read-tree.c

   1 /*
   2  * GIT - The information manager from hell
   3  *
   4  * Copyright (C) Linus Torvalds, 2005
   5  */
   6 #include "cache.h"
   7
   8 static int stage = 0;
   9 static int update = 0;
  10
  11 static int unpack_tree(unsigned char *sha1)
  12 {
  13         void *buffer;
  14         unsigned long size;
  15         int ret;
  16
  17         buffer = read_object_with_reference(sha1, "tree", &size, NULL);
  18         if (!buffer)
  19                 return -1;
  20         ret = read_tree(buffer, size, stage);
  21         free(buffer);
  22         return ret;
  23 }
  24
  25 static int path_matches(struct cache_entry *a, struct cache_entry *b)
  26 {
  27         int len = ce_namelen(a);
  28         return ce_namelen(b) == len &&
  29                 !memcmp(a->name, b->name, len);
  30 }
  31
  32 static int same(struct cache_entry *a, struct cache_entry *b)
  33 {
  34         return a->ce_mode == b->ce_mode &&
  35                 !memcmp(a->sha1, b->sha1, 20);
  36 }
  37
  38
  39 /*
  40  * This removes all trivial merges that don't change the tree
  41  * and collapses them to state 0.
  42  */
  43 static struct cache_entry *merge_entries(struct cache_entry *a,
  44                                          struct cache_entry *b,
  45                                          struct cache_entry *c)
  46 {
  47         /*
  48          * Ok, all three entries describe the same
  49          * filename, but maybe the contents or file
  50          * mode have changed?
  51          *
  52          * The trivial cases end up being the ones where two
  53          * out of three files are the same:
  54          *  - both destinations the same, trivially take either
  55          *  - one of the destination versions hasn't changed,
  56          *    take the other.
  57          *
  58          * The "all entries exactly the same" case falls out as
  59          * a special case of any of the "two same" cases.
  60          *
  61          * Here "a" is "original", and "b" and "c" are the two
  62          * trees we are merging.
  63          */
  64         if (a && b && c) {
  65                 if (same(b,c))
  66                         return c;
  67                 if (same(a,b))
  68                         return c;
  69                 if (same(a,c))
  70                         return b;
  71         }
  72         return NULL;
  73 }
  74
  75 /*
  76  * When a CE gets turned into an unmerged entry, we
  77  * want it to be up-to-date
  78  */
  79 static void verify_uptodate(struct cache_entry *ce)
  80 {
  81         struct stat st;
  82
  83         if (!lstat(ce->name, &st)) {
  84                 unsigned changed = ce_match_stat(ce, &st);
  85                 if (!changed)
  86                         return;
  87                 errno = 0;
  88         }
  89         if (errno == ENOENT)
  90                 return;
  91         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
  92 }
  93
  94 /*
  95  * If the old tree contained a CE that isn't even in the
  96  * result, that's always a problem, regardless of whether
  97  * it's up-to-date or not (ie it can be a file that we
  98  * have updated but not committed yet).
  99  */
 100 static void reject_merge(struct cache_entry *ce)
 101 {
 102         die("Entry '%s' would be overwritten by merge. Cannot merge.", ce->name);
 103 }
 104
 105 static int merged_entry_internal(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst, int allow_dirty)
 106 {
 107         merge->ce_flags |= htons(CE_UPDATE);
 108         if (old) {
 109                 /*
 110                  * See if we can re-use the old CE directly?
 111                  * That way we get the uptodate stat info.
 112                  *
 113                  * This also removes the UPDATE flag on
 114                  * a match.
 115                  */
 116                 if (same(old, merge)) {
 117                         *merge = *old;
 118                 } else if (!allow_dirty) {
 119                         verify_uptodate(old);
 120                 }
 121         }
 122         merge->ce_flags &= ~htons(CE_STAGEMASK);
 123         *dst++ = merge;
 124         return 1;
 125 }
 126
 127 static int merged_entry_allow_dirty(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
 128 {
 129         return merged_entry_internal(merge, old, dst, 1);
 130 }
 131
 132 static int merged_entry(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
 133 {
 134         return merged_entry_internal(merge, old, dst, 0);
 135 }
 136
 137 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old, struct cache_entry **dst)
 138 {
 139         if (old)
 140                 verify_uptodate(old);
 141         ce->ce_mode = 0;
 142         *dst++ = ce;
 143         return 1;
 144 }
 145
 146 static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **dst)
 147 {
 148         struct cache_entry *old = stages[0];
 149         struct cache_entry *a = stages[1], *b = stages[2], *c = stages[3];
 150         struct cache_entry *merge;
 151         int count;
 152
 153         /* #5ALT */
 154         if (!a && b && c && same(b, c)) {
 155                 if (old && !same(b, old))
 156                         return -1;
 157                 return merged_entry_allow_dirty(b, old, dst);
 158         }
 159         /*
 160          * If we have an entry in the index cache ("old"), then we want
 161          * to make sure that it matches any entries in stage 2 ("first
 162          * branch", aka "b").
 163          */
 164         if (old) {
 165                 if (!b || !same(old, b))
 166                         return -1;
 167         }
 168         merge = merge_entries(a, b, c);
 169         if (merge)
 170                 return merged_entry(merge, old, dst);
 171         if (old)
 172                 verify_uptodate(old);
 173         count = 0;
 174         if (a) { *dst++ = a; count++; }
 175         if (b) { *dst++ = b; count++; }
 176         if (c) { *dst++ = c; count++; }
 177         return count;
 178 }
 179
 180 /*
 181  * Two-way merge.
 182  *
 183  * The rule is to "carry forward" what is in the index without losing
 184  * information across a "fast forward", favoring a successful merge
 185  * over a merge failure when it makes sense.  For details of the
 186  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 187  *
 188  */
 189 static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
 190 {
 191         struct cache_entry *current = src[0];
 192         struct cache_entry *oldtree = src[1], *newtree = src[2];
 193
 194         if (src[3])
 195                 return -1;
 196
 197         if (current) {
 198                 if ((!oldtree && !newtree) || /* 4 and 5 */
 199                     (!oldtree && newtree &&
 200                      same(current, newtree)) || /* 6 and 7 */
 201                     (oldtree && newtree &&
 202                      same(oldtree, newtree)) || /* 14 and 15 */
 203                     (oldtree && newtree &&
 204                      !same(oldtree, newtree) && /* 18 and 19*/
 205                      same(current, newtree))) {
 206                         *dst++ = current;
 207                         return 1;
 208                 }
 209                 else if (oldtree && !newtree && same(current, oldtree)) {
 210                         /* 10 or 11 */
 211                         return deleted_entry(oldtree, current, dst);
 212                 }
 213                 else if (oldtree && newtree &&
 214                          same(current, oldtree) && !same(current, newtree)) {
 215                         /* 20 or 21 */
 216                         return merged_entry(newtree, current, dst);
 217                 }
 218                 else
 219                         /* all other failures */
 220                         return -1;
 221         }
 222         else if (newtree)
 223                 return merged_entry(newtree, current, dst);
 224         else
 225                 return deleted_entry(oldtree, current, dst);
 226 }
 227
 228 /*
 229  * Two-way merge emulated with three-way merge.
 230  *
 231  * This treats "read-tree -m H M" by transforming it internally
 232  * into "read-tree -m H I+H M", where I+H is a tree that would
 233  * contain the contents of the current index file, overlayed on
 234  * top of H.  Unlike the traditional two-way merge, this leaves
 235  * the stages in the resulting index file and lets the user resolve
 236  * the merge conflicts using standard tools for three-way merge.
 237  *
 238  * This function is just to set-up such an arrangement, and the
 239  * actual merge uses threeway_merge() function.
 240  */
 241 static void setup_emu23(void)
 242 {
 243         /* stage0 contains I, stage1 H, stage2 M.
 244          * move stage2 to stage3, and create stage2 entries
 245          * by scanning stage0 and stage1 entries.
 246          */
 247         int i, namelen, size;
 248         struct cache_entry *ce, *stage2;
 249
 250         for (i = 0; i < active_nr; i++) {
 251                 ce = active_cache[i];
 252                 if (ce_stage(ce) != 2)
 253                         continue;
 254                 /* hoist them up to stage 3 */
 255                 namelen = ce_namelen(ce);
 256                 ce->ce_flags = create_ce_flags(namelen, 3);
 257         }
 258
 259         for (i = 0; i < active_nr; i++) {
 260                 ce = active_cache[i];
 261                 if (ce_stage(ce) > 1)
 262                         continue;
 263                 namelen = ce_namelen(ce);
 264                 size = cache_entry_size(namelen);
 265                 stage2 = xmalloc(size);
 266                 memcpy(stage2, ce, size);
 267                 stage2->ce_flags = create_ce_flags(namelen, 2);
 268                 if (add_cache_entry(stage2, ADD_CACHE_OK_TO_ADD) < 0)
 269                         die("cannot merge index and our head tree");
 270
 271                 /* We are done with this name, so skip to next name */
 272                 while (i < active_nr &&
 273                        ce_namelen(active_cache[i]) == namelen &&
 274                        !memcmp(active_cache[i]->name, ce->name, namelen))
 275                         i++;
 276                 i--; /* compensate for the loop control */
 277         }
 278 }
 279
 280 /*
 281  * One-way merge.
 282  *
 283  * The rule is:
 284  * - take the stat information from stage0, take the data from stage1
 285  */
 286 static int oneway_merge(struct cache_entry **src, struct cache_entry **dst)
 287 {
 288         struct cache_entry *old = src[0];
 289         struct cache_entry *a = src[1];
 290
 291         if (src[2] || src[3])
 292                 return -1;
 293
 294         if (!a)
 295                 return 0;
 296         if (old && same(old, a)) {
 297                 *dst++ = old;
 298                 return 1;
 299         }
 300         return merged_entry(a, NULL, dst);
 301 }
 302
 303 static void check_updates(struct cache_entry **src, int nr)
 304 {
 305         static struct checkout state = {
 306                 .base_dir = "",
 307                 .force = 1,
 308                 .quiet = 1,
 309                 .refresh_cache = 1,
 310         };
 311         unsigned short mask = htons(CE_UPDATE);
 312         while (nr--) {
 313                 struct cache_entry *ce = *src++;
 314                 if (!ce->ce_mode) {
 315                         if (update)
 316                                 unlink(ce->name);
 317                         continue;
 318                 }
 319                 if (ce->ce_flags & mask) {
 320                         ce->ce_flags &= ~mask;
 321                         if (update)
 322                                 checkout_entry(ce, &state);
 323                 }
 324         }
 325 }
 326
 327 typedef int (*merge_fn_t)(struct cache_entry **, struct cache_entry **);
 328
 329 static void merge_cache(struct cache_entry **src, int nr, merge_fn_t fn)
 330 {
 331         struct cache_entry **dst = src;
 332
 333         while (nr) {
 334                 int entries;
 335                 struct cache_entry *name, *ce, *stages[4] = { NULL, };
 336
 337                 name = ce = *src;
 338                 for (;;) {
 339                         int stage = ce_stage(ce);
 340                         stages[stage] = ce;
 341                         ce = *++src;
 342                         active_nr--;
 343                         if (!--nr)
 344                                 break;
 345                         if (!path_matches(ce, name))
 346                                 break;
 347                 }
 348
 349                 entries = fn(stages, dst);
 350                 if (entries < 0)
 351                         reject_merge(name);
 352                 dst += entries;
 353                 active_nr += entries;
 354         }
 355         check_updates(active_cache, active_nr);
 356 }
 357
 358 static int read_cache_unmerged(void)
 359 {
 360         int i, deleted;
 361         struct cache_entry **dst;
 362
 363         read_cache();
 364         dst = active_cache;
 365         deleted = 0;
 366         for (i = 0; i < active_nr; i++) {
 367                 struct cache_entry *ce = active_cache[i];
 368                 if (ce_stage(ce)) {
 369                         deleted++;
 370                         continue;
 371                 }
 372                 if (deleted)
 373                         *dst = ce;
 374                 dst++;
 375         }
 376         active_nr -= deleted;
 377         return deleted;
 378 }
 379
 380 static char *read_tree_usage = "git-read-tree (<sha> | -m [-u] <sha1> [<sha2> [<sha3>]])";
 381
 382 static struct cache_file cache_file;
 383
 384 int main(int argc, char **argv)
 385 {
 386         int i, newfd, merge, reset, emu23;
 387         unsigned char sha1[20];
 388
 389         newfd = hold_index_file_for_update(&cache_file, get_index_file());
 390         if (newfd < 0)
 391                 die("unable to create new cachefile");
 392
 393         merge = 0;
 394         reset = 0;
 395         emu23 = 0;
 396         for (i = 1; i < argc; i++) {
 397                 const char *arg = argv[i];
 398
 399                 /* "-u" means "update", meaning that a merge will update the working directory */
 400                 if (!strcmp(arg, "-u")) {
 401                         update = 1;
 402                         continue;
 403                 }
 404
 405                 /* This differs from "-m" in that we'll silently ignore unmerged entries */
 406                 if (!strcmp(arg, "--reset")) {
 407                         if (stage || merge || emu23)
 408                                 usage(read_tree_usage);
 409                         reset = 1;
 410                         merge = 1;
 411                         stage = 1;
 412                         read_cache_unmerged();
 413                 }
 414
 415                 /* "-m" stands for "merge", meaning we start in stage 1 */
 416                 if (!strcmp(arg, "-m")) {
 417                         if (stage || merge || emu23)
 418                                 usage(read_tree_usage);
 419                         if (read_cache_unmerged())
 420                                 die("you need to resolve your current index first");
 421                         stage = 1;
 422                         merge = 1;
 423                         continue;
 424                 }
 425
 426                 /* "-emu23" uses 3-way merge logic to perform fast-forward */
 427                 if (!strcmp(arg, "--emu23")) {
 428                         if (stage || merge || emu23)
 429                                 usage(read_tree_usage);
 430                         if (read_cache_unmerged())
 431                                 die("you need to resolve your current index first");
 432                         merge = emu23 = stage = 1;
 433                         continue;
 434                 }
 435
 436                 if (get_sha1(arg, sha1) < 0)
 437                         usage(read_tree_usage);
 438                 if (stage > 3)
 439                         usage(read_tree_usage);
 440                 if (unpack_tree(sha1) < 0)
 441                         die("failed to unpack tree object %s", arg);
 442                 stage++;
 443         }
 444         if (update && !merge)
 445                 usage(read_tree_usage);
 446         if (merge) {
 447                 static const merge_fn_t merge_function[] = {
 448                         [1] = oneway_merge,
 449                         [2] = twoway_merge,
 450                         [3] = threeway_merge,
 451                 };
 452                 merge_fn_t fn;
 453
 454                 if (stage < 2 || stage > 4)
 455                         die("just how do you expect me to merge %d trees?", stage-1);
 456                 if (emu23 && stage != 3)
 457                         die("--emu23 takes only two trees");
 458                 fn = merge_function[stage-1];
 459                 if (stage == 3 && emu23) {
 460                         setup_emu23();
 461                         fn = merge_function[3];
 462                 }
 463                 merge_cache(active_cache, active_nr, fn);
 464         }
 465         if (write_cache(newfd, active_cache, active_nr) ||
 466             commit_index_file(&cache_file))
 467                 die("unable to write new index file");
 468         return 0;
 469 }