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 static void *fill_tree_desc_strict(struct tree_desc *desc,
  51                                    const unsigned char *hash)
  52 {
  53         void *buffer;
  54         enum object_type type;
  55         unsigned long size;
  56
  57         buffer = read_sha1_file(hash, &type, &size);
  58         if (!buffer)
  59                 die("unable to read tree (%s)", sha1_to_hex(hash));
  60         if (type != OBJ_TREE)
  61                 die("%s is not a tree", sha1_to_hex(hash));
  62         init_tree_desc(desc, buffer, size);
  63         return buffer;
  64 }
  65
  66 static int base_name_entries_compare(const struct name_entry *a,
  67                                      const struct name_entry *b)
  68 {
  69         return base_name_compare(a->path, tree_entry_len(a), a->mode,
  70                                  b->path, tree_entry_len(b), b->mode);
  71 }
  72
  73 /*
  74  * Inspect two trees, and give a score that tells how similar they are.
  75  */
  76 static int score_trees(const unsigned char *hash1, const unsigned char *hash2)
  77 {
  78         struct tree_desc one;
  79         struct tree_desc two;
  80         void *one_buf = fill_tree_desc_strict(&one, hash1);
  81         void *two_buf = fill_tree_desc_strict(&two, hash2);
  82         int score = 0;
  83
  84         for (;;) {
  85                 struct name_entry e1, e2;
  86                 int got_entry_from_one = tree_entry(&one, &e1);
  87                 int got_entry_from_two = tree_entry(&two, &e2);
  88                 int cmp;
  89
  90                 if (got_entry_from_one && got_entry_from_two)
  91                         cmp = base_name_entries_compare(&e1, &e2);
  92                 else if (got_entry_from_one)
  93                         /* two lacks this entry */
  94                         cmp = -1;
  95                 else if (got_entry_from_two)
  96                         /* two has more entries */
  97                         cmp = 1;
  98                 else
  99                         break;
 100
 101                 if (cmp < 0)
 102                         /* path1 does not appear in two */
 103                         score += score_missing(e1.mode, e1.path);
 104                 else if (cmp > 0)
 105                         /* path2 does not appear in one */
 106                         score += score_missing(e2.mode, e2.path);
 107                 else if (hashcmp(e1.sha1, e2.sha1))
 108                         /* they are different */
 109                         score += score_differs(e1.mode, e2.mode, e1.path);
 110                 else
 111                         /* same subtree or blob */
 112                         score += score_matches(e1.mode, e2.mode, e1.path);
 113         }
 114         free(one_buf);
 115         free(two_buf);
 116         return score;
 117 }
 118
 119 /*
 120  * Match one itself and its subtrees with two and pick the best match.
 121  */
 122 static void match_trees(const unsigned char *hash1,
 123                         const unsigned char *hash2,
 124                         int *best_score,
 125                         char **best_match,
 126                         const char *base,
 127                         int recurse_limit)
 128 {
 129         struct tree_desc one;
 130         void *one_buf = fill_tree_desc_strict(&one, hash1);
 131
 132         while (one.size) {
 133                 const char *path;
 134                 const unsigned char *elem;
 135                 unsigned mode;
 136                 int score;
 137
 138                 elem = tree_entry_extract(&one, &path, &mode);
 139                 if (!S_ISDIR(mode))
 140                         goto next;
 141                 score = score_trees(elem, hash2);
 142                 if (*best_score < score) {
 143                         char *newpath;
 144                         newpath = xmalloc(strlen(base) + strlen(path) + 1);
 145                         sprintf(newpath, "%s%s", base, path);
 146                         free(*best_match);
 147                         *best_match = newpath;
 148                         *best_score = score;
 149                 }
 150                 if (recurse_limit) {
 151                         char *newbase;
 152                         newbase = xmalloc(strlen(base) + strlen(path) + 2);
 153                         sprintf(newbase, "%s%s/", base, path);
 154                         match_trees(elem, hash2, best_score, best_match,
 155                                     newbase, recurse_limit - 1);
 156                         free(newbase);
 157                 }
 158
 159         next:
 160                 update_tree_entry(&one);
 161         }
 162         free(one_buf);
 163 }
 164
 165 /*
 166  * A tree "hash1" has a subdirectory at "prefix".  Come up with a
 167  * tree object by replacing it with another tree "hash2".
 168  */
 169 static int splice_tree(const unsigned char *hash1,
 170                        const char *prefix,
 171                        const unsigned char *hash2,
 172                        unsigned char *result)
 173 {
 174         char *subpath;
 175         int toplen;
 176         char *buf;
 177         unsigned long sz;
 178         struct tree_desc desc;
 179         unsigned char *rewrite_here;
 180         const unsigned char *rewrite_with;
 181         unsigned char subtree[20];
 182         enum object_type type;
 183         int status;
 184
 185         subpath = strchrnul(prefix, '/');
 186         toplen = subpath - prefix;
 187         if (*subpath)
 188                 subpath++;
 189
 190         buf = read_sha1_file(hash1, &type, &sz);
 191         if (!buf)
 192                 die("cannot read tree %s", sha1_to_hex(hash1));
 193         init_tree_desc(&desc, buf, sz);
 194
 195         rewrite_here = NULL;
 196         while (desc.size) {
 197                 const char *name;
 198                 unsigned mode;
 199                 const unsigned char *sha1;
 200
 201                 sha1 = tree_entry_extract(&desc, &name, &mode);
 202                 if (strlen(name) == toplen &&
 203                     !memcmp(name, prefix, toplen)) {
 204                         if (!S_ISDIR(mode))
 205                                 die("entry %s in tree %s is not a tree",
 206                                     name, sha1_to_hex(hash1));
 207                         rewrite_here = (unsigned char *) sha1;
 208                         break;
 209                 }
 210                 update_tree_entry(&desc);
 211         }
 212         if (!rewrite_here)
 213                 die("entry %.*s not found in tree %s",
 214                     toplen, prefix, sha1_to_hex(hash1));
 215         if (*subpath) {
 216                 status = splice_tree(rewrite_here, subpath, hash2, subtree);
 217                 if (status)
 218                         return status;
 219                 rewrite_with = subtree;
 220         }
 221         else
 222                 rewrite_with = hash2;
 223         hashcpy(rewrite_here, rewrite_with);
 224         status = write_sha1_file(buf, sz, tree_type, result);
 225         free(buf);
 226         return status;
 227 }
 228
 229 /*
 230  * We are trying to come up with a merge between one and two that
 231  * results in a tree shape similar to one.  The tree two might
 232  * correspond to a subtree of one, in which case it needs to be
 233  * shifted down by prefixing otherwise empty directories.  On the
 234  * other hand, it could cover tree one and we might need to pick a
 235  * subtree of it.
 236  */
 237 void shift_tree(const unsigned char *hash1,
 238                 const unsigned char *hash2,
 239                 unsigned char *shifted,
 240                 int depth_limit)
 241 {
 242         char *add_prefix;
 243         char *del_prefix;
 244         int add_score, del_score;
 245
 246         /*
 247          * NEEDSWORK: this limits the recursion depth to hardcoded
 248          * value '2' to avoid excessive overhead.
 249          */
 250         if (!depth_limit)
 251                 depth_limit = 2;
 252
 253         add_score = del_score = score_trees(hash1, hash2);
 254         add_prefix = xcalloc(1, 1);
 255         del_prefix = xcalloc(1, 1);
 256
 257         /*
 258          * See if one's subtree resembles two; if so we need to prefix
 259          * two with a few fake trees to match the prefix.
 260          */
 261         match_trees(hash1, hash2, &add_score, &add_prefix, "", depth_limit);
 262
 263         /*
 264          * See if two's subtree resembles one; if so we need to
 265          * pick only subtree of two.
 266          */
 267         match_trees(hash2, hash1, &del_score, &del_prefix, "", depth_limit);
 268
 269         /* Assume we do not have to do any shifting */
 270         hashcpy(shifted, hash2);
 271
 272         if (add_score < del_score) {
 273                 /* We need to pick a subtree of two */
 274                 unsigned mode;
 275
 276                 if (!*del_prefix)
 277                         return;
 278
 279                 if (get_tree_entry(hash2, del_prefix, shifted, &mode))
 280                         die("cannot find path %s in tree %s",
 281                             del_prefix, sha1_to_hex(hash2));
 282                 return;
 283         }
 284
 285         if (!*add_prefix)
 286                 return;
 287
 288         splice_tree(hash1, add_prefix, hash2, shifted);
 289 }
 290
 291 /*
 292  * The user says the trees will be shifted by this much.
 293  * Unfortunately we cannot fundamentally tell which one to
 294  * be prefixed, as recursive merge can work in either direction.
 295  */
 296 void shift_tree_by(const unsigned char *hash1,
 297                    const unsigned char *hash2,
 298                    unsigned char *shifted,
 299                    const char *shift_prefix)
 300 {
 301         unsigned char sub1[20], sub2[20];
 302         unsigned mode1, mode2;
 303         unsigned candidate = 0;
 304
 305         /* Can hash2 be a tree at shift_prefix in tree hash1? */
 306         if (!get_tree_entry(hash1, shift_prefix, sub1, &mode1) &&
 307             S_ISDIR(mode1))
 308                 candidate |= 1;
 309
 310         /* Can hash1 be a tree at shift_prefix in tree hash2? */
 311         if (!get_tree_entry(hash2, shift_prefix, sub2, &mode2) &&
 312             S_ISDIR(mode2))
 313                 candidate |= 2;
 314
 315         if (candidate == 3) {
 316                 /* Both are plausible -- we need to evaluate the score */
 317                 int best_score = score_trees(hash1, hash2);
 318                 int score;
 319
 320                 candidate = 0;
 321                 score = score_trees(sub1, hash2);
 322                 if (score > best_score) {
 323                         candidate = 1;
 324                         best_score = score;
 325                 }
 326                 score = score_trees(sub2, hash1);
 327                 if (score > best_score)
 328                         candidate = 2;
 329         }
 330
 331         if (!candidate) {
 332                 /* Neither is plausible -- do not shift */
 333                 hashcpy(shifted, hash2);
 334                 return;
 335         }
 336
 337         if (candidate == 1)
 338                 /*
 339                  * shift tree2 down by adding shift_prefix above it
 340                  * to match tree1.
 341                  */
 342                 splice_tree(hash1, shift_prefix, hash2, shifted);
 343         else
 344                 /*
 345                  * shift tree2 up by removing shift_prefix from it
 346                  * to match tree1.
 347                  */
 348                 hashcpy(shifted, sub2);
 349 }