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:
 159  *  - every current entry has to match the old tree
 160  *  - if the current entry matches the new tree, we leave it
 161  *    as-is. Otherwise we require that it be up-to-date.
 162  */
 163 static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
 164 {
 165         struct cache_entry *old = src[0];
 166         struct cache_entry *a = src[1], *b = src[2];
 167
 168         if (src[3])
 169                 return -1;
 170
 171         if (old) {
 172                 if (!a || !same(old, a))
 173                         return -1;
 174         }
 175         if (b)
 176                 return merged_entry(b, old, dst);
 177         if (old)
 178                 verify_uptodate(old);
 179         return 0;
 180 }
 181
 182 /*
 183  * One-way merge.
 184  *
 185  * The rule is:
 186  * - take the stat information from stage0, take the data from stage1
 187  */
 188 static int oneway_merge(struct cache_entry **src, struct cache_entry **dst)
 189 {
 190         struct cache_entry *old = src[0];
 191         struct cache_entry *a = src[1];
 192
 193         if (src[2] || src[3])
 194                 return -1;
 195
 196         if (!a)
 197                 return 0;
 198         if (old && same(old, a))
 199                 *a = *old;
 200         a->ce_flags &= ~htons(CE_STAGEMASK);
 201         *dst++ = a;
 202         return 1;
 203 }
 204
 205 static void check_updates(struct cache_entry **src, int nr)
 206 {
 207         static struct checkout state = {
 208                 .base_dir = "",
 209                 .force = 1,
 210                 .quiet = 1,
 211                 .refresh_cache = 1,
 212         };
 213         unsigned short mask = htons(CE_UPDATE);
 214         while (nr--) {
 215                 struct cache_entry *ce = *src++;
 216                 if (ce->ce_flags & mask) {
 217                         ce->ce_flags &= ~mask;
 218                         if (update)
 219                                 checkout_entry(ce, &state);
 220                 }
 221         }
 222 }
 223
 224 static void merge_cache(struct cache_entry **src, int nr, int (*fn)(struct cache_entry **, struct cache_entry **))
 225 {
 226         struct cache_entry **dst = src;
 227
 228         while (nr) {
 229                 int entries;
 230                 struct cache_entry *name, *ce, *stages[4] = { NULL, };
 231
 232                 name = ce = *src;
 233                 for (;;) {
 234                         int stage = ce_stage(ce);
 235                         stages[stage] = ce;
 236                         ce = *++src;
 237                         active_nr--;
 238                         if (!--nr)
 239                                 break;
 240                         if (!path_matches(ce, name))
 241                                 break;
 242                 }
 243
 244                 entries = fn(stages, dst);
 245                 if (entries < 0)
 246                         reject_merge(name);
 247                 dst += entries;
 248                 active_nr += entries;
 249         }
 250         check_updates(active_cache, active_nr);
 251 }
 252
 253 static char *read_tree_usage = "git-read-tree (<sha> | -m <sha1> [<sha2> [<sha3>]])";
 254
 255 static struct cache_file cache_file;
 256
 257 int main(int argc, char **argv)
 258 {
 259         int i, newfd, merge;
 260         unsigned char sha1[20];
 261
 262         newfd = hold_index_file_for_update(&cache_file, get_index_file());
 263         if (newfd < 0)
 264                 die("unable to create new cachefile");
 265
 266         merge = 0;
 267         for (i = 1; i < argc; i++) {
 268                 const char *arg = argv[i];
 269
 270                 /* "-u" means "update", meaning that a merge will update the working directory */
 271                 if (!strcmp(arg, "-u")) {
 272                         update = 1;
 273                         continue;
 274                 }
 275
 276                 /* "-m" stands for "merge", meaning we start in stage 1 */
 277                 if (!strcmp(arg, "-m")) {
 278                         int i;
 279                         if (stage)
 280                                 die("-m needs to come first");
 281                         read_cache();
 282                         for (i = 0; i < active_nr; i++) {
 283                                 if (ce_stage(active_cache[i]))
 284                                         die("you need to resolve your current index first");
 285                         }
 286                         stage = 1;
 287                         merge = 1;
 288                         continue;
 289                 }
 290                 if (get_sha1(arg, sha1) < 0)
 291                         usage(read_tree_usage);
 292                 if (stage > 3)
 293                         usage(read_tree_usage);
 294                 if (unpack_tree(sha1) < 0)
 295                         die("failed to unpack tree object %s", arg);
 296                 stage++;
 297         }
 298         if (merge) {
 299                 switch (stage) {
 300                 case 4: /* Three-way merge */
 301                         merge_cache(active_cache, active_nr, threeway_merge);
 302                         break;
 303                 case 3: /* Update from one tree to another */
 304                         merge_cache(active_cache, active_nr, twoway_merge);
 305                         check_updates(active_cache, active_nr);
 306                         break;
 307                 case 2: /* Just read a tree, merge with old cache contents */
 308                         merge_cache(active_cache, active_nr, oneway_merge);
 309                         break;
 310                 default:
 311                         die("just how do you expect me to merge %d trees?", stage-1);
 312                 }
 313         }
 314         if (write_cache(newfd, active_cache, active_nr) ||
 315             commit_index_file(&cache_file))
 316                 die("unable to write new index file");
 317         return 0;
 318 }