match-trees.con commit Merge branch 'es/worktree-docs' (6b747fc)
   1#include "cache.h"
   2#include "tree.h"
   3#include "tree-walk.h"
   4
   5static 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
  18static 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
  31static 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
  50static void *fill_tree_desc_strict(struct tree_desc *desc,
  51                                   const struct object_id *hash)
  52{
  53        void *buffer;
  54        enum object_type type;
  55        unsigned long size;
  56
  57        buffer = read_object_file(hash, &type, &size);
  58        if (!buffer)
  59                die("unable to read tree (%s)", oid_to_hex(hash));
  60        if (type != OBJ_TREE)
  61                die("%s is not a tree", oid_to_hex(hash));
  62        init_tree_desc(desc, buffer, size);
  63        return buffer;
  64}
  65
  66static 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 */
  76static int score_trees(const struct object_id *hash1, const struct object_id *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 (oidcmp(e1.oid, e2.oid))
 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 */
 122static void match_trees(const struct object_id *hash1,
 123                        const struct object_id *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 struct object_id *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                        free(*best_match);
 144                        *best_match = xstrfmt("%s%s", base, path);
 145                        *best_score = score;
 146                }
 147                if (recurse_limit) {
 148                        char *newbase = xstrfmt("%s%s/", base, path);
 149                        match_trees(elem, hash2, best_score, best_match,
 150                                    newbase, recurse_limit - 1);
 151                        free(newbase);
 152                }
 153
 154        next:
 155                update_tree_entry(&one);
 156        }
 157        free(one_buf);
 158}
 159
 160/*
 161 * A tree "oid1" has a subdirectory at "prefix".  Come up with a tree object by
 162 * replacing it with another tree "oid2".
 163 */
 164static int splice_tree(const struct object_id *oid1, const char *prefix,
 165                       const struct object_id *oid2, struct object_id *result)
 166{
 167        char *subpath;
 168        int toplen;
 169        char *buf;
 170        unsigned long sz;
 171        struct tree_desc desc;
 172        struct object_id *rewrite_here;
 173        const struct object_id *rewrite_with;
 174        struct object_id subtree;
 175        enum object_type type;
 176        int status;
 177
 178        subpath = strchrnul(prefix, '/');
 179        toplen = subpath - prefix;
 180        if (*subpath)
 181                subpath++;
 182
 183        buf = read_object_file(oid1, &type, &sz);
 184        if (!buf)
 185                die("cannot read tree %s", oid_to_hex(oid1));
 186        init_tree_desc(&desc, buf, sz);
 187
 188        rewrite_here = NULL;
 189        while (desc.size) {
 190                const char *name;
 191                unsigned mode;
 192                const struct object_id *oid;
 193
 194                oid = tree_entry_extract(&desc, &name, &mode);
 195                if (strlen(name) == toplen &&
 196                    !memcmp(name, prefix, toplen)) {
 197                        if (!S_ISDIR(mode))
 198                                die("entry %s in tree %s is not a tree", name,
 199                                    oid_to_hex(oid1));
 200                        rewrite_here = (struct object_id *)oid;
 201                        break;
 202                }
 203                update_tree_entry(&desc);
 204        }
 205        if (!rewrite_here)
 206                die("entry %.*s not found in tree %s", toplen, prefix,
 207                    oid_to_hex(oid1));
 208        if (*subpath) {
 209                status = splice_tree(rewrite_here, subpath, oid2, &subtree);
 210                if (status)
 211                        return status;
 212                rewrite_with = &subtree;
 213        } else {
 214                rewrite_with = oid2;
 215        }
 216        oidcpy(rewrite_here, rewrite_with);
 217        status = write_object_file(buf, sz, tree_type, result);
 218        free(buf);
 219        return status;
 220}
 221
 222/*
 223 * We are trying to come up with a merge between one and two that
 224 * results in a tree shape similar to one.  The tree two might
 225 * correspond to a subtree of one, in which case it needs to be
 226 * shifted down by prefixing otherwise empty directories.  On the
 227 * other hand, it could cover tree one and we might need to pick a
 228 * subtree of it.
 229 */
 230void shift_tree(const struct object_id *hash1,
 231                const struct object_id *hash2,
 232                struct object_id *shifted,
 233                int depth_limit)
 234{
 235        char *add_prefix;
 236        char *del_prefix;
 237        int add_score, del_score;
 238
 239        /*
 240         * NEEDSWORK: this limits the recursion depth to hardcoded
 241         * value '2' to avoid excessive overhead.
 242         */
 243        if (!depth_limit)
 244                depth_limit = 2;
 245
 246        add_score = del_score = score_trees(hash1, hash2);
 247        add_prefix = xcalloc(1, 1);
 248        del_prefix = xcalloc(1, 1);
 249
 250        /*
 251         * See if one's subtree resembles two; if so we need to prefix
 252         * two with a few fake trees to match the prefix.
 253         */
 254        match_trees(hash1, hash2, &add_score, &add_prefix, "", depth_limit);
 255
 256        /*
 257         * See if two's subtree resembles one; if so we need to
 258         * pick only subtree of two.
 259         */
 260        match_trees(hash2, hash1, &del_score, &del_prefix, "", depth_limit);
 261
 262        /* Assume we do not have to do any shifting */
 263        oidcpy(shifted, hash2);
 264
 265        if (add_score < del_score) {
 266                /* We need to pick a subtree of two */
 267                unsigned mode;
 268
 269                if (!*del_prefix)
 270                        return;
 271
 272                if (get_tree_entry(hash2, del_prefix, shifted, &mode))
 273                        die("cannot find path %s in tree %s",
 274                            del_prefix, oid_to_hex(hash2));
 275                return;
 276        }
 277
 278        if (!*add_prefix)
 279                return;
 280
 281        splice_tree(hash1, add_prefix, hash2, shifted);
 282}
 283
 284/*
 285 * The user says the trees will be shifted by this much.
 286 * Unfortunately we cannot fundamentally tell which one to
 287 * be prefixed, as recursive merge can work in either direction.
 288 */
 289void shift_tree_by(const struct object_id *hash1,
 290                   const struct object_id *hash2,
 291                   struct object_id *shifted,
 292                   const char *shift_prefix)
 293{
 294        struct object_id sub1, sub2;
 295        unsigned mode1, mode2;
 296        unsigned candidate = 0;
 297
 298        /* Can hash2 be a tree at shift_prefix in tree hash1? */
 299        if (!get_tree_entry(hash1, shift_prefix, &sub1, &mode1) &&
 300            S_ISDIR(mode1))
 301                candidate |= 1;
 302
 303        /* Can hash1 be a tree at shift_prefix in tree hash2? */
 304        if (!get_tree_entry(hash2, shift_prefix, &sub2, &mode2) &&
 305            S_ISDIR(mode2))
 306                candidate |= 2;
 307
 308        if (candidate == 3) {
 309                /* Both are plausible -- we need to evaluate the score */
 310                int best_score = score_trees(hash1, hash2);
 311                int score;
 312
 313                candidate = 0;
 314                score = score_trees(&sub1, hash2);
 315                if (score > best_score) {
 316                        candidate = 1;
 317                        best_score = score;
 318                }
 319                score = score_trees(&sub2, hash1);
 320                if (score > best_score)
 321                        candidate = 2;
 322        }
 323
 324        if (!candidate) {
 325                /* Neither is plausible -- do not shift */
 326                oidcpy(shifted, hash2);
 327                return;
 328        }
 329
 330        if (candidate == 1)
 331                /*
 332                 * shift tree2 down by adding shift_prefix above it
 333                 * to match tree1.
 334                 */
 335                splice_tree(hash1, shift_prefix, hash2, shifted);
 336        else
 337                /*
 338                 * shift tree2 up by removing shift_prefix from it
 339                 * to match tree1.
 340                 */
 341                oidcpy(shifted, &sub2);
 342}