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(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
 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 {
 119                         verify_uptodate(old);
 120                 }
 121         }
 122         merge->ce_flags &= ~htons(CE_STAGEMASK);
 123         *dst++ = merge;
 124         return 1;
 125 }
 126
 127 static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **dst)
 128 {
 129         struct cache_entry *old = stages[0];
 130         struct cache_entry *a = stages[1], *b = stages[2], *c = stages[3];
 131         struct cache_entry *merge;
 132         int count;
 133
 134         /*
 135          * If we have an entry in the index cache ("old"), then we want
 136          * to make sure that it matches any entries in stage 2 ("first
 137          * branch", aka "b").
 138          */
 139         if (old) {
 140                 if (!b || !same(old, b))
 141                         return -1;
 142         }
 143         merge = merge_entries(a, b, c);
 144         if (merge)
 145                 return merged_entry(merge, old, dst);
 146         if (old)
 147                 verify_uptodate(old);
 148         count = 0;
 149         if (a) { *dst++ = a; count++; }
 150         if (b) { *dst++ = b; count++; }
 151         if (c) { *dst++ = c; count++; }
 152         return count;
 153 }
 154
 155 /*
 156  * Two-way merge.
 157  *
 158  * The rule is to "carry forward" what is in the index without losing
 159  * information across a "fast forward", favoring a successful merge
 160  * over a merge failure when it makes sense.  For details of the
 161  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 162  *
 163  */
 164 static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
 165 {
 166         struct cache_entry *current = src[0];
 167         struct cache_entry *oldtree = src[1], *newtree = src[2];
 168
 169         if (src[3])
 170                 return -1;
 171
 172         if (current) {
 173                 if ((!oldtree && !newtree) || /* 4 and 5 */
 174                     (!oldtree && newtree &&
 175                      same(current, newtree)) || /* 6 and 7 */
 176                     (oldtree && newtree &&
 177                      same(oldtree, newtree)) || /* 14 and 15 */
 178                     (oldtree && newtree &&
 179                      !same(oldtree, newtree) && /* 18 and 19*/
 180                      same(current, newtree))) {
 181                         *dst++ = current;
 182                         return 1;
 183                 }
 184                 else if (oldtree && !newtree && same(current, oldtree)) {
 185                         /* 10 or 11 */
 186                         verify_uptodate(current);
 187                         return 0;
 188                 }
 189                 else if (oldtree && newtree &&
 190                          same(current, oldtree) && !same(current, newtree)) {
 191                         /* 20 or 21 */
 192                         verify_uptodate(current);
 193                         return merged_entry(newtree, NULL, dst);
 194                 }
 195                 else
 196                         /* all other failures */
 197                         return -1;
 198         }
 199         else if (newtree)
 200                 return merged_entry(newtree, NULL, dst);
 201         else
 202                 return 0;
 203 }
 204
 205 /*
 206  * One-way merge.
 207  *
 208  * The rule is:
 209  * - take the stat information from stage0, take the data from stage1
 210  */
 211 static int oneway_merge(struct cache_entry **src, struct cache_entry **dst)
 212 {
 213         struct cache_entry *old = src[0];
 214         struct cache_entry *a = src[1];
 215
 216         if (src[2] || src[3])
 217                 return -1;
 218
 219         if (!a)
 220                 return 0;
 221         if (old && same(old, a)) {
 222                 *dst++ = old;
 223                 return 1;
 224         }
 225         return merged_entry(a, NULL, dst);
 226 }
 227
 228 static void check_updates(struct cache_entry **src, int nr)
 229 {
 230         static struct checkout state = {
 231                 .base_dir = "",
 232                 .force = 1,
 233                 .quiet = 1,
 234                 .refresh_cache = 1,
 235         };
 236         unsigned short mask = htons(CE_UPDATE);
 237         while (nr--) {
 238                 struct cache_entry *ce = *src++;
 239                 if (ce->ce_flags & mask) {
 240                         ce->ce_flags &= ~mask;
 241                         if (update)
 242                                 checkout_entry(ce, &state);
 243                 }
 244         }
 245 }
 246
 247 typedef int (*merge_fn_t)(struct cache_entry **, struct cache_entry **);
 248
 249 static void merge_cache(struct cache_entry **src, int nr, merge_fn_t fn)
 250 {
 251         struct cache_entry **dst = src;
 252
 253         while (nr) {
 254                 int entries;
 255                 struct cache_entry *name, *ce, *stages[4] = { NULL, };
 256
 257                 name = ce = *src;
 258                 for (;;) {
 259                         int stage = ce_stage(ce);
 260                         stages[stage] = ce;
 261                         ce = *++src;
 262                         active_nr--;
 263                         if (!--nr)
 264                                 break;
 265                         if (!path_matches(ce, name))
 266                                 break;
 267                 }
 268
 269                 entries = fn(stages, dst);
 270                 if (entries < 0)
 271                         reject_merge(name);
 272                 dst += entries;
 273                 active_nr += entries;
 274         }
 275         check_updates(active_cache, active_nr);
 276 }
 277
 278 static char *read_tree_usage = "git-read-tree (<sha> | -m [-u] <sha1> [<sha2> [<sha3>]])";
 279
 280 static struct cache_file cache_file;
 281
 282 int main(int argc, char **argv)
 283 {
 284         int i, newfd, merge;
 285         unsigned char sha1[20];
 286
 287         newfd = hold_index_file_for_update(&cache_file, get_index_file());
 288         if (newfd < 0)
 289                 die("unable to create new cachefile");
 290
 291         merge = 0;
 292         for (i = 1; i < argc; i++) {
 293                 const char *arg = argv[i];
 294
 295                 /* "-u" means "update", meaning that a merge will update the working directory */
 296                 if (!strcmp(arg, "-u")) {
 297                         update = 1;
 298                         continue;
 299                 }
 300
 301                 /* "-m" stands for "merge", meaning we start in stage 1 */
 302                 if (!strcmp(arg, "-m")) {
 303                         int i;
 304                         if (stage)
 305                                 die("-m needs to come first");
 306                         read_cache();
 307                         for (i = 0; i < active_nr; i++) {
 308                                 if (ce_stage(active_cache[i]))
 309                                         die("you need to resolve your current index first");
 310                         }
 311                         stage = 1;
 312                         merge = 1;
 313                         continue;
 314                 }
 315                 if (get_sha1(arg, sha1) < 0)
 316                         usage(read_tree_usage);
 317                 if (stage > 3)
 318                         usage(read_tree_usage);
 319                 if (unpack_tree(sha1) < 0)
 320                         die("failed to unpack tree object %s", arg);
 321                 stage++;
 322         }
 323         if (update && !merge)
 324                 usage(read_tree_usage);
 325         if (merge) {
 326                 static const merge_fn_t merge_function[] = {
 327                         [1] = oneway_merge,
 328                         [2] = twoway_merge,
 329                         [3] = threeway_merge,
 330                 };
 331                 if (stage < 2 || stage > 4)
 332                         die("just how do you expect me to merge %d trees?", stage-1);
 333                 merge_cache(active_cache, active_nr, merge_function[stage-1]);
 334         }
 335         if (write_cache(newfd, active_cache, active_nr) ||
 336             commit_index_file(&cache_file))
 337                 die("unable to write new index file");
 338         return 0;
 339 }