/*
* 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;
}
/*
* 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);
}
/*
* 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);
}
