Documentation updates.

[git/dscho.git] / diff.c

/*
 * Copyright (C) 2005 Junio C Hamano
 */
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>
#include "cache.h"
#include "quote.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;
        const char *env_diff_opts;

        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";
         */
        external_diff_cmd = gitenv("GIT_EXTERNAL_DIFF");

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

        done_preparing = 1;
        return external_diff_cmd;
}

#define TEMPFILE_PATH_LEN               50

static struct diff_tempfile {
        const char *name; /* filename external diff should read from */
        char hex[41];
        char mode[10];
        char tmp_path[TEMPFILE_PATH_LEN];
} 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 *const diff_cmd = "diff -L%s%s -L%s%s";
        const char *const 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_quote(name_a);
        name_sq[1] = sq_quote(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_quote(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);
                close(fd);
                if (s->data == MAP_FAILED)
                        goto err_empty;
                s->should_munmap = 1;
        }
        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(struct diff_filespec *s)
{
        if (s->should_free)
                free(s->data);
        else if (s->should_munmap)
                munmap(s->data, s->size);
        free(s);
}

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

        fd = git_mkstemp(temp->tmp_path, TEMPFILE_PATH_LEN, ".diff_XXXXXX");
        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;
        const char *othername;

        othername = (other? other : name);
        if (one && two) {
                prepare_temp_file(name, &temp[0], one);
                prepare_temp_file(othername, &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, othername, 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 DIFF_STATUS_COPIED:
                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 DIFF_STATUS_RENAMED:
                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 DIFF_STATUS_MODIFIED:
                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(p->one);
        diff_free_filespec(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 *const 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 DIFF_STATUS_COPIED:
        case DIFF_STATUS_RENAMED:
                two_paths = 1;
                break;
        case DIFF_STATUS_ADDED:
        case DIFF_STATUS_DELETED:
                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);
}

static void diff_flush_name(struct diff_filepair *p,
                            int line_termination)
{
        printf("%s%c", p->two->path, 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 ? 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 ? 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->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 = DIFF_STATUS_UNMERGED;
                else if (!DIFF_FILE_VALID(p->one))
                        p->status = DIFF_STATUS_ADDED;
                else if (!DIFF_FILE_VALID(p->two))
                        p->status = DIFF_STATUS_DELETED;
                else if (DIFF_PAIR_TYPE_CHANGED(p))
                        p->status = DIFF_STATUS_TYPE_CHANGED;

                /* 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 = DIFF_STATUS_COPIED;
                                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 = DIFF_STATUS_COPIED;
                                break;
                        }
                        if (!p->status)
                                p->status = DIFF_STATUS_RENAMED;
                }
                else if (memcmp(p->one->sha1, p->two->sha1, 20) ||
                         p->one->mode != p->two->mode)
                        p->status = DIFF_STATUS_MODIFIED;
                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 = DIFF_STATUS_UNKNOWN;
                }
        }
        diff_debug_queue("resolve-rename-copy done", q);
}

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

        if (!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 == DIFF_STATUS_UNKNOWN))
                        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_RAW:
                        diff_flush_raw(p, line_termination,
                                       inter_name_termination);
                        break;
                case DIFF_FORMAT_NAME:
                        diff_flush_name(p, line_termination);
                        break;
                }
                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, DIFF_STATUS_FILTER_AON)) {
                int found;
                for (i = found = 0; !found && i < q->nr; i++) {
                        struct diff_filepair *p = q->queue[i];
                        if (((p->status == DIFF_STATUS_MODIFIED) &&
                             ((p->score &&
                               strchr(filter, DIFF_STATUS_FILTER_BROKEN)) ||
                              (!p->score &&
                               strchr(filter, DIFF_STATUS_MODIFIED)))) ||
                            ((p->status != DIFF_STATUS_MODIFIED) &&
                             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 == DIFF_STATUS_MODIFIED) &&
                             ((p->score &&
                               strchr(filter, DIFF_STATUS_FILTER_BROKEN)) ||
                              (!p->score &&
                               strchr(filter, DIFF_STATUS_MODIFIED)))) ||
                            ((p->status != DIFF_STATUS_MODIFIED) &&
                             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);
}