                 if (!strcmp(arg, "-m")) {
 963                         if (stage || merge || prefix)
 964                                 usage(read_tree_usage);
 965                         if (read_cache_unmerged())
 966                                 die("you need to resolve your current index first");
 967                         stage = 1;
 968                         merge = 1;
 969                         continue;
 970                 }
 971
 972                 /* using -u and -i at the same time makes no sense */
 973                 if (1 < index_only + update)
 974                         usage(read_tree_usage);
 975
 976                 if (get_sha1(arg, sha1))
 977                         die("Not a valid object name %s", arg);
 978                 if (list_tree(sha1) < 0)
 979                         die("failed to unpack tree object %s", arg);
 980                 stage++;
 981         }
 982         if ((update||index_only) && !merge)
 983                 usage(read_tree_usage);
 984
 985         if (prefix) {
 986                 int pfxlen = strlen(prefix);
 987                 int pos;
 988                 if (prefix[pfxlen-1] != '/')
 989                         die("prefix must end with /");
 990                 if (stage != 2)
 991                         die("binding merge takes only one tree");
 992                 pos = cache_name_pos(prefix, pfxlen);
 993                 if (0 <= pos)
 994                         die("corrupt index file");
 995                 pos = -pos-1;
 996                 if (pos < active_nr &&
 997                     !strncmp(active_cache[pos]->name, prefix, pfxlen))
 998                         die("subdirectory '%s' already exists.", prefix);
 999                 pos = cache_name_pos(prefix, pfxlen-1);
1000                 if (0 <= pos)
1001                         die("file '%.*s' already exists.", pfxlen-1, prefix);
1002         }
1003
1004         if (merge) {
1005                 if (stage < 2)
1006                         die("just how do you expect me to merge %d trees?", stage-1);
1007                 switch (stage - 1) {
1008                 case 1:
1009                         fn = prefix ? bind_merge : oneway_merge;
1010                         break;
1011                 case 2:
1012                         fn = twoway_merge;
1013                         break;
1014                 case 3:
1015                 default:
1016                         fn = threeway_merge;
1017                         cache_tree_free(&active_cache_tree);
1018                         break;
1019                 }
1020
1021                 if (stage - 1 >= 3)
1022                         head_idx = stage - 2;
1023                 else
1024                         head_idx = 1;
1025         }
1026
1027         unpack_trees(fn);
1028
1029         /*
1030          * When reading only one tree (either the most basic form,
1031          * "-m ent" or "--reset ent" form), we can obtain a fully
1032          * valid cache-tree because the index must match exactly
1033          * what came from the tree.
1034          */
1035         if (trees && trees->item && !prefix && (!merge || (stage == 2))) {
1036                 cache_tree_free(&active_cache_tree);
1037                 prime_cache_tree();
1038         }
1039
1040         if (write_cache(newfd, active_cache, active_nr) ||
1041             commit_lock_file(&lock_file))
1042                 die("unable to write new index file");
1043         return 0;
1044 }