diff options
Diffstat (limited to 'match-trees.c')
| -rw-r--r-- | match-trees.c | 344 |
1 files changed, 344 insertions, 0 deletions
diff --git a/match-trees.c b/match-trees.c new file mode 100644 index 0000000000..1ce0954a3e --- /dev/null +++ b/match-trees.c @@ -0,0 +1,344 @@ +#include "cache.h" +#include "tree.h" +#include "tree-walk.h" + +static int score_missing(unsigned mode, const char *path) +{ + int score; + + if (S_ISDIR(mode)) + score = -1000; + else if (S_ISLNK(mode)) + score = -500; + else + score = -50; + return score; +} + +static int score_differs(unsigned mode1, unsigned mode2, const char *path) +{ + int score; + + if (S_ISDIR(mode1) != S_ISDIR(mode2)) + score = -100; + else if (S_ISLNK(mode1) != S_ISLNK(mode2)) + score = -50; + else + score = -5; + return score; +} + +static int score_matches(unsigned mode1, unsigned mode2, const char *path) +{ + int score; + + /* Heh, we found SHA-1 collisions between different kind of objects */ + if (S_ISDIR(mode1) != S_ISDIR(mode2)) + score = -100; + else if (S_ISLNK(mode1) != S_ISLNK(mode2)) + score = -50; + + else if (S_ISDIR(mode1)) + score = 1000; + else if (S_ISLNK(mode1)) + score = 500; + else + score = 250; + return score; +} + +static void *fill_tree_desc_strict(struct tree_desc *desc, + const unsigned char *hash) +{ + void *buffer; + enum object_type type; + unsigned long size; + + buffer = read_sha1_file(hash, &type, &size); + if (!buffer) + die("unable to read tree (%s)", sha1_to_hex(hash)); + if (type != OBJ_TREE) + die("%s is not a tree", sha1_to_hex(hash)); + init_tree_desc(desc, buffer, size); + return buffer; +} + +static int base_name_entries_compare(const struct name_entry *a, + const struct name_entry *b) +{ + return base_name_compare(a->path, tree_entry_len(a), a->mode, + b->path, tree_entry_len(b), b->mode); +} + +/* + * Inspect two trees, and give a score that tells how similar they are. + */ +static int score_trees(const unsigned char *hash1, const unsigned char *hash2) +{ + struct tree_desc one; + struct tree_desc two; + void *one_buf = fill_tree_desc_strict(&one, hash1); + void *two_buf = fill_tree_desc_strict(&two, hash2); + int score = 0; + + for (;;) { + struct name_entry e1, e2; + int got_entry_from_one = tree_entry(&one, &e1); + int got_entry_from_two = tree_entry(&two, &e2); + int cmp; + + if (got_entry_from_one && got_entry_from_two) + cmp = base_name_entries_compare(&e1, &e2); + else if (got_entry_from_one) + /* two lacks this entry */ + cmp = -1; + else if (got_entry_from_two) + /* two has more entries */ + cmp = 1; + else + break; + + if (cmp < 0) + /* path1 does not appear in two */ + score += score_missing(e1.mode, e1.path); + else if (cmp > 0) + /* path2 does not appear in one */ + score += score_missing(e2.mode, e2.path); + else if (hashcmp(e1.sha1, e2.sha1)) + /* they are different */ + score += score_differs(e1.mode, e2.mode, e1.path); + else + /* same subtree or blob */ + score += score_matches(e1.mode, e2.mode, e1.path); + } + free(one_buf); + free(two_buf); + return score; +} + +/* + * Match one itself and its subtrees with two and pick the best match. + */ +static void match_trees(const unsigned char *hash1, + const unsigned char *hash2, + int *best_score, + char **best_match, + const char *base, + int recurse_limit) +{ + struct tree_desc one; + void *one_buf = fill_tree_desc_strict(&one, hash1); + + while (one.size) { + const char *path; + const unsigned char *elem; + unsigned mode; + int score; + + elem = tree_entry_extract(&one, &path, &mode); + if (!S_ISDIR(mode)) + goto next; + score = score_trees(elem, hash2); + if (*best_score < score) { + free(*best_match); + *best_match = xstrfmt("%s%s", base, path); + *best_score = score; + } + if (recurse_limit) { + char *newbase = xstrfmt("%s%s/", base, path); + match_trees(elem, hash2, best_score, best_match, + newbase, recurse_limit - 1); + free(newbase); + } + + next: + update_tree_entry(&one); + } + free(one_buf); +} + +/* + * A tree "hash1" has a subdirectory at "prefix". Come up with a + * tree object by replacing it with another tree "hash2". + */ +static int splice_tree(const unsigned char *hash1, + const char *prefix, + const unsigned char *hash2, + unsigned char *result) +{ + char *subpath; + int toplen; + char *buf; + unsigned long sz; + struct tree_desc desc; + unsigned char *rewrite_here; + const unsigned char *rewrite_with; + unsigned char subtree[20]; + enum object_type type; + int status; + + subpath = strchrnul(prefix, '/'); + toplen = subpath - prefix; + if (*subpath) + subpath++; + + buf = read_sha1_file(hash1, &type, &sz); + if (!buf) + die("cannot read tree %s", sha1_to_hex(hash1)); + init_tree_desc(&desc, buf, sz); + + rewrite_here = NULL; + while (desc.size) { + const char *name; + unsigned mode; + const unsigned char *sha1; + + sha1 = tree_entry_extract(&desc, &name, &mode); + if (strlen(name) == toplen && + !memcmp(name, prefix, toplen)) { + if (!S_ISDIR(mode)) + die("entry %s in tree %s is not a tree", + name, sha1_to_hex(hash1)); + rewrite_here = (unsigned char *) sha1; + break; + } + update_tree_entry(&desc); + } + if (!rewrite_here) + die("entry %.*s not found in tree %s", + toplen, prefix, sha1_to_hex(hash1)); + if (*subpath) { + status = splice_tree(rewrite_here, subpath, hash2, subtree); + if (status) + return status; + rewrite_with = subtree; + } + else + rewrite_with = hash2; + hashcpy(rewrite_here, rewrite_with); + status = write_sha1_file(buf, sz, tree_type, result); + free(buf); + return status; +} + +/* + * We are trying to come up with a merge between one and two that + * results in a tree shape similar to one. The tree two might + * correspond to a subtree of one, in which case it needs to be + * shifted down by prefixing otherwise empty directories. On the + * other hand, it could cover tree one and we might need to pick a + * subtree of it. + */ +void shift_tree(const unsigned char *hash1, + const unsigned char *hash2, + unsigned char *shifted, + int depth_limit) +{ + char *add_prefix; + char *del_prefix; + int add_score, del_score; + + /* + * NEEDSWORK: this limits the recursion depth to hardcoded + * value '2' to avoid excessive overhead. + */ + if (!depth_limit) + depth_limit = 2; + + add_score = del_score = score_trees(hash1, hash2); + add_prefix = xcalloc(1, 1); + del_prefix = xcalloc(1, 1); + + /* + * See if one's subtree resembles two; if so we need to prefix + * two with a few fake trees to match the prefix. + */ + match_trees(hash1, hash2, &add_score, &add_prefix, "", depth_limit); + + /* + * See if two's subtree resembles one; if so we need to + * pick only subtree of two. + */ + match_trees(hash2, hash1, &del_score, &del_prefix, "", depth_limit); + + /* Assume we do not have to do any shifting */ + hashcpy(shifted, hash2); + + if (add_score < del_score) { + /* We need to pick a subtree of two */ + unsigned mode; + + if (!*del_prefix) + return; + + if (get_tree_entry(hash2, del_prefix, shifted, &mode)) + die("cannot find path %s in tree %s", + del_prefix, sha1_to_hex(hash2)); + return; + } + + if (!*add_prefix) + return; + + splice_tree(hash1, add_prefix, hash2, shifted); +} + +/* + * The user says the trees will be shifted by this much. + * Unfortunately we cannot fundamentally tell which one to + * be prefixed, as recursive merge can work in either direction. + */ +void shift_tree_by(const unsigned char *hash1, + const unsigned char *hash2, + unsigned char *shifted, + const char *shift_prefix) +{ + unsigned char sub1[20], sub2[20]; + unsigned mode1, mode2; + unsigned candidate = 0; + + /* Can hash2 be a tree at shift_prefix in tree hash1? */ + if (!get_tree_entry(hash1, shift_prefix, sub1, &mode1) && + S_ISDIR(mode1)) + candidate |= 1; + + /* Can hash1 be a tree at shift_prefix in tree hash2? */ + if (!get_tree_entry(hash2, shift_prefix, sub2, &mode2) && + S_ISDIR(mode2)) + candidate |= 2; + + if (candidate == 3) { + /* Both are plausible -- we need to evaluate the score */ + int best_score = score_trees(hash1, hash2); + int score; + + candidate = 0; + score = score_trees(sub1, hash2); + if (score > best_score) { + candidate = 1; + best_score = score; + } + score = score_trees(sub2, hash1); + if (score > best_score) + candidate = 2; + } + + if (!candidate) { + /* Neither is plausible -- do not shift */ + hashcpy(shifted, hash2); + return; + } + + if (candidate == 1) + /* + * shift tree2 down by adding shift_prefix above it + * to match tree1. + */ + splice_tree(hash1, shift_prefix, hash2, shifted); + else + /* + * shift tree2 up by removing shift_prefix from it + * to match tree1. + */ + hashcpy(shifted, sub2); +} |