diff.c

/*
 * Copyright (C) 2005 Junio C Hamano
 */
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>
#include "cache.h"
#include "diff.h"
#include "diffcore.h"

static const char *diff_opts = "-pu";
static unsigned char null_sha1[20] = { 0, };

static int reverse_diff;
static int use_size_cache;

static const char *external_diff(void)
{
	static const char *external_diff_cmd = NULL;
	static int done_preparing = 0;

	if (done_preparing)
		return external_diff_cmd;

	/*
	 * Default values above are meant to match the
	 * Linux kernel development style.  Examples of
	 * alternative styles you can specify via environment
	 * variables are:
	 *
	 * GIT_DIFF_OPTS="-c";
	 */
	if (gitenv("GIT_EXTERNAL_DIFF"))
		external_diff_cmd = gitenv("GIT_EXTERNAL_DIFF");

	/* In case external diff fails... */
	diff_opts = gitenv("GIT_DIFF_OPTS") ? : diff_opts;

	done_preparing = 1;
	return external_diff_cmd;
}

/* Help to copy the thing properly quoted for the shell safety.
 * any single quote is replaced with '\'', and the caller is
 * expected to enclose the result within a single quote pair.
 *
 * E.g.
 *  original     sq_expand     result
 *  name     ==> name      ==> 'name'
 *  a b      ==> a b       ==> 'a b'
 *  a'b      ==> a'\''b    ==> 'a'\''b'
 */
static char *sq_expand(const char *src)
{
	static char *buf = NULL;
	int cnt, c;
	const char *cp;
	char *bp;

	/* count bytes needed to store the quoted string. */
	for (cnt = 1, cp = src; *cp; cnt++, cp++)
		if (*cp == '\'')
			cnt += 3;

	buf = xmalloc(cnt);
	bp = buf;
	while ((c = *src++)) {
		if (c != '\'')
			*bp++ = c;
		else {
			bp = strcpy(bp, "'\\''");
			bp += 4;
		}
	}
	*bp = 0;
	return buf;
}

static struct diff_tempfile {
	const char *name; /* filename external diff should read from */
	char hex[41];
	char mode[10];
	char tmp_path[50];
} diff_temp[2];

static int count_lines(const char *filename)
{
	FILE *in;
	int count, ch, completely_empty = 1, nl_just_seen = 0;
	in = fopen(filename, "r");
	count = 0;
	while ((ch = fgetc(in)) != EOF)
		if (ch == '\n') {
			count++;
			nl_just_seen = 1;
			completely_empty = 0;
		}
		else {
			nl_just_seen = 0;
			completely_empty = 0;
		}
	fclose(in);
	if (completely_empty)
		return 0;
	if (!nl_just_seen)
		count++; /* no trailing newline */
	return count;
}

static void print_line_count(int count)
{
	switch (count) {
	case 0:
		printf("0,0");
		break;
	case 1:
		printf("1");
		break;
	default:
		printf("1,%d", count);
		break;
	}
}

static void copy_file(int prefix, const char *filename)
{
	FILE *in;
	int ch, nl_just_seen = 1;
	in = fopen(filename, "r");
	while ((ch = fgetc(in)) != EOF) {
		if (nl_just_seen)
			putchar(prefix);
		putchar(ch);
		if (ch == '\n')
			nl_just_seen = 1;
		else
			nl_just_seen = 0;
	}
	fclose(in);
	if (!nl_just_seen)
		printf("\n\\ No newline at end of file\n");
}

static void emit_rewrite_diff(const char *name_a,
			      const char *name_b,
			      struct diff_tempfile *temp)
{
	/* Use temp[i].name as input, name_a and name_b as labels */
	int lc_a, lc_b;
	lc_a = count_lines(temp[0].name);
	lc_b = count_lines(temp[1].name);
	printf("--- %s\n+++ %s\n@@ -", name_a, name_b);
	print_line_count(lc_a);
	printf(" +");
	print_line_count(lc_b);
	printf(" @@\n");
	if (lc_a)
		copy_file('-', temp[0].name);
	if (lc_b)
		copy_file('+', temp[1].name);
}

static void builtin_diff(const char *name_a,
			 const char *name_b,
			 struct diff_tempfile *temp,
			 const char *xfrm_msg,
			 int complete_rewrite)
{
	int i, next_at, cmd_size;
	const char *diff_cmd = "diff -L'%s%s' -L'%s%s'";
	const char *diff_arg  = "'%s' '%s'||:"; /* "||:" is to return 0 */
	const char *input_name_sq[2];
	const char *path0[2];
	const char *path1[2];
	const char *name_sq[2];
	char *cmd;

	name_sq[0] = sq_expand(name_a);
	name_sq[1] = sq_expand(name_b);

	/* diff_cmd and diff_arg have 6 %s in total which makes
	 * the sum of these strings 12 bytes larger than required.
	 * we use 2 spaces around diff-opts, and we need to count
	 * terminating NUL, so we subtract 9 here.
	 */
	cmd_size = (strlen(diff_cmd) + strlen(diff_opts) +
			strlen(diff_arg) - 9);
	for (i = 0; i < 2; i++) {
		input_name_sq[i] = sq_expand(temp[i].name);
		if (!strcmp(temp[i].name, "/dev/null")) {
			path0[i] = "/dev/null";
			path1[i] = "";
		} else {
			path0[i] = i ? "b/" : "a/";
			path1[i] = name_sq[i];
		}
		cmd_size += (strlen(path0[i]) + strlen(path1[i]) +
			     strlen(input_name_sq[i]));
	}

	cmd = xmalloc(cmd_size);

	next_at = 0;
	next_at += snprintf(cmd+next_at, cmd_size-next_at,
			    diff_cmd,
			    path0[0], path1[0], path0[1], path1[1]);
	next_at += snprintf(cmd+next_at, cmd_size-next_at,
			    " %s ", diff_opts);
	next_at += snprintf(cmd+next_at, cmd_size-next_at,
			    diff_arg, input_name_sq[0], input_name_sq[1]);

	printf("diff --git a/%s b/%s\n", name_a, name_b);
	if (!path1[0][0]) {
		printf("new file mode %s\n", temp[1].mode);
		if (xfrm_msg && xfrm_msg[0])
			puts(xfrm_msg);
	}
	else if (!path1[1][0]) {
		printf("deleted file mode %s\n", temp[0].mode);
		if (xfrm_msg && xfrm_msg[0])
			puts(xfrm_msg);
	}
	else {
		if (strcmp(temp[0].mode, temp[1].mode)) {
			printf("old mode %s\n", temp[0].mode);
			printf("new mode %s\n", temp[1].mode);
		}
		if (xfrm_msg && xfrm_msg[0])
			puts(xfrm_msg);
		if (strncmp(temp[0].mode, temp[1].mode, 3))
			/* we do not run diff between different kind
			 * of objects.
			 */
			exit(0);
		if (complete_rewrite) {
			fflush(NULL);
			emit_rewrite_diff(name_a, name_b, temp);
			exit(0);
		}
	}
	fflush(NULL);
	execlp("/bin/sh","sh", "-c", cmd, NULL);
}

struct diff_filespec *alloc_filespec(const char *path)
{
	int namelen = strlen(path);
	struct diff_filespec *spec = xmalloc(sizeof(*spec) + namelen + 1);
	spec->path = (char *)(spec + 1);
	strcpy(spec->path, path);
	spec->should_free = spec->should_munmap = 0;
	spec->xfrm_flags = 0;
	spec->size = 0;
	spec->data = NULL;
	spec->mode = 0;
	memset(spec->sha1, 0, 20);
	return spec;
}

void fill_filespec(struct diff_filespec *spec, const unsigned char *sha1,
		   unsigned short mode)
{
	if (mode) {
		spec->mode = DIFF_FILE_CANON_MODE(mode);
		memcpy(spec->sha1, sha1, 20);
		spec->sha1_valid = !!memcmp(sha1, null_sha1, 20);
	}
}

/*
 * Given a name and sha1 pair, if the dircache tells us the file in
 * the work tree has that object contents, return true, so that
 * prepare_temp_file() does not have to inflate and extract.
 */
static int work_tree_matches(const char *name, const unsigned char *sha1)
{
	struct cache_entry *ce;
	struct stat st;
	int pos, len;

	/* We do not read the cache ourselves here, because the
	 * benchmark with my previous version that always reads cache
	 * shows that it makes things worse for diff-tree comparing
	 * two linux-2.6 kernel trees in an already checked out work
	 * tree.  This is because most diff-tree comparisons deal with
	 * only a small number of files, while reading the cache is
	 * expensive for a large project, and its cost outweighs the
	 * savings we get by not inflating the object to a temporary
	 * file.  Practically, this code only helps when we are used
	 * by diff-cache --cached, which does read the cache before
	 * calling us.
	 */
	if (!active_cache)
		return 0;

	len = strlen(name);
	pos = cache_name_pos(name, len);
	if (pos < 0)
		return 0;
	ce = active_cache[pos];
	if ((lstat(name, &st) < 0) ||
	    !S_ISREG(st.st_mode) || /* careful! */
	    ce_match_stat(ce, &st) ||
	    memcmp(sha1, ce->sha1, 20))
		return 0;
	/* we return 1 only when we can stat, it is a regular file,
	 * stat information matches, and sha1 recorded in the cache
	 * matches.  I.e. we know the file in the work tree really is
	 * the same as the <name, sha1> pair.
	 */
	return 1;
}

static struct sha1_size_cache {
	unsigned char sha1[20];
	unsigned long size;
} **sha1_size_cache;
static int sha1_size_cache_nr, sha1_size_cache_alloc;

static struct sha1_size_cache *locate_size_cache(unsigned char *sha1,
						 int find_only,
						 unsigned long size)
{
	int first, last;
	struct sha1_size_cache *e;

	first = 0;
	last = sha1_size_cache_nr;
	while (last > first) {
		int cmp, next = (last + first) >> 1;
		e = sha1_size_cache[next];
		cmp = memcmp(e->sha1, sha1, 20);
		if (!cmp)
			return e;
		if (cmp < 0) {
			last = next;
			continue;
		}
		first = next+1;
	}
	/* not found */
	if (find_only)
		return NULL;
	/* insert to make it at "first" */
	if (sha1_size_cache_alloc <= sha1_size_cache_nr) {
		sha1_size_cache_alloc = alloc_nr(sha1_size_cache_alloc);
		sha1_size_cache = xrealloc(sha1_size_cache,
					   sha1_size_cache_alloc *
					   sizeof(*sha1_size_cache));
	}
	sha1_size_cache_nr++;
	if (first < sha1_size_cache_nr)
		memmove(sha1_size_cache + first + 1, sha1_size_cache + first,
			(sha1_size_cache_nr - first - 1) *
			sizeof(*sha1_size_cache));
	e = xmalloc(sizeof(struct sha1_size_cache));
	sha1_size_cache[first] = e;
	memcpy(e->sha1, sha1, 20);
	e->size = size;
	return e;
}

/*
 * While doing rename detection and pickaxe operation, we may need to
 * grab the data for the blob (or file) for our own in-core comparison.
 * diff_filespec has data and size fields for this purpose.
 */
int diff_populate_filespec(struct diff_filespec *s, int size_only)
{
	int err = 0;
	if (!DIFF_FILE_VALID(s))
		die("internal error: asking to populate invalid file.");
	if (S_ISDIR(s->mode))
		return -1;

	if (!use_size_cache)
		size_only = 0;

	if (s->data)
		return err;
	if (!s->sha1_valid ||
	    work_tree_matches(s->path, s->sha1)) {
		struct stat st;
		int fd;
		if (lstat(s->path, &st) < 0) {
			if (errno == ENOENT) {
			err_empty:
				err = -1;
			empty:
				s->data = "";
				s->size = 0;
				return err;
			}
		}
		s->size = st.st_size;
		if (!s->size)
			goto empty;
		if (size_only)
			return 0;
		if (S_ISLNK(st.st_mode)) {
			int ret;
			s->data = xmalloc(s->size);
			s->should_free = 1;
			ret = readlink(s->path, s->data, s->size);
			if (ret < 0) {
				free(s->data);
				goto err_empty;
			}
			return 0;
		}
		fd = open(s->path, O_RDONLY);
		if (fd < 0)
			goto err_empty;
		s->data = mmap(NULL, s->size, PROT_READ, MAP_PRIVATE, fd, 0);
		s->should_munmap = 1;
		close(fd);
	}
	else {
		char type[20];
		struct sha1_size_cache *e;

		if (size_only) {
			e = locate_size_cache(s->sha1, 1, 0);
			if (e) {
				s->size = e->size;
				return 0;
			}
			if (!sha1_object_info(s->sha1, type, &s->size))
				locate_size_cache(s->sha1, 0, s->size);
		}
		else {
			s->data = read_sha1_file(s->sha1, type, &s->size);
			s->should_free = 1;
		}
	}
	return 0;
}

void diff_free_filespec_data(struct diff_filespec *s)
{
	if (s->should_free)
		free(s->data);
	else if (s->should_munmap)
		munmap(s->data, s->size);
	s->should_free = s->should_munmap = 0;
	s->data = NULL;
}

static void prep_temp_blob(struct diff_tempfile *temp,
			   void *blob,
			   unsigned long size,
			   unsigned char *sha1,
			   int mode)
{
	int fd;

	strcpy(temp->tmp_path, ".diff_XXXXXX");
	fd = mkstemp(temp->tmp_path);
	if (fd < 0)
		die("unable to create temp-file");
	if (write(fd, blob, size) != size)
		die("unable to write temp-file");
	close(fd);
	temp->name = temp->tmp_path;
	strcpy(temp->hex, sha1_to_hex(sha1));
	temp->hex[40] = 0;
	sprintf(temp->mode, "%06o", mode);
}

static void prepare_temp_file(const char *name,
			      struct diff_tempfile *temp,
			      struct diff_filespec *one)
{
	if (!DIFF_FILE_VALID(one)) {
	not_a_valid_file:
		/* A '-' entry produces this for file-2, and
		 * a '+' entry produces this for file-1.
		 */
		temp->name = "/dev/null";
		strcpy(temp->hex, ".");
		strcpy(temp->mode, ".");
		return;
	}

	if (!one->sha1_valid ||
	    work_tree_matches(name, one->sha1)) {
		struct stat st;
		if (lstat(name, &st) < 0) {
			if (errno == ENOENT)
				goto not_a_valid_file;
			die("stat(%s): %s", name, strerror(errno));
		}
		if (S_ISLNK(st.st_mode)) {
			int ret;
			char *buf, buf_[1024];
			buf = ((sizeof(buf_) < st.st_size) ?
			       xmalloc(st.st_size) : buf_);
			ret = readlink(name, buf, st.st_size);
			if (ret < 0)
				die("readlink(%s)", name);
			prep_temp_blob(temp, buf, st.st_size,
				       (one->sha1_valid ?
					one->sha1 : null_sha1),
				       (one->sha1_valid ?
					one->mode : S_IFLNK));
		}
		else {
			/* we can borrow from the file in the work tree */
			temp->name = name;
			if (!one->sha1_valid)
				strcpy(temp->hex, sha1_to_hex(null_sha1));
			else
				strcpy(temp->hex, sha1_to_hex(one->sha1));
			/* Even though we may sometimes borrow the
			 * contents from the work tree, we always want
			 * one->mode.  mode is trustworthy even when
			 * !(one->sha1_valid), as long as
			 * DIFF_FILE_VALID(one).
			 */
			sprintf(temp->mode, "%06o", one->mode);
		}
		return;
	}
	else {
		if (diff_populate_filespec(one, 0))
			die("cannot read data blob for %s", one->path);
		prep_temp_blob(temp, one->data, one->size,
			       one->sha1, one->mode);
	}
}

static void remove_tempfile(void)
{
	int i;

	for (i = 0; i < 2; i++)
		if (diff_temp[i].name == diff_temp[i].tmp_path) {
			unlink(diff_temp[i].name);
			diff_temp[i].name = NULL;
		}
}

static void remove_tempfile_on_signal(int signo)
{
	remove_tempfile();
}

/* An external diff command takes:
 *
 * diff-cmd name infile1 infile1-sha1 infile1-mode \
 *               infile2 infile2-sha1 infile2-mode [ rename-to ]
 *
 */
static void run_external_diff(const char *pgm,
			      const char *name,
			      const char *other,
			      struct diff_filespec *one,
			      struct diff_filespec *two,
			      const char *xfrm_msg,
			      int complete_rewrite)
{
	struct diff_tempfile *temp = diff_temp;
	pid_t pid;
	int status;
	static int atexit_asked = 0;

	if (one && two) {
		prepare_temp_file(name, &temp[0], one);
		prepare_temp_file(other ? : name, &temp[1], two);
		if (! atexit_asked &&
		    (temp[0].name == temp[0].tmp_path ||
		     temp[1].name == temp[1].tmp_path)) {
			atexit_asked = 1;
			atexit(remove_tempfile);
		}
		signal(SIGINT, remove_tempfile_on_signal);
	}

	fflush(NULL);
	pid = fork();
	if (pid < 0)
		die("unable to fork");
	if (!pid) {
		if (pgm) {
			if (one && two) {
				const char *exec_arg[10];
				const char **arg = &exec_arg[0];
				*arg++ = pgm;
				*arg++ = name;
				*arg++ = temp[0].name;
				*arg++ = temp[0].hex;
				*arg++ = temp[0].mode;
				*arg++ = temp[1].name;
				*arg++ = temp[1].hex;
				*arg++ = temp[1].mode;
				if (other) {
					*arg++ = other;
					*arg++ = xfrm_msg;
				}
				*arg = NULL;
				execvp(pgm, (char *const*) exec_arg);
			}
			else
				execlp(pgm, pgm, name, NULL);
		}
		/*
		 * otherwise we use the built-in one.
		 */
		if (one && two)
			builtin_diff(name, other ? : name, temp, xfrm_msg,
				     complete_rewrite);
		else
			printf("* Unmerged path %s\n", name);
		exit(0);
	}
	if (waitpid(pid, &status, 0) < 0 ||
	    !WIFEXITED(status) || WEXITSTATUS(status)) {
		/* Earlier we did not check the exit status because
		 * diff exits non-zero if files are different, and
		 * we are not interested in knowing that.  It was a
		 * mistake which made it harder to quit a diff-*
		 * session that uses the git-apply-patch-script as
		 * the GIT_EXTERNAL_DIFF.  A custom GIT_EXTERNAL_DIFF
		 * should also exit non-zero only when it wants to
		 * abort the entire diff-* session.
		 */
		remove_tempfile();
		fprintf(stderr, "external diff died, stopping at %s.\n", name);
		exit(1);
	}
	remove_tempfile();
}

static void run_diff(struct diff_filepair *p)
{
	const char *pgm = external_diff();
	char msg_[PATH_MAX*2+200], *xfrm_msg;
	struct diff_filespec *one;
	struct diff_filespec *two;
	const char *name;
	const char *other;
	int complete_rewrite = 0;

	if (DIFF_PAIR_UNMERGED(p)) {
		/* unmerged */
		run_external_diff(pgm, p->one->path, NULL, NULL, NULL, NULL,
				  0);
		return;
	}

	name = p->one->path;
	other = (strcmp(name, p->two->path) ? p->two->path : NULL);
	one = p->one; two = p->two;
	switch (p->status) {
	case 'C':
		sprintf(msg_,
			"similarity index %d%%\n"
			"copy from %s\n"
			"copy to %s",
			(int)(0.5 + p->score * 100.0/MAX_SCORE),
			name, other);
		xfrm_msg = msg_;
		break;
	case 'R':
		sprintf(msg_,
			"similarity index %d%%\n"
			"rename from %s\n"
			"rename to %s",
			(int)(0.5 + p->score * 100.0/MAX_SCORE),
			name, other);
		xfrm_msg = msg_;
		break;
	case 'M':
		if (p->score) {
			sprintf(msg_,
				"dissimilarity index %d%%",
				(int)(0.5 + p->score * 100.0/MAX_SCORE));
			xfrm_msg = msg_;
			complete_rewrite = 1;
			break;
		}
		/* fallthru */
	default:
		xfrm_msg = NULL;
	}

	if (!pgm &&
	    DIFF_FILE_VALID(one) && DIFF_FILE_VALID(two) &&
	    (S_IFMT & one->mode) != (S_IFMT & two->mode)) {
		/* a filepair that changes between file and symlink
		 * needs to be split into deletion and creation.
		 */
		struct diff_filespec *null = alloc_filespec(two->path);
		run_external_diff(NULL, name, other, one, null, xfrm_msg, 0);
		free(null);
		null = alloc_filespec(one->path);
		run_external_diff(NULL, name, other, null, two, xfrm_msg, 0);
		free(null);
	}
	else
		run_external_diff(pgm, name, other, one, two, xfrm_msg,
				  complete_rewrite);
}

void diff_setup(int flags)
{
	if (flags & DIFF_SETUP_REVERSE)
		reverse_diff = 1;
	if (flags & DIFF_SETUP_USE_CACHE) {
		if (!active_cache)
			/* read-cache does not die even when it fails
			 * so it is safe for us to do this here.  Also
			 * it does not smudge active_cache or active_nr
			 * when it fails, so we do not have to worry about
			 * cleaning it up oufselves either.
			 */
			read_cache();
	}
	if (flags & DIFF_SETUP_USE_SIZE_CACHE)
		use_size_cache = 1;
	
}

static int parse_num(const char **cp_p)
{
	int num, scale, ch, cnt;
	const char *cp = *cp_p;

	cnt = num = 0;
	scale = 1;
	while ('0' <= (ch = *cp) && ch <= '9') {
		if (cnt++ < 5) {
			/* We simply ignore more than 5 digits precision. */
			scale *= 10;
			num = num * 10 + ch - '0';
		}
		*cp++;
	}
	*cp_p = cp;

	/* user says num divided by scale and we say internally that
	 * is MAX_SCORE * num / scale.
	 */
	return (MAX_SCORE * num / scale);
}

int diff_scoreopt_parse(const char *opt)
{
	int opt1, opt2, cmd;

	if (*opt++ != '-')
		return -1;
	cmd = *opt++;
	if (cmd != 'M' && cmd != 'C' && cmd != 'B')
		return -1; /* that is not a -M, -C nor -B option */

	opt1 = parse_num(&opt);
	if (cmd != 'B')
		opt2 = 0;
	else {
		if (*opt == 0)
			opt2 = 0;
		else if (*opt != '/')
			return -1; /* we expect -B80/99 or -B80 */
		else {
			opt++;
			opt2 = parse_num(&opt);
		}
	}
	if (*opt != 0)
		return -1;
	return opt1 | (opt2 << 16);
}

struct diff_queue_struct diff_queued_diff;

void diff_q(struct diff_queue_struct *queue, struct diff_filepair *dp)
{
	if (queue->alloc <= queue->nr) {
		queue->alloc = alloc_nr(queue->alloc);
		queue->queue = xrealloc(queue->queue,
					sizeof(dp) * queue->alloc);
	}
	queue->queue[queue->nr++] = dp;
}

struct diff_filepair *diff_queue(struct diff_queue_struct *queue,
				 struct diff_filespec *one,
				 struct diff_filespec *two)
{
	struct diff_filepair *dp = xmalloc(sizeof(*dp));
	dp->one = one;
	dp->two = two;
	dp->score = 0;
	dp->status = 0;
	dp->source_stays = 0;
	dp->broken_pair = 0;
	diff_q(queue, dp);
	return dp;
}

void diff_free_filepair(struct diff_filepair *p)
{
	diff_free_filespec_data(p->one);
	diff_free_filespec_data(p->two);
	free(p);
}

static void diff_flush_raw(struct diff_filepair *p,
			   int line_termination,
			   int inter_name_termination)
{
	int two_paths;
	char status[10];

	if (line_termination) {
		const char *err = "path %s cannot be expressed without -z";
		if (strchr(p->one->path, line_termination) ||
		    strchr(p->one->path, inter_name_termination))
			die(err, p->one->path);
		if (strchr(p->two->path, line_termination) ||
		    strchr(p->two->path, inter_name_termination))
			die(err, p->two->path);
	}

	if (p->score)
		sprintf(status, "%c%03d", p->status,
			(int)(0.5 + p->score * 100.0/MAX_SCORE));
	else {
		status[0] = p->status;
		status[1] = 0;
	}
	switch (p->status) {
	case 'C': case 'R':
		two_paths = 1;
		break;
	case 'N': case 'D':
		two_paths = 0;
		break;
	default:
		two_paths = 0;
		break;
	}
	printf(":%06o %06o %s ",
	       p->one->mode, p->two->mode, sha1_to_hex(p->one->sha1));
	printf("%s %s%c%s",
	       sha1_to_hex(p->two->sha1),
	       status,
	       inter_name_termination,
	       p->one->path);
	if (two_paths)
		printf("%c%s", inter_name_termination, p->two->path);
	putchar(line_termination);
}

int diff_unmodified_pair(struct diff_filepair *p)
{
	/* This function is written stricter than necessary to support
	 * the currently implemented transformers, but the idea is to
	 * let transformers to produce diff_filepairs any way they want,
	 * and filter and clean them up here before producing the output.
	 */
	struct diff_filespec *one, *two;

	if (DIFF_PAIR_UNMERGED(p))
		return 0; /* unmerged is interesting */

	one = p->one;
	two = p->two;

	/* deletion, addition, mode or type change
	 * and rename are all interesting.
	 */
	if (DIFF_FILE_VALID(one) != DIFF_FILE_VALID(two) ||
	    DIFF_PAIR_MODE_CHANGED(p) ||
	    strcmp(one->path, two->path))
		return 0;

	/* both are valid and point at the same path.  that is, we are
	 * dealing with a change.
	 */
	if (one->sha1_valid && two->sha1_valid &&
	    !memcmp(one->sha1, two->sha1, sizeof(one->sha1)))
		return 1; /* no change */
	if (!one->sha1_valid && !two->sha1_valid)
		return 1; /* both look at the same file on the filesystem. */
	return 0;
}

static void diff_flush_patch(struct diff_filepair *p)
{
	if (diff_unmodified_pair(p))
		return;

	if ((DIFF_FILE_VALID(p->one) && S_ISDIR(p->one->mode)) ||
	    (DIFF_FILE_VALID(p->two) && S_ISDIR(p->two->mode)))
		return; /* no tree diffs in patch format */ 

	run_diff(p);
}

int diff_queue_is_empty(void)
{
	struct diff_queue_struct *q = &diff_queued_diff;
	int i;
	for (i = 0; i < q->nr; i++)
		if (!diff_unmodified_pair(q->queue[i]))
			return 0;
	return 1;
}

#if DIFF_DEBUG
void diff_debug_filespec(struct diff_filespec *s, int x, const char *one)
{
	fprintf(stderr, "queue[%d] %s (%s) %s %06o %s\n",
		x, one ? : "",
		s->path,
		DIFF_FILE_VALID(s) ? "valid" : "invalid",
		s->mode,
		s->sha1_valid ? sha1_to_hex(s->sha1) : "");
	fprintf(stderr, "queue[%d] %s size %lu flags %d\n",
		x, one ? : "",
		s->size, s->xfrm_flags);
}

void diff_debug_filepair(const struct diff_filepair *p, int i)
{
	diff_debug_filespec(p->one, i, "one");
	diff_debug_filespec(p->two, i, "two");
	fprintf(stderr, "score %d, status %c stays %d broken %d\n",
		p->score, p->status ? : '?',
		p->source_stays, p->broken_pair);
}

void diff_debug_queue(const char *msg, struct diff_queue_struct *q)
{
	int i;
	if (msg)
		fprintf(stderr, "%s\n", msg);
	fprintf(stderr, "q->nr = %d\n", q->nr);
	for (i = 0; i < q->nr; i++) {
		struct diff_filepair *p = q->queue[i];
		diff_debug_filepair(p, i);
	}
}
#endif

static void diff_resolve_rename_copy(void)
{
	int i, j;
	struct diff_filepair *p, *pp;
	struct diff_queue_struct *q = &diff_queued_diff;

	diff_debug_queue("resolve-rename-copy", q);

	for (i = 0; i < q->nr; i++) {
		p = q->queue[i];
		p->status = 0; /* undecided */
		if (DIFF_PAIR_UNMERGED(p))
			p->status = 'U';
		else if (!DIFF_FILE_VALID(p->one))
			p->status = 'N';
		else if (!DIFF_FILE_VALID(p->two))
			p->status = 'D';
		else if (DIFF_PAIR_TYPE_CHANGED(p))
			p->status = 'T';

		/* from this point on, we are dealing with a pair
		 * whose both sides are valid and of the same type, i.e.
		 * either in-place edit or rename/copy edit.
		 */
		else if (DIFF_PAIR_RENAME(p)) {
			if (p->source_stays) {
				p->status = 'C';
				continue;
			}
			/* See if there is some other filepair that
			 * copies from the same source as us.  If so
			 * we are a copy.  Otherwise we are a rename.
			 */
			for (j = i + 1; j < q->nr; j++) {
				pp = q->queue[j];
				if (strcmp(pp->one->path, p->one->path))
					continue; /* not us */
				if (!DIFF_PAIR_RENAME(pp))
					continue; /* not a rename/copy */
				/* pp is a rename/copy from the same source */
				p->status = 'C';
				break;
			}
			if (!p->status)
				p->status = 'R';
		}
		else if (memcmp(p->one->sha1, p->two->sha1, 20) ||
			 p->one->mode != p->two->mode)
			p->status = 'M';
		else {
			/* This is a "no-change" entry and should not
			 * happen anymore, but prepare for broken callers.
			 */
			error("feeding unmodified %s to diffcore",
			      p->one->path);
			p->status = 'X';
		}
	}
	diff_debug_queue("resolve-rename-copy done", q);
}

void diff_flush(int diff_output_style)
{
	struct diff_queue_struct *q = &diff_queued_diff;
	int i;
	int line_termination = '\n';
	int inter_name_termination = '\t';

	if (diff_output_style == DIFF_FORMAT_MACHINE)
		line_termination = inter_name_termination = 0;

	for (i = 0; i < q->nr; i++) {
		struct diff_filepair *p = q->queue[i];
		if ((diff_output_style == DIFF_FORMAT_NO_OUTPUT) ||
		    (p->status == 'X'))
			continue;
		if (p->status == 0)
			die("internal error in diff-resolve-rename-copy");
		switch (diff_output_style) {
		case DIFF_FORMAT_PATCH:
			diff_flush_patch(p);
			break;
		case DIFF_FORMAT_HUMAN:
		case DIFF_FORMAT_MACHINE:
			diff_flush_raw(p, line_termination,
				       inter_name_termination);
			break;
		}
	}
	for (i = 0; i < q->nr; i++)
		diff_free_filepair(q->queue[i]);
	free(q->queue);
	q->queue = NULL;
	q->nr = q->alloc = 0;
}

static void diffcore_apply_filter(const char *filter)
{
	int i;
	struct diff_queue_struct *q = &diff_queued_diff;
	struct diff_queue_struct outq;
	outq.queue = NULL;
	outq.nr = outq.alloc = 0;

	if (!filter)
		return;

	if (strchr(filter, 'A')) {
		/* All-or-none */
		int found;
		for (i = found = 0; !found && i < q->nr; i++) {
			struct diff_filepair *p = q->queue[i];
			if (((p->status == 'M') &&
			     ((p->score && strchr(filter, 'B')) ||
			      (!p->score && strchr(filter, 'M')))) ||
			    ((p->status != 'M') && strchr(filter, p->status)))
				found++;
		}
		if (found)
			return;

		/* otherwise we will clear the whole queue
		 * by copying the empty outq at the end of this
		 * function, but first clear the current entries
		 * in the queue.
		 */
		for (i = 0; i < q->nr; i++)
			diff_free_filepair(q->queue[i]);
	}
	else {
		/* Only the matching ones */
		for (i = 0; i < q->nr; i++) {
			struct diff_filepair *p = q->queue[i];
			if (((p->status == 'M') &&
			     ((p->score && strchr(filter, 'B')) ||
			      (!p->score && strchr(filter, 'M')))) ||
			    ((p->status != 'M') && strchr(filter, p->status)))
				diff_q(&outq, p);
			else
				diff_free_filepair(p);
		}
	}
	free(q->queue);
	*q = outq;
}

void diffcore_std(const char **paths,
		  int detect_rename, int rename_score,
		  const char *pickaxe, int pickaxe_opts,
		  int break_opt,
		  const char *orderfile,
		  const char *filter)
{
	if (paths && paths[0])
		diffcore_pathspec(paths);
	if (break_opt != -1)
		diffcore_break(break_opt);
	if (detect_rename)
		diffcore_rename(detect_rename, rename_score);
	if (break_opt != -1)
		diffcore_merge_broken();
	if (pickaxe)
		diffcore_pickaxe(pickaxe, pickaxe_opts);
	if (orderfile)
		diffcore_order(orderfile);
	diff_resolve_rename_copy();
	diffcore_apply_filter(filter);
}


void diffcore_std_no_resolve(const char **paths,
			     const char *pickaxe, int pickaxe_opts,
			     const char *orderfile,
			     const char *filter)
{
	if (paths && paths[0])
		diffcore_pathspec(paths);
	if (pickaxe)
		diffcore_pickaxe(pickaxe, pickaxe_opts);
	if (orderfile)
		diffcore_order(orderfile);
	diffcore_apply_filter(filter);
}

void diff_addremove(int addremove, unsigned mode,
		    const unsigned char *sha1,
		    const char *base, const char *path)
{
	char concatpath[PATH_MAX];
	struct diff_filespec *one, *two;

	/* This may look odd, but it is a preparation for
	 * feeding "there are unchanged files which should
	 * not produce diffs, but when you are doing copy
	 * detection you would need them, so here they are"
	 * entries to the diff-core.  They will be prefixed
	 * with something like '=' or '*' (I haven't decided
	 * which but should not make any difference).
	 * Feeding the same new and old to diff_change() 
	 * also has the same effect.
	 * Before the final output happens, they are pruned after
	 * merged into rename/copy pairs as appropriate.
	 */
	if (reverse_diff)
		addremove = (addremove == '+' ? '-' :
			     addremove == '-' ? '+' : addremove);

	if (!path) path = "";
	sprintf(concatpath, "%s%s", base, path);
	one = alloc_filespec(concatpath);
	two = alloc_filespec(concatpath);

	if (addremove != '+')
		fill_filespec(one, sha1, mode);
	if (addremove != '-')
		fill_filespec(two, sha1, mode);

	diff_queue(&diff_queued_diff, one, two);
}

void diff_helper_input(unsigned old_mode,
		       unsigned new_mode,
		       const unsigned char *old_sha1,
		       const unsigned char *new_sha1,
		       const char *old_path,
		       int status,
		       int score,
		       const char *new_path)
{
	struct diff_filespec *one, *two;
	struct diff_filepair *dp;

	one = alloc_filespec(old_path);
	two = alloc_filespec(new_path);
	if (old_mode)
		fill_filespec(one, old_sha1, old_mode);
	if (new_mode)
		fill_filespec(two, new_sha1, new_mode);
	dp = diff_queue(&diff_queued_diff, one, two);
	dp->score = score * MAX_SCORE / 100;
	dp->status = status;
}

void diff_change(unsigned old_mode, unsigned new_mode,
		 const unsigned char *old_sha1,
		 const unsigned char *new_sha1,
		 const char *base, const char *path) 
{
	char concatpath[PATH_MAX];
	struct diff_filespec *one, *two;

	if (reverse_diff) {
		unsigned tmp;
		const unsigned char *tmp_c;
		tmp = old_mode; old_mode = new_mode; new_mode = tmp;
		tmp_c = old_sha1; old_sha1 = new_sha1; new_sha1 = tmp_c;
	}
	if (!path) path = "";
	sprintf(concatpath, "%s%s", base, path);
	one = alloc_filespec(concatpath);
	two = alloc_filespec(concatpath);
	fill_filespec(one, old_sha1, old_mode);
	fill_filespec(two, new_sha1, new_mode);

	diff_queue(&diff_queued_diff, one, two);
}

void diff_unmerge(const char *path)
{
	struct diff_filespec *one, *two;
	one = alloc_filespec(path);
	two = alloc_filespec(path);
	diff_queue(&diff_queued_diff, one, two);
}