git-apply: pick up default filenames from "diff --git" header line

[git.git] / 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 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 void builtin_diff(const char *name_a,
                         const char *name_b,
                         struct diff_tempfile *temp,
                         const char *xfrm_msg)
{
        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);
        else if (!path1[1][0])
                printf("deleted file mode %s\n", temp[0].mode);
        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])
                        fputs(xfrm_msg, stdout);

                if (strncmp(temp[0].mode, temp[1].mode, 3))
                        /* we do not run diff between different kind
                         * of objects.
                         */
                        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) { /* just playing defensive */
                spec->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;
}

/*
 * 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 err = 0;
        if (!DIFF_FILE_VALID(s))
                die("internal error: asking to populate invalid file.");
        if (S_ISDIR(s->mode))
                return -1;

        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 (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];
                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));
                        sprintf(temp->mode, "%06o",
                                S_IFREG |ce_permissions(st.st_mode));
                }
                return;
        }
        else {
                if (diff_populate_filespec(one))
                        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 *name,
                              const char *other,
                              struct diff_filespec *one,
                              struct diff_filespec *two,
                              const char *xfrm_msg)
{
        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) {
                const char *pgm = external_diff();
                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);
                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();
}

void diff_setup(int reverse_diff_)
{
        reverse_diff = reverse_diff_;
}

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;
        diff_q(queue, dp);
        return dp;
}

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);
        }

        switch (p->status) {
        case 'C': case 'R':
                two_paths = 1;
                sprintf(status, "%c%03d", p->status,
                        (int)(0.5 + p->score * 100.0/MAX_SCORE));
                break;
        default:
                two_paths = 0;
                status[0] = p->status;
                status[1] = 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 change and renames are all interesting. */
        if (DIFF_FILE_VALID(one) != DIFF_FILE_VALID(two) ||
            (one->mode != two->mode) ||
            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)
{
        const char *name, *other;
        char msg_[PATH_MAX*2+200], *msg;

        if (diff_unmodified_pair(p))
                return;

        name = p->one->path;
        other = (strcmp(name, p->two->path) ? p->two->path : NULL);
        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 */ 

        switch (p->status) {
        case 'C':
                sprintf(msg_,
                        "similarity index %d%%\n"
                        "copy from %s\n"
                        "copy to %s\n",
                        (int)(0.5 + p->score * 100.0/MAX_SCORE),
                        p->one->path, p->two->path);
                msg = msg_;
                break;
        case 'R':
                sprintf(msg_,
                        "similarity index %d%%\n"
                        "rename old %s\n"
                        "rename new %s\n",
                        (int)(0.5 + p->score * 100.0/MAX_SCORE),
                        p->one->path, p->two->path);
                msg = msg_;
                break;
        default:
                msg = NULL;
        }

        if (DIFF_PAIR_UNMERGED(p))
                run_external_diff(name, NULL, NULL, NULL, NULL);
        else
                run_external_diff(name, other, p->one, p->two, msg);
}

int diff_needs_to_stay(struct diff_queue_struct *q, int i,
                       struct diff_filespec *it)
{
        /* If it will be used in later entry (either stay or used
         * as the source of rename/copy), we need to copy, not rename.
         */
        while (i < q->nr) {
                struct diff_filepair *p = q->queue[i++];
                if (!DIFF_FILE_VALID(p->two))
                        continue; /* removed is fine */
                if (strcmp(p->one->path, it->path))
                        continue; /* not relevant */

                /* p has its src set to *it and it is not a delete;
                 * it will be used for in-place change, rename/copy,
                 * or just stays there.  We cannot rename it out.
                 */
                return 1;
        }
        return 0;
}

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\n",
                p->score, p->status ? : '?');
}

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;

        /* This should not depend on the ordering of things. */

        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)) {
                        /* Deletion record should be omitted if there
                         * are rename/copy entries using this one as
                         * the source.  Then we can say one of them
                         * is a rename and the rest are copies.
                         */
                        p->status = 'D';
                        for (j = 0; j < q->nr; j++) {
                                pp = q->queue[j];
                                if (!strcmp(pp->one->path, p->one->path) &&
                                    strcmp(pp->one->path, pp->two->path)) {
                                        p->status = 'X';
                                        break;
                                }
                        }
                }
                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 (strcmp(p->one->path, p->two->path)) {
                        /* See if there is somebody else anywhere that
                         * will keep the path (either modified or
                         * unmodified).  If so, we have to be a copy,
                         * not a rename.  In addition, if there is
                         * some other rename or copy that comes later
                         * than us that uses the same source, we
                         * have to be a copy, not a rename.
                         */
                        for (j = 0; j < q->nr; j++) {
                                pp = q->queue[j];
                                if (strcmp(pp->one->path, p->one->path))
                                        continue;
                                if (!strcmp(pp->one->path, pp->two->path)) {
                                        if (DIFF_FILE_VALID(pp->two)) {
                                                /* non-delete */
                                                p->status = 'C';
                                                break;
                                        }
                                        continue;
                                }
                                /* pp is a rename/copy ... */
                                if (i < j) {
                                        /* ... and comes later than us */
                                        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 */
                        p->status = 'X';
        }
        diff_debug_queue("resolve-rename-copy done", q);
}

void diff_flush(int diff_output_style, int resolve_rename_copy)
{
        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;
        if (resolve_rename_copy)
                diff_resolve_rename_copy();

        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *p = q->queue[i];
                if (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++) {
                struct diff_filepair *p = q->queue[i];
                diff_free_filespec_data(p->one);
                diff_free_filespec_data(p->two);
                free(p);
        }
        free(q->queue);
        q->queue = NULL;
        q->nr = q->alloc = 0;
}

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;
        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);
}