--- /dev/null
+#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;
+}
+
+/*
+ * 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, *two_buf;
+ int score = 0;
+ enum object_type type;
+ unsigned long size;
+
+ one_buf = read_sha1_file(hash1, &type, &size);
+ if (!one_buf)
+ die("unable to read tree (%s)", sha1_to_hex(hash1));
+ if (type != OBJ_TREE)
+ die("%s is not a tree", sha1_to_hex(hash1));
+ init_tree_desc(&one, one_buf, size);
+ two_buf = read_sha1_file(hash2, &type, &size);
+ if (!two_buf)
+ die("unable to read tree (%s)", sha1_to_hex(hash2));
+ if (type != OBJ_TREE)
+ die("%s is not a tree", sha1_to_hex(hash2));
+ init_tree_desc(&two, two_buf, size);
+ while (one.size | two.size) {
+ const unsigned char *elem1 = elem1;
+ const unsigned char *elem2 = elem2;
+ const char *path1 = path1;
+ const char *path2 = path2;
+ unsigned mode1 = mode1;
+ unsigned mode2 = mode2;
+ int cmp;
+
+ if (one.size)
+ elem1 = tree_entry_extract(&one, &path1, &mode1);
+ if (two.size)
+ elem2 = tree_entry_extract(&two, &path2, &mode2);
+
+ if (!one.size) {
+ /* two has more entries */
+ score += score_missing(mode2, path2);
+ update_tree_entry(&two);
+ continue;
+ }
+ if (!two.size) {
+ /* two lacks this entry */
+ score += score_missing(mode1, path1);
+ update_tree_entry(&one);
+ continue;
+ }
+ cmp = base_name_compare(path1, strlen(path1), mode1,
+ path2, strlen(path2), mode2);
+ if (cmp < 0) {
+ /* path1 does not appear in two */
+ score += score_missing(mode1, path1);
+ update_tree_entry(&one);
+ continue;
+ }
+ else if (cmp > 0) {
+ /* path2 does not appear in one */
+ score += score_missing(mode2, path2);
+ update_tree_entry(&two);
+ continue;
+ }
+ else if (hashcmp(elem1, elem2))
+ /* they are different */
+ score += score_differs(mode1, mode2, path1);
+ else
+ /* same subtree or blob */
+ score += score_matches(mode1, mode2, path1);
+ 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 unsigned char *hash1,
+ const unsigned char *hash2,
+ int *best_score,
+ char **best_match,
+ char *base,
+ int recurse_limit)
+{
+ struct tree_desc one;
+ void *one_buf;
+ enum object_type type;
+ unsigned long size;
+
+ one_buf = read_sha1_file(hash1, &type, &size);
+ if (!one_buf)
+ die("unable to read tree (%s)", sha1_to_hex(hash1));
+ if (type != OBJ_TREE)
+ die("%s is not a tree", sha1_to_hex(hash1));
+ init_tree_desc(&one, one_buf, size);
+
+ 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) {
+ char *newpath;
+ newpath = xmalloc(strlen(base) + strlen(path) + 1);
+ sprintf(newpath, "%s%s", base, path);
+ free(*best_match);
+ *best_match = newpath;
+ *best_score = score;
+ }
+ if (recurse_limit) {
+ char *newbase;
+ newbase = xmalloc(strlen(base) + strlen(path) + 2);
+ sprintf(newbase, "%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,
+ 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 = strchr(prefix, '/');
+ if (!subpath)
+ toplen = strlen(prefix);
+ else {
+ toplen = subpath - prefix;
+ 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;
+
+ 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);
+}
+