tree-diff.c - jrn/git - Git at Google

 /*
  * Helper functions for tree diff generation
  */
 #include "cache.h"
 #include "diff.h"
 #include "diffcore.h"
 #include "tree.h"

 static char *malloc_base(const char *base, int baselen, const char *path, int pathlen)
 {
 	char *newbase = xmalloc(baselen + pathlen + 2);
 	memcpy(newbase, base, baselen);
 	memcpy(newbase + baselen, path, pathlen);
 	memcpy(newbase + baselen + pathlen, "/", 2);
 	return newbase;
 }

 static char *malloc_fullname(const char *base, int baselen, const char *path, int pathlen)
 {
 	char *fullname = xmalloc(baselen + pathlen + 1);
 	memcpy(fullname, base, baselen);
 	memcpy(fullname + baselen, path, pathlen);
 	fullname[baselen + pathlen] = 0;
 	return fullname;
 }

 static void show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc,
 		       const char *base, int baselen);

 static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2, const char *base, int baselen, struct diff_options *opt)
 {
 	unsigned mode1, mode2;
 	const char *path1, *path2;
 	const unsigned char *sha1, *sha2;
 	int cmp, pathlen1, pathlen2;
 	char *fullname;

 	sha1 = tree_entry_extract(t1, &path1, &mode1);
 	sha2 = tree_entry_extract(t2, &path2, &mode2);

 	pathlen1 = tree_entry_len(path1, sha1);
 	pathlen2 = tree_entry_len(path2, sha2);
 	cmp = base_name_compare(path1, pathlen1, mode1, path2, pathlen2, mode2);
 	if (cmp < 0) {
 		show_entry(opt, "-", t1, base, baselen);
 		return -1;
 	}
 	if (cmp > 0) {
 		show_entry(opt, "+", t2, base, baselen);
 		return 1;
 	}
 	if (!DIFF_OPT_TST(opt, FIND_COPIES_HARDER) && !hashcmp(sha1, sha2) && mode1 == mode2)
 		return 0;

 	/*
 	 * If the filemode has changed to/from a directory from/to a regular
 	 * file, we need to consider it a remove and an add.
 	 */
 	if (S_ISDIR(mode1) != S_ISDIR(mode2)) {
 		show_entry(opt, "-", t1, base, baselen);
 		show_entry(opt, "+", t2, base, baselen);
 		return 0;
 	}

 	if (DIFF_OPT_TST(opt, RECURSIVE) && S_ISDIR(mode1)) {
 		int retval;
 		char *newbase = malloc_base(base, baselen, path1, pathlen1);
 		if (DIFF_OPT_TST(opt, TREE_IN_RECURSIVE)) {
 			newbase[baselen + pathlen1] = 0;
 			opt->change(opt, mode1, mode2,
 				    sha1, sha2, newbase, 0, 0);
 			newbase[baselen + pathlen1] = '/';
 		}
 		retval = diff_tree_sha1(sha1, sha2, newbase, opt);
 		free(newbase);
 		return retval;
 	}

 	fullname = malloc_fullname(base, baselen, path1, pathlen1);
 	opt->change(opt, mode1, mode2, sha1, sha2, fullname, 0, 0);
 	free(fullname);
 	return 0;
 }

 /*
  * Is a tree entry interesting given the pathspec we have?
  *
  * Pre-condition: baselen == 0 || base[baselen-1] == '/'
  *
  * Return:
  *  - 2 for "yes, and all subsequent entries will be"
  *  - 1 for yes
  *  - zero for no
  *  - negative for "no, and no subsequent entries will be either"
  */
 static int tree_entry_interesting(struct tree_desc *desc, const char *base, int baselen, struct diff_options *opt)
 {
 	const char *path;
 	const unsigned char *sha1;
 	unsigned mode;
 	int i;
 	int pathlen;
 	int never_interesting = -1;

 	if (!opt->nr_paths)
 		return 2;

 	sha1 = tree_entry_extract(desc, &path, &mode);

 	pathlen = tree_entry_len(path, sha1);

 	for (i = 0; i < opt->nr_paths; i++) {
 		const char *match = opt->paths[i];
 		int matchlen = opt->pathlens[i];
 		int m = -1; /* signals that we haven't called strncmp() */

 		if (baselen >= matchlen) {
 			/* If it doesn't match, move along... */
 			if (strncmp(base, match, matchlen))
 				continue;

 			/*
 			 * If the base is a subdirectory of a path which
 			 * was specified, all of them are interesting.
 			 */
 			if (!matchlen ||
 			    base[matchlen] == '/' ||
 			    match[matchlen - 1] == '/')
 				return 2;

 			/* Just a random prefix match */
 			continue;
 		}

 		/* Does the base match? */
 		if (strncmp(base, match, baselen))
 			continue;

 		match += baselen;
 		matchlen -= baselen;

 		if (never_interesting) {
 			/*
 			 * We have not seen any match that sorts later
 			 * than the current path.
 			 */

 			/*
 			 * Does match sort strictly earlier than path
 			 * with their common parts?
 			 */
 			m = strncmp(match, path,
 				    (matchlen < pathlen) ? matchlen : pathlen);
 			if (m < 0)
 				continue;

 			/*
 			 * If we come here even once, that means there is at
 			 * least one pathspec that would sort equal to or
 			 * later than the path we are currently looking at.
 			 * In other words, if we have never reached this point
 			 * after iterating all pathspecs, it means all
 			 * pathspecs are either outside of base, or inside the
 			 * base but sorts strictly earlier than the current
 			 * one.  In either case, they will never match the
 			 * subsequent entries.  In such a case, we initialized
 			 * the variable to -1 and that is what will be
 			 * returned, allowing the caller to terminate early.
 			 */
 			never_interesting = 0;
 		}

 		if (pathlen > matchlen)
 			continue;

 		if (matchlen > pathlen) {
 			if (match[pathlen] != '/')
 				continue;
 			if (!S_ISDIR(mode))
 				continue;
 		}

 		if (m == -1)
 			/*
 			 * we cheated and did not do strncmp(), so we do
 			 * that here.
 			 */
 			m = strncmp(match, path, pathlen);

 		/*
 		 * If common part matched earlier then it is a hit,
 		 * because we rejected the case where path is not a
 		 * leading directory and is shorter than match.
 		 */
 		if (!m)
 			return 1;
 	}
 	return never_interesting; /* No matches */
 }

 /* A whole sub-tree went away or appeared */
 static void show_tree(struct diff_options *opt, const char *prefix, struct tree_desc *desc, const char *base, int baselen)
 {
 	int all_interesting = 0;
 	while (desc->size) {
 		int show;

 		if (all_interesting)
 			show = 1;
 		else {
 			show = tree_entry_interesting(desc, base, baselen,
 						      opt);
 			if (show == 2)
 				all_interesting = 1;
 		}
 		if (show < 0)
 			break;
 		if (show)
 			show_entry(opt, prefix, desc, base, baselen);
 		update_tree_entry(desc);
 	}
 }

 /* A file entry went away or appeared */
 static void show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc,
 		       const char *base, int baselen)
 {
 	unsigned mode;
 	const char *path;
 	const unsigned char *sha1 = tree_entry_extract(desc, &path, &mode);
 	int pathlen = tree_entry_len(path, sha1);

 	if (DIFF_OPT_TST(opt, RECURSIVE) && S_ISDIR(mode)) {
 		enum object_type type;
 		char *newbase = malloc_base(base, baselen, path, pathlen);
 		struct tree_desc inner;
 		void *tree;
 		unsigned long size;

 		tree = read_sha1_file(sha1, &type, &size);
 		if (!tree || type != OBJ_TREE)
 			die("corrupt tree sha %s", sha1_to_hex(sha1));

 		if (DIFF_OPT_TST(opt, TREE_IN_RECURSIVE)) {
 			newbase[baselen + pathlen] = 0;
 			opt->add_remove(opt, *prefix, mode, sha1, newbase, 0);
 			newbase[baselen + pathlen] = '/';
 		}

 		init_tree_desc(&inner, tree, size);
 		show_tree(opt, prefix, &inner, newbase, baselen + 1 + pathlen);

 		free(tree);
 		free(newbase);
 	} else {
 		char *fullname = malloc_fullname(base, baselen, path, pathlen);
 		opt->add_remove(opt, prefix[0], mode, sha1, fullname, 0);
 		free(fullname);
 	}
 }

 static void skip_uninteresting(struct tree_desc *t, const char *base, int baselen, struct diff_options *opt, int *all_interesting)
 {
 	while (t->size) {
 		int show = tree_entry_interesting(t, base, baselen, opt);
 		if (show == 2)
 			*all_interesting = 1;
 		if (!show) {
 			update_tree_entry(t);
 			continue;
 		}
 		/* Skip it all? */
 		if (show < 0)
 			t->size = 0;
 		return;
 	}
 }

 int diff_tree(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
 {
 	int baselen = strlen(base);
 	int all_t1_interesting = 0;
 	int all_t2_interesting = 0;

 	for (;;) {
 		if (DIFF_OPT_TST(opt, QUICK) &&
 		    DIFF_OPT_TST(opt, HAS_CHANGES))
 			break;
 		if (opt->nr_paths) {
 			if (!all_t1_interesting)
 				skip_uninteresting(t1, base, baselen, opt,
 						   &all_t1_interesting);
 			if (!all_t2_interesting)
 				skip_uninteresting(t2, base, baselen, opt,
 						   &all_t2_interesting);
 		}
 		if (!t1->size) {
 			if (!t2->size)
 				break;
 			show_entry(opt, "+", t2, base, baselen);
 			update_tree_entry(t2);
 			continue;
 		}
 		if (!t2->size) {
 			show_entry(opt, "-", t1, base, baselen);
 			update_tree_entry(t1);
 			continue;
 		}
 		switch (compare_tree_entry(t1, t2, base, baselen, opt)) {
 		case -1:
 			update_tree_entry(t1);
 			continue;
 		case 0:
 			update_tree_entry(t1);
 			/* Fallthrough */
 		case 1:
 			update_tree_entry(t2);
 			continue;
 		}
 		die("git diff-tree: internal error");
 	}
 	return 0;
 }

 /*
  * Does it look like the resulting diff might be due to a rename?
  *  - single entry
  *  - not a valid previous file
  */
 static inline int diff_might_be_rename(void)
 {
 	return diff_queued_diff.nr == 1 &&
 		!DIFF_FILE_VALID(diff_queued_diff.queue[0]->one);
 }

 static void try_to_follow_renames(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
 {
 	struct diff_options diff_opts;
 	struct diff_queue_struct *q = &diff_queued_diff;
 	struct diff_filepair *choice;
 	const char *paths[1];
 	int i;

 	/* Remove the file creation entry from the diff queue, and remember it */
 	choice = q->queue[0];
 	q->nr = 0;

 	diff_setup(&diff_opts);
 	DIFF_OPT_SET(&diff_opts, RECURSIVE);
 	DIFF_OPT_SET(&diff_opts, FIND_COPIES_HARDER);
 	diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
 	diff_opts.single_follow = opt->paths[0];
 	diff_opts.break_opt = opt->break_opt;
 	paths[0] = NULL;
 	diff_tree_setup_paths(paths, &diff_opts);
 	if (diff_setup_done(&diff_opts) < 0)
 		die("unable to set up diff options to follow renames");
 	diff_tree(t1, t2, base, &diff_opts);
 	diffcore_std(&diff_opts);
 	diff_tree_release_paths(&diff_opts);

 	/* Go through the new set of filepairing, and see if we find a more interesting one */
 	opt->found_follow = 0;
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];

 		/*
 		 * Found a source? Not only do we use that for the new
 		 * diff_queued_diff, we will also use that as the path in
 		 * the future!
 		 */
 		if ((p->status == 'R' || p->status == 'C') && !strcmp(p->two->path, opt->paths[0])) {
 			/* Switch the file-pairs around */
 			q->queue[i] = choice;
 			choice = p;

 			/* Update the path we use from now on.. */
 			diff_tree_release_paths(opt);
 			opt->paths[0] = xstrdup(p->one->path);
 			diff_tree_setup_paths(opt->paths, opt);

 			/*
 			 * The caller expects us to return a set of vanilla
 			 * filepairs to let a later call to diffcore_std()
 			 * it makes to sort the renames out (among other
 			 * things), but we already have found renames
 			 * ourselves; signal diffcore_std() not to muck with
 			 * rename information.
 			 */
 			opt->found_follow = 1;
 			break;
 		}
 	}

 	/*
 	 * Then, discard all the non-relevant file pairs...
 	 */
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];
 		diff_free_filepair(p);
 	}

 	/*
 	 * .. and re-instate the one we want (which might be either the
 	 * original one, or the rename/copy we found)
 	 */
 	q->queue[0] = choice;
 	q->nr = 1;
 }

 int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base, struct diff_options *opt)
 {
 	void *tree1, *tree2;
 	struct tree_desc t1, t2;
 	unsigned long size1, size2;
 	int retval;

 	tree1 = read_object_with_reference(old, tree_type, &size1, NULL);
 	if (!tree1)
 		die("unable to read source tree (%s)", sha1_to_hex(old));
 	tree2 = read_object_with_reference(new, tree_type, &size2, NULL);
 	if (!tree2)
 		die("unable to read destination tree (%s)", sha1_to_hex(new));
 	init_tree_desc(&t1, tree1, size1);
 	init_tree_desc(&t2, tree2, size2);
 	retval = diff_tree(&t1, &t2, base, opt);
 	if (!*base && DIFF_OPT_TST(opt, FOLLOW_RENAMES) && diff_might_be_rename()) {
 		init_tree_desc(&t1, tree1, size1);
 		init_tree_desc(&t2, tree2, size2);
 		try_to_follow_renames(&t1, &t2, base, opt);
 	}
 	free(tree1);
 	free(tree2);
 	return retval;
 }

 int diff_root_tree_sha1(const unsigned char *new, const char *base, struct diff_options *opt)
 {
 	int retval;
 	void *tree;
 	unsigned long size;
 	struct tree_desc empty, real;

 	tree = read_object_with_reference(new, tree_type, &size, NULL);
 	if (!tree)
 		die("unable to read root tree (%s)", sha1_to_hex(new));
 	init_tree_desc(&real, tree, size);

 	init_tree_desc(&empty, "", 0);
 	retval = diff_tree(&empty, &real, base, opt);
 	free(tree);
 	return retval;
 }

 static int count_paths(const char **paths)
 {
 	int i = 0;
 	while (*paths++)
 		i++;
 	return i;
 }

 void diff_tree_release_paths(struct diff_options *opt)
 {
 	free(opt->pathlens);
 }

 void diff_tree_setup_paths(const char **p, struct diff_options *opt)
 {
 	opt->nr_paths = 0;
 	opt->pathlens = NULL;
 	opt->paths = NULL;

 	if (p) {
 		int i;

 		opt->paths = p;
 		opt->nr_paths = count_paths(p);
 		if (opt->nr_paths == 0) {
 			opt->pathlens = NULL;
 			return;
 		}
 		opt->pathlens = xmalloc(opt->nr_paths * sizeof(int));
 		for (i=0; i < opt->nr_paths; i++)
 			opt->pathlens[i] = strlen(p[i]);
 	}
 }
	/*
	* Helper functions for tree diff generation
	*/
	#include "cache.h"
	#include "diff.h"
	#include "diffcore.h"
	#include "tree.h"

	static char malloc_base(const char base, int baselen, const char *path, int pathlen)
	{
	char *newbase = xmalloc(baselen + pathlen + 2);
	memcpy(newbase, base, baselen);
	memcpy(newbase + baselen, path, pathlen);
	memcpy(newbase + baselen + pathlen, "/", 2);
	return newbase;
	}

	static char malloc_fullname(const char base, int baselen, const char *path, int pathlen)
	{
	char *fullname = xmalloc(baselen + pathlen + 1);
	memcpy(fullname, base, baselen);
	memcpy(fullname + baselen, path, pathlen);
	fullname[baselen + pathlen] = 0;
	return fullname;
	}

	static void show_entry(struct diff_options opt, const char prefix, struct tree_desc *desc,
	const char *base, int baselen);

	static int compare_tree_entry(struct tree_desc t1, struct tree_desc t2, const char base, int baselen, struct diff_options opt)
	{
	unsigned mode1, mode2;
	const char path1, path2;
	const unsigned char sha1, sha2;
	int cmp, pathlen1, pathlen2;
	char *fullname;

	sha1 = tree_entry_extract(t1, &path1, &mode1);
	sha2 = tree_entry_extract(t2, &path2, &mode2);

	pathlen1 = tree_entry_len(path1, sha1);
	pathlen2 = tree_entry_len(path2, sha2);
	cmp = base_name_compare(path1, pathlen1, mode1, path2, pathlen2, mode2);
	if (cmp < 0) {
	show_entry(opt, "-", t1, base, baselen);
	return -1;
	}
	if (cmp > 0) {
	show_entry(opt, "+", t2, base, baselen);
	return 1;
	}
	if (!DIFF_OPT_TST(opt, FIND_COPIES_HARDER) && !hashcmp(sha1, sha2) && mode1 == mode2)
	return 0;

	/*
	* If the filemode has changed to/from a directory from/to a regular
	* file, we need to consider it a remove and an add.
	*/
	if (S_ISDIR(mode1) != S_ISDIR(mode2)) {
	show_entry(opt, "-", t1, base, baselen);
	show_entry(opt, "+", t2, base, baselen);
	return 0;
	}

	if (DIFF_OPT_TST(opt, RECURSIVE) && S_ISDIR(mode1)) {
	int retval;
	char *newbase = malloc_base(base, baselen, path1, pathlen1);
	if (DIFF_OPT_TST(opt, TREE_IN_RECURSIVE)) {
	newbase[baselen + pathlen1] = 0;
	opt->change(opt, mode1, mode2,
	sha1, sha2, newbase, 0, 0);
	newbase[baselen + pathlen1] = '/';
	}
	retval = diff_tree_sha1(sha1, sha2, newbase, opt);
	free(newbase);
	return retval;
	}

	fullname = malloc_fullname(base, baselen, path1, pathlen1);
	opt->change(opt, mode1, mode2, sha1, sha2, fullname, 0, 0);
	free(fullname);
	return 0;
	}

	/*
	* Is a tree entry interesting given the pathspec we have?
	*
	* Pre-condition: baselen == 0 \|\| base[baselen-1] == '/'
	*
	* Return:
	* - 2 for "yes, and all subsequent entries will be"
	* - 1 for yes
	* - zero for no
	* - negative for "no, and no subsequent entries will be either"
	*/
	static int tree_entry_interesting(struct tree_desc desc, const char base, int baselen, struct diff_options *opt)
	{
	const char *path;
	const unsigned char *sha1;
	unsigned mode;
	int i;
	int pathlen;
	int never_interesting = -1;

	if (!opt->nr_paths)
	return 2;

	sha1 = tree_entry_extract(desc, &path, &mode);

	pathlen = tree_entry_len(path, sha1);

	for (i = 0; i < opt->nr_paths; i++) {
	const char *match = opt->paths[i];
	int matchlen = opt->pathlens[i];
	int m = -1; /* signals that we haven't called strncmp() */

	if (baselen >= matchlen) {
	/* If it doesn't match, move along... */
	if (strncmp(base, match, matchlen))
	continue;

	/*
	* If the base is a subdirectory of a path which
	* was specified, all of them are interesting.
	*/
	if (!matchlen \|\|
	base[matchlen] == '/' \|\|
	match[matchlen - 1] == '/')
	return 2;

	/* Just a random prefix match */
	continue;
	}

	/* Does the base match? */
	if (strncmp(base, match, baselen))
	continue;

	match += baselen;
	matchlen -= baselen;

	if (never_interesting) {
	/*
	* We have not seen any match that sorts later
	* than the current path.
	*/

	/*
	* Does match sort strictly earlier than path
	* with their common parts?
	*/
	m = strncmp(match, path,
	(matchlen < pathlen) ? matchlen : pathlen);
	if (m < 0)
	continue;

	/*
	* If we come here even once, that means there is at
	* least one pathspec that would sort equal to or
	* later than the path we are currently looking at.
	* In other words, if we have never reached this point
	* after iterating all pathspecs, it means all
	* pathspecs are either outside of base, or inside the
	* base but sorts strictly earlier than the current
	* one. In either case, they will never match the
	* subsequent entries. In such a case, we initialized
	* the variable to -1 and that is what will be
	* returned, allowing the caller to terminate early.
	*/
	never_interesting = 0;
	}

	if (pathlen > matchlen)
	continue;

	if (matchlen > pathlen) {
	if (match[pathlen] != '/')
	continue;
	if (!S_ISDIR(mode))
	continue;
	}

	if (m == -1)
	/*
	* we cheated and did not do strncmp(), so we do
	* that here.
	*/
	m = strncmp(match, path, pathlen);

	/*
	* If common part matched earlier then it is a hit,
	* because we rejected the case where path is not a
	* leading directory and is shorter than match.
	*/
	if (!m)
	return 1;
	}
	return never_interesting; /* No matches */
	}

	/* A whole sub-tree went away or appeared */
	static void show_tree(struct diff_options opt, const char prefix, struct tree_desc desc, const char base, int baselen)
	{
	int all_interesting = 0;
	while (desc->size) {
	int show;

	if (all_interesting)
	show = 1;
	else {
	show = tree_entry_interesting(desc, base, baselen,
	opt);
	if (show == 2)
	all_interesting = 1;
	}
	if (show < 0)
	break;
	if (show)
	show_entry(opt, prefix, desc, base, baselen);
	update_tree_entry(desc);
	}
	}

	/* A file entry went away or appeared */
	static void show_entry(struct diff_options opt, const char prefix, struct tree_desc *desc,
	const char *base, int baselen)
	{
	unsigned mode;
	const char *path;
	const unsigned char *sha1 = tree_entry_extract(desc, &path, &mode);
	int pathlen = tree_entry_len(path, sha1);

	if (DIFF_OPT_TST(opt, RECURSIVE) && S_ISDIR(mode)) {
	enum object_type type;
	char *newbase = malloc_base(base, baselen, path, pathlen);
	struct tree_desc inner;
	void *tree;
	unsigned long size;

	tree = read_sha1_file(sha1, &type, &size);
	if (!tree \|\| type != OBJ_TREE)
	die("corrupt tree sha %s", sha1_to_hex(sha1));

	if (DIFF_OPT_TST(opt, TREE_IN_RECURSIVE)) {
	newbase[baselen + pathlen] = 0;
	opt->add_remove(opt, *prefix, mode, sha1, newbase, 0);
	newbase[baselen + pathlen] = '/';
	}

	init_tree_desc(&inner, tree, size);
	show_tree(opt, prefix, &inner, newbase, baselen + 1 + pathlen);

	free(tree);
	free(newbase);
	} else {
	char *fullname = malloc_fullname(base, baselen, path, pathlen);
	opt->add_remove(opt, prefix[0], mode, sha1, fullname, 0);
	free(fullname);
	}
	}

	static void skip_uninteresting(struct tree_desc t, const char base, int baselen, struct diff_options opt, int all_interesting)
	{
	while (t->size) {
	int show = tree_entry_interesting(t, base, baselen, opt);
	if (show == 2)
	*all_interesting = 1;
	if (!show) {
	update_tree_entry(t);
	continue;
	}
	/* Skip it all? */
	if (show < 0)
	t->size = 0;
	return;
	}
	}

	int diff_tree(struct tree_desc t1, struct tree_desc t2, const char base, struct diff_options opt)
	{
	int baselen = strlen(base);
	int all_t1_interesting = 0;
	int all_t2_interesting = 0;

	for (;;) {
	if (DIFF_OPT_TST(opt, QUICK) &&
	DIFF_OPT_TST(opt, HAS_CHANGES))
	break;
	if (opt->nr_paths) {
	if (!all_t1_interesting)
	skip_uninteresting(t1, base, baselen, opt,
	&all_t1_interesting);
	if (!all_t2_interesting)
	skip_uninteresting(t2, base, baselen, opt,
	&all_t2_interesting);
	}
	if (!t1->size) {
	if (!t2->size)
	break;
	show_entry(opt, "+", t2, base, baselen);
	update_tree_entry(t2);
	continue;
	}
	if (!t2->size) {
	show_entry(opt, "-", t1, base, baselen);
	update_tree_entry(t1);
	continue;
	}
	switch (compare_tree_entry(t1, t2, base, baselen, opt)) {
	case -1:
	update_tree_entry(t1);
	continue;
	case 0:
	update_tree_entry(t1);
	/* Fallthrough */
	case 1:
	update_tree_entry(t2);
	continue;
	}
	die("git diff-tree: internal error");
	}
	return 0;
	}

	/*
	* Does it look like the resulting diff might be due to a rename?
	* - single entry
	* - not a valid previous file
	*/
	static inline int diff_might_be_rename(void)
	{
	return diff_queued_diff.nr == 1 &&
	!DIFF_FILE_VALID(diff_queued_diff.queue[0]->one);
	}

	static void try_to_follow_renames(struct tree_desc t1, struct tree_desc t2, const char base, struct diff_options opt)
	{
	struct diff_options diff_opts;
	struct diff_queue_struct *q = &diff_queued_diff;
	struct diff_filepair *choice;
	const char *paths[1];
	int i;

	/* Remove the file creation entry from the diff queue, and remember it */
	choice = q->queue[0];
	q->nr = 0;

	diff_setup(&diff_opts);
	DIFF_OPT_SET(&diff_opts, RECURSIVE);
	DIFF_OPT_SET(&diff_opts, FIND_COPIES_HARDER);
	diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
	diff_opts.single_follow = opt->paths[0];
	diff_opts.break_opt = opt->break_opt;
	paths[0] = NULL;
	diff_tree_setup_paths(paths, &diff_opts);
	if (diff_setup_done(&diff_opts) < 0)
	die("unable to set up diff options to follow renames");
	diff_tree(t1, t2, base, &diff_opts);
	diffcore_std(&diff_opts);
	diff_tree_release_paths(&diff_opts);

	/* Go through the new set of filepairing, and see if we find a more interesting one */
	opt->found_follow = 0;
	for (i = 0; i < q->nr; i++) {
	struct diff_filepair *p = q->queue[i];

	/*
	* Found a source? Not only do we use that for the new
	* diff_queued_diff, we will also use that as the path in
	* the future!
	*/
	if ((p->status == 'R' \|\| p->status == 'C') && !strcmp(p->two->path, opt->paths[0])) {
	/* Switch the file-pairs around */
	q->queue[i] = choice;
	choice = p;

	/* Update the path we use from now on.. */
	diff_tree_release_paths(opt);
	opt->paths[0] = xstrdup(p->one->path);
	diff_tree_setup_paths(opt->paths, opt);

	/*
	* The caller expects us to return a set of vanilla
	* filepairs to let a later call to diffcore_std()
	* it makes to sort the renames out (among other
	* things), but we already have found renames
	* ourselves; signal diffcore_std() not to muck with
	* rename information.
	*/
	opt->found_follow = 1;
	break;
	}
	}

	/*
	* Then, discard all the non-relevant file pairs...
	*/
	for (i = 0; i < q->nr; i++) {
	struct diff_filepair *p = q->queue[i];
	diff_free_filepair(p);
	}

	/*
	* .. and re-instate the one we want (which might be either the
	* original one, or the rename/copy we found)
	*/
	q->queue[0] = choice;
	q->nr = 1;
	}

	int diff_tree_sha1(const unsigned char old, const unsigned char new, const char base, struct diff_options opt)
	{
	void tree1, tree2;
	struct tree_desc t1, t2;
	unsigned long size1, size2;
	int retval;

	tree1 = read_object_with_reference(old, tree_type, &size1, NULL);
	if (!tree1)
	die("unable to read source tree (%s)", sha1_to_hex(old));
	tree2 = read_object_with_reference(new, tree_type, &size2, NULL);
	if (!tree2)
	die("unable to read destination tree (%s)", sha1_to_hex(new));
	init_tree_desc(&t1, tree1, size1);
	init_tree_desc(&t2, tree2, size2);
	retval = diff_tree(&t1, &t2, base, opt);
	if (!*base && DIFF_OPT_TST(opt, FOLLOW_RENAMES) && diff_might_be_rename()) {
	init_tree_desc(&t1, tree1, size1);
	init_tree_desc(&t2, tree2, size2);
	try_to_follow_renames(&t1, &t2, base, opt);
	}
	free(tree1);
	free(tree2);
	return retval;
	}

	int diff_root_tree_sha1(const unsigned char new, const char base, struct diff_options *opt)
	{
	int retval;
	void *tree;
	unsigned long size;
	struct tree_desc empty, real;

	tree = read_object_with_reference(new, tree_type, &size, NULL);
	if (!tree)
	die("unable to read root tree (%s)", sha1_to_hex(new));
	init_tree_desc(&real, tree, size);

	init_tree_desc(&empty, "", 0);
	retval = diff_tree(&empty, &real, base, opt);
	free(tree);
	return retval;
	}

	static int count_paths(const char **paths)
	{
	int i = 0;
	while (*paths++)
	i++;
	return i;
	}

	void diff_tree_release_paths(struct diff_options *opt)
	{
	free(opt->pathlens);
	}

	void diff_tree_setup_paths(const char *p, struct diff_options opt)
	{
	opt->nr_paths = 0;
	opt->pathlens = NULL;
	opt->paths = NULL;

	if (p) {
	int i;

	opt->paths = p;
	opt->nr_paths = count_paths(p);
	if (opt->nr_paths == 0) {
	opt->pathlens = NULL;
	return;
	}
	opt->pathlens = xmalloc(opt->nr_paths * sizeof(int));
	for (i=0; i < opt->nr_paths; i++)
	opt->pathlens[i] = strlen(p[i]);
	}
	}