match-trees.c

   1 #include "cache.h"
   2 #include "tree.h"
   3 #include "tree-walk.h"
   4 #include "object-store.h"
   5
   6 static int score_missing(unsigned mode, const char *path)
   7 {
   8         int score;
   9
  10         if (S_ISDIR(mode))
  11                 score = -1000;
  12         else if (S_ISLNK(mode))
  13                 score = -500;
  14         else
  15                 score = -50;
  16         return score;
  17 }
  18
  19 static int score_differs(unsigned mode1, unsigned mode2, const char *path)
  20 {
  21         int score;
  22
  23         if (S_ISDIR(mode1) != S_ISDIR(mode2))
  24                 score = -100;
  25         else if (S_ISLNK(mode1) != S_ISLNK(mode2))
  26                 score = -50;
  27         else
  28                 score = -5;
  29         return score;
  30 }
  31
  32 static int score_matches(unsigned mode1, unsigned mode2, const char *path)
  33 {
  34         int score;
  35
  36         /* Heh, we found SHA-1 collisions between different kind of objects */
  37         if (S_ISDIR(mode1) != S_ISDIR(mode2))
  38                 score = -100;
  39         else if (S_ISLNK(mode1) != S_ISLNK(mode2))
  40                 score = -50;
  41
  42         else if (S_ISDIR(mode1))
  43                 score = 1000;
  44         else if (S_ISLNK(mode1))
  45                 score = 500;
  46         else
  47                 score = 250;
  48         return score;
  49 }
  50
  51 static void *fill_tree_desc_strict(struct tree_desc *desc,
  52                                    const struct object_id *hash)
  53 {
  54         void *buffer;
  55         enum object_type type;
  56         unsigned long size;
  57
  58         buffer = read_object_file(hash, &type, &size);
  59         if (!buffer)
  60                 die("unable to read tree (%s)", oid_to_hex(hash));
  61         if (type != OBJ_TREE)
  62                 die("%s is not a tree", oid_to_hex(hash));
  63         init_tree_desc(desc, buffer, size);
  64         return buffer;
  65 }
  66
  67 static int base_name_entries_compare(const struct name_entry *a,
  68                                      const struct name_entry *b)
  69 {
  70         return base_name_compare(a->path, tree_entry_len(a), a->mode,
  71                                  b->path, tree_entry_len(b), b->mode);
  72 }
  73
  74 /*
  75  * Inspect two trees, and give a score that tells how similar they are.
  76  */
  77 static int score_trees(const struct object_id *hash1, const struct object_id *hash2)
  78 {
  79         struct tree_desc one;
  80         struct tree_desc two;
  81         void *one_buf = fill_tree_desc_strict(&one, hash1);
  82         void *two_buf = fill_tree_desc_strict(&two, hash2);
  83         int score = 0;
  84
  85         for (;;) {
  86                 struct name_entry e1, e2;
  87                 int got_entry_from_one = tree_entry(&one, &e1);
  88                 int got_entry_from_two = tree_entry(&two, &e2);
  89                 int cmp;
  90
  91                 if (got_entry_from_one && got_entry_from_two)
  92                         cmp = base_name_entries_compare(&e1, &e2);
  93                 else if (got_entry_from_one)
  94                         /* two lacks this entry */
  95                         cmp = -1;
  96                 else if (got_entry_from_two)
  97                         /* two has more entries */
  98                         cmp = 1;
  99                 else
 100                         break;
 101
 102                 if (cmp < 0)
 103                         /* path1 does not appear in two */
 104                         score += score_missing(e1.mode, e1.path);
 105                 else if (cmp > 0)
 106                         /* path2 does not appear in one */
 107                         score += score_missing(e2.mode, e2.path);
 108                 else if (oidcmp(e1.oid, e2.oid))
 109                         /* they are different */
 110                         score += score_differs(e1.mode, e2.mode, e1.path);
 111                 else
 112                         /* same subtree or blob */
 113                         score += score_matches(e1.mode, e2.mode, e1.path);
 114         }
 115         free(one_buf);
 116         free(two_buf);
 117         return score;
 118 }
 119
 120 /*
 121  * Match one itself and its subtrees with two and pick the best match.
 122  */
 123 static void match_trees(const struct object_id *hash1,
 124                         const struct object_id *hash2,
 125                         int *best_score,
 126                         char **best_match,
 127                         const char *base,
 128                         int recurse_limit)
 129 {
 130         struct tree_desc one;
 131         void *one_buf = fill_tree_desc_strict(&one, hash1);
 132
 133         while (one.size) {
 134                 const char *path;
 135                 const struct object_id *elem;
 136                 unsigned mode;
 137                 int score;
 138
 139                 elem = tree_entry_extract(&one, &path, &mode);
 140                 if (!S_ISDIR(mode))
 141                         goto next;
 142                 score = score_trees(elem, hash2);
 143                 if (*best_score < score) {
 144                         free(*best_match);
 145                         *best_match = xstrfmt("%s%s", base, path);
 146                         *best_score = score;
 147                 }
 148                 if (recurse_limit) {
 149                         char *newbase = xstrfmt("%s%s/", base, path);
 150                         match_trees(elem, hash2, best_score, best_match,
 151                                     newbase, recurse_limit - 1);
 152                         free(newbase);
 153                 }
 154
 155         next:
 156                 update_tree_entry(&one);
 157         }
 158         free(one_buf);
 159 }
 160
 161 /*
 162  * A tree "oid1" has a subdirectory at "prefix".  Come up with a tree object by
 163  * replacing it with another tree "oid2".
 164  */
 165 static int splice_tree(const struct object_id *oid1, const char *prefix,
 166                        const struct object_id *oid2, struct object_id *result)
 167 {
 168         char *subpath;
 169         int toplen;
 170         char *buf;
 171         unsigned long sz;
 172         struct tree_desc desc;
 173         struct object_id *rewrite_here;
 174         const struct object_id *rewrite_with;
 175         struct object_id subtree;
 176         enum object_type type;
 177         int status;
 178
 179         subpath = strchrnul(prefix, '/');
 180         toplen = subpath - prefix;
 181         if (*subpath)
 182                 subpath++;
 183
 184         buf = read_object_file(oid1, &type, &sz);
 185         if (!buf)
 186                 die("cannot read tree %s", oid_to_hex(oid1));
 187         init_tree_desc(&desc, buf, sz);
 188
 189         rewrite_here = NULL;
 190         while (desc.size) {
 191                 const char *name;
 192                 unsigned mode;
 193                 const struct object_id *oid;
 194
 195                 oid = tree_entry_extract(&desc, &name, &mode);
 196                 if (strlen(name) == toplen &&
 197                     !memcmp(name, prefix, toplen)) {
 198                         if (!S_ISDIR(mode))
 199                                 die("entry %s in tree %s is not a tree", name,
 200                                     oid_to_hex(oid1));
 201                         rewrite_here = (struct object_id *)oid;
 202                         break;
 203                 }
 204                 update_tree_entry(&desc);
 205         }
 206         if (!rewrite_here)
 207                 die("entry %.*s not found in tree %s", toplen, prefix,
 208                     oid_to_hex(oid1));
 209         if (*subpath) {
 210                 status = splice_tree(rewrite_here, subpath, oid2, &subtree);
 211                 if (status)
 212                         return status;
 213                 rewrite_with = &subtree;
 214         } else {
 215                 rewrite_with = oid2;
 216         }
 217         oidcpy(rewrite_here, rewrite_with);
 218         status = write_object_file(buf, sz, tree_type, result);
 219         free(buf);
 220         return status;
 221 }
 222
 223 /*
 224  * We are trying to come up with a merge between one and two that
 225  * results in a tree shape similar to one.  The tree two might
 226  * correspond to a subtree of one, in which case it needs to be
 227  * shifted down by prefixing otherwise empty directories.  On the
 228  * other hand, it could cover tree one and we might need to pick a
 229  * subtree of it.
 230  */
 231 void shift_tree(const struct object_id *hash1,
 232                 const struct object_id *hash2,
 233                 struct object_id *shifted,
 234                 int depth_limit)
 235 {
 236         char *add_prefix;
 237         char *del_prefix;
 238         int add_score, del_score;
 239
 240         /*
 241          * NEEDSWORK: this limits the recursion depth to hardcoded
 242          * value '2' to avoid excessive overhead.
 243          */
 244         if (!depth_limit)
 245                 depth_limit = 2;
 246
 247         add_score = del_score = score_trees(hash1, hash2);
 248         add_prefix = xcalloc(1, 1);
 249         del_prefix = xcalloc(1, 1);
 250
 251         /*
 252          * See if one's subtree resembles two; if so we need to prefix
 253          * two with a few fake trees to match the prefix.
 254          */
 255         match_trees(hash1, hash2, &add_score, &add_prefix, "", depth_limit);
 256
 257         /*
 258          * See if two's subtree resembles one; if so we need to
 259          * pick only subtree of two.
 260          */
 261         match_trees(hash2, hash1, &del_score, &del_prefix, "", depth_limit);
 262
 263         /* Assume we do not have to do any shifting */
 264         oidcpy(shifted, hash2);
 265
 266         if (add_score < del_score) {
 267                 /* We need to pick a subtree of two */
 268                 unsigned mode;
 269
 270                 if (!*del_prefix)
 271                         return;
 272
 273                 if (get_tree_entry(hash2, del_prefix, shifted, &mode))
 274                         die("cannot find path %s in tree %s",
 275                             del_prefix, oid_to_hex(hash2));
 276                 return;
 277         }
 278
 279         if (!*add_prefix)
 280                 return;
 281
 282         splice_tree(hash1, add_prefix, hash2, shifted);
 283 }
 284
 285 /*
 286  * The user says the trees will be shifted by this much.
 287  * Unfortunately we cannot fundamentally tell which one to
 288  * be prefixed, as recursive merge can work in either direction.
 289  */
 290 void shift_tree_by(const struct object_id *hash1,
 291                    const struct object_id *hash2,
 292                    struct object_id *shifted,
 293                    const char *shift_prefix)
 294 {
 295         struct object_id sub1, sub2;
 296         unsigned mode1, mode2;
 297         unsigned candidate = 0;
 298
 299         /* Can hash2 be a tree at shift_prefix in tree hash1? */
 300         if (!get_tree_entry(hash1, shift_prefix, &sub1, &mode1) &&
 301             S_ISDIR(mode1))
 302                 candidate |= 1;
 303
 304         /* Can hash1 be a tree at shift_prefix in tree hash2? */
 305         if (!get_tree_entry(hash2, shift_prefix, &sub2, &mode2) &&
 306             S_ISDIR(mode2))
 307                 candidate |= 2;
 308
 309         if (candidate == 3) {
 310                 /* Both are plausible -- we need to evaluate the score */
 311                 int best_score = score_trees(hash1, hash2);
 312                 int score;
 313
 314                 candidate = 0;
 315                 score = score_trees(&sub1, hash2);
 316                 if (score > best_score) {
 317                         candidate = 1;
 318                         best_score = score;
 319                 }
 320                 score = score_trees(&sub2, hash1);
 321                 if (score > best_score)
 322                         candidate = 2;
 323         }
 324
 325         if (!candidate) {
 326                 /* Neither is plausible -- do not shift */
 327                 oidcpy(shifted, hash2);
 328                 return;
 329         }
 330
 331         if (candidate == 1)
 332                 /*
 333                  * shift tree2 down by adding shift_prefix above it
 334                  * to match tree1.
 335                  */
 336                 splice_tree(hash1, shift_prefix, hash2, shifted);
 337         else
 338                 /*
 339                  * shift tree2 up by removing shift_prefix from it
 340                  * to match tree1.
 341                  */
 342                 oidcpy(shifted, &sub2);
 343 }