match-trees.c

   1 #include "cache.h"
   2 #include "tree.h"
   3 #include "tree-walk.h"
   4
   5 static int score_missing(unsigned mode, const char *path)
   6 {
   7         int score;
   8
   9         if (S_ISDIR(mode))
  10                 score = -1000;
  11         else if (S_ISLNK(mode))
  12                 score = -500;
  13         else
  14                 score = -50;
  15         return score;
  16 }
  17
  18 static int score_differs(unsigned mode1, unsigned mode2, const char *path)
  19 {
  20         int score;
  21
  22         if (S_ISDIR(mode1) != S_ISDIR(mode2))
  23                 score = -100;
  24         else if (S_ISLNK(mode1) != S_ISLNK(mode2))
  25                 score = -50;
  26         else
  27                 score = -5;
  28         return score;
  29 }
  30
  31 static int score_matches(unsigned mode1, unsigned mode2, const char *path)
  32 {
  33         int score;
  34
  35         /* Heh, we found SHA-1 collisions between different kind of objects */
  36         if (S_ISDIR(mode1) != S_ISDIR(mode2))
  37                 score = -100;
  38         else if (S_ISLNK(mode1) != S_ISLNK(mode2))
  39                 score = -50;
  40
  41         else if (S_ISDIR(mode1))
  42                 score = 1000;
  43         else if (S_ISLNK(mode1))
  44                 score = 500;
  45         else
  46                 score = 250;
  47         return score;
  48 }
  49
  50 /*
  51  * Inspect two trees, and give a score that tells how similar they are.
  52  */
  53 static int score_trees(const unsigned char *hash1, const unsigned char *hash2)
  54 {
  55         struct tree_desc one;
  56         struct tree_desc two;
  57         void *one_buf, *two_buf;
  58         int score = 0;
  59         enum object_type type;
  60         unsigned long size;
  61
  62         one_buf = read_sha1_file(hash1, &type, &size);
  63         if (!one_buf)
  64                 die("unable to read tree (%s)", sha1_to_hex(hash1));
  65         if (type != OBJ_TREE)
  66                 die("%s is not a tree", sha1_to_hex(hash1));
  67         init_tree_desc(&one, one_buf, size);
  68         two_buf = read_sha1_file(hash2, &type, &size);
  69         if (!two_buf)
  70                 die("unable to read tree (%s)", sha1_to_hex(hash2));
  71         if (type != OBJ_TREE)
  72                 die("%s is not a tree", sha1_to_hex(hash2));
  73         init_tree_desc(&two, two_buf, size);
  74         while (one.size | two.size) {
  75                 const unsigned char *elem1 = elem1;
  76                 const unsigned char *elem2 = elem2;
  77                 const char *path1 = path1;
  78                 const char *path2 = path2;
  79                 unsigned mode1 = mode1;
  80                 unsigned mode2 = mode2;
  81                 int cmp;
  82
  83                 if (one.size)
  84                         elem1 = tree_entry_extract(&one, &path1, &mode1);
  85                 if (two.size)
  86                         elem2 = tree_entry_extract(&two, &path2, &mode2);
  87
  88                 if (!one.size) {
  89                         /* two has more entries */
  90                         score += score_missing(mode2, path2);
  91                         update_tree_entry(&two);
  92                         continue;
  93                 }
  94                 if (!two.size) {
  95                         /* two lacks this entry */
  96                         score += score_missing(mode1, path1);
  97                         update_tree_entry(&one);
  98                         continue;
  99                 }
 100                 cmp = base_name_compare(path1, strlen(path1), mode1,
 101                                         path2, strlen(path2), mode2);
 102                 if (cmp < 0) {
 103                         /* path1 does not appear in two */
 104                         score += score_missing(mode1, path1);
 105                         update_tree_entry(&one);
 106                         continue;
 107                 }
 108                 else if (cmp > 0) {
 109                         /* path2 does not appear in one */
 110                         score += score_missing(mode2, path2);
 111                         update_tree_entry(&two);
 112                         continue;
 113                 }
 114                 else if (hashcmp(elem1, elem2))
 115                         /* they are different */
 116                         score += score_differs(mode1, mode2, path1);
 117                 else
 118                         /* same subtree or blob */
 119                         score += score_matches(mode1, mode2, path1);
 120                 update_tree_entry(&one);
 121                 update_tree_entry(&two);
 122         }
 123         free(one_buf);
 124         free(two_buf);
 125         return score;
 126 }
 127
 128 /*
 129  * Match one itself and its subtrees with two and pick the best match.
 130  */
 131 static void match_trees(const unsigned char *hash1,
 132                         const unsigned char *hash2,
 133                         int *best_score,
 134                         char **best_match,
 135                         const char *base,
 136                         int recurse_limit)
 137 {
 138         struct tree_desc one;
 139         void *one_buf;
 140         enum object_type type;
 141         unsigned long size;
 142
 143         one_buf = read_sha1_file(hash1, &type, &size);
 144         if (!one_buf)
 145                 die("unable to read tree (%s)", sha1_to_hex(hash1));
 146         if (type != OBJ_TREE)
 147                 die("%s is not a tree", sha1_to_hex(hash1));
 148         init_tree_desc(&one, one_buf, size);
 149
 150         while (one.size) {
 151                 const char *path;
 152                 const unsigned char *elem;
 153                 unsigned mode;
 154                 int score;
 155
 156                 elem = tree_entry_extract(&one, &path, &mode);
 157                 if (!S_ISDIR(mode))
 158                         goto next;
 159                 score = score_trees(elem, hash2);
 160                 if (*best_score < score) {
 161                         char *newpath;
 162                         newpath = xmalloc(strlen(base) + strlen(path) + 1);
 163                         sprintf(newpath, "%s%s", base, path);
 164                         free(*best_match);
 165                         *best_match = newpath;
 166                         *best_score = score;
 167                 }
 168                 if (recurse_limit) {
 169                         char *newbase;
 170                         newbase = xmalloc(strlen(base) + strlen(path) + 2);
 171                         sprintf(newbase, "%s%s/", base, path);
 172                         match_trees(elem, hash2, best_score, best_match,
 173                                     newbase, recurse_limit - 1);
 174                         free(newbase);
 175                 }
 176
 177         next:
 178                 update_tree_entry(&one);
 179         }
 180         free(one_buf);
 181 }
 182
 183 /*
 184  * A tree "hash1" has a subdirectory at "prefix".  Come up with a
 185  * tree object by replacing it with another tree "hash2".
 186  */
 187 static int splice_tree(const unsigned char *hash1,
 188                        const char *prefix,
 189                        const unsigned char *hash2,
 190                        unsigned char *result)
 191 {
 192         char *subpath;
 193         int toplen;
 194         char *buf;
 195         unsigned long sz;
 196         struct tree_desc desc;
 197         unsigned char *rewrite_here;
 198         const unsigned char *rewrite_with;
 199         unsigned char subtree[20];
 200         enum object_type type;
 201         int status;
 202
 203         subpath = strchr(prefix, '/');
 204         if (!subpath)
 205                 toplen = strlen(prefix);
 206         else {
 207                 toplen = subpath - prefix;
 208                 subpath++;
 209         }
 210
 211         buf = read_sha1_file(hash1, &type, &sz);
 212         if (!buf)
 213                 die("cannot read tree %s", sha1_to_hex(hash1));
 214         init_tree_desc(&desc, buf, sz);
 215
 216         rewrite_here = NULL;
 217         while (desc.size) {
 218                 const char *name;
 219                 unsigned mode;
 220                 const unsigned char *sha1;
 221
 222                 sha1 = tree_entry_extract(&desc, &name, &mode);
 223                 if (strlen(name) == toplen &&
 224                     !memcmp(name, prefix, toplen)) {
 225                         if (!S_ISDIR(mode))
 226                                 die("entry %s in tree %s is not a tree",
 227                                     name, sha1_to_hex(hash1));
 228                         rewrite_here = (unsigned char *) sha1;
 229                         break;
 230                 }
 231                 update_tree_entry(&desc);
 232         }
 233         if (!rewrite_here)
 234                 die("entry %.*s not found in tree %s",
 235                     toplen, prefix, sha1_to_hex(hash1));
 236         if (subpath) {
 237                 status = splice_tree(rewrite_here, subpath, hash2, subtree);
 238                 if (status)
 239                         return status;
 240                 rewrite_with = subtree;
 241         }
 242         else
 243                 rewrite_with = hash2;
 244         hashcpy(rewrite_here, rewrite_with);
 245         status = write_sha1_file(buf, sz, tree_type, result);
 246         free(buf);
 247         return status;
 248 }
 249
 250 /*
 251  * We are trying to come up with a merge between one and two that
 252  * results in a tree shape similar to one.  The tree two might
 253  * correspond to a subtree of one, in which case it needs to be
 254  * shifted down by prefixing otherwise empty directories.  On the
 255  * other hand, it could cover tree one and we might need to pick a
 256  * subtree of it.
 257  */
 258 void shift_tree(const unsigned char *hash1,
 259                 const unsigned char *hash2,
 260                 unsigned char *shifted,
 261                 int depth_limit)
 262 {
 263         char *add_prefix;
 264         char *del_prefix;
 265         int add_score, del_score;
 266
 267         /*
 268          * NEEDSWORK: this limits the recursion depth to hardcoded
 269          * value '2' to avoid excessive overhead.
 270          */
 271         if (!depth_limit)
 272                 depth_limit = 2;
 273
 274         add_score = del_score = score_trees(hash1, hash2);
 275         add_prefix = xcalloc(1, 1);
 276         del_prefix = xcalloc(1, 1);
 277
 278         /*
 279          * See if one's subtree resembles two; if so we need to prefix
 280          * two with a few fake trees to match the prefix.
 281          */
 282         match_trees(hash1, hash2, &add_score, &add_prefix, "", depth_limit);
 283
 284         /*
 285          * See if two's subtree resembles one; if so we need to
 286          * pick only subtree of two.
 287          */
 288         match_trees(hash2, hash1, &del_score, &del_prefix, "", depth_limit);
 289
 290         /* Assume we do not have to do any shifting */
 291         hashcpy(shifted, hash2);
 292
 293         if (add_score < del_score) {
 294                 /* We need to pick a subtree of two */
 295                 unsigned mode;
 296
 297                 if (!*del_prefix)
 298                         return;
 299
 300                 if (get_tree_entry(hash2, del_prefix, shifted, &mode))
 301                         die("cannot find path %s in tree %s",
 302                             del_prefix, sha1_to_hex(hash2));
 303                 return;
 304         }
 305
 306         if (!*add_prefix)
 307                 return;
 308
 309         splice_tree(hash1, add_prefix, hash2, shifted);
 310 }
 311
 312 /*
 313  * The user says the trees will be shifted by this much.
 314  * Unfortunately we cannot fundamentally tell which one to
 315  * be prefixed, as recursive merge can work in either direction.
 316  */
 317 void shift_tree_by(const unsigned char *hash1,
 318                    const unsigned char *hash2,
 319                    unsigned char *shifted,
 320                    const char *shift_prefix)
 321 {
 322         unsigned char sub1[20], sub2[20];
 323         unsigned mode1, mode2;
 324         unsigned candidate = 0;
 325
 326         /* Can hash2 be a tree at shift_prefix in tree hash1? */
 327         if (!get_tree_entry(hash1, shift_prefix, sub1, &mode1) &&
 328             S_ISDIR(mode1))
 329                 candidate |= 1;
 330
 331         /* Can hash1 be a tree at shift_prefix in tree hash2? */
 332         if (!get_tree_entry(hash2, shift_prefix, sub2, &mode2) &&
 333             S_ISDIR(mode2))
 334                 candidate |= 2;
 335
 336         if (candidate == 3) {
 337                 /* Both are plausible -- we need to evaluate the score */
 338                 int best_score = score_trees(hash1, hash2);
 339                 int score;
 340
 341                 candidate = 0;
 342                 score = score_trees(sub1, hash2);
 343                 if (score > best_score) {
 344                         candidate = 1;
 345                         best_score = score;
 346                 }
 347                 score = score_trees(sub2, hash1);
 348                 if (score > best_score)
 349                         candidate = 2;
 350         }
 351
 352         if (!candidate) {
 353                 /* Neither is plausible -- do not shift */
 354                 hashcpy(shifted, hash2);
 355                 return;
 356         }
 357
 358         if (candidate == 1)
 359                 /*
 360                  * shift tree2 down by adding shift_prefix above it
 361                  * to match tree1.
 362                  */
 363                 splice_tree(hash1, shift_prefix, hash2, shifted);
 364         else
 365                 /*
 366                  * shift tree2 up by removing shift_prefix from it
 367                  * to match tree1.
 368                  */
 369                 hashcpy(shifted, sub2);
 370 }