match-trees.c - jrn/git - Git at Google

 #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) {
 			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,
 		       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 = 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;

 	/*
 	 * 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);
 }
	#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) {
	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,
	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 = 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;

	/*
	* 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);
	}