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-rw-r--r--match-trees.c365
1 files changed, 365 insertions, 0 deletions
diff --git a/match-trees.c b/match-trees.c
new file mode 100644
index 0000000..49398e5
--- /dev/null
+++ b/match-trees.c
@@ -0,0 +1,365 @@
+#include "cache.h"
+#include "tree.h"
+#include "tree-walk.h"
+#include "object-store.h"
+
+static int score_missing(unsigned mode)
+{
+ 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)
+{
+ 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)
+{
+ 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 struct object_id *hash)
+{
+ void *buffer;
+ enum object_type type;
+ unsigned long size;
+
+ buffer = read_object_file(hash, &type, &size);
+ if (!buffer)
+ die("unable to read tree (%s)", oid_to_hex(hash));
+ if (type != OBJ_TREE)
+ die("%s is not a tree", oid_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 struct object_id *hash1, const struct object_id *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 (;;) {
+ int cmp;
+
+ if (one.size && two.size)
+ cmp = base_name_entries_compare(&one.entry, &two.entry);
+ else if (one.size)
+ /* two lacks this entry */
+ cmp = -1;
+ else if (two.size)
+ /* two has more entries */
+ cmp = 1;
+ else
+ break;
+
+ if (cmp < 0) {
+ /* path1 does not appear in two */
+ score += score_missing(one.entry.mode);
+ update_tree_entry(&one);
+ } else if (cmp > 0) {
+ /* path2 does not appear in one */
+ score += score_missing(two.entry.mode);
+ update_tree_entry(&two);
+ } else {
+ /* path appears in both */
+ if (!oideq(&one.entry.oid, &two.entry.oid)) {
+ /* they are different */
+ score += score_differs(one.entry.mode,
+ two.entry.mode);
+ } else {
+ /* same subtree or blob */
+ score += score_matches(one.entry.mode,
+ two.entry.mode);
+ }
+ update_tree_entry(&one);
+ update_tree_entry(&two);
+ }
+ }
+ 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 struct object_id *hash1,
+ const struct object_id *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 struct object_id *elem;
+ unsigned short 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 "oid1" has a subdirectory at "prefix". Come up with a tree object by
+ * replacing it with another tree "oid2".
+ */
+static int splice_tree(const struct object_id *oid1, const char *prefix,
+ const struct object_id *oid2, struct object_id *result)
+{
+ char *subpath;
+ int toplen;
+ char *buf;
+ unsigned long sz;
+ struct tree_desc desc;
+ unsigned char *rewrite_here;
+ const struct object_id *rewrite_with;
+ struct object_id subtree;
+ enum object_type type;
+ int status;
+
+ subpath = strchrnul(prefix, '/');
+ toplen = subpath - prefix;
+ if (*subpath)
+ subpath++;
+
+ buf = read_object_file(oid1, &type, &sz);
+ if (!buf)
+ die("cannot read tree %s", oid_to_hex(oid1));
+ init_tree_desc(&desc, buf, sz);
+
+ rewrite_here = NULL;
+ while (desc.size) {
+ const char *name;
+ unsigned short mode;
+
+ 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,
+ oid_to_hex(oid1));
+
+ /*
+ * We cast here for two reasons:
+ *
+ * - to flip the "char *" (for the path) to "unsigned
+ * char *" (for the hash stored after it)
+ *
+ * - to discard the "const"; this is OK because we
+ * know it points into our non-const "buf"
+ */
+ rewrite_here = (unsigned char *)(desc.entry.path +
+ strlen(desc.entry.path) +
+ 1);
+ break;
+ }
+ update_tree_entry(&desc);
+ }
+ if (!rewrite_here)
+ die("entry %.*s not found in tree %s", toplen, prefix,
+ oid_to_hex(oid1));
+ if (*subpath) {
+ struct object_id tree_oid;
+ oidread(&tree_oid, rewrite_here);
+ status = splice_tree(&tree_oid, subpath, oid2, &subtree);
+ if (status)
+ return status;
+ rewrite_with = &subtree;
+ } else {
+ rewrite_with = oid2;
+ }
+ hashcpy(rewrite_here, rewrite_with->hash);
+ status = write_object_file(buf, sz, OBJ_TREE, 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(struct repository *r,
+ const struct object_id *hash1,
+ const struct object_id *hash2,
+ struct object_id *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 */
+ oidcpy(shifted, hash2);
+
+ if (add_score < del_score) {
+ /* We need to pick a subtree of two */
+ unsigned short mode;
+
+ if (!*del_prefix)
+ return;
+
+ if (get_tree_entry(r, hash2, del_prefix, shifted, &mode))
+ die("cannot find path %s in tree %s",
+ del_prefix, oid_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(struct repository *r,
+ const struct object_id *hash1,
+ const struct object_id *hash2,
+ struct object_id *shifted,
+ const char *shift_prefix)
+{
+ struct object_id sub1, sub2;
+ unsigned short mode1, mode2;
+ unsigned candidate = 0;
+
+ /* Can hash2 be a tree at shift_prefix in tree hash1? */
+ if (!get_tree_entry(r, 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(r, 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 */
+ oidcpy(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.
+ */
+ oidcpy(shifted, &sub2);
+}